First Report of Stemphylium lycopersici Causing Leaf Spot on Chinese chive (Allium tuberosum Rottler. ex Spr.) in China

Chinese chive (Allium tuberosum Rottler. ex Spr.), a perennial plant of the Allium genus, has been widely cultivated and naturalized worldwide. Due to their high nutritional and medicinal properties, Chinese chives have become increasingly popular in food inventories as multifunctional vegetables (Qian et al. 2024). During December 2024, a new leaf spot disease of Chinese chive was observed in Mile (24.24°N, 103.14°E), Yunan Province, China. More than 90% of plants in the field were affected. Initially leaves exhibited brown specks that later expanded into necrotic lesions and rapid tip wilting of the foliage. Leaf pieces (5×5 mm) from six symptomatic leaves were surface sanitized in 75% ethanol for 5 s then transferred to a 0.1% mercuric chloride solution for 30 s. After rinsing three times with sterile distilled water, isolates were grown on potato dextrose agar (PDA) with a 12-h photoperiod at 25 ℃ for 10 days. Four strains were isolated, and colonies were white to dark gray, flocculent in obverse and produced a dark red to pale yellow pigment in the agar reverse. Conidia (n=50) were solitary, light brown, oblong to long elliptic, pointed, constricted at the transverse septum with two to four transverse septa, mostly 46 to 53μm long and 14 to 18 μm wide. Morphological characteristics were consistent with published descriptions of Stemphylium sp (Woudenberg et al. 2017). For molecular identification, the rDNA internal transcribed spacer (ITS) region, glyceraldehyde-3-phosphate dehydrogenase (gpd) gene and calmodulin (cmdA) gene were amplified and sequenced (accession nos. PV554855 - PV554858 (ITS), PV567762 - PV567765 (gpd), and PV567770 - PV567773 (cmdA)) using published primers (Xie et al. 2019). BLASTn analysis of YNML-1 to YNML-4 sequences had highest matches to S. lycopersici with ITS sequences 100% identical (PP998429.1, MK336601.1, MK088144.1, MW243098.1; 540/540 bp); gpd gene sequences 100% identical (MW246804.1, KT957743.1, MW246806.1 , MW246805.1; 892/892 bp); cmdA gene sequences 100.00% identical (KU850896.1, PQ038765.1, KU850895.1, MK895976.1;700/700 bp). A phylogenetic tree was developed by maximum parsimony, maximum likelihood, and Bayesian inference. These four isolates fall into the S. lycopersici clade with strong support. To confirm pathogenicity, fifteen Chinese chive (Pingjiu six) plants were sprayed with conidial suspension (1 ×105 conidia/ml) or sterile water as a negative control. The plants were incubated at 25°C with a 12-h photoperiod and 90% humidity. Small leaf spots appeared after 3 days, and symptoms were similar to those observed in the nursery after 10 days. Control plants treated with sterile water remained asymptomatic. Reisolated strains had the same morphological characteristics and the same ITS, gpd and cmdA sequences as the original isolates, thus fulfilling Koch’s postulates. Pathogenicity tests were performed with three times with similar results. S. lycopersici is widely distributed and can cause a variety of plant diseases (Ben et al.2021;Yang et al.2020).The occurrence of this disease in Mile is a serious threat. This research is critical for effective management, facilitating early detection, and informing targeted control measures.