Adjustment of inoculum levels for the evaluation of carrot genotypes resistance to Meloidogyne incognita

ABSTRACT One of the main phytopathogens that cause enormous economic losses in several agricultural species, including carrots, are the root-knot nematodes belonging to the genus Meloidogyne. Thus, in order to identify the best population level for inoculum of the root-knot nematode (Meloidogyne incognita) for maximum expression of symptoms of this nematode attack on carrots, an experiment was carried out to evaluate the carrot cultivar Brasília (CBR) and the population Pop-750 (CRO). The experiment was carried out in a greenhouse at Embrapa Vegetable, Brasília-DF, in 5 L pots, with six replications, in a 4x2 factorial scheme in a completely randomized design, in the dosages of 0, 1, 5 and 10 thousand eggs and occasional juveniles of 2nd stage (E+J2R). ‘Rutgers’ susceptible tomato cultivar was used as control to verify inoculum efficiency. Inoculation was carried out 30 days after sowing and evaluation 60 days after inoculation. Gall index (GI), egg mass index (EMI), number of eggs plus occasional second stage juveniles per gram of root (E+J2R) and reproduction factor (RF) were performed. There were differences between genotypes and between inoculum levels for all variables evaluated. For CRO, inoculum levels of M. incognita from 1,000 E+J2 the plants already manifested symptoms and changes in all evaluated variables, with ideal levels around 5 to 7 thousand E+J2R, above 7 thousand E+J2R nematode multiplication to express symptoms decreased. For CBR the response variables E+J2 at root and RF inoculum levels close to 5 thousand E+J2R also present the best results, but when the characterization is based on the evaluation of GI and EMI, suitable inoculum levels would be close to 9 and 12 thousand E+J2R.