Morphological characterization and optimization of conditions for conidial production of Elsinoë ampelina, the causal organism of grapevine anthracnose

Abstract

Grape anthracnose, which is caused by Elsinoë ampelina, is a disease that negatively affects grape production. This study aimed to investigate the effects of aeration, temperature, light, and preculture period on the formation of E. ampelina conidia and conidial germination and virulence. The colony morphology on potato dextrose agar (PDA) plates was more diverse than that in PDA bottles. The assessment of different culture methods, temperatures, light conditions, and preculture periods revealed that optimal conidial production occurred on 25‐day‐old colonies grown in PDA bottles at 21°C for 24 hr in the dark. The cultures in PDA bottles consistently produced approximately 5.0 × 106 conidia under these conditions. No conidial formation occurred when the cultures were kept at 25°C in the dark. The highest germination rate of E. ampelina was 80% at 25°C after 24 hr, whereas no germination was observed at 17°C after 12 hr. Pathogenicity tests revealed that symptoms of the disease were observed 4 days postinoculation (dpi) on leaves of Vitis vinifera cv. Red Globe. New conidia were observed on the lesions at 8 dpi. This study provides an effective method for the conidial production of E. ampelina that may also be applicable for other Elsinoë fungal species.

Current status and future prospects of grapevine anthracnose caused by Elsinoe ampelina: An important disease in humid grape‐growing regions

“…The colonies of E. ampelina (Figure 2a,b) show slow growth on artificial media and high variability in colour, including red, yellow, brown, black, white, coral, and dark-brick hues on potato dextrose F I G U R E 1 Typical symptoms of grapevine anthracnose on tendril (a), petiole (b), stem (c), young shoot (d), leaves (e), and berries (f) in the field agar (PDA) (Li et al, 2018;Santos et al, 2018c;Sompong et al, 2012). On PDA, the colony growth rate of Australian and Brazilian isolates ranged from 0.05 to 0.06 mm/day, reaching 1.9-2.5 cm in diameter at 28 days, whereas the colonies of Thai isolates had a size of 3.7-3.8 cm at 35 days (Santos et al, 2018c;Sompong et al, 2012).…”

“…Later on, an efficient method for sporulation was developed using rainwater or distilled water and shaking in darkness for 7 days (Santos et al, 2018b). Additionally, a considerable amount of conidia was reported on 25-day-old colonies grown in PDA bottles kept at 21 °C for 24 hr in the dark (Li et al, 2018). These studies indicate that unfavourable culture conditions (relatively high colony density or liquid culture) and treatments (low temperature or ultraviolet light) may induce the conidia formation of E. ampelina as a stress response.…”

“…Elsinochromes, which are light-dependent and nonhost-selective phytotoxins, are structurally similar to the cercosporin phytotoxin (Yang & Chung, 2010). The colour of elsinochromes is red or orange, which is similar to the colour of E. ampelina colonies (Li et al, 2018;Santos et al, 2018c). Elsinochromes may be potential virulence factors associated with the development of grape anthracnose and further studies are needed to address this gap.…”

“…Acervuli containing short, cylindrical conidiophores bearing conidia are formed on necrotic lesions once the disease is established (Li et al, 2019 ). Conidia are cylindrical to oblong with rounded ends (Figure 2d ), hyaline, and aseptate, 3.4–7.5 × 2.0–3.5 µm (Li et al, 2018 ; Magarey, Coffey, et al, 1993 ; Santos et al, 2018c ; Sompong et al, 2012 ). When the sexual stage occurs, ascospores are produced in asci (12.9–34.3 × 12.6–29.6 µm), which contain eight ascospores each.…”

“…Although some studies have been conducted to elucidate the molecular interactions between grape and E. ampelina (Ahn, Kim, Jo, et al, 2014;Gao et al, 2020), the underlying mechanisms remain unclear. In the past, most of the studies focused on pathogen identification and pathogenicity (Santos et al, 2018a(Santos et al, , 2018c, sporulation induction (Li et al, 2018;Santos et al, 2018b), characterization of the infection and colonization processes (Braga et al, 2019(Braga et al, , 2020Li et al, 2019), identification of resistant cultivars and hybrids (Hopkins & Harris, 2000;Poolsawat et al, 2012), development of molecular markers linked to disease resistance genes (Kim et al, 2008), and expression and screening of disease resistance-related genes (Gao et al, 2012;Seehalak et al, 2011;Vasanthaiah et al, 2010). Although many relevant studies have been published on grapevine anthracnose in recent years, in particular on the two genomes of E. ampelina recently published (Haridas et al, 2020;, a recent review of the literature for this pathosystem is not available.…”