RESUMEN
RESUMEN El cambio de uso de la tierra por diversos factores socio-económicos, climáticos, tecnológicos y culturales han tenido como consecuencia en la provincia de San Luis (Argentina) la pérdida de diversidad biológica, fragmentación y destrucción de hábitat, comprometiendo la existencia de la flora nativa, como es el caso de Leptochloa crinita (Lag.) P.M. Peterson & N. Snow, una especie con buena aptitud forrajera del monte chaqueño. Bajo este contexto, el presente trabajo tuvo como objetivo aplicar biotécnicas como alternativas para una propagación apropiada de este acervo genético. Se evaluó la organogénesis y callogénesis in vitro de diferentes explantos con distintos reguladores de crecimiento en un medio nutritivo Murashige y Skoog. El tratamiento con 6 mg l-1 de 2,4-D estimuló la callogénesis, mientras que los tratamientos combinados de auxinas y citocininas presentaron las mayores tasas de morfogénesis. El desarrollo de esta biotécnica permite disponer de metodologías adecuadas para iniciar ensayos de conservación in vitro, análisis de la variabilidad genética e inicio de programas de domesticación y mejoramiento genético.
ABSTRACT In San Luis (Argentina), land-use change due to a variety of socioeconomic, climatic, technological and cultural factors has caused the loss of biological diversity, fragmentation and habitat destruction, compromising the existence of native flora, such as in the case of Leptochloa crinita (Lag.) PM Peterson & N. Snow, a species with good forage aptitude from the Chaco forest. In this context, the present work aimed to apply biotechniques as an alternative for an appropriate propagation of this gene pool. In vitro organogenesis and callogenesis of several explants were evaluated with different growth regulators on a Murashige and Skoog nutrient medium. Treatment with 6 mg l-1 of 2,4-D stimulated callogenesis, while combined auxin and cytokinin treatments presented the highest rates of morphogenesis. The development of this biotechnique makes it possible to have adequate methodologies to initiate in vitro conservation trials, analysis of genetic variability and the initiation of domestication and breeding programs.
RESUMEN
The incidence of fungi in seeds depends on the sanitary and climatic conditions in which the seeds were produced. So, the objective of this study was to identify the fungi present in commercial lots of Brachiaria brizantha cv. 'Marandu' and'Xaraés' seeds harvested in different areas in Brazil. Seeds from ten lots of each cultivar, produced in the Brazilian states of Mato Grosso do Sul, Mato Grosso, Goiás, Minas Gerais, São Paulo, and Bahia were evaluated as to moisture content, germination and sanity. The experiment was conducted according to a completely random design with eight replications of 50 seeds for each lot. In both cultivars, the seeds were found to be infected with Aspergillus sp., Chaetomium sp., Curvularia sp., Fusarium sp., and Helminthosporium sp; the highest incidences were those of Chaetomium sp. and Fusarium sp. Seeds of the 'Marandu' cultivar were the only ones showing the presence of Phoma sp. and Pyricularia grisea and those of the 'Xaraés' cultivar with Colletotrichum sp. and Nigrospora sp. The incidence of Fusarium sp., Aspergillus and Nigrospora sp. reduces 'Xaraés' seeds germination whereas it does not interfere in the 'Marandu' seeds germination. The presence of the fungus Pyricularia grisea is for the first time reported in tropical forage grass seeds produced in the Southeast and Northeast regions of Brazil.
A incidência de fungos em sementes depende das condições de sanidade e climáticas dos locais de procedência. Assim, o objetivo do presente estudo foi identificar os fungos presentes em lotes comerciais de sementes de Brachiaria brizantha cv. Marandú e Xaraés coletadas em diferentes áreas. Sementes de dez lotes de cada cultivar produzidas nos Estados de Mato Grosso do Sul, Mato Grosso, Goiás, Minas Gerais, São Paulo e Bahia foram avaliados quanto ao teor de água, germinação e a sanidade. Nas sementes de ambos os capins verificou-se a incidência de Aspergillus sp., Chaetomium sp., Curvularia sp., Fusarium sp. e Helminthosporium sp. com maior importância para Chaetomium sp. e Fusarium sp. As sementes de capim-marandú foram as únicas com presença de Phoma sp. e Pyricularia grisea e de capim-xaraés com Colletotrichum sp. e Nigrospora sp. A incidência de Fusarium sp., Aspergillus sp. e Nigrospora sp. reduz a germinação de sementes de capim-xaraés e a ocorrência de fungos não interfere na germinação de capim-marandú. O fungo Pyricularia grisea é relatado pela primeira vez em sementes de gramíneas forrageiras tropicais produzidas no Sudeste e Nordeste do Brasil.