Several studies were carried out to determine (i) thermal requirements for development, egg production and emergence of juveniles, and completion of the life cycle of Meloidogyne incognita and Meloidogyne javanica on cucumber, (ii) the maximum multiplication rate and the equilibrium density of root-knot nematodes on cucumber and yield losses in pot and plastic greenhouse experiments, and (iii) the relationships between relative leaf chlorophyll content (RLCC) and relative cucumber dry top weight biomass (RDTWB) in relation to increasing nematode densities at planting (P-i) in pot experiments. Thermal requirements of M.incognita and M.javanica on cucumber did not differ, irrespective of the biological stage. In the pot experiments, M.javanica completed one generation. The maximum multiplication rate (a) was 833, and the equilibrium density (E) varied according to the effective inoculum densities. The relationship between RDTWB and P-i fitted the Seinhorst damage function model. The RLCC value at 40 or 50days post-inoculation also fitted the damage model and was related to RDTWB. In greenhouse experiments, conducted from 2009 to 2012, M.incognita completed three generations. The values for a and E were 1147 and 625second stage juveniles (J2) per 250cm(3) soil, respectively. The tolerance limit was below zero, and the minimum relative yield ranged from 012 to 034.Postprint (published version

4 5Experiments were conducted to determine the effectiveness and profitability of the Mi-6 resistance gene on tomato in suppressing populations of Meloidogyne javanica in a plastic-7 house with a natural infestation of the nematode. Experiments were also conducted to test 8 for virulence and durability of the resistance. Monika (Mi-gene resistant) and Durinta 9 (susceptible) tomato cultivars were cropped for three consecutive seasons in non-fumigated 10 or in soil fumigated with methyl bromide at 75 g m -2 and at a cost of 2.44 euros m -2 . 11

A population of Meloidogyne javanica virulent to Mi-gene in tomato was identified in Spain. It reproduced similarly on resistant and susceptible tomato cultivars in the greenhouse, microplots, and in the field. In monoxenic cultures, reproduction of the virulent M. javanica was higher than that of an avirulent population on resistant but not on susceptible tomatoes. The virulent population suppressed tomato yield of both resistant and susceptible tomatoes by 29% in microplots. Initial population density (Pi) was inversely correlated with Pf (final population density)/Pi on both resistant and susceptible tomatoes in the field. A negative correlation was found between Pi and tomato yield for the susceptible but not for the resistant cultivar.

Field trials were conducted in a plastic house artificially infested with an avirulent population of Meloidogyne javanica to determine the durability of the resistance mediated by the Mi gene in tomato rootstocks after repeated cultivation for three consecutive years. Treatments included an experimental rootstock cv. PG76 (Solanum lycopersicum · Solanum sp.), a commercial rootstock cv. Brigeor (S. lycopersicum · S. habrochaites), a resistant tomato cv. Monika (S. lycopersicum), and a susceptible cv. Durinta (S. lycopersicum). Based on the reproduction index (RI: number of eggs per g root on the resistant cultivar divided by number of eggs per g root on the susceptible cultivar · 100), rootstock cv. PG76 responded as highly resistant (RI ¼ 7%) after the first cropping cycle (3AE4 nematode generations), showed intermediated resistance (RI ¼ 33%) after the second cropping cycle (3AE3 generations), and was fully susceptible (RI ¼ 94%) after the third cycle (3AE3 generations). In contrast, rootstock cv. Brigeor and resistant cv. Monika retained intermediate resistance levels (RI ¼ 41 and 25%, respectively) after the third cropping cycle. Virulent nematode populations were rapidly selected from an avirulent one after repeated cultivation of resistant tomatoes under field conditions. Bioassays conducted under controlled conditions confirmed that selection for virulence occurred more rapidly in plots with cv. PG76 followed by Brigeor and Monika. The nematode population in the field not exposed to Mi resistance remained avirulent to Mi genotypes. The genetic background of the resistant rootstocks and the frequency of cropping were critical factors for the appearance of virulent nematode populations. Irrespective of nematode infection, all resistant tomatoes yielded more than the susceptible cultivar.

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