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 reduce canopy gas exchange and biomass accumulation of winter wheat. This hypothesis was tested with 16 reduced height isolines in a hard red winter wheat background (Triticum aestivum L. cv Itana). These isolines were grown in the field in Hamden, CT, in 1991, 1992, and 1993, and biomass accumulation, leaf area index, light interception, and canopy gas exchange were measured throughout plant development. Comparisons were made between the four height classes: dwarf (Rht1Rht2), semidwarf Rht1 (Rht1rht2), semidwarf Rht2 (rht1Rht2), and tall (rht1rht2). Biomass of tall isolines was more than 20% greater than that of dwarf isolines early in development in each year and at maturity in 1991. Light interception of tall isolines was 20% greater than that of dwarf isolines during stem elongation in 1992 and at boot stage in 1993. Canopy photosynthesis of tall isolines was also more than 20% greater than that of dwarf isolines early in stem elongation in 1991 and 1992. After spike emergence canopy light interception and photosynthesis did not differ among height classes. The low biomass of dwarf isolines was attributed to reduced light interception and canopy photosynthesis before spike emergence, compared with the taller isolines. Semidwarf isolines did not differ consistently from tall isolines in either biomass light interception, or canopy photosynthesis, hut semidwarf isolines had greater harvest index. Averaged across the three ears, wheat plants of semidwarf stature yielded more than those with either tall or dwarf stature.