SENSITIVITY OF MAIZE HYBRIDS TO CHILLING AND THEIR COMBINING ABILITIES AT 2 DEVELOPMENTAL STAGES

Maize (Zea mays L.), one of the most economically important plants gro wn in North America, is often subjected to cool conditions soon after sowing which can disrupt development. No studies on chilling sensitivi ty of maize at both germination and early growth developmental stages have been reported. To discern differences in chilling sensitivity bet ween the germination and early growth phases, twelve hybrids originati ng from a complete diallel of four inbreds which differed in their sen sitivity to chilling were subjected to laboratory screening tests at b oth these stages. Corresponding field trials were sown and parameters reflecting those evaluated in the;laboratory were assessed. Estimates of general combining abilities and specific combining abilities were p erformed. Some lines that were initally chilling sensitive or tolerant at the germination stage altered their sensitivity to chilling at the early growth stage. This suggests that it is only possible to accurat ely evaluate chilling tolerance of maize by examining plants at both t he germination-emergence and early growth stages as these two stages m ay be under the control of different genetic factors. Furthermore, bas ed on the physiological growth parameters assessed both in the laborat ory and in the held, it is not possible to reliably predict hybrid mai ze cold tolerance from knowledge of the inbreds' responses.