Seleção de antagonistas fúngicos a Fusarium solani e Fusarium oxysporum em substrato comercial para mudas

Testes in vitro são geralmente utilizados para a seleção inicial de agentes de biocontrole contra fungos de solo, faltando metodologias que utilizem solo e/ou substrato. O objetivo deste trabalho foi realizar a seleção massal de isolados fúngicos antagônicos a F. solani e F. oxysporum em substrato comercial para mudas. Foram realizados dois experimentos com os patógenos F. solani e F. oxysporum e com 98 possíveis antagonistas fúngicos, dos gêneros Penicillium claviforme, Penicillium, Aspergillus e Cladosporium. A suspensão dos patógenos foi inserida no substrato, em copos plásticos, sendo acrescentada, cinco dias depois, a suspensão dos demais fungos. Avaliou-se o número de unidades formadoras de colônia de F. solani e F. oxysporum por grama de substrato após nove dias. Dos 98 isolados utilizados contra F. solani, 43 % não diferiram da testemunha e 57% reduziram o seu desenvolvimento em substrato, sendo que os três melhores isolados fúngicos foram do gênero Penicillium claviforme. Os três isolados de Penicillium claviforme selecionados para F. solani também foram eficientes para F. oxysporum.

Germination and adhesion of fungal conidia on polycarbonate membranes and on apple fruit exposed to mycoactive acetate esters

The adhesion and germination of conidia of nine fungal species were assessed on polycarbonate membranes or on the skin of apple fruit in sealed glass bottles injected or not injected with acetate esters. Adhesion was determined after dislodging conidia from surfaces using a sonication probe. Adhesion and germination of conidia of Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Penicillium citrinum, Penicillium claviforme, or Trichoderma sp. on membranes after 48 h were not increased in a 1.84 μg mL–1headspace of butyl acetate (BA), ethyl acetate, hexyl acetate, 2-methylbutyl acetate, pentyl acetate, or propyl acetate. Adhesion and germination of Botrytis cinerea, Penicillium expansum, and Penicillium roquefortii conidia were stimulated by all esters. Only conidia of B. cinerea and P. expansum exhibited increased adhesion and germination on the skin of apple fruit in bottles exposed to 0.92 μg mL–1of BA. Only conidia of B. cinerea and P. expansum produced decay in inoculated puncture wounds on fruit. Freshly made puncture wounds or 24-h-old puncture wounds in fruit were more adhesive than the unpunctured skin of fruit to conidia of B. cinerea or P. expansum. Fresh wounds were more adhesive to both fungi than 24-h-old puncture wounds. The skin and wounds of fruit were as adhesive to B. cinerea conidia as they were to P. expansum conidia. A 4-h exposure to 1.43 μg mL–1of BA increased adhesion of B. cinerea and P. expansum conidia in 24-h-old wounds. Results suggest that acetate–ester stimulation most likely is not a rare phenomenon in the fungi. For nutrient-dependent decay pathogens of apple fruit, acetate esters may be an alternative chemical cue used to maintain adhesion of conidia to wound surfaces.Key words: spore adhesion, spore germination, mycoactive compounds.