Journal of Automated Reasoning | 2019
Efficacy of Commercial Symbiotic Bio-fertilizer Consortium For Mitigating the Olive Quick Decline Syndrome (oqds)
Abstract
The inoculation of soil with a bio-fertilizer (BF), with arbuscular mycorrhiza fungi, characterizes a Symbiotic (S) agriculture mode, aimed at promoting the yield and health of crops through modifications in the rhizosphere as well as in the plant phenotype. The main objective of this study was to reduce the incidence of Olive Quick Decline Syndrome (OQDS, involving Xylella fastidiosa subsp. pauca) that afflicts the olive groves in Apulia (Italy). Non-inoculated control (C) plants were compared with Symbiotic (S) plants inoculated with 20 kg ha of Micosat F ®, through a 15 cm deep scarification, in the groves of seven farms covering an area of 27 ha. In addition to a visual observation of 484 plants, to obtain a gradation of the disease severity, some objective rapid type methods were utilized to survey the plants and soil , namely leaf pH, NIR tomoscopy of the leaves, hay-litter-bag probes coupled with NIR spectroscopy and the prediction of soil induced respiration. The fingerprinting of the S and C types of leaves and litter-bags was ascertained by means of the use of a random forest algorithm in the classification matrices. The results on the symptoms appeared variable: they were significantly mitigated in two groves out of six, but they were aggravated in one. All the rapid measurements became essentials in a “holistic” model which was able to explain over 95% of the average mitigation / null / aggravation response to BF inoculation. The holistic model gathers differential and compositional analyses of the leaf (pH, crude protein, water) and of the soil (respiration), but depends mainly on the fingerprinting of the C and S leaves and litter-bags. Two keys were identified for a successful inoculation: a high degree of variability of the soil conditions permitting hospitality for the BF with enhancement of the microbial activity in the S soil (lowering the fingerprint of the control litter-bags) and homogeneity of the leaves (with increases in the fingerprint of the S leaves treated with BF). In short, the inoculation of diseased plants with one BF consortium is far from being the ultimate remedy to mitigate OQDS in all situations. Further studies are needed, at a field level, to clarify the soil hosting capacity and to define the mycorrhizal and / or endophytic * plant * pathogen interactions, even using rapid methods. DOI: 10.14302/issn.2639-3166.jar-19-2780 Freely Available Online www.openaccesspub.org | JAR CC-license DOI : 10.14302/issn.2639-3166.jar-19-2780 Vol-2 Issue 1 Pg. no. 2 Introduction Over the last decade, a plant desiccation epidemic, called CoDiRO (Olive Quick Decline Syndrome, OQDS), has developed in the olive groves of south Puglia (Italy). One of the main biological factors of this epidemic outbreak has been identified as Xylella fastidiosa subsp. pauca ST53 , a disease that is universally known for having damaged orchards and plants in the Americas . The death of the olive plant follows a process that involves leaf scorching, followed by the death of secondary and primary branches , caused by a prolonged block in the sap flow in the xylem . Scortichini et al. , after a three-year survey, obtained promising results that suggest that an integrated management, which includes regular pruning and soil harrowing, with spring and summer spray treatments with Dentamet® to reduce the severity of X. fastidiosa, may assist in the control of OQDS disease. However, their study scope did not cover the subspecies pauca that is active in Puglia. Upon an attack by pathogens or insects, plants can enlist the help of protective microorganisms and increase their microbial activity to contrast pathogens . However, the delivery of a complex Bio-Fertilizer (BF), based on microbial consortia , can act by modifying the plant s physiology and lowering the in-vivo raw leaf pH, which is a concrete and easy endpoint to measure. Apart from accelerating the metabolism, BF acts on the induction of the genes of resistance present in plants, but which are not expressed without prior contact with pathogens. As a result of the inoculum, a consequent activation or suppression of otherwise silent genes is obtained, which recent studies on the genome of plants have identified as being closely related to contrast and alarm activities toward several phyto-pathologies. A demonstration of this was pertaing to the recovery of pears heavily affected by Erwinia amylovora fire blast . On the basis of the above considerations, the objectives of the present work were: i) to revitalize the root microbiome of the infected plants thus reactivating the symbiotic interactions between the root system of the olive tree and the Arbuscular Mycorrhizae Fungi network; ii) to strengthen the defense capabilities of the olive trees by increasing their resilience to the pathogen, through an activation of the latent gene pool; and iii) to evaluate simple and accessible techniques to measure the health status of the olive trees as well as the biological status of the soil. Experimental Procedure This study involved the use of a complex Bio-Fertilizer (BF), which has been defined as “symbiotic” because it contains arbuscular mycorrhizal fungi, spores and propagules, and other microbial species. The use of this BF also falls within the framework of precision agriculture, because the inoculum is distributed precisely in the proximity of the secondary roots of adult olive trees affected by OQDS. After three months, treated Symbiotic (S) and non-inoculated Control (C) plants logged in seven farms were compared to establish their disease severity, by means of a visual appraisal coupled with rapid new tests, namely: litter-bags (differential and respiratory), foliar NIR scanning (differential and compositional) and foliar pH. A final holistic elaboration gathered all the available results from the three main information tools, concerning the plant-soil-BF interactions, in a model that Corresponding author: Giorgio Masoero, Accademia di Agricoltura di Torino, Via A. Doria 10, 10123, Torino, Italy. E-mail: [email protected] Running title: Mitigation of OQDS (CoDiRO) by means of a bio-fertilizer