Controle de doenças foliares e de flores e qualidade pós-colheita do morangueiro tratado com Saccharomyces cerevisiae

O efeito de diferentes preparações de Saccharomyces cerevisiae foi avaliado sobre o desenvolvimento das doenças do morangueiro, como mancha-de-micosferela (Mycosphaerella fragariae), mancha-de-dendrofoma (Dendrophoma obscurans) e flor-preta (Colletotrichum acutatum) além da qualidade pós-colheita dos frutos. O trabalho foi realizado entre 2004 e 2005 na Universidade Tecnológica Federal do Paraná, Campus Dois Vizinhos. Os tratamentos consistiram de pulverizações semanais de cinco diferentes preparados a partir da levedura S. cerevisiae: suspensão com fermento biológico fresco comercial, suspensão de células de levedura, suspensão autoclavada de células, filtrado de cultura em meio líquido e Agro-MOS®, produto comercial formulado a partir da levedura, além da testemunha com água destilada e do tratamento controle com fungicidas. Nenhuma das preparações apresentou efeito contra a mancha-de-micosferela; preparações com a presença de células vivas e o produto Agro-MOS® apresentaram efeito contra mancha-de-dendrofoma; preparações com suspensão do produto comercial e filtrado de cultura líquida reduziram a incidência de flor-preta em flores e frutos. Preparações de S. cerevisiae com suspensão de células, suspensão autoclavada de células e filtrado de cultura líquida promoveram aumento na produtividade dos morangueiros que variou de 589,6 a 617,8 g planta-1. Preparações de S. cerevisiae, com presença de células vivas ou não, alteraram o metabolismo do morangueiro, aumentando a atividade das enzimas quitinase e glucanase, envolvidas na resistência sistêmica adquirida. Todos os tratamentos, com exceção do tratamento com suspensão autoclavada de células, reduziram a incidência de mofo-cinzento em pós-colheita de frutos.

Escala diagramática para avaliação da severidade da mancha-de-dendrophoma em morangueiro

Uma escala diagramática foi desenvolvida e validada para quantificar a severidade da mancha-de-dendrophoma do morangueiro, causada por Dendrophoma obscurans (Ell &Ev.)H.W. Anderson. A escala considerou os limites de severidade mínima e máxima da doença observados no campo e os níveis intermediários seguiram incrementos logarítmicos, obedecendo-se à "Lei do estímulo de Weber-Fechner". Inicialmente, a estimativa da severidade foi feita sem auxílio da escala em 25 folíolos com diferentes níveis de severidade, por oito indivíduos, sem experiência na avaliação da mancha-de-dendrophoma do morangueiro. Em seguida, os mesmos avaliadores utilizaram a escala diagramática proposta, com seis níveis: 0,9; 2,9; 9,1; 25,2; 53,3 e 79,5%. As avaliações com a escala diagramática obtiveram ótima precisão e alta acurácia para todos os avaliadores. A escala diagramática proposta foi considerada adequada para estimar a severidade de mancha-de-dendrophoma em morangueiro, podendo ser usada em estudos epidemiológicos e na avaliação de estratégias de controle desta doença.

