Comparative epidemiology of three viruses on zucchini squash (Cucurbita pepo L.)

A abobrinha de moita (Cucurbita pepo L.), espécie pertencente à família Cucurbitaceae, apresenta significativa participação na produção mundial e brasileira desta família de plantas. Porém, como em toda cultura de importância econômica, as cucurbitáceas apresentam problemas fitossanitários causados por diferentes agentes etiológicos. Na produção brasileira de abóboras, já foi constatada a presença de 8 vírus, dentre eles os potyvirus PRSV-W (Papaya ringspot virus-type W) e ZYMV (Zucchini yellow mosaic virus) e o tospovirus ZLCV (Zucchini lethal chlorosis virus) têm sido considerados os mais importantes pela predominância em diversas regiões produtoras de cucurbitáceas no país e pelos consideráveis prejuízos que geralmente causam à produção. Considerando que a maioria dos estudos epidemiológicos existentes sobre estas três viroses são poucos e fragmentados, percebe-se que não há estudos que abordam em conjunto todos os parâmetros epidemiológicos de tais vírus. Assim, os objetivos deste trabalho foram estudar o progresso temporal e espacial destas três viroses e verificar a relação entre a epidemiologia das mesmas em campo de abobrinha de moita, além de melhor entender o patossistema em que a clorose letal (causada pelo ZLCV) está inserida Para isso, foram conduzidos experimentos com abobrinha de moita Caserta nos campos experimentais dos Departamentos de Fitopatologia e Nematologia (DFN) e Departamento de Genética (DGN) da Esalq/USP. Primeiramente foram conduzidos em 2009 dois experimentos simultâneos nas áreas do DFN e DGN para estudar a epidemiologia isolada da clorose letal acompanhada da dinâmica populacional do tripes Frankliniella zucchini, vetor deste vírus. Em seguida, em épocas diferentes 3 experimentos foram conduzidos em 2010 com o intuito de comparar as epidemiologias da clorose letal e dos mosaicos comum e amarelo, estes últimos causados por PRSV-W e ZYMV, respectivamente. Nos experimentos apenas com a clorose letal no ano de 2009, o modelo monomolecular foi o que melhor se ajustou aos dados de incidência e através das análises espaciais detectou-se agregação da doença ao final dos dois experimentos. Nos 3 experimentos realizados em 2010, variações na incidência, no ajuste do modelo e no comportamento espacial de cada virose foram freqüentes. Para a clorose letal, o modelo monomolecular ofereceu melhor ajuste apenas na 3ª época de plantio. Nas duas primeiras o modelo gompertz apresentou maior coeficiente de determinação. No comportamento espacial, novamente agregação da doença foi detectada ao final do ciclo da cultura. Para o mosaico amarelo, os modelos que melhores se ajustaram na 1ª, 2ª e 3ª épocas de plantio, foram o logístico e o monomolecular (este nas duas últimas), respectivamente. O padrão espacial desta doença foi ao acaso quando da baixa incidência da doença e agregado nos casos em que elevada incidência ocorreu. Já o mosaico comum apresentou a menor incidência nas 3 épocas. O modelo logístico foi o que melhor se ajustou em todas as épocas e a doença apresentou comportamento espacial ao acaso nos três experimentos. Nos levantamentos do tripes vetor do ZLCV, verificou-se preferência do mesmo por plantas sintomáticas e consideráveis correlações do número de insetos coletados com a incidência da clorose letal.The zucchini squash (Cucurbita pepo L.) belonging to the Cucurbitaceae family, has a good share of world and brazilian output. However, as in every plants of economically important, cucurbits have problems caused by different etiological agents. In the Brazilian production of zucchini squash, already confirmed the presence of 8 viruses, including the potyviruses PRSV-W (Papaya ringspot virus-type W) and ZYMV (Zucchini yellow mosaic virus) and the tospovirus ZLCV (Zucchini lethal chlorosis virus) have been considered the most important viruses by the predominance in several cucurbits producing regions in the Brazil and the considerable damage on production. Whereas the most of the existing epidemiological studies about these three viruses are few and fragmented, it is clear that there are no studies that deal together all the epidemiological parameters of such viruses. The objectives of this work were to study the temporal and spatial progress of these three viruses and the relation between the epidemiology of these viruses in the same field of zucchini squash in addition to better understand the lethal chlorosis pathosystem (caused by ZLCV). Trials were carried out with zucchini squash \'Caserta in the experimental fields of the Departments of Plant Pathology and Nematology (DPP) and Department of Genetics (DGN) at Esalq/USP. The firsts were conducted in 2009 simultaneously in DPP and DGN to study the epidemiology of lethal chlorosis only and to study the population dynamic of thrips Frankliniella zucchini, the vector of this virus. In 2010 three experiments were carried out in different growing seasons in order to compare the epidemiology of the lethal chlorosis, yellow mosaic and common mosaic caused by ZLCV, PRSV-W and ZYMV, respectively. In the experiments with the lethal chlorosis in 2009, the monomolecular model was the best fit to the incidence data and spatial analysis indicated aggregation of the disease at the end of both experiments. In three experiments carried out in 2010, variations in incidence, in the fit of the model and in the spatial distribution of each virus were frequents. For lethal chlorosis, the monomolecular model provided a better fit only in the 3rd growing season. In the first and second growing seasons Gompertz model had the best coefficient of determination. In the spatial distribution, aggregation of disease was detected at the end of the crop cycle again. For yellow mosaic, the models that best fit in the 1st, 2nd and 3rd planting dates were the logistic and monomolecular (this in the last two) respectively. The spatial pattern of this disease were randomly when the disease incidence was low and aggregated when the disease incidence was high. The common mosaic had the lowest incidence in all three seasons. The logistic model was the best fit in all growing seasons and the disease showed a spatial random distribuctions in all experiments. The thrips vector of ZLCV prefer symptomatic plants and good correlations between the number of insects collected with the incidence of lethal chlorosis was found

