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Cytology and Histology

Stomata as an Infection Court for Phytophthora megasperma f. sp. medicaginis in Chickpea and a Histological Study of Infection. M. L. Dale, Department of Botany, University of Queensland, St. Lucia, Queensland, Australia 4072; J. A. G. Irwin, Department of Botany, University of Queensland, St. Lucia, Queensland, Australia 4072. Phytopathology 81:375-379. Accepted for publication 18 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-375.

Stomata located beneath the cotyledons of 7-day-old chickpea seedlings were the preferential infection court for zoospores of Phytophthora megasperma f. sp. medicaginis. Zoospores also accumulated preferentially in the root-hair zone. Penetration usually was intercellular between anticlinal epidermal cell walls, but intracellular penetration did occur via infection pegs produced from swollen germ-tube tips. Although no differences in prepenetration or penetration events were found between a field resistant (CPI56564) and a susceptible cultivar (ICC6334) of chickpea, hyphal growth rate of the fungus was greater through wounded roots of the susceptible cultivar than in the resistant cultivar. There was no significant difference between hyphal growth rates through wounded epicotyl tissue of the resistant and susceptible cultivars. Stomata located at or below the soil line could act as an infection court for zoospores present in surface water, and cultivars that express resistance in the root tissue would appear susceptible if the resistance was not also expressed in the hypocotyl and the lower epicotyl. A soil-line infection court also could be involved in spreading the disease via zoospores present in surface water in the field.