First Report of Phomopsis Fruit Rot of Strawberry in Ohio

During spring (May and June) 1999, ≈30% of the fruit in a 0.5-ha commercial planting of strawberry (Fragaria × ananassa ‘Allstar’) was lost to an unknown fruit rot. The planting was established on black plastic (plasticulture) during summer 1998. Plasticulture is a relatively new system of perennial strawberry production in Ohio that is rapidly gaining popularity among growers (2). It was observed that the plastic beneath the plants in the plasticulture planting was covered with a layer of dead leaves from the previous season's growth, and virtually all rotted fruits were in contact with dead leaves. Fruit rot was rarely observed on fruits that were not in direct contact with dead leaves, and fruits of the same cultivar grown in the traditional matted-row system in an adjacent field did not show rot symptoms. It was postulated that infested dead leaf material could serve as an inoculum source for infection. Fruit rot symptoms were identical to those described for Phomopsis soft rot (1). Isolations were made from infected berries. Berries were soaked in 70% ethanol for 60 s, and tissue sections were placed on potato dextrose agar and incubated at room temperature (≈20 to 22°C). A fungus was isolated consistently from infected tissue. The fungus produced pycnidia in culture, and the fruiting structure and conidia conformed to the description of Phomopsis obscurans (Ellis & Everh.) Sutton (synamorph Dendrophoma obscurans (Ellis & Everh.) H.W. Anderson). Pathogenicity studies were conducted by placing one drop (20 μl) of a conidial suspension (9 × 106 conidia per ml) obtained from 2-week-old cultures on each of five ripe (red) and five immature (pink) detached strawberry fruits. Inoculated fruits were placed on screens in plastic moisture chambers. Five uninoculated fruits served as controls. Within 3 days, whitish lesions appeared on all inoculated fruit; within 8 days, the symptoms observed in the field were reproduced, and lesions were covered by pycnidia. No fruit rot developed on control fruit. The fungus was reisolated from infected fruit to complete Koch's postulates. Although the incidence of Phomopsis leaf blight is increasing in many Ohio strawberry plantings and is becoming a concern to growers, this is the first observation and report of Phomopsis fruit rot in Ohio. Unlike leaf blight, for which it is difficult to directly relate economic loss to disease incidence or severity, losses due to fruit rot can be high, as in this field. As the number of strawberry plantings under plasticulture continues to increase, the importance of Phomopsis leaf blight and fruit rot also may increase. References: (1) J. L. Maas, ed. 1998. Compendium of Strawberry Diseases, 2nd ed. The American Phytopathological Society, St. Paul, MN. (2) E. B. Poling. HortTechnology 3:384, 1993.

Qualitative and quantitative effects of radiation on pycnidial formation by Dendrophoma obscurans

Cultures of Dendrophoma obscurans grown on a 10:2 glucose: casein hydrolysate medium require radiation for sporulation. Far-ultraviolet (253.7 nm), near-ultraviolet (300–425 nm), and blue radiation (400–525 nm) were effective in initiating pycnidial formation. Exposure of cultures to radiation from 500 to 850 nm did not induce sporulation. Pycnidial formation was found to be photoinduced and age dependent. Low intensities of near-ultraviolet radiation administered over long durations were more effective than high intensities of short durations for inducing pycnidial formation.

STUDIES ON FUNGUS PARASITES OF STRAWBERRY LEAVES IN ONTARIO

Four fungi were isolated from lesions on strawberry foliage in Ontario during the growing seasons of 1948 and 1949. They are Mycosphaerella fragariae (Tul.) Lindau. Diplocarpon carliana (Ell. & Ev.) Wolf, Dendrophoma obscurans (Ell. & Ev.) H. W. And., and Gnomonia fructicola (Arnaud) n. comb. (Zythia fragariae Laibach), and they cause the diseases known as leaf spot, leaf scorch, leaf blight and leaf blotch respectively. Apparently this is the first report of Zythiae fragariae in North America and of Dentrophoma obscurans in Canada. From field surveys, strawberry varieties were found to vary in resistance, especially to spot and scorch, and market differences in seasonal distribution of the diseases were also evident. Spot was most prevalent in the spring and fall; scorch increased in severity during the warmer months; and blight became prominent after the cropping period. As a result of inoculation with M. fragariae only the middle-aged leaves of vigorously growing strawberry plants developed lesions. Premier plants, although resistant to spot in the field, proved susceptible when artificially inoculated. Penetration by M. fragariae may occur without lesion formation if the temperature is below 15 °C. Symptom expression was best within the 20°–25 °C range. Adding strips of strawberry leaves to a suspension of conidia of Diplocarpon earliana greatly enhanced spore germination. Only leaves which are old or middle-aged develop scorch lesions, and these may be blotchy or diffuse depending on the variety. Dendrophoma obscurans appears to attack mainly the older leaves near the margins. The conidiophores are long and branched, the conidia slightly pointed, and the pyenidia are dark, leathery, and clumped in culture. Zythia fragariae has simple conidiophores, biguttulate conidia with rounded ends, and soft light brown pyenidia. The name Gnomonia fructicola is proposed for the fungus Gnomonia fragariae Klebahn form fructicola Arnaud because it is considered to be a different species from Gnomonia fragariae Klebahn.