Nitrogen Fertility Influences Growth and Susceptibility of Rhododendrons to Phytophthora ramorum

Abstract

<jats:p>Growth and susceptibility of evergreen <jats:italic>Rhododendron</jats:italic> ‘English Roseum’, ‘Cunningham’s White’, and ‘Compact P.J.M.’ to <jats:italic>Phytophthora ramorum</jats:italic> in response to biweekly nitrogen (N) fertilizer application at rates of 25, 75, and 150 mg N per 11.4-L container was evaluated during two growing seasons. At the end of both growing seasons, horticultural evaluation of the different plants showed that 150 mg N-fertilized cultivars had superior shoot growth, visual quality, leaf color, and the highest leaf N concentration, whereas the 25-mg N cultivars were inferior for these characteristics. Plants fertilized with the 75-mg N rate were typically intermediate to the 150- and 25-mg N plants for the measured characteristics. During the first growing season, the number of flower buds on ‘Cunningham’s White’ and ‘English Roseum’ was not influenced by N rate but the second season bud numbers increased with increasing N fertilizer. Foliar susceptibility to <jats:italic>P. ramorum</jats:italic> was influenced by N fertilizer application rates in the most susceptible cultivars, ‘English Roseum’ and ‘Cunningham’s White’, in which lesion size and infection frequency both increased at higher N rates. The results were variable in ‘Compact P.J.M.’, the most resistant cultivar.</jats:p>

Phenotypic interactions between tree hosts and invasive forest pathogens in the light of globalization and climate change

“…Gremmeniella abietina kills the 1 and 2 year old shoots and needles, thus, when growing under fertile conditions, pines develop a phenotype that makes them more susceptible, leaving fewer cohorts of surviving needles than when growing under normal conditions. The link between fertility and susceptibility has been seen in other invasive pathogens such as Diplodia, Dothistroma or Phytophthora [68][69][70], although little is known about the phenotypic mechanism mediating these effects.…”

Fire severity and the post‐fire soil environment affect seedling regeneration success of the threatened Persoonia hirsuta (Proteaceae)

“…However, increased soil water retention may prove detrimental to plant health if pathogenic oomycetes (such as Phytophthora cinnamomi) are present in the soil. High soil nitrogen has also been identified as a factor accelerating the onset of dieback where P. cinnamomi is present (Marks et al 1973;Hummel et al 2013;Scarlett et al 2013). However, we cannot confirm the mechanisms that could be driving these observations of dieback as these were not tested in this study and some factors were cross-correlated (Appendix S5).…”

Greater rate of nitrogen fertilizer application increases root rot caused by Phytophthora cinnamomi and P. plurivora in container‐grown rhododendron

“…Increasing N fertilizer application rate has also been shown to increase foliar disease in rhododendron inoculated with P . cactorum and Phytophthora ramorum (Hoitink et al, 1986; Hummel et al, 2013) and to increase root rot in other woody plant species inoculated with P . cinnamomi or P .…”