Sphaerellopsis filum on willow rust pustules. Thread- like objects are spore mass produced by S. filum.

Compared with annual crops, SRC is better suited for biocontrol because of the carry-over effect on biological control agents, assuming a 3-5 year harvest interval. Sphaerellopsis filum is a fungal hyperparasite. It attacks a wide range of rust fungi, including willow Melampsora. Under experimental conditions, the hyperparasite can reduce willow rust spore production by up to 98%. Although S. filum occurs only on rusts in nature, it can be cultured on artificial media. This provides the opportunity of growing the fungus in vitro and then reintroducing it into the field.

Previously, only asexual stage of S. filum was known in the British Isles. Asexual conidiospores are waterborne and dispersed mainly by rain splash. Recently, it was found that sexual ascospores occur in S. filum in the UK (Yuan et al., 1998). Ascospores are airborne and, hence, are more efficiently dispersed. Until very recently, it was not clear whether S. filum is specialised in its pathogenicity. Recent studies revealed that S. filum varies in pathogenicity and some strains are significantly more virulent than others to willow Melampsora (Yuan et al., 1999). Answers to the following will help to deploy S. filum more effectively for biocontrol of rust in SRC willow: (a) to what extend S. filum vary in pathogenicity, (b) whether S. filum produces the sexual stage on willow rust and (c) how it spreads.

Yuan, Z. W.; Pei, M. H.; Hunter, T.; Royle, D. J.  (1998)  Eudarluca caricis, the teleomorph of the mycoparasite Sphaerellopsis filum, on blackberry rust Phragmidium violaceum.  Mycological Research 102, 866-868. 

Yuan, Z. W.; Pei, M. H.; Hunter, T.; Ruiz, C.; Royle, D.J. (1999) Pathogenicity to willow rust, Melampsora epitea, of the mycoparasite Sphaerellopsis filum from different sources.  Mycological Research 103, 509-512.