The JA-CsMYC2.1-CsNOMT-Sakuranetin module contributes to differential anthracnose resistance in Camellia sinensis

Transcriptomic studies in resistant and susceptible tea cultivars have been performed to reveal the different defense molecular mechanisms of tea after E. onukii feeding. The molecular mechanism by which tea plants respond to small green leafhopper Empoasca onukii (Matsuda) damage is unclear. Using the resistant tea plant cultivar Juyan (JY) and the susceptible tea plant cultivar Enbiao (EB) as materials, this study performed RNA-seq on tea leaf samples collected at three time points (6h, 12h, 24h) during exposure of the plants to leafhopper to reveal the molecular mechanisms that are activated in susceptible and resistant tea plant cultivars in response to leafhopper damage. The numbers of DEGs in the susceptible tea cultivar during early (6h) and late (24h) stages of leafhopper induction were higher than those in the resistant cultivar at the same time points. The stress responses to leafhopper were most intense at 12h in both tea cultivars. Pathway enrichment analysis showed that most up-regulated DEGs and their related metabolic pathways were similar in the two tea cultivars. However, during the early stage of leafhopper induction (6h), jasmonic acid (JA)-related genes were significantly up-regulated in the resistant cultivar. The terpenoid biosynthetic pathway and the α-linolenic acid metabolic pathway were activated earlier in the resistant cultivar and remained activated until the late stage of leafhopper damage. Our results confirmed that after leafhopper damage, the resistant tea cultivar activated its defense responses earlier than the susceptible cultivar, and these defense responses were mainly related to terpenoid metabolism and JA biosynthetic pathway. The results provide important clues for further studies on resistance strategy of tea plants to pest.

BackgroundRice sheath blight, caused by Rhizoctonia solani Kühn (teleomorph: Thanatephorus cucumeris), is one of the most severe diseases in rice (Oryza sativa L.) worldwide. Studies on resistance genes and resistance mechanisms of rice sheath blight have mainly focused on indica rice. Rice sheath blight is a growing threat to rice production with the increasing planting area of japonica rice in Northeast China, and it is therefore essential to explore the mechanism of sheath blight resistance in this rice subspecies.ResultsIn this study, RNA-seq technology was used to analyse the gene expression changes of leaf sheath at 12, 24, 36, 48, and 72 h after inoculation of the resistant cultivar ‘Shennong 9819’ and susceptible cultivar ‘Koshihikari’ with R. solani. In the early stage of R. solani infection of rice leaf sheaths, the number of differentially expressed genes (DEGs) in the inoculated leaf sheaths of resistant and susceptible cultivars showed different regularity. After inoculation, the number of DEGs in the resistant cultivar fluctuated, while the number of DEGs in the susceptible cultivar increased first and then decreased. In addition, the number of DEGs in the susceptible cultivar was always higher than that in the resistant cultivar. After inoculation with R. solani, the overall transcriptome changes corresponding to multiple biological processes, molecular functions, and cell components were observed in both resistant and susceptible cultivars. These included metabolic process, stimulus response, biological regulation, catalytic activity, binding and membrane, and they were differentially regulated. The phenylalanine metabolic pathway; tropane, piperidine, and pyridine alkaloid biosynthesis pathways; and plant hormone signal transduction were significantly enriched in the early stage of inoculation of the resistant cultivar Shennong 9819, but not in the susceptible cultivar Koshihikari. This indicates that the response of the resistant cultivar Shennong 9819 to pathogen stress was faster than that of the susceptible cultivar. The expression of plant defense response marker PR1b gene, transcription factor OsWRKY30 and OsPAL1 and OsPAL6 genes that induce plant resistance were upregulated in the resistant cultivar. These data suggest that in the early stage of rice infection by R. solani, there is a pathogen-induced defence system in resistant rice cultivars, involving the expression of PR genes, key transcription factors, PAL genes, and the enrichment of defence-related pathways.ConclusionThe transcriptome data revealed the molecular and biochemical differences between resistant and susceptible cultivars of rice after inoculation with R. solani, indicating that resistant cultivars have an immune response mechanism in the early stage of pathogen infection. Disease resistance is related to the overexpression of PR genes, key transcriptome factors, and PAL genes, which are potential targets for crop improvement.

