Some Basic Physiological Characteristics And Root Starch Properties And Their Genotypes Difference In Sweetpotato To Low Potassium Stress

Potassium(K)deficiency(namely low potassium),an important abiotic stress in plants,has become a major limiting element for obtaining crop high yield and good quality.Sweetpotato(Ipomoea batatas(L.)Lam)is a typical K-preferred starchy root crop.However,in China,K deficiency in soils exists commonly in sweetpotato-growing areas,especially in the middle and lower reaches of the Yangtze river,southern China and neighboring areas,that influenced sweetpotato plant growth and root quality formation.In addition,China is short of K fertilizer resources,so it is important to understand plant physiological basis and the variation characteristics of root starch under low K condition.Therefore,field experiment was designed for low-K at a long-term fertilizer plots(NP treatment:nitrogen and phosphorus,and NPK treatment:nitrogen,phosphorus and potassium)in 2011-2013,and pot experiment for K efficiency in 2013.In the paper,the major objectives was to find out screening indices and evaluation for low K-tolerant and K-efficient sweetpotato genotypes,to investigate the physiological responses to low K or no K in three sweetpotato genotypes differing in low K-tolerant ability and K utilization efficiency,and understand their starch physichemical properties and fine structure in storage root under low K.The major results obtained were summarized as follows:1.The significant difference of yield was observed in different sweetpotato genotypes in long-term fertilizer conditions,and the extents of coefficient of variation were very wide.The difference of K sensitivity index(relative root weigh,RRW)was significant.RRW was from 0.40 to 0.98,which be divided into four types(insensitive,low sensitive,moderately sensitive and highly sensitive)by cluster analysis.Under CK treatment,their differences of K utilization efficiency(KUE)of root and whole plant were also significant.RRW and KUE can be used for screening low potassium(K)-tolerant and K efficient sweetpotato materials as two main indices.KUE was more than 200 g g-1 in root that the material can be concluded as K efficient,RRW was more than 0.8 that the material can be considered as low K-tolerant.In thirty-one genotypes,Xushu32 and Xinxiang were low K-tolerant and K-efficient genotypes,Xushu18 and Shangshu19 were moderate,and Ningzishul and Xushu22-5 were the weakest in low K-tolerant and K-efficient.2.Compared with the normal K supply,low K or no K significantly decreased total biomass and root yield,photo synthetic efficiency and chlorophyll(Chl)content of the three cultivars,while increased leaf sucrose and proline content.Chloroplast ultrastucture closely associated with leaf Chl biosynthesis and photosynthate accumulation was obviously damaged.Simultaneously,the marker enzymes involved in anti-oxidative system and starch synthase enzymatic activities were also significantly disturbed.Compared with Xushul 8 and Ningzishul,Xushu32 had higher root yield and better growth performance under low K or no K,which were mainly attributed to its high net photosynthetic efficiency,greater carbohydrate conversion and starch synthesis.The findings indicated that physiological response was closely related to KUE among different sweetpotato genotypes under low K or no K,affecting possibly the plant growth and root starch synthesis.3.Compared with the normal K supply,under low K condition,main components in sweetpotato storage root starch changed to a certain extent.The slight decrease was observedin the whole average granule diameter.Starch To(gelatinization temperature),Tp(peak temperature)and?H(heat enthalpy)were basicially lower than that in CK treatment,and Ningzishul had significant differences in the three characteristic values.Peak viscosity and breakdown viscosity in three genotypes had obvious decrease.Hot paste viscosity,cool paste viscosity in Xushul8 and Ningzishul significantly increased,but Xu32 was on the contrary.Moisture absorption degree of starches in three genotypes were reduced differently.In addition,swelling power of starch increased differently.The findings indicated that there were different effects on root starch composition,granule size,pasting properties and thermal properties in sweetpotato genotypes differing in potassium utilization efficiency under low K.4.Compared with the normal K supply,low K caused certain change of root weight-average(Mw),number-average molecular weight(Mn),polydispersity index(PDI)and root meansquare radius(Rz).There were also certain differences among different genotypes.The increase of Mw,Mn and Rz,and decrease of PDI displayed in Xushul8 and Ningzishu1,and Xushu32 was on the contrary.And also increased of the average chain length and the percent of DP?12,decrease significantly the percent of 24<DP?36 in three genotypes root starch under low K.The external short chain A of amylopectin had more effect on average molecular weight than chain B,and short and medium chain length decided mainly on the physicochemical properties of starch.Chain length of amylopectin is closely related to granule size and its distribution.