Mepiquat chloride effects on potassium acquisition and functional leaf physiology as well as lint yield in highly dense late-sown cotton

Abstract

Incredible accomplishments have been achieved in agricultural production in China, but many demanding challenges for ensuring sustainable cotton production remain. An efficient cropping model characterized with late sowing, higher density and low fertilizer application is a promising alternative to cope with the present high cost cotton production. However, it is not confirm that mepiquat chloride (MC) application is still required in this new planting model. We hypothesized that MC application might reduce lint yield and thus not be necessary in this new system. A 2-year (2015–2016) field experiment was performed to test this hypothesis in which cotton was planted in mid-May at 10 plants m−2 and with single fertilizer application (225 kg N ha-1). MC was sprayed thrice with 5 leaf intervals initiated from the 6th leaf stage in 5 different dosages i.e. 0 (control), 30, 60, 90, and 120 g ha-1. Morphological attributes viz. plant height, main stem diameter, number of fruiting branches, main stem nodes, main stem green leaves and main stem internode length were evidently reduced by 9–40%, 2–13%, 2–11%, 4–27%, 6–24% and 3–19%, respectively. Cotton potassium accumulation was not significantly influenced; specifically the uptake in reproductive organs from MC0 to MC120 of 45 to 44 kg K ha-1 in MC treated plants averaged across two years. Photosynthesis was reduced by 1–26% due to diminished Rubisco activity by 3–37% in MC treated plants and lint yield decreased by 5–27% as MC dosage increased. Furthermore, alpha amylase, beta amylase and total amylase activities were decreased by 2–16%, 3–19% and 1–17% but sucrose transformation rate was increased in the 4th functional leaf from the apex, respectively. Our data suggest that increased accumulation of sucrose and starch in the leaf with reduced photosynthesis, Rubisco and amylase activity could explain the yield loss. Conclusively, MC application is not needed for this new cotton planting model in Yangtze River Valley of China.