New sorghum leaf blight resistance sources: Identification, description and reactions of F1 hybrids

Abstract

Leaf blight [Setosphaeria turcica (Luttrell) Leonard & Suggs] limits sorghum [Sorghum bicolor (L.) Moench.] under sub-humid climates with moderate temperature. Under a severe leaf blight epidemic, 152 sorghum conversion lines were screened for resistance in Isabela, Puerto Rico, in 1985. Among all entries, a mean of 2.4 lesions per leaf was found. One or fewer lesions/leaf were found on 25 lines, 20 of which were not previously known for their leaf blight resistance. In late summer and early fall, resistant sources were crossed with leaf blight susceptible male sterile, ATx623 and TP24, used as females. Leaf blight reactions of the resistant sources (male parents), susceptible female parents (ATx623 and TP24), and F₁ hybrids (ATx623 X resistant sources and TP24 X resistant sources) were evaluated in spring 1986. The t-statistic showed highly significant (P<0.001) differences between resistant male parents (0.4 lesions/leaf) and ATx623 and TP24, respectively. Significant (P<0.05) difference was found between F₁ hybrids (0.9 lesions/leaf) and the male resistant sources (0.4 lesions/leaf). F₁ hybrids were significantly more resistant (P<0.01) than both susceptible female populations. Susceptible female populations ATx623 and TP24 showed no significant difference in their leaf blight readings. More than 25% of leaf blight resistant sources had high seed astringency. Astringency was found in less than 10% of the original screening and was not found in female populations. Astringency appeared dominant in F₁ hybrids. Variability of resistant sources in morphology and origin, decreased resistance and increased variability of F₁ hybrids for leaf blight suggest genetic factors other than a sole dominant resistance allele are influencing leaf blight reactions in sorghum.