Polymeric Encapsulate of Streptomyces Mycelium Resistant to Dehydration with Air Flow at Room Temperature.

Encapsulation is one of the technologies applied for the formulation of biological control agents. The function of the encapsulating matrix is to protect the biological material from environmental factors, while dehydration allows for its viability to be prolonged. An advantage of dehydrated encapsulation formulations is that they can be stored for long periods. However, vegetative cells require low-stress dehydration processes to prevent their loss of viability. Herein we describe the fabrication of a dehydrated encapsulate of the Streptomyces CDBB1232 mycelium using sodium alginate with a high concentration of mannuronic acid; sodium alginate was added with YGM medium for mycelium protection purposes. The encapsulation was carried out by extrusion, and its dehydration was carried out in a rotating drum fed with air at room temperature (2-10 L min-1). The drying of the capsules under air flows higher than 4 L min-1 led to viability loss of the mycelium. The viability loss can be decreased up to 13% by covering the alginate capsules with gum arabic. Compared to conventional dehydration processes, air moisture removal can be lengthy, but it is a low-cost method with the potential to be scaled.

Native soil bacteria isolates in Mexico exhibit a promising antagonistic effect against Fusarium oxysporum f. sp. radicis-lycopersici.

Sinaloa state accounts for 23% of Mexico's tomato production. One constraint on this important crop is the Fusarium crown and root rot, caused by Fusarium oxysporum f. sp. radicis-lycopersici, which has been reported to reduce crop yield by up to 50%. In this study, we set out to identify bacterial populations which could be used to control this disease through natural antagonism. Five tomato rhizospheric soil samples were collected, dried for 1-week, and homogenized. Sub-samples were used to prepare an aqueous solution used to isolate microorganisms in pure cultures. Organisms were purified and grown separately, and used to generate a collection of 705 bacterial isolates. Thirty-four percent from this bank (254 strains) was screened against Forl, finding 27 bacteria displaying in vitro Forl growth inhibition levels from 5% to 60%. These isolates belonged to the genus Bacillus and their 16Sr DNA sequences showed that they are closely related to seven species and they were putatively designated as: B. subtilis, B. cereus, B. amyloliquefaciens, B. licheniformis, B. thuringiensis, B. megaterium, and B. pumilus. One isolate belonged to the genus Acinetobacter. Two B. subtilis isolates (144 and 151) and one B. cereus isolate (171) showed the best antagonistic potential against FCRRT when evaluated on seedlings. Plate and activity assays indicate that these isolates include a diverse repertoire of functional antagonistic traits that might explain their ability to control FCRRT. Moreover, bacteria showed partial hemolytic activity, and future research will be directed at ensuring that their application will be not harmful for humans and effective against Forl in greenhouse or field conditions.

Loss of arbuscular mycorrhizal fungal diversity in trap cultures during long-term subculturing.

Long-term successional dynamics of an inoculum of arbuscular mycorrhizal fungi (AMF) associated with the maize rhizosphere (from traditionally managed agroecosystems in Los Tuxtlas, Veracruz, Mexico), was followed in Bracchiaria comata trap cultures for almost eight years. The results indicate that AMF diversity is lost following long-term subculturing of a single plant host species. Only the dominant species, Claroideoglomus etunicatum, persisted in pot cultures after 13 cycles. The absence of other morphotypes was demonstrated by an 18S rDNA survey, which confirmed that the sequences present solely belonged to C. etunicatum. Members of Diversisporales were the first to decrease in diversity, and the most persistent species belonged to Glomerales.