Gypsophilas commonly cultivated are Gypsophila elegans B. and G. paniculata L. In September of 2009 and 2010, a severe wilt symptom due to crown rot was observed on G. paniculata (cv. Bristol Fairy) in greenhouses in Yeosu, South Korea. The area of cultivation (~8 ha) in Yeosu covers 90% of production in the Jeonnam Province. Disease outbreak was 20 to 30% in affected greenhouses. Early symptoms included brown discoloration surrounding basal stems and slight wilting. Late symptoms included a sunken stem rot next to the roots, root rot, severe wilting, and dying plants. The causal fungus appeared to invade plants through the basal stem, causing a crown rot that prevented the plant from taking up water and nutrients. Crown rot occurred on young and mature plants. Ten fungal isolates were recovered from basal stems and roots of wilted plants. Microconidia were abundantly produced on potato dextrose agar (PDA), V8 juice agar (VA), carnation leaf agar (CLA), and oatmeal agar (OA). Microconidia were single celled, variable, oval-ellipsoid cylindrical, straight to curved, club-to-kidney shaped or spindle shaped on OA, more slender on VA. Macroconidia were not found on any media used. Microconidia on PDA were 5.9 to 15.1 (9.9) × 2.7 to 4.3 (3.5) μm. Germinated conidia (or false conidia) were often formed on CLA. Conidiophores as phialides were singly formed but often branched. Length of conidiophores was up to 31.1 μm on CLA. Small-sized chlamydospores were rarely found. Fusarium isolates (EML-GYP1, 2, and 3) were selected and identified. From extracted genomic DNA, the internal transcribed spacer (ITS) region including 5.8S rDNA was amplified using ITS1F (5′-CTTGGTCATTTAGAGGAAGT-3′) and LR5F (5′-GCTATCCTGAGGGAAAC-3′) primers. Sequence analyses by BLAST indicated that the isolates (GenBank HM560019, HM560020, and HM560021) were most similar to F. proliferatum (EF4534150) with sequence identity values of 99.3, 99.4, and 99.1%, respectively. The causal fungus was determined to be F. proliferatum based on morphological data and ITS rDNA sequences. Pathogenicity tests with the three isolates were performed on 10 plants of G. paniculata using the dipping method. Healthy roots and basal stems were soaked in a conidial suspension adjusted to ~1.2 × 106 conidia/ml (distilled water) for 15 min. Plants were potted in sterile soil, kept in a humid chamber for 72 h, and moved to a greenhouse. The experiment was carried out in duplicate and repeated two times. Similar symptoms to those observed in the greenhouses were seen 7 days after inoculation. The causal fungus was reisolated from the artificially inoculated basal stems, fulfilling Koch's postulates. Control plants whose basal stems and roots were dipped in sterile water showed no crown rot and wilt symptoms. EML-GYP2 was determined to be the most pathogenic. Ten records of disease caused by three Fusarium species (Fusarium sp., F. oxysporum, and F. udum) have been found on gypsophilas (1), but only F. oxysporum has been reported to cause wilt on G. elgans in Korea (2). To our knowledge, this is the first report of crown rot on gypsophila caused by F. proliferatum in Korea as well as the world.
References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/, October 27, 2010, (2) W.-G. Kim and H.-M. Koo. Page 381 in: List of Plant Diseases in Korea. The Korean Society of Plant Pathology, 2009.
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