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Measurement and evaluation of tolerance to cold stress in three exotic maize composites from different areas of Pakistan
Abstract
In 1988, a full-sib recurrent selection program for improved cold tolerance was initiated in three Pakistan-based maize (Zea mays L.) populations, SU, CO, and SC. Selection was based primarily on percent emergence under controlled growth-chamber (11 $\pm$ 1/6 $\pm$ 1$\sp\circ$C day/night) temperatures. Visual selection was practiced in the nursery for agronomic traits. Reciprocal full-sib family selection was also practiced one season in SU and CO. Divergent sub-populations, based on growth-chamber evaluations, were assayed for allozyme frequencies. Bulk composites were made from selections of exotic populations, and were evaluated in field and growth chamber trials. Fresh-shoot weight, dry-shoot weight, and chlorophyll reading indicated significant linear responses to entry position in tray in growth chamber. Vigor traits were sensitive to the position of the entry's tray. Reciprocal differences were observed for days to 50% emergence, total emergence, fresh shoot weight, and dry shoot weight; these differences were not associated with differences in seed size. Association of Mdh2, Pgd2, and Glu1 loci with cold-tolerance was indicated. Population SC had the greatest genetic divergence from the adapted Nebraska population, NS(F-CT)C9, whereas SU and CO populations had the greatest similarity to NA(F-CT)C9. The nature and intensity of selection, and differences in the genetic constitution of exotic populations, were two probable reasons for degree of divergence between the two groups. Genotypic correlations of shoot weights with total emergence and chlorophyll reading were positive and higher than correlations of speed of emergence (days to 50% emergence) with total emergence, shoot weight, and chlorophyll reading. Total emergence and shoot weight appeared to have common genes. These genes were apparently pleiotropic in their action and/or linked relative to genes controlling speed of emergence, shoot weight, and total emergence. Selection for cold-tolerance during seedling growth resulted in simultaneous improvement of other agronomic traits, including grain yield. Exotic germplasm was superior to an adapted Nebraska population in seedling cold-tolerance.
Subject Area
Agronomy|Genetics|Botany
Recommended Citation
Khan, Kiramat, "Measurement and evaluation of tolerance to cold stress in three exotic maize composites from different areas of Pakistan" (1991). ETD collection for University of Nebraska-Lincoln. AAI9211492.
https://digitalcommons.unl.edu/dissertations/AAI9211492