Genetic factors affecting maize tolerance to low temperatures at emergence and germination.

On the basis of the percentage of plants emerging under laboratory cold-test conditions, inbred lines were divided into tolerant (T), semi-tolerant (I) and sensitive (S) to low temperatures. Tolerance to low temperature is, then, an inheritable and varietal plant characteristic.On average, local varieties showed the best emergence, followed by double crosses, single crosses and inbred lines in that order. Some tolerant hybrids and inbred lines had quite high emergence after 27 days at 6 °C. Thus the tolerant inbred lines Bc-130 E-5 and T-193/II had more emerged seeds (78 and 75% with embryo roots and 52 and 47% with stalk apices, respectively) with longer embryo roots and stalk apices than the sensitive inbred lines T-145/11 and W-8 at the end of this treatment.The two-year average emergence of 56 reciprocal single crosses and their parental inbred lines cold-tested at 6 °C and 8 °C indicates that the degree of tolerance to low temperatures is strongly dependent on the germination ability of the maternal parent of the cross, i. e. on maternal effect. The genetic mechanism of this inheritance is rather complex. The higher stand density of single crosses over inbred lines may be explained by complementary gene action in the seed embryo. The characteristics of the maternal parent were important in determining not only the percentage of germinated plants, but also the speed of germination and growth of the embryo root and stalk apex. With each parental inbred line the percentage emergence differed according to whether the line was used as the maternal or pollen parent in the crosses.