Pigeon pea grain physical characteristics and resistance to attack by the bruchid storage pest

Five grain physical traits comprising grain length, breadth, hardness, testa thickness and 1000-grain mass (TGM) were evaluated for their relative influence on the susceptibility of six pigeon pea genotypes to the bruchid (Callosobruchus maculatus F.). Correlation studies and path analysis were employed to assess the interrelationships and contributions of the traits studied. Heritability in broad sense, H2 (bs) of selected trait(s) was also studied. Results showed that some of the genotypes differed as to their grain physical characteristics. Genotypes ICPL 87 and ICPL 161 had low susceptibility indices and were classified as having moderate levels of resistance. Resistant genotypes were, in addition to low susceptibility indices, characterized by low ovipositon count, grain damage and grain mass loss. Correlation studies showed that testa thickness was the only physical character having strong correlation with susceptibility index (r = -0.753, P<0.01). However, the low heritability estimate of the trait suggests that selection of pigeon pea genotypes through this trait may be unreliable. Path coefficient analysis revealed that TGM had the highest direct effect of +1.369 with susceptibility index, although, their total correlation coefficient was low (+0.215). There were opposing influences of the four negative indirect effects of the other traits which resulted in the low total correlation value observed. The high heritability estimate of TGM indicated a better prospect for the improvement of the crop species through selection of the trait. TGM and testa thickness were therefore considered to be the most important factors responsible for resistance to bruchid, but TGM was more reliable for use in the selection of pigeon pea for improvement. All the traits assessed expressed higher magnitude of phenotypic coefficient of variation (PCV) relative to the genotypic coefficient of variation (GCV).