2007 Annual Report 1a.Objectives (from AD-416) The purpose of this agreement is to build a science based relationship, whereby OBI and AFRS pursue advancements in peach transformation and the introduction of novel traits into peach that will add value to the cultivars and address grower and consumer concerns. The first trait to be introduced into peach will be resistance to Plum pox virus (PPV). 1b.Approach (from AD-416) AFRS and OBI will seek to improve peach transformation systems that are currently inefficient. Modification of regeneration and transformation protocols will be combined with the testing of a wide range of peach germplasm. Hairpin constructs for the development of plum pox virus resistance through gene silencing will be constructed and tested. These will be combined with gene promoters that are highly expressed or expressed only in target tissues. The chlorophyll ab binding promoter, preferentially expressed in green tissues, will be one such promoter tested. Transgenic peach plants will be evaluated for gene silencing, and silenced lines will be evaluated for plum pox virus resistance. 3.Progress Report This report serves to document research conducted under a non-funded cooperative agreement with Okanagan Specialty Fruits. Additional details of research can be found in the report for the parent project 1931-21000-001-00D, Genetic Improvement of Fruit Crops and in the publication included in the parent project report (Srinivasan, C. and Scorza, R. 2007. The influence of genotype on the induction of Somatic embryos from in vitro cultured zygotic embryos and adventitious shoot regeneration from cotyledons of peach and nectarine. Acta Hort. 738:691-696). Over 10,000 peach explants were isolated and exposed to regeneration and gene transfer (transformation) treatments during the report period. These studies demonstrated that in the absence of gene transfer treatments, immature peach embryos can produce high rates of regeneration – up to 80%. Gene transfer did not occur in any tissues evaluated to date suggesting that even in a system where regeneration of peach is optimized, gene transfer remains a significant limiting factor for genetic engineering of peach. Progress on the project was monitored by an onsite visit and through phone and e-mail communication.