Raymundo Saúl García-Estrada

Efecto de biocontrol e inhibición germinativa de Bacillus spp. sobre zoosporas de Phytophthora capsici

The oomycete Phytophthora capsici is a pathogen of economic importance in tomato ( Solanum lycopersicum L.) and chili ( Capsicum annuum L.) crops. The objective of this work was to evaluate the effect of germinative inhibition and biocontrol of two isolates of the genus Bacillus on zoospores of P. capsici . The isolates were identified as Bacillus amyloliquefaciens and B. thuringiensis . In the in vitro tests of the germination of zoospores of P. capsici , the percentages of inhibition with cell suspension of B. amyloliquefaciens and B. thuringiensis were significant with 88.15 and 97.05% respectively, while, the filtrates showed 24.30% of inhibition. In the in vivo study, tomato seedlings treated with cell suspension of B. amyloliquefaciens and B. thuringiensis , showed lower severity of the disease caused by P. capsici with 22.22 and 27.78% respectively, compared to that observed in chili seedlings where values of 61% were obtained. The tomato and chili seedlings treated with bacterial filtrates showed up to 94% severity. With cell suspension of B. amyloliquefaciens and B. thuringiensis the efficiency of biocontrol was 72 and 77% respectively, which show that these microorganisms can be used as biocontrol agents of P. capsici in tomato and chili plants.

Diversity of mucoralean fungi in soils of papaya ( Carica papaya L.) producing regions in Mexico

Mexico is the fifth largest producer of papaya worldwide and has recently reported problems with mucoralean fungi in this crop. These fungi are considered saprophytes in the soil and are ubiquitous in nature. In this work, they were isolated from soil in regions of intensive papaya cultivation in Mexico. Collections were made in the states of Colima, Oaxaca and Veracruz in Apr 2016. A total of 72 mucorales fungal isolates was obtained and morphologically characterized and then molecular characterization (28S ribosomal region) of 25 representative isolates was carried out. Phylogenetic analysis of the sequences confirmed the presence of the species Gilbertella persicaria, Rhizopus oryzae, Rhizopus stolonifer, Mucor circinelloides and Mucor hiemalis, which cause soft rot in papaya fruits, therefore, spores of these fungi found in the orchard soils can be considered as a constant source of contamination that affects healthy fruits. Additionally, Choanephora cucurbitarum, Mucor ellipsoideus, Rhizopus homothallicus, Rhizopus microsporus, Rhizopus schipperae, Lichteimia ramosa, Gongronella butleri, Cunninghamella bertholletiae and Cunninghamella blakesleeana were identified which are considered to have agricultural, biotechnological and medical importance.

Actividad antifúngica in vitro del aceite esencial de ajo (Allium sativum L.) contra Alternaria tenuissima

Due to the environmental problems generated by the chemical control of phytopathogenic fungi, it is necessary to look for alternatives for their control. The essential oil of garlic may be a viable alternative for the control of A. tenuissima . In this study, the volatile compounds of garlic essential oil were analyzed by Gas Chromatography-Mass Spectrometry. Radial growth in vitro and biomass of A. tenuissima in presence of the garlic essential oil. Diallyl disulphide and diallyl sulphide were identified in 23.64 and 20.33%, respectively, among other compounds in a smaller proportion. At a concentration of 1000 ppm, the radial growth and biomass production were inhibited 100 and 86.20%, respectively, it compared with control PDA-Tween 80 without oil. The medium and minimum inhibitory concentrations obtained for A. tenuissima were 229 and 1, 023 ppm, respectively. The spore germination of the fungus was inhibited 88.89% with medium minimum concentration and 94.17% with minimum inhibitory concentration. Garlic essential oil showed antifungal capacity against A. tenuissima , inhibiting spore germination, radial growth and biomass production.

Fast technique for the identification of Gilbertella persicaria via optical microscopy

Gilbertella persicaria is an important phytopathogen that is confused with Mucor spp. and Rhizopus spp. The main distinguishing characteristic of G. persicaria is the presence of appendages in sporangiospores, and their observation by conventional staining techniques generally fails. A technique is described using light microscopy for fast and reliable diagnosis.