Relationships between grain yield and growth rates of plant parts as influenced by male sterile cytoplasms, plant densities, and hybrids in corn (Zea mays L.)

The setback in the use of Texas male sterile cytoplasm (Tms) by the corn blight disease (Helminthosporium maydis) encouraged the use of other and newer types of cytoplasmic male sterility (Cms and Sms) in hybrid seed corn production. Additional physiological information needed to be obtained concerning these new materials;Experiments were conducted near Ames in 1978 and 1979, to determine the yield performance of corn hybrids with Cms or Sms, and the relationships between ear development and growth of tassel and stem internodes in the male sterile and male fertile plants under varying plant densities;Wf9CmsHt x B37Ht, B37CmsHt x B73Htht, A554MysHtht x W182 and Mo17WmsHtht x B73 and their fertile counterparts were studied at 34,594, 54,362, and 74,130 plants/ha densities in 1978. In 1979, Wf9CmsHt x B37Ht, B37CmsHt x B73Htht, B73CmsHt x N28Ht and Wf9Ht x C103Ht separately having Cms and Tms were studied at 39,536, 59,304, 79,072, and 98,840 plants/ha densities. Plant part measurements were taken at four sampling periods between 23 July and 17 August 1979 for the fertile and sterile counterparts of B73 x N28 and Wf9 x C103 (high density tolerant and intolerant hybrids, respectively) at the four plant densities used in 1979. The measurements were top ear, tassel and internode growths by weight and length. Sugar contents were also estimated by Brix values. Other measurements for all hybrids included date of 75% silking, percent barrenness, stand count at harvest, and grain yields. Silage yield was determined in 1978;Results of the studies indicated that high plant densities reduced yields of hybrids but that the hybrids differed in the degree of response to the high density effect. Most of the hybrids with male sterile cytoplasm had significantly greater grain yields than the same hybrids with fertile cytoplasm at high densities. Days to silking and percent barrenness were reduced by the sterile cytoplasm, but it did not affect stand at harvest and silage yield in 1978. The Cms and Tms cytoplasms had similar grain yields in 1979. There were greater growths of tassel and internodes than of the ear during the two earliest sampling periods which corresponded with the time of late and final development of tassel and pollen. These results indicated potential competition against the ear. The sterile cytoplasm had a greater decrease in growth of tassels and stem internodes than did the fertile as density increased, which was interpreted as evidence of less competition with the ear. The stem sugar did not vary for cytoplasm but did for hybrid and density, being lower with increased density;The conclusions from the studies are that the Cms and Sms are similar in their responses at high plant densities and that the advantage of sterile plants over the fertile is the result of less competition of tassel and internodes with the ear in the sterile plants during pollen development with the result that the sterile plants are more tolerant to high plant density than are the fertile counterparts