CANOPY LIGHT INTERCEPTION - GAS-EXCHANGE, AND BIOMASS IN REDUCED HEIGHT ISOLINES OF WINTER-WHEAT

A reduction in stem height may reduce light interception and thus redu ce canopy gas exchange and biomass accumulation of winter wheat. This hypothesis was tested with 16 reduced height isolines in a hard red wi nter wheat background (Triticum aestivum L. cv Itana). These isolines were grown in the field in Hamden, CT, in 1991, 1992, and 1993, and bi omass accumulation, leaf area index, light interception, and canopy ga s exchange were measured throughout plant development. Comparisons wer e made between the four height classes: dwarf (Rht1Rht2), semidwarf Rh t1 (Rht1rht2), semidwarf Rht2 (rht1Rht2), and tall (rht1rht2). Biomass of tall isolines was more than 20% greater than that of dwarf isoline s early in development in each year and at maturity in 1991. Light int erception of tall isolines was 20% greater than that of dwarf isolines during stem elongation in 1992 and at boot stage in 1993. Canopy phot osynthesis of tall isolines was also more than 20% greater than that o f dwarf isolines early in stem elongation in 1991 and 1992. After spik e emergence canopy light interception and photosynthesis did not diffe r among height classes. The low biomass of dwarf isolines was attribut ed to reduced light interception and canopy photosynthesis before spik e emergence, compared with the taller isolines. Semidwarf isolines did not differ consistently from tall isolines in either biomass light in terception, or canopy photosynthesis, hut semidwarf isolines had great er harvest index. Averaged across the three ears, wheat plants of semi dwarf stature yielded more than those with either tall or dwarf statur e.