tmp445A.tmp

Journal of Horticultural Research 2016, vol. 24(1): 79-91 DOI: 10.1515/johr-2016-0010 _______________________________________________________________________________________________________

COMPETITIVE ABILITY OF CAPSICUM ANNUUM L. RELATIVE TO THE WEED AMARANTHUS LIVIDUS L. Abdessatar OMEZINE1*, Jaime A. TEIXEIRA DA SILVA2** 1

Institution of Agricultural Research and Higher Education, Tunis, Tunisia 2 Retired, Miki-cho, Japan Received: September 2015; Accepted: April 2016

ABSTRACT Amaranthus lividus is the most frequently reported troublesome weed in the production of Capsicum annuum in some regions because it is an aggressive invader, difficult to control, and reduces yield significantly. The effects of A. lividus on the growth of C. annuum ‘Baklouti’ were evaluated under greenhouse conditions. Three experiments were conducted to determine the effect of A. lividus on the biomass accumulation of C. annuum seedlings for 40 days. In an additive experiment, to one C. annuum seedling and 1, 2, 3 or 4 A. lividus seedlings were grown per pot. The second experiment was established to assess C. annuum intracompetition using from one to six plants per pot as the density. In a replacement experiment, C. annuum and A. lividus seedlings were transplanted into pots with different proportions of both plants (1/5, 2/4, 3/3, 4/2, 5/1). Competition by A. lividus reduced C. annuum plant dry weight by as much as 93%. However, C. annuum had little effect on A. lividus, reducing dry weight by 31.3% at a 5:1 ratio of C. annuum: A. lividus. Relative yield analysis between C. annuum and A. lividus demonstrated the competitive advantage of C. annuum over A. lividus. The relative crowding coefficient of both plants changed significantly in the presence of the other plant, at any ratio. The aggressivity of C. annuum was higher at its lower proportion and C. annuum was more aggressive towards itself than towards A. lividus when its density increased. Key words: aggressivity; allelopathy; competition; relative crowding coefficient; relative yield; weeds INTRODUCTION In Tunisia, Capsicum annuum L. (Solanaceae), or peppers in general, is an important commercial crop grown on a wide range of soils at altitudes varying from sea level to 2000 m, both for internal consumption and for export. C. annuum is ranked fifth (in terms of acreage) after tomato, watermelon, potato and onion (Boughalleb & El Mahjoub 2005). In Africa, Tunisia is the third largest producer of C. annuum after Nigeria and Egypt, and the third largest exporter (in terms of tonnage) after Morocco and South Africa (FAO 2013). In 2008 and 2010, Tunisia was ranked 12 and 11, in terms of global production with a world rank of 45 and 53, respectively in export terms (FAO 2013). The yield of C. annum in Tunisia averages 12.5 t/ha, which is relatively low compared to yield

*Corresponding authors: e-mail: *[email protected]; **[email protected]

observed in other Mediterranean countries such as Spain (35 t·ha-1), Italy (28 t·ha-1), Greece (23 t·ha-1), and Morocco (14 t·ha-1) (Boughalleb & El Mahjoub 2005). These low yields are due to difficulties in establishing efficient control measures. One of the main problems affecting crop yield and quality is weed interference (Hager et al. 2002; Boatright & McKissick 2004). Severe weed infestations can reduce yield by at least 50-87% and some weeds, among them Amaranthus lividus, may act as alternate hosts of insects, pests and diseases (Boatright & McKissick 2004). Effective weed management is thus one of the many critical components of successful C. annuum production. The genus Amaranthus is represented by approximately 60 species (Holm et al. 1997; Wiersema & Leon 2013), widely distributed in tropical, subtropical and temperate regions (Carvalho et

- 10.1515/johr-2016-0010 Downloaded from PubFactory at 07/31/2016 10:38:24AM via free access

80

A. Omezine, J.A. Teixeira da Silva

____________________________________________________________________________________________________________________

al. 2006). A. lividus is among the most abundant weeds occurring in and affecting vegetable crops, lawns, pastures, gardens and row crops (Murphy et al. 2010) throughout the warm temperate and tropical regions of New and Old Worlds (Wiersema & León 2013). It is responsible for significant yield losses in many crops, which varies with the density of A. lividus. For example, the yield of C. annuum was reduced by 67% when it competed with four A. lividus plants·m-2 (Morales-Payan et al. 2002). In another uncontrolled study, three A. lividus plants·m-2 interfered with C. annuum, reducing yield by 33% (Morales-Payan et al. 2003). Maximum yield loss was 65% when six A. lividus plants were grown per m2 or 30% with a single A. lividus plant·m-2 (MoralesPayan & Stall 2002). Those studies, however, failed to assess the ratio of C. annuum: A. lividus (i.e., the density of one species relative to the other), and thus served as the basis for this study with the hypothesis that the growth and successful survival of one species would change in the presence of the other. In Tunisia, and even around the world, limited information is available on chemical and biological weed control, including that of specific weeds like A. lividus (Murphy et al. 2010). However, the only measure to control A. lividus and other weeds in vegetable crop stands, including those of C. annuum, particularly in low-income countries, is cultural methods, particularly periodic hoeing and hand pulling throughout the growing season. This process is laborious, starts early in the season when the weeds are small and the process is frequently repeated throughout the season. Thus, to find a mechanism that is able to limit particular plants growth using plant density could theoretically reduce, or remove, the need for chemical control, and serve as a practical, low-cost technique for rural farmers globally. If our first hypothesis held true (i.e., that C. annum could negatively influence the growth of A. lividus), it then becomes important to determine the level of interaction when the ratio of each was varied. Except for the Morales-Payan-associated papers listed above, no systematic research has been conducted thus far to explore the competitive behavior of C. annuum towards weeds. Against this background, lack of detailed information about the effect of A. lividus on the growth of C. annuum and

