Growth response to temperature of two maize (Zea mays L.) hybrids with differing levels of cold tolerance : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science in Plant Science (Seed Technology), Massey University

Abstract

Low temperatures are a hazard to maize production especially in high altitude and high latitude areas (Eagles, 1979; Hardacre and Eagles, 1986) where it may cause substantial yield reductions through its accumulated effect on vegetative and reprodutive growth. Cold tolerant cultivars with rapid emergence and growth at low temperatures have been identified in highland tropical genotypes and are being developed in New Zealand (Eagles, 1979; Hardacre and Eagles, 1986). Growth of one such hybrid A665 x NZlA was compared in this study to that of an established hybrid, A665 x H99, but identified as of warm weather at two field and one glass house environments. The hybrids were planted in the field on 26th October and 26th November, 1991, and in the glass house on 30th April, 1992. Glass house grown plants were later transferred to two controlled temperature environments set at 28/22°C and 16/6°C during the grain filling period. Both hybrids had comparable high percentage laboratory germination. However A665 x NZlA emerged earlier than A665 x H99 at all plantings, though only significantly so at the October planting were mean temperatures were lowest ( < 15°C). Seedling emergence rates did not differ significantly. Seedling dry weights at about 7 weeks after planting were highest in the glass house planting where mean temperatures were highest (19°C) and lowest in the October planting, where temperatures the lowest. A665 x H99 had faster leaf growths than A665 x NZlA at all plantings although differences were not significant between the hybrids. Across plantings the hybrids had their greatest leaf appearance rates and leaf area growth rates in the November planting where temperatures were the highest and their lowest rates in the glass house where the photoperiod was longest (14 hrs). Maximum leaf area and leaf area index were however attained in the October planting where although temperatures were lowest and hence suppressed leaf growth, the extended growth periods resulted in larger leaf areas and leaf area indices. The lowest leaf areas and leaf area indices were obtained in the glass house primarily because the plants there were much smaller than those in the field. Days to anthesis did not differ significantly between the hybrids though A665 x NZlA reached mid-silk earlier than A665 x H99 at all plantings. Across plantings the hybrids reached mid-silk earliest in the November planting and latest in the glass house planting where temperatures were highest and the photoperiod longest, respectively. At anthesis total plant dry weights (TPDWT) at all plantiIJ.gs did not differ significantly between the hybrids. Across plantings the TPDWT were highest in the October planting and lowest in the glass house where temperatures were lowest and highest, respectively. During the reproductive period A665 x H99 still maintained a larger but non significant TPDWT than A665 x NZlA in the field plantings. At both temperatures (28/22°C and 16/6°C) in the controlled temperature environments, A665 x H99 had significantly greater TPDWT than A665 x NZlA. These temperatures did not influence the coefficients of growth, which must already have been established during the first 30 days of grain growth prior to moving plants from the glass house. A665 x H99 had significantly greater cob and grain growths than A665 x NZ1A in the October and glass house plantings where mean temperatures were higher (> 16°C) during the early reproductive period and the onset of the linear dry matter accumulation phase. In the November planting where mean temperatures were low (< 16°C) during the early phase of reproduction and then further declined, cob and grain growth of the hybrids did not differ significantly. However the cob and grain growths of A665 x H99 were more retarded than those of A665 x NZlA. In the October planting and at 28/22°C where the hybrids had time to reach physiological maturity days, to physiological maturity and the duration of the grain filling period did not differ significantly between the hybrids. A665 x H99 had greater final crop grain yield than A665 x NZlA in the environments where temperatures were higher during the reproductive growth (October and glass house plantings). In the November planting where temperatures were lower A665 x NZlA yielded higher though only slightly. Across plantings grain yields were highest in the October planting where temperatures were the highest during grain growth, and lowest in the controlled environments which was mainly a reflection of the small plant size. The main yield component which was different between the hybrids was total grain number. A665 x H99 had more total grains than A665 x NZIA at all plantings and these differences were significant so in the October and glass house plantings