Mini-incubators improve the adventitious rooting performance of Corymbia and Eucalyptus microcuttings according to the environment in which they are conditioned.

We addressed a major challenge in the in vitro clonal propagation of Corymbia citriodora, Eucalyptus urophylla and E. benthamii by using an ex vitro adventitious rooting strategy in a mini-incubator. Mini-incubators were placed in four environments for rooting. A shade house with no fogging system and a greenhouse with no ventilation but with a fogging environment had the best performance in terms of rooting, root growth and survival of microcuttings. Daily recording of the temperature within each mini-incubator in each environment allowed the verification of negative correlations between the maximum average temperature and the survival, adventitious rooting and root growth. The ideal maximum air temperature for the efficient production of clonal plants was 28.4°C (± 5.5°C), and the minimum was 20.3°C (± 6.2°C). E. benthamii was more sensitive to higher temperatures than C. citriodora and E. urophylla. Nevertheless, placing mini-incubators in the shade house with no fogging system resulted in a stable and uniform performance among the three species, with 100.0% survival and 81.4% rooting. Histological sections of the adventitious roots revealed connection with the stem vascular cambium. Therefore, our experimental system demonstrated the potential of mini-incubators coupled with the proper environment to optimize the adventitious rooting performance of microcuttings.

Biological control of Phytophthora root rot of avocado with microorganisms grown in organic mulches

Organic mulches colonized with microbial biocontrol agents, termed bioenhanced mulches, were tested for their ability to reduce Phytophthora root rot of avocado (Persea americana Mill.). Benomyl-resistant mutants of Gliocladium virens (KA 230-1) and Trichoderma harzianum (KA 159.2) isolated from suppressive soils and selected as efficient antagonists of P. cinnamomi were evaluated for their ability to colonize different mulches under controlled laboratory conditions. Sudangrass and a coarse yardwaste were found to be better substrates than a fine yardwaste, woodwaste or rice hulls for biocontrol agents propagules production. The most suitable conditions for colonization were an optimum temperature of 24 C, a moisture content of 20 ( per cent) for sudangrass and 30 ( per cent) for the coarse yardwaste, and a continuous light exposure during a 15-day incubation period. In the greenhouse, fresh sudangrass and coarse yardwaste colonized with G. virens and used as a surface mulch proved to be the best combination for reducing the population of P. cinnamomi in 4-liter pots containing artificially-infested soil. Healthy avocado roots made up 31-37 ( per cent) of the roots in the G. virens-mulch combinations compared to 0 ( per cent) healthy in infested controls after two months.

Efeito de extratos proteícos de milho sobre a produçäo de aflatoxina B / Effect of corn proteic extracts on aflatoxin B production

Testou-se o efeito de extratos proteícos de milho à base de NaC1 5% sobre a produçäo de aflatoxina B, em meio de cultura líquido contendo, 2% de extrato de levedura e 20% de sacarose. Dois métodos de extraçäo foram avaliados a partir do peso seco do micélico do fungo Aspergillus flavus e da quantidade de aflatoxina B produzida. Os extratos proteícos das três variedades testadas estimularam o crescimento micelial do fungo. Obteve-se uma maior concentraçäo proteíca nos extratos previamente tratados com acetona. Contudo, os dois métodos se mostraram igualmente viáveis como instrumento na diferenciaçäo varietal do milho, caracterizando a suscetibilidade de "Pipoca Americana" com altos níveis de aflatoxina produzida. "Centralmex N" e "Centralmex O2" apresentaram uma menor produçäo de aflatoxina que o controle. Os resultados sugerem que a composiçäo proteíca do milho pode apresentar elementos tanto eliciadores como inibidores à produçäo de aflatoxina B