Location: Southern Horticultural Research2017 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 phenotype, 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.
A protocol to screen for drought tolerance under greenhouse conditions has been developed and used successfully to select rabbiteye and southern highbush genotype with drought tolerance. Two breeding selection MS 1408 and MS 2276 were identified as having high level of drought tolerance. A hydroponic system to screen for high pH tolerance in rabbiteye and southern highbush genotypes was developed. Using this system, three rabbiteye breeding selection, MS 1110, MS 1228, and MS 1239 exhibited high level of tolerance to high pH. Both MS 1228 and MS 1239 have the rabbiteye cultivar ‘Baldwin’ as a male parent in their pedigree. Baldwin was developed and released by the USDA ARS from a cross between ‘Tifblue' and Ga 6040. 'Tifblue' is one of the parents of ‘Premier’, and ‘Onslow'; rabbiteye cultivars which are known to have high levels of tolerance to high soil pH. An effective screening method for evaluating resistance (antixenosis) to the Spotted Wing Drosophila (SWD) in rabbiteye and southern highbush was developed. One hundred berries were sampled from 88 blueberry genotypes and examined for the presence or absence of SWD feeding damage or egg laying. During the test, we observed that SWD females misplaced or abort some of their eggs by ovipositing, not inside the fruit, but on top of the berry surface, fully exposing eggs to the air. These aborted eggs invariably shrivel and die. Hence, we developed a possible index that might more accurately detect antixenosis in a preferred fruit host. We termed this index the Oviposition Success Index (OSI). Of the 88 genotypes tested, three breeding selections, MS 1130, MS 1228, and MS 778, were identified to be more antixenosis based on the OSI. MS 1228 was crossed to two susceptible parents and the F1 seeds will be used to develop mapping populations to validate this result. To discover loci for resistance to the powdery mildew, an association mapping study was conducted with a panel of 101 Hydrangea macrophylla cultivars evaluated for powdery mildew resistance for three years at the Tennessee State University (TSU) nursery crop research station. The panel genotyped with 3,819 Genotyping-by-Sequencing (GBS)-based markers. Using genome wide association mapping, 34 Single nucleotide polymorphism markers (SNPs) for resistance were detected at p < 0.0001. Of these, three SNPs were tightly linked to the resistance locus which could be useful for marker-assisted.
1. Development of a new thornless erect blackberry cultivar. Blackberry cultivars from the northern states grow poorly in the Gulf Coast region of the U.S., for several reasons, including their high chilling requirement and susceptibility to heat stress. 'Sweetie Pie' is a new thornless erect blackberry cultivar developed and released by the ARS researchers in Poplarville, Mississippi, for the Gulf Coast region. The new cultivar was released for use by local fresh market and U-pick farm operations as well as home owners. 'Sweetie Pie' has exceptional flavor, excellent quality, and resistance to rosette (double blossom) disease. In addition, it is a relatively late ripening season cultivar which has high yield, good growth and high level of heat tolerance.
2. ‘Bluefest’ rabbiteye blueberry. ‘Bluesfest’ is a productive new rabbiteye blueberry developed and released by ARS researchers in Poplarville, Mississippi. Important attributes of ‘Bluesfest’ include its mid-to-late season ripening period with exceptionally light blue color, small and dry scar, and berry size exceeding that of fruit of ‘Powderblue’, an industry standard. 'Bluesfest' was released as a public domain cultivar and genetic materials of this cultivar were deposited at the USDA ARS National Clonal Germplasm Repository, Corvallis, Oregon.
3. ‘Gumbo’ southern highbush blueberry. ARS researchers in Poplarville, Mississippi, released ‘Gumbo’ southern highbush blueberry. Southern highbush blueberries continue to expand in the Gulf Coast region of the United States. Growers are interested in low-chill southern highbush cultivars that are well adapted to the region. Gumbo came from a cross between G 695 and MS 6 which was made in 2003. ‘Gumbo’ is a new cultivar that characterized by large and vigorous bush, large berry with small dry scar, and high yield.
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