First Report of Colletotrichum fructicola Causing Anthracnose on Peanut (Arachis hypogaea) in China

Peanut (Arachis hypogaea L.) is an important cash crop and oil crop around the world. In August 2021, symptoms of leaf spot were found on nearly 50% of peanut plants in the peanut planting base of Xuzhou Academy of Agriculture Sciences, Jiangsu, China. Symptoms began as small, round or oval, dark brown spots on the leaf. As the spot expanded, the center of the spot became gray to light brown and the spot was covered with small black dots. Fifteen leaves with typical symptoms were randomly collected from fifteen plants in three fields about a kilometer apart from each other. Leaf pieces (5 × 5 mm) were cut from the junction part of diseased and healthy leaf tissue, sterilized with 75% ethanol for 30 s and 5% NaClO for 30 s, washed 3 times with sterile water, placed on full strength potato dextrose agar (PDA) and incubated at 28°C in darkness. Five days after incubation, 12 isolates were obtained. Fungal colonies were white to gray on the upper surface and orange to gray on the reverse side. Conidia were single-celled, cylindrical and colorless after maturation, and were 12 - 16.5 × 4.5 - 5.5 μm (n = 50) in size. Ascospores were one-celled, hyaline, with tapering ends and one or two large guttulates at the center, and measured 9.4 - 21.5 × 4.3 - 6.4 μm (n = 50). Based on morphological characteristics, the fungi were preliminarily identified as Colletotrichum fructicola (Prihastuti et al. 2009; Rojas et al. 2010). Single spore isolates were cultured on PDA medium and two representative strains (Y18-3 and Y23-4) were selected for DNA extraction. The internal transcribed spacer (ITS) rDNA region, partial actin gene (ACT), partial calmodulin gene (CAL), partial chitin synthase gene (CHS), partial glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH), and partial beta-tubulin 2 gene (TUB2) were amplified. The nucleotide sequences were submitted to Genbank (accession numbers of strain Y18-3: ITS: ON619598; ACT: ON638735; CAL: ON773430; CHS: ON773432; GAPDH: ON773436; TUB2: ON773434; accession numbers of strain Y23-4: ITS: ON620093; ACT: ON773438; CAL: ON773431; CHS: ON773433; GAPDH: ON773437; TUB2: ON773435). The phylogenetic tree was constructed using MEGA 7 based on the tandem of six genes (ITS-ACT-CAL-CHS-GAPDH-TUB2). The result showed that isolates Y18-3 and Y23-4 reside in the clade of C. fructicola species. To determine pathogenicity, conidial suspensions (107/mL) of isolate Y18-3 and Y23-4 were sprayed on ten 30-day-old healthy peanut seedlings per isolate. Five control plants were sprayed with sterile water. All plants were kept moist at 28°C in the dark (> 85% RH) for 48 h and then transferred to a moist chamber at 25°C with a 14-h photoperiod. After two weeks, typical anthracnose symptoms similar to those observed in the field appeared on leaves of inoculated plants, whereas controls remained asymptomatic. C. fructicola was re-isolated from symptomatic leaves but not from controls. Koch's postulates verified that C. fructicola was the pathogen of peanut anthracnose. C. fructicola is a well-known fungus causing anthracnose on many plant species worldwide. In recent years, new plant species infected by C. fructicola have been reported, like cherry, water hyacinth and Phoebe sheareri (Tang et al. 2021; Huang et al. 2021; Huang et al. 2022). To our knowledge, this is the first report of C. fructicola causing peanut anthracnose in China. Thus, it is recommended to pay close attention and take necessary prevention and control measures against potential spread of peanut anthracnose in China. .