Abstract:

The infection structures of Colletotrichum gloeosporioides on rubber trees would be clarified through microscopic observation to provide scientific basis for the anthracnose prediction in rubber trees. After rubber trees leaves treated with decolorizing agent (0.15% trichloroacetic acid-ethanol solution∶chloroform, 5∶1) for 12 h and 1% Congo red staining agent for 3 h, the developmental process and infection structure of C. gloeosporioides infection were clearly observed. Under the inoculation condition of 28 ℃ and 100% humidity, the crest-time of conidial germination was within 2-6 h after inoculated in rubber tree leaves at the light green phase. More than 85% of conidia were germinated after 12 h inoculation. The crest-time of appressorium formation was within 8-12 h after inoculation. About 75% germ tubes generated appressoria and appressoria began forming infection pegs after 12 h inoculation. The crest-time of infection pegs formation was at 24 h inoculation, while several germ tubes formed at the other top of the germinal conidium. The appressorium germinated to produce secondary appressorium, which further infected surrounding cells and caused leaves sporadic lesions at 36 h inoculation. After 48 h inoculation, Germ tubes of abundant branched differentiated into hyphae, some of which produced secondary conidia on the top. A large number of typical anthracnose spots formed. The hyphae spread vertically and horizontally on the leaf surface and gradually formed a net-like distribution after 72 h inoculation. As the hyphae expanded, a series of pathological changes occurred in the leaf tissue. In this study, a method for staining C. gloeosporioides in rubber tree leaves with good staining effects, simplicity, and efficiency was established, which further clarified the infection structures of C. gloeosporioides.

Key words: rubber tree, anthracnose, Colletotrichum gloeosporioides, staining method, infection structure