Effects of the Mycoparasite Sphaerellopsis filum on Overwintering Survival of Stem Rust in Perennial Ryegrass

Abstract

Gordon, T. C, and Pfender, W. F. 2012. Effects of the mycoparasite Sphaerellopsis ftlum on overwintering survival of stem rust in perennial ryegrass. Plant Dis. 96:1471-1481.--Sphaerellopsis filum is a mycoparasite of Puccinia graminis subsp. graminicola, a rust fungus that causes widespread crop damage on perennial ryegrass grown for seed. In observations taken over the winter months, S. filum was found naturally colonizing 2% of P. graminis subsp. graminicola uredinia on first-year plantings and 25% of the uredinia on second-year plantings of perennial ryegrass. In controlled experiments conducted in glasshouses and growth chambers, S. filum applied to rust-inoculated plants reduced the lifetime spore production of P. graminis subsp. graminicola pustules by half, from 39,000 to 18,000 spores/pustule . Mist duration, temperature, and P. graminis subsp. graminicola pustule age at the time of 5. filum inoculation had significant effects on the proportion of P. graminis subsp. graminicola pustules infected by 5. filum. Fifty percent of all P. graminis subsp. graminicola pustules were infected when S. filum was inoculated onto erumpent pustules and incubated above 5°C for 48 h while exposed to mist. Plants inoculated with both fungi under controlled conditions and then planted into the field had a significantly greater proportion of P. graminis subsp. graminicola pustules infected with S. filum, and a significantly reduced P. graminis subsp. graminicola overwintering population, compared with plants inoculated with P. graminis subsp. graminicola only. First-year stands of perennial ryegrass treated in the field with monthly applications of S. filum had more than 10 times the proportion of pustules infected with S. filum and 50% less P. graminis subsp. graminicola disease compared with the nontreated controls. In comparison, plants with one application of fungicide during the winter had 98% lower P. graminis subsp. graminicola severity than the P. graminis subsp. graminicola-only control There were no effects of S. filum or fungicide application on rust severity in 2-or 3-year-old perennial ryegrass stands.Perennial ryegrass (Lolium perenne L.) is a cool-season seed crop intensively cultivated in the Pacific Northwest of the United States, New Zealand, and parts of Europe (3,37,38). The most damaging disease of perennial ryegrass in the Pacific Northwest is stem rust, caused by the fungus Puccinia graminis subsp. graminicola Z. Urb. If untreated with fungicide, stem rust can cause reductions in seed yields exceeding 90% (24).Weather conditions and host growth during the cropping season (spring and summer) play a major role in determining the severity of the stem rust epidemic. These factors have been combined into a mathematical model that predicts disease severity based on daily weather inputs, host stage, and initial spring rust severity (25,26,28). The model predicts that disease severity during the course of the epidemic is proportional to the initial amount of rust in the spring, if all other variables are held...

Incidence, Identification, and Mycoparasitic Activity of Clonostachys epichloë, a Hyperparasite of the Fungal Endophyte Epichloë typhina

“…Mycoparasitism is widespread in nature (Jeffries 1995;Jeffries and Young 1994), and has been intensely studied as a potential biocontrol measure in fungal diseases. For instance, the mycoparasite Sphaerellopsis filum decreases the winter survival of Puccinia graminis in perennial ryegrass (Gordon and Pfender 2012), Clonostachys rosea has potential as a biocontrol agent for the control of alfalfa blossom blight caused by B. cinerea (Li et al 2004), while Sphaerodes retispora may play a similar role against watermelon wilt caused by Fusarium oxysporum (Harveson et al 2002).…”

Genetic diversity and specialisation of Eudarluca caricis on some graminaceous Puccinia species

“…For example, P. coronata is abundant for much of the year on weedy populations of H. lanatus which is itself abundant in many areas of Europe. P. coronata can be a serious problem in growing seed crops of Lolium perenne and may be partly controlled by E. caricis (Gordon & Pfender, 2012). The present results suggest that E. caricis on P. coronata and perhaps other rusts infecting wild or weedy grasses such as H. lanatus might be virulent on strains of P. coronata infecting L.…”

“…The enemy release hypothesis suggests that organisms which become invasive may do so because they have moved to a new geographic area without the natural enemiespathogens and pestswhich regulate them in their range of origin (Evans, 2008). Natural enemies of rusts are therefore of interest from two points of view: they may help regulate agricultural and horticultural pests (Fleming, 1980;Vandermeer et al, 2009;Gordon & Pfender, 2012); and they may reduce the effectiveness of rusts as biocontrol agents.…”

“…It can easily be cultured in artificial media, although it is not found sporulating in nature except in association with rusts. In favourable systems, it can sometimes usefully reduce losses due to certain rusts (Morris et al, 1994;Gordon & Pfender, 2012), although this requires the population of E. caricis to be substantial at the start of the season and therefore able to increase sufficiently rapidly to slow down rust development before the rust becomes damaging. This is unlikely in most agricultural settings, but can occur if, for example, a population of rust on a weed pre-exists the development of severe epidemics on the crop, providing a reservoir from which E. caricis can spread to the rust on the crop.…”

Cladobotryum mycophilum as Potential Biocontrol Agent

“…Thus, Ampelomyces quisqualis, a mycoparasite specific to Erysiphales, has been studied as a biocontrol agent [20], and Sphaerellopsis filum has been used for the control of plant rust disease caused by Puccinia graminis subsp. graminícola [21], among other examples. However, the aggressive fungicolous taxa most studied and used in agriculture is Trichoderma, the genus by excellence [22][23][24].…”