Submitted to: Photosynthetica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 2004
Publication Date: February 23, 2005
Citation: Pettigrew, W.T., 2004. Cotton genotypic variation in the photosynthetic response to irradiance. Photosynthetica. 42(4): 567-571, 2004. Interpretive Summary: Photosynthesis, the process whereby plants convert sunlight, carbon dioxide, and water into sugars used for the growth of the plant, is an integral part of plant growth, development, and yield production. Understanding how photosynthesis varies among cotton types could provide new insight into methods to improve yield production. This study looked at how photosynthesis varied among different cotton types under changing sunlight conditions. Photosynthesis was measured on leaves of 8 different cotton lines under conditions of full sunlight, two different levels of shade, and complete darkness. The two cotton lines whose leaves had the smaller okra leaftype shape, photosynthesized at a higher level under all the various sunlight levels. One of the reasons for the increased photosynthesis of these two lines is that they also had a higher concentration of chlorophyll (the green color pigment) in their leaves. This higher photosynthesis at all light levels means that not only do the okra leaf shape cotton lines produce more sugar for growth under full sunlight, but also means that they can maintain a higher sugar production even when clouds pass over and partially block the sunlight. Breeders and agronomists may now be able to the use this knowledge to produce and/or combine varieties with production systems for creating a high photosynthesizing, long duration crop canopy that could ultimately lead to higher yields.
Technical Abstract: Although genotypic differences have been detected in the photosynthetic performance of cotton (Gossypium hirsutum L.), research remains sparse concerning genotypic differences for the photosynthetic response to changing light levels. The photosynthetic response of 8 cotton genotypes to changing light status was investigated under field conditions during the 1998 through 2000 growing seasons. Equations developed to describe the photosynthetic light response demonstrated that, across all light levels, the two okra leaftype genotypes photosynthesized at a greater rate per unit leaf area than all of the six normal leaftype genotypes. This superior photosynthetic performance of the okra leaftype genotypes can be partially explained by their 13% greater leaf chlorophyll (Chl) concentration relative to that of the normal leaftype genotypes. While the 37% reduction in leaf size brought upon by the okra leaf trait may have concentrated the amount of photosynthetic machinery per unit leaf area, the lack of sufficient canopy leaf surface area suppresses the potential yield development that could accompany the higher photosynthetic rate per unit leaf area.