Citrus Diseases Exotic to Florida: Citrus Tristeza Virus–Stem Pitting (CTV-SP)

This document is one in a series designed to provide important information on the causal agent, symptoms, and transmission of exotic citrus diseases. This information can be used as an educational tool to raise awareness about these diseases and for scouting and identification efforts. Disseminating information about the diseases to the citrus industry may prevent their introduction and spread in Florida. This document will focus on the exotic viral disease caused by isolates of citrus tristeza virus–stem pitting (CTV-SP). Original version: Chung, Kuang-Ren, and Ronald Brlansky. 2006. “Citrus Diseases Exotic to Florida: Citrus Tristeza Virus– Stem Pitting (CTV-SP)”. EDIS 2006 (7). https://doi.org/10.32473/edis-pp149-2006.

Consumers' Perceptions and Preferences toward Florida Orange Juice

Faced with reduced domestic supply, competition from imports, and high production costs, the Florida citrus industry and Florida growers need to understand how consumers perceive Florida-produced orange juice and whether they value it more than OJ produced elsewhere. We conducted a national survey to understand consumers' perceptions and confirmed that consumers have a superior perception of Florida OJ, which could lead to higher rates of willingness-to-buy and willingness-to-pay.

Price transmission between international and domestic prices in the Brazilian citrus sector

The orange juice chain is a representative sector of the Brazilian agribusiness sector and its performance warrants analysis to identify strategies to enhance its competitiveness. Analysis of asymmetry in food value chain is important because it provides valuable information on market structure and performance. We use an asymmetric threshold error correction model to examine threshold, short- and long-run asymmetries on price transmission from international to domestic prices of oranges in Brazil. We use monthly data on international frozen concentrated orange juice prices and domestic prices of oranges in Brazil for the period from January 1996 to December 2020 in the analysis. We find evidence of threshold and asymmetries in short- and long-run price transmission and asymmetric adjustment towards a long-run relationship between international and domestic orange prices in Brazil. Decreases in international prices that lead to reductions in marketing margins are passed on quickly to domestic prices, but this is not the case for increases in international prices. We discuss implications for the Brazilian citrus industry.

Threat to Citrus in a Global Pollinator Decline Scenario: Current Understanding of Its Pollination Requirements and Future Directions

Pollinators are vital for world biodiversity and their contribution to agricultural productivity is immense. Pollinators are globally declining with reports such as colony collapse being documented. Citrus exhibits a varying degree of pollination requirements due to its vast cultivars being developed all the time. The article intends to understand the breeding system of a few commercially important Citrus groups and discern its dependency on pollination services. The threat related to pollinator decline to the Citrus industry is measured not only by its reliance on pollinators but also the requirement of the consumers and manufacturers who mostly seek seedless varieties. Therefore, the threat can be tackled by developing high-quality seedless varieties where pollination requirement is absent. Although the importance of pollinators on several self-incompatible varieties cannot be negated, the impact of pollinator decline on its production will entirely depend upon the demand of the market.

Influence of Rootstock on the Leaf Volatile Organic Compounds of Citrus Scion Is More Pronounced after the Infestation with Diaphorina citri

Nowadays, citrus greening or Huanglongbing is considered the most destructive disease in the citrus industry worldwide. In the Americas and Asia, the disease is caused by the putative pathogen, ‘Candidatus Liberibacter asiaticus’ and transmitted by the psyllid vector, Diaphorina citri. It has been shown that volatile organic compounds (VOC) that are released from citrus leaves attract the psyllid vector. Herein, we tested whether the rootstock influenced the stored VOC profile in the scion leaves and if these influences were altered after infestation with D. citri. The VOC profiles of the hexane-extracted leaves of the mandarin hybrid ‘Sugar Belle’ that were grafted on three different rootstocks (C-35, sour orange (SO), and US-897) with and without infestation with D. citri were studied. The GC-MS analysis showed that the scion VOC profiles of the non-infested control trees were similar to each other, and rootstock was not a strong influence. However, after one month of infestation with D. citri, clear differences in the scion VOC profiles appeared that were rootstock dependent. Although the total scion leaf VOC content did not differ between the three rootstocks, the infestation increased scion monoterpenes significantly on US-897 and C-35 rootstock, increased terpene alcohols on US-897 and SO rootstock, and increased sesquiterpenes on SO. Infestation with D. citri significantly reduced fatty acids and fatty acid esters across all of the rootstocks. Therefore, our results suggest that rootstock choice could influence scions with an inducible volatile defense by enhancing the amounts of VOCs that are available for repelling vectors or for signaling to their natural enemies or parasitoids. According to this study, US-897 may be the best choice among the three that were studied herein, due to its diverse and robust VOC defense response to infestation with D. citri.

Silencing of Aquaporin Homologue Accumulates Uric Acid and Decreases the Lifespan of the Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae)

The Asian citrus psyllid, Diaphorina citri Kuwayama is devastating the citrus industry worldwide. It transmits ‘Candidatus Liberibacter asiaticus’, the pathogen of Huanglongbing in citrus. RNA interference is an excellent tool for functional genomics and for screening target genes for pest control. Herein, we silenced the aquaporin (AQP) gene (DcAQP) homologue in D. citri to study its functionality and whether it could be a good target for a control strategy. AQP is an integral membrane channel protein that aids in the rapid flux of water and other small solutes that move across the lipid membrane. In Hemiptera, it is well established that AQP plays important roles in adjusting to physiological challenges including (1) regulating osmotic stress between the gut lumen and hemolymph after imbibing large quantities of a low nitrogen, sugar-rich liquid diet; (2) avoiding or preventing dehydration and desiccation; and (3) surviving at elevated temperatures. The dsRNA-DcAQP was applied twice to nymphs of the 4th and 5th instars through a soaking technique. Silencing AQP caused a significant increase in nymph mortality. Emerged adults showed malformations and a shorter lifespan. Silencing DcAQP provoked alterations in some metabolites and increased the uric acid content in emerged adults. DcAQP could be a useful target to control D. citri.

