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"The center of origin and domestication of Jatropha curcas L. is Mexico. This crop can be affected by several phytopathogenic fungi and insect pests that diminish the quality of the seeds. The aim of this study was to evaluate the antagonistic and enthomopathogenic activity of rhizospheric bacteria (B. subtilis, B. mojavensis, B. thuringiensis and Lysinibacillus sphaericus) against Fusarium verticillioides and Leptoglossus zonatus. The antagonistic activity of rhizobacteria was evaluated against F. verticillioides by dual culture technique on potato dextrose agar. Moreover, the effect of B. thuringiensis and L. sphaericus was evaluated on the mortality and development of L. zonatus. The results demonstrated that rhizobacteria inhibited the mycelial growth (26 to 55 %) and affected the hyphal morphology of F. verticillioides regardless of the culture medium and cultivation time tested. B. mojavensis (40.4 to 54 %), L. sphaericus (39.6 to 55 %) and B. subtilis (38.5 to 50%) caused the highest percentages of inhibition. On the other hand, B. thuringiensis and L. sphaericus showed no enthomopathogenic activity because they did not affect the mortality or development of L. zonatus."

Avocados (Persea americana Mill.) are economically and nutritionally valuable despite their susceptibility to several fungal diseases. This study was conducted in an agroecosystem of avocado trees in Mexico. The air samples were collected every week by gravimetric methods at a height of 2 m from the ground level. Fungal colonies were isolated and transferred onto PDA and identified using morphological methods. During air sampling, different meteorological variables were measured. The symptoms of avocado diseases were determined by visual observations. To the best of our knowledge, this is the first study on aeromycological characterization in an avocado agroecosystem. Thirty-two airborne fungal genera were identified; Fusarium (97.2 %) and Colletotrichum (94.4 %) were the most common fungal pathogens present in the atmosphere of avocado. In addition, seven genera of important phytopathogenic fungi of other crops (Alternaria, Capnodium, Pestalotia, Stemphylium, Rhizopus, Curvularia, and Phyllachora) were isolated. The maximum concentration of total fungi was observed in June (358 CFU m−3) and the minimum in September (83 CFU m−3). The total fungal concentrations were significantly negatively correlated with the temperature. The symptoms of five diseases of avocado, viz. anthracnose, scab, spot, canker trunk, and vascular wilt, were identified in the area study. It was observed that the symptoms of all the above-mentioned diseases were present in June; and in the same month, the fungal concentrations were highest.

Ustilago maydis, a dimorphic fungus causing corn smut disease, serves as an excellent model to study different aspects of cell development. This study shows the influence of chitosan, oligochitosan and glycol chitosan on cell growth and physiology of U. maydis. These biological macromolecules affected the cell growth of U. maydis. In particular, it was found that chitosan completely inhibited U. maydis growth at 1mg/mL concentration. Microscopic studies revealed swellings on the surface of the cells treated with the polymers, and chitosan caused complete destruction of the membrane and formation of vesicles on the periphery of the cell. Oligochitosan and chitosan caused changes in oxygen consumption, K(+) efflux and H(+)-ATPase activity. Oligochitosan induced a faster consumption of oxygen in the cells, while glycol chitosan provoked slower oxygen consumption. It is noteworthy that chitosan completely inhibited the fungal respiratory activity. The strongest effects were exhibited by chitosan in all evaluated aspects. These findings showed high sensitivity of U. maydis to chitosan and provided evidence for antifungal effects of chitosan derivatives. To our knowledge, this is a first report showing that chitosan and its derivatives affect the cell morphology and physiological processes in U. maydis.

The antifungal activities of chitosan and oligochitosan have been used to control postharvest decay of the fruits. The effect of chitosan and oligochitosan on mycelium growth, spore germination, and mitochondrial function of Rhizopus stolonifer was evaluated in order to establish a connection between fungus development and the main organelle in charge to provide energy to the cell. The mycelium growth of R. stolonifer was significantly reduced on minimum media amended with chitosan or oligochitosan. The highest antifungal indexes were obtained on media containing chitosan or oligochitosan at 2.0 mg ml(-1). Microscopic observation showed that chitosan and oligochitosan affected the spore germination and hyphae morphology. Both polymers increased oxygen consumption of R. stolonifer. Respiratory activity was restored with NADH in permeabilized treated and untreated cells, and was inhibited with rotenone and flavones. Complex III and IV were inhibited by antimycin A and cyanide, respectively, in treated and untreated cells. Chitosan and oligochitosan increased NADH dehydrogenase activity in isolated mitochondria. However, there were not changes in the cytochrome c oxidase and ATPase activities by effect of these polymers. These results suggest that both chitosan and oligochitosan affect the development of R. stolonifer and might be implicated in the mitochondrial dysfunction.

Effects of chitosan, oligochitosan and the essential oils of clove and cinnamon were evaluated on hyphal morphology, cell wall thickness, minimum medium pH changes and respiration of Rhizopus stolonifer. Changes in hyphal morphology were observed due to chitosan or oligochitosan treatment in this fungus. Mycelial branching, abnormal shapes and swelling were showed on hyphae of R. stolonifer treated with chitosan, whereas the development of hyphae was markedly inhibited by the effect of oligochitosan. Clove and cinnamon oils caused few morphological changes in the hyphae of R. stolonifer. Cell wall thickness was increased approximately 2- to 3-fold by effect of chitosan, oligochitosan and the essential oil of clove. R. stolonifer grown in minimum medium generated a decrease in the medium's pH. However, the addition of chitosan or oligochitosan caused increases in pH of medium culture. The highest pH value (5.4) was observed in the presence of chitosan. The respiration of R. stolonifer was stimulated at low concentrations of chitosan, oligochitosan or essential oils. Significant changes in morphology and physiology of this fungus were demonstrated by the effect of all evaluated compounds. The most important changes were induced on cells of R. stolonifer treated with chitosan and oligochitosan.