Sugarcane Orange rust in Brazil: a study on pathogen populations and varietal behavior

A ferrugem alaranjada da cana-de-açúcar, causada pelo fungo Puccinia kuehnii, apesar de ser centenária, foi detectada no Brasil apenas no final de 2009, após causar uma grande epidemia na Austrália em 2000. Pela recente detecção, não há estudos que comparam as populações brasileiras de P. kuehnii e a reação, em condições controladas, de importantes variedades de cana-de-açúcar ao patógeno. Assim, este trabalho analisou e comparou o comportamento de variedades de cana-de-açúcar inoculadas com seis diferentes populações de P. kuehnii coletadas em diferentes locais no Brasil, além de verificar a variabilidade patogênica e genética destas populações. Para isso, inoculou-se populações de P. kuehnii coletadas em Piracicaba (SP), Araras (SP), Ribeirão Preto (SP), Paranacity (PR), Nova Alvorada do Sul (MS) e Dourados (MS). As variedades de cana-deaçúcar utilizadas foram: SP89-1115, SP81-3250, RB85-5156, RB86-7515, RB92- 5211, RB96-6928, CTC 3, CTC 6, CTC 8, CTC 9, CTC 13, CTC 15 e CTC 18. Em todas as inoculações avaliaram-se os períodos de incubação e de latência da doença, a severidade, o número total de pústulas e a porcentagem de pústulas abertas. Além disso, as regiões ITS e IGS de todas as populações de P. kuehnii foram sequenciadas e comparadas entre si e com sequências do patógeno da Austrália, Papua Nova Guiné, Indonésia, Filipinas, Japão, China, Guatemala, Panamá, Jamaica, Costa Rica, Nicaraguá, México e Estados Unidos. Os resultados mostraram que a porcentagem de pústulas abertas é o melhor parâmetro para separar e classificar as variedades de cana-de-açúcar quanto ao grau de resistência ao patógeno. O período de incubação da doença variou de 7 a 10 dias e o período de latência, de 9 a 19 dias. As populações de P. kuehnii não constituem diferentes raças virulentas e a população coletada em Araras (SP) é uma raça mais agressiva do patógeno. Para as regiões IGS e ITS, as seis populações de P. kuehnii utilizadas apresentam sequências idênticas entre si e entre todas as sequências de P. kuehnii do continente americano depositadas no \"GenBank\". Para estas duas regiões, as populações utilizadas no trabalho diferem de sequências da Austrália, China, Filipinas, Havaí (EUA), Indonésia, Japão, Papua Nova Guiné e Samoa. A disseminação do patógeno além da Ásia e Austrália parece ter ocorrido após a epidemia da doença na Austrália em 2000. No entanto ainda não se sabe ao certo como o patógeno teria chegado à América em 2007 e à África em 2011.Despite being a century disease, sugarcane orange rust, caused by the Puccinia kuehnii, was only reported in 2009 Brazil, after having caused an epidemic in Australia in 2000. Because it was recently detected in Brazil, there are no studies that compare P. kuehnii populations in Brazil and the reaction, under controlled conditions, of important sugarcane varieties to the pathogen. This study compared the performance of sugarcane varieties inoculated with six different populations of P. kuehnii collected in different sites in Brazil. We also studied the pathogenic and genetic variability of these pathogens populations. In order to carry out this study, P. kuehnii populations were collected in the municipalities of Piracicaba (SP), Araras (SP), Ribeirao Preto (SP), Paranacity (PR), Nova Alvorada do Sul (MS), and Dourados (MS). The sugarcane varieties used were: SP89-1115, SP81-3250, RB85- 5156, RB86-7515, RB92-5211 RB96-6928, CTC 3, CTC 6, CTC 8, CTC 9, CTC 13, CTC 15, and CTC 18. For all inoculations, we evaluated the incubation period, latent period, disease severity, total number of pustules, and percentage of open pustules. Furthermore, the ITS and IGS rDNA regions of all P. kuehnii populations were sequenced and compared with sequences from Australia, China, Costa Rica, Guatemala, Indonesia, Jamaica, Japan, Mexico, Nicaragua, Papua New Guinea, the Philippines, Panama, and the United States. The results showed that the percentage of open pustules is the best parameter to separate and classify the resistance of sugarcane varieties to the pathogen. The incubation period of the disease ranged from 7 to 10 days and the latent period from 9 to 19 days. There are no P. kuhenii virulent races and the population collected in Araras (SP) is a more aggressive race. For the IGS and ITS regions, the six P. kuehnii populations have identical sequences which were identical to all P. kuehnii sequences found in the American continent deposited at the GenBank accession. The P. kuehnii used in this study is different from populations found in Australia, China, Hawaii (USA), Indonesia, Japan, Papua New Guinea, the Philippines, and Samoa. The pathogen dissemination over Asia and Australia seems have occurred after the 2000 epidemic in Australia. However, it is unknown still how the pathogen reached America in 2007 and Africa in 2011

