VIEW ARTICLE

Ecology and Epidemiology

Vertical Distribution in Soil of and Induction of Disease by Strands of Phymatotrichum omnivorum. S. C. Alderman, Research assistant, Department of Plant Pathology, University of Arizona, Tuscon 85721, Present address of senior author: Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; R. B. Hine, professor, Department of Plant Pathology, University of Arizona, Tuscon 85721. Phytopathology 72:409-412. Accepted for publication 28 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-409.

Soil cores to a depth of 90 cm were taken in cotton fields infested with Phymatotrichum omnivorum near Marana, AZ, from June 1979 through April 1980. Total viable strand lengths (VSL) of P. omnivorum of 0.1 and 0.2 cm (per 50 g soil) were recovered at depths of 15–30 and 30–60 cm, respectively, in June 1979, whereas no viable strands were recovered at 0–15 or 60–90-cm depths. VSL increased during July and peaked during August and September, when maximum VSL of 0.1, 0.4, 1.0, and 0.6 cm (per 50 g soil) were recorded for depths of 0–15, 15–30, 30–60, and 60–90 cm, respectively. VSL declined after November. In April 1980, VSL at depths of 0–15, 15–30, 30–60, and 60–90 cm were 0.0, 0.2, 0.3, and 0.05 cm, respectively. All infected taproots contained viable strands at depths of 0–15, 15–30, and 30–45 cm during field collections made in July and August 1978 and 1979. Percentages of roots from which viable strands were recovered fell to 35–50% (0–15-cm root depth), 53–77% (15–30-cm root depth) and 76–96% (30–45-cm root depth) in later collections made from November to February (before plow down). P. omnivorum was isolated from internal noncortical tissue of all infected cotton roots collected from the field in August. Isolations fell to 40–80% in September and no positive recoveries were made after October. Inoculation of cotton plants with strands in field, laboratory, and greenhouse studies did not result in disease. Further studies indicated that sclerotia germinated only from broken strand fragments attached to the sclerotia.