SOME STUDIES ON THE GROWTH, SPORULATION AND SECONDARY METABOLITES OF AN ISOLATE OF CURVULARIA LUNATA (WAKK.) BOED

Abstract

Some aspects of the growth, sporulatlon and secondary metabolites of a local Isolate of Curvularia lunata <Wakk> Boed. were Investigated In this study. Solid media studies showed that generally, there was not such difference between cultures of the fungus derived from single spare or agar block inoculum In terms of growth, sporulation, pigment production and aroma production under conditions of alternating 12 hours of light and 12 hours of darkness dally at 23.5 °c. The cultures were also non-sporulatlng on the three media. On PDA and PDA + 0.05% malt extract, orange-apricot coloured colonies developed In the early stages of growth, and the colour changed to brown with age. On CDA, colour of the colonies was less Intense. A sweet, pleasant and fruity aroma similar to that of the local 'chiku' fruit was also produced by the fungus on the three media. The aroma however, was more Intense in cultures grown on PDA or PDA + 0.05% malt extract than on CDA. The growth, sporulation and aroma production of the Isolate were found to be unaffected by exposure of the fungus to continuous light or continuous darkness on PDA. Pigment formation of the fungus on the other hand was found to be markedly affected by these light conditions. When cultures of the fungus on the three media were exposed to blacklight and different regimes of blacklight, no marked differences in the growth, pigment and aroma production of the cultures were observed compared to the control cultures which were not exposed to blacklight. Sporulation however was stimulated in all the cultures on the three media when they were exposed to blacklight and different regimes of blacklight. Sporulation was observed generally to be moderate in cultures on PDA and CDA, and such less abundant in cultures on PDA + 0.05% malt extract. Spores formed in cultures on PDA or PDA + 0.05% malt extract were also found to generally rounder and shorter whilst those on CDA were more elongated. Besides this, sporulation of the fundus was also found to be affected by different blacklight regimes to which it was exposed but no trend in the degree of abundance of sporulation was observed. The results of studies on solid media also indicated that there was a) no correlation between sporulation and pigment production of the fungus; b) no correlation between sporulation and aroma production of the fungus; and c) no correlation between pigment and aroma production of the fungus Isolation of the pigment produced by the fungus was achieved with a Soxhlet apparatus with chloroform, as the extraction solvent. The pigment was analysed and identified as cynodontin or 1,4,5,8-tetrahydroxy-2-methylanthraquinone. Pigment production by the fungus in liquid medium was found to be influenced by various factors such as the type of liquid medium used as well as carbon sources, nitrogen sources or growth factors present in the medium. An optimum combination of glucose/maltose and sodium nitrate concentration was found to a more vital factor than the carbon: nitrogen ration (C:N) for pigment production. The optimum conditions for pigment production was in Czapek-Dox liquid medium containing 50 g/L of glucose or maltose as sole carbon source and 2 g/L of NaNO3 as sole nitrogen source. The sweet and fruity aroma produced by the fungus on solid media was also formed by the fungus in basal liquid medium. The type of carbon source, nitrogen source or growth factor present in the medium was found to have an influence on both the quality and the intensity of the aroma. The effect of nitrogen source on aroma quality was also found to be more pronounced that the effect of carbon source or growth factor. The greatest intensity of the aroma was found in cultures and a peak responsible for the aroma was obtained using GLC analysis.