The Technical Research Of Vigorous Growth Control By Spraying KH₂PO₄ On The Leaf Of Strawberry

In recent years,the strawberry industry of China has been growing rapidly,making China the maximal strawberry producer around the world.Strawberry is identified as the hypothermophilous species,and thus its vigorous growth majorly results from the relative high temperature and excessive fertilizer application.Characterized as a significant factor causing the decrease of yield and fruit quality,the vigorous growth not only leads to the imbalance of vegetative growth and reproductive growth,but also results in the poor ventilation and light conditions along with increases of diseases and insect pests.Therefore,the scientific control of vigorous growth is of great significance to the production of strawberry.In this study,we applied the KH₂PO₄ to control the vigorous growth of strawberry by foliage spraying.Via conducting diverse experiments,the optimal concentration and frequency of KH₂PO₄ spraying were identified in the process of controlling the strawberry vigorous growth and improve the fruit quality.Strawberry（Fragaria×ananassa Duch.cv.‘Akihime’）planted in spatial soilless culture mode in the facility was used as the experimental material.In the treatment groups,the spraying concentrations of KH₂PO₄ solutions were set to 0.25%,0.5%,0.75%,1%,2%and 4%,respectively;the spraying frequencies were set to 3 days（3 d/time）and 6 days（6 d/time）.Each treatment group at different spraying frequencies was respectively denominated as T1～T6 and T7～T12.The control group was sprayed with deionized water and denominated as CK1 and CK2,respectively.After 30 days of treatment,samples were employed to measure the indexes of plant growth,physiology and biochemistry.After the maturation of fruits,samples were employed to test fruit quality and output indexes.The main results are as follows:1.Under two different spraying frequencies,the treatments of 2%and 4%KH₂PO₄ both had caused damage to strawberry plants and leaf margins drying.There was no significant differences in the SOD activity,relative electrical conductivity and malondialdehyde content of strawberry leaves when KH₂PO₄ concentration was 0.25%to 1%.When KH₂PO₄ concentration was 2%,the SOD activity,relative electrical conductivity and malondialdehyde content of strawberry leaves increased significantly.Therefore,the concentration of KH₂PO₄ solution that is used on the leaves to control strawberry vigorous growth is recommended to sustain below2%.2.The concentration of KH₂PO₄ solution that was sprayed on the strawberry leaves above0.5%could inhibit the shoot vegetative growth of strawberry plants,including the decreased leaf area,petiole length and the shoot dry and fresh weight.The spraying of KH₂PO₄ with suitable concentration（0.5%～1%）inhibited the vegetative growth.Nevertheless,it promoted the root activity and increased Chl content in leaves,simultaneously improved the photosynthetic performance and photosynthetic energy efficiency.The results also proved that0.75%KH₂PO₄ had the best effect at both treatment frequencies.3.After spraying KH₂PO₄ on leaves,the absorption and distribution of elements,enzyme activities of nitrogen metabolism and hormone levels in plants were influenced.The results showed that the KH₂PO₄ spraying promoted the accumulation of potassium and phosphorus in the shoot,and reduced the absorption of nitrogen.The activities of Glutamine synthetase and dehydrogenase in leaves were significantly increased after spraying KH₂PO₄ with suitable concentration.The spraying of KH₂PO₄ led to the decrease of IAA and GA₃contents and the increase of ABA content in leaves.In addition,spraying KH₂PO₄ solution with greater concentration can lead to the more significant changes of the contents of IAA,GA₃and ABA.The concentration of KH₂PO₄ above 0.75%also increased the content of ZT in strawberry leaves.4.The appropriate control of strawberry vigorous growth not only improved the yield of strawberry,but also improved the fruit quality.The spraying of KH₂PO₄under 0.75%concentration could sustain the yield and fruit weight of single crop,total phenols,flavonoids,anthocyanins,ascorbic acid,soluble solids,and soluble sugars contents in the highest level,and the spraying effect of 0.75%KH₂PO₄ was the best 6 d/time.The fruit hardness did not decrease significantly while maintaining high nutrient quality.In conclusion,it was recommended to spray 0.75%KH₂PO₄ solution on the leaves for 6 d/time to control the growth of strawberry.