15 to 20-day-old plants presented small round grey-brownish spots (1-2 mm diameter) and the lesions extended to 30 mm forming concentric rings that covered the entire leaf (Figure 1). Cream to black sporodochia appeared in case of high humidity (Figure 2).
Figure 1. (Photo by Agroinnova)
The symptoms affected 5-10% of the plants cultivated in 5 hectares of tunnels. 30 to 60% of the leaves was damaged. Phytopatologists from the Centro di Competenza per l'Innovazione in Campo Agro-ambientale (AGROINNOVA) of the Università degli Studi di Torino isolated a fungus morphologically correspondent to Myrothecium spp. The DNA was later used for a PCR reaction with ITS1/ITS4 primers, thus leading to its identification as M. verrucaria.
Figure 2. (Foto Agroinnova)
In order to confirm its pathogenicity, Agroinnova's phytopatologists inoculated 15-day-old plants and placed them in a unit at a temperature between 20 and 24°C with a high humidity level. After 7 days, similar spots to those observed in tunnels appeared on 60-70% of inoculated plants. Inoculated plants showed no symptoms.
A fungus morphologically identified as Myrothecium was consistently isolated.
Researchers reported that "this is the first report of M. Verrucaria on spinach not only in Italy, but worldwide." At the moment, the disease affects various companies in Lombardy. Losses are still limited, but the disease could spread. It is very important that plants are closely monitored at this stage."
It is difficult to understand the origin of the disease, though it can be transmitted through seeds. Its sudden appearance in northern Italy could be due to the increase in temperatures caused by climate change.
Specific studies are being carried out to understand the environmental factors that lead this disease. They are being carried out within Emphasis - Effective Management of Pests and Harmful Alien Species – Integrated Solutions, a project started by the European Commission as part of the Horizon 2020 programme.
Source: Garibaldi A., Gilardi G., Franco-Ortega S., Gullino M. L., 'First Report of Leaf Spot of Spinach (Spinacia oleracea) Caused by Myrothecium verrucaria in Italy', August 2016, Plant Disease, Vol.100 (8), pag. 1786.
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