Cultural Management of Huanglongbing: Current Status and Ongoing Research

[EN] Huanglongbing (HLB), formerly known as greening, is a bacterial disease restricted to some Asian and African regions until two decades ago. Nowadays, associated bacteria and their vectors have spread to almost all citrus-producing regions, and it is currently considered the most devastating citrus disease. HLB management can be approached in terms of prevention, limiting or avoiding pathogen and associated vectors to reach an area, or in terms of control, trying to reduce the impact of the disease by adopting different cultural strategies depending on infestation/infection levels. In both cases, control of psyllid populations is currently the best way to stop HLB spread. Best cultural actions (CHMAs, TPS system) to attain this goal and, thus, able to limit HLB spread, and ongoing research in this regard is summarized in this review.This work was funded by the EU H2020 Innovation Action Program (grant 817526) and by the Fundo de Defensa da Citricultura (Fundecitrus).Alquézar-García, B.; Carmona, L.; Bennici, S.; Miranda, MP.; Bassanezi, RB.; Peña, L. (2022). Cultural Management of Huanglongbing: Current Status and Ongoing Research. Phytopathology. 112(1):11-25. https://doi.org/10.1094/PHYTO-08-21-0358-IA1125112

Economic Impacts of Huanglongbing Disease in São Paulo State

The main objective of this paper is to estimate the potential impacts of the increasing dissemination of the Huanglongbing (HLB) disease in citrus orchards in São Paulo State, Brazil, which is the largest world producer of orange juice and to discuss the importance of phytosanitary programs in order to control the disease’s spreading in the territory. The methodology applied to evaluate the impacts and to discuss the importance of phytossanitary programs is the Cost-Benefit Analysis approach. A model has been used to project the orchard size and production along 20 years as well as to estimate the costs of production and disease control for the same period. Some assumptions have been made about the disease spread, prices and other variables for two basic scenarios: one considering the presence of an official phytosanitary program to eradicate and control the HLB, jointly implemented by Fundecitrus, which is a private institution; and the second one without the official program. The revenues for each scenario have been estimated and accumulated for 20 years, likewise the costs. The losses caused by the HLB considered to evaluate the avoided losses in the scenarios comprised basically those related to production reduction (yield) and reduction of the orchards’ size. Cost-benefit ratios have been calculated for both scenarios. Regarding the CBA results for economic impacts, we found that for each Real invested by government and by Fundecitrus in the phytosanitary program, there is an avoided loss that amounts to R$ 57.3, which consists on a very high benefit-cost ratio for this kind of investment. When the additional costs imposed to farmers to manage the HLB is computed in the CBA analysis, the ratio falls to 4.6, however it is still higher than one, indicating that this phytosanitary “investment” is recommendable. Despite criticisms on this approach and the assumptions made, it provides elements to decision making, for both public and private actors and it allows having some approximation of impacts. Estimating those impacts is relevant to prove policy makers that phytosanitary policy has a high net benefit for society. It is worth-mentioning that other economic and social losses might be incorporated in the analysis

Cultural Management of Huanglongbing: Current Status and Ongoing Research

Huanglongbing (HLB), formerly known as greening, is a bacterial disease restricted to some Asian and African regions until two decades ago. Nowadays, associated bacteria and their vectors have spread to almost all citrus-producing regions, and it is currently considered the most devastating citrus disease. HLB management can be approached in terms of prevention, limiting or avoiding pathogen and associated vectors to reach an area, or in terms of control, trying to reduce the impact of the disease by adopting different cultural strategies depending on infestation/infection levels. In both cases, control of psyllid populations is currently the best way to stop HLB spread. Best cultural actions (CHMAs, TPS system) to attain this goal and, thus, able to limit HLB spread, and ongoing research in this regard is summarized in this review.Peer reviewe

Características da pulverização em citros em função do volume de calda aplicado com turbopulverizador

