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Developing higher-yielding wheats by extending leaf duration
December 30, 2002
One research project of Andreas Fischer in MSU's Plant Sciences and Plant Pathology Department will yield information about how leaf duration, tiller number and active leaf surface influence yield.
The performance of a recently released spring wheat variety, Reeder, stimulated this research, because it has shown high yield while maintaining high grain protein during trials in Montana and North Dakota.
Several wheat varieties differing in these parameters were compared in field experiments under both dryland and irrigated conditions in 2001. Reeder maintained green leaves for one-to-two weeks longer than other varieties tested. While dry conditions led to a decrease in tillers in all the tested varieties, Reeder was more successful than most at maintaining high tiller numbers under dry conditions.
It appears reasonable that, under optimal growth conditions, an extension of leaf area and leaf duration leads to increased yield. On the other hand, stay-green varieties may not be able to mature and completely recycle nitrogen from their leaves in dry climates, and this would lead to poorly developed, low-protein grains. Therefore, breeders have selected for varieties that mature early in areas with a dry climate such as Montana.
The first year of this project allowed several important observations. The average extension of leaf duration for the varieties was measured using a chlorophyll meter on a large number of flag leaves. These data demonstrated that 50 percent chlorophyll loss in flag leaves occurred about seven days later in Reeder than in most varieties compared. In addition, Reeder and McNeal had a delayed water loss from maturing ears. In greenhouse testing, Reeder had slightly delayed loss of total chlorophylls and leaf proteins compared to several other spring wheat varieties, confirming an altered senescence.
To study the influence of leaf duration on yield during 2001 field experiments, ears were collected twice per week, and fresh weights and dry weights were determined. The time patterns of whole-ear dry matter accumulation between early- and late-maturing varieties were comparable.
Reeder was among the highest-yielding under irrigated and, especially, dry conditions, even though the average dry weights of Reeder ears were lower during grain filling.
The main difference between Reeder and another modern, high-yielding variety (McNeal) is the number of tillers. The varieties tested in 2001 fell into four categories: high-yielding varieties with low (McNeal) and high (Reeder) tiller numbers, and low-yielding varieties with relatively high (such as Thatcher, an older variety) and low tiller numbers.
The 2001 field studies showed that two different, independent strategies lead to high yields: the formation of few, but heavy ears, and the formation of a high number of relatively small ears. The latter strategy was correlated with a conspicuous stay-green phenotype. Additionally, Reeder was more successful at bearing fruit in its smaller heads than older varieties such as Thatcher. We need to confirm this conclusion in further field experiments and to understand the physiological basis of the correlation between tiller number, leaf duration and yield.
While high yield can be achieved by a large number of relatively small ears, it is unclear if the corresponding tillers are formed and flower early or late. To investigate this, Reeder, NcNeal and Thatcher were to be tested in 2002 under both dryland and irrigated conditions.
Andreas Fischer (406) 994-5908
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