Improving boll capsule wall, subtending leaves anatomy and photosynthetic capacity can increase seed cotton yield under limited drip irrigation systems

Drought stress is considered to be the main source of yield reduction around the world. Improving plant performance under stressful environments by understanding growth and physio-biochemical responses are important. However, the detail mechanism of how boll capsule wall and subtending leaves anatomy, physiobiochemical characteristics and key enzymes i.e. Ribulose-1,5-bisphosphate carboxylase (RUBPC) and phosphoenolpyruvate carboxylase (PEPC) affect cotton (Gossypium hirsutum L.) yield have not yet been reported. To cover this knowledge gap, a two-year field experiment evaluated three drip irrigation rates [W-1 (4800 m(3) ha(-1)), W-2 (3840 m(3) ha(-1)) and W-3 (2880 m(3) ha(-1))] effects on cotton main stem leaves, boll subtending leaves, capsule wall anatomy, biomass accumulation, RUBPC and PEPC activity. Compared with W-1, W-2 had 10.4-15.7 %, 8.3-24.6 %, 4.4-22.7 % and 5.0-15.3 % higher boll subtending leaf net photosynthetic rate, chlorophyll content, RUBP and PEPC activity at 21-42 days after anthesis. The palisade tissue thickness at 35 DAA (days after anthesis) and the ratio of palisade tissue to sponge tissue (p/s) of boll subtending leaf during 21-49 DAA were 7.7 % and 3.6-10.2 % higher for W-2 over W-1. Under W-2 treatment,improvements in these attributes significantly prolonged biomass accumulation rate (T, 6.9 d and 22.1 d) of main stem leaves and boll subtending leaf resulted in the maximum growth rate of seed cotton weight (Vx, 0.195 g d(-1)). Conclusively, higher photosynthetic capacity of the boll subtending leaves during 21-42 DAA and thicker capsule wall are the main drivers for achieving higher seed cotton weight under limited drip irrigation systems in arid region.