Location: Southern Horticultural Research2014 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.
Research on small fruits and ornamental plants is focused on understanding the genetic basis for environmental tolerance and breeding new cultivars with superior traits. The ongoing blueberry breeding project involves both rabbiteye and southern highbush. Rabbiteye blueberries are native to the southeast and have improved tolerance to high soil pH and drought.Southern highbush blueberries have enhanced berry size and flavor. Last year 144 crosses were made with rabbiteye blueberries to improve berry traits and mechanical harvesting. 157 crosses were made with southern highbush blueberries to improve environmental tolerance and disease resistance. The majority of breeding was done among recurrently selected parents although about 5% of crosses involved mixing rabbiteye with southern highbush and/or different species. Progeny from 2013 crosses were germinated and established for field plantings. Approximately 7,000 seedlings from 2012 crosses were established in field nursery plantings and over 40 selections were made in the seedling nursery from 2011. Initial selections were based on fruit quality factors including size, color, firmness, picking scar size, and flavor. Elite plants were propagated via soft wood cuttings. Four advanced rabbiteye blueberry and three southern highbush selections are being prepared for release as new, elite cultivars. In this manner, all stages of the blueberry breeding program were moved forward. In order to quantify environmental tolerance traits in blueberry, hydroponic greenhouse studies on pH tolerance were completed on five rabbiteye and five southern highbush cultivars. Measures of growth, plant weight, root weight, chlorophyll and leaf mineral content were collected over three months for statistical analyses between pH treatments and cultivars. Screening for improved drought resistance in blueberries was also completed on five rabbiteye and five southern highbush cultivars by measuring stomatal closure due to drought stress. In addition to greenhouse studies, additional plants were introduced to the breeding program and crosses were made to better understand the genetic basis and inheritance of environmental tolerance traits. Observations of pollination, seed count per fruit, and germination of viable seedlings is in progress. In order to better understand the genes and gene networks involved in superior environmental tolerance, the transcriptomes for rabbiteye blueberry and the model plant Pityopsis ruthii, a native endangered species with extraordinary drought and submergence tolerance, were sequenced. DNA sequencing was completed on multiple tissues and unique gene profiles were generated as a reference for future studies on genes that are expressed in drought and pH tolerant plants. To that end, physiological responses were recorded for Pityopsis ruthii plants during six weeks of drought stress and tissue was collected for gene expression studies. Sequencing data was used to identify molecular markers for rabbiteye blueberry to unambiguously determine species background of elite materials, confirm hybridization in crosses and verify the parents, and estimate relatedness between materials in the breeding program. Markers and genes that were sequenced and identified this past year are expected to be linked with superior environmental tolerance traits determined by greenhouse and in vitro screens in future experiments.
1. Vernicia fordii ‘Spiers’, is a new tung tree for tung oil production in the Gulf Coast region. ARS scientists in Poplarville, Mississippi, released a new cultivar for tung oil production in the Gulf Coast. ‘Spiers’ was selected for its exceptional fruit production and late flowering. Most of the tung oil used in the U.S. is imported. Landowners and entrepreneurs seeking to produce domestic tung oil in the Gulf Coast region can use ‘Spiers’ to protect against crops loss due to late frost events. Oil analysis of ‘Spiers’ demonstrates a 6% increase in alpha-eleostearic acid content, which provides the chemical utility and value to tung oil. Late flowering and high quality oil traits found in ‘Spiers’ provide domestic growers with a combination of traits not found in any other cultivars. Spiers’ also has outstanding vigor; soil adaptability; environmental tolerance to heat, sun, and drought; and disease and insect resistance with no significant pathogens or pests.
2. Five new tropical hibiscus cutlivars ‘USS Mississippi’, ‘USS Alabama’, ‘USS Missouri’, ‘USS Tennessee’, and ‘USS Texas’. ARS scientists in Poplarville, Mississippi, released five new evergreen and compact ornamental Hibiscus rosa-sinensis cultivars for use in the landscape in USDA cold hardiness zone 10 or warmer. ‘USS Mississippi’ has flowers that are yellow-orange with a white eye. ‘USS Alabama’ has large orange flowers with splotch of red at the base of the petal giving it a red eye. ‘USS Missouri’ has an attractive form and red flowers. ‘USS Tennessee’ has uniformly yellow flowers with a small red eye appearance. ‘USS Texas’ has olive green foliage and hunter-orange flowers. The germplasm was released for free general propagation and distribution to breeders. In addition to landscape use, ornamental plant nurseries, landscape architects and designers, and homeowners can use the new hibiscus cultivars as a summer-flowering accent shrub for patios, pools, or other outside areas in the south.
Pounders Jr, C.T., Scheffler, B.E., Rinehart, T.A. 2013. 'Ebony Embers', 'Ebony Fire', 'Ebony Flame','Ebony Glow' and 'Ebony and Ivory' Dark-Leaf Crapemyrtles. HortScience. 48(12)1568-1570.
Sakhanokho, H.F., Islam-Faridi, M.N., Blythe, E., Smith, B.J., Rajasekaran, K., Majid, M. 2014. Morphological and cytomolecular assessment of intraspecific variability in scarlet eggplant (Solanum aethiopicum L.). Journal of Crop Improvement. 28:437-4453.
Wadl, P., Rinehart, T.A., Dattilo, A., Pistrang, M., Vito, L., Milstead, R., Trigiano, R. 2014. Propagation and conservation of the federally endangered perennial species Pityopsis ruthii. HortScience. 49:194-200.
Trigiano, R.N., Rinehart, T.A., Dee, M.E., Wadl, P.A., Poplawski, L., Ownley, B.H. 2014. First Report of Aerial Blight of Ruth’s Golden Aster (Pityopsis ruthii) caused by Rhizoctonia solani in the United States. Plant Disease. 98(6):855.
Sakhanokho, H., Pounders, C. and Blythe, E. 2013. Alginate Encapsulation of Begonia Microshoots for Short-Term Storage and Distribution. The Scientific World Journal, Article ID 341568, DOI:10.1155/2013/341568.