Genetics and inheritance of fertility restoration of several male-sterile cytoplasms in corn (Zea mays. L.)

There has been limited use of male-sterile cytoplasm in the production of hybrid seed corn (Zea mays L.) since the 1970 epiphytotic of southern corn leaf blight (Helminthosporium maydis), race T. Corn researchers have since been studying the characteristics of other male-sterile cytoplasms in an attempt to replace the Texas source. Information regarding the inheritance of fertility restoration of these cytoplasms is essential in evaluating their potential usefulness. The inheritance of fertility restoration of several male-sterile cytoplasms was evaluated from fertility data of individual plants of F₁, F₂, and backcross generations. Inbreds Ky21 and T115 were used as restorer lines. The effect of planting date on fertility restoration of the various male-sterile cytoplasms also was determined. Restorers Ky21 and T115 fully restored the fertility of sterilized lines containing T, SC, and S-group male-sterile cytoplasms, but only partially restored the fertility in C, RE, and El Sal cytoplasms. Cytoplasms T and SC reacted similarly in fertility restoration and appear to belong to the same group. The fertility restoration of most S-group cytoplasms was similar when crossed by T115, but variations among these cytoplasms were observed when crossed by Ky21. Fertility data obtained from crosses containing C, RB, and El Sal cytoplasms were too variable to determine the inheritance of their fertility restoration. These cytoplasms appear, however, to belong to the same group. Date of planting had little effect on fertility restoration of T, SC, and S-group cytoplasms. The fertility expression of C, RB, and El Sal cytoplasms was greatly affected by date of planting, with fertility restoration being inhibited more in the later plantings. The results of this study suggest that since restoring and nonrestoring inbreds differ in genotype with respect to fertility restoration, any statement concerning the fertility restoration of a certain male-sterile cytoplasm is true only with respect to the particular restorer and sterilized lines used in the cross.