losses caused to growth, and the rapid spread of A. lividus in vegetable production systems in Tunisia, North Africa and elsewhere around the world, this study set out to address three key objectives, conducted in three separate experiments: (1) to examine the effect of A. lividus density on C. annuum growth during the seedling stage, which is the most sensitive growth stage; (2) to obtain the appropriate plant density of C. annuum to minimize intracompetition; (3) to test the competitive ability of C. annuum towards the weed A. lividus using a replacement method. The hope was that a suitable C. annuum : A. lividus ratio could be found to ensure maximum weed control at no cost, since costs are traditionally associated with chemical control or weeding. To test these objectives, different competition indices were employed. MATERIALS AND METHODS To study inter- and intra-specific competition between a crop C. annuum ‘Baklouti’ and a weed A. lividus, three pot experiments were performed under greenhouse conditions. They were conducted at the Superior Institute of Agricultural Sciences (ISA) of Chott-Mariem (Sousse, Tunisia) in the fall of 2010 and repeated in 2011. The experimental units were plastic containers (8 cm in diameter and 10 cm deep) filled with standard horticultural potting medium (sand, manure, perlite; 1 : 1 : 1, v / v). Based on the previous observations, this container size was chosen to provide unrestricted C. annuum and A. lividus growth for 40 days after planting. C. annuum seeds were sown in standard horticultural potting medium and transplanted at the true two-leaf stage into experimental containers. A. lividus seeds were collected from local field stands in C. annuum fields near ISA. A. lividus seeds were sown in experimental pots and thinned after emergence to the numbers described in Experiments 1 and 3. The pots were irrigated with 50 ml of potable water every two days from the start to the end of the experiment. The salinity (mass of dissolved salts) of the water was 1.2 g dm-3. After 40 days since capsicum transplantation, the whole plant dry weight (DW) was determined as explained next. The experimental design was completely randomized with five experimental units.


81

Competition between Capsicum annuum and Amaranthus lividus

____________________________________________________________________________________________________________________

In the additive experiment (Exp. 1), one C. annuum seedling was planted per pot, together with 1, 2, 3 or 4 A. lividus seedlings, which were spaced 2 cm apart of C. annuum seedling. In the second experiment (Exp. 2), intracompetition between C. annuum seedlings was studied. In one pot 1, 2, 3, 4, 5 or 6 plants were grown. In the replacement experiment (Exp. 3), there were six plants in one pot grown as a mixture of C. annuum and A. lividus seedlings in different proportions. The following combinations were evaluated: (1) 100% C. annuum (6 plants/pot, as monoculture); (2) 83.3% C. annuum (5 plants/pot) + 12.7% A. lividus (1 plant/pot); (3) 66.6% C. annuum (4 plants/pot) + 33.3% A. lividus (2 plants/pot); (4) 50% C. annuum (3 plants/pot) + 50% A. lividus (3 plants/pot); (5) 33.3% C. annuum (2 plants/pot) + 66.6% A. lividus (4 plants/pot); (6) 16.6% C. annuum (5 plants/pot) + 83.3% A. lividus (5 plants/pot); (7) 0% C. annuum (i.e., an Amaranthus monoculture). Forty days after transplanting C. annuum, total dry weight (DW) of C. annuum and A. lividus were determined, as explained next. At 40 DAP, C. annuum and A. lividus biomass was separated. Roots of each plant were washed gently and thoroughly to remove soil particles so that the root tissues remained intact. DW was determined by drying the whole plant in an oven for 48 h at 80 °C. The relative performance of each species in the A. lividus / C. annuum combination was calculated. The relative yield (RY) of both species was analyzed graphically as described by de Wit (1960) and Harper (1977). The RY of A. lividus (RYa), the RY of C. annuum (RYc) and the total relative yield (RYT) of both species were calculated separately according to the following equations (Harper, 1977): RYa = yield of A. lividus in the mixture / yield of A. lividus in monoculture; RYc = yield of C. annum in the mixture / yield of C. annuum in monoculture; RYT = RYc + RYa. A value of RYT = 1 indicates that C. annuum and A. lividus are demanding the same limiting resources, RYT > 1 indicates that the two species make different demands on resources, so competition is avoided and RYT < 1 indicates that there is mutual antagonism between C. annuum and A. lividus (de Wit & Goudriaan 1978).

The relative crowding coefficient (RCC) was used to determine the competitive ability of a plant to obtain limited resources when grown in a community setting compared to its ability to utilize those resources when grown in a monoculture (Aminpanah 2013). RCC was calculated for both species using the formula of Hoffman and Buhler (2002): RCC = [(DWc 1 × 5 / DWa 5 × 1) + (DWc 2 × 4 / DWa 4 × 2) + (DWc 3 × 3 / DWa 3 × 3) + (DWc 4 × 2 / DWa 2 × 4) + (DWc 5 × 1 / DWa 1× 5) + (DWc 6 × 0 / DWa 0 × 6)], where DWc n × n is the DW of C. annuum at a ratio of n : n and DWa n × n is the DW of A. lividus at different ratios. Thus, for example, DWc 1 × 5 / DWa 5 × 1 = the DW of one Capsicum plant and five Amaranthus plants per pot divided by the DW of five Amaranthus plants and one Capsicum plant per pot. According to this definition, an RCC value > 1 signifies a competitive advantage for C. annuum compared to A. lividus and the larger the RCC value, the greater the competitiveness with C. annuum. In contrast, an RCC value of < 1 indicates that A. lividus is more competitive than C. annuum. An RCC value = 1 indicates that there is no competition or competitive advantage or disadvantage between both species. An increase in the RCC value for a species as the proportion in the plant mixture increases indicates that the relative competitiveness of that species has increased (Morales-Payan et al. 1999; Williams & McCarthy 2001; Zarochentseva 2012). The third index assessed was aggressivity, which is often used to determine the competitive relationship between C. annuum and A. lividus in a mixed crop. The aggressivity of C. annuum (Ac) was calculated as follows (McGilchrist & Trenbath 1971): Ac = (DW Capsicummix / DW Capsicummono) − (DW Amaranthusmix / DW Amaranthusmono), where mix = mixture of both crops; mono = monoculture. If Ac = 0, then both crops are equally competitive; if Ac is positive, then C. annuum is dominant, and if Ac is negative, then C. annuum is weak. Mean data sets of five replicates per treatment in completely randomized design and repeated twice were subjected to one-way analysis of variance (ANOVA), and means were separated using Fisher’s protected LSD at P = 0.05.


