A homeobox encodes a transcription factor containing a DNA-binding motif consisting of 180 bp termed the homeodomain and it is known to play an important role in regulating morphogenesis in fungi and other eukaryotes. The 10 genes encoding homeobox transcription factors were identified from the Colletotrichum orbiculare genome. In this study, we functionally analyzed CoHox4, one of the 10 homeobox genes conserved in C. orbiculare. CoHox4-knockout mutants exhibited a marked decrease in vegetative hyphal growth compared with the wild type. Observation of hyphal growth in the early stage of culture revealed increased hyphal branching of CoHox4 knockout mutants compared with the wild type. Conidia formed by CoHox4 knockout mutants were 1.35-times longer than those formed by the wild-type. The elongated conidia formed abnormal appressoria on glass and host leaves. Furthermore, virulence of the CoHox4-knockout mutants was markedly reduced on intact and injured cucumber cotyledons. In addition, they had low sensitivity to calcofluor white. These results suggest that CoHox4 regulates morphological differentiation such as vegetative hyphal growth, conidial morphology and appressorial formation and is required for full virulence of this fungus.

In June 2015, a postharvest fruit rot of passion fruit (Passiflora edulis × P. edulis f. flavicarpa) was found in Hahajima, Bonin islands, Tokyo, Japan. A fungus with black pycnidia was often isolated from the rotted fruits. The fungus described recently as Diaporthe fructicola was demonstrated to reproduce natural symptoms. This fungus has pathogenicity to leaves and stems of passion fruit. It was also pathogenic to the fruits of lemon. We propose to call the new disease as Fruit Rot (migusare-byo in Japanese).

A severe postharvest rot of acerola (Barbados cherry) fruits (cv. Kanmikei) was found in Okinawa Prefecture, Japan in 2017. A fungus frequently isolated from the diseased fruits was identified as Gilbertella persicaria based on morphological, cultural characteristics and sequence similarity of rDNA-ITS regions. Symptoms were reproduced on acerola fruits after inoculation with the isolates, which were then reisolated. This is the first report of fruit rot of acerola caused by G. persicaria in Japan, and we propose the name “migusare-byo” in Japanese.