First report of Macrophomina phaseolina causing crown and root rot of strawberry in Spain

Huelva in southern Spain is a major production area for strawberry (Fragaria x ananassa). At the end of the 2006 season (May-June) collapsed and dying strawberry plants were observed on several cultivars in four fields (Fig. 1). Cut crowns of symptomatic plants revealed dark brown necrotic areas on the margins and along the woody vascular ring (Fig. 1). Roots of affected plants were also shown to be necrotic. Macrophomina-like isolates developed from surface-disinfested symptomatic tissues plated on potato dextrose agar amended with 250 mg/L of chloramphenicol.

Dark, oblong-shaped sclerotia were observed in infected crown tissue and in culture after 5 to 7 days incubation at 25°C (Fig. 2). They had an average length of 107 (217 to 62) μm and width of 71 (110 to 35) μm. Sequenced rDNA fragments of a single sclerotium isolate CH 724 (Spanish Type Culture Collection, CECT 20715; GenBank Accession No. AM410964) presented a 99% identity with Macrophomina phaseolina (Tassi) Goidanich. Morphological and molecular results confirmed this species as M. phaseolina (Holliday & Punithalingam, 1970).

Six single sclerotium isolates of M. phaseolina from strawberry were used for pathogenicity tests. Each isolate was used to inoculate six strawberry runner plants (cv. Camarosa) growing in pots of coconut fibre substrate for 5 weeks. Plants were inoculated by inserting a colonised toothpick into each crown (Mertely et al., 2005). An equal number of uninoculated plants treated similarly were left as controls. After 58 days, the incidence of plant death ranged from 67% to 100% depending on isolate (Fig. 3). M. phaseolina was reisolated from all symptomatic plants. Uninoculated plants remained symptomless.

Although M. phaseolina has been reported on other crops in Spain, this is the first report of the pathogen on strawberries in this important production area. Similarly, this pathogen has been reported recently from strawberry-growing areas of other countries using alternatives to methyl bromide (Mertely et al., 2005; Zveibil & Freeman, 2005. Crown and root rot in strawberries caused by M. phaseolina may be an emerging disease following the phase-out of methyl bromide.