Abstract

Maize (Zea mays L.) is the most important cereal crop in Africa. However, its production is under serious threat due to the increasing occurrence of abiotic stress factors such as heat stress. In this study, 18 maize inbred lines were screened for basal and acquired thermotolerance using the water bath and growth chamber techniques, respectively. Based on the water bath technique, highly significant differences (P<0.001) in coleoptile growth among the inbred lines under heat stress, non-stress (control) and across environments were observed. Coleoptile growth was used to calculate heat tolerance index (HTI) of each inbred line. Based on the results, EM86Y, EM578Y, HM63Y, HM1472Y and AO595Y were depicted as tolerant to basal heat stress. With regards to the growth chamber study, three stress indices, namely, HTI, heat susceptibility index (HSI) and tolerance (TOL) were used to determine inbred lines exhibiting acquired thermotolerance. Results obtained showed that EM88Y and KO315Y were tolerant, while HM48Y and CM321Y were semi-tolerant to acquired heat stress. Basal thermotolerance is useful prior to emergence, while acquired thermotolerance is effective after crop emergence. Combining these mechanisms of tolerance in single inbred lines is highly recommended.