Inoculation methods and conidial densities of Fusarium oxysporum f. sp. radicis lycoperici in tomato

摘要

Fusarium oxysporum f.sp. radicis-lycopersici (Forl) is one of the most destructive necrotrophic pathogens affecting tomato crops,causing considerable field and greenhouse yield losses. The use of resistant cultivars is a safe, non-contaminating and reliablecontrol method to eradicate or mitigate this disease. However, it is still necessary to determine the best inoculum density,sufficient to induce levels of resistance or susceptibility. In this study, inoculum concentrations of 3, 5 and 8 x 10 6 microconidia permL of Forl were evaluated by root immersion and seed spraying in twenty tomato genotypes (Solanum spp.) in a completelyrandomized design. The germplasm was mainly introduced tomato species from the Genetic Resources Program of the Universityof California at Davis, USA. The inoculation was done by immersion of roots and by sprinkling of seeds at the time of sowing. Forthe inoculation by immersion of roots, tomato seedlings of 15 days emergence were used. The wounds were created in root tipsthen they submerged into the each conidial suspension. Finally, they transplanted into the plastic pots in a greenhouse. Regardingthe inoculation by sprinkling of the seed, 20 seeds of each genotype were placed in plastic pots then sprayed with thecorresponding conidial suspension. In both cases, the disease index was calculated. This allowed classifying the genotypes asresistant and susceptible. With the root immersion method all the genotypes evaluated showed susceptible. Significant differenceswere observed (p≤0.01) between genetic materials at different inoculum doses with the inoculation of seeds. This allowedclassification of genotypes Solanum parviflorum LA 1326, Solanum chesmanii f. minor LA1401, Solanum chmielewskii LA1306,Solanum pimpinellifolium LA722, Solanum pimpinellifolium LA2184 as resistant to Forl with disease index of 3, 4, 5, 8 and 12%respectively, at a inoculum concentration of 3x10 6 microconidia per mL. These genotypes could be included in a genetic breedingprogram for resistance to crown and root rot caused by Forl.