Introduction. Mexico is one of the most important producers and exporters of blackberries in the world. During postharvest handling, blackberry fruits are exposed to the attack of phytopathogenic fungi. Materials and methods. To obtain Rhizopus stolonifer isolates, samples of leaves and rhizospheric soils were placed on Petri plates containing Potato Dextrose Agar (PDA). In addition, fruits were also placed in humidity chambers at 25 °C. To describe the infection process on blackberry fruits by Rhizopus stolonifer, samples were taken at different intervals for a period of 72 h. All fungal isolates obtained were maintained on PDA. The bacterial colonies were isolated and purified by streaking on PDA. The antagonistic activity of the bacteria was assessed against R. stolonifer by dual culture technique on PDA. To detect the production of siderophores, the chrome azurol S assay was carried out. Results. The infection process of R. stolonifer on blackberry fruits was described for the first time in this work. Eighty-six bacterial isolates from different parts of the plant and rhizospheric soil were obtained. Bacterial isolates with antagonistic activity were identified and the production of siderophores was measured. Four isolates showed antagonistic activity against R. stolonifer. Bacillus subtilis obtained from soil was the most effective isolate. Conclusion. In this study we isolated and identified antagonistic bacteria with potential for biocontrol on Rhizopus stolonifer obtained from blackberry fruits. To our knowledge this is the first report regarding this topic.

Rhizopus stolonifer (Ehrenb.:Fr.) Vuill mitochondria contain the complete system for oxidative phosphorylation, formed by the classical components of the electron transport chain (complexes I, II, III, and IV) and the F(1)F(0)-ATP synthase (complex V). Using the native gel electrophoresis, we have shown the existence of supramolecular associations of the respiratory complexes. The composition and stoichiometry of the oxidative phosphorylation complexes were similar to those found in other organisms. Additionally, two alternative routes for the oxidation of cytosolic NADH were identified: the alternative NADH dehydrogenase and the glycerol-3-phosphate shuttles. Residual respiratory activity after inhibition of complex IV by cyanide was inhibited by low concentrations of n-octyl gallate, indicating the presence of an alternative oxidase. The K(0.5) for the respiratory substrates NADH, succinate, and glycerol-3-phosphate in permeabilized cells was higher than in isolated mitochondria, suggesting that interactions of mitochondria with other cellular elements might be important for the function of this organelle.

The effect of chitosan was evaluated in three isolates of Rhizopus stolonifer from infected tomatoes that were harvested in different regions of the state of Morelos, Mexico. Changes in the membrane integrity of spores, modifications in pH media and the proteins released were analysed in each isolate against three different molecular weights of chitosan at three fixed concentrations. There was an observed decline in the integrity of spores in the presence of chitosan at all the concentrations evaluated. The protein released was different depending on the isolate, kind of chitosan and used concentration. There was a significant difference in the pH changes on the growth media for all the tested isolates. Chitosan of high molecular weight showed the best results to inhibit the infection caused by R. stolonifer on the tomato fruits. The severity of symptoms of soft rot was not related with the molecular weight of chitosan.

The effect of chitosan (2 mg/ml) on the functionality of the plasma membrane of the Rhizopus stolonifer was studied. This study focuses on the changes in the integrity of the plasma membrane, external minimum medium pH, membrane potential, potassium efflux and determination of membrane phospholipids and proteins and of the H + -ATPase enzymatic kinetic activity. The results demonstrated that the membrane integrity diminishes gradually during 6 h of incubation, that there was no change in the external minimum medium pH and that the spores treated with chitosan showed the lowest membrane potential compared with the control. The results also revealed an increase of five times of potassium efflux by the addition of chitosan. There were no significant observed differences in the content of total phospholipids in both treatments. However, protein content was reduced approximately 40% and total H + -ATPase activity decreased 52% in the presence of chitosan. Chitosan treatments diminished the kinetic parameters (Vmax and Km) of the H + -ATPase activity. The damage to the plasma membrane of R. stolonifer by the presence of chitosan alters the H + -ATPase, affecting the physiological and metabolic functions of this phytopathogen fungus.

The chemical, physicochemical and rheological characteristics of Oxalis tuberosa starch were investigated. Oxalis starch presented an apparent amylose content of 33%, similar to maize starch used as control, with a granule size between 25–50 μm with oval and elliptical shapes and A-type X-ray diffraction pattern. The gelatinization temperature of oxalis starch was 64.0°C, that was lower than the one determined in maize starch (73.0°C), with an enthalpy value of 12.2 J/g, which was similar to that of maize starch. Both oxalis and maize starch pastes behaved as weak viscoelastic systems with the elastic character (G′) predominating over the viscous character (G′′). An increase in the level of solids in the pastes increased the values of the moduli. The results suggest that heating the systems (gelatinization), causes a more pronounced enhancement in the structure of the maize starch pastes than in that of oxalis starch pastes. Overall, it was concluded that due to its physicochemical, functional and rheological properties, Oxalis starch could be suitable for testing its use in the cosmetic and in the food industry.