Location: Southern Horticultural Research2015 Annual Report
The long-term objective of this project is to develop improved germplasm for woody ornamental and small fruit crops adapted to the Gulf Coast Region where the effects of both biotic and abiotic stresses are exacerbated by frequent weather extremes. Objective 1. Design and apply phenotyping methods to identify and measure traits associated with environmental tolerance in southern-adapted small fruit and woody ornamental crops, especially in underutilized and native germplasm that can be incorporated into existing breeding programs. Objective 2. Identify markers and/or genes that are associated with environmental tolerance in breeding populations and evaluate indirect selection strategies for drought, heat, and poor soil tolerance designed to improve the efficiency and accuracy of selection during breeding. Objective 3. Design and test high throughput sequencing methods to uncover genes differentially expressed in response to environmental stress. Objective 4: Accelerate the genetic improvement and cultivar development for small fruit and woody ornamental genera with the genetic resources developed in Objectives 1, 2, and 3.
Understanding the genetic basis for plant tolerance to environmental stress is critical to protecting agriculture productivity in the U.S. and worldwide. The Thad Cochran Southern Horticultural Laboratory will lead research on the vulnerability of specialty crops to drought, heat, flood and poor soils, and to develop tools to incorporate selection for superior environmental tolerance into existing breeding programs. Scientists will develop innovative and rigorous phenotyping to more quickly and efficiently quantify traits associated with drought and poor mineral soil tolerance in small fruit and woody ornamental crops. Germplasm will be evaluated by modification and refinement of greenhouse methods. Initial focus will be on improved selection in southern adapted blueberry germplasm including existing cultivars. Subsequent efforts will focus on selection criteria for seedling populations to produce criteria directly applicable to southern blueberry breeders. Proposed research is designed to connect phenotypes associated with stress tolerance to specific genotypes allowing rapid, precise selection of traits in existing breeding lines using indirect selection by molecular markers. Molecular studies will also contribute significantly to understanding the genetic basis for environmental tolerance traits and the inheritance and segregation of these traits in existing conventional breeding programs for blueberry. Scientists will also identify novel genes and gene expression patterns associated with severe stress and recovery in native plants exhibiting superior environmental tolerance to drought and flooding to increase our understanding of existing abiotic stress tolerance models. Initial experiments will use Pityopsis ruthii, which is an endangered, native plant that exhibits extreme environmental tolerance. Results from phenotyping, genotyping, and gene expression studies will be incorporated into our conventional breeding programs to enhance efficiency and to advance development and application of new breeding tools. Blueberry parents and seedling populations at all stages of development are available for phenoptype, marker and genotype studies as well as breeding for new, improved cultivars. An extensive blueberry species and cultivar collection is also available on site along with breeding materials from collaborating universities and the National Clonal Germplasm Repository.
Over 300 crosses were made among select rabbiteye and southern highbush blueberry parents and seed were harvested. Progeny from 2014 crosses were germinated and are being established for field plantings in 2015. Approximately 3,000 seedlings from 2013 crosses were established in field nursery plantings (as opposed to containers) and nearly 300 selections were made from the seedling nursery from 2012 and 2013 crosses; plants of these are being propagated via soft wood cuttings for testing at Poplarville and Stone County, MS locations. One new rabbiteye blueberry cultivar, ‘Bluesfest’ was released as new public domain cultivar in 2015 while two other elite rabbiteyes and three elite southern highbush selections are being increased via micropropagation by private labs in preparation for their release as patented cultivars. Collaborative research with other blueberry geneticists was initiated and involved providing numerous interspecific blueberry hybrids for use in breeding for environmental stress tolerance. A collaborative study focused on locating sources of resistance to the Spotted Winged Drosphilla fruit fly in blueberries is in progress with the field screening and bench assay of diverse blueberry genotypes is being conducted. Additionally, six advanced muscadine grape strains derived from the USDA-ARS breeding and genetics research program have been propagated for multi-site testing including TX, MS and NC State University. Also, two genetically modified muscadine grape constructs of the University of Florida, cultivars Alachua and Delicious, are being evaluated for disease resistance, seedlessness, and berry quality. In order to better understand the genetics of the blueberry germplasm at hand and devise a sound hybridization scheme, an analysis of the genome size and number of chromosomes was undertaken using a cell counting techniques. Seventy-five (75) blueberry taxa including rabbiteye and southern highbush cultivars as well as some species such as Vaccinium arboreum and V. pallidum, both of which are supposedly drought and poor soil tolerant, were determined. Both species typically have two sets of chromosomes, but the genome size results suggest that a few individual V. pallidum plants have four sets of chromosomes, or twice as many as expected. Cuttings were taken from these potentially tetraploid plants and propagated. Actively growing roots from these plants will be collected and used for traditional chromosome spread to confirm the tetraploid nature of these plants. Also, the potentially tetraploid V. pallidum plants were hybridized with V. corymbosum plants, and the resulting seeds were collected and are being vernalized. Seedlings from these crosses will be screened for tolerance to both drought and poor soil. Cuttings were made from 10 southern highbush and 10 rabbiteye cultivars for use in the screening experiment (Objective 1) for pH and drought tolerance. In order to better understand the genes and gene networks involved in superior environmental tolerance, gene expression data was generated for the model plant Pityopsis ruthii, a native endangered species with extraordinary drought and submergence tolerance, after subjecting it to six weeks of drought conditions. DNA sequencing will be compared to physiological responses.
1. New blueberry release for extended harvest season. USDA-ARS scientists at the Thad Cochran Southern Horticultural Laboratory, in Poplarville, MS released a productive and high quality mid-late season rabbiteye blueberry called ‘Bluesfest’ that will extend the harvest season for growers in the region and provide insurance against late spring frosts that frequently cause significant crop loss. The midseason ripening rabbiteye blueberry ‘Powderblue’ is among more popular rabbiteye blueberries mostly due to its exceptionally light blue fruit that results from a thick natural waxy coating on berry skins. However, the relatively small berries of ‘Powderblue’ may at times sell for less than larger berries of other cultivars. ‘Bluesfest’ is a productive new rabbiteye blueberry that has mid-to-late season ripening period, exceptionally light blue color, and berry size exceeding the fruit of ‘Powderblue’.
2. Three new crapemyrtle cultivars for landscape use. USDA-ARS scientists at the Thad Cochran Southern Horticultural Laboratory, in Poplarville, MS released three new crapemyrtle cultivars ‘Miss Frances’, ‘Miss Gail’ and ‘Miss Sandra’. 'Miss Gail' stands out because of its superior purple flower color, 'Miss Frances' because of its superior red flower color along with an attractive green foliage, and 'Miss Sandra' because of its elite purple flower color and tight vertical growth habit. All three cultivars were evaluated for 9 years and showed field tolerance to common crapemyrtle diseases such as bacterial spot, powdery mildew, and Cercospora leaf spot. These releases can be used by both public and private sector breeders as parental materials in crosses to add value to new crapemyrtle cultivars.
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