Reaction of some tomato cultivars and hybrids to late blight (P-infestans Mont. de Bary)

Late blight (P. infestans Mont. de Bary) is one of the most common diseases of tomato in Serbia and it causes great economical losses. Control of this pathogen with fungicides is not always efficient and satisfactory. The solution is in the growing of less sensitive i.e. resistant cultivars and hybrids of tomato. The programme of breeding of tomato for resistance to late blight in Serbia started in 1980. Tomato genotypes, bearers of Ph-2 gene of resistance to late blight and sensitive genotypes which have good yield and quality were hybridized. New lines and hybrids of tomato were more resistant than their sensitive parents. Testing of lines and F-1 hybrids showed the intermediate type of heredity to late blight. During 2003, in order to test the resistance of these new lines, cultivars and hybrids to P. infestans, we inoculated the plants artificially, in greenhouse conditions. We researched 7 lines and 16 cultivars and tomato hybrids, and tested twenty, six weeks old plants from each genotype. Plants were inoculated with suspension of fungi spores in concentration of 10(5)sporangia/mL. The inoculums were prepared from fungi culture 15 days old, grown on rye and agar on 18 degrees C. After inoculation, plants spent 48 hours on 18 degrees C, in condition of great humidity. The resistance, i.e. sensibility, depending on surface covered with necrotic spots has been evaluated 10 days after inoculation. The results, presented on a scale from I to VI, showed that the tested tomato genotypes could not be considered resistant. Hybrids Zlatni Jubilej F-1 and Luna F-1, cultivar Gruzanski Zlatni and line P3 are in category - very tolerant (I). Middle sensitive (III) were Nada F-1 and Jasenicki Jabucar, while other genotypes were very sensitive. The most sensitive (VI) were cultivars Narvik and Adonis