Location: Crop Genetics and Breeding Research2016 Annual Report
1. Identify new sources of maize germplasm with resistance to aflatoxin and insects, and identify new sources of sorghum germplasm with improved insect resistance. 1A. Evaluate exotic maize germplasm from the Germplasm Enhancement of Maize (GEM) program, International Center for the Improvement of Maize and Wheat (CIMMYT), and the U.S. maize germplasm collection for resistance to infection by Aspergillus flavus and aflatoxin contamination. 1B. Screen for resistance to ear- and kernel-feeding stink bugs, sap beetles, thrips and maize weevil in maize germplasm from the GEM, the CIMMYT, and the U.S. maize germplasm collection. 1C. Evaluate sorghum lines from the U.S. germplasm collection for anthracnose resistance. 1D. Screen for whorl-feeding fall armyworm and head-feeding sorghum midge resistance in sorghum lines from the U.S. germplasm collection. 2. Develop maize and sorghum germplasm adapted to the southeastern United States with enhanced resistance to diseases and insects. 2A. Develop maize germplasm with reduced aflatoxin accumulation, increased resistance to insects, and enhanced agronomic performance in the southern Coastal Plain region. 2B. Develop sorghum germplasm with improved disease and insect resistance and high yield potential.
Objective 1: Exotic maize germplasm from the Germplasm Enhancement of Maize (GEM) Program, the International Maize and Wheat Improvement Center (or CIMMYT), Mexico, and the U.S. maize germplasm collection will be screened for resistance to multiple insects and diseases, and reduced aflatoxin contamination. Equal priority will be given to the GEM and exotic germplasm, since the GEM germplasm will likely have better agronomic traits but the exotic germplasm may have better adaptation to the South. Such a combination has the potential that allows us to identify new germplasm resistant to multiple insects, diseases, and reduced mycotoxin contaminations. To effectively serve the seed industries, the screenings of maize insect pests will focus on ear- and kernel-feeding insects, in particular, stink bugs, sap beetles, thrips and maize weevil. The genetic and biochemical bases for the biotic stress resistance in these newly identified germplasm lines will be further examined. Three genetic studies (i.e., diallel analysis, xenia effect, and heterosis) will be used to elucidate the genetic mechanisms, whereas phytoalexins and other secondary metabolites of plants will be examined to elucidate biochemical and physiological bases of biotic stress resistance. A similar approach is utilized for the screening of sorghum germplasm for resistance to multiple biotic stress factors. Previously identified disease resistant and agronomically-elite germplasm in the U.S. germplasm collection will be screened for resistance to fall armyworm, foliar anthracnose disease, and sorghum midge. The genetic mechanisms of insect and disease resistance will be examined utilizing three genetic studies (i.e., North Carolina Design II, heterosis, and xenia effect). The contributions of the secondary metabolites to biotic stress resistance in sorghum will also be examined. Objective 2: New maize breeding crosses will be made by recombining germplasm with superior agronomic traits with the newly identified germplasm that confers multiple insect and disease resistance and with reduced mycotoxin contamination. New maize germplasm will be developed by continuously screening and continuous self-pollination of the segregating populations. At the same time, recombinant inbred lines (RILs) will also be developed to identify DNA markers for the newly-developed multiple pest-resistant maize germplasm lines. New sorghum breeding crosses will also be made using the newly identified sorghum germplasm lines that are resistant to multiple biotic stresses and with good yield potential. The breeding crosses will be continuously screened and selected, and self-pollinated to develop and release new sorghum germplasm lines (B lines, or maintainer lines). The best B lines will also be converted into A lines (or cytoplasmic-nuclear male sterile lines) to serve the seed industries. At the same time, recombinant inbred lines will also be developed and used to identify DNA markers for the newly-developed multiple biotic stress-resistant sorghum germplasm lines at both vegetative and reproductive growth stages.
