Selection criteria for tolerance to low temperatures during the initial growth phases in maize (Zea mays L.)
1992
Landi, P. | Conti, S. (Bologna Univ. (Italy). Istituto di Agronomia Generale e Coltivazioni Erbacee)
Tolerance to low temperatures in initial growth phases is an essential requisite to allow early sowings in maize (Zea mays L.). The objective of this study was to identify the traits most suitable to evidence, in local environments, differences among genotypes in order to carry out selection programs for cold tolerance. Two hundred-fifty-six crosses were investigated over two years in early sowing and evaluated for percentage of field emergence (PE), rate of emergence (TME), growing degree days from sowing to emergence (TSE), ratio between seedling dry weight 45 days after sowing and growing degree days from field emergence to harvesting (PM/TER), ratio between dry weight per plot and growing degree days from sowing to harvesting (PP/TSR), and visual score of the vegetative growth at harvesting (VV). In the coldest year the broad sense heritability values (h2b) were higher for all the traits except TME and TSE. The G x E interaction was of appreciable magnitude for all traits but PM/TER and PP/TSR, for which the h2b values on a plot basis over two years were 26 and 23%, respectively. The analysis of the expected genetic gains for different testing procedures evidenced that, given the same number of replications, for PM/TER and PP/TSR the one-year evaluation is negligibly less efficient than that performed for two-years. A selection based on VV proved to be scarcely efficient due to its low h2b and to a not sufficiently high correlation with PP/TSR. Since the latter variable can be easily detected and summarizes the performances of the traits dealing with cold tolerance, it proves to be the most suitable trait for selection
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