Preliminary Studies On Diversity Of Endophytic Fungi In Common Cucurbit Plants And Their Effects On Diseases

Many cucurbitaceous plants, providing fruits and vegetables, are important economic crops. Thereare rich endophytic fungal resources in cucurbitaceous plants, some of the endophytic fungi possessingthe potential for biocontrol. So far, only a few studies have been reported on endophytic fungal diversityin cucumber. This study tried to discover the diversity of endophytic fungi in common cucurbit plantsthrough sample collection, isolation, cultivation and identification, and carry out preliminary studies onthe effects of endophytic fungi on four common phytopathogenic fungi by means of plate confrontationtest and artificial inoculation. This will lay a foundation for further exploitation and utilization of theendophytic fungal resources.Seventy-six asymptomatic cucurbit plants belonging to nine species, were collected from sixlocalities (Haidian, Daxing and Yanqing of Beijing, Wuxi of Jiangsu, Yuanyang of Henan, Binzhou ofShandong), and a total of633fungal isolates were obtained using tissue culture method. Based onmorphological characteristics and ITS rDNA sequences,58genera were identified from539fungalisolates, among them Colletotrichum, Fusarium, Chaetomium, Alternaria, Rhizophycnis, AspergillusPlectosphaerella and Thielavia were dominant. Colletotrichum was mainly distributed in overgroundparts of plants, while Fusarium in roots and lower stems, and Rhizopycnis in roots, showing obviouspositional difference of colonization.Significant differences existed in relative abundance of main endophytic fungal genera anddiversity of the endophytic fungi among different kinds of the cucurbit plants growing in Yuanyang,Henan. The relative abundance of Colletotrichum in snake gourd reached44.7%, higher markedly thanthat in luffa8.0%. The relative abundance of Fusarium in cucumber reached32.4%, far higher than thatin other cucurbits, and that in pumpkin was the lowest, only3.0%.Thirteen Thielavia isolates and eight Diaporthe isolates were isolated only from the samplesoriginated from Daxing of Beijing, and seven Botryosphaeria isolates were isolated only from thesamples originated from Yuanyang of Henan. The floristic composition and diversity of the endophyticfungi in luffa growing in Wuxi of Jiangsu and in Yuanyang of Henan were obviously different. Thefloristic composition of endophytic fungi in cucumber growing in greenhouse and in open field was alsodifferent. This showed that geographical location and cultivation condition might have a significantinfluence on diversity of the endophytic fungi in cucurbit plants.Plate confrontation test of all the endophytic fungal isolates against four phytopathogenic fungiwas carried out. There were20,4,18and5isolates with Antagonism Index at80%or above againstRhizoctonia solani J. G. Kühn, Sclerotinia sclerotiorum (Lib.) de Bary, Fusarium oxysporum f. sp.cucumerinum Owen, and Colletotrichum orbiculare (Berk．&Mont．) Arx, respectively, and1,58,16and15isolates producing inhibition band against the four phytopathogenic fungi respectively.Twenty-five isolates with obvious inhibition band were selected to investigate the fungistasis of theirfermentation liquor sterilized by means of filtration or autoclaving. There were19,3and4isolatesshowing distinct inhibition to colonial growth of S. sclerotiorum, F. oxysporum f. sp. cucumerinum and C. orbiculare resprectively.Twenty isolates, producing inhibition band in plate confrontation test, were selected to assay theirplant growth-promoting activity. Among them,11isolates obviously increased plant height, maximalleaf area, wet weight or dry weight of cucumber plants tested40days after inoculation. Isolate Xf1significantly increased all of the four factors. In plant inoculation test with15isolates, showing highAntagonism Index to R. solani in plate confrontation test, isolates Wgl1, K2ls1and H3ls1reduceddisease severity of cucumber Rhizoctonia root and stem rot with relative control effects of54.0%,57.1%and64.3%respectively.