Occurrence of Pink Patch of Perennial Ryegrass Caused by Limonomyces roseipellis in Italy.

Abstract

In March 1999, an unusual pink gelatinous mycelium was observed on several cultivars of perennial ryegrass (Lolium perenne L.) turf grown in experimental plots in Saint Andrea d'Agliano, Perugia (central Italy). Approximately 50% of the turf area showed symptoms on susceptible varieties. The same symptoms, although with lower severity, were observed during the following year in two experimental fields in northern Italy. The presence of mycelium on infected leaf blades was extensive during periods of high relative humidity and high temperature. The disease decreased progressively when weather conditions became dry and cold. A fungus, characterized by pink colonies, was consistently isolated from leaves of affected plants on potato dextrose agar (pH 5.5). On the basis of the presence of clamp connections and binucleate hyphal cells, the fungus was identified as Limonomyces roseipellis Stalpers & Loerakker, the causal agent of pink patch of turfgrass (1,3). For the pathogenicity test, one isolate of L. roseipellis was grown on maize flour and sand medium (2) at 22 ± 2°C for 14 days. Inoculum (20 g) was added to a sterile mixture of sand and peat moss (1:1; 640 g). Two hundred seeds of L. perenne (cv. Amadeus) were sown in boxes containing infested or noninfested soil as a control. Boxes were kept in a greenhouse at 22 ± 2°C, 80% relative humidity, and 14 h of sunlight per day. Four to five weeks after sowing, typical lesions resembling natural symptoms were observed only on plants grown in inoculum-infested soil, and L. roseipellis was consistently reisolated from diseased plants. Pink patch is probably underestimated in turf since the symptoms are less severe compared with red thread caused by Laetisaria fuciformis (McAlpine) Burdsall, and the development of mycelium of Limonomyces roseipellis is slower.