SINTOMATOLOGIA E ETIOLOGIA DA MANCHA-FOLIAR DO FUMO (Nicotiana tabacum) CAUSADA POR Cercospora nicotianae

Abstract

Tobacco cultivation is an agribusiness responsible for sustaining more than 208,000 families across Brazil, with more than 186,000 in the South region, and tobacco blind spot has little emphasis in the literature due to its low frequency. The objective of this work was to record and describe the symptoms and etiology of Cercospora nicotianae incident on tobacco leaves. In April 2019 and 2024, leaves showing symptoms were collected and analyzed under a stereoscopic microscope. Symptoms were recorded with the naked eye (photography) under a stereomicroscope. Using lactophenol (blue cotton dye), semipermanent slides (direct collection and histological section) were prepared for microscopic recording. The morphology and morphometry of the macro and microscopic structures were obtained for identification and comparison with the description by Chupp (1953). Scientific illustrations were created from the symptomatological and etiological tables. Symptoms of cercosporiosis or tobacco frog's eye spot were pale brown in color, showed blighting of the apex on the adaxial surface, distributed throughout the leaf blade, forming spherical, irregular, angular or subspherical, confluent lesions, presenting from 2 to 15 mm in diameter, in the center it showed concentric striations, some lesions showed very thin chlorotic halos, amphigenous stomatal tissue (signs), leaf blight advancing in the apical region of the leaves, lesions with perforation symptoms. The conidiophore had variable septation, most were unbranched and could rarely be detected. Its dimensions were 145-(66.05)-18.06 x 2.78-(4.2)-6.18 µm. The length of the isolate analyzed in Urutaí, GO, is 4 times shorter, and the width matches the description by Chupp (1953). The conidiogenic cell presented 2-8 scars, many of which gave rise to genicules that allowed the conidiophore to bend. The detected conidiogenic cell scar had a subtruncated to rounded shape at the top and its size ranged from 95.61-(26.90)-6.14 x 2.1-(3.75)-5.10 um. The conidia were also quite variable, all hyaline in color, acicular, clavate at the base, slightly truncated at the apex, multiseptated, varying from 3-(10)-24 septa, the conidial apex was blunt to rounded, and their Dimensions ranged from 196.15-(92.69)-2.79 x 1.09-(3.00)-24.00 µm. The C/L ratio helps to understand the relationship between length and width, being 3 times to 88 times longer than it is wide.