1a. Objectives (from AD-416)
Develop improved cultivars and enhanced germplasm of strawberry, blueberry, and black raspberry that possess desirable horticultural traits, including broad environmental adaptation, disease resistance, longer fruiting season, high yield, and excellent fruit and plant quality characteristics. Develop methodologies to more effectively and precisely identify and select disease-resistant small-fruit genotypes.
1b. Approach (from AD-416)
Small fruit germplasm from established cultivar materials to wild types will be evaluated using both classical and molecular techniques. Scientists will develop improved disease screening methods, identify and evaluate disease resistant germplasm, and develop improved methods of incorporating the resistance into superior germplasm. Genetic aspects of both pathogen and host variation will be studied. Concurrent with selection for disease resistance, breeding will emphasize selection for other factors necessary to the development of successful cultivars, with particular emphasis on fruit quality and phytonutrients, environmental adaptation, and adaptation to mechanization. Vaccinium (blueberry and cranberry) breeding and disease work will be carried out at Chatsworth, New Jersey, and Fragaria (strawberry) and Rubus (blackberry and raspberry equals brambles) work will be carried out at Beltsville, Maryland.
3. Progress Report
Summer-fruiting production system for strawberry. ARS scientists at Beltsville, Maryland, conducted the first replicated yield evaluations of multiple-fruiting cultivars and breeding selections in a novel summer-fruiting production system developed on site. Evaluations of fall-fruiting strawberry selections. ARS scientists at Beltsville, Maryland, and Kearneysville, West Virginia, together with University of Maryland scientists at Queenstown, Maryland, conducted evaluations of the first fall-fruiting breeding selections developed for a novel fall-fruiting production system developed by ARS. Blueberry fruit quality evaluations. The results from fruit harvested in 2008 showed that 43 rabbiteye blueberry cultivars had widely varying fruit qualities. ‘Clara’ had the highest percentage of soluble solids content (18.9%) and ‘Ethel’ had the highest percentage of titratable acidity at 1.14%. Northern Highbush, such as ‘Bluecrop’, ‘Duke’, and ‘Elliott’, included for comparison purposes, had higher percentages of citric acid as compared to rabbiteye cultivars which had high percentages of malic acid. The highest anthocyanin and total phenolic contents were found in ‘Early May’ with 476mg and 660mg per100g of fresh weight, respectively. Genetic control of parthenocarpy in highbush blueberry. Crosses have been completed to further evaluate the previously developed genetic model. Seedlings will be germinated in Fall 2009, and planted to field in 2010. Crosses for more vigorous plant types within this germplasm have been made. This research may allow the development of highbush blueberry cultivars that will be better able to set and develop fruit with lesser levels of pollination. Enhancement of parthenocarpic fruit development in rabbiteye blueberry. For the second year, rabbiteye blueberry cultivars were brought into the greenhouse in early spring and allowed to flower. Flowering interval, fruit set, fruit size, and ripening dates are being tabulated. Variability between 2008 and 2009 suggest that a third year of evaluation may be needed. Field produced fruit is also being collected to evaluate correlations between greenhouse and field fruit development. This research should allow a better understanding of the cross-pollination needs among rabbiteye blueberry cultivars, and may lead to the development of more self-fruitful cultivars. Fungal and viral disease studies in blueberry and cranberry. dsRNA fungal viruses were discovered that may contribute to biocontrol of the fairy ring disease of cranberry. Blueberry cultivars were identified that are amenable to tissue culture and regeneration procedures (as part of an ongoing transformation project). Sequence data were collected from several blueberry and cranberry pathogens that will be used for the design of probes for rapid detection. Leafhoppers were identified as potential vectors of Blueberry red ringspot virus.
1. Fairy ring disease of cranberry, causal agent and life cycle. Fairy ring is a serious fungal disease of cranberry that kills vines and is difficult to control. The causal agent and mechanism of spread were unknown. We positively identified the causal agent as a new species of Helicobasidium. We have further determined that this organism has a complex life cycle and an alternate host that contributes to the genetic diversity and spread of the disease in cultivated cranberry beds.
2. Accurately estimating levels of fungal disease resistance. Experiments in blueberry demonstrated that a minimum of six years, and possibly as many as nine years are needed to derive accurate estimates of resistance to the fungal infections, mummy berry shoot blight and mummy berry fruit infection. This research aids in understanding resistance in cultivars and the process needed for accurate estimation of resistance.
3. Factors influencing mummy berry disease severity. Modeling studies of mummy berry disease of blueberry demonstrated that temperature and the amount and frequency of precipitation in January-March were predictive factors of springtime disease severity. This research aids in understanding the parameters that affect disease and may contribute to an understanding of ways to reduce infection.
5. Significant Activities that Support Special Target Populations
Matching funds summer intern grant (internal) to support a minority student.