Turf disease detection IX. Acidovorax avenae

Agrostis stolonifera L. is a popular cool season species used in temperate climate zones for golf course greens. Abiotic and biotic stresses are common during the summer months and therefore intensive management is required to prevent disease and maintain turf quality throughout the growing season. In recent years, bacterial aetiolation (caused by Acidovorax avenae y Xanthomonas translucens) has emerged as a growing concern for many greenkeepers (Giordano et al. 2012; Roberts et al. 2014).

Aetiology of bacterial aetiolation

Bacterial aetiolation is a disease affecting a wide range of monocotyledonous plants, especially grasses such as turf. The disease is characterised by absence of green colour on leaves, stems and other plant parts. Instead of a healthy green colour, plants affected by bacterial aetiolation may have yellowish, whitish or even transparent tones. They are characterised by elongation and weakening of stems and internodes.

Causative agent of bacterial aetiolation

The causative agent of bacterial aetiolation in turfgrass is the bacterium Acidovorax avenae subsp. avenae. This Gram-negative, aerobic, non-fluorescent member of the β-proteobacteria, of the order Burkholderiales was first diagnosed in turf in 2010 by pathogenicity assays and 16S rDNA sequence analysis.

Up to that date the only pathogenic bacteria of note in turfgrass are those of the genus Xanthomonas.

Symptoms of Bacterial Etiolation in Lawns

Bacterial aetiolation caused by Acidovorax avenae subsp. avenae on Agrostis is characterised by several distinctive symptoms:

Image 1. Symptoms of Bacterial aetiolation in sheet form.

• Starts as small areas (15 to 30cm) irregularly textured, fading from their natural green to a pale yellow.
• Lengthening of internodesInfected parts of the plant may show elongated and weak internode growth, resulting in an abnormally long and slender appearance. Ethylation is a process in which plants elongate abnormally by separating the nodes from each other.
• Weakness and wiltingInfected plants may show signs of general weakness, with wilted leaves and a general sickly appearance.
• Growth arrestBacterial infection can stunt normal plant growth, resulting in slow development and a stunted appearance.
• Death of the plantIn severe cases of infection, the plant may die due to the general weakening caused by the bacteria.

Most susceptible species

The species that has been observed to be most affected is Agrostis stolonifera, typically used on golf greens and putting greens. However, some outbreaks have also been detected on Lolium perenne in Japan although it is much less widespread in this one. It has also been shown to be able to attack Agrostis tenuis, P. annuaand F. arundinacea under certain conditions

Bacterial Etiolation: Occurrence and Dispersal

Appearance

Stress causes a major impact and can be observed in areas of the green with high traffic. It is at this time that the bacteria in the Acidovorax avenae causes a decline leading to losses of grass areas.

Dispersion

Dispersal of the pathogen is by splashing rain and/or wind, which transports the bacterial exudate platelets present on the leaves and is facilitated by small wounds caused by rubbing between the leaves.

Factors Influencing Emergence

• Temperature: The optimum temperature for growth is between 24°C and 35°C.
• Stress: Drought stress or nutritional deficiencies can weaken turf and make it more susceptible to disease. The use of humidity probes can help us to monitor this infection factor.
• Other factors: Excess nitrogen, lack of sunlight, leaf damage, mowing too low below 2.6 mm, misuse of growth regulators, excessive traffic.

Disease Control

The options for controlling bacterial infections in turfgrass are extremely limited and the search for new control methods is a topic of current interest. In particular, research is being carried out on the use of Acylbenzolar-S-methyl (ASM)a synthetic analogue of salicylic acid (SA)

Experiments in controlled environments with oxytetracycline y streptomycin sulphate significantly reduced bacterial decline symptoms when plants were pre-treated as foliar spray suspensions prior to inoculation with the bacteria.

However, the application of ammonium sulphate and growth regulators such as Trinexapac-ethyl (TE) significantly increase symptoms.

Early and accurate diagnosis can lead to appropriate management recommendations and avoid unnecessary and ineffective fungicide treatments (Sundin et al. 2016). Although an effective management option has not yet been developed, early diagnosis can avoid misdiagnosis as a fungal disease and thus avoid misuse of fungicides.

Analysis and diagnosis of bacterial aetiolation

The initial symptoms can be confused with other diseases or conditions of agrostis turf, making diagnosis of the problem very complex. Damage from this disease is very severe on highly maintained greens due to stress or traffic due to frequent mowing, harrowing or topdressing.

Real-time quantitative polymerase chain reaction (qPCR) has been widely used in the detection and quantification of plant pathogens (Lopez et al. 2010; Pritchard et al. 2012b; Wang et al. 2015). The ability to rapidly amplify and sensitively detect pathogen DNA by real-time PCR allows technicians to provide definitive diagnostic results within one day (Schena et al. 2004).

Source: Giordano, P. R., Chaves, A. M., Mitkowski, N. A., and Vargas, J. M., Jr. 2012. Identification, characterization, and distribution of Acidovorax avenae subsp. avenae associated with creeping bentgrass etiolation and decline. Plant Dis. 96:1736-1742.

Source: Netsu, O., Komatsu, K., Yoshimura, T. et al. First report of brown stripe on perennial ryegrass (Lolium perenne L.) caused by Acidovorax avenae. J Gen Plant Pathol 88, 399-404 (2022).