Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/22/1999
Publication Date: N/A
Interpretive Summary: Nematodes are microscopic worms that live in the soil. They can be devastating to certain crops because of the damage they cause while feeding on roots. Some plants have natural resistance to nematodes, and plant breeders have tried to develop varieties of important crops that a re nematode resistant. Cotton breeders have had some success, but the costs of developing nematode-resistant cotton varieties has been a serious obstacle. There need to be better ways developed for assessing which plants are nematode resistant and which are not. We have used modern techniques of molecular biology in studies with cotton to try to determine what in the plant makes it resistant to nematode damage. In studies with cotton, we have been successful in isolating fragments of DNA (the genetic blueprint of the plant) that tell whether or not the plant will be nematode resistant. These studies will be important in ultimately developing varieties of cotton that will not be damaged by nematodes when grown on American farms.
Technical Abstract: The root-knot nematode not only seriously impairs cotton roots but also significantly increases the incidence and severity of Fusarium wilt. To tag, map and clone the root-knot nematode resistant gene (RNR), several approaches have been used. First, we developed ten pairs of DNA pools from nearly-isogenic lines (NILs) for the RNR and used as templates in PCR analysis of the NILs. A total of 700 random decamer primers were screened from which 6 DNA fragments showing apparent difference between the susceptible and resistant lines were identified; one of them is present in all resistant lines but not in the susceptible lines. This DNA fragment was shown single-copy in the cotton genome by Southern analysis. Second, a partial BAC library (2.3 genome coverages) was previously generated from the G. hirsutum TAMCOT. The library was screened using the cloned sugar beet cyst nematode resistant gene Hs1pro-1 cDNA as a probe and two positive eBACs were isolated. Third, studies have demonstrated that some domains of the genes resistant to nematodes, bacteria, fungi, and viruses are highly conserved at the amino acide sequence level among a variety of plant species. One 500 bp and one 700 bp bands were obtained and cloned. Three random clones from the 500 bp band were sequenced. The results showed that the nucleotide sequences of these clones have similarities of 61-63 percent to the soybean disease resistance protein homolog genes, Nicotiana glutinosa virus resistance gene and the Arabidopsis downy mildew resistance gene. To determine the relationships of these DNA markers and clones with the RNR genes, three mapping populations are being developed. To clone the RNR genes by map-based cloning, a large-insert BAC library is being developed from the Auburn 623.