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.

RESUMO: O controle de baratas realizado através da aplicação de inseticidas químicos exerce alta pressão seletiva sobre as populações e introduz substâncias sintéticas no ambiente, motivando a procura por outros métodos de controle, como os fungos entomopatogênicos. Os objetivos deste trabalho foram investigar a patogenicidade do isolado JAB 42 de Aspergillus westerdijkiae a fêmeas e ootecas de Periplaneta americana e demonstrar o mecanismo de ação sobre ootecas. Suspensões contendo 106 a 108 conídios/mL do isolado foram usadas para infectar fêmeas e ootecas. A ação do fungo foi analisada pela mortalidade e outras variáveis, e por microscopia eletrônica de varredura. O isolado JAB 42 de A. westerdijkiae é patogênico a ootecas de P. americana, tendo baixa capacidade de matar fêmeas. Foi observada a adesão, germinação, penetração e extrusão do fungo sobre ootecas da barata.

ABSTRACT: Cockroach control is performed by the application of chemical insecticides which exert high selective pressure on populations and introduces synthetic substances in the environment, motivating the search for other methods of control such as entomopathogenic fungi. The objectives of this study were to investigate the pathogenicity of the JAB 42 Aspergillus westerdijkiae to females and oothecae of Periplaneta americana and to demonstrate its mechanism of action on oothecae. Suspensions containing 106 to 108 conidia/ml were used to infect females and oothecae. Mortality and other variables such as scanning electron microscopy were used to demonstrate the mechanism of action of the fungus. The isolated JAB 42 A. westerdijkiae is pathogenic to oothecae of P. americana, with low capacity to kill females. Adhesion, germination, penetration and extrusion of the fungus on the cockroach oothecae were observed.