Location: Horticultural Crops Research
Project Number: 5358-22000-039-27
Start Date: Oct 01, 2013
End Date: Sep 30, 2018
Objective 1. Inoculum will be introduced into soils as either inoculated rhododendron leaf disks, or ‘naked’ chlamydospores at the start of the experiment. To prevent drying, all inoculum will be covered in 1 cm of soil and will be routinely watered. Periodically over time these sources will be tested for their ability to initiate infection of plant tissues. We will assess infection of both leaves and roots. For each assessment period, uninfected rhododendron leaf disks will be placed atop infested soil for 3 days and watered sufficiently to maintain leaf wetness. The disks will be collected, incubated for 7 days, then surface sterilized and plated in selective media to assess for colonization by P. ramorum. To test the ability of inoculum within soil to infect root balls, during the same 3 day period as the leaf assays we will place potted rhododendron plants on the soil surface. After the exposure period the root balls will be gently removed from the pot and washed. Wounded rhododendron leaves will then be placed at the bottom of the pot, and the plants will be returned and generously watered. After 4 days, the bait leaves will be retrieved and assessed for colonization by P. ramorum as described above. Objective 2. Infected rhododendron leaf disks will be placed in small, nylon mesh bags. These will either be left on the soil surface, or buried in soil columns at depths ranging between 1 cm and 10 cm. At each sampling period, a subsample of leaf disks will be retrieved and assessed for the potential to produce inoculum: disks will be rinsed, then placed in Falcon tubes with deionized water to stimulate the formation of sporangia, which will be filtered and quantified by using microscopy and qPCR. After testing for inoculum-production, all samples will be surface sterilized and plated in selective media to assess survivability of P. ramorum in leaf debris at each depth.