Infection process of Colletotrichum gloeosporioides f. sp. malvae on Malvaceae weeds

Abstract

Colletotrichum gloeosporioides f. sp. malvae is highly pathogenic on Malva pusilla and Malva parviflora but not on Malva neglecta and Abutilon theophrasti . Germination of conidia was higher on agar discs than on leaf surfaces of the Malvaceae hosts and safflower. Germination, however, was considerably reduced on agar discs when the number of conidia applied was increased. Timing of the germination process and morphology of pre-penetration structures were similar on the leaf surface of the five host species examined. Slightly more than 4% of melanized appressoria developed infection structures within epidermal cells of M. pusilla, A. theophrasti and safflower. Levels of penetration were lower ( M. parviflora and M. neglecta. Colletotrichum gloeosporioides f. sp. malvae penetrated plant cuticles directly and produced infection structures within epidermal cells 31–36 h after inoculation. The mode of infection of C. gloeosporioides f. sp. malvae involved intracellular vesicles, large-diameter primary hyphae that constricted at transcellular penetration sites and secondary hyphae. Development of primary hyphae and production of secondary hyphae was extensive on the susceptible hosts M. pusilla and M. parviflora . In the moderately resistant hosts M. neglecta and A. theophrasti colonization was stopped by a hypersensitive reaction of cells adjacent to initial infection sites and no secondary hyphae were produced. Our study strongly suggests that determinants of host-pathogen compatibility or incompatibility do not operate during the pre-penetration phase of C. gloeosporioides f. sp. malvae , but are activated a few days after successful penetration.