First Report of Calonectria Leaf Spot Caused by Calonectria colhounii (Anamorph Cylindrocladium colhounii) on Rhododendron in Belgium.
Belgium is among the most essential Rhododendron-producing areas in Europe, with an annual sale of roughly 1.6 million vegetation. In June 2010, an outbreak of leaf spots on a number of 1000’s of Rhododendron cv. Marcel Menard vegetation befell at a nursery close to Gent. Diseased vegetation confirmed darkish brown leaf spots that enlarged and at last resulted in leaf drop. Signs developed most explicitly on this cultivar, particularly after customary repotting throughout Could or June and when repotting was adopted by a number of days of unusually heat temperatures (30 to 35°C).
The vanguard of diseased leaf tissue was excised, floor disinfected with 1% NaOCl for 60 s, and rinsed twice with sterile distilled water earlier than being plated onto potato dextrose agar (PDA). After 5 days of incubation at 21°C at midnight, Cylindrocladium-like fungal colonies with white aerial mycelium and amber-brown progress inside the agar constantly developed. Mycelium was transferred aseptically to recent plates of PDA and incubated for 10 to 14 days at 17°C underneath a 12-h fluorescent mild routine to check the morphological traits.
Conidiophores confirmed a penicillate association of fertile branches, producing two to 6 phialides. They arose from a stipe and terminated in a clavate vesicle (Three to five μm). Conidia have been straight, cylindrical, rounded at each ends, three septate, and measured 60 to 70 × Four to six μm. Yellow subglobose to oval perithecia have been abundantly produced. Asci have been clavate, 4 spored, and measured 100 to 150 × 15 to 30 μm. Ascospores have been hyaline, three septate, and measured 50 to 65 × 5 to six μm.
These traits are per these of Calonectria colhounii Peerally (1). The β-tubulin gene was PCR-amplified with DNA extracted from the mycelium and the T1 and T2 primers (3), sequenced straight with a BigDye Terminator Cycle Sequencing Equipment (Utilized Biosystems, Carlsbad, CA), and the DNA sequence was deposited. BLASTn alignment confirmed 99% identification with the β-tubulin DNA sequence derived from Calonectria colhounii CBS 293.79. A spore suspension (105 conidia per ml) was ready from a 1-week-old tradition, and 50-μl drops have been used to inoculate the abaxial facet of 10 indifferent 1-year-old leaves from Rhododendron cv.
Cunningham’s White. Ten management leaves have been inoculated with water. The leaves have been positioned in a moist chamber and incubated at 21°C at midnight. After 5 to six days, all spore-inoculated leaves confirmed lesions an identical to these on the naturally contaminated leaves, whereas the water-inoculated leaves remained symptom free. Following the unique process, the fungus was reisolated from the diseased leaves and the morphological traits of the ensuing tradition have been the identical as these of the inoculated isolate, finishing Koch’s postulates.