82


____________________________________________________________________________________________________________________

RESULTS AND DISCUSSION Additive experiment (Exp. 1) Many factors interact to determine the outcome of competition between a weed and a crop. Among these factors, weed population density is a major factor. It is well known that crop density is important in limiting the competitive effect of weeds. Many other factors such as soil type and climate are beyond the control of farmers but crop density can be more easily controlled. This study aimed to take advantage of this basic biological fact to try and control a weed (A. lividus) in pepper production systems using pot experiments. Seedlings in the most sensitive growth stage of the plant were used. A. lividus density had a significant effect on the DW of C. annuum. DW accumulation of C. annuum decreased as A. lividus density increased (Fig. 1). At all densities, either one or four A. lividus plants negatively interfered with and reduced C. annuum DW. This significant reduction of C. annuum DW accumulation at all densities of A. lividus suggests that the growth of C. annuum plants was retarded by the concomitant growth of A. lividus. C. annuum plants accumulated maximum DW (20.01 g/pot) when grown without A. lividus while lowest DW was obtained when one C. annuum plant was grown with four A. lividus plants (0.46 g/pot). DW was reduced by about 80.8% due to competition from one A. lividus plant and by 97.7% when A. lividus was planted at a density of four plants. This relation implies that one A. lividus plant at lowest density had a greater effect on C. annuum growth than one A. lividus plant at a higher density. What is surprising is how so few A. lividus plants/pot were able to reduce the growth of C. annuum. It is likely that not only competition to nutrients but also other types of interactions, including allelopathy, are involved. The study of Berry et al. (2006) showed that the density of A. lividus, 1 to 2 plants/m2 , caused a 10% yield reduction of cucumber. Also, Morales-Payan and Stall (2002) reported that C. annuum yield was reduced by 67% when competing with 6 A. lividus per square meter of field throughout an entire season. These effects of A. lividus on the DW of C. annuum reflect the

competitive ability of A. lividus (Procópio et al. 2004) and also its aggressiveness (Silva et al. 2009). However, the accumulation of A. lividus DW was modified by its density and was significantly influenced by the presence of C. annuum. The highest accumulation of A. lividus DW was observed with four A. lividus plants associated with one C. annuum plant (52.33 g/pot) while the lowest DW accumulation (35.77 g/pot) occurred when one A. lividus plant grew in the presence of one C. annuum plant. The DW accumulation of individual C. annuum plants decreased as A. lividus density increased but also, the DW accumulation of individual A. lividus plant decreased when its density increased (Fig. 2). Moreover, the total mean DW / plant (C. annuum + A. lividus) decreased with increase of A. lividus density (Fig. 2). A similar relation was found by Ronchi and Silva (2006) in experiment with young coffee plants growing with four weeds. Intraspecific competition experiment (Exp. 2) In the intraspecific experiment, an increase in C. annuum density increased the DW accumulation/pot up to five plants/pot, but decreased rapidly at six plants/pot while the DW accumulation per individual plant was not influenced (Fig. 3), which is a typical reaction concerning yield of total biomass. Agarwal et al. (2007) noted that the yield of C. annuum fruit increased with its population growth up to 120,000 plants/ha resulting in the highest marketable yield but not influencing fruit mass; however, exceeding this population in the field, fruit yield decreased significantly. Jolliffe and Gaye (1995) reported that leaf area, leaf DW and shoot DW of C. annuum decreased significantly as plant population reached 11.1 plants/m2. In our study of intraspecific competition, the observed increase in DW was not proportional to density. At a high density of C. annuum (6 plants/pot), the total DW of C. annuum was 164.4 g/pot whereas at a low density (1 plant/pot), total DW of C. annuum was 36.8 g/pot. In other words, a dry weight of one C. annuum plant was 27.4 g when the density was 6 plants/pot and 36.8 g when the density was 1 plant/pot. Jolliffe and Gaye (1995) showed that


83


____________________________________________________________________________________________________________________

Dry weight acumulation of each species per pot (g)

a high population (11.1 plants/m2) of C. annuum decreased biomass accumulation per unit land area. However, Harper (1977) found that the total DW of Amaranthus retroflexus / pot was relatively constant but DW/plant decreased as A. retroflexus density increased. Density affects plant architecture, alters growth and developmental patterns and influences carbohydrate production and partitioning. Plant density may influence the development and growth of vegetable crops, including onion (Asaduzzaman et al. 2015). The plasticity of plants is the capacity for marked variation in an individual plant phenotype as a result of environmental influences on that genotype during development in which an individual plant can grow larger or smaller depending on the resources available to it in its habitat (Price et al. 2003; Dekker 2011). High densities decreased the absolute growth rates of C. annuum but promoted shoot biomass accumulation per unit land area (Jolliffe & Gaye 1995). Spehia et al. (2014) noted that plant height of C. annuum changed significantly in response to spacing: closer spacing resulted in maximum plant height, but wider spacing resulted in the highest number of fruits. Quinto and Barraza (2009) found that phenotypic plasticity of C. annuum can be affected by treatments, since a significant effect of plant density was detected on stem diameter, leaf area and leaf number, but plant height was less plastic. In their study, stem DW, leaf DW, fruit DW and total DW per plant decreased as plant density increased. This phenotypically plastic ability of C. annuum based on morphological traits (Lahbib et al. 2012) allows them 60

Cap/pot Am/pot Total/pot

50 40 30

a

to rapidly adapt to changing environments and enables them to continue to survive and reproduce across variable environments (Tétard-Jones et al. 2011). Replacement experiment (Exp. 3) 1. Dry weight accumulation The DW accumulation of C. annuum (Cap/pot) increased with the number of pepper seedlings/pot (and proportion to A. lividus) A similar trend concerning number of plants and proportion to C. annuum was shown for A. lividus (Fig. 4). The highest DW per pot was at highest proportion of pepper in the mixture. The accumulation of DW by individual C. annuum plants increased as its ratio in the mixture decreased. A similar trend was observed for A. lividus in the mixture. The DW accumulation of individual plants, either Capsicum or Amaranthus, changed as their ratio in the mixture changed: from 1.43 to 3.58 g when the proportion of Capsicum changed from 5 to 1 plants/pot and from 6.37 to 1.72 g when the proportion of Amaranthus changed from 1 to 5 plants/pot. Thus, as the density of C. annuum increased, it inhibited the growth of its own population more than it inhibited the growth of A. lividus population. The same was true for A. lividus representing a classic case of mutual antagonism. The reduction of DW of either of C. annuum or A. lividus as its density increased might be due to the production of allelochemicals by C. annuum (Radhouane & Rhim 2014) and/or A. lividus (Jala & Wongsarasin 2012). The DW calculated for plants of both species did not depend on their mutual proportions (Fig. 5).

