To clarify the existence of latent infection and infection stages of the pathogens causing anthracnose on mangos grown in rainout shelters during bud formation, flowering, and the early stages of fruit set, we collected healthy-looking apical buds, flower buds, inflorescences and fruitlets and attempted to isolate the pathogens using an ethanol immersion treatment. We observed salmon-colored conidial masses on all organs sampled and isolated 34 isolates. Based on polymerase chain reaction analysis using species-specific primers, 23 isolates were identified as Colletotrichum gloeosporioides and the remaining 11 as C. acutatum; both were shown to be pathogenic to mango fruit (cv. Irwin). We generated a nitrate non-utilizing (nit) mutant of anthracnose fungus C. gloeosporioides isolate S754 (nit1) and used it in inoculation tests at various early stages of fruit set in an orchard to determine the time of infection. The nit1 isolate was recovered from lesions on fruit with latent infections that were inoculated at each stage: apical bud (inoculated in January), flower bud (February), inflorescence (April) and fruitlet (May). The isolate was recovered in greatest quantity from fruit inoculated at the fruitlet stage and in lowest quantity from fruit inoculated at the apical bud stage. These results show that these two species of Colletotrichum may both be present in healthy-looking apical buds, flower buds, inflorescences, and fruitlets and that infection during flowering, fruit set or fruit enlargement may remain latent within plant tissues for long periods, only causing lesions in the fruit peel after harvest.
A 10-fold-diluted suspension of a fertilizer paste (product name: TP, Taki Chemical, Hyogo) was tested for suppression of violet root rot of apple caused by Helicobasidium mompa in infested kuroboku soil (soil texture: L), gray lowland soil (SL, LiC) and brown forest soil (HC, SL). In pot experiments with infested soils, disease severity on apple rootstocks (Malus prunifolia var. ringo) in all soils treated with TP was lower than on those treated with tap water. These results suggested that a fertilizer paste applied to the soil surface around the trunk bases of apple trees will suppress disease in most apple orchards.
Incidence or severity of seedling rot was examined for rice seedlings grown from iron-coated seeds under various conditions or stages in pots infested with Pythium arrhenomanes to determine the best management practices. Disease incidence was significantly higher in flooded conditions than in drained. Rice seedlings were susceptible from just after germination, i.e., pigeon-breasted stage to the first-leaf stage, and became resistant to infection after the second-leaf stage. Disease severity was similar at 10-25°C when soils were flooded at different temperatures during the susceptible early stage. These results suggest that keeping the water drained from soils from germination until the first-leaf stage will control the disease on rice germinated from iron-coated seeds directly sown into flooded paddy fields.