This is the second year for a project to improve salt tolerance in rice with an innovative fungal technique. Encouraging results were reported with “symbiotic” plants in the first year. Research in 2008 focused on larger field trials. An important goal is to develop a practical system for rice farmers to utilize in varying field conditions.

Rice plants in one part of the study were given a seed soak treatment with common fungal species found in California rice fields. This process confers desirable traits such as decreased water consumption and increased metabolic efficiency. It also imparts an ability in treated plants to resist detrimental impacts from elevated levels of salinity. The specific metabolic processes involved are not well understood.

Treated plants demonstrated both salt and cold tolerance, as well as increased plant biomass and seed yield. Growth and yield enhancement were also examined.

Field trials

Three different fungal species were used in field trials at experimental sites with elevated salinity levels or cold-water stress. The fungal types were tested for their ability to confer salt and/or cold tolerance. Symbiotic plants at the cold tolerance site were larger and thicker early in rice seedling development. Stress tolerance in symbiotically treated plants may play a role during seedling stage (or at other developmental stages) in rice plant growth.

Treated plants subjected to environmental stress, especially during seedling stage, showed a positive response in growth, survival, and plant yields. In the absence of stress, no differences were observed between treatments.

Laboratory results

Under laboratory conditions, dramatic growth response in seedlings occurred in treated rice plants even in the absence of stress. Treated seedlings showed more than a five-fold increase in plant biomass. The root systems in symbiotic plants were also much more extensive. Fine root hairs also appear more abundant.

These results suggest that symbiosis, particularly in young plant seedlings, could be beneficial for the early establishment and survival of young rice plants. Higher salt- and cold-tolerance tests are planned for future experiments.

Fungi examined

Another part of this research examined more closely the different fungal species that could be used in this technique. Specific lines of rice seed were chosen that have demonstrated cold- and salt-tolerance – or yield benefits. Fungal species from these successful lines were isolated for further functional testing under laboratory and greenhouse conditions.

An array of fungal species that impart yield enhancement or stress tolerance to rice plants could, conceivably, be cataloged and banked to use with different rice cultivars and in different growing conditions. Hence, native fungal species may prove to be a valuable resource for rice production, especially in areas with elevated salinity or other marginal conditions.

Forty-one seed lines were examined and analyzed for growth enhancement and other functional benefits with Alternaria or Curvularia, and Fusarium species. All native fungal species showed some growth response compared to untreated controls. Importantly, more than 80 percent of the growth response measured was statistically significant.

Isolated fungal species were also tested on M-206 rice. Rice seedlings were symbiotically colonized and are being assessed for growth response, yield enhancement, fluid usage, salt and cold tolerance and decrease in nitrogen use under laboratory and greenhouse conditions.

Growth Response via Symbiosis

      NS=0                                   S=100%
         Sterilization, germination and colonization via imbibition

      NS=0                                   S=100%
         Seedling growth response

      NS=0                                   S=100%