This work was conducted to evaluate the effect of Fusarium verticillioides on the early stage development of maize seedling/plants, considering different inoculum potentials of this fungus in seeds, under controlled conditions. To obtain seeds with different inoculum potentials of that fungus, the osmo-priming technique as referred to in literature was used. By this technique, the non-germinated seeds of the same lot, exhibiting typical structures of F. verticillioides, were grouped into five categories according to a grading system that was established based on the visible area of the seeds covered by the fungal structures. Seeds of each category were sowed in soil substrate and plants were grown under controlled conditions, 25ºC and 16 h light/day, for 25 days. All variables used, plant population (stands), speed of seedling emergence, and height/weight of emerged plants, were negatively affected by the increase of the inoculum intensity of the fungus initially present in the seeds. The regression equation showed high values of correlation coefficient (>0.85) for all variables, except for plant height which presented correlation coefficient of 0.77. The most severe effect of the fungus in this study occurred on the root system of the emerged plants as determined by the highest inoculum intensity of the pathogen on the planted seeds.

O fungo Sclerotinia sclerotiorum, agente etiológico da doença conhecida como mofo branco em diversas culturas de importância econômica, tais como feijão, soja e algodão, é comumente disseminado através de sementes e capaz de causar perdas elevadas na qualidade das sementes e na produtividade dessas espécies. Neste trabalho, o objetivo foi avaliar os efeitos de diferentes potenciais de inoculo inicial desse fungo nas sementes de feijão usando dois isolados do fungo e dois genótipos de feijão (Pérola e Ouro Negro) artificialmente inoculados. As sementes foram semeadas em solo e o cultivo foi conduzido em condições ambientais controladas, favoráveis ao desenvolvimento da doença mofo branco. As variáveis analisadas foram: germinação; sanidade; índice de velocidade de emergência; estande inicial e final; e massa seca da parte aérea e da raiz. Constatou-se que, com o aumento do potencial de inóculo nas sementes, houve redução gradual dos valores de germinação, índice de velocidade de emergência, estandes e comprimento e massa seca de parte aérea e raiz. Estes resultados evidenciam a importância do potencial do inóculo inicial de S. sclerotiorum associado às sementes de feijão, tanto na disseminação do patógeno quanto nos danos diretos causados no campo, reduzindo o potencial produtivo das plantas emersas.

The fungus Sclerotinia sclerotiorum, causal agent of white mold disease on several economically important crops, such as bean, soybean, and cotton, is commonly disseminated through seeds and can cause high losses on their quality and in productivity of these species. The aim of this study was assessing the effects of different initial inoculums potentials of this fungus on common bean seeds using two different strains of the fungus and two genotypes of common beans (Pérola and Ouro Negro) artificially inoculated. Seeds were sown on soil and the cultivation was performed under controlled environmental conditions favorable to development of the white mold disease. Variables assessed were: germination; seed health; emergence speed index; initial and final seedling number; and dry weight of aerial parts and roots. It was found that with the gradual increase in inoculum potential in the seeds also occurred gradual reduction in the values of: germination; emergence speed index; seedling stand; and length and dry mass of aerial parts and roots. These results show the importance of initial inoculum potential of S. sclerotiorum present in common bean seeds, as much in disseminating the pathogen as on direct damages caused in field by reducing productive potential of the emerged plants.