Population structure and association mapping to detect QTL controlling tomato spotted wilt virus resistance in cultivated peanuts

Tomato spotted wilt(TSW)is a serious virus disease of peanut in the United States.Breeding for TSWV resistance would be facilitated by the implementation of marker-assisted selection in breeding programs;however,genes associated with resistance have not been identified.Association mapping is a type of genetic mapping that can exploit relationships between markers and traits in many lineages.The objectives of this study were to examine genetic diversity and population structure in the U.S.peanut mini-core collection using simple sequence repeat(SSR)markers,and to conduct association mapping between SSR markers and TSWV resistance in cultivated peanuts.One hundred and thirty-three SSR markers were used for genotyping 104 accessions.Four subpopulations,generally corresponding to botanical varieties,were classified by population structure analysis.Association mapping analysis indicated that five markers:pP GPseq5D5,GM1135,GM1991,TC23C08,and TC24C06,were consistently associated with TSW resistance by the Q,PCA,Q+K,and PCA+K models.These markers together explained 36.4%of the phenotypic variance.Moreover,pP GPseq5D5 and GM1991 were associated with both visual symptoms of TSWV and ELISA values with a high R^2.The potential of these markers for use in a marker-assisted selection program to breed peanut for resistance to TSWV is discussed.

Development of Root Phenotyping Platforms for Identification of Root Architecture Mutations in EMS-Induced and Low-Path-Sequenced Sorghum Mutant Population

Sorghum’s natural adaptation to a wide range of abiotic stresses provides diverse genetic reserves for potential improvement in crop stress tolerance. Growing interest in sorghum research has led to the expansion of genetic resources though establishment of the sorghum association panel (SAP), generation of mutagenized populations, and recombinant inbred line (RIL) populations, etc. Despite rapid improvement in biotechnological tools, lack of efficient phenotyping platforms remains one of the major obstacles in utilizing these genetic resources. Scarcity of efforts in root system phenotyping hinders identification and integration of the superior root traits advantageous to stress tolerance. Here, we explored multiple approaches in root phenotyping of an ethyl methanesulfonate (EMS)-mutagenized sorghum population. Paper-based growth pouches (PGP) and hydroponics were employed to analyze root system architecture (RSA) variations induced by mutations and to test root development flexibility in response to phosphorus deficiency in early growing stages. PGP method had improved capabilities compared to hydroponics providing inexpensive, space-saving, and high-throughput phenotyping of sorghum roots. Preliminary observation revealed distinct phenotypic variations which were qualitatively and quantitatively systemized for association analysis. Phenotypes/ideotypes with root architecture variations potentially correlated with Pi acquisition were selected to evaluate their contribution to P-efficiency (PE). Sand mixed with P-loaded activated alumina substrate (SAS) provided closely to natural but still controlled single-variable conditions with regulated Pi availability. Due to higher labor and cost input we propose SAS to be used for evaluating selected sorghum candidates for PE. The ability of rapidly screening root phenotypes holds great potential for discovering genes responsible for relevant root traits and utilizing mutations to improve nutrient efficiency and crop productivity.

Comparison of Stem Damage and Carbohydrate Composition in the Stem Juice between Sugarcane and Sweet Sorghum Harvested before and after Late Fall Frost

A late fall frost may significantly affect sugar crops’ stem sugar composition, yield and juice quality for biofuel and bioproduct manufacture. Research on the effects of late fall frost in sugarcane is well documented, but information is lacking for sweet sorghum. Three and six commercial cultivars of sugarcane and sweet sorghum, respectively, were selected and evaluated for exposure to a late fall frost (-2.8&degC) in Griffin, Georgia, USA. Under the same controlled environmental conditions in a screen house, the late fall frost induced more damage to sugarcane than sweet sorghum stems. The frost caused damage to sugarcane tissue and for juice to exude from stems, whereas similar behavior was not observed for sweet sorghum. In both sugarcane and sweet sorghum, the glucose/fructose ratio was significantly reduced, but this change may not be totally directly related to the frost effect. Overall, these initial results suggest that sweet sorghum may have a better tolerance to fall frost than sugarcane. Two sweet sorghum cultivars, Grassl and M81E, responded well to the late fall frost, and they can possibly be used as feedstocks for biofuel/bioproduct manufacture in areas susceptible to frosts including northern regions of the Southeastern US.