The arbuscular mycorrhizal fungus (AMF) Glomus deserticola can alleviate the deleterious effect of Verticillium dahliae on the growth and yield of pepper when pathogen attack occurs during the vegetative stage of growth. As biotic stresses can alter the activity of reaction oxygen species scavenger enzymes, our first objective was to determine if V. dahliae caused biochemical changes in asymptomatic leaves even before the onset of first visible symptoms of the disease in plants, laying special emphasis on antioxidant enzymes. The second aim was to assess if AMF modified the metabolism in leaves of Verticillium-inoculated plants. Results showed that V. dahliae caused metabolic changes in asymptomatic leaves even before plants had developed disease symptoms, but there were some differences between non-mycorrhizal and mycorrhizal plants. Non-mycorrhizal pepper inoculated with the pathogen exhibited an early enhancement of superoxide dismutase (SOD) activity, which was not co-ordinated with increases in any peroxidase activity. The presumably subsequent accumulation of H 2 O 2 could be related to the quick progress of the disease observed in these plants. On the other hand, mycorrhizal plants did not show simultaneous co-ordination among different antioxidant enzymes, but they had more balanced SOD, catalase and guaiacol peroxidase activities in leaves during the first month after pathogen inoculation than non-mycorrhizal ones. This fact could be related to the longer maintenance of photosynthetic rates in pathogen-infected plants associated with AMF observed in previous studies.U. S.
Verticillium dahliae Kleb. is a vascular pathogen that alters water status and growth of pepper plants and causes drastic reductions in yield. Its control is difficult because it can survive in field soil for several years. The application of arbuscular mycorrhizal fungi (AMF) as bioprotector agents against V. dahliae is an alternative to the use of chemicals which, in addition, is more respectful with the environment. The establishment of the mutualistic association of plant roots and AMF involves a continuous cellular and molecular dialogue between both symbionts that includes the preactivation of plant defense responses that may enhance the resistance or tolerance of mycorrhizal plants to soil-borne pathogens. Some AMF can improve the resistance of Capsicum annuum L. against V. dahliae. This is especially relevant for pepper cultivars (i.e. cv. Piquillo) that exhibit high susceptibility to this pathogen. Compared with non-mycorrhizal plants, mycorrhizal pepper can exhibit more balanced antioxidant metabolism in leaves along the first month after pathogen inoculation, which may contribute to delay both the development of disease symptoms and the decrease of photosynthesis in Verticillium-inoculated plants with the subsequent benefit for yield. In stems, mycorrhizal pepper show earlier and higher deposition of lignin in xylem vessels than nonmycorrhizal plants, even in absence of the pathogen. Moreover, AMF can induce new isoforms of acidic chitinases and superoxide dismutase in roots. Mycorrhizal-specif ic induction of these enzymatic activities together with enhanced peroxidase and phenylalanine ammonia-lyase in roots may also be involved in the bioprotection of Verticillium-induced wilt in pepper by AMF.Additional key words: biological control, Capsicum annuum, mycorrhizal symbiosis, Verticillium dahliae Kleb. ResumenRevisión. Los hongos micorrícico arbusculares (MA) como agentes bioprotectores del pimiento frente a la seca inducida por Verticillium spp.Verticillium dahliae Kleb. altera el estado hídrico y el crecimiento de las plantas de pimiento y reduce la producción del fruto. El empleo de hongos micorrícico arbusculares (MA) como bioprotectores contra V. dahliae es una alternativa al uso de productos químicos más respetuosa para el medio ambiente. La asociación entre las raí-ces de las plantas y los hongos MA conlleva un diálogo celular y molecular entre ambos simbiontes, que incluye la preactivación de respuestas de defensa en la planta, lo cual puede incrementar la resistencia o tolerancia de las plantas micorrizadas hacia los patógenos edáficos. Algunos hongos MA incrementan la resistencia del pimiento (Capsicum annuum L.) contra V. dahliae. Esto es especialmente relevante cuando el cultivar (cv. Piquillo, por ejemplo) es muy susceptible hacia el patógeno. En comparación con las plantas no micorrizadas, las hojas de las plantas de pimiento micorrizadas muestran un metabolismo antioxidante más equilibrado a lo largo del primer mes tras la inoculación del patógeno, lo que puede retrasar el desc...
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