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

Location of Fungal Hyphae in Seeds 117colonization ofstigmatic tissue bythe pathogeninfected panicle showinghoney dew stageinflorescence atprotogyny stagemicro- andmacroconidiapseudomorph(sclerotial formation)ascosporesconidiacollateralhostssclerotia in placesof seedasci containingascosporessclerotiainfestedseedperithecium showingasci and paraphysesL.s.stromagerminatingsclerotiaFIGURE 5.8 Disease cycle of ergot of pearl millet caused by Claviceps fusiformis. (Reproducedwith permission from Chahal, S.S., Thakur, R.P. and Mathur, S.B. 1994. Seed-BorneDiseases and Seed Health Testing of Pearl Millet. Danish Government Institute of SeedPathology for Developing Countries, Copenhagen, Denmark.)uninfected part of the floret. The development of this cell plate is completed within8 days of infection in pearl millet (Roy, 1984).The ovary wall is also infected, and intercellular hyphae emerge in between theepidermal cells to form the extramatrical sphacelial stage (Campbell, 1958; Roy,1984). The development of ergot sclerotium begins with the development of pseudoparenchymatousor plectenchymatous sclerotic tissue in the lower half of the ovary(Roy, 1984; Bandyopadhyay et al., 1990). This tissue gradually increases, carryingthe conidial pouches at the top. Finally the sclerotium formation is completed andthe entire ovary is filled with pseudoparenchymatous hyphal mass.After invading stigma and style, C. paspali permeates the ovary wall inP. dilatatum and spreads outward, emerging between the cells of the outer epidermisand forming a plectenchymatous extrametrical stroma around the ovary(Figure 5.9D). The fungus grows to a lesser extent toward the inside. The hyphaeon the surface transform into conidiophores forming conidia (Figure 5.9D) and the