VIEW ARTICLE

Effect of Soil Temperature and Host Maturity on Infection of Carrot by Rhizoctonia solani. J. P. Mildenhall, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; P. H. Williams, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 63:276-280. Accepted for publication 30 August 1972. DOI: 10.1094/Phyto-63-276.

Carrots grown in soil at various temperatures developed severe crown rot and cavity spot at 20, 24, and 28 C when inoculated with Rhizoctonia solani, but little infection occurred at 16 C. When greenhouse-grown carrots were inoculated with R. solani at 5- and 7-day intervals 8-45 days after seeding, severe crown rot and cavity spot occurred. Older carrots, both in the field and in the greenhouse, were as susceptible to R. solani as the young seedlings. Anatomical studies on the tap root of carrots inoculated at various ages showed that the fungus rapidly colonized the cortex. On young seedlings, prior to cambial division, the fungus penetrated the endodermis and entered the vascular system. On older seedlings, ingress of the hyphae was limited by the cambium.