Characterization and Pathogenicity of <i>Colletotrichum</i> Species on <i>Philodendron tatei</i> cv. Congo in Gansu Province, China

Abstract

In recent years in China, leaf spot caused by <i>Colletotrichum</i> species has been an emerging disease of <i>Philodendron tatei</i> cv. Congo. From 2016 to 2019, typical symptoms, appearing as circular or ovoid, sunken, and brown lesions with a yellow halo, were commonly observed on <i>P. tatei</i> cv. Congo in and around Lanzhou, Gansu Province, China. Conidiomata were often visible on infected leaf surfaces. Leaf disease incidence was approximately 5 to 20%. A total of 126 single-spored <i>Colletotrichum</i> isolates were obtained from leaf lesions. Multilocus phylogenetic relationships were analyzed based on seven genomic loci (ITS, <i>ACT</i>, <i>GAPDH</i>, <i>HIS3</i>, <i>CAL</i>, <i>CHS-1</i>, and <i>TUB2</i>) and the morphological characters of the isolates determined. These isolates were identified as three <i>Colletotrichum</i> species in this study. A further 93 isolates, accounting for 74% of all <i>Colletotrichum</i> isolates, were described as new species and named as <i>Colletotrichum philodendricola</i> sp. nov. after the host plant genus name, <i>Philodendron</i>; another two isolates were named as <i>C. pseudoboninense</i> sp. nov. based on phylogenetic and morphological relativeness to <i>C. boninense</i>; the other 31 isolates, belonging to the <i>C. orchidearum</i> species complex, were identified as a known species-<i>C. orchidearum</i>. Both novel species <i>C. philodendricola</i> and <i>C. pseudoboninense</i> belong to the <i>C. boninense</i> species complex. Pathogenicity tests by both spray and point inoculations confirmed that all three species could infect leaves of <i>P. tatei</i> cv. Congo. For spray inoculation, the mean infection rate of leaves on the three species was only 4.7% (0 to 12%), and the size on lesions was mostly 1 to 2 mm in length. For point inoculation, 30 days after nonwounding inoculation, the infection rate on leaves was 0 to 35%; in wounding inoculation, the infection rate of leaves was 35 to 65%; wounding in healthy leaves greatly enhanced the pathogenicity of these three species to <i>P. tatei</i> cv. Congo; however, the sizes of lesions among the three species were not significantly different. To our knowledge, this is the first report of <i>Colletotrichum</i> species associated with anthracnose diseases on <i>P. tatei</i> cv. Congo. Results obtained in this study will assist the disease prevention and appropriate management strategies.