First report of bacterial leaf blight of white flowered calla lily caused by Xanthomonas campestris pv. zantedeschiae in Taiwan

Leaf blight symptoms on white-flowered calla lily (Zantedeschia aethiopica) were observed during the springs of 2002 and 2003 in some nurseries in the Yang Ming Shan area, Taipei, Taiwan. The symptoms first appeared on the lower sides of leaves as small spots. The centers of the spots quickly turned brown and were surrounded by yellowish halos. The brown spots and the halos enlarged rapidly and coalesced into irregular dry, necrotic lesions. Some of these necrotic lesions became torn and partially detached or with a shothole effect. These symptoms are as those described for Xanthomonas campestris pv. Zantedeschiae (Joubert & Truter, 1972, Bradbury, 1986).

Isolations from diseased leaves consistently yielded bacterial colonies that were yellow and glistening on Luria-Bertani agar media. Five representative isolates were chosen for further characterisation. All isolates were Gram-negative, aerobic rods, and produced yellow, water insoluble xanthomonadin pigments which were identified by thin layer chromatography (Schaad et al., 2001). The isolates were positive for catalase and b-galactosidase, and negative for oxidase, nitrate reductase, urease, and tryptophanase (indole production). All hydrolysed starch, gelatin, esculin and produced acids from metabolising lactose, sucrose, glucose and arabinose but not from rhamnose, dulcitol, mannitol and sorbitol. The bacterium was thus presumptively identified as a Xanthomonas spp. The almost complete 16S rDNA sequence of isolate XczA5 (1,502 bp; GenBank accession number AY605124) was determined and compared with available 16S rDNA sequences in GenBank. The sequence was highly similar (99%) to those of some xanthomonads including X. campestris pv. campestris (AE012540) and X. axonopodis pv. citri (AE012082).

Bacterial suspensions (10⁸ CFU per ml) were injected into leaves of white flowered calla lily to fulfill Koch's postulates. Inoculated plants were kept in a growth chamber at 28°C. Symptoms typical of X. campestris pv. zantedeschiae (Joubert & Truter, 1972) developed within 4 to 7 days in all four inoculated plants and were identical to those observed on diseased material in nurseries. Control plants were inoculated with sterile distilled water and showed no symptoms. The bacterium was readily re-isolated from diseased plants.

Bacterial leaf blight of white flowered calla lily was first reported in South Africa, and the pathogen was described as X. campestris pv. zantedeschiae (Joubert & Truter, 1972). This is a little recorded pathogen. Bradbury (1986) records the known distribution at that time exclusively to South Africa and also records no other xanthomonads from Zantedeschia spp. This is the first occurrence of this bacterium on white-flowered calla lily in Taiwan. The XczA5 isolate was deposited in the National Collection of Plant Pathogenic Bacteria (NCPPB) with the accession number NCPPB 4326.