Cultivar differences in germination and field establishment of maize (Zea mays L.) in response to seed ageing and low water availability
Radicle emergence and coleoptile emergence are important components of germination. The responses of these processes to external water potential in different tropical maize cultivars were examined using polyethylene glycol (PEG 4000). Low external water potential reduced the onset, rate and the final percentage of radicle and coleoptile emergence. The length of the radicle and shoot after seven days of imbibition was also reduced by low water potential. Cultivars differed in the rate and final percentage of germination, coleoptile emergence and radicle and coleoptile length at low water potential. Maize coleoptiles were more sensitive to low water potential than radicles. The critical value for coleoptile emergence was lower than -0.73 MPa. Germination in PEG was not able consistently to distinguish known drought tolerant cultivars which had low initial germination (low quality) at high water potential (0 MPa). There appeared to be genotypic variation in radicle and shoot growth at low water potentials. It is suggested that although selection of cultivars for their ability to germinate with initial rains was possible this may not be a useful basis for superior establishment of maize crops in Sri Lanka. An adaptation of the technique of controlled deterioration (CD) demonstrated that maize seed ageing may take place in the soil. When seed was aged either under constant temperature or under fluctuating temperature the base temperature for ageing maize was 30 degree days. There was a genotypic variation for ageing, thus selection for ageing susceptibility could be feasible using CD test. Radicles were more sensitive than coleoptiles to ageing and there was genotypic variation for such conditions. Home saved maize seeds that are used by many Sri Lankan farmers were shown to be low in vigour, which suggested that under tropical conditions significant seed deterioration takes place during storage. Storing seeds on the cob enclosed by the husk can reduce the extent of deterioration. It is suggested that selection of cultivars of maize for better storage could be feasible because genotypic variation for this exists. The time of planting is important in order to optimise crop establishment. Excess rains as well as shortage of moisture reduce field emergence. Results suggest that the optimum rainfall for good crop establishment of maize is around 50 to 60 mm.