The Effect of C and S Group Cytoplasms on Resistance to Southern Corn Leaf Blight

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Abstract
Quantitative differences in disease resistance to randomly selected isolates of Bipolaris maydis occurred among C and S group male-sterile cytoplasms (cms) [in Zea mays]. Cms-pathogen isolate interactions were observed among 18 isolates of B. maydis and 17 male-sterile cytoplasms within the 38-11 .times. FR372 corn genotype. Greater average disease development associated with several cytoplasmic male-steriles indicated that cms-H, cms-I, cms-EK, cms-RB and cms-VG may be less desirable than others as alternatives to cms-T. Cms-EK, cms-IA and cms-TA in the Ky-21 line, and the R6-24 and R6-35 lines with normal cytoplasm, were reciprocally crossed in all combinations. The progeny were inoculated with B. maydis isolate Ch-448. Significant differences in disease reactions confirmed the association of cytoplasm source with quantitative differences in disease resistance. Cms-EK conferred lower resistance, and cms-IA and cms-TA conferred higher resistance to B. maydis isolate Ch-448 in the 38-11 .times. FR372 and Ky-21 genotypes. The quantitative differences in disease resistance and cms-pathogen isolate interactions observed indicate that cytoplasms differ in reaction to isolates of B. maydis, and that isolates of the pathogen differ in their response to cms. The potential for large-scale use of a single male-sterile cytoplasm to cause selection of pathogen strains more aggressive on plants with that cytoplasm is indicated.

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