Publication

A study of kernel growth in wheat

Date
1986
Type
Thesis
Abstract
Two field experiments were conducted to investigate the hypothesis that caryopsis weight at anthesis determines potential kernel weight of wheat (Triticum aestivum L.) at maturity. Potential kernel weight is the weight that is attained by a kernel with optimum growing conditions. The experiments were done at Lincoln College in the 1980-81 and 1981-82 seasons. In the first experiment Rongotea and Kopara were compared under two plant populations (150 and 400 plants per m²) and 3 levels of nitrogen (0, 50 and 100 kg N per ha) applied at the tillering stage. The second experiment was conducted with Rongotea at 250 plants per m². A single shading treatment of 50% full sunlight for 30 days before anthesis and two spikelet removal treatments were applied immediately after ear emergence. All these treatments were used to alter the caryopsis weight at anthesis. Plants were thinned at anthesis to investigate the effect of reduced competition or increased assimilate supply on mature kernel weight in both experiments. The dry weight of the carpel, caryopsis or kernel in florets 1 and 3 of the 8th spikelet on the mainstem ear was measured from immediately after ear emergence to maturity. Final kernel weight, growth rate and caryopsis weight at anthesis were significantly higher in floret 1 than floret 3 in both cultivars and all treatments in both experiments. One of the noteworthy findings of this study was the higher sink strength in floret 3 than floret 1. For each microgram of caryopsis weight at anthesis floret 3 produced between 140 and 148 micrograms of final kernel weight, whereas in floret 1 the figures were between 95 and 78 micrograms respectively depending on season. The differences in final kernel weight between cultivars, floret positions and treatments were related to the differences in absolute growth rate and caryopsis weight at anthesis. In the first experiment low plant population increased kernel weight significantly and tended to increase the growth rate and caryopsis weight at anthesis. Nitrogen had no effect on any aspect of kernel or caryopsis weight at anthesis. In the second experiment spikelet removal increased final kernel weight and growth rate compared to shading and control treatment and tended to increase caryopsis weight at anthesis. Thinning at anthesis increased the final kernel weight and growth rate significantly only in the first experiment. For detail analysis carpel and caryopsis growth was divided into 3 phases. The pre- and post-anthesis exponential phases which occurred approximately 7 and 14 days before and after anthesis respectively. From 7-14 days after anthesis the kernel grew at a steady rate for about 25-32 days. This was defined as linear phase. The growth rate ranged from 1.1 to 1.7 mg day⁻¹ per kernel in first experiment depending on cultivar and floret position. Between floret positions growth rate varied from 1.3 to 1.8 mg day⁻¹ kernel⁻¹ in second experiment. Kernel growth rate during the period of linear growth over both years, floret positions and cultivars was significantly correlated with final individual kernel weight. The durations of the linear phases were not different among the treatments within the same experiments or floret positions and did not appear to be related to potential kernel weight. During the pre-anthesis exponential phase the relative growth rates did not differ significantly among treatments in both florets and experiments except thinning treatment in first experiment. However, the caryopsis weight at anthesis was significantly different among treatments in both florets and experiments and these differences were maintained in kernel growth rate during the linear phase and final kernel weight. There were significant positive correlations between caryopsis weight at anthesis and growth rate during linear phase and between caryopsis weight at anthesis and final kernel weight at both florets and years. To test the hypothesis that caryopsis weight at anthesis determines potential kernel weight two years data were critically analysed together. Due to seasonal difference in temperature the two years' data were not comparable. A covariance analysis was carried out to overcome this problem. Following this analysis it was revealed that there was no difference in either the slopes or position of the relationship between caryopsis weight at anthesis and final kernel weight in floret 1, but there was a difference in position and not in the slopes of floret 3 for both years. Therefore the results support the hypothesis that caryopsis weight at anthesis determines potential kernel weight in floret 1. During the pre-anthesis growth phase, the relative growth rates did not differ among treatments at both florets and years. There were significant differences in carpel weights among different treatments during this phase except in floret 1 position of first experiment. The results strongly suggest that within the scope of this study the potential kernel weight of floret 1 was largely determined by caryopsis weight at anthesis but this relationship was not consistent for floret 3 where presumably other factors were operating.
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