Molecular Mapping of the Tomato Spotted Wilt Virus Resistance Gene Sw-7 in Tomato

Abstract: Tomato spotted wilt virus (TSWV), vectored by several thrips species, is the causal agent of devastating tomato crop losses in many areas of the world. Recently, field tests have demonstrated that there are TSWV isolates that overcome the resistance gene Sw-5, derived from Lycopersicon peruvianum L. However, Sw-7, a new source of TSWV resistance, has been introgressed from L. chilense Dun. This new gene has demonstrated field resistance to various isolates of this disease including greenhouse trials utilizing isolates that overcome Sw-5. In order to determine the genetic location of Sw-7, we screened over 200 SSR and InDel molecular markers from across the tomato genome. We used the homozygous (Sw-7/Sw-7) Ck12 line and one of the susceptible (Sw-7+/ Sw-7+) recurrent backcross parents (Fla 7482B) along with six BC1 and F2 plants segregating for Sw-7. The results of this screening suggested that Sw-7 resided near SSR20 on chromosome 12. To confirm the linkage of Sw-7 and SSR20 we tested this SSR marker and others on chromosome 12 using 94 BC1 and F2 progeny segregating for Sw-7. Additionally, we screened 47 lines segregating for Sw-7 under high natural TSWV field pressure conditions in northern Florida. As a result of these studies we have narrowed the location of the L. chilense-derived DNA with Sw-7. This region resides between markers T1263 (45.0 cM) and SSR20 (58.2 cM), according to the “Tomato EXPEN-2000” map found on the Sol Genomics Network. Our efforts are now focused on determining the precise position of Sw-7 in relationship with the markers available in this region and the AFLP markers previously reported.

Authors: Keri G. Dockter, Derek S. O’Neil, and David L. Price, Brigham Young University, Provo, UT; John Scott, GCREC, Wimauma, FL; and Mikel R. Stevens, Brigham Young University, Provo, UT

Poster# 3 - Specified Source(s) of Funding: Brigham Young University

Early Phenotypic Mutation Results Induced by Ethyl Methyl Sulfonate (EMS) on Species of Penstemon

Abstract: With recent concern for preserving natural resources, use of drought-tolerant ornamentals may become a valuable method of lowering water usage for homeowners. The mostly herbaceous perennial Penstemon genus offers drought-tolerance, some level of acceptance in urban landscape and an enormous amount of genetic diversity. With around 280 different species, Penstemon is among the largest genera of herbaceous perennials native to North America. Chemical mutagenesis with EMS has been used to induce novel phenotypes in a vast number of crops both agronomic and ornamental. This mutagen may prove to be a valuable tool in helping to further domesticate Penstemon for use in urban landscaping. The scope of this research is to identify the phenotypic effects of EMS on several different species of Penstemon. In preliminary tests, we have treated Penstemon strictus with concentrations ranging from 0.025% to 3% EMS. These concentrations have already shown a wide array of mutations in the juvenile vegetative growth. Among the surviving plants treated with 0.675% EMS, common mutations include: dwarfing (32%), fused leaves (11%), and variegation in the leaf tissue (1%). Since Penstemon are often clonally propagated, these induced mutations, along with the natural beauty and diversity of Penstemon, may produce superior cultivars which are economically beneficial and environmentally friendly.

Authors: Rhyan B. Dockter, Shaun R. Broderick, James D. Daley, Shawna L. Daley, Mitchell A. Mendenhall, Bryson J. Ewell, Brad Geary, and Mikel R. Stevens, Brigham Young University, Provo, UT

Poster# 2 - Specified Source(s) of Funding: Brigham Young University

Seed Propagation of Sphaeralcea (Globemallow)

Abstract: Plants of Sphaeralcea are flowering perennials with bright orange to red flowers that add color to landscapes. They are drought-tolerant and considered pioneer species because of their ability to establish quickly in harsh conditions. Three species are native to the Intermountain West and considered desirable for low-water landscapes: S. grossulariifolia, S. parvifolia, and S. munroana. While plants of Sphaeralcea are available in the industry, they are not widely distributed because of difficulty with seed propagation and dormancy breaking. A reasonably successful strategy for breaking physical seed dormancy in Sphaeralcea is seed nicking. However, this method is not cost-effective on a large scale because the seeds are small (<1 mm in diameter) and seed nicking is labor-intensive. We hypothesized that seeds of Sphaeralcea might exhibit double dormancy. In February 2009, seeds in lots of 50 each were exposed to physical (seed nicking, rock tumbling for 24 hr, and hot-water scarification) and physiological (6 weeks cold-moist stratification) dormancy breaking strategies, alone and in combination to test this hypothesis (n = 5). After dormancy treatments were complete, seeds were germinated on moist filter paper in plastic Petri dishes held on a bench top at 21 °C. Germination was recorded as radicle emergence from the seed. We found no interaction between species and treatment in percent germination among the three species (P = 0.87). Germination of seed after nicking alone was 52%. Germination of seed after 6 weeks cold-moist stratification was only 5%. However, the combination of nicking and 6 weeks cold-moist stratification significantly enhanced seed germination over either of these dormancy breaking strategies alone (84%). Seed germination percent after rock tumbling alone was 26%, significantly greater than hot-water scarification. Cold-moist stratification did not improve germination when combined with physical dormancy breaking strategies other than nicking. Our data suggest that Sphaeralcea may exhibit double dormancy. Future work should focus on evaluating different rock-tumbler media and time of tumbling to find a viable alternative to nicking for breaking physical seed dormancy in these species.

Authors: Ailina Smith and Heidi Kratsch, Utah State University, Logan, UT

Poster# 7 - Specified Source(s) of Funding: Utah State University Undergraduate Research and Creative Opportunities program