Necrotrophic pathogenic bacteria, fungi and oomycetes are widely distributed and are responsible for significant crop losses. Host plants deploy different defense mechanisms and appropriate immune responses to defend them against these pathogens. Regardless of the pathogen's lifestyle, infection activates plant immune responses either through Pathogen/Microbe Associated Molecular Pattern (P/MAMP) or through Effector Triggered Immunity (ETI). However, as R-genes are not usually associated with resistance to necrotrophs, resistance is largely dependent on the balanced interplay between crucial phytohormones in complex signaling pathways involving jasmonic acid (JA), ethylene, salicylic acid (SA) and abscisic acid (ABA). An increase in salicylic acid levels enhances susceptibility to necrotrophic pathogens but promotes resistance to hemibiotrophs, whereas a deficiency in SA or SA signaling has either no significant impact or affects resistance only at the primary infection site. The same fashion is observed for JA signaling system that appears to elicit resistance against diseases caused by necrotrophic pathogens and can trigger systemic immunity conferring resistance against them. On the other hand, ABA can play a positive or negative role in plant defense responses to necrotrophs as ABA-mediated defense responses are dependent on specific plant-pathogen interactions. Understanding plant immune response against necrotrophic pathogens may lead to the development of resistant or tolerant crop cultivars.

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Brown rot or bacterial wilt of potato caused by Ralstonia solanacearum, is an economically important disease. Potato, cv. Nicola, was found to be relatively highly resistant to the infection with R. solanacearum and showed 15.12% wilt disease index, meantime, cv. Kara showed intermediate resistance with 37.40% disease index while, cv. Spunta was susceptible and showed 80.33% disease index. The role of defense-related enzymes in imparting resistance in potato against R. solanacearum was investigated by quantifying enzymes activity and gene expression of three defenserelated enzymes, peroxidase, polyphenol oxidase and catalase. Peroxidase showed maximum activity 0.

During 2013-2014 growing seasons, forty three isolates of Pestalotiopsis spp. were recovered from guava leaves and fruits showed scab symptoms from different regions in EL-Beheira governorate. Five Pestalotiopsis species were recognized according to the morphological characteristics of fungal colony (Colony color, Size and number of acervulii) and conidia (length, width, and color of median cells, length and the number of apical and basal appendages); they were P. psidii, P. microspora, P. clavispora, P. neglecta and Pestalotiosis spp. All the isolates recovered were pathogenic to the cv. Balady of guava fruits. However, P.psidii isolates were the most highly pathogenic followed by P. neglecta, P. clavispora, P. microspora and Pestalotiopsis spp, respectively. RAPD-PCR analysis using five random oligonucleotide primers revealed DNA fingerprints and considerable variations were revealed with primers tested.  Bar primer showed a common band for all Pestalotiopsis isolates and species at 500bp, while BAQ, 18 and A9B4 exhibited banding pattern similar for all isolates of the same species which were different from that of the other species. Scab disease control of infected fruits by chitosan as a natural product was tested. The in vitro 2.5% chitosan application significantly inhibited the growth of Pestalotiopsis spp. tested by 86.53% on agar plates. The in vivo tests on fruits, the chitosan treatment to artificially infected fruits reduced the development of symptoms at the different chitosan concentrations, i.e., 1.5%, 2% and 2.5%. The 2.5% chitosan was the most effective concentration for scab disease control in guava fruits. It is the first report of identification five different Pestalotiopsis  species affecting guava fruits and leaves in EL-Beheira Governorate, Egypt. Also, the study supported the view that chitosan offers a safe alternative to synthetic fungicides in postharvest scabby control and could be considered as a potential agrochemical of low environment impact.

