Quantitative Trait Loci Conferring Resistance to Fall Armyworm and Southwestern Corn Borer Leaf Feeding Damage

ern corn borer resistance. Few plant breeders have access to insect rearing facilities, which are necessary to Southwestern corn borer (Diatraea grandiosella Dyar) and fall maximize selection efficiency. Negative traits tend to armyworm [Spodoptera frugiperda (J.E. Smith)] damage ratings were measured on an F2-derived maize (Zea mays L.) population segregatmask genetic gains in resistance at early generations of ing for leaf feeding resistance following artificial infestation with neobackcrossing, and levels of resistance tend to be modernates. Damage ratings for each insect were recorded in replicated ate. Quantitative trait mapping can be used to overcome trials at three locations and used in conjunction with a genetic linkage some of these problems and facilitate manipulation of map to identify quantitative trait loci (QTL) associated with resistance. genetic resistance. Significant QTL and their interactions were estimated by multiple Through a series of separate studies, researchers have interval mapping analysis. Resistance to southwestern corn borer leaf identified QTL associated with southwestern corn borer feeding was fit to a model containing eight QTL and two interactions resistance in inbreds developed from Antigua Group 2 explaining 20% of the phenotypic variation. A model containing seven and Dominican Republic Group 1 germplasm. Resistance QTL and one interaction best fit resistance to fall armyworm leaf feedQTL ranging in number from five to nine were identified ing damage, and it explained approximately 14% of the phenotypic variation. Three QTL located on chromosomes 6, 9, and 10 affect in tropical growing conditions accounting for between leaf feeding damage ratings of both insects with similar effects and 32 and 52% of phenotypic variation in three mapping gene action. Minor interaction effects were observed. The QTL on studies (Bohn et al., 1997; Groh et al., 1998; Khairallah chromosomes 1, 5, and 9 correspond to previously identified regions et al., 1998). A majority of the QTL identified by Bohn affecting resistance to southwestern corn borer. Insect resistance genes et al. (1997) also conferred resistance to sugarcane borer including the mir family of genes located on chromosome 6 and the (Diatraea saccharalis Fabricius). A comparison of these glossy15 locus on chromosome 9 fall within chromosomal regions of separate studies by Bohn et al. (2001) further noted the QTL predicted in this study. This study confirms that resistance to consistent identification of genetic regions on chromofall armyworm and southwestern corn borer involves many of the same somes 5 and 9, and that these regions tended to confer reQTL and candidate genes for insect resistance include the glossy15 sistance to sugarcane borer as well. Willcox et al. (2002) candidate locus on chromosome 9. later identified three QTL regions using the same resistant parent (CML67) and a different susceptible parent. Two of the three QTL coincided with earlier studies. F oliar damage to whorl stage maize plants by fall In all studies, a QTL on chromosome 9 in or near bin 3 armyworm and southwestern corn borer can signifihas been identified. The glossy15 gene is located in this cantly reduce grain yield (Williams and Davis, 1984a). region and is a potential resistance gene for fall armyFirst generation larvae infest plants, causing vascular worm resistance. and leaf tissue damage leading to reduced yield potenIn a study estimating combining ability for fall armytial. Literature documents a significant amount of reworm and southwestern corn borer resistance, Williams search devoted to identifying resistant germplasm and et al. (1989) observed a strong correlation of GCA for identifying mechanisms of resistance to southwestern leaf feeding, larvae weights, and larvae number between corn borer. Insect rearing and artificial infestation techthe two pests. The authors suggested that selection for reniques have also been developed so that uniform selecsistance to one insect pest could improve resistance to tion pressure can be applied (Davis, 1997; Wiseman et al., the other. This study was performed in two locations in 1980). In an attempt to address leaf damage by southMississippi and included Mp704 as an inbred resistant western corn borer, genetic resistance has been identito leaf feeding by southwestern corn borer and fall armyfied, and germplasm lines have been developed (Williams worm (Williams and Davis, 1982). Further studies sugand Davis, 1982, 1984b; Williams et al., 1990; CIMMYT, gested that vegetative phase change, which is controlled 1991). by the glossy15 gene, is a primary mechanism affecting There are several problems, however, with using germresistance to first generation fall armyworm and southplasm lines in a breeding program to enhance southwestwestern corn borer (Williams et al., 1998, 2000). Resistant maize lines completed the transition from the juvenile to USDA-ARS Corn Host Plant Resistance Research Unit, Mississippi adult vegetative stage earlier than susceptible lines. LarState, MS 39762. This paper is a joint contribution of USDA-ARS and the Mississippi Agricultural and Forestry Experiment Station and vae of both southwestern corn borer and fall armyworm is published as journal no. J10582 of the Miss. Agric. and Forestry exhibited reduced weight gain and produced less leaf Exp. Stn. Received 10 Nov. 2004. *Corresponding author (tbrooks@ damage on genotypes that moved from the juvenile to msa-msstate.ars.usda.gov). adult phase earlier. In addition, larvae fed lyophylized Published in Crop Sci. 45:2430–2434 (2005). Crop Breeding, Genetics & Cytology doi:10.2135/cropsci2004.0656 Abbreviations: CIM, composite interval mapping; LOD, log10-likelihood ratio; QTL, quantitative trait locus or loci; SSR, simple sequence © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA repeat. 2430 Published online October 27, 2005