Preliminary Studies On Fungal Endophytes In Cucumber Plants

In order to understand the endophytic mycobiota and its variation in cucumber plants, establish foundation for further research on ecology and function of the endophytic fungi from cucumber, endophytic fungi were isolated from 40 symptomless cucumber plants, including different cultivars growing in greenhouse and open field at different stages, collected from Yanqing of Beijing, and some other cucurbitaceous plants collected from other locations. Based on morphological characteristics and 18S rDNA sequence alignments, 19 genera were identified out of 1132 endophytic fungi strains isolated from cucumber root, stem, leaf, and fruit tissues. They are Alternaria Nees, Apiospora Sacc., Arthrinium Kunze, Aspergillus P. Micheli ex Link, Bipolaris Shoemaker, Chaetomium Kunze, Cladosporium Link, Colletotrichum Corda, Corynespora Güssow, Didymella Sacc., Exserohilum K.J. Leonard & Suggs, Fusarium Link, Mortierella Coem., Myrothecium Tode, Neocosmospora E. F. Sm., Nigrospora Zimm., Penicillium Link, Pleospora Rabenh. ex Ces. & De Not., and Rhizoctonia DC. Among them, Exserohilum and Neocosmospora have not been known in previous reports about endophytic fungi. The relative frequency of Alternaria was the highest in all the strains and reached to 36.8%; That of Fusarium was the second and reached to 29.7%. Alternaria and Fusarium were the dominant in endophytic fungi of cucumber.The research results on cucumber endophytic fungi indicated that Alternaria, Aspergillus, Chaetomium, Cladosporium, and Fusarium existed universally in different organs at all stages. The colonizing rate of Alternaria species reached 47% and was far higher in leaves than in other organs, and that of Fusarium species reached 32.5% and was far higher in roots than in other organs. Most of the endophytic fungi showed organ favoritism in different degrees. Some genera of fungi only existed in specified organs. The number of genus and total colonizing rate of endophytic fungi were higher in leaves and roots than in stems and fruits. Along with plant growth, the number of genera of endophytic fungi and the colonizing rates of some fungi increased, but the colonizing rates of Neocosmospora and Chaetomium species decreased from all organs. The colonizing rate of endophytic fungi was the highest in leaves, and next in roots and lower stems. The number of genera of endophytic fungi isolated from the cucumber growing in open field was more than that isolated from the cucumber growing in greenhouse. There were some differences in the genus of endophytic fungi from different cucumber cultivars. There were also some differences in the genus of endophytic fungi isolated on different media. The results could provide some foundation for further researches on ecology and function of endophytic fungi in cucumber.Plate confrontation tests were carried out with 315 strains of endophytic fungi isolated from cucumber and other common cucurbitaceous plants, collected from Yanqing, Daxing of Beijing, and Langfang of Hebei, against four cucumber pathogenic fungi. There were 82 strains to Colletotrichum orbiculare (Berk. & Mont.) Arx, 78 strains to Rhizoctonia solani J.G. Kühn, 16 strains to Fusarium oxysporum f. sp. cucumerinum Owen., and 13 strains to Phytophthora drechsleri Tucker, respectively, with the growth inhibition rate of 30% or above against pathogenic fungi. These strains accounted for 26%, 24.8%, 5.1% and 4.1% of the tested strains. The strains with growth inhibition rate of 50% or above against the four pathogenic fungi accounted for 20.3%, 17.1%, 4.8%, and 3.2% of the tested strains, respectively. Inhibition tests of fermentation liquid of endophytic fungus against pathogenic fungi indicated that the fermentation liquid of the strain F94 had distinct inhibition to growth of Fusarium oxysporum f. sp. cucumerinum and Colletotrichum orbiculare. The growth inhibition rates against the two pathogens reached 64.3% and 52.4% respectively.The results preliminarily revealed the overview of endophytic mycobiota in cucumber plant and gained some knowledge about biological function of endophytic fungi and relationships between them and between them and plants, which could provide some foundation for further researches on resources of endophytic fungi from cucumber plant and their utilization.