Classification of Genotypes of the Target Leaf Spot‐Resistant Gene (ds1) in a Sorghum Collection

Abstract

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal grown worldwide and is especially important in the semiarid tropics because of its tolerance of hot and dry environments. In addition, it has recently been used in biomass production due to its rapid summer growth in temperate zones. One sorghum disease called target leaf spot is caused by the necrotrophic fungus Bipolaris sorghicola (Lefebvre & Sherwin) Alcorn. Resistance to target leaf spot is controlled by a recently identified single recessive resistant gene (ds1). We studied the susceptibility of sorghum to target leaf spot and the polymorphism of ds1 and the geographic distribution of its alleles using selected specimens from a sorghum core collection. Among 86 lines in the National Institute of Agrobiological Sciences (NIAS) Genebank, 34 (39.6%) were susceptible to target leaf spot, each characterized by one of three alleles (S1, S2, and S3 types). The remaining 52 (60.4%) were resistant, with each characterized by one of four alleles (R1, R2, R3, and R4 types). Two new alleles of ds1, namely, the S3 type and the R4 type, were found in this study. The new alleles of ds1 both encoded mature protein. Both lines had an insertion in a promoter region, with one susceptible to target leaf spot and the other resistant, according to the assumption that the insertion altered transcriptional activity. Geographically, both susceptible and resistant alleles were found in African and South Asian lines. Only resistant alleles were found in the lines from East Asia, suggesting either a bottleneck effect or strong selective pressure by target leaf spot in East Asia. With these DNA markers, the susceptibility of sorghum to target leaf spot can be easily classified.