VIEW ARTICLE

Ecology and Epidemiology

Studies on the Use of High- and Low-Nutrient Inoculum for Infection of Wheat by Gaeumannomyces graminis var. tritici. G. C. MacNish, Visiting professor, Department of Botany and Plant Pathology, Oregon State University, Present address of senior author: Department of Agriculture, South Perth, Western Australia 6151; J. M. Liddle(2), and R. L. Powelson(3). (2)Honors student, School of Agriculture, University of Western Australia, Nedlands 6009; (3)Emeritus professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 76:815-819. Accepted for publication 3 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-815.

A series of pot experiments demonstrated that wheat seedlings can be infected by Gaeumannomyces graminis var. tritici using a low-nutrient source of inoculum (i.e., fungal hyphae adhering to sand grains). It is shown that there is a proportional relationship between disease incidence and inoculum density for levels of inoculum ranging from 23 to 225 units per 100 cm³ of soil and seedlings grown for up to 48 days at 10 C, 45 days at 15 C, or 31 days at 20 C. However, in another experiment where wheat was grown for 28 days at 15 C with inoculum densities ranging from 50 to 1,300 units per 100 cm³ of soil, the relationship between disease incidence and inoculum density became nonproportional, and the disease incidence/inoculum density curve became quadratic. The curve reversed direction at about 900 units per 100 cm³ of soil. In other experiments using colonized millet seed inoculum, disease incidence and inoculum density was proportional up to about eight units (seeds) per 100 cm³, but thereafter the relationship was no longer proportional.