At different stages throughout their life cycle, plants often encounter several pathogenic microbes that challenge plant growth and development. The sophisticated innate plant immune system prevents the growth of harmful microbes via two interconnected defense strategies based on pathogen perception. These strategies involve microbeassociated molecular pattern-triggered immunity and microbial effector-triggered immunity. Both these immune responses induce several defense mechanisms for restricting pathogen attack to protect against pathogens and terminate their growth. Plants often develop immune memory after an exposure to pathogens, leading to systemic acquired resistance. Unlike that with harmful microbes, plants make friendly interactions with beneficial microbes for boosting their plant immune system. A spike in recent publications has further improved our understanding of the immune responses in plants as triggered by interactions with microbes. The present study reviews our current understanding of how plant-microbe interactions can activate the sophisticated plant immune system at the molecular level. We further discuss how plant-microbe interaction boost the immune system of plants by demonstrating the examples of Mycorrhizal and Rhizobial association and how these plant-microbe interactions can be exploited to engineer disease resistance and crop improvement.

Fungal diseases are considered a major threat to plant growth and productivity. However, some beneficial fungi growing in the same environment protect plants from various pathogens, either by secreting antifungal metabolites or by stimulating the host immune defense mechanism. Date palms are susceptible to several fungal pathogens. Nevertheless, information on the pathogenic fungal distribution in date palm fields across different seasons is limited, especially that from Qatar. Therefore, the current study’s aim was to evaluate the pathogenic and beneficial fungal diversity and distribution, including the endophytic fungi from the date palm tissues and root-associated soil fungi, during different seasons, for the identification of indigenous biocontrol agents. Our results showed that the highest number of fungal species was isolated in fall and spring, and pathogenic fungi were isolated mainly in spring. This is the first report that in Qatar, Neodeightonia phoenicum and Thielaviopsis punctulata cause date palm root rot disease, Fusarium brachygibbosum and Fusarium equiseti cause date palm wilting, and N. phoenicum causes diplodia disease in date palm offshoots. The combinations of the fungi that did not frequently occur together in date palm rhizosphere soil were investigated to identify indigenous biocontrol agents. Based on the results, we determined that Trichoderma harzianum and Trichoderma longibrachiatum are effective antagonistic fungi against T. punctulata, N. phoenicum, F. brachygibbosum, and Fusarium solani, qualifying them as potential biocontrol agents. Antagonistic activity of endophytic fungi against the pathogens was tested; except for Ulocladium chartarum, no endophytic fungi showed antagonistic activity against the tested pathogens. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Ceratocystis radicicola (anamorph: Thielaviopsis paradoxa) was reported as an economically important pathogen causing serious diseases on date palm such as rhizosis (2) and black scorch (3) or as an associated pathogen with diseased date palm (1). In this study, we report for the first time that C. radicicola also causes black scorch disease in Qatar. In April to May 2013, we conducted a disease survey in 11 farms located in northern and southern Qatar where three infected farms had an average of 10% disease incidence. Infected trees manifested different disease symptoms such as black scorch of leaves, inflorescence blight, and heart and bud rot. Infected tissues were surface sterilized with 1.0% NaOCl for 60 s, rinsed with distilled water, blotted dry, and then plated on potato dextrose agar (PDA) supplemented with 50 mg/liter Rose Bengal. Single fungal colonies were picked from hyphal tips and grown on PDA for 7 days at 25°C for further examination of the mycological characteristics. Colonies of five C. radicicola isolates on PDA developed aerial mycelium with a light gray color in culture plate, which later changed to black. Both light and scanning electron microscopy were employed to delineate species by spore morphology. Colonies produced ovate aleuroconidia (14 to 17 × 9 to 12 μm) and cylindrical phialoconidia (7 to 9 × 3 to 4 μm) characteristic features of C. radicicola. Phialoconidia (endoconidia) were hyaline to brown in chains produced from endoconidiophore, clamydospores (aleuroconidia), which were single with smooth or slightly rough wall. Additionally, C. radicicola produced single alueroconidia from conidiophores. Amplification of ITS rDNA region from fungal genomic DNA of five isolates, using universal primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-CCTCCGCTTATTGATATGC-3′) confirmed the isolated fungus as C. radicicola with no intra-specific variation among the fungal isolates. The length of ITS-rDNA sequence was 534 bp (KJ410228) and had 99 and 93% sequence identity with ITS-rDNA region from C. radicicola (HQ443203) and C. paradoxa (HC415073.1), respectively. A pathogenicity test was conducted using 3-year-old trees from three cultivars (Khalas, Khneezi, and Barhi) growing in sandy loam soil under greenhouse conditions (25 to 29°C and 12/12-h light/dark). Six trees from each cultivar were used for pathogenicity test, where three were inoculated and three other mock-inoculated. Eight millimeter diameter mycelial plugs were obtained from a C. radicicola culture on PDA medium and used to inoculate rachis region and basal petioles of date palm leaves with a 9-mm wound created with a cork borer. Control plants were mock-inoculated with PDA plugs. The inoculated area was covered with wet cotton to prevent dryness and the whole plant was covered for 72 h. Four days post infection (dpi), a rusty black infection appeared on the plants. Fifteen dpi, the whole leaf of inoculated stem showed typical symptoms, from which the fungus was re-isolated and colonies were maintained in PDA for morphological characterization, which were confirmed as C. radicicola. All trees from three cultivars showed symptoms with a variable severity from cultivar to another. To our knowledge, this is the first report of black scorch disease caused by T. punctulata in Qatar. This report highlighted the incidence of black scorch disease in Qatar demanding future research study to control the pathogen. References: (1) Y. M. Al-Raisi et al. New Dis. Rep. 23:23, 2011. (2) C. Linde and W. A. Smit. Plant Dis. 83:880, 1999. (3) P. Suleman et al. Plant Dis. 85:80, 2001.

