Solanaceae plants have strong allelopathic potential, and therefore the action is confirmed through: a) bioassays with liquid or various solvent extracts and residues, b) fractionation, identification, and quantification of causative allelochemicals. Most assessments of allelopathy involve bioassays of plant or soil extracts, leachates, fractions, and residues which support seed germination and seedling growth in laboratory and greenhouse experiments. Plant growth is also stimulated below the allelopathic threshold, however severe growth reductions may be observed above the threshold concentration depending on the sensitivity of the receiving species. Generally, seedling growth is more sensitive than germination, particularly root growth. Some approaches showed that field soil collected beneath donor plants significantly reduced or somewhat promoted the growth of the recipients plants. Petri dish bioassays with aqueous extracts of different parts of donor plants showed considerable phytotoxic activities in a concentration-dependent manner with leaf aqueous extracts being most dominant. Delayed seed germination and slow root growth attributable to the extracts may be baffled with diffusion effects on the rate of imbibition, delayed initiation of germination, and particularly cell elongation; the main factor that is responsible for affecting root growth before and after the tip penetrates the testa. Light and electron microscopy extract analysis at the ultrastructural level are correctly investigated. Several Solanaceae plants have allelopathic potential, and therefore the activities, kinds and quantity of allelopathic compounds differ depending on the plant species. The incorporation of allelopathic substances into agricultural management might scale back the development of pesticides and reduce environmental deterioration.
Protein digestion in insects relies on several groups of proteases, among which trypsin plays a prominent role. In the current study, larvae of Pieris brassicae L. were fed radish leaves treated with 1 mM concentrations of three specific inhibitors of trypsin: AEBSF.HCl [4-(2- -aminoethyl)-benzenesulfonyl fluoride, monohydrochloride], TLCK (N-a-tosyl-l-lysine chloromethyl ketone) and SBTI (Soybean Trypsin Inhibitor) to find their potential effects on gene expression of trypsin. Initially, RT-PCR analysis revealed a gene of 748 bp responsible for synthesizing the digestive trypsin in P. brassicae larvae. Also, qRT-PCR data indicated a statistically greater expression of trypsin gene in the larvae fed 1 mM concentrations of AEBSF.HCl, TLCK and SBTI than the control. Results of the current study indicated that synthetic inhibitors can not only negatively affect the gene expression of P. brassicae trypsin, but also the insect can activate a compensatory mechanism against interruption of protein digestion by inducing more expression of the gene and producing more trypsin into the midgut lumen.
Control failure of pests and selectivity of insecticides to beneficial arthropods are key data for the implementation of Integrated Pest Management (IPM) programs. Therefore, the aim of this study was to assess the control failure likelihood of Plutella xylostella and the physiological selectivity active ingredients to parasitoid Oomyzus sokolowskii (Hymenoptera: Eulophidae) and to predators Polybia scutellaris (Hymenoptera: Vespidae) and Lasiochilus sp. (Hemiptera: Anthocoridae). In bioassays, P. xylostella larvae and O. sokolowskii, P. scutellaris and Lasiochilus sp. adults were used. Concentration-mortality curves of six insecticides for P. xylostella were established. These curves were used to estimate the mortality of P. xylostella at the recommended concentration, in order to check a control failure of insecticides to this pest. Furthermore, the lethal concentration for 90% of populations (LC90) and the half of LC90 were used in bioassays with the natural enemies to determine the selectivity of these insects to insecticides. All tested insecticides showed control failure to P. xylostella, indicated by high LC90 and low estimated mortalities (less than 80%). The cartap insecticide was selective in half of LC90 to Lasiochilus sp. and moderately selective in LC90 and the half of LC90, to Lasiochilus sp. and P. scutellaris, respectively. Deltamethrin was moderately selective in the half of LC90 to predator Lasiochilus sp. Cartap, carbaryl, and deltamethrin reduced the mortality of Lasiochilus sp. in the half LC90. The results also showed that the insecticides methamidophos, carbaryl, parathion methyl and permethrin were not selective to any of the tested natural enemies. The role of insecticides in IPM systems of Brassica crops is discussed based on their control failures to P. xylostella and selectivity to their natural enemies.
