Phytophthora cinnamomi as a Contributor to White Oak Decline in Mid-Atlantic United States Forests

Abstract

McConnell, M. E., and Balci, Y. 2014. Phytophthora cinnamomi as a contributor to white oak decline in mid-Atlantic United States forests. Plant Dis. 98:319-327.To evaluate Phytophthora cinnamomi as a cause of white oak (Quercus alba) decline in mid-Adantic forests, sampling was conducted at 102 sites from 2011 to 2012. Soil and roots from healthy and declining white oak trees were collected. Phytophthora spp. were isolated using baiting and CFU of P. cinnamomi quantified using wet-sieving. Fine roots were scanned and measured. Phytophthora spp. were isolated from 43% of the sites. P. cinnamomi was common; six other species were isolated infrequently. Little difference in lesion size existed on white oak seedlings inoculated with 32 isolates of P. cinnamomi; only 13 isolates caused significant mortality. Soils from white oak versus nine other hosts did not have significantly different CFU. P. cinnamomi was restricted to United States Department of Agriculture hardiness zones six and seven and never found in zone five. The presence of Phytophthora spp. in soil can be associated with white oak fine root health. When Phytophthora spp. were present, white oak trees in zones five and six had less fine roots. In mid-Atlantic oak forests, however, environmental conditions appear to play a key role in determining the impact of P. cinnamomi on the root system. P. cinnamomi alone does not appear to be a causal factor of white oak decline.

Genotypic Diversity of Phytophthora cinnamomi and P. plurivora in Maryland’s Nurseries and Mid-Atlantic Forests

“…(Lamour and Kamoun 2009). Although less common, the A1 mating type of P. cambivora occurs in both mid-Atlantic forests and Maryland nurseries (Bienapfl and Balci 2014;McConnell and Balci 2014), which potentially could stimulate selfing and be responsible for population variations that we have observed in this study.…”

“…These included 80 isolates from forests (76 P. cinnamomi and 4 P. plurivora) and 208 isolates from nurseries (26 P. cinnamomi and 182 P. plurivora). The forest isolates were collected over a decade (from 2002 and 2012) from rhizosphere soil associated with various mature oak trees with and without decline symptoms in mid-Atlantic oak forest ecosystems (Balci et al 2007;McConnell and Balci 2014). Because these forests are not the subject of any sort of management (namely, fungicide applications, watering regimes, plant trade, and so on), isolates recovered from this system served as a baseline for comparison with isolates recovered from the intensively managed nurseries.…”

“…Baits were then placed on the surface of the water and incubated for 3 to 5 days at 18°C. Leaves with discoloration or lesions were rinsed with tap water, followed by distilled water, then blotted dry and plated on clarified V8 (cV8) (10 g of CaCO 3 per 1 liter of V8 juice spun down at 4,000 rpm for 10 min) PARPNH (pimaricin at 10 µg/liter, ampicillin at 200 µg/liter, rifampicin at 10 µg/ml, pentachloronitrobenzene at 25 µg/liter, nystatin at 50 µg/liter, and hymexazol at 50 µg/liter) (Erwin and Ribeiro 1996;Jung et al 1996;McConnell and Balci 2014). Emerging putative Phytophthora colonies were transferred to cornmeal agar slants and maintained at 8 or 15°C.…”

“…found in the United States, P. cinnamomi and P. plurivora are the most widespread (Bienapfl and Balci 2014;McConnell and Balci 2014). P. plurivora is one of eight species once considered part of the P. citricola complex (now delineated into P. capensis, P. caryae, P. citricola, P. pachypleura, P. pini, P. plurivora, P. multivora, and P. acerina) (Bezuidenhout et al 2010, Brazee et al in press, Ginetti et al 2014Henricot et al 2014;Hong et al 2011;Jung and Burgess 2009;Scott et al 2009).…”

“…Unlike P. cinnamomi, P. plurivora is adapted to aquatic environments (e.g., fresh stream water or irrigation water), and can spread to aboveground plant parts through rain splash or overhead irrigation (Brazee et al 2016;Huai et al 2013;Jung et al 2016Jung et al , 2017Nechwatal et al 2011). Ecologically, P. plurivora appears to be not restricted by cold winter temperatures whereas P. cinnamomi is limited in its pathology and spread (Bergot et al 2004;McConnell and Balci 2014). P. cinnamomi is heterothallic and, interestingly, only its A2 mating type has successfully established itself globally (Arentz and Simpson 1986;Cahill et al 2008;Zentmyer 1980).…”