VIEW ARTICLE

Resistance

Estimating the Efficiency of Partial-Vacuum Inoculation of Barley with Ustilago hordei. J. V. Groth, Research Associate, Dept. of Botany, University of British Columbia, Vancouver 8, Canada, Present address of senior author: Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108; C. O. Person, Professor, Dept. of Botany, University of British Columbia, Vancouver 8, Canada. Phytopathology 66:65-69. Accepted for publication 7 July 1975. DOI: 10.1094/Phyto-66-65.

Barley seeds (cultivar Hannchen) were inoculated with various ratios of sporidia of the A and a mating-types of Ustilago hordei. Treatment ratios of A:a ranged from 10,000:1 to 1:10,000. With increasing ratios a significant reduction in percentage of diseased plants was seen at 100:1 and at 1:500. A simple method was devised which, based on the relationship between the treatment ratios and percentages of diseased plants, provided an estimate of n, defined as the average number of sporidia available, per seed, for dikaryon formation and infection resulting in smutting. The value of n was calculated as 135, 201, and 195 for the 100:1, 500:1, and 1000:1 ratios, respectively. The conclusion is that n is sufficiently large, so that with a normal 1:1 mating-type ratio in the inoculum, the probability of disease escape is small. Hence, when less than 100% of the inoculated plants are smutted, which is nearly always the case, the nonsmutted plants must be the result of disease resistance.