This study aimed to elucidate the infectious process of Ramularia areola, the causal agent of ramularia leaf spot, on cotton leaves by using scanning microscopy. Plants from cotton cultivar Nu-Opal at growth stage V4 were inoculated with a 1.5 × 10(5) conidial suspension of R. areola. Leaf samples were collected at 12 hours after inoculation (h.a.i.) and also at 12 and 22 days after inoculation (d.a.i.) and prepared to be observed under scanning electron microscope. At 12 h.a.i., conidia of R. areola started to germinate without formation of appressoria and most of them produced two germ tubes that grew towards the stomata in an attempt to penetrate them. At 12 and 22 d.a.i., hifa of R. areola colonized, inter and intracellularly, the mesophyll cells and sporulation occurred through the stomata present on both adaxial and abaxial leaf epidermis.
Gossypium hirsutum; pathogenesis; ramularia leaf spot