wenty isolates of Streptomyces scabies were isolated from scab lesions on potato tubers collected from three different regions in Behera Governorate during the 2009-2010 growing season. The isolates of S. scabies recovered were totally monomorphic for the morphological and the biochemical characteristics investigated. All isolates were non motile, gram positive, exhibited grey colonies, spiral spore chain and were melanin producers. Meantime the isolates showed positive reaction for catalase activity, starch hydrolysis, casein hydrolysis and gelatine liquefaction. Also, all isolates were tolerant and exhibited growth at NaCl 5, 6 & 7% and at 20, 25 & 30°C at pH 7 & 9. None of the tested isolates were able to grow at pH 5. More variations, however, were revealed for the pathogenicity of twenty isolates. Five out of twenty investigated isolates were found to be highly virulent. The rest of tested isolates were moderately virulent. Spunta was the most tolerant potato cultivar, while cvs. Mondial and Hermis were more susceptible. The highly virulent S. scabies (isolate ST5) was a highly producer of Thaxtomin A, while the moderately virulent isolate (ST10) was poorly toxin producer (1.26 mg/ml medium). The optimal conditions for Thaxtomin A production were 28ºC, pH 8 and 1% cellobiose in medium. The amino acids, i.e. tryptophan, phenylalanine and tyrosine exhibited an in vitro inhibitory effect on the toxin production in the amended oatmeal bran broth medium with highest inhibitory effect was recorded for tryptophan.

Six common fungicides, Dithane M45, Kocide 2000, Ridomil Gold Plus, Score, Equation Pro and Kemazed were tested for controlling the draceana leaf spot fungi. All the tested fungicides significantly decreased the in vitro growth of the tested dracaena leaf spot fungi. Percentage of inhibition on colony diameter ranged between 49.64% with Dithane M45 to 82.18% with Score which was followed by Kemazed (69.15%). However, inhibition of spore germination was the highest (72.8%) by Dithane M45, while inhibition of germ tube reached 89.91% with Kemazed. Meanwhile, in the in vivo tests, treatment with Kemazed decreased disease incidence of leaf spots on potted plants to 16.67% compared to 100% for the untreated inoculated control. On the other hand, the bacterial and fungal biocontrol agents tested proved to be effective against the dracaena leaf spot fungi. The in vitro assays conducted showed that the bacterial biocontrol agents namely, Stenotrophomonas maltophilia, Pseudomonas ultimum, P. fluorescens, P. putida, P. aeruginosa, Bacillus subtilis, B. megaterium, significantly decreased colony growth diameter (76.84-45.69%) of dracaena leaf spot fungi as well as spore germination (48.80-23.20%) and length of germ tube (88.77-65.65%) of the germinated spores compared to untreated control. Treatment with S. maltophilia showed the most consistent highest inhibition effect, followed by P. ultimum, B. subtilis, and B. megaterium, respectively. The in vivo tests of the most effective bacterial bioagents supported the in vitro results. Treatment with S. maltophilia showed the highest effect as it decreased disease incidence and disease index to 29.33% and 7.6%, respectively in comparison with 100% and 83.6% for the untreated inoculated control in the potted dracaena plants (cv. Bicolor). Meanwhile, the in vitro tests of the three Trichoderma spp., i.e. T. harzianum, T. hamatum and T. album showed significant inhibition effect on colony growth diameter of the tested dracaena leaf spot fungi in which T. harzianum showed the highest inhibition effect (75.02%), while T. album was most effective to inhibit spore germination (48%) and germ tube (90.21%) of the germinated spores. The in vivo tests of the fungal biocontrol agents supported the in vitro results. T. album (Bio-Zeid) showed the highest effect and decreased disease incidence and disease index on potted plants to 19.99% and 4.39%, respectively compared with 100% and 92.8% for the untreated inoculated control.