Este trabalho teve como objetivo avaliar o efeito do volume de calda aplicado por um turbopulverizador sobre a deposição e a cobertura em folhas, ramos e frutos de citros. A pulverização foi realizada com um pulverizador tratorizado Arbus 2000/Valência em pomar de laranja 'Natal', com porte médio de 4,0 m, sendo avaliados seis volumes de calda (50; 70; 85; 100; 150 e 200% do volume-padrão utilizado pelo produtor, de 28 L planta-1). Após a pulverização de plantas uniformes com calda contendo cobre e o traçador fluorescente Poliglow 830 YLSS, amostras foram coletadas em nove setores da planta, sendo a avaliação da deposição feita usando-se análise do íon cobre por espectrofotômetro de absorção atômica, e a da cobertura, por meio de imagens digitalizadas analisadas pelo programa para computador IDRISI. A análise estatística mostrou que, na avaliação da cobertura e deposição em citros, a utilização de frutos como estrutura de amostragem tendeu a evidenciar melhor o efeito dos tratamentos. Tanto a deposição quanto a cobertura tenderam a ser maiores nos setores frontal e saia da planta. Tanto a deposição quanto a cobertura não foram prejudicadas pela utilização do volume de 70% (19,6 L planta-1), indicando que tal volume pode substituir o volume de 100% (28 L planta-1) sem prejuízos ao controle de pragas.The aim of this study was to evaluate the efficacy of different carrier volume applied with an airblast sprayer on spray deposition on leaves, branch and fruits in citrus trees. It was used a trailed sprayer Arbus 200/Valência in an orange orchard, variety Natal, with 4,0 m mean height, and six volumes were evaluated (50; 70; 85; 100; 150 and 200% relative to the standard volume in use, 28 L plant-1). After spraying of regular plants with carrier containing copper and Poliglow 830 YLSS as fluorescent tracer, the samples were collected in nine localization of the tree. The evaluation of spray deposition was done with an atomic absorption spectrophotometer by analyze of copper ion. The evaluation of spray coverage was done by digitalized image which were analyzed with IDRISIS software. The analysis statistical showed that in the evaluation of spray coverage and deposition in citrus the use of fruits as sample made to evidence better the effect of the treatments. The spray coverage and deposition had been trend higher upon frontal horizontal sector and upon lower vertical sector of the tree. The spray coverage and deposition had not been prejudiced by the use of 70% rate (19.6 L plant-1) which indicates that this volume can replace the 100% rate (28.0 L plants-1) without disadvantage in the control periods

Nuclear magnetic resonance characterization of metabolite disorder in orange trees caused by citrus sudden death disease

Citrus sudden death (CSD) is a new disease of sweet orange and mandarin trees grafted on Rangpur lime and Citrus volkameriana rootstocks. It was first seen in Brazil in 1999, and has since been detected in more than four million trees. The CSD causal agent is unknown and the current hypothesis involves a virus similar to Citrus tristeza virus or a new virus named Citrus sudden death-associated virus. CSD symptoms include generalized foliar discoloration, defoliation and root death, and, in most cases, it can cause tree death. One of the unique characteristics of CSD disease is the presence of a yellow stain in the rootstock bark near the bud union. This region also undergoes profound anatomical changes. In this study, we analyse the metabolic disorder caused by CSD in the bark of sweet orange grafted on Rangpur lime by nuclear magnetic resonance (NMR) spectroscopy and imaging. The imaging results show the presence of a large amount of non-functional phloem in the rootstock bark of affected plants. The spectroscopic analysis shows a high content of triacylglyceride and sucrose, which may be related to phloem blockage close to the bud union. We also propose that, without knowing the causal CSD agent, the determination of oil content in rootstock bark by low-resolution NMR can be used as a complementary method for CSD diagnosis, screening about 300 samples per hour.FAPESP (The State of Sao Paulo Research Foundation)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq National Council for Scientific and Technological Development)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Financiadora de Estudos e Projetos (FINEP)MCT/FINEP (Ministry of Science and Technology/Studies and Projects Foundation

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