Phytophthora cinnamomi as a possible contributor to white oak (Quercus alba) decline in Mid-Atlantic forests
M. E. MCCONNELL (1), Y. Balci (1). (1) University of Maryland, College Park, MD, U.S.A.
To evaluate the association of <i>Phytophthora cinnamomi</i> with white oak (<i>Quercus alba</i>) decline in Mid-Atlantic U.S. forests, 193 healthy white oaks, 247 declining white oaks, and 182 other plants were sampled at 102 sites between 2011 and 2012. At each site, soil and roots from white oaks and soil from other hosts were collected. <i>Phytophthora</i> species were isolated using a baiting method and <i>P. cinnamomi</i> soil inoculum level was quantified using a wet-sieving method. White oak roots were scanned to measure total fine root lengths. <i>Phytophthora</i> was isolated from 42% of the sites. <i>P. cinnamomi</i> was isolated most commonly, from 60% of positive soils. Over five other species were isolated infrequently, from the remaining 40% of positive soils. <i>P. cinnamomi</i>’s range was restricted to the southern part of the study region in USDA hardiness zones 6 and 7, and not found further north in zone 5. Soils from zone 7 (warmer) had twice as much inoculum as zone 6. Soils from white oaks compared to 16 other hosts did not have significantly different inoculum levels. White oak fine root amounts differed significantly between sampling years and hardiness zones. In both years, fine root amounts were significantly lower from <i>P. cinnamomi</i>-infested trees vs. non-infested trees, except in zone 7. Our data suggests that <i>P. cinnamomi</i> influences root health of white oaks mainly in the southern Mid-Atlantic region and may pose a threat to forests further north if warming trends continue.
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