Research on the biological and chemical control of black-foot disease in grapevine nurseries

Black-foot is one of the most important fungal diseases caused by Cylindrocarpon-like anamorphs in grapevine nurseries worldwide. Since these species are soil-borne pathogens, managing the disease is highly difficult, and no economically plausible and practical tool could eradicate these pathogens from the soil. This study aimed to investigate the effect of endophytic Penicillium fructuariae-cellae and Aspergillus tubingensis isolates in suppressing black-foot disease of grapevines and to compare this effect with fungicide treatments on seedlings. The endophytic fungi were isolated from grapevine, citrus, and banana plants, and their suppressive effects on black-foot pathogens were first screened by dual culture tests in the laboratory. The isolates having a suppressive effect by this test were inoculated on the rhizosphere of grapevine saplings, and two days later, the plants were inoculated with the black-foot pathogens (Cylindrocladiella peruviana, Cylindrodendrum alicantinum, Dactylonectria macrodidyma, D. novozelandica, D. torresensis, and Ilyonectria liriodendri). Moreover, the fungicides (hymexazol, tebuconazole, cyprodinil + fludioxonil, azoxystrobin + difenoconazole, metalaxyl + fludioxonil) were applied to the pathogen-inoculated plants (in a different trial) for comparison with biocontrol performance of P. fructuariae-cellae and A. tubingensis under greenhouse conditions. Wood necrosis, and root dry weight were considered for the suppressive performance of antagonistic isolates and fungicides against the disease. The results indicated that fungicides applied at a dose of 1000 µg·ml-1 suppressed black-foot disease to some extent but could not substantially prevent it. Especially those containing azoxystrobin + difenoconazole, hymexazole and tebuconazole exhibited higher performance in reducing the occurrence of disease. Penicillium fructuariae-cellae prevented root mass reduction and internal wood necrosis in grapevine plants by 85.4% and 25%, respectively, but not for all pathogens. However, Aspergillus tubingensis exacerbated disease severity instead of suppressing it. This study suggests that Penicillium fructuariae-cellae could be a potential antagonistic endophyte for the biological control of black foot disease in grapevine nurseries.