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Abstract
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To study the effects of high temperature on the meiosis of pollen mother cells (PMCs)
and to determine their relationship with grain set, two in situ experiments were conducted between
2010 and 2012 on four wheat cultivars, Kauz, Montana, M6 and Chamran, under normal (normal
cultivation) and terminal heat stress (late cultivation) conditions. Due to the delay in cultivation for
the cultivars under stress conditions, their flowering stage faced heat stress at the end of the growing
season, and therefore, a significant (p ? 0.05) increase was observed in meiotic abnormalities.
Cytogenetic studies discovered that the meiosis in PMCs and the pollen development are strongly
influenced by heat. Based on the results, abnormalities such as precocious chromosome migration to
the poles, laggard chromosomes, micronuclei, absence of metaphase plate, pyknosis, abnormal
cytokines, cytomixis and abnormal tetrad were observed in different cultivars. The sensitive cultivars,
M6 and Montana, had the greatest percentages of meiotic abnormalities. The meiotic abnormalities
showed a significant negative correlation with the number of kernels per spike under terminal heat
stress conditions (r = ??0.54, n =16, p ? 0.01). In other words, due to increasing meiosis abnormalities
under terminal heat stress, the grain set was greatly reduced, especially in the susceptible cultivars.
The result of this experiment showed that studying the meiosis in PMCs can be suggested as one of
the research necessary to improve commercial heat-tolerant cultivars, and to some extent, as a method
for screening tolerant lines in breeding programs.
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