MICROPROPAGATION AND IN VITRO RESISTANCE TESTS AGAINST Phytophthora cinnamomi OF MEXICAN-RACE AVOCADO GENOTYPES R. López-Gómez 1 , M.A.Cortés-Rodríguez 1 , P.C. Herbert-Moreno 1 , J. de la Luz Sánchez-Pérez 1 , I. Vidales-Fernández 2 , S. Fernández-Pavía 3 , A. García- Chávez 1 and R. Salgado-Garciglia 1 . 1 Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Edif. B3, CP 58060 Ciudad Universitaria, Morelia, Michoacán, México Correo electrónico: lgomez@zeus.umich.mx 2 Lab. de Biotecnología Vegetal, INIFAP Campo Exp. Uruapan, Ave. Latinoamericana, Uruapan, Michoacán, México. 3 Instituto de Investigaciones Agrícolas y Forestales, Universidad Michoacana de San Nicolás de Hidalgo, La Posta-Veterinaria, Morelia, Michoacán, México. From the germplasm bank of Mexican-race avocado (Persea americana Mill. var. drymifolia) in INIFAP Uruapan (Michoacán, Mexico), several materials (genotypes) grown by biotechnological means have been selected, 6 of them have high potential resistance to the oomycete Phytophthora cinnamomi. These materials are required to be characterized and evaluated to determine their resistance levels to the infection and propagate them asexually. For this reason, an evaluation for the resistance of these avocado materials against P. cinnamomi, using in vitro bioassays, was proposed. To evaluate these materials, in vitro cultures were established as from axillary and apical buds, following aseptic protocols, shoot regeneration and rooting protocols previously reported. In order to determine the resistance, in vitro plantlets were submitted to an oomycete attack with the application of mycelia segments with chlamidospores in the radical system. The number of buds and roots in each avocado genotype was optimized by modifying the doses of benzyladenine and indolebutyric acid, obtaining an average of 5 shoots per explant and up to 3 roots per bud. From the 6 genotypes tested, only accesions JSP755 and JSP3 showed resistance to in vitro infection by P. cinnamomi. These materials did not show any defoliation symptoms or proliferation of mycelia in radical vascular tissue. KEY WORDS: Persea americana Mill. var. drymifolia, oomycete, avocado root rot. MICROPROPAGACIÓN Y PRUEBAS DE RESISTENCIA IN VITRO A Phytophthora cinnamomi DE MATERIALES DE AGUACATE RAZA MEXICANA R. López-Gómez 1 , M.A.Cortés-Rodríguez 1 , P.C. Herbert-Moreno 1 , J. de la Luz Sánchez-Pérez 1 , I. Vidales-Fernández 2 , S. Fernández-Pavía 3 , A. García- Chávez 1 y R. Salgado-Garciglia 1 . 1 Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana de San Nicolás de Hidalgo, Edif.. B3, CP 58060 Ciudad Universitaria, Morelia, Michoacán, México. Tel-Fax: (55) 443 3 26 57 88, Correo electrónico: lgómez@zeus.umich.mx 2 Lab. de Biotecnología Vegetal, INIFAP Campo Exp. Uruapan, Ave. Latinoamericana, Uruapan, Michoacán, México. 3 Instituto de Investigaciones Agrícolas y Forestales, Universidad Michoacana de San Nicolás de Hidalgo, La Posta-Veterinaria, Morelia, Michoacán, México. Proceedings VI World Avocado Congress (Actas VI Congreso Mundial del Aguacate) 2007. Viña Del Mar, Chile. 12 – 16 Nov . 2007. ISBN No 978-956-17-0413-8.