Studies on the inheritance of chilling tolerance in a systematic genetic series of maize (Zea mays L.) seedlings in a temperature gradient chamber

The inheritance of chilling tolerance in maize seedlings was studied in a t emperature gradient chamber on a systematic genetic series developed using the inbred lines CM 174 and Mo 17 as the parents. The leaf area and shoot d ry mass of the six genotypes were evaluated after 26 days of chilling treat ment. This treatment was begun when the plants were in the 2-leaf stage and was carried out simultaneously at 10 different temperatures from 7.0 to 14 .2 degreesC at intervals of 0.8 degreesC. Among the members of the genetic series, the heterozygotic forms exhibited faster initial development, as indicated by the leaf area and shoot dry mas s, than the homozygotic forms at all the temperatures in the range examined . The development of the F-1 was generally poorer than that of the F-2. The additive dominance model (joint scaling test) could he applied to the inhe ritance of the characters at ail the temperatures. The (h)/(d) ratio demons trated overdominance in all cases and was characteristically much greater t han unity. The model overestimated the values of certain genotypes (P-1, P- 2, F-1), while underestimating the remaining genotypes (BC1, BC1-R, F-2). T he difference between the measured values and the values estimated by the m odel appears to be due to the level of heterozygosity heterozygosity of the maternal line, which is 0% for genotypes P-1, P-2 and F-1 and 100% for gen otypes BC1, BC1-R and F-2.