Potencial de bactérias endofíticas para o controle biológico de doenças e promoção do crescimento na cultura da mandioca

Abstract

Cassava (Manihot esculenta Crantz) is one of the most important crops in the world. However, fungal and bacterial diseases are among the main causes of reduced production. Endophytic bacteria are recognized as efficient biological control agents and represent a promising alternative for disease control and/or for promoting plant growth. Therefore, the objective of this work was to select isolates of endophytic bacteria with potential for the biological control of bacteriosis and root rot in cassava, as well as the ability to promote plant growth. One hundred and forty-five isolates of endophytic bacteria were obtained from healthy tuberous roots of 40 cassava accessions. The isolates were characterized regarding colony morphology, physiology and enzyme production, and were tested in vitro antagonism assays against the phytopathogens Xanthomonas phaseoli pv. manihotis - Xpm (bacteriosis), Phytopythium sp., Fusarium sp., Lasiodiplodia sp. and Neoscytalidium sp. (root rot) and in plant growth promotion trials. Of the total, 50.3% of the isolates were gram-positive, 49.7% gram-negative and 85% showed positive activity for catalase. 72% of the isolates were producers of protease enzymes, 47% amylase, 79% lipase and 28% chitinase. 26.21% produced IAA in medium with added L-tryptophan and 45.52% solubilized inorganic phosphate. In the evaluation of antagonistic activity, 37% inhibited the growth of Xpm, 73.8% of Phytopythium sp., 80% of Fusarium sp. and 77.24% Lasiodiplodia sp. Twelve isolates were selected to control bacteriosis and thirteen for root rot in the in vivo assay. Isolates EM01, EM07, EM73, EM24, EM50, EM22 and EM21 reduced the severity of bacteriosis by between 36% and 65.26%. In cassava roots from the Nova Timboteua accesses, there was a 100% reduction in root rot lesions provided by isolates EM122 (Phytopythium sp. and Fusarium sp.), EM16 (Phytopythium sp. and Lasiodiplodia sp.), EM08 (Fusarium sp.), EM70 (Fusarium sp., Neoscytalidium sp. and Lasiodiplodia sp.), EM95 (Fusarium sp.), EM91 (Fusarium sp. and Neoscytalidium sp.) EM13 (Lasiodiplodia sp.), EM96 (Lasiodiplodia sp. and Neoscytalidium sp.), EM43 (Lasiodiplodia sp.). In the Chifre de Boi accesses, there was a 100% reduction in lesions caused by isolates EM16 (Phytopythium sp., Fusarium sp. and Lasiodiplodia sp.), EM13 (Phytopythium sp. and Lasiodiplodia sp.), EM95 (Phytopythium sp.), EM08 (Phytopythium sp., Fusarium sp. and Lasiodiplodia sp.), EM91 (Phytopythium sp. and Fusarium sp.), EM43 (Phytopythium sp. and Fusarium sp.), EM122 (Phytopythium sp. and Fusarium sp.), EM70 (Fusarium sp.), EM96 (Lasiodiplodia sp. and Neoscytalidium sp.). In the growth promotion assay, isolates EM51 and EM74 contributed to the development of shoots by 56% and 43.75%, respectively, and isolates EM17, EM51, EM30 and EM74 promoted the growth of cassava shoots, with an increase of biometric and biomass parameters in comparison to the control treatment. In a rooting test, isolates EM61, EM74, EM98, EM51 and EM113 provided significant increases in root length and root biomass. The endophytic bacteria isolates were efficient in biological control and as plant growth promoters and can be inserted into a sustainable management program with potential for use in cassava cultivation.