MOLECULAR MAPPING OF THE PY-1 GENE FOR RESISTANCE TO CORKY ROOT-ROT (PYRENOCHAETA-LYCOPERSICI) IN TOMATO

We report the molecular mapping of the py-1 gene for resistance to cor ky root rot [Pyrenochaeta lycopersici (Schneider and Gerlach)] in toma to using RAPD and RFLP marker analysis. DNA from near-isogenic lines ( NILs) of tomato differing in corky root rot resistance was screened wi th 575 random oligonucleotide primers to detect polymorphic DNAs linke d to py-1. Three primers (OPW-04, OPC-02, OPG-19) revealed polymorphis ms between the NILs. Twelve resistant and eight susceptible DNA pools derived from segregating F-3 families were used to confirm that the RA PD markers were linked to the py-1 gene. Two of the linked amplified f ragments, corresponding to OPW-04 and OPC-02, were subsequently cloned and mapped on the tomato molecular linkage map as RFLPs. These clones were located between TG40 and CT31 on the short arm of chromosome 3. Further analysis with selected RFLP markers showed that 7% (8.8 cM) of chromosome 3 of the resistant line 'Moboglan' was introgressed from t he L. peruvianum donor parent. Three RFLP markers (TG40, TG324, and TG 479) from the introgressed Dart of chromosome 3 were converted to clea ved amplified polymorphism (CAP) markers for use in a polymerase chain reaction (PCR) assay. These PCR markers will allow rapid large-scale screening of tomato populations for corky root rot resistance.