Ultrastructural and immunocytochemical investigation of pathogen development and host responses in resistant and susceptible wheat spikes infected by Fusarium culmorum

BackgroundWheat is the most important cereal. One of the environmental stresses is drought that harm the production of many cereals and every year due to low rainfall and frequent droughts, the need to produce plants resistant to this stress is felt. Therefore, identification and evaluation of the genes involved in the production of this resistance in plants are of great importance. By identifying these genes and changing their expression, it is possible to produce resistant plants that can tolerate dehydration and drought, with at least a qualitative and quantitative reduction in yield. ResultsBased on the meta-analysis results obtained in this study, in resistant cultivars ~ 4% (2394/61290) of the probe IDs decreased and ~ 4.5% (2670/61290) increased expression, furthermore in susceptible cultivars ~ 7% (4183/61290) of probe IDs decreased and ~ 6% (3591/61290) increased expression (P value ≤ 0.05). List of up- and downregulated genes was revealed, among the expressed genes of transcription factors Myb3, ethylene-responsive 5a, MIKC-type MADS-box WM24B, and salinity inducible ERF4 in resistant cultivars and transcription factors WRKY15, MADS-box TaAGL8, WRKY39, and Myb in susceptible cultivars, they showed a significant increase in expression, these transcription factors are of great importance in drought stress. Among them, ethylene responsive 5a in resistant cultivars by 3 times and Myb in susceptible cultivars by 2.6 times have shown the highest expression change. Using Cytoscape Hub software, the Phosphoenolpyruvate carboxylase (PEPC) and lyase isocitrate (TaSAG7) genes, which have significantly different expressions in resistant and susceptible wheat cultivars. PEPC and TaSAG7 genes were upregulated in resistant wheat cultivars as well as down regulated in susceptible cultivars. Also, the qPCR results of selected genes were consistent with the outcomes of the meta-analysis. ConclusionsAll microarray data were collected from the NCBI Gene Expression Omnibus site. Libraries with drought-tolerant and susceptible cultivars for wheat were considered under the stress and control conditions from whole leaf tissue. By meta-analysis combined the purposeful results of multiple experiments, and found list of genes expressed in reverse between the two cultivars. These genes can distinguish between different susceptible and resistant wheat cultivars.

Parasitism capacity and searching efficiency of Diaeretiella rapae parasitizing Brevicoryne brassicae on susceptible and resistant canola cultivars

Heterodera glycines, commonly known as the soybean cyst nematode (SCN), has become a major factor in soybean production in the Midwest United States. The influence of five tillage treatments and two treatments of row spacing on SCN population dynamics and yield of SCN-resistant and -susceptible soybean cultivars was investigated in a corn-soybean rotation system in southern Minnesota from 1993 to 1996. No effects of tillage and row spacing were observed on nematode population density. As expected, the susceptible cultivar Sturdy consistently supported higher nematode densities than did the resistant cultivar Bell in 1993 to 1995 and Freeborn in 1996. Nematode reproduction varied among years. Predicted nematode density at equilibrium was 3,800, 13,000, 12,000, and 27,000 eggs per 100 cm3 of soil in plots with the susceptible cultivar and 480, 240, 430, and 700 eggs per 100 cm3 of soil in plots with the resistant cultivars in 1993, 1994, 1995, and 1996, respectively. The effects of tillage and row spacing on soybean yield were inconsistent. The resistant cultivars yielded 653, 195, and 435 kg/ha more (P < 0.05) than the susceptible cultivar in 1994, 1995, and 1996, respectively, but no yield difference between susceptible and resistant cultivars was observed in 1993. Planting resistant cv. Bell increased the yield of the following susceptible cv. Sturdy compared with continual planting of the susceptible cultivar. A sequence with continued resistant cultivar or cultivars, however, produced a higher overall yield and lower nematode density at the end of the 4-year rotation cycle than any sequence in which the susceptible cultivar was included. Yield of resistant and susceptible cultivars was negatively related to the SCN initial population density.

