New approach of rating pathogen-host suitability between (A)-virulent populations of root-knot nematodes and tomato

Suitability of susceptible and resistant tomato cultivars to infestation of (a)-virulent populations of root-knot nematodes has been assessed by considering the amount of sedentary stages into the roots as an additional infestation factor to the reproduction rates. Different tomato-nematode interactions have been studied in strictly standardized glasshouse conditions and infestation assessed by measuring egg masses, eggs, and sedentary stages present in single roots 7 weeks after inoculation with 300 active second stage juveniles (J2). Field nematode avirulent populations and populations selected for virulence were inoculated on susceptible tomato, on tomato carrying the resistance gene Mi.1 in the heterozygous state, and on tomato carrying Mi.1-gene in the homozygous state. Infestation degree of each combination was expressed by means of an index, the Infestation Potential (IP), which integrated all the measured infestation variables. IPs of field populations on susceptible tomato were found to be about 2-fold higher than those of populations selected for virulence. Moreover, IPs of virulent populations on homozygous resistant tomato were lower than those on heterozygous resistant tomato. This kind of approach in determining nematode-tomato suitability can help to predict the impact that virulent root-knot nematode populations may have on resistant tomato cropping.