Characterization of resistant Cucumis germplasm to manage root-knot nematodes Meloidogyne spp.

Plant resistance through grafting susceptible scions onto resistant rootstocks is an effective measure to supress root-knot nematode (RKN) populations and to reduce crop yield losses. However, the reiterative use of specific R genes could select virulent populations for those genes. Cucumis metuliferus is one promising rootstock for melon and cucumber, but there is little information regarding the host suitability to nematode populations from specific production areas, the effect on the population dynamics, the durability of the resistance, the rootstock-scion compatibility and the effect of the nematode on the crop yield quantity and quality. Accordingly, the main objective of this PhD thesis was to evaluate the resistance response of Cucumis metuliferus to Meloidogyne spp. and its compatibility with melon, its resistance durability in crop rotation with Mi1.2 resistant tomato and the effect of the rootstocks and nematode population densities on both tomato and melon yield and fruit quality. The specific objectives were i) To evaluate the host suitability of different accessions of Cucumis metuliferus against (a) virulent Mi1.2 isolates of Meloidogyne spp. and its compatibility with melon. ii) To determine the effect of a three years tomato-melon rotation on the population dynamics of M. incognita, the crop yield (quantity and quality), and the durability of the resistance of both tomato Mi1.2 gene and C. metuliferus R genes. The main conclusions obtained from this work was that C. metuliferus is resistant to the main three common Meloidogyne species including virulent isolates to the Mi1.2 resistant gene. The histopathological studies have shown poorly developed giant cells induced by Meloidogyne javanica in C. metuliferus and necrotic areas surrounding the nematode. M. incognita induce the formation of more giant cells but poorly developed and with less number of nuclei per giant cell in resistant than in susceptible plants. C. metuliferus BGV11135 is a compatible rootstock with cantaloupe and piel de sapo type melons without affecting the melon fruit quality. Grafting melon and tomato onto “C. metuliferus” and “Aligator” rootstocks respectively does not increase the crop yield in non-nematode infested soil. The quality of the fruits produced in grafted plants is within the standards. The spring-summer rotation sequence melon-tomato provides more fruit weight yield than the tomato-melon. In infested soil, grafted melon yields more than the ungrafted irrespective of the season. However, grafted melon is more tolerant and experience less maximum yield losses in spring-summer compared to the summerautumn crop. In addition, some melon fruit quality parameters are affected by the nematode in the summer-autumn crop but not in the spring-summer. The reproduction rate of the nematode is affected by the cropping season, the plant material, the initial population density and the virulence to specific R genes. In melon, the reproduction rate of the nematode in ungrafted plants was higher in the spring crop compared to the resistant plants. However, in summer the reproduction rate was lower due to the high mortality. In tomato, the reproduction rate in grafted plants increased progressively in each crop, being higher than the ungrafted at the end of the third tomato crop of tomato-melon rotation due to virulence selection. Virulence to the Mi1.2 was observed in the “Aligator” rootstock after the first tomato crop, but not in C. metuliferus BGV11135. Thus, alternating these two different resistant species was not enough to prevent virulence selection although the level was reduced after using C. metuliferus. The fitness cost parameters of the virulent Mi1.2 subpopulation in the susceptible tomato and melon were reduced with respect to the avirulent subpopulation after the third grafted tomato crop, but not after the second. Cucumis metuliferus is as excellent rootstock to be included in integrated management strategies for control RKN.