Colletotrichum species (Glomerellales, Glomerellaceae) causing walnut anthracnose in China

<i>Colletotrichum</i> species can function as plant pathogens, saprobes or endophytes on a wide variety of plant hosts and are considered amongst the ten most significant genera of plant pathogens globally. China contributes almost half the walnut production in the world. However, <i>Colletotrichum</i> species occurring on walnut remain largely unresolved in China. To explore the <i>Colletotrichum</i> species found on walnut in China, 470 walnut fruit or leaf samples with anthracnose were collected from 14 main walnut-producing regions across seven provinces. A total of 165 <i>Colletotrichum</i> strains were isolated from these samples. The <i>Colletotrichum</i> isolates were identified, based on morphological characteristics and sequence analyses of <i>ACT</i>, <i>CHS-1</i>, <i>GAPDH</i>, ITS and <i>TUB2</i>. Twelve species, including 11 known <i>Colletotrichum</i> species (<i>C.boninense</i>, <i>C.citrulli</i>, <i>C.fioriniae</i>, <i>C.fructicola</i>, <i>C.godetiae</i>, <i>C.juglandicola</i>, <i>C.karsti</i>, <i>C.mengyinense</i>, <i>C.pandanicola</i>, <i>C.peakense</i> and <i>C.siamense</i>) and a novel species (<i>C.chinensis</i> <b>sp. nov.</b>) were identified. The species distribution revealed regional prevalence as follows: <i>C.mengyinense</i> was the most dominant species in Gansu, <i>C.mengyinense</i> and <i>C.siamense</i> in Shandong, <i>C.chinensis</i> in Beijing, <i>C.pandanicola</i> in Shaanxi and <i>C.godetiae</i> in Yunnan. <i>Colletotrichumsiamense</i> was the sole species isolated in Sichuan and Xinjiang Provinces. Koch's postulates were fulfilled, demonstrating that all 12 species cause anthracnose on walnut. This is the first report of <i>C.boninense</i>, <i>C.citrulli</i> and <i>C.karsti</i> as pathogens of walnut anthracnose worldwide.