2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to identify late-blooming tart cherry selections which will have an increased probability of avoiding spring freeze injury to the pistils. These late-blooming selections will be added as new accessions in the USDA-ARS tart cherry collection at the PGRU in Geneva and will serve as parental material in the MSU tart cherry breeding program. 1b.Approach (from AD-416) Tart cherry germplasm selections that bloom significantly later than ‘Montmorency’ will be identified. That identification of the late-blooming germplasm is critical to our achieving our goal of developing tart cherry cultivars that are less susceptible to spring freeze damage than ‘Montmorency’. We will evaluate Russian plant material collected in a 1998 exploration trip to Russia. We presume that the original P. fruticosa evolved extremely late bloom time to avoid spring freeze damage in its native habitat in central Russia. We have previously reported that hybrids of P. cerasus x P. fruticosa bloomed significantly later than ‘Montmorency’. We will also be analyzing a newly available seed collection of P. fruticosa and P. fruticosa species hybrids collected from the mountains south of Budapest, Hungary, and seedlings with the winter hardy German landrace cultivar ‘Schattenmorelle’ in their pedigree. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Michigan State University. Additional details of the research can be found in the report for the parent project 1910-21000-015-00D "Conservation and Utilization of the Genetic Resources of Apples, Grapes, and Tart Cherries." Spring freeze damage to tart cherry (Prunus cerasus) flower buds is the major limiting factor to tart cherry production in the U.S. Significant crop reductions from spring freeze events occur about every three years. In 2002, spring freeze damage was particularly severe as ~98% of the tart cherry crop in Michigan was destroyed resulting in a devastating effect on the industry and economy of the fruit-growing regions. One breeding approach to minimize the potential for freeze injury to tart cherry flowers is to develop late-blooming cultivars with increased pistil hardiness. The goal of this project was to identify late-blooming tart cherry selections with increased pistil freeze tolerance among the germplasm in the MSU collection and add any new superior accessions to the USDA-ARS tart cherry collection at the PGRU. Approximately two weeks before the start of cherry bloom there was a devastating period of extremely low temperatures reaching below 0C for seven consecutive nights. Between this early freeze and cherry bloom, MSU Clarksville Horticultural Experiment Station (CHES) did not experience any additional freezing temperatures. Therefore the pistil death that was apparent at cherry bloom was caused by the sustained freeze from April 4 to 10 when the flowers were swollen and in some cases at side green. Montmorency bloomed on April 27 and the identification of the late-blooming seedlings began on April 30, 23 heat units later (base 4.4C). A total of 143 late-blooming selections were identified, with the latest seedling blooming on May 11, 129 heat units later than Montmorency. The average percent pistil death was 26%; however, bloom date and pistil death did not correlate. This lack of a correlation could be due to the fact that the freeze was during bud swell and not during a stage when some of the flowers were more open than others. 31 of the late-blooming selections exhibited 5% or less pistil death. This is compared to the 44% pistil death exhibited by ‘Montmorency’. Only 2 of these 31 selections exhibited acceptable fertility levels, 27e 11 (35) and ‘Tamaris’, respectively. Therefore, only these two selections will be included in the PGRU tetraploid cherry collection as they meet the criteria of late-bloom, freeze tolerant and possessing sufficient fertility for use as parental material in a breeding program. Use of this germplasm has the potential to increase pistil hardiness of bred varieties for the U.S. The potential impacts of these future varieties would include: (1) increased grower and community profits due to the reduced likelihood of a complete crop loss, and (2) enhanced ability to maintain markets that require a stable cherry supply due to reduced yield fluctuations. Monitoring activities for this project include communications by email, phone, and annual reports.