Resumen de Meloidogyne species in cucurbit crops: characterization and quantification of the host-parasite relationship
The infection process of Meloidogyne arenaria, M. incognita and M. javanica was compared on zucchini squash, cucumber, melon, pumpkin and watermelon in a growth chamber. All cucurbits were susceptible to the three isolates although M. javanica showed higher invasion rates, faster development and egg production than M. arenaria. Differences among cucurbits were primarily due to root invasion rates and formation of egg masses. Cucumber and melon were better hosts for nematode invasion and reproduction than zucchini followed by watermelon. The suitability of five zucchini, three cucumber, eight watermelon and seven cucurbit rootstocks genotypes to M. incognita (MiPM26) and M. javanica (Mj05) was determined. The number of egg masses did not differ among the genotypes of zucchini or cucumber, but the reproduction factor did slightly. A marked differenced was observed between the nematode isolates; M. incognita MiPM26 showed lower reproduction traits than M. javanica Mj05, and, in zucchini, only 22% of the females of M. incognita produced egg masses compared to 95% of the M. javanica females. In cucumber, 86% of the M. incognita and 99% of the M. javanica females produced egg masses. Also, populations of the three Meloidogyne species were tested on zucchini and cucumber. A greater parasitic variation was observed on zucchini than cucumber. Zucchini responded as a poor host for M. incognita MiPM26, MiAL09 and MiAL48, but as a good host for MiAL10 and MiAL15. Cucumber was a good host for all the tested populations. The watermelon cultivars did not differ in host status within each nematode isolate, supporting lower reproduction than the cucurbit rootstocks. The top development of field-grown non-grafted watermelon plants was significantly delayed in plots where the nematodes were detected at planting. However, no differences were observed in plots with grafted plants. In plots with nematodes, non-grafted and Titan-grafted plants had similar yield, which was higher than that of RS841-grafted plants. The Titan-Sugar Baby combination was tolerant to M. javanica. The relationship between the Pi and final (Pf) population densities of M. javanica in response to increasing initial inoculum levels and the effect on yield in zucchini cv. Amalthee were determined using a geometric series of 12 Pi from 0 to 51,200 eggs/100 cm3 of soil. The maximum multiplication rate of the nematode was 425, and the equilibrium density was 701,951 eggs/100 cm3 soil. The relative yield, represented as dry top weight, fitted the Seinhorst damage function model and the minimum relative yield (m) was 0.82 and the tolerance limit (T) was 402 J2/100 cm3 soil. Regression analyses indicated a negative relationship between the Pi and the leaf chlorophyll content, fitting the Seinhorst damage-function model. Zucchini cv. Dyamant was planted in a plastic greenhouse with a range of M. javanica Pi from 0 to 861 J2/100 cm3 soil. The maximum multiplication rate of M. javanica under field conditions was 3,093, and the equilibrium density was 1,485 J2/100 cm3 soil. The relationship between Pi and relative yield, represented as fruit weight, fitted the Seinhorst damage function model and m was 0.48, and T was 0.02 J2/100 cm3 soil. The relationship between the Pi and Pf of M. javanica in response to increasing initial inoculum levels and the effect on yield in watermelon cv. Sugar Baby were determined. The maximum reproduction rate of the nematode was 14, and the equilibrium density 49,400 eggs/100 cm3 of soil. Yield data represented as fresh top weight fitted the Seinhorst damage function, and m was 0.65 and T was 74 eggs/100 cm3 of soil. In the field experiments (2011 and 2012), the maximum reproduction rate was 73 and 70, and the equilibrium density 32 and 35 J2/100 cm3 soil. Yield data, represented as fruit weight, fitted the Seinhorst damage function in 2011 and the m and T values were 0.63 and 20 J2/100 cm3 of soil, respectively
