Potato late blight: detached leaf and in planta assays to evaluate Phytophthora infestans colonization in several potato varieties

Late blight caused by the oomycete Phytophthora infestans is one of the most devastating diseases affecting potato (Solanum tuberosum L.). Under favorable conditions, P. infestans can infect leaves and tubers and severely spread in field. The use of resistant cultivars, when available, is considered a sustainable option to control the disease. However, the main strategy is still the oomycide application. Different potato varieties, all cultivated in central Italy, were tested in these experiments. The first aim of this work was to develop a reliable method to phenotypically evaluate the susceptibility of potato varieties to late blight with a detached leaf assay, leaves from adult plants were inoculated with a sporangial suspension of P. infestans and after 3 days foliar lesions were measured. The second aim was to evaluate the development of the infection caused by P. infestans in planta. Molecular approach (qPCR for pathogen quantification) coupled with an analytical approach (HPLC-MS/MS for plant hormones detection) was used. For the in planta assay, 2-week-old seedlings were inoculated with sporangia and kept under controlled conditions in a phytotron. The infection was monitored for 10 days and leaves samples were collected at early, middle and late stages for DNA and plant hormones extraction. The molecular analysis via qPCR was performed in order to estimate P. infestans colonization based on the infection stage and presence/absence of symptoms, while the quantification of phytohormones (salicylic acid and jasmonate) was conducted for a better comprehension of plant response to the infection of hemibiotrophic oomycete P. infestans. This work was supported and funded by the project SOS TATA SVILUPPO DI NUOVE TECNOLOGIE NELL'AGRICOLTURA DI PRECISIONE PER LA PRODUZIONE SOSTENIBILE DI GENOTIPI DI PATATA CON ELEVATE QUALITÀ NUTRIZIONALI, n. F/200088/0103/X45, Asse 1, azione 1.1.3. del Programma Operativo Nazionale «Imprese e Competitività» 2014–2020 FESR.