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Progress in genetics and mapping for resistance in soybean [Glycine max (L.) Merrill] to cyst nematode (Heterodera glycines Ichinohe).

Prakash R. Arelli1, Brian W. Diers2, Vergel C. Concibido3 and Lawrence D. Young4

USDA-ARS-MSA-CG & PRU, Jackson, TN 38301, USA. Email parelli@ars.usda.go
Dept. of Crop Sciences, University of Illinois, Urbana, IL 61801, USA. Email
Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167, USA. Email
USDA-ARS-MSA-CG & PRU, Stoneville, MS 28776, USA. Email


Soybean [Glycine max (L.) Merrill] seed is a major source of protein for animal feed and oil for human consumption. It supplies approximately 65% of the world’s protein meal and 25% of the world’s edible oils. Worldwide, soybean cyst nematode (SCN: Heterodera glycines Ichinohe) is the most destructive pest on soybean crops. The annual yield losses due to SCN in 2002 are estimated to be nearly 9 million metric tons (2 Billion USD). Resistant cultivars reduce losses to SCN and are most cost effective and environmentally safe. Five major genes for resistance are designated and include rhg1, rhg2, rhg3, Rhg4 and Rhg5 from two different sources Peking and PI 88788. Widespread use of these resistance genes caused major shifts in nematode populations and produced more virulent types. Broad based resistance in soybean will reduce nematode shifts. Breeding for SCN resistance is tedious, time-consuming and inefficient. Genetic mapping and marker-assisted selection will improve the efficiency and provide durable resistance. Molecular markers have mapped several major resistance quantitative trait loci in soybean germplasm including rhg1, Rhg4 and Rhg5. Predominantly, QTL for SCN resistance are mapped to linkage Groups A, G and J. Additional sources of resistance have been reported. Unique QTL for SCN resistance are uncovered in diverse lines. These ongoing efforts should reduce yield losses in soybean to SCN. Progress will be discussed.

Media summary

Worldwide, soybean cyst nematode is the most destructive root-parasite on soybean crop. Genetic technologies will reduce yield losses caused by cyst nematode.


Gene pyramiding, Syncytia, Plant Introductions.


Worldwide, soybean seed is a major source of protein for animal feed and oil for human consumption. It supplies approximately 65% protein meal and 25% of the edible oil (Golbitz 2001). World soybean production in 2002 was 185 million metric tons. Diseases have suppressed soybean yield, especially soybean cyst nematode (SCN) continue to cause significant yield losses. Most recent estimates for SCN indicate losses of nearly 9 million metric tons worldwide in 1998 and 7.6 million metric tons in the USA (Wrather et al. 2003). Soybean cyst nematode causes yield reductions by feeding on plant nutrients, retarding root growth, and inhibiting Bradyrhizobium nodulation (Riggs and Schmidt 1987).

Primarily, genetic resistance in cultivars reduce yield losses to SCN. Development of productive cultivars with SCN resistance is a major goal of soybean breeding programs. These efforts are providing cultivars that may yield up to 56% more than susceptible cultivars in infested fields (Young and Hartwig 1988; Wheeler et al. 1997). Soybean growers in the USA have increased their profits by 400 million dollars merely from growing the resistant cultivar Forrest (Bradley and Duffy 1982).

Genetics of resistance

In soybean, inheritance of resistance to SCN is quantitative and complex. It involves three to four major genes and several minor genes (Diers and Arelli 1999). Caldwell et al. (1960) were the first to report that the inheritance of resistance to SCN in cv. Peking, an introduction from China, is conditioned by three recessive genes rhg1, rhg2 and rhg3. A fourth resistance gene Rhg4,is closely linked to the I locus which controls seed coat color, was reported by Matson and Williams (1965). A dominant gene, Rhg5 was identified in Plant Introduction (PI) 88788, and provides resistance to SCN populations found in MO, USA (Arelli et al. 1992; Arelli 1994). Further research has identified several common resistance genes among several PIs and several others that are different (Arelli and Anand 1988; Anand and Arelli 1989; Arelli et al. 1989; Young and Kilen 1994). In more recent studies, several new genes have been identified but have not been designated due to difficulties involved in conducting tests for allelism.

