RELEVANT AND EMERGING PLANT PATHOGENS OF MAIZE AND POTATO: POLYPHASIC APPROACH FOR IDENTIFICATION AND DEVELOPMENT OF DETECTION TOOLS.

Maize (Zea mays) and potato (Solanum tuberosum) are two of the most widely cultivated and economically important crops globally. Maize, a staple crop in many regions, is essential for food, feed, and industrial uses. However, it is susceptible to various pathogens, including Fusarium species, which can cause significant diseases such as crown and stalk rot, and grain infections. Similarly, potato, a key crop in temperate regions, faces threats from pathogens like Colletotrichum coccodes and Rhizoctonia solani, which lead to diseases such as black dot and black scurf, impacting both yield and quality. This thesis aimed to improve the detection, characterization, and management of plant diseases caused by specific fungal pathogens in agricultural crops, enhancing crop protection strategies and it includes three studies. The first study explores the diversity and pathogenicity of Fusarium isolates from symptomatic maize seedlings in Northern Italy collected in 2019 and 2020. Pathogenicity tests revealed 23 isolates causing rotting symptoms in maize seedlings, with disease indexes ranging from 20% to 90%. Multilocus phylogenetic analysis of four genomic loci (tef1-α, rpb2, calm, tub2) identified species within three species complexes (SC), including Fusarium verticillioides and F. annulatum in the F. fujikuroi SC, F. commune in the F. nisikadoi SC, and three lineages within the Fusarium oxysporum SC. Notably, F. annulatum and two lineages of F. oxysporum were reported as maize pathogens for the first time in Italy. Furthermore, maize is affected by Trichoderma afroharzianum, an emerging pathogen of maize, firstly found in Northern Italy in 2020. Considering its use as a biological control agent on several crops, further analyses were performed showing infection rates of maize seed lots up to 71%. In the second study a species-specific SYBR Green quantitative PCR assay was developed for sensitive detection and quantification of T. afroharzianum. Abstract 2 Building upon the molecular tools for pathogen detection, in a third study also a duplex quantitative PCR assay was validated for the simultaneous detection of Colletotrichum coccodes and Rhizoctonia solani AG-3, major pathogens of potato. This method provides an efficient approach for the early identification of both pathogens in potato tubers within a single run. Collectively, these findings enhance understanding of maize and potato seedborne pathogens and contribute to improved diagnostic methods for seed certification and disease management. Molecular techniques not only accelerate pathogen detection but also play a crucial role in integrated pest management programs, biosecurity, and the prevention of disease spread, ultimately reducing the economic and environmental impact of plant diseases.