O conhecimento sobre os efeitos indesejáveis do uso de fungicidas convencionais, associado à preocupação de órgãos reguladores e consumidores quanto à qualidade dos alimentos, tem estimulado a busca por novas alternativas para o controle de doenças de plantas. O objetivo deste trabalho foi avaliar, em laboratório e em campo, a atividade antifúngica de 16 óleos essenciais sobre Phakopsora euvitis , agente causal da ferrugem da videira. Foram utilizados os óleos essenciais de orégano, menta piperita, pimenta preta, nim, eucalipto globulus , citronela, canela, manjerona, alecrim, manjericão, camomila azul, cânfora branca, cravo, gengibre, tomilho branco e melaleuca. No laboratório foram realizados dois experimentos: no primeiro, foi avaliada a germinação de esporos, em meio ágar-água acrescido do óleo essencial, nas concentrações de 0,0, 0,1, 0,5, 1, 2 e 4% (v/v), e sobre este foi depositada a suspensão de esporos. No segundo experimento, aplicaram-se os óleos essenciais em folhas destacadas de videira, seguindo-se a inoculação dos esporos de P. euvitis , avaliando-se a germinação dos esporos. A partir dos dados obtidos foram calculadas as percentagens de inibições da germinação de esporos e a dose letal (DL90). Em plantas de videira no campo foi realizada uma aplicação dos óleos essenciais, na concentração de 1%, e avaliada a severidade da ferrugem, após 15 e 30 dias. As DL90 dos óleos essenciais variaram entre 0,39% (nim) e 3,9% (orégano). Os óleos essenciais mais eficientes sobre P. euvitis , em condições in vitro , foram os de camomila azul, citronela, eucalipto globulus , gengibre, nim e tomilho branco. Na aplicação realizada em campo todos os óleos essenciais reduziram significativamente a severidade da ferrugem, destacando-se os óleos essenciais de canela, citronela, nim e tomilho branco. Aspectos relacionados à fitotoxicidade necessitam ser elucidados. Os óleos essenciais avaliados apresentam potencial para serem utilizados no manejo da ferrugem da videira, contudo estudos complementares fazem-se necessários.
O presente trabalho teve como objetivo avaliar a atividade antifúngica in vitro de dez óleos essenciais sobre o crescimento micelial e a germinação de esporos de Sphaceloma ampelinum, agente causal da antracnose da videira. Foram utilizados os óleos essenciais de uva (Vitis vinifera), tangerina (Citrus reticulata), laranja doce (Citrus aurantium), citronela (Cymbopogon winterianus), canela (Cinnamomum zeylanicum), eucalipto (Eucalyptus staigeriana), anis estrelado (Illicium verun), alecrim (Rosmarinus officinalis), cravo (Eugenia caryophyllus) e tomilho branco (Thymus vulgaris) nas concentrações de 0,3 e 1% em relação ao volume total, os quais foram incorporados em meio de cultura ou suspensão de esporos. Determinaram-se as percentagens de inibições do crescimento micelial e da germinação de esporos. Constatou-se que os óleos essenciais de canela, tomilho branco e cravo proporcionaram os melhores efeitos de inibição sobre o crescimento micelial e a germinação de esporos de S. ampelinum e merecem mais estudos, para comprovação de sua eficiência em condições de campo.
Citrus black spot (CBS) is caused by Phyllosticta citricarpa, which is classified as a quarantine organism in certain countries whose concerns are that CBS-infected fruit may be a pathway for introduction of the pathogen. This study evaluated the reproductive capability and viability of P. citricarpa under simulated conditions in which the whole fruit, peel segments, or citrus pulp with CBS lesions were discarded. Naturally infected ‘Midknight’ Valencia orange and ‘Eureka’ lemon fruit, either treated using standard postharvest sanitation, fungicide, and wax coating treatments or untreated, were placed into cold storage for 5 weeks (oranges at 4 °C and lemons at 7 °C). Thereafter, treated and untreated fruit were incubated for a further 2 weeks at conditions conducive for CBS symptom expression and formation of pycnidia. The ability of pycnidia to secrete viable pycnidiospores after whole fruit and peel segments or peel pieces from citrus pulp were exposed to sunlight at warm temperatures (±28 °C) and ±75% relative humidity levels was then investigated. The combination of postharvest treatments and cold storage effectively controlled CBS latent infections (>83.6% control) and pycnidium formation (<1.4% of lesions formed pycnidia), and the wax coating completely inhibited pycnidiospore release in fruit and peel segments. Pycnidiospores were secreted only from lesions on untreated fruit and peel segments and at low levels (4.3–8.6%) from peel pieces from pulped treated fruit. However, spore release rapidly declined when exposed to sunlight conditions (1.4% and 0% after 2 and 3 days, respectively). The generally poor reproductive ability and viability of CBS fruit lesions on harvested fruit, particularly when exposed to sunlight conditions, supports the conclusion that citrus fruit without leaves is not an epidemiologically significant pathway for the entry, establishment, and spread of P. citricarpa.
Citrus black spot (CBS) symptom expression on sweet oranges has been reported to be affected by the fruit developmental stage and inoculum concentration in greenhouse conditions. However, there is little information concerning the period in which the fruit is susceptible in commercial orchards. This study assessed the influence of fruit age and inoculum concentration of Phyllosticta citricarpa on CBS intensity and fruit drop in the field. Two field trials were conducted in commercial ‘Valencia’ orchards in São Paulo state, Brazil. Fruit were inoculated from October (petal fall stage) to July (c.6.5 cm diameter), with 101, 103 and 105 pycnidiospores/ml. CBS symptoms and fruit drop were observed in higher levels for fruit inoculated from October to February than from March to July. In both trials, when fruit were inoculated 10 times from October to July or single‐inoculated in November or December, high CBS severities of 11%–22% were observed and the proportion of fruit remaining on the tree was 48%–77%; in contrast, noninoculated fruit had severity below 1.1% and 90% remained on the tree. Inoculations in November or December of green fruit with 1.5–3.0 cm diameter using 105 pycnidiospores/ml were associated with higher CBS intensity and fruit drop and shorter incubation period than inoculations with lower concentrations. This work provides a better understanding of fruit stages and P. citricarpa inoculum concentrations most related to symptom expression and losses under natural conditions and may be helpful for improvement of CBS management in the São Paulo citrus belt.
ABSTRACT-This study aimed to evaluate the fungitoxic (antifungal) effect of seven essential oils on Plasmopara viticola, the causal agent of grapevine downy mildew. The cinnamon, eucalyptus globulus, marjoram, melaleuca, peppermint, oregano and white thyme essential oils were compared with the mancozeb + metalaxyl-M fungicide. Three experiments were conducted to evaluate the effect of essential oils on spore germination. The first experiment evaluated the effect of direct contact of essential oils on the pathogen; the second evaluated the effect of volatile compounds on the pathogen and the third assessed the behavior of essential oils, when applied to vine leaves in field conditions, on the pathogen. All essential oils inhibited the spores' germination, but in varying degrees, in addition, presenting fungistatic activity. All the essential oils showed chemical instability when the incubation time or the interval between products application where increased, all oils decrease antifungal activity percentage. Noteworthy, the cinnamon and the eucalyptus globulus essential oils were the most fungitoxic (antifungal) on P. viticola. Index terms: Fungicidal activity, fungistatic activity, alternative control, spore germination. FUNGITOXICIDADE DE ÓLEOS ESSENCIAIS SOBRE
Effect of inoculation time and Phyllosticta citricarpa spore concentration on the expression of CBS symptoms on fruit.
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