Effects Of Paecilomyces Variotii Extracts On Leaf Growth And Fruit Quality In ‘Gala’ Apple

Apple is one of the four major fruits in the world,and China ranks first in the world in terms of apple production and consumption.Consumers’demand for fruit quality is gradually increasing,while excessive application of chemical fertilizers in orchards can cause environmental pollution and affect apple quality.Therefore,the synergistic improvement of chemical fertilizer reduction and fruit quality is the key of current research.Foliar fertilizer application currently suffers from low utilization efficiency and limited concentration.Paecilomyces Variotii Extracts（ZNC）is a new biostimulant that enhance nutrient uptake and utilization,improve and enhance crop quality and yield,however,studies on the effect of ZNC on apple quality and foliar fertilizer utilization efficiency are still relatively few.In this study,eight-year-old’Gala’apple trees were used as test materials in the core demonstration garden of the Fruit Tree Research Institute,Shandong Academy of Agricultural Sciences.The foliar sprays of Paecilomyces Variotii Extracts 0 ng·mL^-1（CK）,5 ng·mL^-1（T1）,15 ng·mL^-1（T2）,30 ng·mL^-1（T3）and 0.3%KH₂PO₄（K0）,0.3%KH₂PO₄+5 ng·mL^-1（K1）,0.3%KH₂PO₄+15 ng·mL^-1（K2）,0.3%KH₂PO₄+30 ng·mL^-1（K3）,were applied at 40 d,60 d,and 80 d after flowering,respectively.Determination of leaf growth,photosynthetic characteristics,and fruit quality of’Gala’apple.The main findings are as follows:（1）Different concentrations of ZNC treatment significantly promoted apple leaf growth.Leaf area and dry weight increased,and chlorophyll a,chlorophyll b,and total chlorophyll content showed a trend of first increasing and then decreasing in the three sprays.Compared with CK,the total chlorophyll content of plants in T1,T2,and T3 treatments increased by35.7%,20.1%,and 21.9%,respectively,and the net photosynthetic rate of plants in T2 and T3treatments increased by 8.7μmol·m^-2s^-1and 4.3μmol·m^-2s^-1,respectively,while the difference in T1 treatment was not significant.（2）Different concentrations of ZNC treatment significantly improved apple fruit quality.The single fruit weight increased by 15.4%,41.5%,and 29.8%after T1,T2,and T3treatments respectively;the fruit surface brightness increased by 23.2%,36.2%,and 24.6%respectively;the relative content of anthocyanin increased by 12%,24%,and 62%,and the soluble solids content increased by 18.6%,25%,and 22.1%,respectively;the soluble sugar content increased by 16.8%,38.5%,and 12.5%,respectively.Vitamin C content increased by8.4%,18.5%,and 14.8%;starch content decreased by 9.6%,12.6%,and 17.6%,and the aroma variety of the fruit increased,while the inner quality and appearance of the fruit improved.（3）A mixture of different concentrations of ZNC and 0.3%KH₂PO₄further promoted leaf growth.The leaf area and dry and fresh weight of the leaves increased to different degrees in different times of spraying,and the variation of leaf thickness was not significant.Compared with K0,the total chlorophyll content of K1,K2,and K3 treatments increased cumulatively by 13.5%,6.4%,and 6.5%,respectively,on three treatments,net photosynthetic rate,transpiration rate,and stomatal conductance were significantly increased,the actual photochemical quantum efficiency,photosynthetic performance of the leaves were improved and dry matter accumulation was increased.The mixture of ZNC with 0.3%KH₂PO₄at different concentrations significantly improved fruit quality compared to KH₂PO₄alone.Compared with K0,the single fruit weight of K1,K2,and K3 treatments increased by 11.9%,17.2%,and 32.2%,respectively.There was no significant change in fruit shape index,and the fruit surface brightness increased by 7.7%,19.2%,and 6.4%,respectively;the relative anthocyanin content increased by 53.1%,93.8%,and 75%,respectively,promoting fruit coloration.The soluble solids and vitamin C content also got significantly higher,starch content decreased and aroma variety increased.As a foliar fertilizer booster,ZNC extract has the following functions:（1）Application of ZNC alone is beneficial to the growth of apple leaves and improvement of apple fruit quality,and the best effect is at 15～30 ng·mL^-1.（2）Application of ZNC can improve the utilization of foliar fertilizer,and the most suitable concentration is 15 ng·mL^-1.