2011 Annual Report
Juglans microcarpa, J. major, J. cathayensis all crossed with J. regia (Serr) generated > interpsecific hybrids. In addition to the hybrid seeds which went into tissue culture via embryo rescue, a second group of hybrid seeds were stratified, germinated and are now three month old seedlings in the green house. This material will be inoculated with Agrobacterium tumefaciens in the next few weeks and crown gall (CG) incidence rated. The 2010-11 screening data showed open pollinated seedlings from J. microcarpa mother trees exhibited the greatest degree of CG resistance. Twenty five percent of tested seedlings show CG resistance 6 months post inoculation. Clonal material taken from these CG resistant seedlings (dormant cuttings)was rooted and cultivated under greenhouse conditions. Rooting efficiency ranged from 0% to 38%. Eight successfully rooted J. microcarpa accessions (2-18 plantlets/accession), grown under greenhouse conditions, were screened for crown gall resistance. Five J. microcarpa accessions from this group continued to exhibit crown gall resistance. Seven novel Juglans microcarpa × J. regia hybrids were micropropagated for greenhouse evaluations of resistance to P. citricola and P. cinnamomi in late summer 2011. Three trials were established to assess resistance of 22 diverse almond/ peach rootstocks to Phytophthora spp. and replant disease complex. The field trial to evaluate resistance to the replant complex was established at the old orchard site near Parlier (i.e., the site where replant soil was collected for the greenhouse trial). Half of the plots at the old orchard site were strip fumigated in fall 2010 with Telone C35, which is known to prevent replant disease. The other plots remained non-fumigated as a control. In the field trial, resistance to the replant complex will be evaluated according to severity of growth suppression in the non-fumigated soil, relative to plant growth in the fumigated soil. All of the trials use randomized complete block designs with 5 replicate blocks of multiple plants for each combination of rootstock and soil treatment. Complete data from the trials will be available at the end of summer 2011. Several of the rootstocks with plum parentage in their backgrounds are expressing relatively high resistance to P. niederhauseri.