Histopathologic study of Colletotrichum spp. in coffee plantlets.
Lins S. R., Abreu M. S., Alves E.
Author Affiliation: Departamento de Fitopatologia, Universidade Federal de Lavras, Cx. Postal 3037, CEP 37.200-000, Lavras, MG, Brazil.
Fitopatologia Brasileira 32 : 488-495
Abstract : The process of infection, coloniation and reproduction of different isolates of Colletotrichum sp. in coffee (cv. Rubi) plantlets obtained by embryo culture was examined by scanning electron microscopy. Plants produced in vitro were inoculated with spore suspension (5µlitre of 106 conidia/ml) on the hypocotyl region and leaves. Isolates of C. gloeosporioides [Glomerella cingulata] were obtained from stem (IS) and leaves (IL) of plants with symptoms of greasy leaf spot and from mango plants with symptoms of anthracnose (IM). Isolates of Colletotrichum dematium were obtained from healthy coffee plants. At 3 h after inoculation (HAI), leaves and hypocotyl fragments were transferred to 1.5-ml microtubes containing modified Karnovsky's fixative solution. Samples were collected at 3, 5, 12, 16, 24, 48, 72, 96, 114 and 144 HAI. The conidia of all isolates adhered more frequently to the depressions in hypocotyls and guard cells, forming a septum at 5 HAI. Germ tubes were observed at 12 HAI starting from the extremities, and laterally in the conidia. Appressoria were produced by C. dematium (globoses, trilobullated, and foot and comma-shaped) and C. gloeosporioides (globoses) at 12 HAI. C. gloeosporioides (IH and IF) produced conidiogenic cells at 48 HAI. Acervuli were produced by C. gloeosporioides at 72 HAI and by C. dematium at 96 HAI. C. gloeosporioides isolated form mango colonized coffee plant tissues, producing canidiogenic cells without the production of acervuli. The most virulent isolates were IS and IL.