Location: Crop Genetics and Breeding Research2018 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 were focused on the genetic improvement of corn and sorghum for yield related traits and resistance to biotic stresses. For maize breeding efforts, inbreds and breeding accessions from Germplasm Enhancement of Maize (GEM) program from North Carolina, International Maize and Wheat Improvement Center (CIMMYT) and the U.S. National Plant Germplasm System (NPGS-GRIN database), including Ex-PVP lines, were evaluated for resistance to whorl and ear feeding insects, and reduced aflatoxin accumulation. In addition, other maize germplasm lines from cooperators were evaluated for foliar and ear-feeding insect resistance from 2013 to 2017. Accessions with good resistance and good agronomic traits were identified and incorporated into our breeding program. A total of 642 new breeding crosses were made and advanced for maize germplasm development by screening for insect and disease resistance, low aflatoxin accumulation, heat and drought tolerance, and good agronomic traits (e.g., no lodging and good yield potential). Seventeen advanced elite inbred lines, developed by our program, were crossed with six tester lines to evaluate combining ability for yield and aflatoxin reduction. The hybrids were evaluated in the field for four years (2014-2017), and the data will be used to select which of these lines to release. A collection of B73-teosinte introgression lines was acquired and seed was increased for future experiments. In multidisciplinary collaborative maize research efforts in our region, we participated in the South Eastern Regional Aflatoxin Trial (SERAT) for the last five years. Five to seven hybrids from our team were entered into the trial every year and our location also served as a test location. 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. Three cycles of selection were completed, based primarily on agronomic potential. Future efforts will focus on biotic stress resistance in the selected materials. In addition, we also participated in the Georgia state variety trial for corn, and evaluated 312 commercial corn hybrids for ear-feeding insect resistance over five years, and provided the information for growers to use for hybrid selection, and for the purpose of assessing efficacy of new transgenic technology and for monitoring Bt resistance in natural insect pest populations with existing technology. We also have participated in the Genomes to Fields (G2F) project since its inception in 2014. 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 approx. 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 published, as well as inbred ear images from the first two years. For sorghum research, over 500 accessions were screened in the field at Tifton, GA for anthracnose resistance. Resistant entries were identified and breeding crosses were initiated. The sugarcane aphid outbreak started in 2014, and has caused severe yield and economic losses ever since, which required us to focus on providing growers with short- and long-term solutions for this invasive pest. For long-term solution, we are working on new germplasm screening and development. A total of 797 germplasm lines (405 entries for grain sorghum and 397 entries for bioenergy sorghum germplasm lines) were screened for sugarcane aphid resistance in 2017. A total of 11 breeding crosses were made in 2015 using sorghum inbreds with aphid and fall armyworm resistant parents, and a total of 185 segregating accessions, derived from these crosses were evaluated and advanced in 2017 for germplasm development. The sweet sorghum breeding nursery has also been severely affected by sugarcane aphid. Entries derived from PI 257599 (No. 5 Gambela) were found to be consistently the most resistant. Most of these entries also show few disease symptoms. A mapping population (N109A x PI 257599) is currently in the F4 stage of development. DNA was collected from F2 plants in 2016 and F3 families were phenotyped for aphid response in the field in 2017. For collaborative sorghum research, we began participating in a five-year area-wide Integrated Pest Management project for sugarcane aphid management in 2016, in addition to continuously participating in the Georgia State Variety Test from 2013-2017. A total of 223 commercial grain and forage/hay sorghum hybrids were evaluated for anthracnose, sugarcane aphid, and other insects, which provided growers with short-term solutions on aphid management by identifying the best sorghum hybrids in our region. Bird damage was also assessed in the grain sorghum trials.
Cuevas, H.E., Prom, L.K., Copper, E.A., Knoll, J.E., Ni, X. 2017. Genome-wide association mapping of anthracnose (Collectotrichum sublineolun) resistance in the U.S. sorghum association panel. The Plant Genome. II:170099.
Knoll, J.E., Anderson, W.F., Harris-Shultz, K.R., Ni, X. 2018. The environment strongly affects estimates of heterosis in hybrid sweet sorghum. Sugar Tech. 20(3):261-274. https://doi.org/10.1007/s12355-018-0596-0.
Punnuri, S., Harris-Shultz, K.R., Knoll, J.E., Ni, X., Wang, H. 2017. The genes BM2 and BLMC that affect epicuticular wax deposition in sorghum are allelic. Crop Science. 57:1552-1556.
Harris-Shultz, K.R., Ni, X., Wadl, P.A., Wang, X., Wang, H., Huang, F., Flanders, K., Seiter, N., Kerns, D., Meagher Jr, R.L., Xue, Q., Reisig, D., Buntin, D., Cuevas, H.E., Brewer, M., Yang, X. 2017. Microsatellite markers reveal a predominant sugarcane aphid (Homoptera: Aphididae) clone is found on sorghum in seven states and one territory of the USA. Crop Science. 57:2064-2072.
Goggin, F.L., Quisenberry, S.S., Ni, X. 2017. Feeding Injury. In: H.F. van Emden and R. Harrington (eds.). Aphids as Crop Pests, 2nd edition. CAB International, Oxfordshire, UK, pp. 303-322.
Gage, J., Jarquin, D., Romay, M., Lorenz, A., Buckler IV, E.S., Kaeppler, S., Alkhalifah, N., Bohn, M., Campbell, D., Edwards, J.W., Ertl, D., Flint Garcia, S.A., Gardiner, J., Good, B., Hirsch, C., Holland, J.B., Hooker, D., Knoll, J.E., Kolkman, J., Kruger, G., Lauter, N.C., Lawrence-Dill, C., Lee, E., Lynch, J., Murray, S., Nelson, R., Petzoldt, J., Rocheford, T., Schnable, J., Schnable, P., Scully, B.T., Smith, M., Springer, N., Srinivasan, S., Walton, R., Weldekidan, T., Wisser, R., Xu, W., Yu, J., De Leon, N. 2017. The effect of artificial selection on phenotypic plasticity in maize. Nature Communications. 8:1348. https://doi.org/10.1038/S41467-017-01450-2.