Effect of Normal Cytoplasms on Resistance to Southern Corn Leaf Blight and on Other Traits of Maize1

Abstract

Maize (Zea mays L.) hybrids having Texas male‐sterile cytoplasm are much more susceptible to Race T of Helminthosporium maydis Nisikado and Miyake than normal cytoplasm hybrids. This has raised questions about the effects of different normal cytoplasms on resistance to Race O of H. maydis.We evaluated 222 reciprocal plant‐to‐plant crosses, involving 60 diverse germplasm sources, in a 3‐stage series of tests for cytoplasmic effects on susceptibility to H. maydis and other traits. F2 and F3 crosses were used in the second and third stages, respectively, to eliminate maternal seed effects. The crosses were subjected to both Race O and Race T of H. maydis.In the second stage of testing one cross was found to have an appreciable reciprocal effect on susceptibility to H. maydis. This cross, along with several others, also showed significant reciprocal differences for such traits as height, maturity, and yield. However, when the three crosses having the largest differences between reciprocals were retested using fresh seed, the differences observed the previous year were not found. We conclude that many, if not all of the apparently significant differences found in the second stage of testing were due to sampling variation or maternal seed effects, and that the normal maize cytoplasms we tested had no measurable effect on susceptibility to H. maydis or on several other traits.