Abstract
Head lettuce (Lactuca sativa L.) is an important crop for fresh consumption in China. In Shandong Province, head lettuce is planted in spring and in autumn each year. Because of the on-and-off rain for three weeks, head lettuce plants planted directly into the field in Jiyang City, in July 2017, 20% of the plants rapidly showed symptoms of rotting, water-soaked lesions on roots and stem bases, and then death. The diseased plants first appeared in low-lying areas prone to water accumulation. One-millimeter pieces were excised from water-soaked roots and stem bases, dipped in a 0.2% calcium hypochlorite solution for 10 min, then placed on V8 medium, and incubated in the dark at 28°C for 5 d. Two Pythium-like strains were isolated from the roots and stems. The isolates transferred to CMA and grown for 7 d, and the morphological characteristics of the two isolates on corn meal agar (CMA) were white with dense, cottony, aerial and well-branched mycelia. The two isolates produced sporangia, oogonia, antheridia and oospores. Most of the sporangia were lobate. The oogonia were smooth, nearly globose and terminal. Oospores were globose, smooth and aplerotic. The average dimensions of 50 oogonia and oospores respectively ranged from 19.5 to 25.2 (av. 23.1) µm and 17.8 to 22.3 (av. 19.9) µm. The antheridia were broadly sac-shaped. The isolates morphological characteristics were consistent with P. aphanidermatum (van der Plaats-Niterink, 1981). The COI gene and ITS region of the rDNA were amplified and sequenced using primers FM55/FM52R (Long et al. 2012) and ITS1/ITS4 (White et al. 1990), respectively. The two aligned COI sequences were identical for both isolates, as were the two ITS sequences. BLASTn analysis of the 1,133-bp COI sequence (accession no. MT952703) resulted in a 100% identity with accession number AY129164 from Lactuca sativa, which belongs to P. aphanidermatum, and the 808-bp ITS sequence (accession no. MT921597) showed a 99% identity with Genbank accession number HQ643442 belonging to P. aphanidermatum. Koch's postulates were conducted by first soaking corn kernels for 24 h in water, and then autoclaving for 2 h at 121˚C. Isolate SDHL-1 was grown on CMA for 10 days, after which agar plugs were transferred to the sterilized corn kernels and incubated at 28℃ for approximately 15 d, until the corn kernels were covered in white hyphae. Ten healthy head lettuce plants were transplanted into a sterilized loam potting soil artificially infested with the corn inoculum (3 g inoculum per 100 g loam mixture). Inoculated plants and noninoculated controls were maintained in a greenhouse at 28°C and 100% relative humidity with a 12-h photoperiod; the experiment was repeated once. All twenty inoculated plants exhibited symptoms within one week similar to those observed. Pythium aphanidermatum was recovered only from the water-soaked roots and stem bases of inoculated plants and the re-isolated cultures again identified based on morphological characteristics and sequencing of the ITS and COI genes. No symptoms were observed on the control plants. Sclerotinia sclerotiorum is reported to cause stem base rot of L. sativa in China (Zhou et al. 2011). To our knowledge, however, this is the first report of root rot of head lettuce caused by Pythium aphanidermatum. Identification of the pathogen will assist in devising strategies to reduce yield loss.
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Claims 15
Claim · model-written summary
Twenty percent of field head lettuce developed water-soaked root and stem-base lesions followed by death in July 2017.
- Taxon
- head lettucee0
- Outcome
- symptoms of rotting, water-soaked lesions on roots and stem bases, and then deathe0
- Value
- 20%e0
- Setting
- Jiyang Citye0
Not reportedDirection
Verbatim
e0“head lettuce plants planted directly into the field in Jiyang City, in July 2017, 20% of the plants rapidly showed symptoms of rotting, water-soaked lesions on roots and stem bases, and then death.”
Claim · model-written summary
Diseased lettuce first appeared in low-lying areas prone to water accumulation.
Verbatim
e0“The diseased plants first appeared in low-lying areas prone to water accumulation.”
t0“Head Lettuce”
Claim · model-written summary
Two Pythium-like strains were isolated from lettuce roots and stems.
.jpg?width=60){kind=small}
PythiumOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
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Verbatim
e0“Two Pythium-like strains were isolated from the roots and stems.”
Claim · model-written summary
The isolates had white, dense cottony aerial branched mycelia and produced sporangia, oogonia, antheridia and oospores.
- Taxon
- Pythium aphanidermatumPythium aphanidermatumt0
- Outcome
- white with dense, cottony, aerial and well-branched myceliae0
- Qualifier
- The two isolates produced sporangia, oogonia, antheridia and oosporese0
Verbatim
e0“the morphological characteristics of the two isolates on corn meal agar (CMA) were white with dense, cottony, aerial and well-branched mycelia. The two isolates produced sporangia, oogonia, antheridia and oospores.”
t0“Pythium aphanidermatum”
Claim · model-written summary
Sporangia were mostly lobate and oogonia were smooth, nearly globose and terminal.
- Taxon
- Pythium aphanidermatumPythium aphanidermatumt0
- Outcome
- sporangia were lobatee0
- Qualifier
- The oogonia were smooth, nearly globose and terminale0
Verbatim
e0“Most of the sporangia were lobate. The oogonia were smooth, nearly globose and terminal.”
t0“Pythium aphanidermatum”
Claim · model-written summary
Oospores were globose, smooth and aplerotic, while antheridia were broadly sac-shaped.
