Study of heterosis in Bangladeshi Chilli (Capsicum annuum L.) Landraces

Estudio de la heterosis en variedades nativas de chile (Capsicum annuum L.) de Bangladesh

M. Hasanuzzaman¹, M. A. Hakim^2,3*, M. M. Hanafi², Abdul Shukor-Juraimi⁴, M. M. Islam⁵, A. K. M. Shamsuddin⁶

¹ Department of Genetics and Plant Breeding.

³ Department of Agricultural Chemistry, HSTU, Dinajpur 5200, Bangladesh.

⁴ Department of Crop Science.

⁵ Department of Forest Management, Universiti Putra Malaysia, 43400 UPM Serdang Selangor, Malaysia.

⁶ Department of Genetics and Plant Breeding, BAU, Mymensingh, Bangladesh.

Received: September, 2012.
Approved: August, 2013.

Abstract

Keywords: Capsicum annuum L., indigenous X exotic cross, yield.

Resumen

El chile es un cultivo comercial importante en Bangladesh pero su rendimiento promedio es muy bajo (0.89 t ha ¹) y la potencialidad genética de las variedades nativas de chile de Bangladesh para desarrollar variedades híbridas no se ha evaluado. El objetivo de este estudio fue conocer el comportamiento heterótico siguiendo el modelo de Gardner y Eberhart (1966) II. Seis diferentes padres divergentes homocigóticos CCA 2, CCA 5, BARI Morich 1, CCA 11, CCA 15 y CCA 19 se usaron para estimar la heterosis. Hubo una cantidad significativa de heterosis en el rendimiento y las características que contribuyeron al rendimiento. La estimación de la heterosis varietal para rendimiento por planta fue significativamente positiva en CCA 5 y BARI Morich 1. En BARI Morich 1, la heterosis varietal significativa y positiva para el rendimiento por planta se asoció con las estimaciones significativas y positivas de heterosis para el número de frutos por planta y el número de semillas por fruto, sugiriendo que estos rasgos de rendimiento contribuyeron a la heterosis final manifiesta a través del rendimiento. Las cruzas nativas X exóticas mostraron una cantidad significativa de heterosis. Se puede enfatizar las cruzas nativas X exóticas para un buen rendimiento del fruto, particularmente si se usan como híbridos comerciales. Los híbridos de BARI Morich 1XCCA 19 and CCA 5 X BARI Morich 1 mostraron un mejor rendimiento.

Palabras clave: Capsicum annuum L., cruza nativo X exótico, rendimiento.

INTRODUCTION

Heterosis is an important avenue for increasing yield and other economic traits in capsicum peppers (Joshi, 1986). Chilli (Capsicum annuum L.) is a diploid (2n = 24) species and genetically self-pollinated and chasmogamous crop whose flowers open only after pollination (Lemma, 1998), and 2 to 96 % out-crossing was observed under open pollination (Tanksley, 1984; Pickersgill, 1997; AVRDC, 2000). Cross-pollination is caused by bees, by thrips and ants to a limited scale and rarely by wind (AVRDC, 2000).

Landrace varieties as parents show high heterosis and the fruit quality is higher than those of the landrace parents; besides, they show a rather good shape, smooth skin and large fruits (Milerue et al., 2000). Expression of heterosis in F1 hybrids of Capsicum species depends upon parents, which may be selected based on plant vigor, fruit size and yield (Greenleaf, 1947). According to Melchinger (1999), starting with genetically divergent populations as heterotic groups has advantage of maximum exploitation of heterosis and hybrid performance. Higher efficiency of inter-population improvement leads to superior hybrids by using divergent rather than genetically similar heterotic groups (Melchinger and Gumber 1998; Reif et al., 2007). Genetic diversity between parents, recognized as a requirement for maximal expression of heterosis, has probably arisen through diversity in origin (geographical separation), in ancestral relationships, in gene frequencies or in morphological traits (Virmani, 1996).

Average green chilli yield was 1.69 t ha^-1 during 2010-2011 (BBS, 2011), which is lower than the 1.59 t ha^-1 (dried chilli) obtained in India during 20112012 (MoA, 2012). Developing hybrid varieties with desirable qualities could reverse the low productivity trend, but heterosis in chilli has not been reported yet in Bangladesh. Therefore, the objective of this study was to estimate heterosis among six parents of chilli (Capsicum annuum L.).

MATERIALS AND METHODS

Experimental site and soil characteristics

This experiment was carried out at the Research and Development Farm of Lal Teer Seed Limited (23.9763° N and 090.3539° E), Gazipur, Bangladesh, from October 2007 to July 2009. The soil was clay loam, slightly acidic (soil pH 6.0 to 6.5) and low in nitrogen content.

Plant materials

Chilli genotypes CCA 2 (P1), CCA 5 (P2), CCA 15 (P5) and CCA 19 (P6) were Bangladeshi landraces, BARI Morich 1(P3) released by BARI, Bangladesh (center of origin Sri Lanka) and CCA 11 (P4) (collected from Thailand), were crossed in a diallel mating system excluding the reciprocals in winter season 20072008. The six genotypes were supplied by Lal Teer Seed Limited, Bangladesh. In the next winter season (2008-2009), all the six parents and their 15 F1's were studied.

