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Approximately 2 to 3 weeks before harvest, diseased plants began to wilt and collapse.
Estimated disease incidence was 50 to 55%. In order to identify the causal agent, symptomatic
tissues from five diseased plants were cut into small pieces, surface sterilized with 70% ethanol
for 1 min, rinsed three times in sterile distilled water, and placed on potato dextrose agar
(PDA). Five isolates with uniform morphology were derived from infected tissue. The colonies
had fast-growing, white, cottony aerial mycelium, and produced profuse numbers (184
sclerotia/Petri plate on average) of small, black, irregularly shaped sclerotia, less than 2 mm
in diameter. Based on morphological features, the isolates were identified as Sclerotinia minor
Jagger (Kohn 1979). To confirm the species identity, the internal transcribed spacer region of
nuclear rDNA of a representative isolate, 15-2, was amplified using the primer pair ITS1/ITS4
(White et al. 1990). Sequence analysis of the ITS region revealed 100% nucleotide identity
between isolate 15-2 (GenBank accession no. OL423632) and 14 isolates of S. minor from
different parts of the world (e.g., accession nos. AB516661, KY707828, and KC836493).
Pathogenicity tests were conducted by artificial inoculation of 55-day-old lettuce plants cv.
Majska kraljica grown on commercial growth substrate in l liter pots. The obtained isolates
were grown on PDA for 7 days and mycelial plugs, 5 mm in diameter, were cut from the
margin of the colony and placed mycelium-side down on undamaged ground-level leaves of
lettuce plants. Two plugs per isolate were placed onto five plants each for a total of 10
replicates per isolate. Five negative control plants were inoculated similarly with sterile PDA
plugs. Inoculated plants were covered with transparent plastic bags, sprayed with water (under
the plastic) twice a day for 3 to 5 days to maintain high humidity, and kept in a growth
chamber at 22°C (13 h light). After 7 to 10 days, all pathogen-inoculated plants developed
lettuce drop disease symptoms, whereas the control plants remained symptomless. The
pathogen was reisolated from symptomatic leaves and Koch’s postulates were completed by
confirming the identity of the isolates. S. minor is a widespread pathogen of different host
crops grown in many European countries. In southeast Europe, it has only been detected in
North Macedonia on sunflower. To our knowledge, this is the first report of S. minor on
lettuce in Serbia. Although S. sclerotiorum is currently the dominate lettuce drop pathogen in
the country, S. minor has the potential to cause significant yield losses under favorable
conditions. Precise identification and monitoring of shifts in pathogens responsible for causing
lettuce diseases is crucial for designing effective management strategies.
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Estimated disease incidence was 50 to 55%. In order to identify the causal agent, symptomatic
tissues from five diseased plants were cut into small pieces, surface sterilized with 70% ethanol
for 1 min, rinsed three times in sterile distilled water, and placed on potato dextrose agar
(PDA). Five isolates with uniform morphology were derived from infected tissue. The colonies
had fast-growing, white, cottony aerial mycelium, and produced profuse numbers (184
sclerotia/Petri plate on average) of small, black, irregularly shaped sclerotia, less than 2 mm
in diameter. Based on morphological features, the isolates were identified as Sclerotinia minor
Jagger (Kohn 1979). To confirm the species identity, the internal transcribed spacer region of
nuclear rDNA of a representative isolate, 15-2, was amplified using the primer pair ITS1/ITS4
(White et al. 1990). Sequence analysis of the ITS region revealed 100% nucleotide identity
between isolate 15-2 (GenBank accession no. OL423632) and 14 isolates of S. minor from
different parts of the world (e.g., accession nos. AB516661, KY707828, and KC836493).
Pathogenicity tests were conducted by artificial inoculation of 55-day-old lettuce plants cv.
Majska kraljica grown on commercial growth substrate in l liter pots. The obtained isolates
were grown on PDA for 7 days and mycelial plugs, 5 mm in diameter, were cut from the
margin of the colony and placed mycelium-side down on undamaged ground-level leaves of
lettuce plants. Two plugs per isolate were placed onto five plants each for a total of 10
replicates per isolate. Five negative control plants were inoculated similarly with sterile PDA
plugs. Inoculated plants were covered with transparent plastic bags, sprayed with water (under
the plastic) twice a day for 3 to 5 days to maintain high humidity, and kept in a growth
chamber at 22°C (13 h light). After 7 to 10 days, all pathogen-inoculated plants developed
lettuce drop disease symptoms, whereas the control plants remained symptomless. The
pathogen was reisolated from symptomatic leaves and Koch’s postulates were completed by
confirming the identity of the isolates. S. minor is a widespread pathogen of different host
crops grown in many European countries. In southeast Europe, it has only been detected in
North Macedonia on sunflower. To our knowledge, this is the first report of S. minor on
lettuce in Serbia. Although S. sclerotiorum is currently the dominate lettuce drop pathogen in
the country, S. minor has the potential to cause significant yield losses under favorable
conditions. Precise identification and monitoring of shifts in pathogens responsible for causing
lettuce diseases is crucial for designing effective management strategies.
- 601 -
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