Cylindrocladium pauciramosum causes root and collar rot of Polygala myrtifolia in Spain

A. Pérez-Sierra¹*, L.A. Álvarez¹, B. Henricot², J. García-Jiménez¹ and J. Armengol¹

¹ Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Camino de Vera s/n. 46022 Valencia, Spain
² Royal Horticultural Society, Wisley, Surrey GU23 6QB, UK

*aperesi@eaf.upv.es

Accepted for publication 16/05/05

Polygala myrtifolia (Polygalaceae) or milkwort is an evergreen shrub (Fig. 1), commonly found in Mediterranean gardens. In November 2004, plants of P. myrtifolia showing foliar chlorosis, wilting of the shoots, with collar and root rot (Fig. 2) were observed in Valencia, eastern Spain. A Cylindrocladium spp. was isolated from the infected parts.

Figure 1: Healthy plant of Polygala myrtifolia	Figure 2: Collar rot of Polygala myrtifolia caused by Cylindrocladium pauciramosum

Single conidial isolates were grown on carnation leaf agar under near-ultraviolet light at 25şC for 7 days (Crous & Wingfield, 1994). The macroconidiophores (Fig. 3) were septate, 115-185 (170) µm long, with a terminal pear-shaped vesicle (Fig. 4), measuring 4-8 (7) µm in width. Phialides (12 x 4 µm) were doliform to reniform, with conidia 40-58 x 3.5–5 µm, cylindrical with rounded ends, one septate. Chlamydospores were brown and formed microsclerotia. These features agree with the description of C. pauciramosum (Schoch et al., 1999). Further confirmation was obtained by sequence analysis. The 5’ end of the b-tubulin gene was amplified using the primers T1 and Bt2b (Henricot & Culham, 2002). The sequence of the amplified product was deposited in GenBank (accession number AY923867). Comparison with other sequences in GenBank revealed that the isolates described here were identical with C. pauciramosum (DISTEF-G 192) from P. myrtifolia in Italy.

Figure 3: Macroconidiophores of Cylindrocladium pauciramosum isolated from P. myrtifolia	Figure 4: Terminal vesicle, macroconidiophore of C. pauciramosum

To confirm pathogenicity, wounds made at the base of the stems of 1-year-old plants of P. myrtifolia were inoculated with an aqueous suspension of 2 x 10⁵ conidia per ml. Control plants were treated with sterile distilled water. The inoculated plants developed symptoms similar to those observed in natural infections (Fig. 5). C. pauciramosum was reisolated from the diseased parts of the inoculated plants.

Figure 5: Wilting of P. myrtifolia shoots on inoculated plants.

This disease was first reported in Europe only recently, affecting P. myrtifolia in Italy (Polizzi & Crous, 1999). C. pauciramosum has a wide host range and attacks many other ornamentals, although this is the first record on any known host from Spain. The disease affects relatively small numbers of plants at present, with reports of 3% losses in nurseries.

References

Crous PW, Wingfield MJ, 1994. A monograph of Cylindrocladium, including anamorphs of Calonectria. Mycotaxon 51, 341-435.

Henricot B, Culham A, 2002. Cylindrocladium buxicola, a new species affecting Buxus spp., and its phylogenetic status. Mycologia 94, 980-997.

Polizzi G, Crous PW, 1999. Root and collar rot of milkwort caused by Cylindrocladium pauciramosum, a new record for Europe. European Journal of Plant Pathology 105, 407-411.

Schoch CL, Crous PW, Wingfield BD, Wingfield MJ, 1999. The Cylindrocladium candelabrum species complex includes four distinct mating populations. Mycologia 91, 286-298.

The British Society for Plant Pathology