Y. M. Shen,
C. H. Chao,
F. C. Wang,
H. L. Liu and
T. C. Huang, Plant Protection Laboratory, Taichung District Agricultural Research and Extension Station, Changhua, Taiwan, R.O.C.
Eustoma (Eustoma russellianum) is an economically important cut flower in Taiwan. Each year more than 1.7 million dozen flowers, mainly exported to Japan in the winter, are produced in greenhouses. In January 2011, eustoma plants with stem and leaf blight symptoms were observed in some greenhouses in Changhua County, Taiwan, at an incidence of 2%. Brown and rotten lesions were presented on the stem and nearby leaves, with white mycelia growing on the surface and black sclerotia (up to 7 mm long) produced inside the stem. Infected plants were completely blighted and eventually died. Diseased stem tissues collected from the field were surface sterilized for 3 min in 0.6% NaOCl, rinsed with sterilized distilled water, and plated on potato dextrose agar. White fungal colonies were consistently isolated. The cultures produced large sclerotia at the peripheries of the plates. Internal transcribed spacer (ITS) sequences of two voucher isolates were determined and deposited in GenBank (Accession Nos. JQ653934 and JQ653935). The sequences were 100% identical to that of Sclerotinia sclerotiorum strain ATCC MYA-4521 (Accession No. FJ810516). In addition, PCR amplified DNA fragments (approximately 630 bp) were obtained by the S. sclerotiorum specific primer pair MP_SsF and MP_UniR (1). On the basis of morphology, ITS sequence homology, and the specific PCR detection, the fungus was identified as S. sclerotiorum. The two fungal isolates (BCRC34830 and BCRC34831) were deposited in Bioresource Collection and Research Center, Hsinchu, Taiwan. Pathogenicity tests were conducted on 1-month-old, second flush eustoma cultivars Ex Rosa Pink Flash and Rosina Blue Ver. 2 after primary flowers had been harvested in the greenhouse. Fungal inoculum consisting of Tref horticultural substrate and wet sterilized rice colonized by S. sclerotiorum BCRC34830 (substrate-rice-water ratio of 2:1:1) was placed near the base of the plants. Ten plants of each cultivar were inoculated with about 800 g of the mixture. Sterile mixture applied to an equal number of plants served as negative controls. Eight plants of each cultivar showed blight symptoms after 1 month of incubation at an average temperature of 26°C. All control plants remained healthy. The pathogen reisolated from the inoculated stems produced sclerotia identical to those isolated in the field, fulfilling Koch's postulates. The pathogenicity test was repeated with similar results. S. sclerotiorum has been reported on eustoma in Argentina (2). To our knowledge, this is the first report of Sclerotinia blight on eustoma in Taiwan. Although the disease was not prevalent on eustoma, the inoculum could be dormant in the greenhouse soil. Awareness of the potential perennial problem could increase the quality of the flowers exported and benefit the flower industry.
References: (1) S. Hirschhäuser and J. Fröhlich. Int. J. Food Microbiol. 118:151, 2007. (2) S. Wolcan et al. Plant Dis. 80:223, 1996.