Resistance Breeding for Northern Corn Leaf Blight with Dominant Genes, Polygene, and Their Combinations-Effects on Disease Traits

Resistance breeding is the most effective method to control northern corn leaf blight (NCLB). The objectives were to (1) Assess effects of dominant genes (Ht(s)), polygene (PG), and their combinations to disease rating (DR), number of lesions per leaf (NLPL), and lesion size (LS); (2) Estimate genetic components, general combining abilities (GCA), and heritability under two Line x Tester analyses; and (3) Determine gene action through mid-parent heterosis (MPH) and better-parent heterobeltiosis (BPH) analysis. A total of 163 genotypes, including 120 crosses, their parents, and 10 hybrid checks, were evaluated under two NCLB artificial inoculations in 2015 and 2016. The results indicated that PG had the best resistance to DR, NLPL, and LS in crosses, followed by PGHt(s) and single Ht(s). Ht1 had both resistant and susceptible lesions. Ht2 and Ht3 expressed more resistance to LS significantly, while Htm1 and Htn1 had more resistance to NLPL. Htm1/Ht2, PG/Htm1, and the other 11 combinations were found excellent for NCLB resistance. Line x Tester analysis showed that additive effects were more important, and GCA of Ht(s) reduced disease traits. However, lower narrow sense heritability indicated that additive effects were low. MPH and BPH results showed that dominant and over-dominant gene actions existed for DR and NLPL.