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

Penetration and Establishment of Fungi in Seed 87fsstistyfsoovhstmngfshychaApdBFIGURE 4.3 (Color figure follows p. 146.) Indirect infection via stigma, style, and ovarywall. A, Diagram to show infection movement from stigma, style, and ovary wall (arrows)to the ovule. Hyphae may enter ovule via funiculus, micropyle, or ovule surface. B, Diagramof part of ovary wall showing various avenues (cuticle, epidermal cells, stomata, cracks orwounds, nectary, and hairs) for hyphae to penetrate the ovary wall. (Abbreviations: c, crackor wound; fu, funiculus; fs, fungal spore; h, hair; ha, haustorium; hy, hypha; m, micropyle;ng, nectary gland; o, ovary; ov, ovule; pd, pedicel; st, stomata; sti, stigma; sty, style; vs,vascular supply.)first few days after fertilization. On reaching the stigma, ascospores germinate, andthe germ tubes penetrate the stigma-style and grow down to the ovary (Agrios, 1988;Shaw and Mantle, 1980). Campbell (1958) and Webster (1986) have doubted thisinfection route. However, Luttrell (1977) has clearly shown that the primary infectionby ascospores and secondary infection by conidia of Claviceps paspali on Paspalumdilatatum occur through the stigma and the style (Figure 4.4A to C). The hyphaegrow downward inside the style to the ovary and permeate in its inner layers. Asimilar path of ovary infection is observed in sorghum for C. sorghi (Bandyopadhyayet al., 1990) and for pearl millet by C. fusiformis (Thakur, Rao, and Williams, 1984;Willingale and Mantle, 1987). The infection in pearl millet by C. fusiformis occurson fresh receptive stigmas, and hyphae follow the path normally taken by pollentubes. Colonization of the ovary by the fungus predominantly takes place along theabaxial wall toward the vascular trace supplying the ovary (Willingale and Mantle,1987). Prakash, Shetty, and Safeeulla (1980), using artificially inoculated pistils of