Microbial inoculation and fertilizer application on growth of cowpea and spore-based assemblages of arbuscular mycorrhizal fungi in its rhizophere.

In this study, the effect of microbial inoculants and fertilizer application on cowpea (BRS Pujante) growth and on the structure and composition of arbuscular mycorrhizal fungi (AMF) assemblages were evaluated. A completely randomized experiment was set up involving 17 treatments: four with AMF, three with nodulating bacteria, six with AMF + nodulating bacteria, two with phosphorus, one with nitrogen and one control (reference) in five replicates. Plant growth and nutritional content, mycorrhizal colonization, glomerospores number, spore-based AMF assemblages and ecological indices were evaluated. Mycorrhizal inoculants associated with Bradyrhizobium BR3267 strain were more effective than the Microvirga BR3296 strain. Multidimensional scaling analysis showed that Acaulospora longula treatments were more similar among themselves, and distinct from the other treatments. A difference was observed in the structure of AMF community assemblage between treatments with G. albida + Bradyrhizobium BR 3267 and A. longula, with greater Shannon diversity and Pielou equitability indices in the first treatment and greater dominance in the treatment with A. longula only. Long-term studies are required to determine if the successful establishment of A. longula among indigenous species persists over time and if its dominant behavior is not deleterious to the AMF native community.

Sporulation of arbuscular mycorrhizal fungi using Tris-CHl buffer in addition to nutrient solutions

A produção de inóculo é um dos entraves na aplicação de fungos micorrízicos arbusculares (FMA) em larga escala. O objetivo deste trabalho foi avaliar o efeito de soluções nutritivas associadas a tampão Tris-HCl sobre a esporulação dos FMA. Foram conduzidos dois experimentos em casa de vegetação, um para cada hospedeiro, painço (Panicum miliaceum) e sorgo (Sorghum vulgare), usando como substrato areia:vermiculita (1:1 v/v), onde foram aplicados cinqüenta esporos de Gigaspora margarita, Scutellospora heterogama e Glomus etunicatum. O substrato foi irrigado com as seguintes soluções nutritivas: Hoagland com 3 mM P (S1), Long Ashton II com 15,9 mM P (S2) e Hoagland com 20 mM P (S3), com ou sem 50 mM de tampão Tris-HCl (pH 6,5); o tratamento controle, que consistiu de solo: areia:vermiculita (2:1:1 v/v) recebeu água deionizada. Após 10 semanas não houve diferença na esporulação, nos tratamentos com sorgo, exceto para G. etunicatum. Porém, no experimento com painço os tratamentos com solução nutritiva diferiram significativamente. A esporulação de S. heterogama aumentou após adição do tampão nas soluções S1 e S2, enquanto a de G. etunicatum foi incrementada no substrato irrigado com S1 + tampão e S3, independente da presença do tampão. A produção de esporos de G. margarita foi maior nas soluções S1 e S3, ambas com tampão, porém diferenças significativas foram observadas somente em relação à solução S2, sem tampão. A utilização de soluções nutritivas e a adição de tampão podem contribuir para o aumento da esporulação de FMA; porém, como demonstrado, cada sistema substrato, FMA e hospedeiro deve ser avaliado separadamente, para estabelecimento das condições mais favoráveis para produção de inóculo em larga escala.

Germination and germ tube growth of the arbuscular mycorrhizal fungi Gigaspora albida in different substrates

The role of substrate on germination of Gigaspora Albida Schenck & Smith was investigated, Spores were desinfested with 0.5(per cent) sodium hypochlorite (20 min.) and placed on Petri dishes over a Millipore filter, with one of the following media: a- 1(per cent) water-agar; b- water-agar + aqueous extract of roots of Panicum miliaceum L.; c- salt medium of Murashige & Skoog (MS) or sterelized sand; and incubated in the dark at room temperature (28 C+-2). The experimental design was at random with four treatments and four replicates. Germination was evaluted every 7 days until the 28th day. The water-agar medium was the most feasible for spore germination at the 7th day, followed by the MS medium at the 14th day. Conversely, the sand and the root extract medium did not allow high germination. Spores maintained in water-agar also presented longer germ tubes than spores in the other treatments . Auxiliary cells were observed at the beginning of formation of hyphal branching in all treatments, however they were more numerous in the water-agar medium.