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Root rot is a serious disease of garlic in the Shandong Province of China. Infected plants display symptoms such as dwarfed garlic bulbs, yellowing of leaves starting from the periole, discoloration of the basal stem, and rot. The aim of this study was the identification of the main pathogens involved in garlic root rot. Fifty garlic plants with root rot were collected from the five main production areas of garlic in the Shandong Province. Isolates was incubated using selective medium and identified using morphological method and the ribosomal DNA internal transcribed spacer (ITS) sequence alignment, followed by the confirmation of pathogenicity and the identification of biological characteristics of the putative pathogens. The isolation frequency of Pythium isolated from garlic root was 45%, resulting in a total of 12 isolates. According to morphological identification and ITS sequence alignment, the 12 isolates were further identified as Pythium sylvaticum Compbell & Hendrix, Pythium heterothallicum Compbell & Hendrix, Pythium paroecandrum Drechsler, and Pythium violae Chesters & Hickman. All 12 isolates were pathogenic when inoculated on the root collar and roots of garlic plants. The optimal temperature of Pythium growth was 20–25 °C and pH was 6–7. Pythium sylvaticum, Pythium heterothallicum, Pythium paroecandrum, Pythium violae, and Pythium sp. 845 us-2 were identified as causal agents of garlic root rot.

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.

A new species, Dendrographium multiseptatum, is described and illustrated from specimens collected on rotten twigs in China. This fungus is characterized by synnematous conidiophores with polytretic conidiogenous cells producing obclavate, 6–9-distoseptate, pale brown conidia.