Association of Phytophthora cinnamomi with White Oak Decline in Southern Ohio

Abstract

A decline syndrome and widespread mortality of mature white oak tree (Quercus alba) associated with wet and low-lying areas has been recently observed in southern Ohio forests. Previous studies have isolated Phytophthora cinnamomi from white oak rhizospheres. In 2008 and 2009, P. cinnamomi population densities in two healthy and two declining white oak stands at Scioto Trail State Forest were quantified and potential roles of three environmental drivers of Phytophthora spp.–induced decline were assessed: soil texture, soil moisture, and topography. Significantly higher P. cinnamomi propagule densities were found in declining stands in both years but propagule densities were not associated with soil moisture content. Trends in population densities were not correlated with soil moisture or topographic position within field sites. There was a positive, exponential relationship between overall P. cinnamomi population levels and soil moisture on a seasonal scale in 2008 but not 2009. Sites with greater soil clay content were associated with greater decline. Effects of P. cinnamomi inoculum and periodic flooding on root health of 1-year-old potted white oak trees grown in native soil mixes in the greenhouse were examined. Root systems of potted oak were significantly damaged by soil inoculation with P. cinnamomi, especially under flooding conditions. Results of these studies support the hypothesis that P. cinnamomi is a contributing agent to white oak decline in southern Ohio.

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

“…Furthermore, the isolates were nearly equally aggressive, a testament to the virulence of the P. cinnamomi population in eastern U.S. forests. Other studies have also shown the pathogenicity of P. cinnamomi isolates from the eastern United States on various oak trees (6, 30,46) and, similar to our findings, little variation existed in aggressiveness of P. cinnamomi (18,61). Although little difference in pathogenicity was detected among the isolates, variation was found when seedling mortality rates were compared.…”

“…In another study, when a white oak forest stand was sampled intensively, CFU levels were seven dmes greater on declining white oak trees than on oak trees without any crown dieback (10). The same conclusion was reached when CFU of declining white oak stands of the same forest site were quantified for 2 years and found to be significantly greater at declining trees than at healthy ones both years (46). The latter study also confinned the field finding in an inoculum doseresponse study using white oak seedlings and showed that greater inoculum levels resulted in significant root damage.…”

“…were isolated from all textures but sandy (29). In southern Ohio, soils free of P cinnamomi also had a much higher percentage of sand than infested, clayey soils collected from a white oak stand (46). The more frequent isolation of P. cinnamomi from fine-textured soils may be due to a higher amount of calcium present in non-sandy soils, which have a higher cation exchange o .aj.,u Fig.…”

“…Similarly, in P. cinnamomiinfected Q. saber and Q. ilex forests in Europe, site conditions and unusual climatic events were thought to have contributed to & P. cinnamomi-inducsd oak decline (14,16,24,45,53). Such conclusions were also reached with pot experiments; damage to oak seedlings was shown to increase when they were subjected to drought or saturated condidons (33,40,42,46,53). Changing climate conditions in Europe that have resulted in warmer, wetter winters and droughty summers with periods of heavy rainfall are suspected to have changed the delicate balance between oak species and P. cinnamomi and may have led to current oak decline problems in certain locadons (13,24).…”

Emergent insects, pathogens and drought shape changing patterns in oak decline in North America and Europe

“…Phytophthora cinnamomi, P. quercina (an oak-specific species), and several other Phytophthora spp. have been detected in recent decades in Europe (Jung et al, 1999(Jung et al, , 2002Gallego et al, 1999;Vettraino et al, 2002;Balci and Halmschlager, 2003) and in North America (Table 1; Balci et al, 2007Balci et al, , 2010Nagle et al, 2010). Although their role is not yet completely understood, it may be exacerbated by changing climate conditions (reviewed by Brasier, 1996;Jönsson, 2006).…”