Characterization of a novel tomato mutant resistant to the weedy parasites Orobanche and Phelipanche spp.

Orobanche and Phelipanche, commonly known as broomrape, are dicotyledonous holoparasitic flowering plants that cause heavy economic losses in a wide variety of plant species. Breeding for Orobanche resistance is still one of the most effective management strategies for this weed. However, previous efforts to find broomrape-resistant tomato (Solanum lycopersicon) genotypes have been unsuccessful. Here, we report on the isolation and characterization of a fast-neutron-mutagenized M-82 tomato mutant, Sl-ORT1. The Sl-ORT1 mutant showed resistance to Phelipanche aegyptiaca as compared to cultivar M-82; segregation analysis suggested a single recessive ort1 allele. Sl-ORT1 broomrape resistance was reflected in a lower number of broomrapes per plant, reduced P. aegyptiaca fresh weight per plant, and the absence of broomrape's negative effect on plant host growth and yield. Sl-ORT1 was shown to be resistant to high concentrations of P. aegyptiaca seeds, and to another three broomrape species: Phelipanche ramosa, Orobanche cernua, and Orobanche crenata. Grafting experiments demonstrated that roots, rather than shoots, are necessary for Sl-ORT1 broomrape resistance. In addition, Sl-ORT1 was shown to be resistant to broomrape under field conditions. Since yield parameters are slightly affected by the mutation, this resistance gene should be introduced into tomato varieties with different genetic backgrounds; this newly identified Orobanche-resistant mutant may be further utilized in breeding programs for Orobanche resistance.