Effects Of Planting On Fiber Quality And Within-boll Yield Components As Mediated By Sucrose Metabolism In Cotton Bolls

Cotton is an important cash crop.Its yield and quality are partly regulated by environmental factors during growth and development,and temperature has an important influence on cotton yield and quality.The differences in the transport of carbohydrates from leaves subtending cotton bolls to cotton bolls and the distribution of assimilates between embryos and fibers under different temperature conditions were explored to provide a theoretical basis for solving cotton yield and quality problems.The upland cotton lines A705(high lint percentage,low seed index)and A201(low lint percentage,high seed index)differing in cotton boll traits were used as experimental materials.The two lines were planted in the experimental station of Jiangxi Agricultural University(JXAU)across2016 to 2017.Different temperature conditions during the development of cotton boll were created by setting early planting date(April 12,2016,April 15,2017)and late planting date(May 6,2016,May 28,2017).On the commence of peak flowering white flowers from the proximal positions on middle fruiting branches were labeled.Samples(bolls and their subtending sympodial leaves)were taken at 5 days post anthesis(DPA),10 d,17d,24 d,31d,38 d and 45 d,respectively for the analysis of carbohydrate(sucrose,hexose and starch)and sucrose metabolism enzyme(vacuolar acid invertase,cell wall acid invertase,sucrose synthase,sucrose synthase)activities.The dynamic changes of them with cotton fiber,ovule and seed coat and planting dates effects on them and yield components and fiber parameters were investigated.The main findings are as follows:1.Under the lower temperature conditions due to late planting,the maturation period of cotton bolls is longer relative to early planting,and the development is more fully completed.Boll size,seed mass per boll and seed index were increased,and lint percentage was decreased by late planting.Fiber length,unity index,elongation at break and fiber strength were higher in late planting than in early planting,but not for the micronaire,Late planting exhibited primarily better fiber quality than early planting.2.The concentration of hexose in the early stage of fiber growth(fast fiber elongation)was higher in late planting than in early planting.Sucrose concentration peaked later in late planting than in early planting.The activity of CWIN enzyme with fibers in late planting was higher than that in early planting.The higher concentration of hexose in late planting lasted longer during fiber growth,and in turn resulted in a faster elongation in fibers compared to early planting,which was consistent with the observation that late planting expressed superior fiber quality relative to early planting.3.The concentration of hexose with embryos was higher in late planting than in early planting.The higher concentration of hexose at the early stage of the embryo developmentis beneficial to promote cell division and increase the number of cells.The higher concentration of hexose at the later stage is beneficial to the full development of the embryo.Late planting embryos had higher VIN and CWIN enzyme activities than early planting at the beginning of embryos development,which matched with the higher hexose concentration at that time.4.The late planting seed coat has a higher concentration of hexose,as the same for late-planted embryos.Seed coat during early stage has higher starch concentration in early planting.Furthermore,the transformation rate of starch is lower in early planting than late planting.The decreased starch synthesis or promoted starch decomposition into hexose may be caused by low temperature.which may lead to higher hexose concentration,and thus longer seed development in late planting.5.Sucrose concentration was increased,and starch concentration was decreased,and VIN and CWIN enzyme activity were decreased in the cotton boll-subtending leaf by late planting,which suggest that more sucrose may be decomposed into hexose in the early planting compared to late planting.At the same time,it indicated that under the condition of late planting,the bolls may receive more assimilates from boll-subtending leaves,which is consistent with the higher hexose concentration in seeds and fibers,and is consistent with the more fully completed development on late planting bolls.