Location: Crop Genetics and Breeding Research2017 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, International Maize and Wheat Improvement Center (CIMMYT) and U.S. national germplasm center (GRIN database) 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 in 2017. A total of 391 segregating populations are being evaluated in 2017. These were selected from the 185 breeding crosses 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. Several advanced backcross corn populations are being developed using elite, but aflatoxin susceptible, lines as the recurrent parent. A haploid inducer line has been acquired and seed increased using the greenhouse. (We have found that this particular line grows better in the greenhouse than the field at this location.) We will investigate the use of the haploid inducer to accelerate the development of advanced-backcross recombinant inbred lines (RILs) populations for genetic mapping. A subset of our highest-yielding aflatoxin-resistant corn hybrids were evaluated for yield, aflatoxin, and other traits at four planting densities in the field in 2016. Lower densities appeared to produce slightly greater yields, while density did not affect aflatoxin, except in one commercial check. In multidisciplinary collaborative/cooperative research efforts in our region, we continue to participate in the South Eastern Regional Aflatoxin Trial (SERAT). Six hybrids from our team were entered into the trial in 2016 and our location again served as a test location. A meta-analysis describing the progress made in the last ten years of the SERAT was recently published. The Georgia State Variety Tests for corn and sorghum hybrids were evaluated for insect resistance in 2016. We also worked with other scientists from the Aflatoxin Mitigation Center of Excellence (AMCOE) project by evaluating and selecting from breeding populations derived from 4-way and 8-way breeding crosses with high level of aflatoxin resistance from Texas A&M at Tifton, Georgia, for disease, insect, and aflatoxin resistance. These are also being selected for agronomic traits in the breeding nursery. For the fourth 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. The first two years of genotypic, phenotypic, and weather data from this project are now publicly available. For sorghum research, sugarcane aphid damage was severe in 2016, which requires us to focus on providing growers with short- and long-term solutions for this invasive pest. We are participating in the newly-funded areawide integrated pest management (IPM) project for sugarcane aphid management, in addition to participating in the State Variety Test to identify the best sorghum hybrids for farmers. A total of 82 commercial grain and forage sorghum hybrids were evaluated with four replications in the 2016 State Variety Trial. 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 subset of 71 sorghum germplasm lines acquired from national germplasm center (GRIN database) have been screened for key disease and insect pests, which include the sugarcane aphid, the fall armyworm, and the sorghum midge in 2016. New crosses with aphid and fall armyworm resistance have been made in 2015, and seeds of F3 have been generated in the field season of 2016, and the F3 plants are being evaluated in the field in 2017. Much of the lab's sweet sorghum breeding nursery was severely affected by sugarcane aphid in 2015 and 2016, but a few entries were identified with apparent high levels 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 were advanced in 2016. A mapping population (N109A x PI 257599) is currently in the F3 stage of development. DNA was collected from F2 plants in 2016 and F3 families will be phenotyped for aphid response in the field in 2017. 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, were screened for resistance in Tifton, Georgia, in 2016; most were susceptible, but some showed possible resistance. These will be retested in 2017.
Chu, X., Wang, W., Yoon, S.C., Ni, X., Heitschmidt, G.W. 2017. Detection of aflatoxin B1 (AFB1) in individual maize kernels using short wave infrared (SWIR) hyperspectral imaging. Biosystems Engineering. 157:13-23.
Ni, X., Cottrell, T.E., Toews, M.D., Tillman, P.G., Buntin, G.D. 2016. Diurnal activities of the brown stink bug (Hemiptera: Pentatomidae) in and near tasseling corn fields. Journal of Entomological Science. 51(3):226-337.
Wahl, N., Murray, S., Isakeit, T., Krakowsky, M.D., Windham, G.L., Williams, W.P., Guo, B., Ni, X., Knoll, J.E., Scully, B.T., Xu, W., Mayfield, K. 2017. Identification of resistance to aflatoxin accumulation and yield potential in maize hybrids in the Southeast Regional Aflatoxin Trials (SERAT). Crop Science. 57:202-215.
Guo, B., Ji, X., Ni, X., Fountain, J.C., Li, H., Abbas, H.K., Lee, D., Scully, B.T. 2017. Evaluation of maize inbred lines for resistance to pre-harvest aflatoxin and fumonisin contamination in the field. The Crop Journal. 5:259-264. doi:10.1016/j.cj.2016.10.005.