Photosynthates competition within the boll–leaf system is alleviated with the improvement of photosynthetic performance during the succession of Xinjiang cotton cultivars

Abstract

The yield of cotton (Gossypium hirsutum L.) has increased steadily with the release of different cultivars over the years in Xinjiang, China. However, the reasons for this increased yield have been controversial. As the sympodial leaf and boll within the boll–leaf system of cotton develop together, their competition for photosynthates is intense during their growth, which may be an important factor influencing boll weight. Consequently, we speculated that shortening period during which the sympodial leaf and boll develop together, which would alleviate photosynthates competition, might contribute to boll growth during the succession of cotton cultivars. To test this hypothesis, changes in yield characteristics and photosynthetic performance were studied by examining the main cotton cultivars from four breeding eras (1980s, 1990s, 2000s, and 2010s) in the Xinjiang early-maturing cotton region. The results showed that the single boll weight and the number of bolls increased gradually, and the yield increased steadily with cultivar succession. In the boll–leaf system of cotton, the rapid growth period of the sympodial leaves moved forward, thus reducing the time during which the sympodial leaves and bolls developed simultaneously; at the same time, the rapid growth duration of boll was extended during cultivar succession. In addition, the succession of cotton cultivars was accompanied by increased leaf area, increased leaf photosynthetic rate (Pn) after flowering, and an extension of photosynthetic functional duration within the boll–leaf system. Compared with the sympodial leaves, the photosynthetic performance of the main-stem leaves was improved more obviously in the same boll–leaf system. Therefore, during cotton cultivar succession in Xinjiang, the photosynthates competition between sympodial leaf growth and boll development was significantly alleviated within a boll–leaf system with the improvement of photosynthetic performance, which may further extend the rapid growth duration of boll, thus enhancing single boll weight and yield of cotton.