| Moldy core is common fruit diseases on apple.It causes fruit droping before harvest,and moldy core or core rot during storage,which seriously affects the yield and quality of apple.The occurrence of moldy core is closely related to fruit structure,and the varieties of opening carpel cavities are with high incidence.A clear understanding of infection characteristics is the basis for making effective control strategies.Tricothecium roseum and Alternaria alternata are the main pathogens causing moldy core in China.In this study,the infection pathway of Red delicious are studied by means of GFP tagged T.roseum strain and the construction of A.alternata fluorescence labeled strain and the characteristics of flowering infection were studied.Based on the infection characteristics,sets of control schemes was made and field experiments were carried out to evaluate the control effects.The main results are as follows:1.The floral tissues of Red delicious were inoculated with Trichothecium roseum GFP tagged strain TR45 at flowering stage and infection pathway was observed and analyzed at different stages.The results showed that T.roseum could infect petals,stamens and pistil.Most of floral remnants were enclosed in the calyx tube 10-15 d after falling flower.T.roseum entered into the united style through the orifice between the separated styles and extended from the style tube to the base of the style along the pluricellular hairs.At about 30 d after flower falling,intervening tissues and carpel cavities wall gradually cracked,forming a channel through the carpel cavities and style — sinus,which gradually expanded with the enlargement of the fruit.At about 60 d after flower falling,the hyphae expanded into the carpel cavities along the open sinus.Finally,the carpel cracks,hyphae invaded the pulp tissue and caused decay.These results showed that the style tube was the main channel of infection in young fruit period,the same as in Fuji,but the sinus opening of Red delicious variety was significantly earlier than Fuji,and hyphae could enter the carpel cavities earlier,which may be a reason for the higher incidence of Red delicious.2.Alternaria alternata is one of the main pathogens of moldy core.In order to clarify the infection characteristics of A.alternata into carpel cavities,the construction of A.alternata fluorescence labeled strain and the characteristics of flowering infection were studied.In view of the thick cell wall and large pigment deposition of A.alternata,which may affect the fluorescence observation of the labeled strains,the GFP gene was ligated withthe chitin binding protein(CBP)gene to construct plasmid.The transformant ZQ65 showed strong fluorescence,and there were no significant difference in spore,hyphae,colony morphology,growth rate and pathogenicity with A.alternata wild type strains.ZQ65 spore suspension was inoculated on floral tissues at flowering stage.48 h later,pathological changes occurred in anther,filament,style,petal.The results showed that A.alternata CBP-GFP-labeled strain ZQ65 can infect apple floral tissues,which could be used as a tool to study apple tissue infection.3.Experiments on the control of moldy core were carried out in Baishui,Shaanxi province,Tianshui,Gansu province and Sanmenxia,Henan province in 2018 and 2019.Five treatments were designed: Spraying polyoxin+acaricide 2 times after flowing and before bagging,acaricide 3-5 times between bagging and mature stage.Spraying polyoxin 4 times,before bagging.Spraying polyoxin+acaricide 3 times after flowing and before bagging.Spraying polyoxin+acaricide 2 times after flowing and before bagging and releasing the predator mites 3 times.Spraying biocontrol agent DP03-4 4 times between 80% falling and bagging.The results showed that,compared with the control group(Spraying polyoxin+acaricide 2 times after flowing and before bagging),the control effect of these treatments was less than 40%,and there was no obvious control effect on mites associated with carpel cavities.4.A preliminary study was conducted on the habits of mites associated with carpel cavities.It was found that the mites could feed on hyphae and spores of A.alternata and T.roseum,and reproduce on PDA medium.Two species of mites were preliminarily identified,which are Tarsonemuz confocus Ewing and Tyrophagus putrescentiae Schrank,which feed on fungai.Field experiments showed that mites could carry T.roseum conidia and mycelium.The statistical results showed that the occurrence of mites was significantly correlated with moldy core(P<0.05).These results showed that mites can carry pathogenic conidia and mycelium,and as transmission may play a role in the development of moldy core. |
