Pedigree selection for spotted pod borer resistance in the segregating generation of Cowpea (Vigna unguiculata (L.) Walp.)

Abstract

Cowpea [Vigna unguiculata (L.) Walp.] is an important pulse crop grown across the world mainly in tropical and subtropical regions. Being a drought-tolerant and warm-weather crop, it is a promising food and forage species in a typical tropical lowland climate. Low productivity in cowpea is mainly attributed by the severe attack of pest complexes, diseases, low fertile soils and lack of inputs. Among the various obstructions responsible for diminishing the production of cowpea, the predominant factor is the damage caused by insect pests. Among the various insect pest causing economic losses, the spotted pod borer, Maruca vitrata (Lepidoptera: Crambidae) acts as the most damaging one. Hence, the present investigation was conducted in the Department of Plant breeding and Genetics, College of Agriculture, KAU, Vellanikkara with the objective of Pedigree selection from early segregating generations of cowpea hybrids for resistance against spotted pod borer. Ambavane (2018) identified that ten superior F2 lines from the cross Vellayani Jyothika × EC 98668 were resistant to spotted pod borer. The present study involved the reconstitution of the above cross and the pedigree analysis of resultant segregating material. Through hybridisation between Vellayani Jyothika and EC 98668, ten hybrid plants were produced. These hybrids were evaluated on morphological basis for resistance. Seeds from F1 hybrid were then sown to raise the F2 population. A population size of 500 plants was maintained in the F2 population and individual plant observations were taken for analysing their quantitative characters. The F2 population showed high variability for the characters like days to 50 per cent flowering, plant height, no. of pods per plant, pod length and grain yield per plant. However, low variability was observed in characters like no. of primary branches per plant, no. of seeds per pod and 100 seed weight. Selection was not carried out in the F2 population and the seeds were forwarded to raise the next generation. The genetic variability studies of the F2 population revealed that high PCV, GCV, heritability and GAM was recorded for characters like pod length, grain yield per plant and 100 seed weight. In F3 population, morphological and biochemical observations was carried out with the objective to select superior lines showing resistance to pod borer. The F3 population showed reduced variability for all quantitative characters except No. of seeds per pod compared to F2 population. The genetic variability studies of the F3 population also showed a similar trend like F2 population and showed high PCV, GCV, heritability and GAM for characters like pod length, grain yield per plant and 100 seed weight. Analysis of morphological basis of resistance to pod borer revealed a negative correlation of pod wall thickness, trichome density on pod and bud with pod damage. With respect to the biochemical basis of resistance to pod borer, total sugar content and total protein content showed significant positive correlation with pod damage. However, total phenol content and polyphenol oxidase activity was found to be negatively correlated with pod damage and the correlation was non-significant. Based on the correlation study and taking into account of the work of earlier studies, it is evident that the biophysical characters like pod wall thickness, pod trichome density, bud trichome density and biochemical characters like total sugar content, total protein content, total phenol content and polyphenol oxidase activity are highly associated with spoted pod borer resistance. Based on these results, a selection criteria was fixed. Thirty superior plants from F3 population were selected. These plants could be further evaluated to identify high yielding resistant lines.