COMPARATIVE LIGHT-MICROSCOPY STUDY OF HISTOLOGICAL ALTERATIONS CAUSEDBY MAL-DE-RIO-CUARTO VIRUS IN 2 MAIZE (ZEA-MAYS L.) CULTIVARS DIFFERING IN TOLERANCE TO THE VIRUS

Mal de Rio Cuarto virus is the agent of the disease called ''Mal de Ri o Cuarto'' affecting maize (Zea mays L.) with loss of grain and foliag e production. This work is a comparative light miscrocopy of histologi cal alterations caused by this virus in leaves, stems and roots of a s usceptible and a tolerant maize cultivar. Leaf alterations of both cul tivars were observed in three types of vascular bundles, the Ist and 2 nd order being the most affected. Enations in the tolerant cv. were sm aller than in the susceptible one, and they appeared at a more advance d stage in plant development. In stems, vascular bundles type I were a ltered in both cultivars, whereas vascular bundles type 2 showed anoma lies only in the susceptible cv. In roots, the first modification obse rved in the vascular tissue and pericycle of susceptible and tolerant cultivars was the presence of cells with dense protoplasm. In general, the alterations in the analyzed organs of the susceptible cv. were mo re pronounced, and they appeared earlier than in the tolerant cv.