Amorphophallus konjac anthracnose caused by Colletotrichum siamense in China

Occurrence and characterization of viruses infecting Amorphophallus in Yunnan, China

Viral diseases are becoming an important problem in Amorphophallus production due to the propagation of seed corms and their trade across regions. In this study, combined-High-Throughput Sequencing, RT-PCR, electron microscopy, and mechanical inoculation were used to analyze virus-like infected Amorphophallus samples in Yunnan province to investigate the distribution, molecular characterization, and diversity and evolution of Amorphophallus-infecting viruses including three isolates of dasheen mosaic virus and three orthotospoviruses: mulberry vein banding associated virus (MVBaV), tomato zonate spot virus (TZSV) and impatiens necrotic spot virus (INSV). The results showed that DsMV is the dominant virus infecting Amorphophallus, mixed infections with DsMV and MVBaV to Amorphophallus were quite common in Yunnan province, China. This is the first report on infection of Amorphophallus with MVBaV, TZSV, and impatiens necrotic spot virus (INSV) in China. This work will help to develop an effective integrated management strategy to control the spread of Amorphophallus viral diseases.

Characteristics of Amorphophallus konjac as indicated by its genome

Amorphophallus konjac, belonging to the genus Amorphophallus of the Araceae family, is an economically important crop widely used in health products and biomaterials. In the present work, we performed the whole-genome assembly of A. konjac based on the NovaSeq platform sequence data. The final genome assembly was 4.58 Gb with a scaffold N50 of 3212 bp. The genome includes 39,421 protein-coding genes, and 71.75% of the assemblies were repetitive sequences. Comparative genomic analysis showed 1647 gene families have expanded and 2685 contracted in the A. konjac genome. Likewise, genome evolution analysis indicated that A. konjac underwent whole-genome duplication, possibly contributing to the expansion of certain gene families. Furthermore, we identified many candidate genes involved in the tuber formation and development, cellulose and lignification synthesis. The genome of A. konjac obtained in this work provides a valuable resource for the further study of the genetics, genomics, and breeding of this economically important crop, as well as for evolutionary studies of Araceae family.

Colletotrichum siamense Strain LVY 9 Causing Spot Anthracnose on Winterberry Holly in China

Winterberry holly (Ilex verticillata) is an economically valuable landscaping ornamental plant. Serious outbreaks have been reported, in its leaf tips curl upward, irregular black brown spots appear on leaves, and extensive defoliation is commonly observed. The incidence in Hangzhou was estimated at 50% and resulted in large economic losses for growers in 2018. Samples were collected from the main cultivation area in Zhejiang Province. In total, 11 fungal isolates were obtained from diseased leaves through a single-spore purification method, and isolate LVY 9 exhibited strong pathogenicity. Based on morphology and molecular phylogenetic analyses based on multilocus sequence typing of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), internal transcribed spacer (ITS) regions, actin (ACT), calmodulin (CAL), and chitin synthase (CHS-1) genes, we identified the pathogen as Colletotrichum siamense, causative agent of anthracnose of winterberry holly.

Konjac anthracnose is caused by Colletotrichum gloeosporioides in Yunnan Province of China

Konjac (Amorphophallus konjac) is an economically important traditional crop in Fengqing County, Yunnan Province, China. Anthracnose symptoms were observed on this crop in June and July of 2020. The plants developed round, oval, or irregular leaf spots with brown edges and central taupe spots, and exhibited serious defoliation and tree weakness. Disease incidence in affected fields reached up to 35%. Anthracnose caused significant economic losses in konjac production and became a limiting factor of the konjac industry in Fengqing County. To date, no control measures of konjac anthracnose have been reported and tested in China. To determine the causal pathogen, symptomatic leaves were collected and cut into 5 mm2 pieces. The leaf peces were surface sterilized in 70% ethanol for 10 s, followed by treatment with 0.1% mercuric chloride for 3 min and three rinses in sterile distilled water. The tissue pieces were transferred onto potato dextrose agar (PDA) and incubated at 28°C. After 4 days of incubation, hyphal tips from leaf pieces were transferred to new PDA to generate pure cultures. The hyphae were initially white, and then became dark green; red-orange conidial masses were observed on the mycelium plate surface at a growth rate of 13.14 mm/day. The conidia, observed under 400× magnification, were colorless, long-oval to fusiform, one-celled, and 15.4 to 18.2 × 3.3 to 5.9 μm in size. To identify the isolate, the genomic DNA of the pathogen was extracted using the CTAB method. The internal transcribed spacer (ITS) region, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, and β-tubulin (TUB) gene were PCR amplified using the ITS1/ITS4, GDF/GDR, and Bt2a/Bt2b primer pairs, respectively (Lee et al. 2020). BLASTn search of the obtained 536 bp ITS fragment (GenBank accession no. MT785772), 229 bp GAPDH sequence (MW187543), and 717 bp TUB sequence (MW187544) revealed a 99.44% to 99.63% sequence homology (100% query cover) with ITS (JQ005152, 99.44%), GADPH (JQ005239, 99.63%), and TUB (JQ005587, 99.60%) sequences of the C. gloeosporioides type strain CBS 112999, respectively. The highest homology with other Colletotrichum species was only 98.16%, including C. siamense, the causal agent of anthracnose in A. paeoniifolius and A. konjac (Prasad et al. 2017; Wu et al. 2020). To complete Koch's postulates, leaves of 3-month-old konjac plants grown in the field were sprayed with a conidial suspension (106 spores/ml) of the isolate YNFQ-1 (sterile water was used as a negative control). Approximately 5 days after inoculation with YNFQ-1, symptoms similar to those in natural conditions appeared, whereas the negative control plants and fruits inoculated with the sterile water had no disease. The pathogen was re-isolated (strain YNFQ-1) from inoculated leaf tissues, and its identity was confirmed with both morphological and molecular (DNA sequences) tools, thus fulfilling Koch's postulates. The culture properties, morphological characteristics, and molecular identification confirmed the identity of the pathogen as C. gloeosporioides. There have been many reports about anthracnose of Amorphophallus; C. siamense causes anthracnose on A. paeoniifolius in India (Prasad et al. 2017) and A. konjac in Hubei, China (Wu et al. 2020), and C. gloeosporioides causes anthracnose of A. muelleri in Yunnan, China (Yang et al. 2020). To the best of our knowledge, this is the first report of C. gloeosporioides causing anthracnose on A. konjac in Fengqing County, China. The results are expected to have important implications in the diagnosis, control, and future research of anthracnose on A. konjac.