BackgroundPlant-parasitic nematodes are one of the major constraints to soybean production around the world. Plant-parasitic nematodes cause an estimated $78 billion in annual crop losses worldwide, with a 10–15% crop yield loss on average. Consequently, finding and applying sustainable methods to control diseases associated with soybean is currently in serious need.MethodsIn this study, we isolated, purified, characterized, and identified a novel cyanobacterial strain Oscillatoria sp. (blue-green alga). Based on its microscopic examination and 16S rRNA gene sequence, the aqueous and methanolic extracts of Oscillatoria were used to test their nematicidal activity against Meloidogyne incognita hatchability of eggs after 72 h of exposure time and juvenile mortality percentage in vitro after 24, 48, and 72 h of exposure time and reduction percentage of galls, eggmass, female number/root, and juveniles/250 soil. Also, the efficacy of the extract on improving the plant growth parameter and chlorophyll content under greenhouse conditions on soybean plant cv. Giza 111 was tested. Finally, the expression of PR-1, PR-2, PR-5, and PR15 (encoding enzymes) genes contributing to plant defense in the case of M. incognita invasion was studied and treated with Oscillatoria extract.ResultsThe aqueous and methanolic extracts of Oscillatoria sp. had nematicidal activity against M. incognita. The percentage of mortality and egg hatching of M. incognita were significantly increased with the increase of time exposure to Oscillatoria extract 96.7, 97, and 98 larvae mortality % with S concentration after 24, 48, and 72 h of exposure time. The aqueous extract significantly increased the percentage of Root-Knot nematodes (RKN) of egg hatching, compared with Oxamyl and methanol extract at 96.7 and 97% after 72 h and 1 week, respectively. With the same concentration in the laboratory experiment. Furthermore, water extracts significantly reduced the number of galls in soybean root, egg masses, and female/root by 84.1, 87.5, and 92.2%, respectively, as well as the percentage of J2s/250 g soil by 93.7%. Root, shoot lengths, dry weight, number of pods/plant, and chlorophyll content of soybean treated with Oscillatoria water extract were significantly higher than the control increasing by 70.3, 94.1, 95.5, and 2.02%, respectively. The plant defense system's gene expression was tracked using four important pathogenesis-related genes, PR-1, PR-2, PR-5, and PR15, which encode enzymes involved in plant defense.ConclusionsOscillatoria extract is a potential nematicide against root-knot nematode invasion in soybean.

It has been confirmed the association of oxalic acid with pathogenicity of Sclerotinia sclerotiorum isolates in the present study. The highly virulent SS 34 isolate of Sclerotinia sclerotiorum was found to be highly oxalic acid producer while the weakly virulent SS 2 isolate was poorly oxalic acid producer. The moderately virulent isolates, however, showed intermediate potential for oxalic acid production. These results were confirmed and explained at the molecular level analysis of Sclerotinia sclerotiorum isolates. The protein banding pattern based on the SDS-Page at 53-12 kDa showed ten bands for the highly virulent SS 34 isolate while only one protein band was recognized for the weakly virulent SS 2 isolate at this molecular weight. The moderately isolates however, showed intermediate number of bands of 3-6 bands at this protein range. Meantime, the highly virulent SS34 isolate showed unique protein bands at both53 kDa and 42 kDa, while, not any of the other analyzed isolates exhibited bands at this protein molecular weight. The only protein band recognized for the weakly virulent SS 2 isolate was at 24 kDa where all isolates showed protein bands at this molecular weight. Five primers were used to study the genetic variability between the tested isolates and the primer R3 showed enough potential to differentiate between the highly virulent and the weakly virulent isolates as nine bands were recognized with the highly virulent isolate while only four bands were existed for the weakly virulent one. The moderately virulent isolates, however, showed intermediate number of bands of 5-8 bands. Meantime, on the basis of the phylogenetic analysis and the constructed dendrogram based on the SDS-Page of the isolates protein and that based on the random amplified polymorphic DNA (RAPD), It was clear that the highly virulent Sclerotinia sclerotiorum SS 34 isolate and the weakly virulent SS 2 isolate were located in two distinct distant clusters. The moderately virulent S. sclerotiorum isolates, however, were located in intermediate sub-clusters.