Quantitative Trait Loci for Antibiosis Resistance to Corn Earworm in Soybean

bean pests including the soybean looper (Pseudoplusia includens Walker) (All et al., 1989). In more than 25 yr since the discovery of soybean [Glycine max There are several reasons for the difficulty experi(L.) Merr.] resistance to defoliating insects, attempts to introgress enced in breeding for PRI in soybean. Resistant germthis trait into elite germplasm have been relatively unsuccessful. Resisplasm is of low agronomic quality. Insect resistance is tance to defoliating insects in soybean is expressed as a combination of antibiosis (toxicity) and antixenosis (nonpreference). Both of these inherited quantitatively in all three resistant PIs (Sisson resistance modes are inherited quantitatively in soybean. The objecet al., 1976; Luedders and Dickerson, 1977; Rufener et tives of this study were (i) to use restriction fragment length polymoral., 1989; Kenty et al., 1996), making full introgression phism (RFLP) maps to identify quantitative trait loci (QTLs) in soydifficult and increasing the potential for inferior yield bean for antibiosis against corn earworm (CEW) (Helicoverpa zea through linkage drag (Zeven et al., 1983; Young and Boddie), (ii) to determine the relative magnitude, gene action, and Tanksley, 1989). Resistance in these PIs is expressed genomic locations of these QTLs, and (iii) to compare them to prethrough two distinct mechanisms; antibiosis (Painter, viously detected soybean antixenosis QTLs. Restriction fragment 1951; Lambert and Kilen, 1984a) and antixenosis (or length polymorphism maps were constructed in three soybean F2 nonpreference) (Clark et al., 1972; Kogan and Ortman, populations segregating for antibiosis against CEW: ‘Cobb’ 3 1978). Antibiosis describes insect resistance in which PI171451, Cobb 3 PI227687, and Cobb 3 PI229358. Antibiosis was feeding on the plant results in mortality or disruption measured as larval weight gain in a detached leaf assay. The RFLP data were associated with insect bioassay data to detect QTLs for of growth, development, or physiology in the insect. antibiosis in each cross. Variance component heritability estimates Antixenosis, or nonpreference, describes resistance in for antibiosis in the three crosses were 54, 42, and 62% in Cobb 3 which the insect is either repelled from or not attracted PI171451, Cobb 3 PI227687, and Cobb 3 PI229358, respectively. An to its normal host plant. Antibiosis and antixenosis can antibiosis QTL on Linkage Group (LG) M was detected in both be assayed separately, although their effects may overCobb 3 PI171451 and Cobb 3 PI229358 (R2 values of 28 and 22%, lap (i.e., an antibiotic chemical may also repel). Soybean respectively). An antixenosis QTL was also significant at this location breeding programs which have worked with PRI have in the same two crosses. This was the only insect-resistance QTL that primarily selected lines based on assays for only one was detected for both antibiosis and antixenosis. Antibiosis QTLs of the two resistance mechanisms, perhaps under the were also detected on LGs F and B2 in Cobb 3 PI227687 (R2 5 33 assumption that they are genetically indistinct. Howand 12%, respectively), and LGs G and J in Cobb 3 PI229358 (R2 5 ever, the genetic independence of antibiosis and anti19% for each). Antibiosis was conditioned by the PI (resistant parent) allele at the QTLs on LGs G, M, and B2, whereas the susceptible xenosis in PRI has been suggested for some time parent, Cobb, provided antibiosis alleles at the QTLs on LGs F and J. (Painter, 1951; Manglitz and Danielson, 1994). Through the detection of QTLs contributing to antibiosis against defoliating insects in soybean and comparison of such QTLs to those previously detected for soybean antiP resistance to insects (PRI) has been a diffixenosis (Rector et al., 1998, 1999), we will attempt to cult trait for soybean breeders to efficiently introshow that the failure of efficacious introgression of PRI gress into elite cultivars. In more than 25 yr since high into soybean cultivars may be due in part to the lack levels of PRI were discovered in the soybean plant introof selection for both resistance components. ductions PI171451, PI227687, and PI229358 (Van Duyn Quantitative traits can be dissected into their individet al., 1971), only three soybean cultivars have been ual Mendelian components by statistically associating released with these PIs in their parentage (Bowers, 1990; their inheritance with that of markers on a genetic map Hartwig et al., 1990, 1994). None of these cultivars com(Thoday, 1961; Paterson et al., 1988). The advent of bines high levels of PRI with competitive yields and DNA marker technology in genetic mapping (Botstein none is popular among soybean growers today. Insect et al., 1980; Williams et al., 1990; Akkaya et al., 1992; Vos resistance in these PIs has been demonstrated against et al., 1995) has allowed the construction of saturated a number of defoliating insect species (Luedders and genetic maps in many crop species (O’Brien, 1993) inDickerson, 1977; Lambert and Kilen, 1984a; All et al., cluding soybean (Shoemaker and Specht, 1995; Keim 1989) including the corn earworm, a common pest of et al., 1997; Cregan et al., 1999), and the identification soybean in the southeastern USA. Resistance against of QTLs for a variety of agronomically important traits CEW has been closely correlated with other major soyincluding CEW antixenosis resistance in soybean (Rector et al., 1998, 1999). Molecular markers have also been B.G. Rector, USDA ARS, Insect Biology and Population Management Research Lab, P.O. Box 748, Tifton, GA 31793; J.N. All, Dep. Abbreviations: AFLP, amplified fragment length polymorphism; of Entomology, Univ. of Georgia, Athens, GA 30602-2603; W.A. CEW, corn earworm; cM, centiMorgan; LG, linkage group; LOD, Parrott and H.R. Boerma, Dep. of Crop and Soil Sciences, Univ. of logarithm of the odds; PI, plant introduction; PRI, plant resistance Georgia, Athens, GA 30602-7272. Received 16 Nov. 1998. *Correto insects; QTL, quantitative trait locus; RFLP, restriction fragment sponding author ([email protected]). length polymorphism; SSR, simple sequence repeat; USDA/ISU, United States Department of Agriculture/Iowa State Univ. Published in Crop Sci. 40:233–238 (2000).