In this section:
Pasture Microbiology
Rhizobiology (root nodule bacteria research)
The rhizobiology team comprising Ross Ballard, Nigel Charman and Liz Drew provides rhizobial support to legume development programs across Australia.
The work is underpinned by an extensive and growing collection of root nodule bacteria (rhizobia) that currently exceeds 1000 pure and authenticated strains of rhizobia. It is complemented by a collection of 800 soils that conserve in situ a rich diversity of naturalised rhizobial germplasm. These soils will provide new rhizobial strains for legume development programs, well into the future.
The supply of rhizobia for alkaline soil pasture legumes is a priority of the program. Rhizobia are provided to pasture development programs across Australia. Elite strains are selected and their performance comprehensively assessed in greenhouse and field studies culminating in the recommendation of elite strains to the commercial manufacturers of rhizobial inoculants. Presently, efforts are underway to select new strains for Melilotus messanensis, a legume that has demonstrated considerable potential on salt affected soils but whose future development is clearly being constrained by a lack of appropriate rhizobia. The selection of better strains for lucerne, Lotus and Hedysarum also feature prominently in the rhizobiology program.
An innovative aspect of the program is the development of plant lines and in particular medics that will readily nodulate and fix abundant amounts of nitrogen with the rhizobia that reside in most soils. Following the extensive glasshouse selection of plant genotypes with this “rhizobially promiscuous” trait, the seed of advanced breeding lines of strand medic (F7 generation) is being multiplied to enable field evaluation of the most promising material in 2007. If successful, this approach will see the first pasture legume specifically bred to be ‘rhizobially promiscuous’, released in Australia. The approach is presently being applied to other species including balansa clover and sub-clover.
Pathology
The team coduncts pasture pathology research in support of the annual medic and lucerne breeding programs. There are three principal areas of activity.
The first is focused on the interaction of annual medics with root lesion nematode (Pratylenchus neglectus). Comprehensive field studies, using cutting edge DNA technologies have shown that medics limit the population density of P. neglectus and therefore provide farmers with a valuable tool to control numbers of this pathogen in cropping systems. The flip-side of this work has shown that the medic root systems themselves are damaged by the nematode, resulting in yield losses. In response a selection program was initiated and has resulted in the identification of several medic lines that incur minimal root damage, even at high levels of nematode exposure. The work is most advanced for strand medic with several F4 lines (derived from a cross with the cultivar Herald) showing very good levels of tolerance to the nematode. The tolerance of several advanced lines are now being evaluated in field trials.
The second area of activity centres about the selection of medics with resistance to the foliar disease powdery mildew. Over the last 10 years this disease has emerged as a significant threat to medic pastures with the frequency of both heavy infections and yield losses in the field observed to be on the increase. Whilst glasshouse studies have confirmed the high susceptibility of many of the commercial cultivars, they have also led to the identification of lines with much greater levels of resistance. Presently, the relative resistance of medic lines at different stages of phenological development is being assessed, to ensure the best possible resistant material is progressed into the medic breeding program at SARDI.
The third and relatively new area of pathology activity is examining the impact of root diseases on the establishment and production of lucerne sown in low rainfall mallee environments. Funded by National Action Plan, this project is attempting define the causative agents of root disease and to quantify their impact on production. A recent survey of lucerne pastures sown in the spring of 2005 has shown that about 25% of the paddocks had significant levels of seedling root disease. Efforts are currently underway to identify the pathogens involved. Longer term the objective of the work is to provide management and breeding strategies to improve the reliability of lucerne establishment in low rainfall regions.
