Evaluation of bacillus megaterium strain AB4 as a potential biocontrol agent of alternaria japonica, a mycopathogen of Brassica oleracea var. italica.

Alternaria japonica causes annual losses of up to 25 % of the world broccoli crops, for this reason this research focused on the development of biopreparations containing Bacillus megaterium to prevent the outbreak of this disease caused by Alternaria japonica in the crop of Brassica oleracea var. italica. During the laboratory phase two types of biopreparations were evaluated, the first biopreparation was obtained by liquid fermentation composed of 40 g.L-1 of fava bean flour and 5 g.L-1 of ground brown sugar. This showed a maximum cell growth of 3.8 × 108 CFU. mL-1; while the second biopreparation was obtained by solid fermentation composed of wheat bran and it achieved a maximum cell growth of 4.7 × 109 CFU. g-1. In the fieldwork phase the aforementioned biopreparations were applied in an open-field crop. At the end of the cultivation period, the degree of the disease in leaves and in the inflorescences was measured and through the statistical analysis, a significant difference was evidenced (α = 0.05). On the broccoli leaves the disease index values ​​do not exceed 15.56 % and the disease index for postharvest florets was around 38 %. The evaluated variables showed a statistical similarity with the chemical treatment, thus determining the effective effect of the biopreparations.

Evaluation of the infection process by Lecanicillium fungicola in Agaricus bisporus by scanning electron microscopy.

BACKGROUND: Lecanicillium fungicola causes dry bubble disease in Agaricus bisporus mushrooms leading to significant economic losses in commercial production. AIMS: To monitor the infection process of L. fungicola in Brazilian strains of A. bisporus. METHODS: The interaction between the mycelium of L. fungicola (LF.1) and three strains of A. bisporus (ABI 7, ABI 11/14 and ABI 11/21) was studied. Electron microscopy and X-ray microanalyses of vegetative growth and basidiocarp infection were evaluated. RESULTS: Micrographs show that the vegetative mycelium of the Brazilian strains of A. bisporus is not infected by the parasite. The images show that the pathogen can interlace the hyphae of A. bisporus without causing damage, which contributes to the presence of L. fungicola during the substrate colonization, allowing their presence during primordial formation of A. bisporus. In the basidiocarp, germ tubes form within 16h of infection with L. fungicola and the beginning of penetration takes place within 18h, both without the formation of specialized structures. CONCLUSIONS: Scanning electron microscopy enabled the process of colonization and reproduction to be observed within the formation of phialides, conidiophores and verticils of L. fungicola. The formation of calcium oxalate crystals by the pathogen was also visible using the X-ray microanalysis, both at the hyphae in the Petri plate and at basidiocarp infection site.