Date palm is an important subsistence crop in arid regions due to its ability to grow under adverse environmental conditions such as high temperature, salinity and drought. Nevertheless, ideal conditions for its growth and production are also favourable to fungal diseases such as black scorch disease caused by Ceratocystis radicicola. The aim of this study was to develop a method of biological control through the isolation, identification and examination of the effectiveness of bioagents in controlling black scorch disease. Twenty-five isolates of Trichoderma spp. were isolated from the rhizosphere of healthy date palm trees and morphological, microscopic and molecular approaches confirmed the identity of 11 isolates as Trichoderma harzianum species complex (THSC). In vivo study, application of both spore suspension and culture filtrates of T. harzianum decreased the size of necroses caused by C. radicicola. Additionally, scanning electron microscopy (SEM) showed lysis of the hyphal pathogen and phialoconidia along with scattered aleurioconidia. Results from the volatile metabolic assay and SEM suggested potential roles of cell wall degradation enzymes and volatile substances produced by T. harzianum as two collective mechanisms leading to degrade the cell wall of the pathogen and inhibit fungal growth. Altogether, results from our study demonstrated the efficacy and utility of using bioagents to control black scorch disease which could improve date palm yield.

Introduction: Pathogen attacks impose natural selection on plants to evolve complex arrays of defensive strategies. Among the diverse defensive mechanisms evolved by plants to withstand pathogen attack, the ability to synthesize an arsenal of low-molecular weight volatile and non-volatile chemicals including phenolics helps them to prepare a robust defense response against pathogen entry. Systemic induction and accumulation of low molecular weight phenolics is observed in response to various diseases and thus are studied as markers for resistance to pathogens. Phenolics that exhibit anti-oxidant activity exert their inhibitory effects on pathogen colonization via protein precipitation and iron depletion.Phytochemical analysis have been proved that date palm is rich source of phenol. Very little information is available on the inherent Date palm phenolic content that has been involved as resistance factors. All the studies are focused on phenolic content from date palm fruit and its property. Here we focusing on comparative analysis of phenolics from different cultivars leaf and how it affect the different pathogenic fungi. Material and Methods: We conducted a genome mining analysis of date palm whole genome available in the NCBI site, to detect the presents of enzyme involved in the secondary metabolite pathway. Analyzed the presents of receptor protein specific for the recognition of fungal pathogen.Five date palm pathogens were isolated from the diseased date palm and surrounding soil from the date palm field located in northern region of Qatar. Leaf, shoot and root samples collected from the diseased date palm and rhizosphere soil collected from near the diseased date palm. Samples were stored at 40?C in aseptic condition until further use. Sterilized plant samples were plated in the potato dextrose agar (PDA) for the fungal isolation and the soil were plated on molten agar for fungal isolation. The plates were incubated at 250?C until single colony appeared. The isolated fungi were examined under microscope. Based on the microscopic and physical characteristics fungi were identified.The pathogenicity were determined with detached leaf inoculation analysis and in vivo pathogenicity analysis with three date palm cultivar varieties. Detached leaf inoculation analysis performed in laboratory condition and the in vivo pathogenicity conducted in green house with controlled growth condition. The date palm varieties used in this current study are Khalas, Khneezi and Barhi. All the four pathogens, Fusarium solani, Fusarium oxysporum, Rhizectonia solani Fusarium sp and Ceratocystis radicicola were used for pathogenicity analysis.Total phenolic were extracted from three date palm culvars through water extraction procedure. Extraction performed with different temperature range. Comparative analysis of antifungal property of total phenolics from different date palm cultivars such as Khalas, Khneezi and Barhi was carried out after optimizing extraction temperature. Antifungal activity is determined with disc diffusion analysis. 100 μl of extract impregnated filter disc (10 mm in diameter) placed on the PDA plate followed by fungal disc placed on the disc. Plates were incubated at 250?C and the fungal growth monitored. Experiment repeated in triplicate along with control. Results and conclusion: The genome mining analysis of date palm result revealed 45 enzyme sequences from shikimate pathway, which is a support for the active synthesis of phenolic content in date palm. Plant phenolics synthesize via shikimate-phenylpropanoid-flavonoid pathways and include phenolic acids, flavanoids, tannins and less common stilbenes and lignins. Presents of chitin elicitor receptor kinase in date palm indicate the phytopathogenic fungal detection ability of date palm.From the isolated fungi, the date palm pathogenic fungi were screened and subcultured. Five pathogenic fungi were isolated, Fusarium solani, Fusarium oxysporum, Rhizectonia solani, Fusarium sp and Ceratocystis radicicola. Pathogenicity of all the five isolated fungi were confirmed by analyzing necrosis caused on the date palm leaf (Fig. 1). The frequency of necrotic lesion and disease susceptibility found more in Khneezi than Khalas and Barhi.Water extraction procedure conducted at 400?C for 24 hrs were accepted as standardized phenolic extract for antifungal activity. Growths of the fungi were measured after 3 day and 5 days of incubation to determine the antifungal activity of phenolic extract (table 1). Phenolic extract from the Khalas showed more antagonistic activity against Rhizectonia solani whereas phenolic extract from Barhi showed more inhibitory activity against Fusarium solani, Fusarium oxysporum and Ceratocystis radicicola. In all the experiment Khneezi showed week inhibitory activity this supports our previous susceptibility study (not published) in that Khneezi showed more susceptible to C.radicicola. This result is an evident for the disease resistant activity of date palm phenolics.