Dr. Mark Mazzola is a research plant pathologist with the U.S. Department of Agriculture, Agriculture Research Service (USDA-ARS), located at the Washington State University Tree Fruit Research Laboratory in Wenatchee. He was born in Boston, MA, on 25 April 1960. He received a B.S. in forestry from the University of Vermont, Burlington, and an M.S. degree in forest pathology from the same institution under the direction of Dr. Dale R. Bergdahl. For his Ph.D. research, he switched from forest pathology to soilborne pathogens and biological control, studying under the guidance of Dr. R. James Cook at Washington State University, Pullman. After graduating in 1990, he worked for 5 years as a postdoctoral associate, first with Drs. Frank White and Jan Leach at Kansas State University and then as a national research initiative postdoctoral fellow with the USDA-ARS Root Disease and Biological Control Research Unit at Pullman. In 1995, he assumed the present position with the USDA-ARS at Wenatchee, WA, with a research focus on soilborne diseases of deciduous fruit trees.
Dr. Mazzola is recognized for his contributions in resolving the etiology of apple replant disease and for pioneering a potential means of biological control of the disease that reduces dependence on fumigants such as methyl bromide. This work is summarized in a series of papers published in Phytopathology. The apple replant disease is distributed worldwide and is especially an economic constraint to the apple industry of the Pacific Northwest. Historically, the apple replant etiology was attributed to accumulation of arsenic in the orchard soil following years of use as an insecticide. Although methyl bromide was used for control of apple replant disease, changes in soil nutrient status after fumigation were believed to be responsible for disease control, because a biotic causal agent had not been identified.
He used a simple but elegant approach to establish that soilborne microorganisms are involved, and then sought to identify the pathogens responsible for apple replant disease. First, he perfected an apple seedling test for the disease from soil collected within and bordering the apple orchard being studied. Although planted in the same soil types, apple seedlings were stunted when grown in soil from sites where apple trees had been removed; seedlings grew normally in soil collected from sites adjacent to affected orchards. He showed by pasteurization that the stunting effect of the old orchard soil was eliminated by moist-heat treatment at 50°C for 30 min. After ruling out the possibility of bacteria and nematodes as major etiological agents, Dr. Mazzola focused on soilborne fungi. Cylindrocarpon destructans, Phytophthora cactorum, Pythium spp., and Rhizoctonia solani were consistently isolated from the roots of stunted seedlings and, when added to soil, caused stunting similar to that observed for seedlings grown in orchard soil. Orchards were shown to have different mixtures of these four pathogens, with Rhizoctonia and Pythium spp. being the most important in the Pacific Northwest.
He is recognized for discovering the first practical alternative to soil fumigation for control of apple replant disease. Using the apple seedling bioassay system that he developed, disease was controlled by planting the orchard soil with three 28-day cycles of wheat. The cycling of wheat markedly reduced apple root infection by Rhizoctonia and Pythium spp. and disease control was as effective as soil pasteurization. Dr. Mazzola observed that successive cycles of wheat significantly increased Pseudomonas populations in the apple rhizosphere, with P. putida becoming the predominant species associated with disease suppression. More recently, he has shown that the process is limited to specific wheat cultivars that select for specific genotypes of P. putida that effectively colonize the apple rhizosphere. His research demonstrates how an orchard disease complex can be managed by transforming a soil from conducive to suppressive by successive planting of wheat to stimulate a shifting in the microbial composition of the rhizosphere. The apple industry, including organic apple growers, recognizes the advances Dr. Mazzola has made in solving the chronic apple replant disease problem, and is using the control method before reestablishing apple orchards.
Dr. Mazzola has been active in APS by serving as associate and senior editor for Phytopathology and as chair of the Soil Microbiology and Root Disease Committee. For the 1999 joint APS/ CPS meeting held in Montreal, he co-organized a symposium, “Molecular Techniques in Ecological Studies of Soil Microbial Communities.” In addition to APS, he is a member of the American Association for the Advancement of Science, the American Society for Microbiology, and the International Society for Molecular Plant-Microbe Interactions. He has been an invited speaker at national and international meetings organized by various scientific organizations, and served on a USDA competitive grants panel. He is a member of the Xi Sigma Pi and Phi Kappa Phi Honor Societies. He serves as a member of the graduate faculty at Washington State University, and supports the programmatic activities of the Department of Plant Pathology.