Inoculant made of encapsulated Frankia: assessment of Frankia growth within alginate beads.

The growth of Frankia cells within alginate beads was inhibited when the amount encapsulated exceeded 0.5 to 2.5 µg protein/ml of beads. Frankia growth was observed not only in the beads incubated in nutrient media (with of without combined N), but also in those incubated in air provided they retained enough nutrients. The results allow some recommendations to be made for the preparation of Frankia inoculants.

Aerial Nodules in Casuarina cunninghamiana.

A complete survey of La Réunion Island showed that, in 40- to 50-year-old Casuarina cunninghamiana plantations located in the northeast at an altitude above 400 m, some trees bore aerial nodules as high as 6 to 7 m up the trunk. The nodules exhibited a significant specific acetylene reduction by the ARA method (0.77 mumol of C(2)H(4) per h/g [dry weight] of nodule) at the time of sampling (June 1990). Aerial nodules were also found on a Casuarina glauca trunk. Preliminary observations show that anatomically aerial and underground nodules do not differ significantly. In addition to host plant genetic determinants, aerial nodule formation is assumed to require sufficient rainfall, an abundance of Frankia spp. in the soil and air, and rhytidome on the tree trunk.

Free-living Rhizobium strain able to grow on n(2) as the sole nitrogen source.

A Rhizobium strain isolated from stem nodules of the legume Sesbania rostrata was shown to grow on atmospheric nitrogen (N(2)) as the sole nitrogen source. Non-N(2)-fixing mutants isolated directly on agar plates formed nodules that did not fix N(2) when inoculated into the host plant.

Nodulation of acacia species by fast- and slow-growing tropical strains of Rhizobium.

Thirteen Acacia species were classified into three groups according to effective nodulation response patterns with fast- and slow-growing tropical strains of Rhizobium. The first group nodulated effectively with slow-growing, cowpea-type Rhizobium strains; the second, with fast-growing Rhizobium strains; and the third, with both fast- and slow-growing Rhizobium strains. The Rhizobium requirements of the Acacia species of the second group were similar to those of Leucaena leucocephala.

Polyacrylamide-entrapped Rhizobium as an inoculant for legumes.

Pot experiments showed that Rhizobium japonicum cells entrapped in a polyacrylamide gel could be used as an inoculant for soybeans and compared favorably to laboratory-made peat base inoculant containing the same bacterial strain.

Diurnal variations of nitrogenase activity in the field.

Nitrogenase activity was determined in situ by repeated assays at regular intervals to compare the patterns of diurnal variations occurring in a rice field, a grassland, and a peanut field. In the rice field only one peak occurred (mid-day), whereas the other systems exhibited typical two-peak patterns, which were suspected to be induced by climatic conditions or possibly by a specific rhythm of exudation. Observed data on diurnal variations in nitrogenase activity were fitted to different models of diurnal variation comprised of computed periodic curves.