Analysis Of The Unknown Disease On 'Ruixue' Apple Fruit

‘Ruixue' is a new late-maturing yellow apple variety which is selected and bred by Northwest A&F University.It has high yield,good taste,and pleasant fragrance.It can be stored for 6 months under normal temperature conditions.However,in recent years,it's discovered that the fruit of ‘Ruixue' has irregular brown spots around the stem after picking.The spots are light brown during this period,but they gradually turn to dark brown as the storage time prolongs,and the lesion area gradually expands.In severe cases,the entire fruit surface is brown to varying degrees.This study investigated the prevalence situation of ‘Ruixue' apple in different regions,the differences of different bagging types,and the dynamic changes of the microenvironment in fruit bags.By analyzing and comparing the phenolic substances as well as the mineral elements in the peels of normal and diseased fruit,we're trying to find the causes of the unclear diseases in ‘Ruixue'.The main findings we obtained are as follows:1.Investigation of the incidence in ‘Ruixue' in different regions.It began to have disease during the harvest time in early October.The 6-year-old ‘Ruixue' dwarf tree in Baishui County has the lowest incidence rate of 37% and the incidence is the lightest.The 4-year-old dwarf tree in Qingcheng County has a higher incidence rate of 53%.A 4-year-old high-hanging head-hanging fruit tree has the highest incidence rate of up to 65%,and the incidence is most serious.It shows that the incidence rate of dwarf trees is generally lower than that of high-stake-changing heads,and the incidence rate of old trees is lower than that of young trees and the situation is less severe.2.Differences of prevalence situation in different bagging types.Compared with the non-bagging fruit,both the double-layer bag and the single-layer bag were found to have diseased fruit in the early stage of harvest,and there was no disease in the unwrapped fruit.The incidence rate of double-layer bags is higher than that of single-layer bags.As the storage time lasts after harvest,the degree of the disease situation gradually increases,from the initial browning of the stem to the browning of the whole fruit surface,but if unwrap the apple in advance,the prevalence situation would significantly be reduced.3.Analysis of temperature changes in bagged apples with different bags.The double-layer fruit bag has a more profound effect on the temperature inside the bag than the single-layer fruit bag.‘Ruixue' in the double-layer bag and single-layer bag both reaches its temperature peak.The maximum temperature in the double-layer bag can reach 46.8°C around 14:00 while it's up to 43.1°C in the single-layer bags.In July and August,the fruit is in a critical period when the fruit grows rapidly.At this time,the sever change of temperature in the bag is really bad to the growth and development of the fruit.It is presumed that high temperature may be one of the main causes of the diseases of ‘ Ruixue' fruits.4.Analysis of the different minerals in normal fruits and diseased fruit.The Ca/K ratio and Ca/P ratio after bagging are all lower than those of unwrapped fruits.The Ca/Mg ratio,Ca/K ratio,and Ca/P ratio are significantly lower in the bagged fruits,which was significantly different from that of the ‘Ruixue' bagged fruit and unwrapped fruit(P<0.05).The single Ca content of the fruit does not necessarily lead to the occurrence of disease,but maybe relates to other mineral elements in the fruit.Therefore,balanced fertilization and enhanced absorption of calcium of ‘Ruixue' is worth further study.