Genotype x environment interaction in advanced breeding lines of Cowpea (Vigna unguiculata (L.) Walp)

Abstract

Cowpea (Vigna unguiculata (L.) Walp) is an important tropical and subtropical annual legume crop grown for its green pods, grains and is also being used as a forage crop. It is one among the widely cultivated and consumed grain legumes, globally. As the grains contain high amount of protein (23.4 %) possessing better biological value on dry weight basis, cowpea is often considered as “vegetable meat”. Its ability to fix atmospheric nitrogen and drought tolerance makes it a suitable component in all major cropping systems. The present study entitled ‘Genotype x environment interaction in advanced breeding lines of Cowpea (Vigna unguiculata (L.) Walp)’ was an attempt to identify suitable and stable lines for general cultivation as a dual purpose type (both as grain purpose and vegetable purpose). Materials used for the study comprised of five cowpea cultures in stabilized F 7 generation developed as a result of pedigree selection from two crosses at the Department of Plant Breeding and Genetics, College of Agriculture, Vellanikkara, along with two check varieties, Anaswara and Kanakamony. The crop was raised during February 2021 to May 2021 over three environments viz., RARS Pattambi, CoA Vellanikkara and RRS Vyttila. Field experiments were laid out in plots of size 65 m 2 adopting randomized block design (RBD) with three replications. Observations were recorded on twelve characters: plant height (cm), number of branches, days to first flowering, days to first harvest, days to last harvest, number of pods per plant, pod length (cm), pod weight (g), number of seeds per pod, test weight (g), grain yield per plant (g) and protein content (%). All the observations were recorded at the time of harvest except for days to first flowering. The recorded observations were subjected to individual, location wise analysis of variance (ANOVA) followed by pooled analysis of variance (pooled ANOVA) over three locations. From the pooled ANOVA, the characters that exhibited significant genotype x environment (G x E) interaction were further assessed for stability using three models of stability. The Eberhart and Russell model, the Additive Main effects and Multiplicative Interaction effects (AMMI) model and the Genotype main effects plus Genotype-by- Environment interaction effect (GGE) biplot were the three models of stability used for the study.ANOVA revealed significant difference between lines for all the twelve characters considered. However, the Bartlett’s test for examining the homogeneity of error variance was found to be significant only for six characters. These six characters viz., days to first flowering, days to last harvest, number of pods per plant, number of seeds per pod, grain yield per plant and protein content were subjected to pooled ANOVA across three environments. Significant G x E interaction was observed in the six characters considered and were hence forwarded for analysing the stability. The Eberhart and Russell model recognizes a stable genotype as the one with high mean performance, non-significant regression (bi) as well as deviation from regression (S 2 di) values. The genotypes were ranked according to their mean values and stability parameters and it was observed that genotype L 2 with the lowest score was the most stable one followed by L 1 and L 3 respectively. The AMMI model with its additive as well as multiplicative formulations could interpret the complex G x E patterns effectively through the AMMI biplots. Genotypes were scored and then ranked , according to their stability index (SI) value computed on the basis of rank of AMMI stability value (rASV) and the rank of performance for each character (rY). It was observed that L 2 with its lowest score ranked as the best and stable genotype followed by L 1 and L 5 . The GGE biplot model enabled effective interpretation of genotype x environment interaction by providing visual understanding of genotype and test- environment evaluation through mean versus stability graph, ranking of genotypes, ranking of environments and which won where analysis. On an overall basis it was - - identified from GGE biplot method that L 1 , L 2 and L 3 were the most stable and superior performing genotypes. Comparison of results from the three models of stability confirmed L 1 and L 2 as the most stable and promising genotypes. Hence these genotypes can be evaluated in large fields so as to confirm with the results and for checking the suitability of these genotypes to be released as a variety.