First Report of Postharvest Anthracnose of Kiwifruit Caused by Colletotrichum fioriniae in Liaoning and Sichuan Province, China

Abstract

Kiwifruit (Actinidia spp.) is one of the most important fruit crops in China. Post-harvest anthracnose symptoms were observed on kiwifruit in October 2021. Kiwifruits ‘Longcheng 2’ (n=200) were obtained from an orchard in Kuandian city of Liaoning province, China (124°32′E, 40°20′N). And cultivar ‘Cuiyu’ (n=100) were harvested from orchards in Mianzhu city, Sichuan Province, China (104°03′E, 31°15′N). After storage at 24 °C and 80% relative humidity (RH) for 8 days, the disease incidence of ‘Longcheng 2’ and ‘Cuiyu’ was 30% and 15%, respectively. Symptoms of diseased fruits appeared as water-soaked, irregular and light brown lesions. Orangish conidial masses were observed on some fruits. Ten lesion margins (5×5 mm) from ‘Longcheng2’ or ‘Cuiyu’ were respectively excised, surface sterilized by 70% ethanol (1 min), 1% NaOCl (5 min), washed, dried, plated on potato dextrose agar (PDA), and incubated at 25 °C for 5 days. Eight isolates were obtained from ‘Longcheng 2’ (LC1-3 to LC1-10) and nine strains from ‘Cuiyu’ (CY1-2 to CY1-10). The representative isolates LC1-3 and CY1-2 were put on PDA, and appeared white to pale gray on the upper side. However, isolate LC1-3 secreted red pigments after 7 days of culture. Conidia of LC1-3 were hyaline, smooth-walled, single-celled, cylindrical (3.0 to 4.9×7.2 to 14.7 µm, n=50). Ellipsoidal single cell conidia of CY1-2 were hyaline, and ranged in size from 3.2 to 5.0×8.5 to 13.9 µm (n=50) born on conidiophores. Appressorium of isolates LC1-3 and CY1-2 were globose to ellipsoid with 4.2 to 7.4×7.3 to 10.8 µm and 3.0 to 4.9×6.3 to 10.3 µm in size, respectively (n=50) (Fu et al. 2019 ). Four genes (ACT, CHS, GAPDH, TUB2) and the ITS region were successfully amplified and sequenced from all isolates (Weir et al. 2012). Based on sequence alignment, the isolates from ‘Longcheng 2’ or ‘Cuiyu’ were identical. BLAST analysis of the ACT, CHS, GAPDH, ITS and TUB2 sequences of LC1-3 (ON018724, ON018722, ON018720, OM980324, ON018718) or CY1-2 (ON018725, ON018723, ON018721, OM980325, ON018719) showed high similarity with C. fioriniae (CBS 128517; JQ949613, JQ948953, JQ948622, MH865005, JQ949943) were 97.1% to 99.7% or 98.1% to 99.7%, respectively. Phylogenetic analysis using concatenated sequences (maximum likelihood method) with MEGA 11 showed LC1-3 and CY1-2 were located within the same clade with C. fioriniae. Previous studies showed that C. fioriniae was classified into three subclades (Damm et al. 2012; Fu et al. 2019). However, LC1-3 and CY1-2 were located within a new subclade, namely the subclade IV. To test pathogenicity, healthy and mature kiwifruits ‘Donghong’, ‘Cuiyu’, ‘Xuxiang’, ‘Hayward’ and ‘Jinyan’ were surface sterilized. Each un-wounded fruit was dropped with 10 μl conidial suspension (105 conidia/ml) on the fruit surface. All fruits were placed into a plastic box and stored at 24 °C under 80% RH. Each treatment consisted of 10 fruits and were repeated three times. After 8 days, typical anthracnose lesions were observed on all inoculated fruits. Whereas, the controls treated with sterile distilled water remained asymptomatic. The pathogens re-isolated from diseased fruits were similar morphological and identical to the original isolates, fulfilling Koch’s postulates. Anthracnose caused by C. fioriniae has been reported on many fruits (Ling et al. 2020; Waller et al. 2021), but to our knowledge, this is the first report of anthracnose on kiwifruit caused by C. fioriniae. The results will provide valuable information for avoiding post-harvest anthracnose on kiwifruit.