Until recently only perfunctory attention has been given to effects of cytoplasms in maize on agronomic performance. Interest in cytoplasms increased substantially after Helminthosporium maydis race T devastated the 1970 corn crop in various areas of the United States. This experience emphasized the importance of cytoplasm diversity. However, very little is known about the effects of different cytoplasms on agronomic performance.
The objective of this study was to determine the effect of four cytoplasms in four different inbred line backgrounds on agronomic characters and disease reaction. Four inbreds (N28, Mo17, C121E, B37) selected for this study had been backcrossed seven generations for conversion to the three cytoplasms, cms-T, cms-S and cms-C, including the normal cytoplasms; 16 combinations were studied.
A split plot randomized complete block design with six replications was used and the following characteristics were studied: grain yield, kernel weight, days to silk, leaf area, number of leaves per plant, Stewart's wilt, stalk section weight, rind thickness and stalk crushing strength. Most measurements were taken on an individual plant basis within a plot but averaged to give a plot mean. Statistical analyses and correlation coefficients were determined on a plot basis (Table 1).
Estimates of yield were made but the results may be meaningless due to severe drought. Two of the six replications were hand pollinated and the remaining four were allowed to open pollinate; grain was produced on the hand pollinated material but very little on the open pollinated. Differences in grain weight among inbred lines were significant but among cytoplasms were not, nor was the inbred line by cytoplasm interaction. A more refined experiment with more replications and with additional pollen sources would be essential to determine whether different cytoplasms affect yield. Significant differences among cytoplasms were found for leaf area, Stewart's wilt, ear height, days to mid silk and crushing strength. Cytoplasm cms-S had greater leaf area, higher Stewart's wilt rating and greater ear height than the other cytoplasms. The C cytoplasm had the highest crushing strength and the normal cytoplasm the lowest. Cytoplasms T and C had two days later mid silking date than the normal and S cytoplasms. A significant interaction of inbred lines by cytoplasms was observed for probe moisture, ear height, and crushing strength. Although different cytoplasms appeared to affect some of the traits studied, further studies should be conducted to confirm the results obtained in this study.
J. Osuna Ayala* and M. S. Zuber
*Postdoctoral Fellow, FAPESP and FMVAJ
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