Jaikumar, N. S., S. S. Snapp, J. A. Flore, and W. Loescher. 2014. Photosynthetic responses in annual rye, perennial wheat, and perennial rye subjected to modest source:sink ratio changes. Crop Science 54:274-283.

Newly developed perennial cereals have been developed as alternatives to annual food crops. These provide novel contexts in which to study source vs. sink limitations of plant productivity. This is one of the first investigations of source:sink effects on photosynthesis, seed size, and regrowth in perennial cereal crops as well as in the commercially important annual rye (Secale cereale L.). Through experimental manipulations of field-grown plants, we studied the effect of manipulations of source:sink ratio (25% decreases and 100% increases) on photosynthetic rate in perennial wheat [Triticum aestivum L. × Thinopyrum elongatum (Host) D. R. Dewey], perennial rye [S. cereale × Secale strictum (C. Presl) C. Presl subsp. strictum (syn. Secale montanum Guss.)], annual wheat (Triticum aestivum L.), and annual rye. We measured carbohydrate pools, seed size, and regrowth as further indices of source vs. sink limitation. Perennial wheat showed sink limitation throughout. Annual and perennial rye appeared to be colimited. Low source:sink ratios in perennial wheat and rye were associated with up to 25% higher photosynthetic rates while high source:sink ratios led to up to 20% decreases. Seed size showed more stability under source:sink manipulation in perennials than in annuals while regrowth of perennials was not affected by source sink ratio, and all three species showed more stability of seed size in response to source:sink manipulation than annual wheat. Our results are consistent with perennial cereals operating below their maximum photosynthetic capacity, in contrast to annual wheat, and following a conservative reproductive strategy. By selecting for greater sink strength in perennial wheat, breeders may be able to achieve higher rates of photosynthesis and support higher yields in this new crop.

DOI: 10.2135/cropsci2013.04.0280

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