Susceptibility of fruits of the 'Valência' and 'Natal' sweet orange varieties to Guignardia citricarpa and the influence of the coexistence of healthy and symptomatic fruits

Abstract

of fruits of the 'Valência' and 'Natal' sweet orange varieties to Guignardia citricarpa and the influence of the coexistence of healthy and symptomatic fruits. Fitopatologia Brasileira 31: 337-341. 2006. ABSTRACTThe importance of the presence of symptomatic fruits with citrus black symptoms (CBS) on the disease severity level in subsequent crop production was assessed in an orchard planted with Valência and Natal sweet orange varieties. Additionally, the period of susceptibility of the fruits of these varieties was evaluated.Fruits were covered with paper bags at the stage of 75% fallen petals and were then exposed to natural infection at weekly intervals, from October 2000 to April 2001. This process was carried out in plants where the fruits from the previous harvest had been picked as well as in plants where fruits remained until natural drop. The evaluation of disease severity used a scale that varied from 0 (absence of symptoms) to 6 (severe symptoms). It was observed that, for the Valência and Natal varieties, conidia of Phyllosticta citricarpa that had formed on the lesions of fruits from the previous harvest did not significantly increase the severity of disease on the fruits of the subsequent harvest period. In this study, the protection of the fruits until 10 weeks after petal drop did not affect the number of lesions, indicating that ascospore discharges after that date were, probably, responsible for disease severity. Fruits exposed between the 20 th and 24 th week after 75% of the petals had fallen were symptomatic, indicating that, at this stage, the fruits were still susceptible to the pathogen.Additional keywords: Citrus sinensis, Phyllosticta citricarpa, conidia, ascospores. RESUMO Suscetibilidade de frutos das variedades de laranja 'Valência' e 'Natal' à Guignardia citricarpa e a influência da coexistência de frutos sadios e sintomáticos Em pomar de laranjeiras 'Valência' e 'Natal' avaliou-se a importância da presença de frutos sintomáticos da mancha preta citros (MPC) na severidade da doença nos frutos cítricos da safra subseqüente. Adicionalmente, avaliou-se o estádio de suscetibilidade dos frutos dessas variedades. Frutos foram protegidos com sacos de papel cristal a partir do estádio de 75% de pétalas caídas em outubro de 2000, até abril de 2001. Frutos foram expostos, em intervalos semanais, da 1 a à 24 a semana. Esse processo se deu tanto em plantas onde os frutos da safra remanescente foram previamente colhidos, como naquelas cujos frutos sintomáticos da safra remanescente permaneceram até a sua queda natural. Avaliou-se a severidade da doença usando uma escala de notas que variou de 0 (ausência de sintomas) a 6 (sintomas severos). Observou-se que para as duas variedades os conídios de Phyllosticta citricarpa, formados nas lesões dos frutos da safra remanescente, não provocaram incremento significativo na severidade da doença dos frutos da safra subseqüente. A proteção dos frutos até 10 a semana após a queda de pétalas não influenciou na quantidade final de lesões, indicando que as desca...

Pest risk assessment and additional evidence provided by South Africa on Guignardia citricarpa Kiely, citrus black spot fungus - CBS - Scientific Opinion of the Panel on Plant Health

“…However, even in endemic areas such as Brazil where the disease is particularly severe, wetness durations during the infection periods are shown to be in the order of 10 hours per day (Reis et al, 2006). This suggests a lower requirement for leaf wetness duration than that reported in the literature or a potential for withstanding periods of dryness during the infection process.…”

“…This suggests a lower requirement for leaf wetness duration than that reported in the literature or a potential for withstanding periods of dryness during the infection process. Therefore, the following values were considered for D 50 : 0 hours for no interruption; 3 hours as a value which is often found in the literature as being a generally acceptable period of leaf wetness interruption (Rossi et al 2007;Xu and Butt, 1993); 14 hours as a long interruption according to the meteorological data shown by Reis et al (2006).…”

“…Fruit is susceptible to infection for up to 4-6 months after petal fall, (Baldassari et al, 2006;Kotzé, 1981Kotzé, , 2000McOnie, 1964b;Reis et al, 2003) and there is a long incubation period which may last for 2-12 months (Kellerman and Kotzé, 1977;McOnie, 1967). Lemon leaves remain susceptible from development up to 10 months of age (Truter et al, 2004; but, with the exception of lemons, leaves rarely show symptoms during their life span (up to approximately 3 years) (Kiely, 1948;McOnie, 1967).…”

Controle da pinta preta dos frutos cítricos em cultivo orgânico com agentes de biocontrole e produtos alternativos

“…Em áreas de ocorrência da pinta preta, a decomposição das folhas cítricas caídas ao solo é de extrema importância, haja vista que dependendo da umidade, época do ano e do estádio de decomposição foliar, há liberação dos ascósporos, que é a principal fonte de inóculo do patógeno (Baldassari et al, 2006). Segundo Swift et al (1979) e Aerts (1997), os três principais fatores que influenciam a decomposição, em ordem de importância, são as condições climáticas, composição química das folhas e os organismos presentes no solo, que são determinados pelo microclima.…”

“…Para o ano agrícola 2005/2006 também foi avaliada a decomposição de folhas cítricas, que são a principal fonte de inóculo de G. citricarpa (Baldassari et al, 2006). A avaliação da taxa de decomposição foi feita pela análise de perda de massa utilizando-se "litter bags", segundo metodologia de Fernandes et al (2006), modificando-se o diâmetro da malha para 0,5 x 0,5 cm e dimensões de 60 x 40 cm.…”