Differences in Growth in Response to Temperature of Maize Hybrids Varying in Low Temperature Tolerance

Abstract

Two hybrids of maize (Zea mays L.) were compared for low temperature tolerance using a range of characters. The hybrid A665 × H99 (CBD) originated in the Corn Belt of the U.S.A. NZlA × 5-113 (CT) was produced in New Zealand; it is of highland tropical origins and in previous work grew faster than Corn Belt Dent (CBD) hybrids at low temperatures. The objective of this work was to determine if the two hybrids grew at different rates in two contrasting temperature environments approximating those which can occur after planting in New Zealand. Growth analysis, chlorophyll concentration and chlorophyll fluorescence were used to estimate the differences between these hybrids. The plants were grown continuously in a 22/18°C day/night temperature environment or transferred to a 16/14°C environment at the 2-mature-leaf stage. Plants were harvested immediately prior to transfer at the 2-mature-leaf stage and at the 5-mature-leaf stage of development. Differences in dry weight and leaf area were compared with net assimilation rate, chlorophyll concentration and chlorophyll fluorescence as estimates of photosynthetic capacity. Shoot dry weight of CBD was greater than that of CT at 22/18°C, but the reverse was true at 16/14°C, showing that CT hybrids were more tolerant of the transfer to cool temperatures than CBD hybrids. In both environments the leaf areas of CBD and CT were similar. Net assimilation rate and chlorophyll concentration was greater for CT at 16/14°C, suggesting a greater photosynthetic efficiency at lower temperatures. This argument was supported by a slower decline in chlorophyll fluorescence for CT grown at 16/14°C. The coolest temperature treatment used in this work was less effective in discriminating between hybrids for differences in growth in cool environments, compared with the longer periods at 16/6°C of previous work.