Efeito de Saccharomyces cerevisiae na síntese de fitoalexinas em sorgo, na germinação e formação de apressórios por fungos fitopatogênicos e na proteção de pepino a Colletotrichum lagenarium e sorgo a Colletotrichum sublineolum. / Effect of Saccharomyces cerevisiae in phytoalexin synthesis in sorghum, on germination and appressorium formation by plant pathogenic fungi and in the protection of cucumber against Colletotrichum lagenarium and sorghum against Colletotrichum sublineolum.

AUTOR(ES)

Solange Maria Bonaldo

DATA DE PUBLICAÇÃO

2005

RESUMO

The yeast Saccharomyces cerevisiae has potential in the control of diseases in some plants by the ability to induce resistance and elicits defence mechanisms. However, in the process of purification of elicitor (s) present in the cell wall of S. cerevisiae a low efficiency was observed during the process, making difficult to carry out experiments, mainly in field. Thus, to optimize the process of extraction of the elicitor (s) present in the cell wall of the yeast, cells in suspension were autoclaved by minutes or hours, once or in sequence. After autoclaving the carbohydrate and proteins content of these preparations were determinate and they were tested in phytoalexin accumulation in sorghum mesocotyls, previously treated or not with the abrasive carborundum, and conidia germination and appressorium formation by Colletotrichum lagenarium and Colletotrichum sublineolum. Because of the higher carbohydrate content and the highest elicitor activity in sorghum mesocotyls, the preparation autoclaved by 4 hours in sequence was selected for the purification process. Ion exchange chromatography (IEC) using Tris-HCl or ammonium bicarbonate buffer for column elution, were used to separate fractions with higher elicitation activity from those exhibiting lower elicitation activity. Fractions from the chromatography obtained using either buffer induced the accumulation of phytoalexin in sorghum mesocotyls, previously treated or not with the abrasive carborundum. However, the fractions from the chromatography with ammonium bicarbonate buffer were able to inhibit in 100% the conidia germination and appressorium formation by the phytopathogens. In the protection of cucumber in growth chamber, there was a reduction in symptoms only when the cucumber seedlings were treated with the fractions from the IEC with Tris-HCl buffer, two days before the inoculation with the fungus. In greenhouse, fraction from the IEC with ammonium bicarbonate buffer was able to protect cucumber seedlings against C. lagenarium, but without increase peroxidases activity. Sorghum plants treated with the fractions, obtained using either buffer, exhibited reduced infection in the treated leaves and leaves just above, with phytoalexin production. The highest phytoalexin production in sorghum plants was observed in leaves treated with the crude preparation of the yeast autoclaved by 4 hours sequentially. The results of the present study indicate the presence of termoestable compounds in the cell wall of the yeast, released in higher concentrations in function of the sequential autoclavage, that are able to induce phytoalexin accumulation in sorghum mesocotyls and leaves, with antifungal activity on C. sublineolum and C. lagenarium and potential to induce local resistance in cucumber against C. lagenarium and local and systemic resistance in sorghum against C. sublineolum.

ASSUNTO(S)

fitoalexina sorghum yeast cucumber purificação anthracnose fungo fitopatogênico levedura sorgo antracnose phytoalexin purification pepino plant pathogenic fungi

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