Mapping and marker technology

Recent genetic marker technology in soybean has facilitated the identification, localization, and characterization of QTL associated with SCN resistance. Weisemann et al. (1992) used molecular markers to map SCN resistance gene in cv. Peking. Two molecular markers, pbLT24 and pbLT65 were found to be associated with the SCN resistance gene Rhg4 on Linkage Group (LG) A2. Concibido et al. (1994) found three RFLP markers A85, B32 and K69 associated with SCN resistance in PI 209332. These were located on LGs A, J and G, respectively. Several studies confirmed SCN resistance on LG A2 (Mahalingam and Skorupska 1995; Chang et al. 1997; Webb et al., 1995; Cregan et al. 1999a). Recently, simple sequence repeats (SSRs) have mapped close to rhg1 on LG G with SSR309 (Mudge et al. 1997; Cregan et al. 1999b). However, there are some inconsistencies in reports. Qui et al. (1999) and Vierling et al. (1996) have reported QTL on different locations. Most recently, Meksem et al. (2001) confirmed the importance of both genes rhg1 and Rhg4 and proposed a bigenic model in cv. Forrest for resistance to the SCN (PA3) population.

Current mapping efforts for SCN resistance include Yue et al. (2001a; 2001b) and Schuster et al., (2001). New LGs Dla , D2 and E were identified in PIs 89772 and 438489B. Mapping in Glycine soja ((PI 468916) has identified a new major QTL region (near Satt 288) on LG G (Wang et al., 2001). Glover et al. (2004, in press) confirmed a QTL on LG J in Near isogenic line populations from PI 88788 and designated as cq SCN-003. Two research groups using positional cloning claimed to have cloned and patented rhg1 and Rhg4 candidate alleles (Hauge et al. 2001; Meksem et al. 2001). Their use in marker assisted selection (MAS) programs is an infringement of the patents. These legal issues compel researchers to identify new sources of SCN resistance, and seek new research directions. Most recently, Lu et al. (2003) reported new QTL in PI 467312 for nematode populations PA5 and PA14. These need to be confirmed.

Resistance to emerging nematode isolates or races that are more aggressive in virulence

There are over a hundred sources of resistance in G. max to the soybean cyst nematode populations (Arelli et al. 2000). Early searches identified sources of resistance in cv. Peking, PI 90763, cv. Ilsoy, and PI209332 (Ross and Brim 1957), PI 88788 (Hartwig and Epps 1970), PI 437654 (Anand et al. 1985) that are currently used for developing resistant cultivars. Other sources of resistance to soybean cyst nematode have been identified in the USA (Young 1990; 1995). Cultivar LongKang 792 from PR China was found to have resistance to several nematode populations (Liu et al. 1985). Arelli et al. (1997; 2000) reported 118 lines as having varying levels of resistance to nematodes and identified those that are especially resistant to SCN Races 1 and 2. Of all the sources of resistance, soybean PI 437654 has the most comprehensive resistance (Arelli et al. 1997). Most recently, two nematode populations that reproduce on PI 437654 have been identified (Young 1999) and soybean PI 567516C was found to be resistant to LY1 nematode population (Young 1999).

Cluster analyses

Information on the genetic relationships of the PIs at the molecular level could provide clues for identifying unique sources. In general, genetically unrelated PIs are likely to have fewer resistance genes in common than closely related PIs. Several soybean lines including PIs 507354, 467312, 567516C, 567328, Cloud, and 438503A are found to be unrelated, and therefore may have novel genes for SCN resistance (Diers et al. 1997; Xie et al. 1998; Zhang et al. 1999).


In soybean, resistant cultivars reduce yield losses to SCN. Newly identified genes, unrelated to rhg1 , Rhg4 and Rhg5 will be more effective for durable resistance and will not infringe existing patents. Additional studies are also needed to confirm newly identified QTL for SCN resistance. Phenotyping soybean with several isolates of nematode populations will identify QTL for broader resistance. Selecting QTL with high regression values will improve the efficiency of MAS. Finally, effective management practices will also enhance durable resistance in soybean.


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