Produção, armazenamento, estabilidade e eficiência de linhagens de Dicyma pulvinata no biocontrole para o mal-das-folhas da seringueira.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Dicyma pulvinata is a mycoparasite found in different geographic areas of Brazil and in other countries; however, it is still little studied. This fungus shows potential for the biocontrol of South American Leaf Blight of the rubber tree, Hevea brasiliensis, caused by Microcyclus ulei. This disease severely limits latex production and restricts the development of new plantations in the humid regions of Brazil and Latin America. The objective of the present work was to study D. pulvinata, to develop technology for mass-production of this biocontrol agent. In this way, the effect of different substrates, production methods, regimes of light, temperature and nutritional sources in the growth and sporulation of the antagonist was evaluated, as well as methods of drying and storage of the produced spores. The compatibility of the fungus with agrotoxins as well as the effect of the addition of adjuvant to inoculum was also studied. Four strains of the mycoparasite were evaluated under field conditions. Finally, genetic instability of two strains of D. pulvinata from our collection was determined after successive replications using the molecular techniques, RAPD and RFLP. The method found to be most efficient for large-scale production of D. pulvinata was culture in polypropylene bags, using parboiled rice as substrate. The carbon sources glucose and sucrose allowed the fastest growth of the colonies, while sucrose and starch improved the sporulation of the fungus. In parboiled rice, additional carbon sources produced no difference from the control while ammonium sulphate was the most favourable among the tested nitrogen sources. Photoperiods of 0 and 6 hours of light promoted greater mycelial growth of fungus and continuous light favoured sporulation. In relation to temperature, it was observed that the fungus grows and germinates between 19 and 25 C. In spore drying experiments, three days in a desiccator was the optimum period. In the germination tests, with six hours of incubation at 25 C, 90 % of spores germinated. In storage, spores after harvest were found to be to be short-lived, indicating the necessity of developing formulated preparations. Results obtained with Biodac showed that this material is a viable alternative as support for culture and propagation of the hyperparasite. The action of D. pulvinata in the field was proven, where strains CEN 62 and CEN 93 had similar control levels to the usual fungicide. The control agent, however, demonstrated incompatibility with the evaluated agrotoxins, except with Malathion. The addition of adjuvants to the suspensions of spores of the antagonist did not inhibit growth and sporulation, indicating that any one of these products could be used as a component in the formulations of spores of D. pulvinata. Studies on the stability of two strains of D. pulvinata, showed that this fungus readily presents alterations of colonial morphology, characterized by the formation of sectors. Strains producing sectors were shown to possess genetic alterations as evidenced by variations in bands obtained in RAPD and RFLP analyses. In this work, methods of production and storage have been optimised, the efficiency in field and the genetic stability of D. pulvinata strains demonstrated. These data may then contribute to the establishment of the use of D. pulvinata as an agent of biocontrol for leaf blight of rubber.

ASSUNTO(S)

ciências biológicas biocontrole dicyma pulvinata mal-das-folhas seringueira

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