Location: Southern Horticultural Research Unit
2025 Annual Report
Objectives
1. Discover and characterize superior traits from natural collections, mutants, and interspecific populations to enhance stress tolerance in woody ornamental species, such as Hibiscus.
1.A. Generate genetic information and characterize the genetic diversity and population structure of important ornamental species.
1.B. Characterize and develop improved germplasm with superior ornamental value and wide adaptation to prevalent conditions in southeastern U.S.
1.C. Use phenotypic and genomic tools to identify quantitative trait loci and candidate genes associated with important traits in Rosa and Weigela.
2. Develop and use novel tissue culture and transformation systems to improve key horticultural traits of blueberry, muscadine grape, and woody ornamental plants.
2.A. Develop a regeneration and transformation system to improve Hibiscus mutabilis.
2.B. Develop new germplasm of muscadine grapes using induced mutation, invitro ploidy manipulations, and wide hybridization.
3. Dissect the genetics and environmental factors affecting fruit quality and adaptation traits in blueberry and muscadine grape.
3.A. Use genomics resources to discover genomic regions associated with fruit quality and adaptation traits in blueberry.
3.B. Dissect the genetics and environmental factors affecting fruit quality and adaptation traits in muscadine grape.
4. Use conventional and genomic technologies to breed improved blueberry cultivars with excellent flavor and broad adaptation to biotic and abiotic stresses.
4.A Use interspecific hybridization to introduce useful genetic variability, incorporate adaptation traits into existing germplasm, and develop new rabbit-eye cultivars.
4.B Establish field trials and develop and implement effective breeding system for rapid development of improved blueberry germplasm.
Approach
Genetic diversity in Weigela. A diverse population will be characterized for horticultural traits and genotyped. Population structure, principal components, and phylogenetic analyses will be performed to assess the structure of the diversity. Principal component analysis will be performed to investigate the relationships among trait variables and the factors underlying genotype variation.
Comparative genomics of Hibiscus species. 27 genotypes from nine Hibiscus species will be sequenced using different sequencing platforms. The pan-genomes will be assembled, annotated, and phylogenetic analyses will be performed to determine the relationship between tested species.
Induction of mutation and polyploidy in Weigela. Vegetative buds from mature plants of four Weigela species and three concentrations of colchicine solution and three durations will be used in meristem culture in modified Murashige and Skoog media for the induction of polyploidy.
GWAS of important traits in Rosa. A diverse panel of 125 Rosa genotypes will be evaluated for different horticultural traits and genotyped. The SNPs data will be used to analyze the genetic diversity and locate genomic regions associated with important traits.
Develop a regeneration and transformation system to improve Hibiscus mutabilis. Agrobacterium rhizogenes transformation will be performed and gene construct containing the gene of interest and selectable marker will be used. PCR or RT-PCR test will be conducted on putative transgenic microshoots and hairy roots to select stably transformed plants.
Generation of interspecific grape hybrids. For this purpose, 14 reciprocal crosses between V. rotundifolia and seven accessions of V. mustangensis will be performed. In addition, 36 reciprocal crosses between, V. rotundifolia and nine Vitis species will be performed. F1 seeds will be soaked for 3 days in various concentrations of oryzalin to induce polyploidy. Phenotypic observations by means of visual observations, leaf thickness, and flow cytometry will be used to identify the interspecific hybrids.
Map genomic regions associated with important traits. A diverse panel of 264 SHB genotypes will be characterized for phenology and fruit quality traits and genotyped using the 3,000 DArT array platform. GWAS analysis and linkage mapping will be performed to identify genomic regions associated with traits of interest.
Dissect the genetics and environmental factors affecting fruit quality and adaptation traits in muscadine grapes. Parents and 516 individuals will be characterized for different fruit quality traits and resistance to Pierce’s disease. GBS will be used to genotype the individuals and data will be used in QTL analysis.
Progress Report
Significant progress has been achieved by ARS scientists at Poplarville, Mississippi, with the project as illustrated by the following specific activities:
Development of Dwarf/Compact Hibiscus cultivars. The hibiscus species H. hamabo and H. mutabilis are aesthetically attractive ornamental plants, but they both grow very tall, easily reaching 15 ft tall and 10-15 ft wide. Therefore, there is a need for dwarf and compact type cultivars for both the consumers and the commercial nursery industry. To tackle this issue, ARS scientists approached the problem using two different methods. The first method is through plant transformation or genetic engineering. This method generally requires a tissue culture method coupled with selection using a selectable marker along with an appropriate dose of the selectable marker on the one hand and a step involving Agrobacterium-based transformation on the other hand. ARS scientists developed and optimized a micropropagation system for H. mutabilis and identified a selectable marker along with its appropriate dose for plant transformation. The second phase of this method, the plant transformation step, is ongoing. The second method for developing dwarf and compact hibiscus plants involved using antimitotic agents to induce polyploidy. ARS scientists successfully developed dwarf and compact plants in two Hibiscus species, H. hamabo and H. mutabilis, that are being currently evaluated for release to consumers and commercial nurseries.
