Southern Leaf Blight (SLB), Northern Leaf Blight (NLB), and Gray Leaf Spot (GLS) caused by Cochliobolus heterostrophus, Setosphaeria turcica, and Cercospora zeae-maydis respectively, are among the most important diseases of corn worldwide. Previously, moderately high and significantly positive genetic correlations between resistance levels to each of these diseases were identified in a panel of 253 diverse maize inbred lines. The goal of this study was to identify loci underlying disease resistance in some of the most multiple disease resistant (MDR) lines by the creation of chromosome segment substitution line (CSSL) populations in multiple disease susceptible (MDS) backgrounds. Four MDR lines (NC304, NC344, Ki3, NC262) were used as donor parents and two MDS lines (Oh7B, H100) were used as recurrent parents to produce eight BC3F4:5 CSSL populations comprising 1,611 lines in total. Each population was genotyped and assessed for each disease in replicated trials in two environments. Moderate to high heritabilities on an entry mean basis were observed (0.32 to 0.83). Several lines in each population were significantly more resistant than the MDS parental lines for each disease. Multiple quantitative trait loci (QTL) for disease resistance were detected for each disease in most of the populations. Seventeen QTL were associated with variation in resistance to more than one disease (SLB/NLB: 2; SLB/GLS: 7; NLB/GLS: 2 and 6 to all three diseases). For most populations and most disease combinations, significant correlations were observed between disease scores and also between marker effects for each disease. The number of lines that were resistant to more than one disease was significantly higher than would be expected by chance. Using the results from individual QTL analyses, a composite statistic based on Mahalanobis distance (Md) was used to identify joint marker associations with multiple diseases. Across all populations and diseases, 246 markers had significant Md values. However further analysis revealed that most of these associations were due to strong QTL effects on a single disease. Together, these findings reinforce our previous conclusions that loci associated with resistance to different diseases are clustered in the genome more often than would be expected by chance. Nevertheless true MDR loci which have significant effects on more than one disease are still much rarer than loci with single disease effects.

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In this study we mapped the QTL Qgls8 for gray leaf spot (GLS) resistance in maize to a ~130 kb region on chromosome 8 including five predicted genes. In previous work, using near isogenic line (NIL) populations in which segments of the teosinte (Zea mays ssp. parviglumis) genome had been introgressed into the background of the maize line B73, we had identified a QTL on chromosome 8, here called Qgls8, for gray leaf spot (GLS) resistance. We identified alternate teosinte alleles at this QTL, one conferring increased GLS resistance and one increased susceptibility relative to the B73 allele. Using segregating populations derived from NIL parents carrying these contrasting alleles, we were able to delimit the QTL region to a ~130 kb (based on the B73 genome) which encompassed five predicted genes.

Southern Leaf Blight, Northern Leaf Blight, and Gray Leaf Spot, caused by ascomycete fungi, are among the most important foliar diseases of maize worldwide. Previously, disease resistance quantitative trait loci (QTL) for all three diseases were identified in a connected set of chromosome segment substitution line (CSSL) populations designed for the identification of disease resistance QTL. Some QTL for different diseases co-localized, indicating the presence of multiple disease resistance (MDR) QTL. The goal of this study was to perform an independent test of several of the MDR QTL identified to confirm their existence and derive a more precise estimate of allele additive and dominance effects. Twelve F 2:3 family populations were produced, in which selected QTL were segregating in an otherwise uniform genetic background. The populations were assessed for each of the three diseases in replicated trials and genotyped with markers previously associated with disease resistance. Pairwise phenotypic correlations across all the populations for resistance to the three diseases ranged from 0.2 to 0.3 and were all significant at the alpha level of 0.01. Of the 44 QTL tested, 16 were validated (identified at the same genomic location for the same disease or diseases) and several novel QTL/disease associations were found. Two MDR QTL were associated with resistance to all three diseases. This study identifies several potentially important MDR QTL and demonstrates the importance of independently evaluating QTL effects following their initial identification.

