Nematode-induced root damage can cause a range of problems in affected sportsturf. Experience has shown that the severity of many of the common turf symptoms can be alleviated by applying biostimulants, but how do these materials act on plants to improve their physiology and growth?
Extracts of the brown seaweed Ascophyllum nodosum seem particularly effective in reducing nematode damage. Most of the symptoms produced by nematodes can be traced back to the changes and damage they cause in the plant roots (main image). Consequently, any technique which will induce the production of new (uninfected) plant roots will aid the turf in coping with nematode attack.
Work in our laboratory has confirmed that seaweed extracts can stimulate new root production in nematode affected turfgrass. This new root can immediately reduce the affects of the nematode damage and, often, improvement in turf condition occurs within a few days.
There are also lots of scientific data showing that plant growth can be improved by seaweed extracts in other cases of biological induced stress (e.g. fungal infection) or when abiotic stresses (e.g. high salinity) act on plants.
Much of the information on the mode of action of biostimulants comes from experiments using a small plant, Arabidopsis thaliana. This plant is widely used to investigate plant physiology and genetics and, like turfgrass, it responds well to applications of seaweed extract.
Scientists at the Nova Scotia Agricultural College in Canada showed recently that the growth of Arabidopsis experiencing high salt stress could be significantly improved by treatment with Ascophyllum nodosum extracts (Figure 1).
Perhaps the most significant aspect of this work was that the scientists were able to monitor the effects of the seaweed extracts on Arabidopsis plant metabolism. They found that, only twenty-four hours after seaweed application, the activity of 184 Arabidopsis genes had increased and, within five days, over 250 plant genes were responding positively to the biostimulant.
Detailed analysis of the affected genes showed that some were involved in plant responses to stress. These changes observed within the plant indicate that biostimulants can affect plant performance by modifying their most fundamental processes i.e. gene function.
Genes influence all aspects of plant biology, ranging from their growth and reproduction to defence against pests and pathogens. An ability to modify gene activity using biostimulants may provide an extremely powerful method to manipulate turfgrass performance. However seaweed extracts are complex mixtures of chemicals and a lot of work will be required to identify exactly which chemicals affect specific plant genes.
A second area of research, which is producing promising results, concerns a bacterial protein known as Harpin which is being marketed as a biopesticide with significant biostimulatory properties.
Harpin protein is produced by Erwinia, a bacterial plant pathogen which causes the fireblight disease in apples and pears. When Harpin is applied to a plant leaf it binds to plant cell receptors, initiating a series of complex signalling pathways in the cells which culminate in changes in gene activity.
While most pesticides act directly on the target pest, Harpin, elicits a natural defense mechanism in the plant (analogous to a broad spectrum immune response in animals) making it resistant to a wide range of fungal, bacterial, and viral diseases. The changes in gene activity also stimulate aspects of plant growth including nutrient uptake, photosynthesis, reproduction and general plant vigour.
Research data from the USA has demonstrated that Harpin also reduces the effects of both endoparasitic and ectoparasitic nematode attack in a wide range of agricultural crops. This led to the realisation that Harpin may also provide a means to manage nematode damage in turfgrass. Trials in North America using Harpin have shown that bermuda grass turf infected with sting nematodes responded with improvements in leaf colour, root growth and, most significantly, a reduction in nematode levels.
Recent work in our laboratory has confirmed that the plant biostimulatory effects of Harpin protein on turfgrass can be as significant as those induced by Ascophyllum nodosum extracts (Figure 2). Currently our research is attempting to determine if Harpin protein application to turfgrass can also reduce the levels of the most important European turfgrass nematodes.
As increasing numbers of plant protection products are withdrawn from use in Europe, it seems that biostimulants may help fill the gap by delivering a range of novel and effective pest and disease management tools for turf production.