Effect Of Phosphorus Application On Sweet Potato(Ipomoea Batatas(L.)Lam.) Potential Storage Root Endophytohormone Metabolism And Storage Root Number

The experiment was a combination with field trial and pot-sand culture.There five phosphorus application rates were set up:P₀（0 g/kg P₂O₅）、P_0.02（0.02 g/kg P₂O₅）、P_0.04（0.04 g/kg P₂O₅）、P_0.06（0.06 g/kg P₂O₅）、P_0.08（0.08 g/kg P₂O₅）,and two main sweetpotato varieties“YS25”and“PS32”as trial materials.The aims of this experiments were to shed light on the patterns of endo-phytohormones metabolism on storage root formation,young roots and above-part development,storage root number at ridge closure stage（40 days after planting）,as well as yield and commertial characteristics under phosphorus at and harvest time（120 days after planting）.The pot-sand culture mainly measured agronomic traits and determined endo-phytohormone content and relative genes expression in potential storage root during storage root formation（0～40 days after planting）.Whlie the field trial was designed to investigated on storage root characteristics at ridge closure period（40 days after planting）,and the yield also yield components as well as storage root commercial characteristics were measured at harvest time（120 days after planting）.The results as follow:（1）At the early stage of sweet potato growth and development（0～40d after planting）,compared with no phosphorus application（P₀）,moderate phosphorus application(P_0.04)significantly increased expression level of SRD1,Ibkn1,Ibkn2 and Ib MADS1 genes.Meanwhile endo-phytohormones synthesis key gene NIT4,APRT and OPR3 were significant expression,while significantly decreased the expression of GA₃OX₄ and AAO genes.Thus,the IAA,ZR and Me-JA content in potential storage root were significant higher under moderate phosphorus application(P_0.04),while GA₃and AAO were significant lower.The ratio of IAA/ZR exhibited significantly increased at（0～20 days after planting）while significantly decreased（20～40 days after planting）.Therefore moderate phosphorus application(P_0.04)significantly promote young root development.Compared with P₀,moderate phosphorus application(P_0.04)significantly increased root number,total root length,root surface area,root volume,number of root tips,average root diameter and total root fresh weight,thus promoted potential storage root development that with significantly higher fresh weight and diameter.（2）Optimun root morphology under moderate phosphorus application(P_0.04),significantly increased root activity,thus promoted water and nutrition absortion for aboved-part development.Compared with P₀,moderate phosphorus application(P_0.04)significantly increased leaf number,leaf fresh weight,leaf area,stem diameter,stem fresh weight,longest stem length and total fresh weight of the two varieties;hence advantageous to promote photosynthesis,allocation and accumulation from source to sink.Compared with P₀,the above-part dry weight,root dry weight and whole plant dry weight as well as root dry weight radio were significantly increased,while decreased above-part dry weight radio under moderate phosphorus application(P_0.04),as result significantly increased R/T value,promoted storage root formation.（3）Therefore,compared with P₀,moderate phosphorus application(P_0.04)significantly increased storage root number,single root fresh weight and storage root weight per plant.Besides increased the storage root number that root diameter in range of 5～10 mm,so increased average storage root diameter.（4）Compared with P₀,moderate phosphorus application(P_0.04)increased commodity rate of two varieties,significantly increased the rate of medium-sized sweet potato,decreased the coefficient of variation of root weight and root diameter of commercial storage root,but had no significant effect on the ratio of straight to vertical,improved the uniformity ofstorage root during harvest time（120d after planting）,improved the appearance quality of sweet potato,and significantly increased the yield of two varieties of sweet potato.（5）While excessive P application significantly reduced IAA and ZR contents,increased GA3 and ABA contents in potential root tubers,which was not conducive to root development in the early growth stage of two varieties of sweet potato,reduced shoot growth;reduced photosynthetic product synthesis at leaves,decreased distribution and accumulation of photosynthetic products to roots,and was significantly inhbited on storage root formation.Thus in ridge closure period（40d after planting）,the number of storage root per plant and the weight of storage root per plant were significantly decreased.The number of commercial tubers and the rate of medium-sized tubers and storage root yield were significatly decreased at harvest time（120 d after planting）.