Growing food with less water: Chilean research team finds solutions in extreme environments

• Finding ways to grow food with less water in the face of droughts, higher temperatures and other abiotic stresses is a global challenge.
• Professor Milko Jorquera and his team of researchers at Universidad de La Frontera in Temuco, Chile, are searching for answers in extreme environments.
• Tomato plants inoculated with rhizobacteria isolated from the root zone of flowering plants in the Atacama Desert exhibit greater rates of survival and growth when subjected to periods of water stress.

Droughts and other extreme events pose a growing risk to food security in a changing climate. In Chile, ongoing drought conditions have been experienced for over ten years, limiting the water available for irrigated agriculture. When combined with other abiotic stresses such as higher temperatures, soil salinity and poor water quality, plants are at increased risk of dehydration with consequent losses for farmers. The race is on to find ways of growing plants with less water. A team of researchers have been looking for solutions in some interesting places.

Professor Milko Jorquera leads the Applied Microbial Ecology Laboratory at Universidad de La Frontera in Temuco, Chile, and is part of the Network for Extreme Environment Research (NEXER). Milko and his former PhD student, Dr Marcia Astorga-Eló, have recently published some of their research into reducing water scarcity stress in tomatoes in Scientific Reports.

‘Tomatoes are an important vegetable crop grown in Chile and around the world, but they are highly susceptible to water scarcity stress in arid and semi-arid regions,’ said Professor Jorquera. ‘In my laboratory we study interactions between microorganisms and plants to determine ways to beneficially promote plant growth under stressful conditions.’

Milko and his team search for microorganisms in a range of extreme environments, from the Atacama Desert to Patagonia and Antarctica. ‘In the Atacama Desert, which is one of the driest places on the earth, the seeds of ephemeral plants can lie dormant in the soil for many years,’ he said. ‘When it does rain, the seeds germinate and the plants grow and flower in a short period of time. We call these Flowering Desert (FD) events and a representative plant that we have studied is Cistanthe longiscapa.’

Professor Jorquera and Dr Astorga-Eló isolated bacteria from the soil and root zone - or ‘rhizosphere’ - of the Cistanthe plants and cultured them in the laboratory. These bacteria are called rhizobacteria and often form a symbiotic relationship with plants. ‘We collected the top 10 centimetres of soil, placed it into sterile plastic bags and transported it on ice back to our laboratory in southern Chile,’ explained Milko.

The concept behind the research is that the rhizobacteria and plants have co-evolved in the Atacama Desert, a place characterised by extreme temperatures, high UV irradiation and permanently low availability of water and nutrients. Further to this, many species of rhizobacteria are known to promote the growth of plants, including agricultural crops, pastures, cereals and fruit trees.

‘These members of plant microbiota are referred to as Plant Growth Promoting Rhizobacteria (PGPR) and in an earlier study we identified that wheat plants inoculated with PGPR from the Atacama Desert grew better under water shortage conditions,’ said Professor Jorquera. The team has found similar results in their research on avocadoes, with bacterial consortia reducing the effects of salt and water stress. Milko explained, ‘In this study, we wanted to assess if similar results could be achieved on tomatoes as they are high users of water.’

Dr Astorga-Eló and Professor Jorquera isolated 72 strains of rhizobacteria from the desert soil samples and then conducted a range of in vitro tests to determine the presence of plant growth promoting traits, which reduced the number of strains to 23. From there, the researchers genotyped the strains based on 16S rRNA gene partial sequencing, then conducted compatibility tests to determine if any of the bacterial strains inhibited the growth of other strains.

‘We identified nine potentially suitable strains that were used to formulate three rhizobacteria consortia comprising Bacillus, Paenibacillus and Brevibacillus isolates. These three consortia were then used to inoculate tomato plants in a greenhouse experiment,’ said Milko.

The process of inoculation involved the application of a rhizobacterial suspension to the seeds of the tomato plants at or before the time of sowing, then again at different stages of the plant’s growth with the fourth and final inoculation occurring 40 days after the first. The seedlings were then subjected to a water scarcity stress experiment with irrigation withheld for 24, 72 or 120 hours. The team measured aspects of plant growth including survival, height and fresh shoot weight up until day 60.

‘Our results revealed that a significantly higher percentage of inoculated seedlings survived water stress compared to the uninoculated controls,’ said Professor Jorquera. ‘When it came to plant growth, our experiments also showed that tomato plants inoculated with PGPR consortia and subjected to periods of water stress exhibited significantly greater plant height and weight.’

What does this mean for food production in a changing climate? The NEXER team’s research has significant implications for boosting agricultural production in the face of the growing threat of abiotic stresses, such as water shortages and soil salinity. ‘To put this research into practise would require the commercialisation of the rhizobacterial consortia that we have identified in partnership with private agribusinesses’, said Milko. ‘Ideally the rhizobacteria would be cultured consistently on a large scale to allow farmers to inoculate tomato seeds during irrigation events.’

Professor Jorquera’s research, as part of the NEXER team, is continuing and demonstrates that the answers to some of the challenges facing agriculture today can indeed be found in some extreme places.