An Assessment of Two Genes for Cercospora Leaf Spot Resistance in the Southernpea (Vigna unguiculata (L.) Walp.)1

Abstract The gene Cls 1 and the recessive gene cls 2 each conditions a high level of resistance to a leaf spot incited by Cercospora cruenta Sacc. Two Cercospora leaf spot (CLS) resistant breeding lines, CR 17-1-34 (homozygous for Cls 1 ) and Ala. 963.8 (homozygous for cls 2 ), were crossed with each other and with each of 3 susceptible cultivars. The F 1 and F 2 progenies of these crosses, the backcrosses of the CR 17-1-34 × Ala. 963.8 cross, and the parental lines were grown in a field experiment in which a natural CLS epiphytotic was allowed to develop. Cls 1 was completely dominant in all crosses; no evidence was found that either modifying factors or environment had any significant impact on its expression. The cls 2 allele was found not to be a complete recessive under weak epiphytotic conditions, but an incomplete dominant that was highly influenced by the environment when in the heterozygous condition. Cls 1 and cls 2 were neither allelic nor linked.