Cover story 6 IT IS COMMONknowledge that stressed plants will not achieve optimum performance or yield. But what does stress actually do to a plant? New oat research results have found a direct link between how plant stress limits kernel fill and reduces yield. And the results could lead to the development of more efficient and effective oat varieties for Ontario farmers. Art McElroy, research coordinator with PhytoGene Resources Inc., recently wrapped up a two-year study evaluating how oat kernels fill and determining how plant stressors — disease pressures and environmental effects — impact the kernels, and ultimately yield. He started his research with the results from earlier oat studies where he noticed a strong correlation in yield to kernel weight in a well-filled kernel. McElroy believes changes in the kernel patterns suggest stress effects, and as expected, some kernels will not develop fully. “It all comes down to grain development and kernel fill,” explains McElroy who, working with his son and fellow planter breeder, Michel McElroy, set out to develop a more refined, and less costly approach to oat breeding by selecting individual traits linked to yield, in an effort to combine the desirable traits in superior cultivars. “Grain development is intricately linked to yield, kernel size, and test weight, that’s why grain development and kernel fill have been our focus for this plant breeding research.” EVALUATING OAT KERNELS Several parameters were used to evaluate grain development, and by extension, stress tolerance and susceptibility — including the number of kernels set, frequency of unfilled kernels and grain fill. “There were three main ingredients necessary for this study — a large number of elite lines to provide a range of genetic backgrounds, several sites to offer different stresses, and the ability to evaluate all the oat kernels from the representative samples,” says McElroy. It has been difficult to measure oat losses in the past because many oat kernels that are small or unfilled are often lost during combine harvest or at sample cleaning when they simply blow away. Traditionally, these kernel losses are not consistent across test sites, making it harder to collect accurate data. McElroy had his work cut out for him to find a way to collect and evaluate kernel losses because, he says, “these need to be retained because there is so much more to be learned about stress from poorly filled or unfilled kernels.” The greatest challenge was to develop a device to measure kernel ‘size’. It is difficult to accurately measure kernel fill (which is directly linked to yield) because well- and poorly-filled oat kernels are almost the same width. However, thickness is related to kernel mass, so McElroy developed a device to measure kernel thickness rapidly and precisely. “Grain fill, or the kernel thickness, is an excellent indication of plant stress,” he explains. “The number of kernel sets, unfilled kernels, and placement along the panicle can tell us at what point in the plant’s development it was stressed. This information can also help us understand grain development and genetic selection.” Initial study results found that the number of kernel sets and the frequency of filled kernels are the two major factors affecting yield. McElroy says that both are determined very early in the growth cycle, at about the 4-leaf stage, and there was genetic variability for both. The biggest surprise came from previous oat research that determined unfilled kernels were not ‘aborted kernels’ (a common understanding), since there was no flower development or pollination to begin with. This new finding means that existing kernels don’t benefit from any unused resources, like carbohydrates, from the unfilled kernels because each kernel has its own ‘pipeline’ of nutrient requirements right to the main stem of the plant. “Unfilled kernels represent a direct loss of yield potential,” says McElroy, explaining that, if a plant has 30 per cent unfilled kernels, a farmer’s yield is directly reduced by 30 per cent. Improved stress tolerance ACHIEVING OAT KERNEL FILL Jeanine Moyer continued on page 8 • This study’s novel approach to determining how oat stressors impact yield will go a long way to help plant breeders develop more effective selection techniques. • Each kernel has its own ‘pipeline’ of nutrient requirements right to the main stem of the plant. • If a plant has 30 per cent unfilled kernels, a farmer’s yield is directly reduced by 30 per cent. • By deconstructing the panicle and measuring the kernels, McElroy was able to determine when the plant was stressed. WHAT YOU NEED TO KNOW
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