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Registration of 'Oklee' Wheat relatively early maturing and produces spikes 1.3 d earlier 'Oklee' is a hard red spring wheat (Triticum aestivum L.) than 2375 and 0.6 d earlier than Oxen (PI 596770), the most (Reg. no. CV-963, PI 634553) developed and released by the widely grown cultivar in Minnesota since the late 1990s. Oklee Minnesota Agricultural Experiment Station in cooperation is a semidwarf cultivar and averages 75 cm, the same height with USDA-ARS in January 2003. It was named after a town as Oxen, and is 3 cm shorter than 2375 in Minnesota trials. in its region of adaptation in northwest Minnesota. Oklee was In 35 Minnesota trials conducted from 1998 through 2002, released on the basis of its high grain yield, high grain volume Oklee yielded 3664 kg ha Ϫ1 compared to 3482 kg ha Ϫ1 for weight, high grain protein content, and early maturity. In addi-2375 and 3825 kg ha Ϫ1 for Oxen. Oklee was evaluated in tion, Oklee has moderate resistance to Fusarium head blight 29 environments in the Uniform Regional Hard Red Spring (FHB, caused primarily by Fusarium graminearum Schwabe). Wheat Nursery in 1998 and 1999 and yielded an average of Oklee was derived from the cross '2375'/SBF0670, made 3456 kg ha Ϫ1 compared to an average of 3470 and 3503 kg by the former Pioneer Hi-Bred spring wheat breeding program ha Ϫ1 produced by the check cultivars, 2375 and Verde (PI in the USA. The cultivar 2375 (PI 601477, syn. Pioneer 2375) 592561, Busch et al., 1996), respectively. Oklee has moderately has the pedigree Olaf//Era/Suqamuxi 68/3/Chris/ND487//Lark strong straw and a lodging rating of 2.3 when scored on a and was widely grown in Minnesota during the mid-1990s due scale of 0 (erect) to 9 (lodged) in 21 environments at which to its moderate resistance to FHB. SBF0670 is an unreleased lodging occurred from 1998 thru 2002. By comparison, the line whose pedigree contains hard red spring lines once promicultivars 2375, Oxen, and Verde had lodging ratings of 3.5, nent in the region including 'Chris' (CItr 13751, Heiner and 2.6, and 2.1, respectively. Johnston, 1967), 'Era' (CItr 13986, Heiner and McVey, 1971), Oklee has moderate resistance to FHB in misted, inoculated and 'Butte'. field nurseries, similar to the resistance of 2375. In 11 FHB The F 2 population producing Oklee was selected for leaf nurseries from 1998 through 2001, Oklee averaged 23.6% disrust (caused by Puccinia triticina Eriks.) and stem rust (caused eased spikelets, 16.7% visually scabby kernels (VSK), and by Puccinia graminis Pers.: Pers.) resistance in a field planting 8.8 mg kg Ϫ1 of the mycotoxin deoxynivalenol (DON). The at St. Paul in 1993. The F 3 generation was advanced by single cultivar 2375 averaged 22.7% diseased spikelets, 17.5% VSK, seed descent in a greenhouse. The selection resulting in Oklee and 9.8 mg kg Ϫ1 DON. In the same trials, the resistant check was selected from a single plant in an F 4 headrow in 1994 and 'BacUp' (PI 596533, Busch et al., 1998) and the susceptible this seed was increased in a winter nursery in Arizona during check ...

Hilliard' (Reg. no. CV-1163, PI 676271), a soft red winter (SRW) wheat (Triticum aestivum L.) developed and tested as VA11W-108 by the Virginia Agricultural Experiment Station, was released in March 2015. Hilliard was derived from the cross '25R47'/'Jamestown'. Hilliard is widely adapted, from Texas to Ontario, Abbreviations: FHB, Fusarium head blight; SRW, soft red winter.