SSR mapping and confirmation of the QTL from PI96354 conditioning soybean resistance to southern root-knot nematode

Root-knot nematodes (Meloidogyne spp.) can cause severe yield loss of soybean [Glycine max (L.) Merr.] in the southern production region of the USA. Planting root-knot nematode-resistant cultivars is the most effective method of preventing yield loss. DNA marker-assisted breeding may accelerate the development of root-knot nematode-resistant cultivars. RFLP markers have previously been used to identify quantitative trait loci (QTLs) conferring resistance to southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] (Mi) in a F_2:3 soybean population created by crossing the resistant PI96354 and the susceptible ’Bossier.’ A major QTL on linkage group (LG) O conditioning 31% of the variation in Mi gall number and a minor QTL on LG-G conditioning 14% of the gall variation were reported. With the development of SSR markers for soybean improvement, a higher level of mapping resolution and semi-automated detection has become possible. The objectives of this research were: (1) to increase the marker density in the genomic regions of the QTLs for Mi resistance on LG-O and LG-G with SSR markers; and (2) to confirm the effect of the QTLs in a second population and a different genetic background. With SSR markers, the QTL on LG-O was flanked by Satt492 and Satt358, and on LG-G by Satt012 and Satt505. Utilizing SSR markers flanking the two QTLs, marker-assisted selection was performed in a second F_2:3 population of PI96354× Bossier. Results confirmed the effectiveness of marker-assisted selection to predict the Mi phenotypes. By screening the BC₂F₂ population of Prichard (3)×G93–9009 we confirmed that selection for the minor QTL on LG-G with flanking SSR markers would enhance the resistance of lines containing the major QTL (which is most-likely Rmi1). Received: 29 September 2000 / Accepted: 17 April 2001     

Breeding Plants for Resistance to Nematodes

Plant breeders and nematologists have developed improved cultivars of important crop species with resistance to plant-parasitic nematodes. The effectiveness of these breeding efforts has depended on the availability of efficient screening procedures, identification of adequate sources of durable resistance, nature of the nematode feeding habit, and knowledge of the inheritance of resistance. These factors determine to a large degree the breeding method and potential success of the research. Systematic searches for nematode resistance have identified resistant germplasm lines within crop species or from related species. When the resistance gene(s) is from related species, incongruity barriers or sterility of the resulting hybrids often must be overcome. In these situations, backcrossing is usually necessary to incorporate the resistance gene(s) and recover the desirable commercial traits of the crop species. If the resistance gene(s) is present within the crop species, the choice of breeding method depends on the inheritance of the resistance, type of screening procedure, and other important breeding objectives for the species. In the future, plant molecular biologists and geneticists will make available novel sources of nematode resistance through incorporation of transgenes from other genera. These efforts will likely require conventional breeding strategies before commercial utilization of an improved resistant cultivar.