Maize is one of the most important crops in the world. Heilongjiang province has the largest maize area in China. Plant-parasitic nematodes are important agricultural pests, which cause huge economic losses every year and have attracted global attention. Potato rot nematode Ditylenchus destructor is a plant-parasitic nematode with a wide range of hosts and strong survival ability in different environments, which brings risks to agricultural production. In 2020, D. destructor was detected in seven maize fields in Heilongjiang province. Morphological identification and molecular approach were used to characterize the isolated D. destructor. The observed morphological and morphometric characteristics were highly similar and consistent with the existing description. The DNA sequencing on the D2/D3 region of the ribosomal DNA 28S and the phylogenetic analysis showed that D. destructor population obtained from maize and other isolates infesting carrot, sweet potato, and potato were in subclade I supported by a 96% bootstrap value. Additionally, the phylogenetic analysis of the ITS rRNA gene sequence further indicated that this D. destructor population from maize clustered in a clade I group and belonged to ITS rRNA haplotype C. An inoculation experiment revealed that D. destructor was pathogenic on the maize seedlings in pots and caused the disease symptoms in the stem base of maize seedlings. This is the first report of D. destructor causing stem rot of maize in Heilongjiang province, and contributes additional information on disease control and safe production of maize in the region.

Black scurf and stem canker on potato (Solanum tuberosum L.), caused by Rhizoctonia solani, is one of the most important soil-borne diseases throughout the world. Isolates of R. solani anastomosis group (AG) 3-PT have been reported as the predominant cause of the disease on potato (Carling 1996) and the same results were also obtained in Heilongjiang Province, China (Yang et al. 2017). In October 2020, 14 diseased potato tubers (cv. Youjin-885) with symptoms typically associated with black scurf were found in Hegang City of Heilongjiang in Northeast China, where potatoes are grown for propagation in the breeding nursery. Pieces of sclerotia were removed from the surface of the potato and were surface sterilized with 70% ethanol for 30 s and 0.5% NaClO for 1 min, then rinsed three times with sterile distilled water and placed on potato dextrose agar (PDA) at 25°C in the dark. After incubation for 48 to 72 h, mycelia resembling Rhizoctonia were microscopically examined for morphological characteristics, and hyphal tips transferred to fresh plates of PDA. The characteristics of the observed isolate were typical of R. solani Kühn, which include hyphal branching at right angles, a septum near the branching point and a slight constriction at the branch base (Yang et al. 2015). Hyphal cells were also determined to be multinucleate by staining with 1% safranin O and 3% KOH solution (Bandoni 1979). PCR amplification and DNA sequencing of the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA) was performed by using the universal primers ITS4/ITS5 (White et al. 1990). The resulting sequence of 700 bp (GenBank accession no. OL770460) showed more than 99% identity to AG 2-2IV isolates present in GenBank (e.g. AB911322; KR259910). On the basis of morphological characteristics and molecular analysis, the isolate was identified as R. solani AG 2-2IV. Pathogenicity of the isolate was tested in greenhouse conditions. Pathogen-free minitubers (cv. Favorita) of approximately the same size (10 to 20 g) were allowed to sprout at room temperature for 10 days. The minitubers were then planted in autoclaved soil in a plastic pot (4 L capacity), placed in a greenhouse at 18 - 27°C (night-day) with 50% relative humidity and watered as required. The pots were inoculated with 7-mm-diameter mycelial plugs (from one PDA petri plate) near the minituber, which was then covered with potting mix. The control pots were inoculated with sterile plugs of PDA. Each treatment consisted of 10 plants, and the experiment was repeated three times. Two months after stems emerged, plants and progeny tubers were harvested and assessed for disease. Stem cankers typical of R. solani infection and black scurf were observed on plants grown in pots inoculated the mycelial plugs, but the control plants remained disease free. Fungi reisolated from symptomatic stems and tubers were identified as R. solani AG 2-2IV using morphological characters and ITS sequences.Sclerotia were observed on PDA by incubating at 25oC in the dark. Although eight AGs have been previously shown to cause black scurf and stem canker in Heilongjiang (Li et al. 2014; Yang et al. 2015; Yang et al. 2017; Yang et al. 2019; Yang et al. 2020), to our knowledge, this is the first report of AG 2-2IV causing disease on potatoes in Heilongjiang Province, the main potato seed production area of China. Early detection of R. solani AG 2-2IV during potato seed production is necessary to prevent its dispersal via infected tubers to other fields across China. The information of which AG is present will assist in developing management strategies for this disease.

Potato (Solanum tuberosum) is the fourth-largest food crop worldwide. China is the world’s largest potato producer with 22% of global potato production occurring in the country (Jansky et al. 2009)...

Maize (Zea mays L.) is one of the most important crops worldwide. In September 2020, five maize plants and soil samples were received from a farmer. The samples were collected from a maize field in...