Seleção, identificação e aplicação de leveduras no controle da murcha-de-fusário em Vigna unguiculata (L.) Walp

Abstract

Cowpea fusarium wilt caused by Fusarium oxysporum f. sp. tracheiphilum (Fot) is reported in many producing regions causing production and productivity losses in Brazil and worldwide. There is no efficient control measure for this disease, as the pathogen produces chlamydospore-like resistance structures capable of remaining inactive for long periods of time under adverse conditions. The integrated use of host genetic resistance coupled with the application of antagonist yeasts is presented as a control alternative to this disease. In this context, the objective of this work was to investigate the pathogenicity and resistance of different cowpea genotypes to Fot, as well as the application of antagonistic yeast strains as biological control agents of cowpea fusarium wilt. Fot isolates were evaluated by the method of dipping or immersing roots of conidial suspended plants using two genotypes considered susceptible to the pathogen under greenhouse conditions. Isolates CFS-296 and CMM-732 promoted disease with wilting, yellowing and reduced growth in cv. BR-17 Gurguéia and IPA-206. From these isolates, twenty genotypes were characterized for resistance and interference in height, root length, number of leaves, number of branches, stem diameter, green biomass and plant dryness in relation to the disease. The genotypes presented different resistance to disease in relation to pathogen isolates, affecting the morphological characteristics of the plants. All genotypes were highly resistant to CMM-732, except the Casa Amarela-06 genotype, which was susceptible. While for CFS-296, six genotypes were moderately resistant, five susceptible and nine highly susceptible. Thirty strains of yeast isolated from cowpea plant parts were selected and characterized for inhibitory and antibiotic action in vitro on the most aggressive isolate (CMM-732), and compared with the two pathogenic isolates, demonstrating that the strains CFS-644, CFS-652 and CFS-699 were effective in reducing mycelial growth for CFS-296, as well as CFS-738 for CMM-732 isolate. In the bioprotective assay, cowpea seeds and 6-day old twinned plants treated with four yeasts by immersion and spraying at a concentration of 1x106 cells mL-1 respectively, as well as inoculated with the two pathogenic isolates, showed a reduction of 12-46%. of the severity of the disease. In particular, the CFS-652-treated Encruzilhada-04 genotype reduced the disease infection by 46%. Use of yeast biocontrol combined with host resistance has been shown to be an alternative management approach to fusarium wilt.