c d

b

c

a

b

a

d

e

20 b

10

b

b

b

0 0

1

2

3

4

Density of Amaranthus lividus (number of plants per pot)

Fig. 1. Effect of density of Amaranthus lividus grown in the pots with one Capsicum annum plant on the dry weight (DW) of C. annuum and A. lividus accumulated during 40 days, per pot. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across densities. Bars represent means ± SE (n = 10)


84


Dry weight accumulation of Capsicum and Amaranthus per plant (g)

____________________________________________________________________________________________________________________

a

40

Cap/plant Ama/plant Total/plant

35 30

b a

25

a

b

c

20

d

c d

15 10

b

b

5

e

b

b

0 0

1 2 3 Density of Amaranthus lividus (number of plants per pot)

4

Fig. 2. Effect of density of Amaranthus lividus grown in the pots with one Capsicum annuum plant on the total dry weight (TDW) of C. annuum and A. lividus accumulated during 40 days, on a per plant basis. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across densities. Bars represent means ± SE (n = 10) Dry weight accumulation of Capsicum per plant and pot (g)

250

a DW/plant DW/pot

200

b c

150 d 100 a

e

f

50

a

a

a

a

a

0 1

2

3

4

5

6

Density of Capsicum annuum (number of plants per pot)

Fig. 3. Dry weight (DW) accumulation of Capsicum annuum during 40 days on a per plant and on a per pot basis as affected by plant density. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across densities. Bars represent means ± SE (n = 10) Dry weight accumulation of each species in the mixture per pot (g)

16

12 10

a

Cap/pot Ama/pot Total dry/pot

14

a

a

bc

cd

b

e

a

b

f b

8

d

f 6

c

c

d

e d

e f

4 2 0 c6a0

c5a1

c4a2 c3a3 c2a4 Proportion of each species in the mixture

c1a5

c0a6

Fig. 4. Dry weight (DW) accumulation in Capsicum annuum and Amaranthus lividus plants grown in the mixture, expressed on a per-pot basis. c and Cap = Capsicum, Ama and a = Amaranthus. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across proportions. Bars represent means ± SE (n = 10)


85


Dry weight accumulation of each species in the mixture in gram per pot

____________________________________________________________________________________________________________________

8 Cap/plant Ama/plant DW/plant

a

7

6 5 a

b

4

2

b

c

3 e

f

a

d

a

a

c

a

d

e

a

a

f a

1 0 c6a0

c5a1

c4a2 c3a3 c2a4 Proportion of each specisin the mixture

c1a5

c0a6

Fig. 5. Dry weight (DW) accumulation in Capsicum annuum and Amaranthus lividus plants grown in the mixture, expressed on a per-plant basis. c and Cap = Capsicum, Ama and a = Amaranthus. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across proportions. Bars represent means ± SE (n = 10)

2.

Relative yields The relative yields of C. annuum (RYc / pot and RYc / plant) and A. lividus (RYa / pot and RYa / plant) and the relative total yield (RYT / pot and RYT / plant) obtained from the replacement series are shown in Fig. 6 and 7. These parameters provide support for the competitive interaction of each species. These yield parameters were significantly affected by the mixture ratios. The relative yield (RYc/pot) of C. annuum increased as its ratio decreased from 0.46 at 5 C. annum plants to 0.85 at 1 C. annuum plant (Fig. 6). RYa/pot decreased from 0.79 to 0.37 when the proportion of A. lividus plants in the mixture increased from 1 to 5 plants/pot. The RY of each species was < 1, indicating that there was mutual antagonism between both species. In this case, it is difficult to determine if the species were antagonistic or whether both were competitively using the same resources since RYT obscures the behavior of each species. Future experiments that examine nutrient levels in the soil and plants at each ratio could elucidate this mechanism. The RYT (RYc + RYa) of the mixtures did not change significantly with each mixture combination (Fig. 6). This value greater than unit indicates that the two species (C. annuum and A. lividus) used available resources more efficiently than expected based on their respective yields when species were considered individually. Values > 1 indicate that while two species compete for different resources, there is also

probably some degree of resource complementarity between them (Fetene 2013). When two competing species share the same resource by occupying different areas or habitats, then spatial resource partitioning occurs (Yachi & Loreau 2007). The coexistence of plant species may result from niche partitioning, or from differences in resource requirements among species while in the process of complementarity, a more diverse plant community can use resources more completely, and thus be more productive (Fridley 2001). Differences in plant species richness can affect ecosystem processes through partitioning of resources, whereby plants in more diverse communities may increase total resource capture, and thus increase net primary production. Such complementarity of resource use may occur in space or time, or depend on the type of resource (Ewel 1986). Species that are deeply rooted have more access to water and nutrients, which are not available to more shallowly rooted species (Johnson et al. 2000). The number of C. annuum roots decreased with increasing depth and distance from the stem (Gough 2001). From another perspective, C. annuum explored upper layers of the soil while A. lividus explored deeper layers (personal observation). There was a competitive advantage of C. annuum over A. lividus when the ratio of C. annuum in relation to A. lividus was either 5/1 or 4/2, resulting in higher C. annuum RY per plant (0.79 and 0.36) and decreased A. lividus RY (0. 09 and 0.13) (Fig. 7).