Seedless Muscadine grapes. Muscadine grapes are native to Southeastern United States. They are renowned for their health benefits, but their thick skin and big seeds are hindrance to their widespread commercialization. One way to achieve seedlessness in muscadines is to develop triploid muscadine plants. This can be done by hybridizing a diploid (2n = 40) muscadine with a tetraploid (4n = 80) muscadine plant. Naturally occurring muscadine plants and commercial muscadine cultivars are diploid. ARS scientists successfully managed to create tetraploid muscadine plants. These tetraploid muscadine plants are being cared for now both in the greenhouse and the field. Once they start flowering, they will be crossed with diploid plants to generate seedless triploid muscadine grapes.
Improving the genetic base of blueberries. Blueberry breeders tend to rely on a limited number of elite cultivars to develop new varieties, which can contribute to the narrowing of the blueberry genetic base, thus making plants potentially more susceptible to pathogens. For this reason, ARS scientists developed interspecific blueberry hybrids from naturally occurring diploid (2n = 24) blueberry species. These interspecific diploid blueberry hybrids were then converted to tetraploid (4n = 48) hybrids so that they can be crossed with highbush blueberry plants, that are generally tetraploid, to develop new and genetically diverse elite cultivars, thus helping to broaden the genetic base of commercial blueberry cultivars that are less susceptible to pathogens. Also, ARS scientists have identified two advanced rabbiteye blueberry selections that are candidates for release to consumers and commercial nurseries.
Genetic evaluation of Fruit quality traits in blueberry. The analysis of phenotypes within the southern high bush (SHB) blueberry germplasm collection revealed substantial variation in fruit-related traits across different observation years. Genome Wide Association Study (GWAS) conducted on normalized phenotypic values identified significant peaks, which were supported by one out of two to four observation years.
Patenting of muscadine grape cultivars. A request for patent applications for two muscadine cultivars has been cleared by USDA. One of the patent applications has been submitted already and the other one will be submitted soon.
Accomplishments
1. Development of dwarf and compact Hibiscus hamabo and H. mutabilis plants. Compact and dwarf plants require less space to grow. They are easier to manage and are ideal for containers or limited spaces, especially in urban settings. ARS scientists at Poplarville, Mississippi successfully developed dwarf and compact plants in two Hibiscus species, H. hamabo and H. mutabilis, that are being currently evaluated for release to consumers and commercial nurseries.
2. Creation of synthetic tetraploid muscadines. Synthetic tetraploids were developed by ARS researchers at Poplarville, Mississippi using interspecific diploids. This achievement can pave the way to the development of seedless muscadine grapes by crossing these tetraploids with diploids.
3. Introduction of tetraploid interspecific blueberry hybrids. ARS researchers at Poplarville, Mississippi developed interspecific blueberry hybrids from naturally occurring diploid blueberry species which were then converted to tetraploids. This is a valuable resource to cross with tetroploid highbush blueberry plants to develop new, genetically diverse blueberry cultivars.This achievement will help broaden the genetic base of commercial blueberries and help make future elite cultivars less susceptible to pathogens.
Review Publications
Bowden, A.T., Knight, P.R., Ryals, J.B., Coker, C.E., Langlois, S.A., Broderick, S.R., Blythe, E.K., Sakhanokho, H.F. 2025. Evaluation of Honey as a Rooting Adjuvant for Cutting Propagation of Three Common Nursery Crops. Agriculture. 15(3)/256. https://doi.org/10.3390/agriculture15030256.
Babiker, E.M., Nagasaka, K., Nishiyama, S., Yamane, H., Tao, R. 2025. Phenological variation associates with the stability of fruit quality traits in cultivated tetraploid blueberry. G3: Genes, genomics, genetics. 1-39. https://doi.org/10.1093/g3journal/jkaf108 c.
Chen, S., Malinowski, D., Sakhanokho, H.F., Revynthi, A., Wu, X. 2025. Estimation of Genome Size Variation in Hibiscus rosa-sinensis. HortScience. 60(8), 1282-1288.