Turfgrass Disease Research Advances
Posted: January 28, 2016
A Sustainable Solution Aims at Environmental Stewardship and Reduced Input
Development of disease management approaches based on environmental stewardship is a growing trend in turfgrass industry. Traditionally, there has been a heavy reliance on chemical approaches to manage diseases. This has resulted in undesired social impacts in urban and suburban environments, unnecessary financial inputs, as well as the development of resistant pathogen populations. I believe that development of an innovative approach to disease management through integration of host defense response elicitors, investigation of population biology and host adaptation, and detection and quantification of inoculum for targeted application of fungicides can be employed as important components of a sustainable disease management strategy.
Investigation of systemic acquired resistance (SAR) in perennial ryegrass revealed that infection by the gray leaf spot pathogen, Magnaporthe oryzae, causes an accumulation of endogenous free salicylic acid (SA) in the ryegrass leaf blades. Applications of known plant defense activators such as SA and benzothiadiazole (BTH) suppressed gray leaf spot disease while enhancing expression levels of pathogenesis-related proteins. Disease incidence and severity were significantly decreased when plants were treated with SA and BTH prior to inoculation. Regardless of the host-pathogen interaction, products of several of these genes are known to accumulate to a higher degree and play a pivotal role in plant defense against pathogen infection. These results suggest that an early and higher induction of these genes by systemic resistance inducers may provide perennial ryegrass with substantial advantage to defend itself from infection by M. oryzae.
Effects of application timing of different concentrations of salicylic acid (SA) (days prior to inoculation of plants with Magnaporthe oryzae) on A, incidence and B, severity of gray leaf spot disease in perennial ryegrass turf. Solid white bars = untreated control plants, dotted bars = 1.5 mM SA-treated plants, stripped bars = 2.5 mM SA-treated plants, and black bars = 3.5 mM SA-treated plants. Each bar represents average percentage of disease incidence for three replicates (}standard error).
Microscopic analysis of aniline-blue-stained callose deposition during Magnaporthe oryzae development on perennial ryegrass. Nonpenetrated papillae showing localized deposition of callose beneath the attempted penetration sites as seen by epifluoroscent microscopy with A, UV filter and B, white light. Penetrated callose deposited papilla on epidermal cell, as viewed by epifluoroscent microscopy with C, UV filter and D, white light, in which M. oryzae has established secondary hyphae. A = appressorium, GC = germinating conidia, PGT = primary germ tube, and SH = secondary hyphae. Inset in C is a greater view of the penetrated callose. Bar = 10 μm.
(Rahman, A., Kuldau, G. A., and Uddin, W. 2014. Induction of salicylic acid–mediated defense response in perennial ryegrass against infection by Magnaporthe oryzae. Phytopathology 104:614-623)
The majority of fungicides used by the golf turf industry are for control of dollar spot, caused by Sclerotinia homoeocarpa. Calendar spray programs are a common practice, where applications are largely based on calendar days and weather forecasts. Premature applications of fungicides often lead to unnecessary use of chemicals. Through molecular detection of pathogen DNA and the quantification of pathogen biomass, my lab is working on development of a technique to determine the “critical mass” of S. homoeocarpa fungal biomass required in host plants to incite dollar spot. Determination of this critical mass will aid in further development of disease forecasting models; thus, providing an accurate recommendation for initiation of fungicide spray programs.
Further research undertaken in my lab is to evaluate the genetic diversity of S. homoeocarpa in the eastern United States. Our research has confirmed that there are two distinct groups of isolates causing dollar spot within the transition zone, an area where both C3 (cool-season) and C4 (warm-season) grasses are widely grown. Of interest to my lab is to what extent these isolates are capable of infecting the opposite host types.
As part of our efforts to support golf course superintendents in producing quality turf in Pennsylvania, my outreach program provides assistance through our Turfgrass Disease Clinic. The clinic offers disease diagnosis and management recommendations. Visit the Turfgrass Disease Clinic for information on turfgrass sample submission.