Acid tolerant lucerne rhizobia (P2 FP05)

The Acid Tolerant Lucerne Rhizobia project is identifying new rhizobia strains to expand the range of lucerne into more acidic soils which have previously restricted lucerne growth by reducing rhizobial survival and nodulation.

Commercialisation of a rhizobium strain identified by this project will facilitate the expansion of lucerne into new regions of Australia where soil acidity is the major constraint to lucerne adoption. It will also improve lucerne performance in many areas where production is currently inhibited by soil acidity and significantly increase root growth and nodulation on acidic soils. This will result in improved lucerne establishment, higher levels of nitrogen fixation and increased persistence of lucerne stands on acidic soils.

Objectives:

• Identify, evaluate and recommend a rhizobium strain with improved tolerance to acidic soils, for use in commercial lucerne inoculants
• Quantify the level of improvement made with the new rhizobia compared to plant traits in soils of low pH, and containing aluminium.

Activities

In 2008, more than 250 strains, most isolated from acid soils in southern NSW where lucerne expansion is likely, were screened in a low pH solution culture system to identify strains with potential tolerance. The 30 most promising strains were refined down to 11 unique strains based on a diversity analysis that used morphological and molecular techniques. These 11 strains are now being compared in a range of field and greenhouse experiments to assess their performance in acid soils and to fix nitrogen. 

Detailed evaluation of 17 experiments sown at 10 field locations in SA, Vic. and NSW has identified three rhizobia strains that have improved second year nodulation over the current commercial strain. The improved performance of the new strains are greatest at the McLaren flat sit in SA, with soil pH¬Ca <4.5, where the best strains are nodulating 67 percent of plants compared to the average of 31 percent for the two entries of the commercial strain.

Two of these strains are also highly effective at nitrogen fixation and are therefore good prospects for commercialisation.The combination of low pH solution culture experiments and detailed nodulation assessments across multiple field sites are also helping  to develop a clearer picture of pH constraints to nodulation than has previously been available.

The data demonstrate that with the current strain, nodulation is likely to be significantly below potential at pH Ca 4.8.  The new strain is likely to improve nodulation across a broad range of soil types down to pHCa 4.5 and this will improve lucerne production on approximately 1M ha where it is currently sown.The FFI CRC acid tolerant rhizobia team anticipates that all lucerne sold in Australia will be inoculated with the improved strain from 2012-13.

For further information about this project, email project leader, Alan Humphries.