Seed sowing, cultivation and crossing

In 2007-2008, the parental materials were sown on September 26, 2007 in seedling trays and transplanted into the field on November 3, 2007. Crossing was done in a 6X6 diallel design excluding reciprocals between December 2007 and April 2008. The mature F₁ fruits were harvested and dried and seeds were threshed and stored in a gene bank. In 2008-2009, the seeds of six parents and their 15 F₁'s were sown in seedling trays on September 10, 2008. Seedlings age of 4 to 5 leaves were transplanted to the field on October 16, 2008. Raised beds 1.5 m width were prepared for transplanting; plant to plant distance was 50 cm, row to row distance 70 cm and bed to bed distance 1.0 m which was used as drain. The experimental design was randomized complete block with three replications and the experimental unit was 3.5 mX1.5 m.

Components of heterosis in a diallel cross were estimated according to the Gardner and Eberhart (1966) model II. The analysis was performed on individual environments using the DIALLEL-SAS05 program (Zhang et al., 2005). The linear model (Zhang et al., 2005) was:

where Y_ij=mean of the cross between the ith and j^th parental populations, μ_v=mean of all parental populations, v_i=varietal effects of parental population I, v_j= varietal effects of parental population j, h= average heterosis contributed by all parental populations used in crosses, h_i= average contributions of individual parental population i to the expression of heterosis, h_j= average contributions of individual parental population j to the expression of heterosis, s_ij= specific heterosis (specific combining ability, SCA) that occurs when parental population i is crossed to parental population j, k= 0 when i= j and k= 1 when i≠j.

RESULTS AND DISCUSSION

Analysis of variance due to heterosis

The variances due to heterosis were significant for days to 50 % flowering, fruit length, fruit weight, number of seeds per fruit, number of fruits per plant and yield per plant (Table 1). These results suggested the presence of non-additive gene effects for these characters. Variation due to heterosis (overall heterosis) was partitioned into average, variety and specific heterosis.

Significant average heterosis (parents vs. F₁) of days to 50 % flowering, fruit length, fruit weight, number of fruits per plant, and yield per plant, showed heterosis. Variety heterosis was estimated to judge overall contribution of a variety to its array heterosis. The variance due to variety heterosis was significant for days to 50 % flowering, fruit length, fruit weight, number of seeds per fruit, number of fruits per plant and yield per plant. This result indicated the differences among the parental arrays for the heterosis of these characters (Table 1).

Importance of heterosis among crosses was assessed by variances due to specific heterosis which were significant for days to 50 % flowering, fruit length, fruit weight, number of seeds per fruit, number of fruits per plant and yield per plant. The results related to variance of different components of heterosis indicated that each significantly contributed to the total heterosis of the crosses. Souza and Maluf (2003) observed significant mean heterosis, varietal heterosis and specific heterosis components obtained from the Gardner-Eberhart (1966) analysis in number of seeds per fruit; however, mean heterosis was not significant in total fruit yield in Capsicum chinense. The varietal heterosis component of total fruit yield was not significant either, indicating that there were no significant differences among hybrid arrays of the different parental lines. The significance of the specific heterosis component in yield indicated that there are specific hybrid combinations with a high degree of heterosis. Therefore, in spite of the significance of the parental effects, the per se parental performance is not a good indicator of the hybrid total yield. The sum of the squares of all heterosis components contributed significantly to the treatment sum of the squares, showing the importance of non-additive genetic effects (dominance or epistasis) for the expression of number of seeds per fruit.

Among the six parents, only CCA 5 and BARI Morich 1 had significant positive estimates of yield per plant (Table 2) and significant positive estimates of heterosis for number of fruits per plant was expressed in BARI Morich 1, suggesting that this yield contributing trait contributed to the final heterosis observed through yield. Fruit weight played a significant role in parent CCA 5 by contributing significant variety heterosis in yield per plant. A significant positive estimate of number of seeds per fruits and plant height also was observed in BARI Morich 1. Souza and Maluf (2003) reported a significants positive and negative variety heterosis in seeds number per fruit, which is similar to the present result, but they found no parent significance for total fruit yield.

Specific heterosis of the crosses

Crosses P2XP3 and P3XP6 showed significant heterosis in fruit yield per plant and yield per plant, but in cross P3XP6 only number of seeds per fruit was significant (Table 3). These results are consistent with those obtained by Souza and Maluf (2003) who reported that 7 out 10 crosses were significant for specific heterosis in total fruit yield.

Top two yields per plant were obtained in cross P3XP6 (898.87g) and P2XP3 (833.63 g) (Table 4). In these two crosses parent BARI Morich 1 (Parent 3) was common, CCA 5 (Parent 2) and CCA 19 (Parent 6) were indigenous (Bangladesh) and BARI Morich 1 (Parent 3) was exotic (Sri Lanka). Indigenous X exotic crosses showed significant heterosis and they could be used for good fruit yield, as commercial hybrids, as well as for developing hybrid varieties. In hybrids among Asian lines there is high heterosis, indicating genetic diversity and potential for improving hot pepper using genotypes from different regions, along with elite inbred lines from local cultivars (Marame et al., 2009).

The high heterosis observed in this study suggests the usefulness of using genetically diverse germplasm in a breeding program. This is in agreement with the observations of Gill et al. (1973) and Shifriss and Sacks (1980) who reported that genetic divergence of the parents in Capsicum species is highly related to the heterosis of the F₁. Very closely or distantly related parents showed low heterosis, but crosses between parents of intermediate divergence classes tended to show higher heterosis effect for fruit yield, fruit length and fruit weight (Geleta et al., 2004) and large heterosis.

CONCLUSIONS

Bangladeshi land races have genetic potential for developing hybrid. This potentiality can be explored by crossing it with exotic Asian genotypes.

We are thankful to the Ministry of Higher Education Malaysia for financial support through the Research University Grant Scheme to Universiti Putra Malaysia.

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