Comparison of the Virulence of Isolates of Tilletia indica.Causal Agent of Karnal Bunt of Wheat, from India, Pakistan, and Mexico. M. R. Bonde, Research Plant Pathologist, Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Frederick, MD 21702. G. L. Peterson, Biologist, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Frederick, MD 21702; G. Fuentes-Davila, Research Plant Pathologist, Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT), Mexico; S. S. Aujla, Associate Director of Research, and G. S. Nanda, Professor of Plant Breeding, Department of Plant Breeding, Punjab Agricultural University, Ludhiana, India 141 004; and J. G. Phillips, Consulting Statistician, USDA, ERRC, Philadelphia, PA 19118. Plant Dis. 80:1071-1074. Accepted for publication 9 June 1996. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/PD-80-1071.

Four Tilletia indica teliospore field populations, two from Mexico and one each from India and Pakistan, were tested for virulence on five Karnal bunt-resistant cultivars, one moderately susceptible, and two Karnal bunt highly susceptible wheat cultivars. The five resistant cultivars represented the most Karnal bunt-resistant germ plasm in the breeding programs at the International Maize and Wheat Improvement Center (Centro Internacional de Mejoramiento de Maiz y Trigo [CIMMYT]), Mexico, and the Department of Plant Breeding, Punjab Agricultural University, Ludhiana, India. Plants at the boot stage were inoculated by injecting into the boot 1 ml of a water suspension containing 10,000 allantoid sporidia per ml, incubated in a mist chamber for 3 days, then maintained until maturity in a greenhouse. All inoculated and control wheat spikes were harvested individually, and percentages of T. indica-infected seeds were determined. In addition, infected seeds from 10 randomly selected infected spikes per treatment were examined to estimate the proportion of each infected seed converted to a sorus. On the most resistant wheat cultivar (HD-29), percentage of seeds infected varied from 10 to 30%, depending on pathogen aggressiveness. On the most susceptible cultivar (Bacanora), infection varied from 55 to 84%. Although there were differences in pathogen aggressiveness, there was no evidence of the existence of races among the field populations. Wheat cultivars resistant to the Mexican fungal populations also were resistant to those from Asia, and vice versa; there was a significant correlation (P ≤ 0.05) between percentage of seeds infected and extent of fungal colonization of infected seeds with all but one pathogen population when comparing resistant versus other wheat cultivars.

Keyword(s): disease resistance, partial bunt, smut