Research activities have been continuously focused on the genetic improvement of corn and sorghum for yield related traits, resistance to Aspergillus flavus infection and aflatoxin accumulation, and damage caused by disease and insect pests. For maize breeding efforts, inbreds and hybrids from Germplasm Enhancement of Maize (GEM) program from North Carolina, CIMMYT and Germplasm Resource Information Network (GRIN) were evaluated for resistance to whorl and ear feeding insects, and aflatoxin accumulation. In addition, Ex-PVP and other maize germplasm lines with maize weevil resistance and aflatoxin resistance were evaluated for foliar and ear-feeding insect resistance. A subset of 16 intermated B73 and Mo17 (IBM) recombinant inbred lines, and 10 CIMMYT inbreds with maize weevil resistance were evaluated for multiple insect resistance in 2016. A total of 185 new experimental hybrids made in 2015 utilizing the parents of insect and disease resistance, heat and drought tolerance were also evaluated for insect resistance and good agronomic traits (e.g., no lodging and good yield potential). A series of segregating populations at varying stages are being evaluated continuously with the goal of pyramiding aflatoxin, insect, and abiotic resistance in the improved genetic backgrounds for yield. A set of 17 inbred corn lines (GT-lines) developed by our CRIS was crossed with six ex-PVP testers in a factorial (Design II) mating design. These 102 hybrids, along with six commercial checks, were evaluated in the field for two years for yield and agronomic traits. At the same time they were also evaluated for aflatoxin resistance in a separate field by inoculation with the side-needle technique. As expected, the commercial checks had the highest yields, but some experimental entries were not statistically different from the checks, and some had significantly lower aflatoxin concentration. Across the two years of the test, GT1329 x LH195 (162.5 bu/ac and 23.9 ppb) and GT1214 x LH210 (162.2 bu/ac and 30.3 ppb) had the best combination of high yield and low aflatoxin. An outbreak of southern rust (Puccinia polysora) in 2014 allowed us to screen for resistance to this disease. GT1208 and GT1209 had good general combining ability for resistance. The disease did not occur at a high enough level in 2015 to permit screening. For sorghum research, sugarcane aphid damage was severe in 2015, which requires us to focus on providing growers with short- and long-term solutions for this invasive pest. We participated in the newly-funded areawide Integrated Pest Management (IPM) project for sugarcane aphid management at present, in addition to participating in the State Variety Test to identify the best sorghum hybrids for farmers to utilize immediately. For long-term solution, we are working on new germplasm development. We have made progress on new germplasm development for grain and sweet sorghum. A total of 144 sorghum germplasm lines acquired from GRIN have been screened for key disease and insect pests, which include the fall armyworm, and the sugarcane aphid. New crosses with aphid and fall armyworm resistance have been made in 2015, and seeds of F2 have been generated in the greenhouse, and the F2 plants are being evaluated in the field in 2016. Much of our sweet sorghum breeding nursery was severely affected by sugarcane aphid, but a few entries were identified with apparent high level of resistance. Entries derived from PI 257599 (No. 5 Gambela) were the most resistant. Most of these entries also had few disease symptoms. These materials will be advanced in 2016, and a mapping population will be developed. Nine other potential sources of sugarcane aphid resistance were also identified in 2015; these have been crossed with elite sweet sorghum lines in the greenhouse. Forty-five additional accessions, listed in the literature as resistant in other locations, have been acquired from GRIN and will be screened for resistance in Tifton, Georgia in 2016. In multidisciplinary collaborative/cooperative research efforts in our region, we continuously participate in a multiple state research project of Aflatoxin Mitigation Center of Excellence (AMCOE) in 2016 to examine the experimental hybrids for insect damage and aflatoxin accumulation; and participated in a team effort to differentiate plant defensive responses in a maize inbred line and its mutant in fungal infection and aflatoxin contamination in corn ears at pre-harvest. We also work with other scientists from the AMCOE project by evaluating and selecting from breeding populations derived from 4-way breeding crosses with high level of aflatoxin resistance from Texas A&M at Tifton, Georgia for disease, insect, and aflatoxin resistance. We also continuously participated in the South Eastern Regional Aflatoxin Trial (SERAT) Program with six entries from our team, and the State Variety Tests for corn and sorghum hybrids for insect resistance in 2015. For the third year, we are participating in the Genomes to Fields (G2F) project. This is a multi-location G x E study involving scientists from ARS and universities from across the U.S. and Canada. Each year we have planted 500 hybrid plots at our location, and record yield and other phenotypic data, which are shared with the G2F collaborators. A WatchDog mini weather station is used to log in-field weather conditions, and these data are also shared with the G2F team. All G2F data will be made publicly available on CyVerse (formerly iPlant) after the initial manuscript is published. The first manuscript, based on 2014 environmental data, has been submitted, and is currently in revision.
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Yang, L., Fountain, J., Wang, H., Ni, X., Ji, P., Lee, R.D., Kemerait, R.C., Scully, B.T., Guo, B. 2015. Stress sensitivity is associated with differential accumulation of reactive oxygen and nitrogen species in maize genotypes with contrasting levels of drought tolerance. International Journal of Molecular Sciences. 16:24791-24819. doi: 10.3390/ijms161024791.
Ni, X., Riley, D.G., Sparks, Jr., A.N. 2015. Unusual aggregation and foraging behavior of imported cabbageworm (Lepidoptera: pieridae) adults on blue vervain flowers. Journal of Entomological Science. 50(3):252-253.
Potter, T.L., Olson, D.M., Ni, X., Raines, G.C. 2015. A re-examination of corn (Zea mays L.) ear volatiles. Phytochemistry Letters. 14:280-286. https://doi.org/10.1016/j.phytol.2015.10.026.
Scully, B.T., Krakowsky, M.D., Ni, X., Tapp, P.J., Knoll, J.E., Lee, R.D., Guo, B. 2015. Registration of maize inbred line 'GT888'. Journal of Plant Registrations. 10:87-92.
Uchimiya, M., Ni, X., Wang, M.L. 2016. Structure-reactivity relationships between fluorescent chromophores and antioxidant activity of grain and sweet sorghum seeds. Journal of Food Science and Nutrition. 4(6)811-817.
Niu, Y., Qureshi, J.A., Ni, X., Head, G.P., Price, P.A., Meagher Jr, R.L., Kerns, D., Levy, R., Yang, X., Huang, F. 2016. F2 screen for resistance to Bacillus thuringiensis Cry2Ab2-maize in field populations of Spodoptera frugiperda (Lepidoptera: Noctuidae) from the southern United States. Journal of Invertebrate Pathology. 138(2016): 66-72. doi.10.1016/j.jip.2016.06.005.