ABSTRACT Due to the harmful potential and existence of numerous races of lettuce downy mildew (Bremia lactucae Regel), several countries carry out the monitoring of these races through the use of differential cultivars of lettuce (Lactuca sativa L.) The identification of resistance to other important diseases in these cultivars would be of great value for the lettuce’s breeding, allowing the simultaneous selection for diseases. Among soil pathogens, the most important are the root-knot nematodes (Meloidogyne spp.) due their damage and difficulty of control. Thus, the present work evaluated the resistance of these differential cultivars (C-Set) against the two most important nematode species for the crop, M. javanica and M. incognita. The experiment was conducted in a completely randomized design, with eight replicates and initial population of 1000 eggs and juveniles. The evaluations were performed by the criteria of reproduction factor and reproduction index, 75 d after inoculation. Data were submitted to ANOVA and averages were compared by the Scott-Knott test (p < 0.05). All cultivars are considered susceptible to M. incognita by the reproduction factor, ‘Argelès’, ‘Bedford’, ‘Design’ and ‘Grand Rapids’ are considered as slightly resistant by the reproduction index. However, to M. javanica ‘Argelès’, ‘Kibrille’, ‘Balesta’, ‘Colorado’, ‘Design’, ‘Bartoli’, and ‘NunDm15’ are classified as resistant by the reproduction factor and very resistant by the reproduction index, and can be used as resistance source for simultaneous selection to downy mildew and this species of nematode.

A entrada de agentes fitopatogênicos em novas localidades através de mudas infectadas constitui uma das principais formas de disseminação. Meloidogyne enterolobii é uma espécie de nematoide altamente virulenta que tem causado sérios danos a plantas cultivadas no Brasil. Neste trabalho é relatada a primeira ocorrência de M. enterolobii em mudas de muricizeiro (Byrsonima cydoniifolia), uma planta nativa da Amazônia e em mudas de goiabeira (Psidium guajava), no Estado de Mato Grosso. Com base nos caracteres morfológicos do padrão perineal de fêmeas, região labial dos machos e no fenótipo isoenzimático de esterase, foi confirmado que a espécie encontrada tanto nas mudas de muricizeiro quanto nas de goiabeira é M. enterolobii.

Spreading of plant pathogens through seedlings is one of the main ways of introducing pathogens in places free of these agents. Meloidogyne enterolobii is a highly virulent species of nematode responsible for serious damage to plants grown in Brazil. In this study the occurrence of M. enterolobii on young individuals of muricizeiro (Byrsonima cydoniifolia), a native species of the Amazon forest, is made for the first time together with the first report of the occurrence of this nematode on guava (Psidium guajava) in the State of Mato Grosso, Brazil. Based on morphological characters of the perineal pattern of females, lip region of males and the esterase isoenzyme phenotype, we confirmed that the species found in both of B. cydoniifolia and P. guajava is M. enterolobii.