High spatial resolution fluorescence imagery for optimized pest management within a Huanglongbing-infected citrus grove

Huanglongbing (HLB), or citrus greening disease, has significantly decreased citrus production all over the world. The disease management currently depends on the efficient application and adequate distribution of insecticides to reduce the density of the disease vector, the Asian citrus psyllid. Here, we use a novel fluorescent-based method to evaluate insecticide distribution in an HLB-infected citrus grove in Florida. Specifically, we evaluated six different locations within citrus trees, the top and bottom sides of leaves, the effect of application approach (tractor vs airplane), and different application rates. We found that despite the insecticide distribution being highly variable among the different locations within a tree, the top of the leaves received an average increase of 21 times more than the bottom of the leaves. Application by tractor also resulted in a 4- to 87-fold increase in insecticide coverage compared to aerial application, depending on the location in the tree and side of leaf. When taken into context regarding the type of insecticide that is applied (systemic vs contact), these results can be used to optimize a pest management strategy to effectively target psyllids and other pests while minimizing the time and money spent on insecticide application and reducing risk to the environment.

Selection of Alternaria Fungi Control Treatments in a Citrus Grove through the Lens of the Electre Technique: A Case Study in San Luis Potosi, Mexico

Aims: To evaluate the cost-effectiveness of five control treatments (pesticides) for an Alternaria fungi variety in a citrus grove in Mexico. Study Design: Field applications of pesticides were used to combat an infestation of the Alternaria fungus. Place and Duration of the Study: The study took place in an orange citrus grove in Ciudad Fernandez, San Luis Potosí, Mexico, from October 2018 to August 2019. Methodology: Field trials with five control treatments were applied to randomly selected rows of infected orange trees. The assessment of treatments was carried out using the multi-criteria decision method (MCDM) known as ELECTRE with six evaluation criteria: cost, effectiveness, toxicity (e.g., environmental impact), difficulty of preparation, ease of application, and expiration date. Results: The results reveal that the best option to control the fungus of the Alternaria is the use of a biological product based on microorganisms, instead of standard options such as agrochemicals, or synthetic preparations known as “broths.” A sensitivity analysis reveals that the result may be affected by changing the weight of the criteria. Conclusion: The best treatment is the biological product because it is the most effective treatment to control the fungi plague, it is not toxic or expensive, and it does not have a measurable impact on the environment. However, the results are sensitive to changes in the weight of the criteria.

Restructuring citrus endophytic diversity through potential indigenous endophytes could eliminate huanglongbing pathogen Candidatus Liberibacter asiaticus

Background Huanglongbing (HLB) is a major botanical pandemic of citrus crops caused by Candidatus Liberibacter asiaticus (Clas). It is important to understand the different mechanisms involved in interaction of pathogen with plants to develop novel management strategy against HLB. However, until now there has been no control strategy to manage this disease in vitro and on large scale in citrus grove. We found that, indigenous endophyte Bacillus subtilis L1-21, a patented strain isolated from healthy citrus tree, may have the potential to reduce the impact of pathogen through restructuring of core endophytes. Results A novel half-leaf method was developed to test the efficacy of B. subtilis L1-21 against Clas. Concentration of B. subtilis L1-21 at 104 cfu ml− 1 resulted in a 1000-fold reduction in Clas copy densities per gram of leaf midrib (107 to 104) by 4 d after treatment. With endophytes, where HLB incidence was reduced to < 3% and Clas copy density was reduced from 109 to 104 pathogen g− 1 of diseased leaf midrib. We found that 16 of 93 tree samples became Clas-free and functional pathways and pathogen resistance genes were regulated in diseased citrus trees after treatment. Conclusions This is the first large-scale study using an indigenous endophyte and shows its potential utility in sustainable disease management through strengthening the citrus microbiome.

Factors Governing Total and Permanganate Oxidizable C Pools in Agricultural Soils from Southern Italy

The present investigation was aimed to quantify the three principal components of the soil carbon (C) stock, namely inorganic, organic and permanganate oxidizable, in 0–5 cm and 5–30 cm soil layers, of the main Mediterranean agricultural land coverages: olive grove, olive forest, citrus grove, vineyard, arable irrigated, arable rainfed and natural soil covered by Mediterranean scrub and garrigue. We assessed the contribution of soil properties and climatic variables on soil TOC and POxC by Pearson’s correlations, multiple linear regressions, principal component analyses and variance partitioning. NAT and both olive cropping systems showed the highest TOC concentration while the other land covers showed values ranging between 8.0 and 26.6 g kg−1. Soil POxC represented between 0.5% and 2.2% of the total soil C. A large number of interrelated factors govern soil C accumulation in Mediterranean agroecosystems. Rainfall and temperature had a selective effect on soil C distribution between the sampling areas, while among soil properties, texture exerted a prominent effect, resulting in positive effects from clay and negative effects from sand. Soil POxC concentration showed a similar trend to soil TOC in all land uses although on each of them represent a different TOC portion.

