In vitro effect of UV-C irradiation on Guignardia citricarpa and on postharvest control of citrus black spot

ABSTRACT Black spot, caused by Guignardia citricarpa, is one of the main diseases affecting citrus fruits. UV-C irradiation is known to have potential to be used as an alternative method to supplement or replace the use of fungicides, especially because it promotes resistance against pathogens. The aim of this work was to evaluate the in vitro effects of UV-C irradiation on G. citricarpa development and on the control of black spot in postharvest orange. Additionally, changes in skin color of the fruit as a result of UV-C treatment were evaluated. Mycelial growth, conidial germination and appressoria formation were evaluated in vitro after fungal exposure to different irradiation doses. Also, 'Valência' oranges naturally infected were submitted to different irradiation doses to check the possibility of in vivo control. Fruit were stored at 25ºC/80% RH and evaluated 3, 7, 10 and 14 days after treatment and area under the disease progress curve was calculated. UV-C irradiation affected conidial germination of G. citricarpa and apressorium formation. UV-C irradiation was not able to control citrus black spot on fruit at a satisfactory level; however, incidence of quiescent black spot lesions was lower on postharvest 'Valência' orange treated with 7.28 and 15.66 kJ m -2 . Low UV-C doses did not affect the visual aspect of fruit. Thus, UV-C irradiation can contribute for the reduction of postharvest losses caused by citrus black spot and reduce the use or doses of fungicides on disease control. Key words: Citrus sinensis, conidia, mycelium, peel color, physical control. RESUMO Efeito in vitro da irradiação UV-C sobre Guignardia citricarpa e no controle pós-colheita da pinta preta dos citros A pinta preta, causada por Guignardia citricarpa, é uma das principais doenças que afetam frutos cítricos. A irradiação UV-C tem potencial para ser utilizada como método alternativo para suplementar ou substituir o uso de fungicidas, especialmente por promover resistência contra patógenos. O objetivo deste trabalho foi avaliar os efeitos da irradiação UV-C sobre o desenvolvimento in vitro de G. citricarpa e no controle da pinta preta em laranja pós-colheita. Adicionalmente, foram avaliadas as alterações na cor da casca dos frutos. Crescimento micelial, germinação de conídios e formação de apressórios foram avaliados in vitro após a exposição do fungo a diferentes doses de irradiação. Frutos de laranja 'Valência' naturalmente infectados foram submetidos a diferentes doses de irradiação (0,52; 1,04; 3,13; 7,28; 15,66 e 31,20 kJ m -2 ) para verificar a possibilidade de controle in vivo. Os frutos foram armazenados a 25ºC/80% UR e avaliados 3, 7, 10 e 14 dias após o tratamento e a área abaixo da curva de progresso da doença foi calculada. A exposição à UV-C afetou a germinação de conídios de G. citricarpa e a formação de apressórios. A irradiação com UV-C não foi capaz de controlar a pinta preta de maneira satisfatória; no entanto, a incidência de lesões de pinta preta quiescentes foi menor em laranjas 'Valência' tratadas em pós-colheita com 7,28 e 15,66 kJ m -2 . Doses baixas de UV-C não afetaram o aspecto visual dos frutos. Portanto, a irradiação UV-C pode contribuir para a redução de perdas pós-colheita causadas pela pinta preta dos citros e reduzir o uso ou as doses de fungicidas no controle desta doença. Palavras-chave: Citrus sinensis, conídios, controle físico, cor da casca, micélio

Biology of the citrus blackfloy, Aleurocanthus woglumi Ashby (Hemiptera: Aleyrodidae), in three host plants

