China is the world’s leading kiwifruit producer (Belrose 2016). In September 2016, brown/black spot disease was found on leaves and fruit peel in several kiwifruit orchards in Taishun County, Zhejiang Province and Liupanshui City, Guizhou Province. Diseased leaves and fruit exhibited small irregular brown to black spots (1-2 mm), which exapanded (3-5 mm) and became necrotic with age. Affected leaves became blighted by the fall. Ten orchards in each city were investigated, and approximately 45% of trees were symptomatic in Taishun and Liupanshui (Fig. 1 A-C). Symptomatic tissues of twenty typical infected leaves and fruit were cut into 4-5 mm pieces, surface-sterilized, rinsed three times in sterile distilled water, and cultured on 1.5% potato dextrose agar (PDA) with streptomycin and tetracycline. Petri dishes were incubated at 25°C under a 12-h light / dark cycle. Hyphal-tip from the growing edge of colonies cultured for 3 days at 25°C was transferred to PDA to obtain pure cultures. Fungal colonies were ...

The prevalence of kiwifruit (Actinidia sp.) postharvest rot disease in China was studied from October to December 2014. Approximately 30% of fruits were observed with milky-white, sour-smelling, watery internal tissue (Fig.1a). To identify the causal agent of the disease, 100 fruits (Jinyan’, ‘Hongyang’, ‘Jinkui’, ‘Guichang’ and ‘Qinmei’ cultivars) were arbitrarily collected from Hubei, Sichuan, Henan, Chongqing, Jiangxi, Guizhou and Shaanxi province and stored in controlled-atmosphere rooms (4°C, 2% O2, 5% CO2). After 60 days, 28 fruit were observed to have postharvest rot. Botryosphaeria dothidea (Fig.1b) and Diaporthe nitschke (anamorph: genus Phomopsis), the two most important postharvest fungal pathogens of kiwifruit in China (Li et al. 2015; Zhou et al. 2015), were isolated from most fruits. Most Diaporthe sp. strains were identified morphologically and molecularly as D. ambigua (Fig.1c), previously reported to cause rot in stored kiwifruits in Chile (Auger et al. 2013). Five previously-unidentified...

Postharvest rot disease of kiwifruit has recently become a serious problem in China, the world’s largest kiwifruit (Actinidia sp.) cultivating and exporting country (Huang and Zhong 2013). During cold storage, symptoms begin as slightly shriveled areas on fruit peel. After 6–10 days at room temperature, the inside of these infected fruits becomes milky white and watery, then finally, severely decayed and sour smelling (Fig. 1A). Botryosphaeria dothidea and Phomopsis sp. were previously identified in affected fruits in Sichuan Province and Shanghai fruit market respectively (Li et al. 2015; Zhou et al. 2015), but kiwifruit rot-causing pathogens have not been systematically studied across China. Between October and December 2014, we collected kiwifruit of 5 cultivars (‘Jinyan’, ‘Hongyang’, ‘Jinkui’, ‘Guichang’ and ‘Qinmei’) from 7 provinces (Hubei, Sichuan, Henan, Chongqing, Jiangxi, Guizhou and Shaanxi), China’s main kiwifruit-cultivating regions. After 2 months’ cold storage, 28 fruits developed soft rot symptoms. Symptomatic fruits were surface-sterilized in 70% ethanol for 10 s, 0.1% mercuric chloride for 1 min, then three rinses in sterile distilled water. Samples of internal tissue were placed on potato dextrose agar (PDA) and incubated at 25°C for 3 days with an alternating light-dark cycle. Emerging colonies were transferred to new PDA plates by the hyphal-tip method to obtain pure cultures. The common pathogens Botryosphaeria dothidea and Phomopsis sp. were isolated from most rotting fruit, but four novel, morphologically identical isolates were identified from ‘Jinyan’ cultivars from Wuhan (Hubei province). Confocal optical microscopy revealed a match to Pestalotiopsis microspora (Speg.; Batista & Peres, 1966). Conidia were slightly curved, fusiform to clavate, five-celled with constricted septa. Dimensions were 17.2–21.1 µm by 4.8–7.7 µm, with hyaline apical and basal cells. Apical cells had two (22%) or three appendages 9.8–21.3 µm long. The three median cells were brown to olive green (Fig. 2). Identification was confirmed by sequencing one isolate (KFRD-2). The rDNA internally transcribed spacer (ITS) and beta-tubulin (BT) regions were amplified using ITS4/ITS5 and Bt2A/Bt2B primers, respectively (Hu et al. 2007). A BLAST search of GenBank showed that the ITS and BT sequences of the isolates (GenBank accession nos. KR703275 and KU377338) were 100% homologous with P. microspora (accession nos. EU273522 and JN314419). For pathogenicity testing of mature A. chinensis ‘Jinyan’ fruit, we applied 10 µl spore suspension (1 × 106 conidia/ml) to the upper area of each of ten fruits (five wounded, five unwounded), and 10 µl sterile water to the bottom (negative control). In a second test, a mycelial plug (5 mm) of actively-growing P. microspora was rubbed onto the upper area of ten fruits (five wounded, five unwounded), while the bottom area of each fruit (negative control) was treated with sterile agar. Fruit were incubated at 22/18°C (day/night), 80% humidity. Typical symptoms were observed on all wounded, infected sites after 6 days (Fig. 1B), but none on unwounded fruit or negative control areas. Experiments were repeated three times and the fungus was re-isolated each time and identified as P. microspora by morphological and molecular analysis. This is the first report of P. microspora causing kiwifruit rot in China. The economic importance of kiwifruit industry in China warrants further study of postharvest rot disease caused by P. microspora. References: A. C. Batista et al. Atas Inst. Micol. 3: 92,1966. H. L. Hu et al. Fungal Divers. 24:1, 2007. H. W. Huang and C.H. Zhong. Beijing Science Press. 4, 2013. Q. Li et al. Ann Rept Kansai PL Prot. 57: 31, 2015. Y. Zhou et al. Plant Dis. 99: 699, 2015.