02656nas a2200289 4500008004100000022001400041245008900055210006900144260002900213300001400242490000700256520181900263653002002082653001302102653001502115653002702130653001402157653001602171100002102187700001902208700001802227700001602245700002202261700001202283700001602295856005502311 2010 eng d a1365-305900aEffect of host factors on the susceptibility of Rhododendron to Phytophthora ramorum0 aEffect of host factors on the susceptibility of Rhododendron to  bBlackwell Publishing Ltd a301–3120 v593 a

Phytophthora ramorum causes sudden oak death (SOD) in western coastal forests of the USA. In Europe, the pathogen is mainly present in the nursery industry, particularly on Rhododendron. Because of the primary role of Rhododendron as a host and potentially as a vector, the effect of Rhododendron host factors on P. ramorum susceptibility and sporulation was investigated. Inoculation methods using either wounded or non-wounded detached leaves were applied to 59 Rhododendron cultivars and 22 botanical species, replicated in three separate years. All Rhododendron species and cultivars were susceptible when using wounded leaves, but not when using non-wounded leaves, suggesting a resistance mechanism operating at the level of leaf penetration. Using a regression tree analysis, the cultivars and species were split into four susceptibility classes. Young leaves were more susceptible than mature leaves when wounded, but less susceptible when non-wounded. This effect was not correlated with leaf hydrophobicity or the number of leaf hairs. The presence or the type of rootstock did not affect the cultivar susceptibility level. Sporangia and chlamydospore production in the leaf lesions varied widely among Rhododendron cultivars and was not correlated with the susceptibility level. The susceptibility to P. ramorum correlated well with the susceptibility to P. citricola and P. hedraiandra × cactorum, suggesting that the resistance mechanisms against these species are non-specific. Susceptibility to P. kernoviae was low for most cultivars. These findings have implications for detection, spread and disease control, and are therefore important in pest risk assessment.

10ahost resistance10aleaf age10aleaf hairs10aPhytophthora kernoviae10arootstock10asporulation1 aDe Dobbelaere, I1 aVercauteren, A1 aSpeybroeck, N1 aBerkvens, D1 aVan Bockstaele, E1 aMaes, M1 aHeungens, K uhttp://dx.doi.org/10.1111/j.1365-3059.2009.02212.x