Photosynthetic characteristics of the subtending leaf and the relationships with lint yield and fiber quality in the late-planted cotton

To investigate the photosynthetic characteristics in the subtending leaf of cotton (Gossypium hirsutum L.) boll (LSCB), and their relationships with lint yield and fiber quality under cool temperature due to late planting, field experiments during 2009 to 2011 were conducted using two different cool temperature-tolerant cultivars, Kemian 1 (temperature-tolerate) and Sumian 15 (temperature-sensitive), at three planting date (25 April, 25 May and 10 June) in Nanjing (118°50′E, 4 32°02′N), China. First, the chlorophyll components in LSCB decreased with days post-anthesis, as well as soluble sugar content, amino acid content and C/N ratio. In addition, Pn, ΦPS II and Fv/Fm significantly decreased, indicating that Pn depression in LSCB was due to non-stomata closure. Second, under cool temperature due to late planting (from 25 April to 25 May and/or 10 June), Pn depression was due to stomata closure. Compared to Sumian 15, Kemian 1 demonstrated superior photosynthetic capacity. Furthermore, under cool temperature, lint biomass and seed biomass significantly decreased in parallel with the lint distribution rate, seed distribution rate and lint/seed ratio, whereas carpel distribution rate increased. These changes under cool temperature led to low lint yield and fiber strength. According to CVs and variance among three planting dates, Sumian 15 was more sensitive to cool temperature than Kemian 1.