86


____________________________________________________________________________________________________________________

Relative yield of each species (g dry weight per pot)

This suggests that C. annuum growth can reduce the growth of A. lividus when its proportion is 5/1 or 4/2 where the values are 0.85 and 0.35. For both species, RY is < 1, which denotes that for both species interspecific competition was greater than intraspecific competition. In such a case, the biomass of either species is reduced in the presence of the other species (Williams & McCarthy 2001). The relative total yield (g TDW/pot) was constant and greater than 1. However, the RY for both plants was not constant and was < 1 (Fig. 6). RYc followed the hypothetical line except at the ratio c2a4, where it deviated from its hypothetical curve. RYa was also < 1 but above the hypothetical line. RYa deviated from the hypothetical line for at least two proportions (c3a3, and c4a2). These results indicate, first, that the two species have different demands for resources, and second, that A. lividus was more competitive than C. annuum when the density of C. annuum was greater than three plants although less than three C. annuum plants per pot made C. annuum more competitive than A. lividus. In such a case, there was benefit to A. lividus and damage to C. annuum. Second, the competition between both plants occurred for the same environmental resources, which were used more efficiently by A. lividus. A comparison between C. annuum and A. lividus shows that the relative yield of each plant and relative total yield of C. annuum and A. lividus in a competitive relationship were reduced as their proportion in the mixture changed, as verified by the 1,4

a

a

concavity of the RYc and RYa curves (Fig. 7). In addition, RYT was < 1.0, which indicates antagonist competition (de Wit & Goudriaan 1978), which suggests interference caused by the allelopathic action. Radhouane and Rhim (2014) reported that C. annuum is toxic intra-specifically and inter-specifically against pear millet. Tsuchiya et al. (1994) stated that the yields and quality of C. annuum in Korea had been decreasing due to continuous cropping, suggesting that allelopathy may have accounted for this phenomenon since the water or organic solvent extracts of leaves, stems, roots and soil in which plants had been cultivated inhibited seed germination. Moreover, these authors reported that the methanolic extracts of the stem and roots of C. annuum strongly inhibited radicle growth, while the methanolic extracts of leaves and roots and aqueous root extract inhibited hypocotyl growth of C. annuum seedlings. This allelopathic potential of different parts of the C. annuum plant may be applied to weed management (Gonzalez et al. 1992, 1993). Capsaicin, abundant in the Capsicum genus (C. annuum, C. frutescens and C. chinense) (Al Othman et al. 2011), may act as an inhibiting allelochemical after being released into soil after the decomposition of senescent pepper tissues or by exudation from their roots and its effectiveness increases as the dose increases, although the effectiveness differs among target plants (Kato-Noguchi & Tanaka 2003). a

a

c

b

a

1,2 1

a

0,8 0,6

a b

e

0,2

e

c d

0,4

RYc/pot RYa/pot RYT/pot

d

0 c5a1

c4a2 c3a3 c2a4 Proportion of each species in the mixture

c1a5

Fig. 6. Relative yields (RY) in g, dry weight per pot of Capsicum annuum (RYc) and Amaranthus lividus (RYa) as well as relative yield total (RYT) estimated from Capsicum and Amaranthus grown in competition in a replacement experiment. c = Capsicum, a = Amaranthus. Dashed lines refer to the relative hypothetical productivity when there is no interference by one species with another. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across proportions. Bars represent means ± SE (n = 10)


87


____________________________________________________________________________________________________________________

RYc/plant RYa/plant RYT/plant

Relative yield of each species (g dry weight per plant)

1,2 1

a

a

0,8 0,6

a

a

0,4 0,2

b

b c

e

d

d c

e

0 c5a1

c4a2

c3a3

c2a4

c1a5

Proportion of each species in the mixture

Fig. 7. Relative yields (RY) in g, dry weight per plant of Capsicum annuum (RYc) and Amaranthus lividus (RYa) as well as relative yield total (RYT) estimated from Capsicum and Amaranthus grown in competition in a replacement experiment. c = Capsicum, a = Amaranthus. Dashed lines refer to the relative hypothetical productivity when there is no interference by one species with another. Data was separated by ANOVA, and significant differences assessed by the F-test and LSD at P = 0.05, and indicated by different letters across proportions. Bars represent means ± SE (n = 10) Table 1. Values of relative crowding coefficients (RCC) and aggressivity for the mixture of Capsicum annuum and Amaranthus lividus as affected by plant density evaluated after 40 days after planting Proportions of Capsicum : Amaranthus 1/5 (16.6%) 2/4 (33.3%) 3/3 (50.0%) 4/2 (66.6%) 5/1 (83.3%)

RCC of Capsicum annuum 5.10 ± 1.21 a 2.65 ± 0.95 b 2.09 ± 0.81 c 1.24 ± 0.62 e 1.38 ± 0.35 d

RCC of Amaranthus lividus 0.82 ± 0.21 e 1.65 ± 0.35 d 2.95 ± 0.51 a 2.53 ± 0.65 b 2.20 ± 0.15 c

Means of aggressivity 1.88 ± 0.11 a 0.38 ± 0.09 b −0.70 ± 0.12 c −2.00 ± 0.15 d −5.71 ± 0.21 e

Means ± SE in each column followed by same letters at superscripts are not significantly different at p = 0.05 based on LSD test. Experiment was repeated twice.

3. Relative crowding coefficient RCC (Table 1) was used to measure the competitiveness of A. lividus against C. annuum and the competitiveness of C. annuum against A. lividus. For C. annuum, RCC decreased from 5.10 to 1.24 as its proportion increased from 1Cap/5Al to 4Cap/2Al, respectively. The RCC of the proportion 5Cap/1Al was slightly larger than the proportion 4Cap/1Al. However, the RCC of C. annuum at two proportions (1Cap/5Al and 2Cap/4Al) was greater than that of A. lividus. The RCC of A. lividus increased from 0.82 to 2.95 as its proportion decreased from 1Cap/5Al to 3Cap/3Al, respectively but decreased from 2.95 to 2.20 as its proportion decreased from 3Cap/3Al to 5Cap/1Al, respectively. However, the RCC of A. lividus at three proportions (3Cap/3Al, 4Cap/2Al and 5Cap/1Al) were greater than that of C. annuum. Species with a higher RCC indicate that it is more competitive, or the stronger competitor (Fischer

et al. 2001). When the proportions 1Cap/5Al, 4Cap/2Al, C. annuum was a superior competitor than A. lividus. However, at the proportions were 3Cap/3Al, 2Cap/4Al, and 5Cap/1Al, A. lividus was a superior competitor than C. annuum. A. lividus had lower RCC values than C. annuum when its proportion was larger than 16.6%, indicating that A. lividus was less aggressive towards C. annuum than vice versa (Table 1). Aminpanah et al. (2012) showed that the RCC values for aboveground DW, root DW, tiller number, leaf area, and height were higher for two weed species (Echinochloa crus-galli (L.) P. Beauv. and Echinochloa oryzicola Vasinger) than cultivated Oryza sativa L. ‘Hashemi’, indicating that both weed species were superior competitors to rice. 4. Aggressivity The aggressivity of C. annuum (Table 1), which is the difference between the relative dry yields of


