P-630 - Decoding the role of Potato Mop Top Virus genome segments in foliar dwarfism

PMTV is a soilborne, tri-partite single-stranded RNA virus that causes tuber necrosis and foliar abnormalities in potatoes, including leaf curling, yellowing, and stunted growth (dwarfism). While PMTV consists of three genomic segments namely RNA1 (RNA-dependent RNA polymerase), RNA2 (coat protein), and RNA3 (triple gene block), the specific contribution of each RNA segment to symptom development remain poorly understood. Here, we investigated the role of PMTV RNA segments in inducing morphological and cellular abnormalities in infected potato plants. PMTV-positive plants with equal expression of all three RNA segments were regenerated in tissue culture. Infected plants exhibited characteristic foliar symptoms between 6 to 10 weeks. Quantitative RT-PCR analysis across different tissues (leaves, stems, roots, microtubers) revealed that RNA1 and RNA3 maintained high and stable expression, while RNA2 levels significantly declined after the first generation of successive culture. Despite this reduction, dwarfism persisted, suggesting a dominant role of RNA1 and RNA3 in morphological alterations. Ultrastructural observation of PMTV-positive leaf tissue showed open stomata under light conditions, disorganized chloroplast, multivesicular structures, and enlarged intracellular spaces in the area of mesophyll cells. Transmission electron microscopy further revealed virus-like crystalline inclusions, chloroplast shrinkage, and decreased starch granules.  These findings highlight RNA1 and RNA3 roles in PMTV-induced dwarfism, offering insights into host-virus interactions and control.