Interactions between Indigenous Endophyte Bacillus subtilis L1-21 and Nutrients inside Citrus in Reducing Huanglongbing Pathogen Candidatus Liberibacter Asiaticus

Huanglongbing (HLB) pathogen Candidatus Liberibacter asiaticus (CLas) brings a great concern about the phloem nutrient transport in diseased plants. There is an urgent need to find the best management strategies to reduce the losses in the citrus industry worldwide. Endophytic bacteria are negatively affected by CLas pathogen, and these endophytes are associated with improved availability of nutrients and pathogen resistance. This study underpins the relationship between CLas pathogen, endophyte population and nutrients availability in citrus plants. The citrus plants were treated with Bacillus subtilis L1-21 and Hoagland solution to find out synergism efficacy to mitigate citrus HLB. We showed that citrus shoots in the presence of 50% Hoagland solution displayed maximum number of endophytes with 6.28 × 103 to 3.04 × 105 CFU/g. Among 50 candidate strains, B. subtilis L1-21 emerged as potential antagonist against surrogate strain Xanthomonas citri subsp. citri. The citrus half-leaf method identified that application of endophyte L1-21 with 50% Hoagland solution successfully reduces the CLas abundance. We point out that this combination results in a higher number of endophytes population with 2.52 × 104 to 9.11 × 106 CFU/g after 60 days, and reduces CLas pathogen abundance in asymptomatic HLB plants. In HLB symptomatic citrus plants, B. subtilis L1-21 potentially increases the endophyte population from 1.11 × 104 to 5.26 × 107 CFU/g in the presence of Hoagland solution, and pathogen abundance was reduced from 9.51 × 105 to 1.06 × 104 copies/g. Altogether, we suggested that the presence of endophyte L1-21 with Hoagland solution is more effective in HLB asymptomatic citrus plants, but a slight reduction of pathogen was observed in symptomatic plants. The findings revealed the role of indigenous citrus endophyte B. subtilis L1-21 along with other nutrients in the reduction of CLas pathogen abundance inside symptomatic and asymptomatic plants in citrus endophyte–nutrient–pathogen interplay.

Preliminary Findings of New Citrus Rootstocks Potentially Tolerant to Foot Rot Caused by Phytophthora

Phytophthora spp. are one the most common soil-borne pathogens in citrus crops, in which Phytophthoranicotianae and P. citrophthora are the most relevant species, causing disease problems worldwide, such as foot rot and gummosis of the trunk, branch canker, brown rot of fruit, feeder root rot in orchards, and seedling damping-off in nurseries. Phytophthora-tolerant citrus rootstocks are essential for its control and for the success of the citrus industry. The aim of this study was to determine the susceptibility of new citrus rootstocks with low HLB incidence to Phytophthora diseases. Thus, plants of several commercial and new citrus rootstocks originating in different breeding programs were inoculated with an isolate of P. nicotianae. Thirty days post inoculation (DPI), the damage of lesion length in stem was measured for each plant. These results displayed a different susceptibility response to the damage caused by P. nicotianae among the citrus rootstocks tested. Thus, eleven new citrus rootstocks (B11R3T25, B11R5T25, B11R5T49, B11R5T60, B11R5T64, N40R1T18, N40R1T19, N40R3T25, WGFT + 50-7, UFR-6, and CL-5146), which have not been previously studied against Phytophthora diseases, improved the tolerance effect of Carrizo citrange. Our findings provide useful information for citrus growers on rootstock selection to address incidence problems caused by Phytophthora spp.

Adaptive Performance of Five Varieties of Hybrid Citrus in Jingzhou Area Hubei Province

In order to understand the growth habits and freeze resistance of the hybrid citrus variety in Jingzhou area, and to provide reference for the introduction of the variety in fruit farmers, and to promote the development of the local citrus industry, the main biological and freeze resistance characteristics of the five hybrid citrus variety were investigated. The results showed that:(1)The growth potential of ‘Wo gan’ and ‘Daya’ were the strongest, followed by ‘Aiyuan 38’ and ‘Chunjian’, and the weakest growth was ‘Buzhihuo’;(2) On the performance of summer and autumn shoots, ‘Daya’ and ‘Wogan’ were the longest, ‘Chunjian’ was moderate, ‘Aiyuan 38’ and ‘Buzhihuo’ were the weakest; (3) On the aspect of freeze resistance, ‘Aiyuan 38’was the strongest, followed by ‘Daya’ and ‘Wogan’, the freeze resistance of ‘Chunjian’ was more weak and ‘Buzhihuo’ was the weakest;(4) On the other aspects, such as the leaf shape, leaf size, color of tender leaf, thorn density, flower size, inflorescence and so on also had the big difference, but the petal number and the petal color were similar. It could be seen that ‘Daya’ and ‘Wogan’ had the best growth potential in Jingzhou area, but their freeze resistance were weak. The growth potential of ‘Aiyuan 38’ and ‘Chunjian’ were in the middle, ‘Aiyuan 38’ had best freeze resistance. The growth potential and freeze resistance of ’Buzhihuo’ in Jinzhou area was the weakest.