88


____________________________________________________________________________________________________________________

C. annuum and A. lividus, was significantly influenced by the ratio of the species’ combination. The increase in the proportion of C. annuum from 1Cap/5Al to 5Cap/1Al (16.6% to 83.3%) decreased the aggressivity of C. annuum from +1.88 to −5.71, respectively, However, at the proportions of 1Cap/5Al and 2Cap/4Al (16.6% and 33.3%), aggressivity was positive and at the proportions of 3Cap/3Al, 4Cap/2Al and 5Cap/1Al (50% to 83.3%), aggressivity was negative. The aggressivity values for C. annuum decreased with its proportion in a pot. It was dominant at 1 and 2 seedlings per pot and not dominant at higher proportions. The aggressivity of C. annuum is modified by its own presence (autoaggressivity) as well as by the presence of A. lividus. From these results, increasing proportion of C. annuum in the mixture decreased its aggressivity and increased the aggressivity of A. lividus while the higher rate of C. annuum reduced its aggressivity. Wahla et al. (2009) showed that when the aggressivity value of one component is positive, then that component is more competitive than the other, and has a dominant effect (Bhatti et al. 2006). Our results support the findings of Sarkar and Chakraborty (2000), Sarkar and Sanyal (2000) and Sarkar and Kundu (2001), who reported the dominant effect of sesame (Sesamum indicum L.) having a “positive” aggressivity value when grown in association with mungbean (Vigna radiata L.), mashbean (Vigna mungo (L.) Hepper) and groundnut (Arachis hypogaea L.), respectively. The aggressivity of S. indicum + A. hypogaea at a 3 : 2 row ratio (Sarkar and Chakraborty, 2000), of S. indicum + V. mungo at a 2 : 1 row ratio (Sarkar & Sanyal 2000), S. indicum + V. radiata at a 3 : 2 row ratio (Sarkar & Kundu 2001) had a positive value of 0.37, 0.07 and 0.26, respectively. From our results, the control of A. lividus is highly recommended, in order to prevent its competition, probably for nutrients, water, and light, thus reducing Capsicum growth. In this study, the effect of A. lividus competition may have been overestimated due to pot size. Pot size probably contributed to nutrient competition due to constraints in root growth caused by a small soil volume. Markham and Halwas (2011) found a significant reduction in plant growth when soil volume was reduced. Moreover, plants grown with neighbors tend to be smaller

than plants grown alone (Laird & Aarssen 2005). Moreover, taking into account that interference among neighboring plants occurs after a specific plant density has been reached (Aldrich 1987; Ronchi & Silva 2006), in addition to competition between plants, intra-specific competition among individuals of the same species almost certainly had also occurred, mainly at higher densities. Under field conditions, soil volume restriction to root growth is probably much lower than that observed in pots, so field trials would be required to test this hypothesis and to see whether the same growth responses of both crops would result in the field. Moreover, in Tunisia, A. lividus densities in Capsicum fields are usually much higher than those examined in this study. Hachem (2003) reported 4550 seedlings of A. lividus / 50 cm2 in the field where C. annuum was cultivated. This density could lead to a higher degree of competition reported in our study. CONCLUSIONS The harmful effects of A. lividus competition on Capsicum plant growth varied greatly depending on A. lividus density. These adverse effects of A. lividus on Capsicum growth were brought about probably through competition mainly for essential nutrients and light. The increase in the density of A. lividus significantly decreased the growth of C. annuum seedlings. The results from the replacement series indicate that the competitive relation between C. annuum and A. lividus changed with the proportion of each species in the mixture. A. lividus was a superior competitor than C. annuum at c3a3, c4a2 and c5a1. The same tendency was observed for C. annuum, at c1a5 and c2a4, in which C. annuum was a superior competitor than A. lividus. These results suggest that under competitive conditions, C. annuum produces more than expected when it is found at a lower proportion in the mixture thus intraspecific competition is more important than interspecific competition. The same can be said for A. lividus, which suffered from competitive interference when it was more abundant in the mixture (i.e., it suffered more from intraspecific competition than from competition with C. annuum plants). However, a single factor, such as proportion, is not


89


____________________________________________________________________________________________________________________

enough to predict interference between two species. Future studies should evaluate the effect of water, light and nutrients on the co-growth of these species. Under the present experimental conditions, when even one A. lividus plant was able to significantly decrease the dry weight of C. annuum seedlings, the control of A. lividus is highly recommended to prevent competition with C. annuum and to increase the growth (and consequently productivity and yield) of C. annuum. REFERENCES Agarwal A., Gupta S., Ahmed Z. 2007. Influence of plant densities on productivity of bell pepper (Capsicum annuum L.) under greenhouse in high altitude cold desert of Ladakh. Acta Horticulturae 756: 309-314. DOI: 10.17660/ActaHortic.2007.756.32. Aldrich R.J. 1987. Predicting crop yield reductions from weeds. Weed Technology 1: 199-206. Al Othman Z.A., Ahmed Y.B.H., Habila M.A., Ghafar A.A. 2011. Determination of capsaicin and dihydrocapsaicin in Capsicum fruit samples using high performance liquid chromatography. Molecules 16: 8919-8929. DOI: 10.3390/molecules16108919. Aminpanah H., Sharifi P., Firouzi S. 2012. Interference interactions of two species of Echinochloa genus with rice. Chilean Journal of Agricultural Research 72: 364-370. DOI: 10.4067/S0718-58392012000300010. Aminpanah H. 2013. Influence of nitrogen rate on competition between two rice (Oryza sativa L.) cultivars and barnyardgrass (Echinochloa crus-galli (L.) P. Beauv). International Journal of Biosciences 3: 90-103. DOI: 10.12692/ijb/3.4.90-103. Asaduzzaman M., Robbani M., Ali M., Hasan M.M., Begum M., Hasan M.M. et al. 2015. Mother bulb weight and plant density influence on seed yield and yield attributes of onion. International Journal of Vegetable Science 21: 98-108. DOI: 10.1080/19315260.2013.825897. Berry A.D., Stall W.M., Rathinasabapathi B., MacDonald G.E., Charudattan R. 2006. Aggressivity: cucumber vs. amaranth. Weed Technology 20: 986991. DOI: 10.1614/wt-04-270.1. Bhatti I.H., Ahmad R., Jabbar A., Nazir M.S., Mahmood T. 2006. Competitive behaviour of component crops in different sesame-legume intercropping systems. International Journal of Agriculture and Biology 8(2): 165-167. Boatright S.R., McKissick J.C. 2004. 2003 Georgia farm gate value report. Area Report No. 04-01. The Uni-

