Resistant tomato cultivars are an important tool to control Meloidogyne spp., which cause the highest yield losses attributed to plant-parasitic nematodes. However, the repeated cultivation of Mi resistant cultivars can select virulent populations. In the present study, the susceptible tomato cv. Durinta and the resistant cv. Monika were cultivated from March to July in a plastic greenhouse for 3 years to determine the maximum multiplication rate, maximum nematode density, equilibrium density, relative susceptibility and population growth rate of M. incognita; these were used as proxy indicators of virulence and yield losses. The values of population dynamics and growth rate on the resistant tomato increased year by year and were higher when it was repeatedly cultivated in the same plot compared to when it was alternated with the susceptible cultivar and the level of resistance decreased from very to moderately resistant. The relationship between the nematode density at transplanting (Pi) and the relative yield of tomato fitted to the Seinhorst damage model for susceptible, but not resistant, cultivars. The tolerance limit and the relative minimum yield were 2–4 J2 per 250 cm3 of soil and 0.44–0.48, respectively. The tomato yield did not differ between cultivars at low Pi, but it did at higher Pi values, at which the resistant yielded 50% more than the susceptible. This study demonstrates the utility of population dynamics parameters for the early detection of selection for virulence in Meloidogyne spp., and that three consecutive years were not sufficient to select for a completely virulent population.
Giné, A.; López-Gómez, M.; Vela, M.; Ornat, C.; Talavera, M.; Sorribas, F.; Verdejo, S. Plant pathology Vol. 63, num. 6, p. 1446-1453 DOI: 10.1111/ppa.12217 Data de publicació: 2014-12-01 Article en revista
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.
In annual plants affected by in¿orescence-invading smut pathogens, avoidance of infection is crucial, while in the event
of infection, the existence of different degrees of tolerance could also affect the interaction dynamics. Two experiments
were performed with Digitaria sanguinalis spikelets vacuum inoculated with ustilospores of Ustilago syntherismae. In
the ¿rst experiment, they were sown in pots and mature plants were checked to detect internal hyphae. Observations
revealed the presence of symptomless mycelium in a few plants. In the second experiment the spikelets, from two
different lots, were grown in a chamber. The objective was to explore the importance of two factors in the degree of
seedling infection, one genotypic – type of germination (TG; radicular or coleoptilar) and one environmental – 48 h
dark treatment (DT) applied just after germination. Analysis of the infection frequency showed that all the main effects
(seed lot origin, TG and DT) were signi¿cant, while interactions were not. For TG, the estimated least square mean
infection percentages were 66% for radicular germination and 46% for coleoptilar germination. Darkness increased
seedling infection by 25%
Cortada, L.; Sorribas, F.; Ornat, C.; Kaloshian, I.; Verdejo-Lucas, S. Plant pathology Vol. 57, num. 6, p. 1125-1135 DOI: 10.1111/j.1365-3059.2008.01906.x Data de publicació: 2008-12 Article en revista