Recent research in plant biology has focused on endophytic rhizobacteria and their effects on plant growth and development. Endophytic refers to bacteria that live within a plant for at least part of their life cycle without causing disease. Rhizobacteria are root-associated bacteria that can have a harmful, neutral or beneficial effect on plant growth.
Botanical scientists have focused on those rhizobacteria that form symbiotic or beneficial relationships with plants. Their research priority has been with food crops. Their goal is to produce healthy soils that support healthy roots that are needed to overcome water scarcity and drought conditions.
Stress in plants has been associated with an increase in ethylene production, which causes plant tissue damage. Remember what happened to that banana you left on the kitchen table for several days? That ripening is the result of ethylene. Plant physiologists label ethylene as a stress-induced hormone. Turfgrass under stress also produces ethylene. The accumulation of ethylene is associated with reduced root and shoot growth, and an increase in leaf senescence (i.e., causing plant tissues to mature and age faster and essentially “ripen”).
How can turfgrass suppress the production of ethylene under drought stress? And if the plant doesn’t make ethylene, would that plant have the ability to tolerate drought? A specific rhizobacteria, Paraburkholderia aspalathi, produces an enzyme that suppresses or blocks ethylene production. Therefore, researchers at Rutgers University investigated this rhizobacteria for the ability to help creeping bentgrass overcome drought stress.
Creeping bentgrass (Agrostis stolonifera Penncross) was transplanted from putting green field plots into the greenhouse. Roots were uniformly trimmed and plants separated into individual tillers that were surface sterilized to minimize microbial interaction from the field soil. Plants were transplanted into containers with a sterilized fritted clay root zone. They were irrigated, fertilized, maintained in the greenhouse for 30 days and then transferred into growth chambers at 50% relative humidity, 12 hours daylight at 73 F (23 C) and 12 hours dark at 65 F (18 C).
Plants were inoculated with P. aspalathi strain WSF23 by drenching the soil with a prepared bacterial solution and inoculated again 24 hours later. A total of eight containers containing six plants each were inoculated, and a second set of plants were not inoculated. Six days later, all plants were not irrigated for 35 days to simulate drought-stress conditions. Next, all plants were irrigated for 15 days to evaluate post-stress recovery. Another set of inoculated and non-inoculated plants was maintained under well-watered conditions with no drought stress. Various plant-physiological parameters were measured for all plants.
Creeping bentgrass inoculated with the rhizobacteria had significantly more growth (measured by tiller growth) compared to non-inoculated plants under drought-stress and well-watered conditions. Roots of inoculated plants had significantly greater root length, higher root surface area, more root volume and better root viability (i.e., function) compared to non-inoculated plants. Since there was no significant accumulation of ethylene to “stress out” the inoculated turfgrass, those plants can produce more tillers and roots. Turfgrass with healthier roots has better drought tolerance and better recovery after drought stress.
Higher carbohydrates in crown tissues in inoculated plants provided an indication of better recovery after drought. Carbohydrate storage in crown tissues during drought stress is important to supply energy for tiller growth during drought stress and to produce new tillers when water becomes available.
In summary, this research showed that a specific rhizobacteria successfully interacted with creeping bentgrass roots; the rhizobacteria produced an enzyme that reduces the turfgrass’s ability to produce ethylene; with ethylene suppressed, the turfgrass was more drought tolerant; and the roots were healthier and functioning at full capacity. Perhaps someday the successful delivery of beneficial rhizobacteria to turfgrass root zones will be a common practice like the way fungicides are applied today. A request to current and future turfgrass scientists: Figure out how to grow and maintain healthy populations of plant-growth-promoting bacteria in turfgrass soils.
Source: Errickson, W., N. Zhang and B. Huang. 2023. Promotive effects of endophytic rhizobacteria on tiller and root growth in creeping bentgrass during drought stress and post-stress recovery involving regulation of hormone and sugar metabolism. Crop Science 63:2583-2593.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 24-year member of GCSAA.