Pyrenophora tritici-repentis is a common component of the internal flora of wheat seed. A model of seed infection and transmission of P. tritici- repentis was developed based primarily on research with soft white winter wheat. Spores of the pathogen germinate on the wheat floret. The fungus initially colonizes the surfaces of the lemma, palea, or glume, and reaches the seed via mycelial proliferation. Penetration of the kernel pericarp is direct via appressoria. The pathogen ramifies throughout the pericarp, where it remains viable for at least three years. Maximal seed infection results from spike inoculation at kernel milk stage. In naturally infected wheat seeds, P. tritici-repentis is found throughout the pericarp but seldom in the seed coat or embryo. Seed transmission occurs in a non-systemic manner. The emerging coleoptile is externally infected by hyphal growth from the infected pericarp, and the first and second seedling leaves may be infected by external hyphal growth from the coleoptile. Transmission efficiency varies with seed lot and ranges from 0 to 92%. Factors affecting seed transmission are not well understood; they include soil temperature and may also include age of seed, wheat cultivar, developmental stage when seed infection occurred, and soil moisture during emergence. Infected seed may provide inoculum for tan spot epidemics and for dispersal of fungal strains to new geographic locations.

English

9806|AGRIS 9802

Jose Juan Caballero

CIMMYT Publications Collection