Occurrence Regularity Of Apricot Bud Gall And Mechanism Of Bud Gall Produce And Study On Apricot Varieties Resistance

Apricot bud gall occurs widely in apricot orchards, with numerous galls ofvarious sizes being seen easily around branches, which have negative effects ofapricot growth and cause great economic losses. Apricot bud gall caused by Acalitusphloeocoptes (Nalepa) was investigated and studied in field and indoor. The presentstudy was to identify the eriophyoid mite, to investigate its overwintering place andstages, population dynamics in the field and dispersal modes, to observe anatomicalmorphology and ultrastructure of injured apricot bud, to test endogenous hormone ofapricot bud. Cultivars of apricot infested by A. phloeocoptes and resistance wereinvestigated. Correlation analysis was conducted between genetic diversity andresistance of A. phloeocoptes. Molecular markers linked to the resistant gene ofapricot bud gall were studied. The results of this study will provide evidence forintegrated control of A. phloeocoptes and the apricot marker-assisted selectionsystem.The results summarized as followings.1. Acalitus phloeocoptes (Nalepa) was identified as the pest causing apricot budgall according to morphological characteristics observed using scanning electronmicroscopy. The eriophyoid mite mainly infested young apricot buds, and they wouldthen proliferate and deform gradually, and form acanthoid gall tumors with varioussizes at last. A. phloeocoptes overwintered mainly as females that survived in theliving galls and accounted for76.4%of the total number of investigation. Theeriophyoid mite infested apricot buds continually from early May to early September,it occurred seriously in May, June and July. Surveys of dispersal modes showed thatthe eriophyoid mite initiatively dispersed by crawling to nearby buds and branches,which was the main way of short-distance dispersal. The average speed of A.phloeocoptes adults was0.33cm/min based on the crawling speed test conducted inlaboratory; whereas the passive dispersal mode was mediated by wind and insects,and wind was mainly long-distance dispersal vehicle of A. phloeocoptes than othermodes. The vehicle of insects included Pseudaulacaspis pentagona(Targioni-Tozzetti), Didesmococcus koreanus Borchsenius and Chilocorus rubidusHope.2. The deform process apricot bud became acanthoid gall tumor structure wasobserved by paraffin. Bud primordium grew in advance and formed new bud axis thatcovered by many new immature leaves, a new bud was formed. The morphology was a bud axis with many buds. The anatomy of injured apricot buds significantly changed.The size of infested bud axis inflated from the lower part to the upper part. Theimmature leaves became smaller obviously whereas the number of leaves increased.Lignification of immature leaves was exacerbated from inner to outer layers. Externalimmature leaves lignified seriously, especially the lower part of leaves nearby budaxis, which lignified completely and thickened remarkably, resulting in leaves’stretching outward and internal immature leaves’ disclosing completely. Theepidermal cells had different sizes, and much thickened and lignified completely.Mesophyll cells arranged loosely and in disorder and disintegrated at last.Ultrastructure of injured bud was observed under transmission electronmicroscopy by ultrathin sectioning. The size and number of starch grains andmitochondria were increased and chloroplast became swollen and irregular shape ininjured bud axis and immature leaves. At last the infected cells of bud axis weremalformed and protoplasm became aggregating. And it difficultly saw any organellein cell but there were many circular or irregular shape pores in it. The cell wall ofimmature leaves became thicker significantly and cytoplasm was dense. There was athin layer of electron dense granules in inside of cell wall. At last there were manypores in infected cell and organelles disintegrated. The electron dense granulesscattered in infected cell.3. The content of endogenous hormone of infected apricot bud by A.phloeocoptes was determined by HPLC (High Performance Liquid Chromatography).Results showed that the content of ZT in infected bud increased obviously and wasmuch larger than healthy, which accelerated cellular divide and promoted apricot budgall formed. The content of IAA in infected bud was lower than in healthy bud soinfected bud didn’t expand normal leaves. Whereas ABA in infected bud was higherthan in healthy, which accelerated browned and died of apricot bud gall. The contentof GA3in infected bud was higher than in healthy bud in stage of early vegetativegrowth, which promoted infected cell proliferation and benefited apricot bud gallformed. However, GA3in infected bud decreased obviously in last vegetative growthso accelerated the procedure of apricot bud gall senescence.ZT/ABA and GA3/ABA in infected bud were higher than in healthy bud in earlyvegetative growth, which accelerated infected bud proliferation and clustered,promoted apricot bud gall formed and spurred nutrimental matter to move to infectedcell. But they decreased rapidly in last growth, which restrained cellular divide and accelerated cell senescence and worsened nutrition conditions, promoted apricot budgall browned. ZT/IAA in infected bud higher than in healthy, which indicated celldivision is greater than elongation in injected cell. It proved that infected bud becamebud gall but didn’t expand normal leaves or stems. IAA/ABA in infected bud waslower than in healthy so the infected cells were not elongation.4. Apricot bud gall by A. phloeocoptes has been found from24investigatedapricot cultivars in three consecutive years. Goldsun, Katy and Italian apricot werecultivars of resistance. Whereas Lanzhou Dajie, Anning18, Zhupishui, Cao andTangwangchuandajie apricot were cultivars of high sensitivity. The genetic diversityof24cultivars of apricot infested by A. phloeocoptes was studied and analysed byUPGMA.16of100ISSR primers could amplify diversity bands. All of24apricotcultivars were divided into three groups, which were European group, Northern Chinagroup and Central Asian group when the. The results of correlation between geneticdiversity and resistance were showed that24apricot cultivars were divided into sixgroups when the coefficient was0.548. Each cultivar clustered in the same groupexpressed the same resistance or sensitivity, which indicated cultivars of closerelationship with the same resistance or sensitivity. Then genetic diversity had somedegree correlation with resistance.5. Molecular markers linked to the resistant gene of apricot bud gall in5apricotcultivars were studied based on ISSR combined with BSA. The results showed that7ISSR primers could amplify polymorphic bands between resistant and susceptibleDNA pools composed of5apricot cultivars.6of the7ISSR primers could amplifypolymorphic bands in resistant DNA pools, which were UBC807、UBC825、UBC841、UBC860、UBC868and UBC881. And one of the7ISSR primers could amplifypolymorphic bands in susceptible DNA pools, which was UBC834. Subsequently,7markers were verified between resistant and susceptible DNA pools of5apricotcultivars and3markers existing steadily in more than3apricot cultivars was found,which were UBC825-R1500、UBC860-R1380and UBC868-R500. It was inferredthat these3ISSR markers were linked to the resistant gene of apricot bud gall.