The present report describes the new occurrence of Tomato mosaic virus (ToMV) in cabbage, bean and Malva neglecta plants in Iran. In this study, sequence analyses of a partial RNA dependent RNA polymerases (RdRp) and complete movement protein (MP) and the coat protein (CP) nucleotide sequences of three new ToMV isolates collected from major crop fields in Iran revealed low genetic variation of RdRp gene compared to the CP and MP genes. The different topologies of the phylogenetic trees constructed, using available open reading frame (ORF1), ORF2 and ORF3 sequences from ToMV isolates, indicated different evolutionary constraints in these genomic regions. Statistical analysis also revealed that with the exception of CP other tested ToMV genes were under negative selection and the RdRp gene was under the strongest constraints. According to the phylogenetic tree it can be inferred from the nucleotide sequences of the complete CP and MP genes, that isolates from Iran and Egypt formed separate groups, irrespective of host origin. However, isolates clustered into groups with correlation to geographic origin but not the host. Analysis of the Ks *, Z* and Snn values also indicated genetic differentiation between ToMV populations. The Tajima’s D, Fu and Li’s statistical values were significantly negative for the RdRp gene of the Asian population which suggests the sudden expansion of ToMV in Asia. Taken together, the results indicate that negative selection and genetic drift were important evolutionary factors driving the genetic diversification of ToMV.
Potato virus Y (PVY) is one of the most destructive viruses infecting potato in Egypt and worldwide. Recent research has shown that a necrotic PVY-NTN strain is infecting potato in Upper Egypt. Chemical control is not effective to control this viral pathogen. An alternative to control PVY infecting potato is using a mild PVY strain to elicit systemic cross protection in potato plants against infection with a severe necrotic strain of PVY. Results of this study showed that a PVY necrotic strain produced a significant lesser number of local lesions on diagnostic plants (Robinia pseudoacacia L.) when these plants were treated first with a mild PVY strain. Data obtained from greenhouse and field experiments indicated that treatment of potato plants (variety Burna) with a mild PVY strain significantly protected potato from infection with a severe necrotic PVY strain, and resulted in a significant increase in tuber yield compared with infected plants without prior treatment with a mild PVY strain. The highest increase in potato tuber yield was obtained when potato plants were inoculated with a mild PVY strain 3 days before challenging with the severe necrotic PVY strain. This study proved that using a mild strain of PVY can significantly protect potato plants from infection with a severe strain of this virus under both greenhouse and field conditions and can present a potential method to reduce losses due to infection of this virus in Assiut governorate and Upper Egypt.
The aim of the present work was to evaluate the selectivity of nicosulfuron, alone and in combinations, applied in post-emergence (V4) of glyphosate and sulfonylurea tolerant (RR/STS) soybean. The experiments were conducted in 2015/16 and 2016/17, in Piracicaba – state of São Paulo (SP). In 2016/17, the experiment was also conducted in Palotina – state of Paraná (PR). The experiment was a randomized block design, with four repetitions and 16 treatments, with combinations of nicosulfuron, glyphosate, chlorimuron, sulfometuron and cloransulam, applied alone or in tank mixture. Crop injury and variables related to agronomic performance were evaluated. Data were subjected to analysis of variance and treatment means were compared by the Tukey test. The results obtained are significant in the positioning of herbicides in RR/STS soybean, since in the five experiments, all the treatments were selective, except for glyphosate + sulfometuron which reduced the yield of a cultivar (CD 2630 RR/STS) in the 2015/16 season.
In August 2016, tomato plants grown during a hot, wet summer with heavy soil flooding, displaying symptoms of wilting, dead plant, root rot with crown and stem rot, at Beni Suef and Fayoum governorates were examined. A number of 16 fungal isolates were isolated from tomato plants displaying the above symptoms. These isolates were classified as belonging to six species, namely: Alternaria solani, Chaetomium globosum, Fusarium solani, Fusarium oxysporum, Pythium spp. and Rhizoctonia solani. Isolates of Pythium spp. were prevalent and were found to be more pathogenic than the other fungal isolates. This species causes damping-off, root rot, sudden death, stem rot and fruit rot. The pathogen was identified as Pythium aphanidermatum based on morphological, cultural, and molecular characteristics. Biogenic silver nanoparticles (AgNPs) were produced using the F. oxysporum strain and characterized by transmission electron microscopy (TEM). The size of these spherical particles ranged from 10 to 30 nm. In vitro, biogenic AgNPs showed antifungal activity against P. aphanidermatum. In greenhouse and field experiments, AgNPs treatment significantly reduced the incidence of dead tomato plants due to root rot caused by P. aphanidermatum compared to the control. All of the investigated treatments were effective and the treatment of root dipping plus soil drenching was the most effective. To the best of our knowledge, this study describes P. aphanidermatum on tomato in Egypt for the first time. Also, biogenic AgNPs could be used for controlling root rot disease caused by this pathogen.