Crop science: microbes boost growth and resilience of legume plants

Lucerne or alfalfa is used as feed for high-producing dairy cows, because of its high protein content and highly digestible fiber. ​

Researchers at Flinders University in South Australia screened hundreds of strains of endophytic actinobacteria, which grow naturally within legume roots and nodules. They identified two strains that were shown in laboratory and glasshouse trials to promote growth in the shoots of legume plants. 

Professor Chris Franco, Australia’s leading actinobacteriologist, who supervised the research, together with Ross Ballard from the South Australian Research and Development Institute, explained that the microbes increased the ability of lucerne to absorb atmospheric nitrogen. 

“We found that the microbes fixed more nitrogen into the plants, so that they grew better - resulting in at least 50% more biomass,​”​ he told FeedNavigator. 

He added that he would expect the 50% increase in growth in glasshouse trials to translate to an increase of at least 20% in the field. ​

Facilitating nitrogen fixation​ ​

The researchers have not yet identified the exact mechanism responsible for this growth, but they do know that these strains promote the growth of rhizobium bacteria. Legumes require a population of these cultures, which form nodules in the roots of the plants to absorb nitrogen. 

A further advantage of the microbes is that they have the potential to reduce the amount of fertilizers used by at least 50%, according to the researchers. 

“​Treated plants absorb more nitrogen, 25% of which remains in the soil after the plant is harvested and can be left over for the next crop. This means that farmers can increase profits by reducing the amount of fertilizers used over two years,​”​ said Professor Franco. 

Feedback from the farming community was that the strains needed to be able to control disease as well as promote growth. So the researchers conducted further tests, which demonstrated that the microbes can help plants grow in diseased soil. 

“​Very often these crops have a problem with establishment because of underlying fungal diseases such as rhizoctonia, phytium and fusarium. These strains help the plant overcome that, to germinate and establish better,​”​ said Professor Franco. 

These findings were substantiated in field trials, which showed that the microbes helped the plants to not only establish better, but also grow better in a drought state. 

Strain survival​

Professor Franco said that another advantage of these strains is that they are particularly robust; their ability to survive temperatures of up to 70-80º C means they can withstand processing techniques such as spray drying. This enables the microbes to be applied as a seed coating, whereby the spores are added to the seed before sowing, or as a sowing drench with a suspension of spores. Being filamentous bacteria, the microbes are not adversely affected by the fungicides used on many farms. 

The next step is for the researchers to conduct more, larger scale field trials, but the obstacle to this is funding. 

“​With any biological product it​’​s always a question of reproducibility. We​’​ve approached a number of companies and hope to obtain some funding. In the meantime, we have enough funds to do a limited number of field trials with lucerne, pea and faba beans,​”​ said Professor Franco. 

Whilst a patent has been lodged for the two strains in relation to their use with lucerne, Professor Franco said the microbes should have a similar effect in any legume plant.