Three integrated tactics were tested to control white rot (caused by Sclerotium cepivorum Berkeley) of Welsh onion (Allium fistulosum L.) in a severely infested commercial Welsh onion field: reducing the population of sclerotia in soil by soil fumigation, controlling germinated sclerotia in the rhizosphere by soil application of simeconazole granules at planting and a soil drench with penthiopyrad later, and reducing the virulence of sclerotia by hilling, with serial lime applications in the winter. To reduce the population of sclerotia, we fumigated the soil with dazomet before planting and sealed the soil by either watering it (dazomet-water) or covering it with PVC sheeting (dazomet-cover). The average number of living sclerotia was reduced from 35.4/100 g of dry soil (average survival, 75.8%) in the untreated control to 7.1/100 g dry soil (25.6%) in dazomet-water and 0.5 (0.9%) in dazomet-cover. The lowered numbers of surviving sclerotia resulted in a clear difference in disease severity at harvest (rate of diseased plants: 96.0% in control, 97.9% in dazomet-water, 24.2% in dazomet-cover). The combination of the inhibition of germinated sclerotia and hilling, with serial lime applications in the winter, efficiently reduced white rot (15.3% of plants diseased). The integration of all three tactics almost completely suppressed white rot (1.6% of plants diseased), confirming the efficiency of this strategy in a severely infested field. This strategy should be tested in different types of infested fields, and the possibility of gradually reducing labor to control white rot should be verified.

A homeobox that encodes a transcriptional factor containing a 180-bp DNA-binding motif, termed the homeodomain, is important in regulating morphogenesis in fungi and other eukaryotes. In this study, we functionally analyzed CoHox2, one of the 10 homeobox genes conserved in Colletotrichum orbiculare, the causal agent of cucumber anthracnose. The number of conidia formed by CoHox2 knockout mutants was reduced to 30% of that by the wild type. However, conidial morphology did not differ significantly between CoHox2 mutants and the wild type. The CoHox2 mutants formed typical appressoria on glass and caused anthracnose on cucumber. As shown in scanning electron micrographs, CoHox2 mutants also formed more setae than the wild type did. These findings suggest that CoHox2 positively regulates conidiation and negatively regulates seta formation. Expression experiments based on fluorescent mCherry protein demonstrated that conidia formed by setae of the wild type have a nucleus. In addition, setae of the wild type incubated on PDA for 7 days had acutely pointed tips and were melanized, whereas those of the wild type incubated on PDA for 13 days had germinated and hyaline hyphae had developed. Thus, setae of the wild type may function in the formation of conidia with a nucleus in the early stage of culture and hyphal growth at the later stage.

The main mango cultivar grown in Japan, cv. Irwin, is susceptible to Colletotrichum species that cause mango anthracnose and requires the application of fungicides several times a year before harvest. Increased consumer demand for safe, secure foodstuffs and the desire to reduce labor and costs are driving the development of mango cultivars with strong resistance to anthracnose. Therefore, in this study, we developed a simple, accurate method to evaluate the susceptibility of mango cultivars to anthracnose to identify anthracnose-resistant breeding stock. For 27 mango cultivars, uncured leaves that had chlorophyll SPAD values of 9.5~24.3 were inoculated with conidial suspensions of C. asianum (Nga-05) containing a minimum of 10⁴ conidia/ml and incubated at 25° to 30°C for 5 days in the dark to promote lesion formation. Disease severity on each of the 27 cultivars was positively correlated with disease severity on inoculated fruits. Cv. Golden Nugget was identified as the most resistant to mango anthracnose. Based on these findings, we concluded that the developed method can be used to efficiently evaluate disease resistance and to identify disease-resistant varieties from genetic resources of mango and mango hybrid progeny.