Increasing Grain Yield in Sorghum

Newswise — The size and number of kernels determines the grain yield of cereal crops. These characteristics are interrelated, since genetic variation in kernel size is often compensated by an adjustment in kernel number. This trade-off is associated with the balance between grain demand for available supply of nutrients and water. The mechanisms underlying genotypic variation in potential kernel size and number remain unclear, the relative importance of potential grain size in grain yield improvement remains uncertain.

A large-seeded sorghum line has been used as a source for improving grain size and quality in the Australian public sorghum breeding program. This line of sorghum produces larger than average kernels, but in fewer numbers. However, large-seeded hybrids tend to have greater grain yield than hybrids with normal kernel size. Dr Zongjian Yang and colleagues at the University of Queensland and Agri-Science Queensland, funded by the Australian Research Council project, investigated kernel development in a large-seeded sorghum line and its hybrid in comparison with normal-seeded lines and hybrids. They examined pre-fertilization floret and ovary development and analyzed post-fertilization kernel-filling characteristics. Results were published in the 2010 March-April issue of Crop Science, published by the Crop Science Society of America, and in the Journal of Experimental Botany. In field experiments, a large-seeded hybrid yielded significantly more grain than a normal-seeded hybrid with the same female parent. The increase in final kernel weight was associated with both an increased rate and extended duration of kernel filling of water. Because of the trade-off between potential kernel size and number, prolonged duration, rather than an increased rate of kernel filling, appeared to be the main mechanism through which the large-seededness increased grain yield. The study further revealed that genotypic differences in kernel development appeared in the early stages of floret formation, with sessile spikelets of large-seeded genotypes having larger growth regions than normal-seeded genotypes. The ovaries of large-sized kernels were larger in volume, with more cells per layer and more vascular bundles in the ovary wall. Due to the large initial volume of ovaries, large kernels showed a faster rate of kernel expansion and water uptake after fertilization, reaching a higher level of maximum water content early in kernel filling. The water status in the kernel is closely related to the kernel filling rate and duration, but it was the effect on duration that delivered the yield improvement. The determination of potential kernel weight prior to fertilization coincided with the timing of panicle branching and the setting of potential kernel number. It is now clear that early stage panicle development is a key aspect of the complex processes that set potential grain size and number, and their trade-off. This improved understanding of the developmental processes associated with potential kernel size is helping to enhance the efficiency of the breeding program at Agri-Science Queensland as it continues to improve grain yield and quality in sorghum. The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://crop.scijournals.org/cgi/content/abstract/50/2/685.

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