Alternative Delivery Systems for the Innoculation of new strains of Stylo

Summary

To release suitable strains of root-nodule bacteria (RNB) that demonstrates effective nodulation of S. sp.aff. S. scabra (now known as Caatinga stylo - Stylosanthes seabrana. Two cultivars, Primar and Unica have been released). To identify alternative delivery systems for establishing effective strains of RNB in soil prior to sowing S. sp.aff. S. scabra. This project is allied to CS.079/CS.153 concerning the selection of new cultivars of stylosanthes from the Stylosanthes hamata and S. seabrana germplasm.

Selection of effective nitrogen fixing strains of rhizobia became essential when it was demonstrated that the performance of S.seabrana was declining because field-grown plants were either not nodulating or not fixing nitrogen. New strains of RNB collected in Brazil in 1994 (l\/IRC separate funding) proved to be effective and persistent over a three year period. Strain CB3481 was released to industry for the 1997/98 growing season and additional effective and field competent strains have been identified. Dry-soil, near-surface sowing of small seeded legumes prior to the onset of seasonal rainfall is frequently the method of choice of producers in clay-soil arable land situations. Soil surface temperatures under these conditions frequently exceed 50C tor 4-6 hr/day and are lethal to rhizobia introduced on the legume seed. Experiments assessing alternative methods of delivery were established at 5 sites in southern Queensland.

The two major treatments were the introduction of the rhizobia to the soil with a cereal crop grown in the season preceding the sowing of the legume and deep placement of the inoculum at the time of sowing the legume. For Caatinga Stylo the introduction of the rhizobia by inoculation of wheat seed sown in May/June was better than placing the rhizobia 10cm below the legume seed in the normal December/January sowing. Deep placement and seed inoculation were better treatments for Jarlbu desmanthus. The needs to inoculate Caatinga stylo and the availability of the selected strain of rhizobia have been publicised by newsletter and field day demonstrations.