Identification, Pathogenicity, and Fungicide Sensitivity of Ascochyta caulina (Teleomorph: Neocamarosporium calvescens) Associated with Black Stem on Quinoa in China

Abstract

Quinoa black stem is a new disease that affects the stems of quinoa plants and is more likely to develop under cool conditions (15 to 25°C, RH = 55 ± 2%). The typical symptoms include the formation of black necrotic lesions on the stem, which can completely wrap around the stem, causing lodging and blanking (development of ‘empty’ and sterile grain on the panicle). Furthermore, the pycnidia form small round protrusions on the surface of the lesions. Phylogenetic analysis revealed that representative isolates LMHS-3 and LMHS-5 were closely related to Ascochyta caulina (teleomorph: Neocamarosporium calvescens). Comprehensive morphological and molecular characterizations confirmed A. caulina as the pathogen that caused quinoa black stem. A. caulina mainly infected quinoa stems and could produce many pycnidia, but it rarely infected quinoa leaves. Pathogenicity testing showed that the most suitable temperature for the onset of quinoa black stem was from 15 to 25°C. When the temperature was increased above 30°C, the conidial germination of A. caulina became malformed, and when the temperature was decreased below 5°C, mycelium growth of A. caulina became extremely slow; thus, both extreme high and low temperatures affected the pathogenicity of A. caulina. Mancozeb and azoxystrobin fungicides were revealed to have had the strongest inhibitory effects on the conidial germination of A. caulina, and in some cases caused malformations in conidial germination. Tebuconazole and difenoconazole had the strongest inhibitory effects on A. caulina mycelial growth and less on the effects on the conidial germination. The results of the present study provide a basis for the recognition and management of quinoa black stem.

A Review of Chenopodium quinoa (Willd.) Diseases—An Updated Perspective

“…It has been established in the genus Neocamarosporium Crous and Wingfield in 2014, which comprises 15 species, including N. betae , N. chenopodii , and N. calvescens. These species share the same large phylogenetic branch with N. calvescens [ 133 , 134 , 135 , 136 , 137 ]. Ascohyta caulina in its asexual form belongs to the family Didymellaceae and has often been confused with A. hyalospora [ 137 ].…”

“…These species share the same large phylogenetic branch with N. calvescens [ 133 , 134 , 135 , 136 , 137 ]. Ascohyta caulina in its asexual form belongs to the family Didymellaceae and has often been confused with A. hyalospora [ 137 ]. Previously, it has also been found to infect eight species of Atriplex and eight species of Chenopodium , including C. album [ 138 ].…”

“…They are 162 × 134 μm in size, on average. Conidia are elliptical or fusiform, light brown, oblong at the top and flat at the base, and measure 17 × 6 μm on average [ 137 ]. Conidia usually have one septum, which is erect or curved ( Figure 14 D).…”

“…Detached inoculated leaves of C. quinoa developed visible symptoms 8 dpi and were grayish white. However, necrotic lesions are rarely seen on the leaves in the field [ 137 ] ( Figure 14 A).…”

Community structure of fungal pathogens causing spikelet rot disease of naked oat from different ecological regions of China

“…Then, the purified strain was inoculated on a PDA plate and stored at 4 °C67 . After dark culture at 25 °C for 1 week, DNA was extracted from the fungal isolates, and sequencing was conducted by Shanghai Personal Biotechnology Co., Ltd. (Shanghai, China).…”