Microscopic study of the morphology and metabolic activity of Fusarium oxysporum f. sp. gladioli treated with Jatropha curcas oil and derivatives

AbstractThe fungus Fusarium oxysporum f. sp. gladioli is one of the main pathogenic microorganisms of the ornamental genus Gladiolus. The attack of this microorganism includes corms and different plant phenological stages. In this study, different microscopic techniques and fluorochromes were used to evaluate the effect of J. curcas oil and acylglycerides, namely trilinolein, triolein, monomyristin and dimyristin, on the morphology, membrane integrity (%), viability (%) and germination (%) of F. oxsporum f sp. gladioli. Phase-contrast optical photomicrographs and scanning microscopy showed that J. curcas oil and the triglycerides triolein and trilinolein caused the formation of numerous vacuoles, alterations in the morphology of the outer covering of the mycelium and conidia, and inhibition of membrane activity in the fungus during 24h of incubation. The fluorochromes used detected no permanent damage to the viability of the conidia. The high germination percentage of the conidia of Fusarium oxysporum f. sp. gladioli indicates that the damage caused by the application of the treatments was fungistatic rather than fungicidal and did not cause cell death

Antifungal activity and ultrastructural alterations in Pseudocercospora griseola treated with essential oils Atividade antifúngica e alterações ultraestruturais em Pseudocercospora griseola tratado com óleos essenciais

Pseudocercospora griseola, the etiologic agent of angular leaf spot of common bean (Phaseolus vulgaris), is an important disease in all bean-producing regions worldwide and may cause extremely high yield losses. The control of this disease is made more difficult by the pathogen's genetic variability and the inefficiency of fungicides. In this study, of 26 essential oils tested at different concentrations, 25 demonstrated efficiency in affecting the germination of strains 63-31 and 63-63 of the pathogen, reaching inhibition levels of between 80% and 100%. Cymbopogon citratus and Cymbopogon martinii inhibited conidia germination at all concentrations; Eugenia caryophyllata, Cinnamomum sp., Thymus vulgaris, Matricaria recutita, Cordia verbenacea, Origanum vulgare, Cymbopogon nardus, at 0.1 and 0.5%; and Zingiber officinale, Mentha arvensis, Chamaecyparis pisifera, Lavandula officinalis, Ocimum basilicum, Pimpinella anisum, Ocimum selloi, Baccharis dracunculifolia, Laurus nobilis, Citrus sinensis, Melaleuca alternifolia and Eucalyptus globulus, at 0.5%. The main constituents identified were cinnamaldehyde in Cinnamomum sp.; eugenol in E. caryophyllata; trans-&#946;-farnesene in M. recutita; pulegone in C. verbenacea; thymol in T. vulgaris; geranial and neral in C. citratus, and geraniol in C. martini. Through transmission electron microscopy (TEM), it was verified that C. citratus, C. martini and E. caryophyllata presented direct fungitoxic action on P. griseola, causing severe damage to the cellular ultrastructure of the conidia, invalidating germination. These results indicated that essential oils are a promising alternative strategy for the control of angular leaf spot in bean, representing less risk to human health and the environment.<br>Pseudocercospora griseola, agente etiológico da mancha angular do feijoeiro comum (Phaseolus vulgaris), é uma doença importante nas regiões produtoras de feijão em todo o mundo e pode causar perdas de produtividade extremamente elevados. O controle dessa doença é dificultado pela variabilidade genética do patógeno e da ineficiência de fungicidas. Neste estudo, de 26 óleos essenciais testados em concentrações diferentes, 25 demonstraram eficiência em inibir a germinação das linhagens 63-31 e 63-63 do agente patogênico, atingindo níveis de inibição entre 80% e 100%. Cymbopogon citratus e Cymbopogon martini inibiram a germinação de conídios em todas as concentrações; Eugenia caryophyllata, Cinnamomum sp., Thymus vulgaris, Matricaria recutita, Cordia verbenacea, Origanum vulgare, Cymbopogon nardus, em 0,1 e 0,5%, e Zingiber officinale, Mentha arvensis, Chamaecyparis pisifera, Lavandula officinalis, Ocimum basilicum, Pimpinella anisum, Ocimum selloi, Baccharis dracunculifolia, Laurus nobilis, Citrus sinensis, Melaleuca alternifolia e Eucalyptus globulus, em 0,5%. Os principais constituintes identificados foram cinamaldeído em Cinnamomum sp.; Eugenol em E. caryophyllata; trans-&#946;-farneseno em M. recutita; pulegona em C. verbenacea; timol em T. vulgaris; geranial e neral em C. citratus e geraniol em C. martini. Através de microscopia eletrônica de transmissão (TEM), verificou-se que C. citratus, C. martini e E. caryophyllata apresentaram ação antifúngica direta sobre P. griseola, causando graves danos na ultraestrutura celular dos conídios, invalidando a germinação. Esses resultados indicaram que os óleos essenciais são uma estratégia alternativa promissora para o controle da mancha angular do feijoeiro, o que representa menos risco para a saúde humana e ao ambiente