versity of Georgia, College of Agricultural and Environmental Science, Center for Agribusiness and Economic Development, 182 p. Boughalleb N., El Mahjoub M. 2005. The effect of soil solarization on Phytophtora nicotianae Breda de Haan var. parasitica (Dastur) G.M. Waterhouse, responsable for syndrome associating root rots and damping-off of pepper (Capsicum annuum L.) in Tunisia. Tropicultura 23: 169-176. [in French with English abstract] Carvalho S.J.P., Buissa J.A.R., Nicolai M., LópezOvejero R.F., Christoffoleti P.J. 2006. Differential susceptibility of Amaranthus genus weed species to the herbicides trifloxysulfuron-sodium and chlorimuron-ethyl. Planta Daninha 24: 541-548. DOI: 10.1590/S0100-83582006000300017. [in Portuguese with English abstract] Dekker J. 2011. Evolutionary ecology of weeds. Weed Biology Laboratory, Department of Agronomy, Iowa State University, Ames, Iowa, USA, 305 p. www.agron.iastate.edu/~weeds/AG517/517Course /EEWbook.html (last accessed 6 April 2016) de Wit C.T., Goudriaan J. 1978. Simulation of ecological processes. Simulation Monographs. Centre for Agricultural Publishing and Documentation (PUDOC), Wageningen, The Netherlands, 175 p. de Wit C.T. 1960. On competition. Verslagen van landbouwkundige onderzoekingen 66:1-82. Ewel J.J. 1986. Designing agricultural ecosystems for the humid tropics. Annual Review of Ecology and Systematics 17: 245-271. DOI: 10.1146/annurev.es.17.110186.001333. FAOSTAT 2013. Pepper. http://faostat3.fao.org (last accessed 6 April, 2016) Fetene M. 2013. Intra- and inter-specific competition between seedlings of Acacia etbaica and a perennial grass (Hyparrenia hirta). Journal of Arid Environments 55: 441-451. DOI: 10.1016/S01401963(03)00052-1. Fischer A.J., Ramírez H.V., Gibson K.D., da Silveira Pinheiro B. 2001. Competitiveness of semidwarf upland rice cultivars against palisadegrass (Brachiaria brizantha) and signalgrass (B. decumbens). Agronomy Journal 93: 967-973. DOI: 10.2134/agronj2001.935967x. Fridley J.D. 2001. The influence of species diversity on ecosystem productivity: how, where, and why? Oikos 93: 514-526. DOI: 10.1034/j.16000706.2001.930318.x. Gonzalez L., Souto X.C., Bolano J.C., Reigosa M.J. 1992. Allelopathic potential of different accessions of Capsicum annuum L. application to weed management. In: Proceedings of the 1992 Congress of the Spanish Weed Science Society, pp. 367-372.


90


____________________________________________________________________________________________________________________

Gonzalez L., Souto X.C., Reigosa M.J. 1993. Potential of different pepper cultivars (Capsicum annuum L.) as weed controllers by allelopathy agents in Galicia (North Spain). In: 8th EWRS Symp.: Quantitative approaches in weed and herbicide research and their practical application. Braunschweig, Germany, pp. 143-150. Gough R.E. 2001. Color of plastic mulch affects lateral root development but not root system architecture in pepper. HortScience 36: 66-68. Hager A.G., Wax L.M., Stoller E.W., Bollero G.A. 2002. Common waterhemp (Amaranthus rudis) interference in soybean. Weed Science 50: 607-610. DOI: 10.1614/00431745(2002)050[0607:CWARII]2.0.CO;2. Harper J.L. 1977. Population biology of plants. Academic Press, University of California, USA, 892 p. Hachem M.W. 2003. Flore adventices de la culture de piment. Projet de Fin d’Étude. Superior Institute Agronomic (Ex ESHE), Chott-Meriem, Sousse, Tunisia, 36 p. Hoffman M.L., Buhler D.D. 2002. Utilizing Sorghum as a functional model of crop–weed competition. I. Establishing a competitive hierarchy. Weed Science 50: 466-472. DOI: 10.1614/00431745(2002)050[0466:USAAFM]2.0.CO;2. Holm L., Doll J., Holm E., Pancho J., Herberger J. 1997. World weeds: natural histories and distribution. John Wiley & Sons, 1129 p. Jala A., Wongsarasin A. 2012. Effect of allelochemical from Amaranthus lividus L. on the germination of chili (Capsicum frutescens L.). Thai Journal of Science and Technology 1: 25-31. Kato-Noguchi H., Tanaka Y. 2003. Effects of capsaicin on plant growth. Biologia Plantarum 47: 157-159. DOI: 10.1023/A:1027317906839. Lahbib K., Bnejdi F., El-Gazzah M. 2012. Genetic diversity evaluation of pepper (Capsicum annuum L.) in Tunisia based on morphologic characters. African Journal of Agricultural Research 7: 3413-3417. DOI: 10.5897/ajar11.2171. Laird R.A., Aarssen L.W. 2005. Size inequality and the tragedy of the commons phenomenon in plant competition. Plant Ecology 179: 127-131. DOI: 10.1007/s11258-004-6737-4. Markham J., Halwas S. 2011. Effect of neighbour presence and soil volume on the growth of Andropogon gerardii Vitman. Plant Ecology & Diversity 4: 265268. DOI: 10.1080/17550874.2011.618515. McGilchrist C.A., Trenbath B.R. 1971. A revised analysis of plant competition experiments. Biometrics 27: 659-671. DOI: 10.2307/2528603. Morales-Payan J.P., Charudattan R., Stall W.M., DeValerio J.T. 2003. Surfactants affect the efficacy of the