Deficit irrigation and the reuse of reclaimed water as strategies to cope with water scarcity in perennial crops. A summary of long-term trials within the H2020 SHUI project

&lt;p&gt;In arid and semi-arid regions, restriction on water for agriculture is fostering the search of alternative water resources, such as the reuse of reclaimed water (RW), and water-saving techniques, such as regulated deficit irrigation (RDI) strategies to cope with forecasted food production requirements. Two long-term experiments carried out by the CEBAS-CSIC team offer two scenarios: 1) Intensive cultivation of citrus in coastal areas and 2) extensive grape production for wine making in inland areas of Spain. Experiments in the Murcia Region (Spain) studied the physiological and agronomic effects of irrigating a young commercial grapefruit orchard with two water sources (saline RW versus conventional water). Water transferred from an irrigation canal (TW; electrical conductivity, EC&amp;#8776;1.3 dS m&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) and RW from a wastewater treatment plant (EC&amp;#8776;3.0 dS m&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) were compared, with control irrigation supplying 100% of the crop evapotranspiration (ETc) while the RDI treatment was irrigated at 50% of ETc during the 2&lt;sup&gt;nd&lt;/sup&gt; stage of fruit growth Although the RDI treatment decreased annual irrigation volume by 13.2%, soil salinity substantially increased in summer in the RDI treatment While these treatments did not negatively affect vegetative growth, yield and fruit quality, trial duration (2008-2010) was short in relation to the commercial life of a citrus grove, requiring further research over a longer term. This highlights the need for a longer-term socio-economic analysis that is possible within projects of SHui&amp;#8217;s duration (2018-2021). In grapevines research initiated in 2012 continues within SHui, to explore the effects of applying two different strategies: a) RDI in comparison with rainfed conditions and a full irrigation control. During the first three seasons (2012-2014), SDI was the preferred strategy to substantially improve yield (by 49%) compared to the rainfed regime, thereby significantly increasing water use efficiency (calculated considering both precipitation and irrigation). However, yield increments at 100% ETc were offset by detrimental effects that full irrigation had on grape composition. In this case, 8 years of these irrigation treatments produced similar results to the first three seasons of water application, suggesting cost benefit analyses of different deficit irrigation treatments over 3 may provide useful results to inform farmer choice&lt;/p&gt;

Potential soil transmission of a novel Candidatus Liberibacter strain detected in citrus seedlings grown in soil from a huanglongbing infested citrus grove

SUMMARYCandidatus Liberibacter spp. are Alphaproteobacteria associated with plants and psyllid vectors. Most cause plant diseases, including Ca Liberibacter asiaticus (Las) associated with citrus huanglongbing (HLB). Replacing HLB-infected by Las-free citrus trees results in fast re-infection despite psyllid control. To check if HLB could be soil-borne, we performed an insect-free greenhouse-experiment with 130 mandarin seedlings in two citrus-grove soils (A and B), non-autoclaved or autoclaved. Liberibacter-specific 16S-rDNA PCR primers to detect Las were used to search for Ca. Liberibacter spp. in mandarin leaves. Seven plants grown in non-autoclaved soil B showed HLB-like symptoms and tested positive after 2.5 and 8.5 months using three different primer systems: two based on the 16S-rDNA gene (primers HLBas/HLBr and OI2c/OI1) and one based on the rplA/rplJ gene (primers LAA2/LAJ5). DNA segments from these plants amplified by primers OI2c/OI1 were cloned and sequenced; they were 95.9 % similar to Las and 94.8% to Ca. Liberibacter africanus (Laf). The DNA product from Liberibacter-group specific PCR primers for the rplA/rplJ gene was 87.6% similar to that of Las and 78.2% of Laf. As the strain obtained originated from soil and was different from existing Ca. Liberibacter species, this strain may be a new species.