Severidade da ferrugem da soja em função do suprimento de potássio e cálcio em solução nutritiva

Entre as estratégias para o controle da ferrugem da soja cita-se a nutrição mineral equilibrada. Objetivou-se, neste trabalho, verificar o efeito do cálcio e do potássio na severidade da ferrugem (Phakopsora pachyrhizi), na fotossíntese potencial e na nutrição de plantas de soja. O delineamento experimental foi em blocos casualizados, com 25 tratamentos, 4 repetições e 2 plantas por repetição. Utilizou-se esquema fatorial 5 x 5, com 5 doses de K (4, 5, 6, 7, 8 mmol L^-1), combinadas com 5 doses de Ca (3, 5, 7, 9, 11 mmol L^-1). As plantas foram inoculadas no estádio V4 e, após nove dias, iniciaram-se avaliações da severidade da ferrugem pelas porcentagens de tecido lesionado, as quais foram transformadas em área abaixo da curva de progresso da doença (AACPS).Também foram avaliados a fotossíntese potencial e o teor de nutrientes na matéria seca de raiz, caule e folhas. O suprimento de Ca reduziu a AACPS em todas as doses de K. O suprimento de K também reduziu a AACPS nas doses 5, 7 e 11 mmol L^-1 de Ca. A menor AACPS foi observada na combinação das doses de 8 e 11 mmol L^-1 de K e Ca, enquanto a maior AACPS foi observada nas doses de 4 e 5 mmol L^-1 de K e Ca. As plantas tratadas com as doses 6 e 5 mmol L^-1 de K e Ca e 5 e 5 mmol L^-1 de K e Ca apresentaram melhor resposta fotossintética. Com o incremento das doses de K na solução, houve aumento dos teores foliares de K e redução linear dos teores foliares de Ca. Com o incremento das doses de Ca em solução nutritiva verificaram-se aumentos nos teores desse elemento e redução linear dos teores de K nas folhas.A balanced mineral nutrition is among the strategies for the control of Asian soybean rust. This work aimed to evaluate the severity of the soybean rust (Phakopsora pachyrhizi), the potential photosynthesis and the nutrition of soybean plants with different levels of K and Ca. The experiment was arranged in a randomized block design with 25 treatments, 4 repetitions and 2 plants per repetition. A 5 x 5 factorial scheme with 5 doses of K (4, 5, 6, 7, 8 mmol L^-1) combined with 5 doses of Ca (3, 5, 7, 9, 11 mmol L^-1) was used. Plants were inoculated at growth stage V4 and after nine days weekly evaluations of disease severity were carried out using percentage of injured tissues, which were transformed into area under the disease progress curve (AUDPCS). Potential photosynthesis and nutrient content in the root, stem and leaf dry matter were also evaluated. The supply of Ca reduced AUDPCS at all doses of K. The supply of K also reduced the AUDPCS at the doses of 5, 7 and 11 mmol L^-1 of Ca. The smallest AUDPCS was observed at the combination 8 and 11 mmol L^-1 of K and Ca, respectively, while the largest AUDPCS was observed at the doses of 4 and 5 mmol L^-1 of K and Ca. The plants treated with 6 and 5 mmol L^-1 of K and Ca and 5 and 5 mmol L^-1 of K and Ca showed better photosynthetic response. Increasing doses of K in the solution promoted increase in K leaf contents and linear decrease in Ca leaf levels. Increasing the levels of Ca in nutrient solution promoted an increase in the content of this element and a linear reduction of K levels in the leaves