A mosca-negra-dos-citros, Aleurocanthus woglumi Ashby, foi detectada no Brasil em 2001. O objetivo deste estudo foi avaliar a biologia, a biometria e a preferência hospedeira de A. woglumi em três plantas hospedeiras (laranja doce, lima ácida Tahiti e manga). Para isso, foram montados experimentos em laboratório, de janeiro a junho de 2006, com insetos coletados em plantas de limão-cravo, C. limonia na área de produção da Faculdade de Ciências Agrárias - UFAM. No estudo da preferência hospedeira, foram avaliados: número de espirais (posturas) e de ovos por planta, número de ovos por espiral por planta, sobrevivência dos imaturos (ovos, ninfas de 1º, 2º, 3º e 4º estádios), enquanto no experimento de biologia foram avaliadas a duração e sobrevivência da fase imatura. O período embrionário foi de 15 dias em média para os três hospedeiros. O estádio de ninfa 4 (pupário) foi o mais longo quando comparado com as outras fases de desenvolvimento. A sobrevivência foi maior nas fases de ninfa 3, ovo e ninfa 2. A duração média do ciclo ovo-adulto foi de 70 dias para os três hospedeiros avaliados. Os ovos são colocados em forma de espiral na face inferior das folhas. As ninfas de 1º estádio locomovem-se a pequenas distâncias da espiral, enquanto as de 2º, 3º e 4º são sésseis e têm cerdas em todo o corpo. Com base na maior oviposição e sobrevivência da fase imatura da mosca-negra em lima ácida Tahiti, esta planta pode ser considerada o hospedeiro mais favorável para A. woglumi.The citrus blackfloy, Aleurocanthus woglumi Ashby, was detected in Brazil in 2001. The aim of this research was to evaluate the biology, biometry and host preference of A. woglumi in sweet orange, acid lime Tahiti and mango. Experiments were set in laboratory conditions with insects collected in rangpur lime plants in Manaus, State of Amazonas, from January to June of 2006. The following parameters were evaluated: number of spirals (ovopositions) and eggs per plant, number of eggs by spiral per plant, survival of the immatures (eggs, 1st, 2nd, 3rd and 4th instars), and length and survival of the immature stage. The mean embrionary period was 15 days for the three hosts. The 4th nymph (puparium) was the longest during nymph development. Second and third instars had the highest survival. The mean length of the egg-adult cycle was 70 days for the three hosts evaluated. The eggs were laid in a spiral shape on the adaxial leaf surface. The 1st instars moved to short distances from the spiral, while the 2nd, 3rd and 4th are sessile and have bristles on the whole body. Based on the highest oviposition and the highest survival of the immature stage of the citrus blackfloy in acid lime Tahiti, this plant can be considered the most suitable host to A. woglumi.CNPqCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES

The Effects of Host, Geographic Origin, and Gender on the Thermal Requirements of Diaphorina citri (Hemiptera: Psyllidae)

Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the vector of the bacteria that causes citrus greening and is considered one of the world`s most important citrus diseases. We examined how host, geographic region, and gender affect the thermal requirements of D. citri. The insects were reared in climatic chambers at constant temperatures of 18, 20, 22, 25, 28, 30, and 32 1 degrees C, 70 +/- 10% RH, and a 14 h photophase. Host plants for D. citri included orange (Citrus sinensis [Rutaceae]) varieties Pera and Natal, the rootstock, Rungpur lime (C. limonia [Rutaceae]) and the natural host, Orange jessamine (Murraya paniculata [Rutaceae]). To study the influence of geographic origin on thermal requirements, we studied D. citri populations from Piracicaba, SP (warmer region) and Itapetininga, SP (cooler region). The duration and survival of the development stages and the duration of the total development (egg-adult) did not differ significantly on the different hosts, but it did vary with temperature. Nymphs of D. citri created on the different hosts have the same thermal requirements. The thermal requirements for this species collected from the two climate regions were identical; males and females also had the same thermal requirements.Fapesp[04/14216-6]Fundecitru

Distribuição vertical, danos e controle cultural de Stenoma catenifer Walsingham (Lepidoptera: Elachistidae) em pomar de abacate

Stenoma catenifer Walsingham is the major pest in avocado groves (Persea americana Mill.) in the Neotropical region. Management has been difficult for many reasons related to the reduced knowledge on its bioecology and the avocado growing systems. The goal of this work was to study the vertical distribution of S. catenifer in avocado plants, the gagging effect of infested fruit on its survival, and the losses caused. The experiments were conducted in a commercial grove located at the Sao Tomas de Aquino, State of Minas Gerais, Brazil, during the 2001/2002 and 2002/2003 growing season. S. catenifer was observed especially at the lower and central part of the plant, and the inner canopy was the least attacked in comparison with the north, south, east and west quadrants. These results may be important indicators for the use of am adequate sampling procedure. The highest percentage of attacked fruit had one to four larvae; in some cases up to eight individuals per fruit were found. The losses caused by the borer varied during the agricultural season, with figures close to 5% in a single evaluation, and the harvest loss may reach 27%. The bagging of infested fruit caused mortality of S. catenifer, as observed through the evaluation carried out four days later