Location: Crop Genetics and Breeding Research2015 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 Iowa, North Carolina, and Texas were evaluated for resistance to whorl and ear feeding insects, and aflatoxin accumulation. In addition, Ex-PVP and other maize germplasm lines with good aflatoxin resistance were evaluated for foliar and ear-feeding insect resistance. In late 2014 an outbreak of Southern rust occurred in our corn fields at levels high enough to assess our material for resistance. Several sources of resistance to this disease were identified. In 2015, 75 inbred maize selections are being evaluated for aflatoxin resistance for a second year. A set of 114 hybrids are also being evaluated for a second year for aflatoxin resistance, as well as for yield and other agronomic traits. A subset of 16 intermated B73 and Mo17 (IBM) recombinant inbred lines, and 10 International Maize and Wheat Improvement Center (CIMMYT) inbreds with maize weevil resistance were evaluated for multiple insect resistance in 2015. A total of 296 new experimental hybrids made in 2014 utilizing the parents of insect and disease resistance, heat and drought tolerance were also evaluated for insect resistance and good agronomic traits (e.g., lodging and yield potential). Ninety segregating populations at varying stages were evaluated with the goal of pyramiding aflatoxin, insect, and abiotic resistance in the improved genetic backgrounds. In addition, a set of 23 heat- and drought-tolerant maize germplasm from the Germplasm Resources Information Network (GRIN) has also been evaluated again for whorl-feeding fall armyworm resistance in the southern Coastal Plain region in 2014. Ten maize weevil resistant inbred lines were evaluated for whorl- and ear-feeding insect resistance. Two maize germplasm lines with fall armyworm resistance will be released next year. For sorghum research in 2014, 226 sorghum entries were screened for agronomic traits and resistance to anthracnose in the field. These germplasm lines were also assessed for resistance to the new pest - sugarcane aphid. Some promising entries were identified and will be re-screened in 2015. Selections were made from 57 F2 breeding populations in 2014. In the winter of 2014-15, 73 new F1 crosses were confirmed in the greenhouse using DNA markers, and were advanced to the F2 generation. These crosses have been planted in the field in 2015 for initial selection. The two-year study to assess the effect of planting dates on sorghum midge and bird damage on 25 commercial hybrids has been completed in 2014. A sorghum recombinant inbred line (RIL) mapping population was acquired from collaborators at Purdue University, and has been screened in the field for disease resistance for two years. A total of 144 sorghum germplasm lines acquired from GRIN have been planted in 2015 to screen for key disease and insect pests, which include the new devastating insect pest - sugarcane aphid. 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 2015 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 and 8-way breeding crosses with high level of aflatoxin resistance (Texas A&M), and 28 experimental hybrids (Texas A&M) at Tifton location 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. Geneticists also continues in the Genomes to Fields (G2F) project with both hybrid and inbred tests at our location in 2015. This is a multi-location Genotype x Environment interaction study involving scientists from ARS and universities across the U.S. and Canada.
1. Fall armyworm (FAW) is one of the most destructive insect pests in corn. Twenty maize lines from the USDA-ARS germplasm enhancement of Maize (GEM) Program were evaluated for whorl-feeding FAW resistance for two years. Diversity and abundance of predator insects in each experimental plot were also conducted. Three inbred lines that were derived from tropical maize lines originated from Uruguay, Cuba and Thailand were identified as the best FAW-resistant germplasm lines. Although the abundance and diversity of predators differed by year the two-year data showed that FAW injury ratings were negatively correlated to the predator abundance and diversity.
Ni, X., Xu, W., Blanco, M.H., Williams, W.P. 2014. Evaluation of fall armyworm resistance in maize germplasm lines using visual leaf injury rating and predator survey. Insect Science. 21(5):541-555.
Ni, X., Toews, M.D., Buntin, G., Carpenter, J.E., Huffaker, A., Schmelz, E.A., Cottrell, T.E., Abdo, Z. 2014. Influence of brown stink bug feeding, planting date and sampling time on common smut infection of maize. Insect Science. 21(5):564-571.
Ni, X., Lei, Z., He, K., Li, X., Li, X., Xu, W. 2014. Integrated pest management is the lucrative bridge connecting the ever emerging knowledge islands of genetics and ecology. Insect Science. 21(5):537-540.
Xie, H., Zhao, L., Wang, W., Wang, Z., Ni, X., Cai, W., He, K. 2014. Changes in life history parameters of corn leaf aphid, Rhopalosiphum maidus (Homoptera: Aphididae), under four different elevated temperature and CO2 combinations. Journal of Economic Entomology. 107:1411-1418.
Zhang, C., Wong, A., Zhang, Y., Ni, X., Li, X. 2014. Common and unique cis-acting elements mediate xanthotoxin and flavone induction of the generalist P450 CYP321A1. Scientific Reports. 4:6490.
Fountain, J.C., Scully, B.T., Ni, X., Kemerait, R.C., Lee, R.D., Chen, Z., Guo, B. 2014. Environmental influences on maize-Aspergillus flavus interactions and aflatoxin production. Frontiers in Microbiology. doi: 10.3389/fmicb.2014.00040.
Harris-Shultz, K.R., Ni, X., Wang, H., Knoll, J.E., Anderson, W.F. 2015. Use of benzimidazole agar plates to assess fall armyworm (Lepidoptera: Noctuidae) feeding on excised maize and sorghum leaves. Florida Entomologist. 98(1):394-397.
Cottrell, T.E., Wood, B.W., Paulsen, C.M., Ruberson, J.R., Ni, X. 2015. Distribution of the black pecan aphid on pecan leaf surfaces: an overview. Acta Horticulturae. 1070:159-165.
Harris-Shultz, K.R., Ni, X., Anderson, W.F., Knoll, J.E. 2015. Evaluation of whorl damage by fall armyworm (Lepidoptera:Noctuidae) on field and greenhouse grown sweet sorghum plants. Journal of Entomological Science. 50(1):14-27.
Ni, X., Wilson, J.P., Toews, M.D., Buntin, G., Lee, R., Li, X., Lei, Z., He, K., Xu, W., Li, X., Huffaker, A., Schmelz, E.A. 2014. Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre-harvest corn fields to improve management tactics. Insect Science. 21(5):572-583.
Xu, L., Ni, X., Wang, Z., He, K. 2014. Effects of photoperiod and temperature on diapause induction in Conogethes punctiferalis (Lepidoptera: Pyralidae). Insect Science. 21(5):556-563.