- Taxon
- Pythium aphanidermatumPythium aphanidermatumt0
- Outcome
- Oospores were globose, smooth and aplerotice0
- Qualifier
- antheridia were broadly sac-shapede1
Verbatim
e0“Oospores were globose, smooth and aplerotic.”
e1“The antheridia were broadly sac-shaped.”
t0“Pythium aphanidermatum”
Claim · model-written summary
Oogonia dimensions ranged from 19.5 to 25.2 µm with average 23.1 µm.
- Taxon
- Pythium aphanidermatumPythium aphanidermatumt0
- Organ / stage
- oogoniae0
- Outcome
- dimensionse0
- Value
- 19.5 to 25.2 (av. 23.1) µme0
Not reportedDirection
Verbatim
e0“The average dimensions of 50 oogonia and oospores respectively ranged from 19.5 to 25.2 (av. 23.1) µm and 17.8 to 22.3 (av. 19.9) µm.”
t0“Pythium aphanidermatum”
Claim · model-written summary
Oospore dimensions ranged from 17.8 to 22.3 µm with average 19.9 µm.
- Taxon
- Pythium aphanidermatumPythium aphanidermatumt0
- Organ / stage
- oosporese0
- Outcome
- dimensionse0
- Value
- 17.8 to 22.3 (av. 19.9) µme0
Not reportedDirection
Verbatim
e0“The average dimensions of 50 oogonia and oospores respectively ranged from 19.5 to 25.2 (av. 23.1) µm and 17.8 to 22.3 (av. 19.9) µm.”
t0“Pythium aphanidermatum”
Claim · model-written summary
Isolate morphology was consistent with P. aphanidermatum.
- Taxon
- P. aphanidermatumPythium aphanidermatume0
- Outcome
- morphological characteristics were consistent with P. aphanidermatume0
Verbatim
e0“The isolates morphological characteristics were consistent with P. aphanidermatum (van der Plaats-Niterink, 1981).”
Claim · model-written summary
Both isolates had identical COI sequences and identical ITS sequences.
- Taxon
- Pythium aphanidermatumPythium aphanidermatumt0
- Outcome
- COI sequences were identicale0
- Qualifier
- as were the two ITS sequencese0
Verbatim
e0“The two aligned COI sequences were identical for both isolates, as were the two ITS sequences.”
t0“Pythium aphanidermatum”
Claim · model-written summary
The COI sequence had 100% identity to a P. aphanidermatum reference.
- Taxon
- P. aphanidermatumPythium aphanidermatume0
- Gene
- COIe0
- Outcome
- identitye0
- Value
- 100%e0
- Comparator
- accession number AY129164e0
Not reportedDirection
Verbatim
e0“BLASTn analysis of the 1,133-bp COI sequence (accession no. MT952703) resulted in a 100% identity with accession number AY129164 from Lactuca sativa, which belongs to P. aphanidermatum”
Claim · model-written summary
The ITS sequence had 99% identity to a P. aphanidermatum reference.
- Taxon
- P. aphanidermatumPythium aphanidermatume0
- Gene
- ITSe0
- Outcome
- identitye0
- Value
- 99%e0
- Comparator
- Genbank accession number HQ643442e0
Not reportedDirection
Verbatim
e0“the 808-bp ITS sequence (accession no. MT921597) showed a 99% identity with Genbank accession number HQ643442 belonging to P. aphanidermatum”
Claim · model-written summary
All twenty inoculated lettuce plants developed similar symptoms within one week, while controls remained symptomless.
- Taxon
- Head Lettucet0
- Treatment
- inoculatede0
- Interactor
- Pythium aphanidermatumPythium aphanidermatumt1pathogen
- Outcome
- exhibited symptomse0
- Value
- All twentye0
- Qualifier
- within one weeke0
- Comparator
- control plantse1
Not reportedDirection
Verbatim
e0“All twenty inoculated plants exhibited symptoms within one week similar to those observed.”
e1“No symptoms were observed on the control plants.”
t0“Head Lettuce”
t1“Pythium aphanidermatum”
Claim · model-written summary
Pythium aphanidermatum was recovered only from inoculated roots and stem bases and reidentified by morphology and sequences.
- Taxon
- Pythium aphanidermatumPythium aphanidermatume0
- Outcome
- recovered only from the water-soaked roots and stem bases of inoculated plantse0
- Qualifier
- re-isolated cultures again identified based on morphological characteristics and sequencing of the ITS and COI genese0
Verbatim
e0“Pythium aphanidermatum was recovered only from the water-soaked roots and stem bases of inoculated plants and the re-isolated cultures again identified based on morphological characteristics and sequencing of the ITS and COI genes.”
Claim · model-written summary
This is reported as the first head lettuce root rot report caused by Pythium aphanidermatum.
- Taxon
- head lettucee0
- Interactor
- Pythium aphanidermatumPythium aphanidermatume0pathogen
- Outcome
- first report of root rote0
Verbatim
e0“this is the first report of root rot of head lettuce caused by Pythium aphanidermatum”