The Perfect Match: Adjusting High Tree Density to Rootstock Vigor for Improving Cropping and Land Use Efficiency of Sweet Orange

The rise in the productivity of sweet orange in Brazil has been related to the use of superior rootstocks and higher tree density, among other factors. In order to investigate whether the cropping system and the land use efficiency would benefit from more intensive cultivation, the performance of Valencia sweet orange was evaluated over nine years on four rootstocks, which induced contrasting vigor, at 513, 696 and 1000 treesha1. Agronomic Institute of Campinas (IAC) 1697 and IAC 1710 citrandarins, and diploid and allotetraploid (4) Swingle citrumelos were classified as semidwarfing, super-standard, standard, and dwarfing rootstocks, respectively. The fruit yield per tree was decreased at higher tree densities, notably for more vigorous rootstocks. Conversely, the cumulative productivity was increased over the evaluation period by 27% at 1000 treesha1, irrespective of the rootstock, and the most vigorous rootstock resulted in 2.5 times higher production than the dwarfing one on average. Most fruit quality parameters were seldom influenced by the tree density, while the rootstock was a decisive factor in improving the quality and the soluble solids content. Dwarfing rootstocks allowed for harvesting 17% more fruit per minute by manual pickers. Because the tree row volume per area is lower with such rootstocks, even at higher tree density, spray volume can be reduced, although appropriate equipment should be developed for better spray coverage on smaller trees. Nine years after planting under strict vector control, the cumulative incidence of huanglongbing-symptomatic trees on IAC 1710 was double that on Swingle 4. Taken together, the results suggested that the land use efficiency in the citrus industry can be further improved by planting vigorous rootstocks at moderate to high tree densities. Nevertheless, obtaining highly productive semi-dwarfing and dwarfing rootstocks is the sine qua non for making high-density pedestrian sweet orange orchards more profitabl

Graft Compatibility Classification within Aurantioideae Based on Biometric Traits and the Anatomy of Graft Union

Citrus relatives are a relevant source of valuable traits for use in citrus breeding, including resistance to diseases such as Huanglongbing (HLB). Resistant rootstocks may impact tree responses to HLB. This requires graft compatibility, which has been poorly investigated within the Aurantioideae. In this study, the biometric characteristics and the anatomy of the graft union of 86 scion/rootstock combinations were assessed. This comprised 18 genotypes/species and 8 genera from Citrinae, Balsamocitrinae, and Clauseninae subtribes sensu Swingle and Reece. Most graft combinations were found to be noncompatible. Phylogenetic proximity did not ensure successful grafting as, for example, Orange jasmine autografts failed, whereas some intergeneric grafts were successful (>60% of graft-take). Plant scion height was directly related to graft-take, but the correlation between the scion and rootstock stem diameters was not a reliable indicator of graft compatibility. Rangpur/Tabog, Tabog/Rangpur, Wampee/Rangpur, Wampee/Pomeroy, Wampee/Swingle, Pomeroy/Wampee, and Swingle/Wampee were the most compatible intergeneric graft combinations. Graft-take success for this was at similar levels to those of sweet orange grafted on common citrus rootstocks. The position as a scion or rootstock in the combination affected the performance and was specific to the genotypes tested. The lack of differentiation between xylem-derived calli and the accumulation of phenolic compounds at the graft union were clear anatomical and biochemical markers, respec-tively, of incompatibility for most Aurantioideae combinations. In the field, within a set of the ten most promising combinations, Hamlin/Rangpur (control) was the only one that became infected by ‘Candidatus Liberibacter asiaticus’. This was first observed 12 months after planting. Overall, the assessment of biometric traits and anatomy of the graft union allowed Aurantioideae genotypes to be divided into four clusters, with respect to their graft compatibility, as follows: fully compatible with high graft-take and plant growth; potentially compatible with high graft-take but lower plant growth; partially incompatible with lower graft-take and poor plant growth; and fully incompatible with a complete absence of graft-take.Peer reviewe