Frequência de fungos associados ao colapso do meloeiro e influência da densidade de inóculo e isolados de Menosporascus cannonballus na severidade da doença

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

This study aimed to verify the frequency of fungi associated to melon (Cucumis melo L.) roots with collapse symptoms and their correlation with physical, chemical and microbiologic characteristics of soils. It also aimed to analyze the influence of inoculum densities and strains of Monosporascus cannonballus on the melon collapse, evaluating suitable methods to quantify disease. Melon plants with collapse symptoms and soil samples were collected from 10 producing areas, located in the counties of Mossoró and Baraúna (State of Rio Grande do Norte) and Quixeré (State of Ceará). The isolation frequency (FI) of fungi was obtained for each area, while the soil samples were analyzed in relation to physical, chemical and microbiologic characteristics. Monosporascus cannonballus inoculum densities of 0.1, 0.5, 1, 5, 10, 25 and 50 cfu/g of soil were essayed for collapse severity (SD), plant length (CP), shoot fresh biomass (BFPA) and root fresh biomass (BFR), shoot dry biomass (BSPA) and root dry biomass (PSR), areas of first and second true leaves (A1FD and A2FD), accumulated leaf area (AFA), total volume of plant (VTP), total fresh biomass of plant (BFTP) and total dry biomass of plant (BSTP). In the variability essay were utilized 44 strains of M. cannonballus with inoculum density of 10 cfu/g of soil. In the FI survey, high prevalences were verified for Fusarium solani and Macrophomina phaseolina (100%), while lower values were verified for Rhizoctonia solani (40%), M. cannonballus (30%) and Sclerotium rolfsii (30%). Fusarium solani and M. phaseolina presented similar FI, ranging from 1.6 to 60.0%, while M. cannonballus showed FI from 0.0 to 71.1%, R. solani from 0.0 to 18.0% and S. rolfsii from 0.0 to 13.3%. The FI of F. solani and M. cannonballus were respectively higher in melon type Orange (57.1%) and Cantaloupe (40.9%), as well as in areas with one or two years (45.4%) andwith more than five years (48.2%) of cropping. The FI of F. solani and M. cannonballus were inversely correlated (r = -0.79), and were influenced by the amount of Bacillus spp. in the soil (r = -0.71 and 0.80, respectively). The FI of M. phaseolina correlated with phosphorus level (r = 0.68), the FI of R. solani with flocculation degree (r = 0.67), field capacity (r = -0.81), pH (r = -0.75), aluminum level (r = 0.85) and total acidity (r = 0.69). The FI of S. rolfsii correlated with the permanent wilting point (r = -0.78) and soil available water (r = 0.75). The progress curves of SD, CP, A1FD, A2FD and AFA, related to inoculum densities, were adjusted by non-linear logistic model. Low inoculum densities (0.1, 0.5 and 1 cfu/g of soil) produced high levels of SD, ranging from 15.6 to 53.1%. Densities from 20 to 50 cfu/g of soil did not substantially increase SD. In the essay with different M. cannonballus strains, the analyzed variables propitiated formation of threesimilarity groups and evidenced strain variability within and among areas. High coefficients of correlation and determination confirmed the fit of SD with A1FD, A2FD and AFA in two essays demonstrating potential use to quantify the melon collapse.

ASSUNTO(S)

variabilidade inoculação variability root pathogen cucumis melo:fungo disease assessment melon monosporascus cannonballus patógeno radicular melão fitopatologia

ACESSO AO ARTIGO

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