Perennial hybrids of Oryza sativa × Oryza rufipogon: Part II. Carbon exchange and assimilate partitioning

Oryza species differ in their degree of perenniality, which has implications for patterns of carbon distribution in the plant. Interspecific F₁ hybrids of Oryza sativa × Oryza rufipogon were compared with their parental lines to assess whether they differed in assimilate storage and distribution at flowering and after maturity of the first cohort of panicles. The F₁ hybrids varied widely in plant type, but on average they had small plant size and low main tiller weights at anthesis, similar to O. rufipogon, and had intermediate tiller numbers and final single plant weights similar to cultivated rice. O. rufipogon had higher concentrations of starch in stems at anthesis, while interspecific hybrids exhibited comparatively low leaf, stem + sheath, and root sugar concentrations. Near anthesis, substantial ¹⁴C label remained in the source (flag) leaf in O. sativa and F₁ hybrids, while in O. rufipogon more label was exported to sink tissues. The hybrids partitioned more ¹⁴C label to panicles than did cultivated rice and less to leaf sheaths than either parent. Hybrids that had previously been identified as having above-average carbon exchange rates (CER) did not differ consistently from the low-CER hybrids in carbohydrate dynamics. The cultivated species itself maintains some perennial features, and changes in these traits might increase productivity.