Genetic Divergence for Resistance to Shootfly, Atherigona soccata Rond. in Sorghum, Sorghum bicolor (L.) Moench and its Relationship with Heterosis

Genetic diversity analysis was conducted on a set of 20 sorghum [Sorghum bicolor (L.) Moench] cultivars having resistance to shootfly (Atherigona soccata Rond.), originating from different geographic regions, and representing different taxonomic groups. The genetic diversity for shootfly resistance was assessed using multivariate analysis (D2 statistic and canonical variate analysis), and geographic/taxonomic divergence. The grouping of cultivars based on genetic divergence was found more accurate and relevant than that based on either geographic or taxonomic divergence. Both D2 and canonical variate analyses gave very similiar clustering patterns over the years analysed. Trichome density contributed mainly toward genetic divergence in shootfly resistance, followed by glossiness. Based on the presence or absence of these traits, the cultivars resistant to shootfly were classified into four major clusters. Resistant cultivars IS 844 and IS 1054 formed separate clusters over the years. Heterosis for shootfly resistance was found associated with genetic divergence but not with geographic or taxonomic divergence.