Quantification of damage and yield losses caused by Root-knot nematode in lettuce in Brazil

ABSTRACT The objective of this work was to quantify damage and yield losses in lettuce parasitized by Meloidogyne javanica, as well as the growth characteristics of naturally cultivated field plants infested by this pathogen. The experimental area consisted of four seedbeds of 10.0x1.60 m cultivated with 160 plants in each, totaling 640 plants. The damages and yield loss were quantified in four evaluations (Ev1, Ev2, Ev3, and Ev4), with each evaluation corresponding to a cultivation cycle. The four plantings were made in the consecutive form. The fresh mass weight and dry mass weight (FMW and DMW, respectively), gall number (GN), and final population of the nematodes (FP) were evaluated. The population increase of M. javanica caused a reduction in the FMW and DMW in all evaluations. In Ev1 and Ev2, 100% of the plants were commercialized. In Ev3 and Ev4, 7% and 65% of the plants, respectively, could not be commercialized. The Ev4 was completely unviable since the produce had losses of U$ 7.42; U$ 23.19 and U$ 1,484.10 for the cultivation of 640; 2,000 and 128,000 plants, respectively. The economic threshold in Ev4 was 10,151 nematodes/plant or 109 galls/plant.