Phaeoacremonium inflatipes, P. aleophilum, and Phaeomoniella chlamydospora are three recently described fungi that are involved in the development of symptoms of young vine decline and measles. Up to the present time it is not clear whether the fungi are already present in the propagation material, in mother plants, in scion or rootstock or in rooted cuttings which become infected during preparation, A detection method using nested-PCR is being developed to provide a rapid, sensitive, and specific test to determine the presence of these fungi in grapevine propagation materials.
Field experiments are being conducted to explore the epidemiology and biology of the young vine decline organisms and measles. P. Inflatipes and P. aleophilum are suspected to produce aerial fruiting structures and P. chlamydospora is known to produce pycnidia, microslerotia, and chlamydospora; however, the mode of dissemination of these fruiting structures is unclear. Spore traps were placed in select vineyards in northern and southern California where measles and young vine decline are known to occur. Initial results show that the 3 pathogens could be air borne fungi. This study will elucidate how the fungi spread and under what condition the spores are released to re-infect plants.
Our previous results showed that fresh wounds sustained by the plant at any time during the year, from pruning or other injuries, could provide suitable infection court for the pathogen. Also, that the 3 organisms are capable of infecting old wounds (4 months or older) and invading adjacent green tissues. The experiments were repeated this year to confirm these results.
Cuttings of 20 rootstocks were inoculated with measles and young vine decline organisms and allowed to callus and root following standard nursery procedures. After more than 1 year of growth (in pots inside the lath house), they are currently being evaluated for length of vascular streaking and %recovery of the pathogen. This study was conducted to determine differences in susceptibility of the rootstocks to measles and young vine decline organisms.
Development of a selective medium to facilitate isolation and recovery of the organisms causing measles and young vine decline, in infected tissue, spore traps and soil, is in progress. This will be particularly useful in soil isolation.
Greenhouse and field experiments are being conducted to determine the relation between levels of boron and susceptibility to measles and young vine decline. We are also presently looking at soil, plant, and water analyses from areas that have high incidences of the disease to see any relationship.