Transcriptomic Response of Huanglongbing-Infected Citrus sinensis Following Field Application of a Microbial Fermentation Product

Huanglongbing (HLB) is considered the most destructive disease in Citrus production and threatens the future of the industry. Microbial-derived defense elicitors have gained recognition for their role in plant defense priming. This work assessed a 5% (V/V) microbial fermentation application (MFA) and its role in the elicitation of defense responses in HLB-infected Citrus sinensis trees following a foliar application with a pump sprayer. Using a PCR detection method, HLB infection levels were monitored in healthy and infected trees for 20months. Nutrient analysis assessed N, P, K, Ca, Mg, Mn, Zn, Fe, B, and Cu concentrations in the trees. MFA significantly increased Cu concentrations in treated trees and resulted in the stabilization of disease index (DI) in infected trees. Initial real-time qPCR analysis of defense-associated genes showed a significant increase in pathogenesis-related protein 2 (PR2) and phenylalanine ammonia lyase (PAL) gene expression in healthy and HLB-infected trees in response to MFA. Gene expression of PR2 and PAL peaked 6h post-microbial fermentation application during an 8-h sampling period. A transcriptomic assessment using GeneChip microarray of the hour 6 samples revealed differential expression of 565 genes when MFA was applied to healthy trees and 909 genes when applied infected citrus trees when compared to their respective controls. There were 403 uniquely differentially expressed genes in response to MFA following an intersectional analysis of both healthy and infected citrus trees. The transcriptomic analysis revealed that several genes associated with plant development, growth, and defense were upregulated in response to MFA, including multiple PR genes, lignin formation genes, ROS-related genes, hormone synthases, and hormone regulators. This study provides further evidence that MFA may play an important role as a plant elicitor in an integrated pest management strategy in citrus and other agronomically important crops.

Determining leaf nutrient concentrations in citrus trees using UAV imagery and machine learning

Nutrient assessment of plants, a key aspect of agricultural crop management and varietal development programs, traditionally is time demanding and labor-intensive. This study proposes a novel methodology to determine leaf nutrient concentrations of citrus trees by using unmanned aerial vehicle (UAV) multispectral imagery and artificial intelligence (AI). The study was conducted in four different citrus field trials, located in Highlands County and in Polk County, Florida, USA. In each location, trials contained either ‘Hamlin’ or ‘Valencia’ sweet orange scion grafted on more than 30 different rootstocks. Leaves were collected and analyzed in the laboratory to determine macro- and micronutrient concentration using traditional chemical methods. Spectral data from tree canopies were obtained in five different bands (red, green, blue, red edge and near-infrared wavelengths) using a UAV equipped with a multispectral camera. The estimation model was developed using a gradient boosting regression tree and evaluated using several metrics including mean absolute percentage error (MAPE), root mean square error, MAPE-coefficient of variance (CV) ratio and difference plot. This novel model determined macronutrients (nitrogen, phosphorus, potassium, magnesium, calcium and sulfur) with high precision (less than 9% and 17% average error for the ‘Hamlin’ and ‘Valencia’ trials, respectively) and micro-nutrients with moderate precision (less than 16% and 30% average error for ‘Hamlin’ and ‘Valencia’ trials, respectively). Overall, this UAV- and AI-based methodology was efficient to determine nutrient concentrations and generate nutrient maps in commercial citrus orchards and could be applied to other crop species.

Effect of Gypsum and Etepon on Crop Yield Siamese Orange (Citrus Nobilis Var. Microcarpa L.)

This study aims to determine the effect of Gypsum and Etepon on the yield of Siamese orange (Citrus nobilis Var Microcarpa. L) conducted in Belancan Village, Kintamani District, Bangli Regency from December 2020 to July 2021. This study used a randomized block design (RAK) with 2 factors arranged in a factorial manner. The first factor that was tried was the dose of gypsum fertilizer (G) which consisted of 4 levels, namely: G0 (0 g/tree), G1 (250 g/tree), G2 (500 g/tree) and G3 (750 g/tree. While the second factor is the concentration of etepon (E) which consists of 3 levels, namely: E0 (0 ml/l water/tree), E1 (0.75 ml//l water/tree) and E2 (1.5 ml/l water)/tree). Thus, there were 12 combination treatments, each of which was repeated 3 times so that 36 citrus trees were needed. The results showed that the interaction between the dose of gypsum and the concentration of etepon had no significant effect on all observed variables. The highest harvested fruit weight per tree was obtained at a dose of gypsum 750 g/tree which was 6.32 kg or an increase of 70.35% when compared to treatment without gypsum which was only 3.71 kg. The highest harvested fruit weight per tree was obtained in the etepon treatment with a concentration of 1.5 ml/l/tree, which was 6.54 kg, an increase of 51.38% compared to the treatment without etepon, which was only 4.32 kg. Keywords: dose, etepon, gypsum, Siamese orange, yield

Individual Protective Covers (IPCs) for Young Tree Protection from the HLB Vector, the Asian Citrus Psyllid

Psyllid exclusion is the most effective strategy to keep citrus trees free from HLB. Individual protective covers (IPCs) are a novel strategy based on psyllid exclusion of individual trees using a protective mesh bag. This new 3-page publication summarizes the knowledge we have accrued from our 3-year-long field studies using the IPC system and provides recommendations that can help with effective use of this technology. By F. Alferez, U. Albrecht, S. Gaire, O. Batuman, J. Qureshi, and M. Zekri.https://edis.ifas.ufl.edu/hs1425

Exotic and Emergent Citrus Viruses Relevant to the Mediterranean Region

Citrus production in the Mediterranean area is of considerable importance, in both cultural and economic terms, and the viability of the industry greatly depends on proper phytosanitary management. In this review, we focus on exotic and emerging dangerous citrus viruses that have still not been reported in the countries of the Mediterranean area, that are not yet regulated or that are restricted to certain small areas. We also discuss the contribution that old and new technologies may offer for valuable surveys aimed at promoting the adoption and sharing of better control measures and the production of pathogen-tested citrus trees and rootstocks.