Effects of plant density and mepiquat chloride application on cotton boll setting in wheat–cotton double cropping system

Sowing cotton directly after harvesting wheat in the Yangtze River Valley of China requires early mature of cotton without yield reduction.Boll-setting period synchronisation and more yield bolls distributed at the upper and middle canopy layers are also required for harvesting.The objective of this study is to quantify the individual and interaction effects of plant density and plant growth regulator mepiquat chloride(MC)on temporal and spatial distributions of yield bolls,as well as yield and yield components.During the 2013–2016 cotton growing seasons,the experiments were conducted on a shortseason cotton cultivar CRRI50 at Yangzhou University,China.Various combinations of plant density(12.0,13.5 and 15.0 plants m^(–2))and MC dose(180,270 and 360 g ha^(–1))were applied on cotton plants.The combination of 13.5 plants m^(–2)and 270 g ha^(–1)MC resulted in the greatest boll number per unit area,the highest daily boll setting number and more than 90%of bolls positioned within 45–80 cm above the ground.In conclusion,appropriate MC dose in combination of high plant density could synchronize boll-setting period and retain more bolls at the upper and middle canopy layers without yield reduction in the system of direct-seeded cotton after wheat harvest,and thus overcome the labor-intensive problem in current transplanting cropping system.

Increasing plant density increases Bt toxin concentration of boll wall in cotton by decreasing boll setting speed

Background: In order to uncover the mechanism of significantly reduced insect resistance at the late developmental stage in cotton(Gossypium hirsutum L.),the relationship between boll setting rate under different planting densities and Bacillus thuringiensis(Bt)insecticidal concentrations in the boll wall were investigated in the present study.Two studies were arranged at Yangzhou,China during the 2017–2018 cotton growth seasons.Five planting densities(15000,25000,45000,60000 and 75000 plants per hectare)and the flower-removal treatment were imposed separately on Bt cotton cultivar Sikang3 to arrange different boll setting rates,and the boll setting rates and Bt toxin content were compared.Results: Higher boll setting rate together with lower Bt toxin contents in boll wall was observed under low planting density,whereas lower boll setting rate and higher Bt toxin contents were found under high planting density.Also,higher Bt protein concentration was associated with higher soluble protein content,glutamic-pyruvic transaminase(GPT),and glutamic oxaloacetate transaminase(GOT)activities,but lower amino acid content,and protease and peptidase activities.It was further confirmed that a higher boll setting rate with lower Bt protein content under flower-removal.Conclusions: This study demonstrated that the insecticidal efficacy of boll walls was significantly impacted by boll formation.Reduced protein synthesis and enhanced protein degradation were related to the reduced Bt toxin concentration.