Histopathology of Seed-Borne Infections - Applied Research Center ...

Penetration and Establishment of Fungi in Seed 91gtABCDFIGURE 4.6 SEM photomicrographs of cotton boll surface showing germination and penetrationof Colletotrichum capsici conidia. A, Three-septate conidia and germinating conidia— one of the germ tubes appears to penetrate the cuticle without producing an appressorium.B, Appressoria (arrows) produced on guard cells. C, Appressoria (arrows) on a multicellulartrichome. D, Direct penetration by germ tube and formation of appressorium in the cavity ofthe stomata. (Abbreviation: gt, germ tube.) (From Roberts, R.G. and Snow, J.P. 1984. Phytopathology74: 390–397. With permission.)4.3.2 ROUTES FOR INFECTION FROM OVARY TO OVULE AND SEEDVarious options open to the hyphae to invade the ovule and seed after reaching insidethe ovary are (1) funicular vascular supply for systemic or localized systemic,vascular pathogens; (2) funicular parenchyma for systemic nonvascular pathogensand also for pathogens entering through stigma-style and reaching the placentae inthe ovary; (3) ovule and seed surface consisting of integuments and seed coat,chalaza, and raphe (when present) for pathogens causing localized ovary and fruitwall infection that permeates on to ovules and seeds beneath infection courts, andalso for fungal hyphae that grow out of the placentae, funiculus, and ovary wall inthe locule and reach the ovule and seed surface; and (4) the micropyle for hyphaeof fungal pathogens following strictly the path of the pollen tube and also for freegrowingmycelium in the locule (Figures 4.1A and 4.3A). The ovule and seed surfacemay be invaded directly through the cuticle and epidermal cells, or entry may take