ABSTRACT
Seedling rot disease in rice leads to significant loss in the production of seedlings. This research was conducted to explore yeasts that could be used as biological control agents against rice seedling rot disease caused by Curvularia lunata and Helminthosporium oryzae. In total, 167 epiphytic yeast strains were evaluated, revealing that 13 of these yeast strains demonstrated antagonistic activities against fungal pathogens and either C. lunata DOAC 2313 or H. oryzae DOAC 2293. The volatile organic compounds (VOCs) and biofilm produced were possible antagonistic mechanisms in vitro for all the antagonistic yeast strains. Using nursery trays in a greenhouse, this study evaluated the control of rice seedling rot disease caused by these two fungal pathogens using antagonistic yeasts, identified in the present study and from our previous study. Torulaspora indica DMKU-RP31 and Wickerhamomyces anomalus YE-42 were found to completely control rice seedling rot disease caused by both of these fungal pathogens. Furthermore, W. anomalus DMKU-RP04 revealed 100% disease control when the disease was caused by H. oryzae. This is the first report on using antagonistic yeasts to control rice seedling rot disease caused by C. lunata and H. oryzae. These three antagonistic yeasts also showed promising potential for development as biocontrol agents against rice seedling rot disease caused by fungi.
ABSTRACT
The phylloplane is an important habitat for yeasts and these yeasts may have antagonistic activities against pathogens and could be used as biocontrol agents. To investigate rice phylloplane yeasts, 282 strains were isolated from 89 rice leaf samples and identified as 15 known yeast species in the phylum Ascomycota and 35 known and two potential new species in the phylum Basidiomycota. The majority of rice phylloplane yeasts belonged to the phylum Basidiomycota. The evaluation of antagonistic activities of 83 yeast strains against rice pathogenic fungi Pyricularia oryzae, Rhizoctonia solani, Fusarium moniliforme, Helminthosporium oryzae and Curvularia lunata revealed that 14 strains inhibited these pathogens. Among the antagonistic strains, Torulaspora indica DMKU-RP31, T. indica DMKU-RP35 and Wickerhamomyces anomalus DMKU-RP25 inhibited all rice pathogens tested, and the production of volatile organic compounds, fungal cell wall degrading enzymes and biofilm were the possible antagonistic mechanisms against all rice pathogens tested in vitro. These yeast strains were evaluated for controlling rice sheath blight caused by R. solani in rice plants in the greenhouse and were found to suppress the disease by 60.0-70.3%, whereas 3% validamycin suppressed by 83.8%. Therefore, they have potential for being developed to be used as biocontrol agents for rice sheath blight.
ABSTRACT
The ecology and diversity of phylloplane yeasts is less well understood in tropical regions than in temperate ones. Therefore, we investigated the yeast diversity associated with the phylloplane of corn, an economically important crop in Thailand, by a culture-dependent method. Thirty-six leaf samples were collected and 217 yeast strains were isolated by plating leaf-washings. The strains were grouped by PCR-fingerprinting and representative strains were identified by analysis of the D1/D2 domain of the large subunit rRNA gene. In total, 212 strains were identified within 10 species in the Ascomycota and 32 species in the Basidiomycota. Five strains represented potential new species in the Basidiomycota, one strain was recently described as Papiliotrema plantarum, and four strains belonged to the genera Vishniacozyma and Rhodotorula. A higher number of strains in the Basidiomycota (81.6%) was obtained. Hannaella sinensis was the species with the highest occurrence. Principal coordinates analysis ordinations of yeast communities revealed that there were no differences in the similarity of the sampling sites. The estimation of the expected species richness showed that the observed species richness was lower than expected. This work indicated that a majority of yeast associated with the phylloplane of corn plant belongs to the phylum Basidiomycota.
ABSTRACT
During a survey of the yeast community associated with the phylloplane of corn in Thailand, a basidiomycetous yeast strain belonging to the genus Papiliotrema was isolated. Analyses of the D1/D2 domains of the 26S (LSU) rRNA gene and complete ITS region supported the recognition of a novel species, for which the name Papiliotrema plantarum sp. nov. is proposed (type strain DMKU-CP801T=CBS 15220T=PYCC 7257T). Another strain of P. plantarum sp. nov., isolated in French Guiana, was found to be sexually compatible with the Thai isolate and mycelium with clamp connections, basidia and basidiospores were observed in culture. The basidial morphology of P. plantarum combined features previously observed for Papiliotrema bandonii and Papiliotrema fuscus, which represent the only sexual species hitherto known in the genus, i.e. transversely septate basidia, with sexual structures of the Tremella type.
