Introduction
Chilli is one of the most important commercial and spice crops in India. Hence, India emerged as the foremost producer and exporter of chilli contributing one-fourth in the world market. In chilli, fruits are the harvestable, marketable and consumable economic products. Chilli produces fruits with varying orientations and numbers. The fruit orientation and fruit number node−1 are referred to as fruiting habit traits. The fruit orientation is either pendant or erect (Lee et al., Reference Lee, Cho, Kim, Park and Kim2008) and the number of fruits at a node is either one (solitary) or more than one (clustered). The fruit orientation is inherited as a recessive gene (up) in chilli (Lee, Reference Lee1994).
Farmer/producer and consumer preferences for fruiting habit vary from region to region. For example, cultivars bearing small erect fruits are more preferred over other types in Thailand (Milerue et al., Reference Milerue, Chuwongse, Struss and Wasee2016). Hence, green fruit yield, the harvestable and consumable economic product need to be maximized under preferred fruiting habit background. We hypothesize that the green fruit yield in chilli is not affected by fruiting habit traits and hence, it should be possible to develop high green fruit yielding cultivars with a preferred combination of fruiting habit traits. This study was carried out to test this hypothesis.
Experimental
Eight genotypes [CMS6B, CMS10B, CMS8B, Phule Jyothi (PJ), Pusa Sadabahar (PS), Pant C-1 (PC1), Japani Long (JL) and Gowribidanur local (GB)] with four distinct fruiting habit traits – solitary erect (SE), solitary pendant (SP), clustered erect (CE) and clustered pendant (CP) (online Supplementary Table S1) (Anilkumar et al., Reference Anilkumar, Mohan Rao, Ramesh, Bhavani, Mangalagowri and Ashwini2018) were chosen for the study.
Eight genotypes were crossed to generate ten F1 crosses of six types (CE × SE, CP × SP, CE × CP, CE × SP, CP × SE and SE × SP) in the poly-house during the 2015 rainy season. F1 plants were selfed to develop F2 and backcrossed to their respective recessive parents (Anilkumar and Mohan Rao, Reference Anilkumar and Mohan Rao2018; Anilkumar et al., Reference Anilkumar, Mohan Rao, Ramesh, Bhavani and Pranesh2020) to develop backcross populations during the 2016 summer at the experimental plots of the Department of Genetics and Plant Breeding (GPB), University of Agricultural Sciences (UAS), Bangalore, India.
Out of 10 crosses, one representing the cross involving parents differing for fruit orientation [PS × PJ] and one representing the cross involving parents differing for both fruits node−1 and fruit orientation [JL × CMS10B] were selected for the development of near-isogenic lines (NILs). A pair of NILs for fruit orientation from PS × PJ (PS – clustered erect and PS – clustered pendant) and three pairs of NILs for both fruits node−1 and fruit orientation from JL × CMS10B (JL:clustered erect and JL:clustered pendant, JL:clustered erect and JL:single erect and, JL:clustered erect and JL:single pendant) were developed by three cycles of backcrosses to PS and JL, respectively. The F2, backcross populations and four pairs of NILs constituted the experimental material.
F2 and backcross populations were evaluated during the 2016 and 2017 rainy seasons and four pairs of NILs were evaluated during the 2017 rainy season. Data were recorded on fruit length (cm), fruits plant−1, average fruit weight (g) and green fruit yield plant−1 (g). Plants in each F2, backcross and NILs were grouped into different fruiting habit classes (online Supplementary Table S2) based on visual assessment. The significance of fruit yield and its component traits among different fruiting habit classes were examined using two samples ‘t’ test and ‘F’ test (Fisher, Reference Fisher1950) as appropriate. All the analyses were performed using RStudio version 1.2.133 (RStudio team, 2019).
Discussion
In both F2 and backcross generations evaluated during the 2016 and 2017 rainy seasons, average fruit length, fruits plant−1, average fruit weight and green fruit yield plant−1 were comparable among plants producing either single/cluster fruits or pendant/erect fruits (Fig. 1). Similarly, in F2 and backcross generations derived from crosses involving parents differing for both fruits node−1 and fruit orientation, fruit length, fruits plant−1, average fruit weight and green fruit yield plant−1 were comparable among the plants producing any fruiting habit trait combinations, namely SP, SE, CP and CE as indicated by ‘F’ test during both the seasons (online Supplementary Tables S3 & S4). These results suggest a lack of either desirable/undesirable effects in favour of any fruiting habit trait concerning green fruit yield and its component traits. Although individuals belonging to F2 and backcrosses share comparable genetic backgrounds, they do not share a similar background. Hence, the chances of the confounding effect of genetic background on the differences between fruiting habit classes for green fruit yield and its component traits in F2 and backcross generations cannot be ruled out. The chances of the confounding effect of genetic background are minimized when NILs are used for investigating the effect of fruiting habit traits on green fruit yield.
Box-Whisker plots depicting the effect of (1) fruits node-1 and (2) fruit orientation on fruit yield and its component traits in A. F2 population and B. Back cross populations derived from crosses involving parents contrasting fruits node-1 and fruit orientation in chilli.
In one of the four pairs of NILs derived from PS × PJ (differing only for fruit orientation), the estimates of fruit length, fruits plant−1, average fruit weight and green fruit yield plant−1 were comparable between cluster-erect and cluster-pendant fruiting habit classes as indicated by ‘t’ statistic (Table 1). In other three pairs of NILs (derived from JL × CMS10B) differing for both the fruiting habit traits, fruits plant−1 and green fruit yield plant−1 were higher in the single-pendant fruiting habit class than those in single-erect class; while average fruit weight and fruit length were higher in cluster-pendant class than those in cluster-erect fruiting habit class as indicated by significant ‘F’ test (Table 1). Thus, the results from NILs indicate that plants bearing pendant fruits (irrespective of whether they are clustered or single) produce a large number of heavier and longer fruits than those bearing erect fruits. NILs share isogenic genetic background except for fruiting habits. Whereas F2 and backcrosses share a genetic background from both parents accounting for differences in results.
Relationship of fruits node−1 and fruit orientation with fruit yield and its component traits in NILs in chilli
Non-significant differences between fruiting habit classes for fruit yield and its contributing traits in both F2 and backcross populations and one pair of NILs indicated the lack of influence of fruiting habits on fruit yield and its contributing traits. However, there was a significant difference between NIL pairs with different fruiting habits developed from another pair of parents differing for both fruit orientation and fruits node−1. These results indicate the possibility of developing high yielding cultivars that produce pendant fruits.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S1479262121000058.
Acknowledgement
The senior author gratefully acknowledges the financial support from the University Grant Commission (UGC), New Delhi, India in the form of National Fellowship for students of other backward classes (NF-OBC) (F./201617/NFO201517OBCKAR47283)/(SAIII/Website) for pursuing a PhD degree.
Author's contribution
Conceptualization of research (AMR, SR); designing experiments (CA, AMR, SR, TLP); the contribution of experimental material (AMR); execution of field/lab experiments and data collection (CA); analysis of data and interpretation (CA, AMR, SR); preparation of the manuscript (CA, SR, AMR).
