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United States Department of Agriculture

Agricultural Research Service

Title: Susceptibility of Wheat to Tilletia Indica During Stages of Plant Development

Authors
item Goates, Blair
item Jackson, Eric

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2005
Publication Date: January 1, 2006
Citation: Goates, B., Jackson, E.W. Susceptibility of wheat to tilletia indica during stages of plant development. Phytopathology. 96: 962-966

Interpretive Summary: Karnal bunt is a disease of wheat caused by the fungus Tilletia indica, which partially converts wheat kernels into a black mass of fungal spores. The disease was first reported in the US in 1996. Despite minor overall yield and quality losses in the US and elsewhere, the disease has caused considerable international quarantine concern. Quarantine regulations are currently activated with slight trace levels of the disease in grain, or the presence of a single fungal spore in grain used for seed. Plant development stages reported to be susceptible to infection vary considerably. Experiments were designed to better define the susceptibility period and disease potential by inoculating wheat spikes at different growth stages under optimal conditions for disease development. Spikes of a resistant and susceptible cultivar were inoculated at eight growth stages ranging from awns emerging to soft dough. Spikes were susceptible only after they began to emerge from the plant and were vulnerable to infection up to soft dough stage. Both cultivars had similar overall relative trends in the level of infection which peaked when spikes were inoculated after complete emergence from the plant, but before the onset of flowering. Infection tapered off gradually in spikes inoculated after flowering. The results demonstrated for the first time that the disease can develop and produce a fairly high percentage of diseased kernels after initial inoculation of spikes at growth stages as late as milk and soft dough stages under ideal climatic conditions for disease development. The results also demonstrated that infection from air-borne inoculum is not possible at boot or awns emerging stages, which are commonly referred to as the most susceptible stages. This information should allow a more precise assessment of the risk of infection during growth of wheat and enable improved disease management decisions.

Technical Abstract: Karnal bunt of wheat is caused by the fungus Tilletia indica, which partially converts kernels into sori filled with teliospores. Despite minor overall yield and quality losses, the disease has caused considerable international quarantine concern. Plant development stages reported to be susceptible to infection vary considerably. A study was designed to better define the susceptibility period and disease potential by inoculating spikes at different growth stages with naturally liberated secondary sporidia under optimal conditions for disease development. Spikes of a resistant and susceptible cultivar were inoculated at eight growth stages from awns emerging to soft dough. Spikes were susceptible only after emerging from the boot and were susceptible up to soft dough stage where small amounts of disease occurred. Both cultivars had similar overall relative trends in the level of infection which peaked when spikes were inoculated after complete emergence, but before the onset of anthesis. Infection tapered off gradually in spikes inoculated after anthesis. The results broadened the known susceptibility period to include stages long after anthesis, and demonstrated that infection from air-borne inoculum is not possible at boot or awns emerging stages, which are commonly referred to as the most susceptible stages.

Last Modified: 9/10/2014
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