Evaluating Teosinte Introgressions in a B73 Background for Gray Leaf Spot and Southern Leaf Blight Resistance.

Gray Leaf Spot [(GLS), causal agent Cercospora zeae-maydis] and Southern Leaf Blight [(SLB), causal agent Cochliobolus heterostrophus] are two important maize diseases in the United States.  Current control methods for SLB and GLS include using crop rotation, conventional tillage, and resistant cultivars for which breeders are constantly mining for novel resistance alleles. Teosinte (Zea mays ssp. Parviglumis) offers a good source of potentially novel resistance alleles as it is a wild progenitor and easily forms hybrids with maize. To investigate the potential use of teosinte as a source for disease resistance, 775 teosinte near isogenic lines (NILs), developed by Sherry Flint-Garcia, USDA-ARS; Columbia, MO were evaluated. The NILs were developed from ten different teosinte accessions using B73 as a recurrent parent for four generations of backcrossing followed by two generations of selfing, forming BC₄S₂ populations. The BC₄S₂ populations were then genotyped using 728 informative single nucleotide polymorphisms (SNP) markers. SLB disease evaluations were conducted on eight of the ten NIL populations in 2009 and all ten NIL populations in 2010 in Clayton, NC. GLS disease evaluations were conducted on eight of the ten populations in 2009 and nine NIL populations in 2010 in Andrews, NC.  Joint mapping identified teosinte introgressions significantly associated with SLB and GLS resistance respectively. For SLB, selections were made in bins 2.04, 3.04, 3.05, and 8.05, yielding 38 NIL lines. For GLS, selections were made in bins 2.04, 3.06, 4.07, 5.03, 8.06, and 9.03, yielding 41 NIL lines. In order to confirm that these introgressions carried disease resistance QTL and to further characterize their effects, NIL lines carrying these introgressions were backcrossed to B73 to produce F_2:3 families for each cross. The F_2:3 families have been and will be evaluated for each respective disease to determine whether the targeted introgressions are indeed associated with disease resistance.