Resumen de Population dynamics of Meloidogyne spp. on tomato and cucumber and biologically-based management strategies
The general objective of the thesis was to determinate the population dynamics of Meloidogyne on tomato and cucumber, the yield losses caused by the nematode and the effect of biologically-based management strategies to reduce the nematode population growth rate and the damage that cause to the crop. The specific objectives and the main results are: i) To elaborate phenology models of Meloidogyne in cucurbit crops. The thermal requirements of M. incognita and M. javanica on cucumber, zucchini-squash were similar, but different than watermelon. On watermelon, thermal requirements of M. incognita and M. javanica to complete the life cycle differed. ii) To characterize the population dynamics of M. incognita on cucumber and tomato and the yield losses caused by the nematode. The population growth rate of M. incognita on cucumber was higher in summer-autumn than spring-summer, but the tolerance limit and the minimum relative yield were similar between cropping periods. On tomato, population growth rate on the resistant cultivar was lower than the susceptible. The tolerance limit was similar between cultivars, but the minimum relative production was higher on the resistant. The population growth rate on the resistant cultivar increased progressively each year of repeated cultivation. The evolution of the parameters of the nematode population along years allows the early detection of the selection of virulence. iii) To characterize the effect of the hybrid rootstock RS841 on the population dynamics of M. incognita and the cucumber production in a plàstic greenhouse. The population growth rate of the nematode on grafted cucumber was higher than the ungafted, without any differences in the tolerance limit and the minimum relative yield. In our conditions, the rootstock RS841 is not resistance neither tolerant. iv) To detect fungal egg parasites of Meloidogyne vegetable production systems. Forty sites were sampled at the end of the cropping cycle, 30 under integrated and ten under organic production. Fungal egg parasites of Meloidogyne were detected in all organic sites and in the majority of the integrated. The level of parasitism was higher than 40% in some of them. Pochonia chlamydosporia, Fusarium sp. and Plectosphaerella cucumerina, were the most frequented fungi, but only the relative frequency of P. chlamydosporia was positively related to the percentage of parasitism in both production systems. v) To characterize suppressive soils to Meloidogyne spp. in organic horticulture. The fluctuation of Meloidogyne population density was carried out, and the fungal egg parasites in two organic production sites under greenhouse. Moreover, pot experiments were carried out to certify the soil supressiveness of both soils. Concurrently, genetic microbial profiles were obtained by and compared with a non-suppressive soil by DGGE, and were compared with a non-suppressive soil. Furthermore, genetic patterns differentiated suppressive from non-suppressive soils. vi) To determine the effect of the vegetal resistance and the application of Bioact WG (Purpureocillium lilacinum strain 251) on Meloidogyne incognita in a tomatocucumber rotation. Plant resistance was the only factor able to suppress nematode densities, disease severity and yield losses, without any effect of BioAct WG. However, in vitro experiments, the fungus showed high capacity of control. Environmental factors during the crop, such as, the composition of the formulation, and/or physicochemical soil characteristics would have affected its activity.