potential mycoherbicide Phomopsis amaranthicola to suppress Amaranthus lividus in bell pepper. Proceedings, Southern Weed Science Society 56, Section XI, p. 326. Morales-Payan J.P., Charudattan R., Stall W.M., DeValerio J. 2002. Time and number of application of the mycoherbicide Phomopsis amaranthicola affect Amaranthus lividus interference with pepper. Phytopathology 92(6) Suppl.: 58. Morales-Payan J.P., Santos B.M., Stall W.M., Bewick T.A. 1999. Influence of nitrogen fertilization on the competitive interactions of cilantro (Coriandrum sativum) and purple nutsedge (Cyperus rotundus). Journal of Herbs, Spices & Medicinal Plants 4: 5966. DOI: 10.1300/J044v06n04_07. Morales-Payan J.P., Stall W.M. 2002. Time of removal and population density effects of livid amaranth (Amaranthus lividus) on bell pepper (Capsicum annuum). HortScience 37: 747-748. Murphy T.R., Colin D.L., Dickens R., Everest J.W., Hall D., McCarty L.B. 2010. Weeds of Southern turfgrasses. Special Bulletin 31. Cooperative extension service, College of Agricultural and environmental Sciences, The University of Georgia, 208 p. Johnson W.C., Jackson L.E., Ochoa O., van Wijk R., Peleman J., St. Clair D.A., Michelmore R.W. 2000. Lettuce, a shallow-rooted crop, and Lactuca serriola, its wild progenitor, differ at QTL determining root architecture and deep soil water exploitation. Theoretical and Applied Genetics 101: 1066-1073. DOI: 10.1007/s001220051581. Jolliffe P.A., Gaye M.M. 1995. Dynamics of growth and yield component responses of bell pepper (Capsicum annuum L.) to row covers and population density. Scientia Horticulturae 62: 153-164. DOI: 10.1016/0304-4238(95)00766-M. Price T.D., Qvarnström A., Irwin D.E. 2003. The role of phenotypic plasticity in driving genetic evolution. Proceedings of the Royal Society B: Biological Sciences 270: 1433-1440. DOI: 10.1098/rspb.2003.2372. Procópio S.O., Santos J.B., Silva A.A., Martinez C.A., Werlang R.C. 2004. Physiological caracteristics of soybean and common bean crops and three weed species. Planta Daninha 22: 211-216. DOI: 10.1590/S0100-83582004000200006. [in Portuguese with English abstract] Quintero I., Barraza F. 2009. Population density and phenotype plasticity of chilli pepper (Capsicum annuum L.) c.v. Cayene Long Slim. Intropica 4: 5566. [in Portuguese with English abstract] Radhouane L., Rhim T. 2014. Allelopathic interaction of pepper (Capsicum annuum) and pearl millet


91


____________________________________________________________________________________________________________________

(Pennisetum glaucum) intercropped. International Journal of Environment 3: 32-40. DOI: 10.3126/ije.v3i1.9940. Ronchi C.P., Silva A.A. 2006. Effects of weed species competition on the growth of young coffee plants. Planta Daninha 24: 415-423. DOI: 10.1590/S010083582006000300001. Sarkar R.K., Chakraborty A. 2000. Biological feasibility and economic viability of intercropping pulse and oilseed crops with sesame (Sesamum indicum) under different planting patterns in rice-fallow gangetic alluvial land. Indian Journal of Agricultural Sciences 70: 211-214. Sarkar R.K., Kundu C. 2001. Sustainable intercropping system of sesame (Sesamum indicum) with pulse and oilseed crops on rice fallow land. Indian Journal of Agricultural Sciences 71: 90-93. Sarkar R.K., Sanyal S.R. 2000. Production potential and economic feasibility of sesame (Sesamum indicum L.) based intercropping system with pulse and oilseed crops on rice fallow land. Indian Journal of Agronomy 45: 545-550. Silva A.F., Concenço G., Aspiazú I., Ferreira E.A., Galon L., Coelho A.T.C.P., Silva A.A., Ferreira F.A. 2009. Interference of different weed densities in soybean growth. Planta Daninha 27: 75-84. DOI: 10.1590/S0100-83582009000100011. [in Portuguese with English abstract] Spehia R.S., Sharma V., Raina J.N., Bhardwaj R.K. 2014. Growth, yield and economics of greenhouse grown coloured capsicum as influenced by trellis system

and plant spacing. Indian Journal of Agricultural Sciences 84:742-745. Tétard-Jones C., Kertesz M.A., Preziosi R.F. 2011. Quantitative trait loci mapping of phenotypic plasticity and genotype–environment interactions in plant and insect performance. Philosophical Transactions of the Royal Society B: Biological Sciences 366: 1368-1379. DOI: 10.1098/rstb.2010.0356. Tsuchiya K., Lee J.W., Hoshina T. 1994. Allelopathic potential of red pepper (Capsicum annuum L.). Japan Agricultural Research Quarterly 28: 1-11. Wahla I.H., Ahmad R., Ehsanullah, Ahmad A., Jabbar A. 2009. Competitive functions of components crops in some barley based intercropping systems. Int. J. Agric. Biol. 11: 69-72. Wiersema J.H., León B. 2013. World economic plants. A standard reference, 2 ed., CRC Press, 1336 p. Williams A.C., McCarthy B.C. 2001. A new index of interspecific competition for replacement and additive designs. Ecological Research 16: 29-40. DOI: 10.1046/j.1440-1703.2001.00368.x. Yachi S., Loreau M. 2007. Does complementary resource use enhance ecosystem functioning? A model of light competition in plant communities. Ecology Letters 10: 54-62. DOI: 10.1111/j.14610248.2006.00994.x. Zarochentseva O. 2012. Adaptation of methodology calculation relative crowding coefficient for evaluation competition of three species in polyculture. In: 18th International Scientific Conference: “Economics for Ecology”. Sumy, Ukraine, p. 196-197.


tmp445A.tmp

Recommend Documents