Alfalfa root rot is a devastating disease complex found worldwide. Population structure and genetic diversity of fungal pathogens causing alfalfa root rot in north‐east China are not well understood. In this study, 480 fungal isolates were collected from six major alfalfa‐growing regions in Heilongjiang province, China. They were identified as Fusarium tricinctum, F. oxysporum, F. acuminatum, F. solani, F. equiseti, Phoma medicaginis, Plectosphaerella cucumerina, Alternaria alternata, and Chaetomium globosum and caused root rot on alfalfa in greenhouse studies. F. tricinctum was the predominant species among the isolates, and P. medicaginis and C. globosum had not previously been reported causing alfalfa root rot in north‐east China. Of the 73 F. tricinctum isolates identified, the majority were moderately or highly aggressive on alfalfa. No isolate of F. tricinctum was sensitive to carbendazim (1 and 10 μg/ml), indicating that, although commonly used, it is not suitable for management of the disease in this area. F. tricinctum isolates were analysed using AFLP markers and divided into eight genetic groups with 28 pairs of primers. Analysis of molecular variance indicated significant correlation between genetic groups of F. tricinctum isolates and their geographical locations or aggressiveness. Pairwise comparison and STRUCTURE analysis also indicated that geographical locations and aggressiveness of isolates had a significant effect on population differentiation. This study provides insight into the genetic diversity and reproductive biology of F. tricinctum, enhances understanding of the population diversity of alfalfa root rot pathogens in north‐east China, and facilitates development of effective strategies for managing this destructive disease complex.
Rice seedling blight is a globally occurring seedling disease caused by multiple pathogens. It is currently the most common disease affecting rice production in northeast China; hence, determining the causal agents, including its biological characteristics, host range, and fungicide efficacy is vital for its effective management. The present study obtained 45 pathogenic isolates from diseased rice seedlings in Suihua, Heilongjiang Province, China. Of these, five pathogens were identified based on their morphology and molecular identification, while 10 oomycete isolates were identified as Pythium aristosporum—the first to be reported in rice seedling blight. Its optimum growth conditions include a temperature of 25 °C, pH 6, and photoperiod of 24 h. Except for soybean (Glycine max (L.) Merr.), black soybean (Glycine max var.), and cucumber (Cucumis sativus L.), P. aristosporum can potentially infect and cause seedling blight on other hosts, such as wheat (Triticum aestivum L.), maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench), alfalfa (Medicago sativa L.), oats (Avena sativa L.), and white clover (Trifolium repens L.). Its isolates were found to be highly sensitive to metalaxyl + propamocarb (EC50 = 0.0138 μg/mL) with 84.1% efficacy at 313 μg/mL. These results can serve as the basis for controlling P. aristosporum.
Aim The aims of this study were to identify the pathogen causing blackcurrant leaf spot, assess the pathogenicity of different isolates, the host range, and the sensitivity to common fungicides, and test the effectiveness of field control for controlling A. alternata in blackcurrants in China, and potentially elsewhere. Methods and results In 2020 and 2021, an uncommon leaf spot on blackcurrants was observed in Harbin (125°42′-130°10′E, 44°04′-46°40′N), Heilongjiang Province, China. Based on morphological, molecular characteristics and phylogenetic analyses, 10 fungal isolates, identified as Alternaria alternata, were obtained from infected blackcurrant leaves of 10 infected plants in this study. To our knowledge, this is the first description of A. alternata as a causal agent of leaf spot on blackcurrants in China. A. alternata has a wide host range and infects eight of 10 crop and ornamental plants evaluated, namely Sorbus pohuashanensis, Malus pumila, Rosa davurica, Padus racemosa, Hippophae rhamnoides, Crataegus pinnatifida, Pyrus ussuriensis, and Sambucus williamsii, but not Viburnum trilobum and Prunus tomentosa. Moreover, ten blackcurrant cultivars were screened and found to have contrasting levels of resistance to A. alternata. One was moderately resistant, four were resistant, four were susceptible, and one was highly susceptible. A. alternata isolate was most sensitive to propiconazole-azoxystrobin, with EC50 values of 0.0038 μg ml−1 and efficacy ranging between 83.34% and 84.13% at 317 μg ml−1 in the field. Conclusions The work reported that A. alternata is the pathogen that causes blackcurrant leaf spot in northern China. It can infect a variety of crop and ornamental plants. Considering the control cost and effect, propiconazole-azoxystrobin is more suitable for controlling leaf spot in the field.
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