| Summary: | Choanephora rot of <i>Chenopodium</i> plants (CRC) was observed at the flowering stages in seven plantations of Shanxi Province, China. CRC had caused leaf, stem, and panicle neck rot of <i>C. quinoa</i>, panicle neck and stem rot of <i>C. formosanum</i>, and stem rot of <i>C. album</i>. Typical symptoms included water-soaked, rapid soft rotting, and abundant sporulation on the whole panicle necks, stems, and leaves. Based on morphological characteristics, phylogenetic analyses, and pathogenicity tests, the pathogens were identified as <i>Choanephoraceae cucurbitarum</i>. Sporangiola and sporangiospore of <i>C. cucurbitarum</i> germinated at 30 °C and were able to germinate by two h post-inoculation (hpi). The germination rates of sporangiola and sporangiospore significantly increased at 3 to 4 hpi, and the germination rates ranged from 91.53 to 97.67%. The temperature had a significant effect on the pathogenicity of <i>C. cucurbitarum</i> the optimum pathogenic temperatures for stems of <i>C. quinoa</i>, <i>C. formosanum</i> and <i>C. album</i> were 30 °C after one day post-inoculation. <i>Choanephoraceae cucurbitarum</i> could infect white and red quinoa panicle necks between 20 and 30 °C, and the average lesion lengths were 0.21 to 3.62 cm. Among the five tested fungicides (boscalid, dimethomorph, isopyrazam, propiconazole, and tebuconazole), isopyrazam showed higher sensitivity to sporangiola germination of <i>C. cucurbitarum</i>, with an EC<sub>50</sub> value of 0.6550 μg/mL. Isopyrazam and tebuconazole strongly inhibited the sporangiospore germination of <i>C. cucurbitarum</i>, which showed EC<sub>50</sub> values of 0.4406 and 0.3857 μg/mL. To our knowledge, the present study found for the first time that <i>C. cucurbitarum</i> is a pathogen causing panicle neck of <i>C. formosanum</i> and stem rot of <i>C. formosanum</i> and <i>C. album</i>, while CRC first appeared in the quinoa panicle necks, and gradually expanded to stems and leaves.
|
|---|