Comparative proteomic analysis of bacterial wilt susceptible and resistant tomato cultivars

MicroRNAs are 21- to 24-nucleotide-long, non-coding RNA molecules that regulate gene expression at the post-transcriptional level. They can modulate various biological processes, including plant response and resistance to fungal pathogens. Hops are grown for use in the brewing industry and, recently, also for the pharmaceutical industry. Severe Verticillium wilt caused by the phytopathogenic fungus Verticillium nonalfalfae, is the main factor in yield loss in many crops, including hops (Humulus lupulus L.). In our study, we identified 56 known and 43 novel miRNAs and their expression patterns in the roots of susceptible and resistant hop cultivars after inoculation with V. nonalfalfae. In response to inoculation with V. nonalfalfae, we found five known and two novel miRNAs that are differentially expressed in the susceptible cultivar and six known miRNAs in the resistant cultivar. Differentially expressed miRNAs target 49 transcripts involved in protein localization and pigment synthesis in the susceptible cultivar, whereas they are involved in transcription factor regulation and hormone signalling in the resistant cultivar. The results of our study suggest that the susceptible and resistant hop cultivars respond differently to V. nonalfalfae inoculation at the miRNA level and that miRNAs may contribute to the successful defence of the resistant cultivar.

Bing, D., Gan, Y. and Warkentin, T. 2011. Yields in mixtures of resistant and susceptible field pea cultivars infested with powdery mildew – defining thresholds for a possible strategy for preserving resistance. Can. J. Plant Sci. 91: 873–880. Powdery mildew (caused by Erysiphe pisi var. pisi DC.) resistance of field pea (Pisum sativum L.) cultivars is dominated by the single gene er1. Monoculture of the er1 gene may encourage pathogen evolution for more virulent race(s) and breakdown of the resistance. We promote the use of cultivar mixtures made up of resistant and susceptible cultivars to limit the pathogen evolution and to preserve the resistant gene in current cultivars. The objective of this study was to evaluate if such cultivar mixtures could cause significant yield losses and to identify the proper ratio of resistant and susceptible cultivars in a mixture. Three powdery mildew resistant cultivars were mixed with 0, 10, 20, or 30% of a susceptible cultivar, and gown in replicated trials at four locations over 2 yr in western Canada. The results show that severe powdery mildew infection caused yield reduction of 21–24%. The threshold of susceptible cultivars in a cultivar mixture depends on yield potential and performance of component cultivars, the severity of powdery mildew, and environments under which a cultivar mixture is grown. When disease severity was high and the resistant cultivar yielded well, 10 to 30% of the susceptible cultivar could be mixed with the resistant cultivars without significant yield reduction compared with the resistant cultivars in pure stand. The study suggests that such cultivar mixtures may be used in field pea production by providing more substrate to the pathogen so that the breakdown of resistant gene er1 may be delayed.

Sudden death syndrome (SDS) of soybean is a complex root rot disease caused by the semi-biotrophic fungus Fusarium solani (F. solani) and a leaf scorch disease; caused by toxins produced by pathogen in the roots. However, the mechanism of soybean resistant to F. solani is still poorly understood. Eighteen soybean cultivars were screened for SDS resistance, with one cultivar showing susceptibility and one cultivar showing resistance to F. solani infection. Histochemical analysis with diaminobenzidine (DAB) and Trypan blue staining indicated an accumulation of reactive oxygen species (ROS) and cell death in surrounding area of SDS which was higher in susceptible cultivar than in resistant cultivar. Furthermore, exogenous salicylic acid (SA) application also induced some level of resistance to F. solani by the susceptible cultivar. A biochemical study revealed that the activities of superoxide dismutase (SOD), peroxidase (POD), and enzymes involved in scavenging ROS, increased in susceptible cultivar after SDS infection. In addition, hydrogen peroxide (H2O2) and malondialdehyde (MDA) content also increased in the susceptible cultivar than in resistant cultivar. High-performance liquid chromatography (HPLC) analysis indicated that free and total salicylic acid (SA) content increased in the susceptible cultivar than in resistant cultivar. In addition, a real-time quantitative PCR analysis showed an accumulation of pathogen related (PR) genes in the resistant cultivar than in susceptible cultivar. Our results show that (i). F. solani infection can increase endogenous SA levels, antioxidase activities, ROS and cell death in susceptible soybean cultivar to induce resistance against Fusarium solani. (ii). F. solani infection induced the expression of SA marker genes in resistant soybean cultivar to enhance resistance.

Macroscopic symptoms were observed in two strawberry cultivars, with the degree of symptom intensity varying depending on the susceptibility of the cultivars, i.e. resistant or susceptible. The symptoms presented as red spots and were observed 30 d following leaf tissue inoculation with the Mycosphaerella fragariae pathogen. A comparison of the superoxide dismutase isoform profiles obtained by gel electrophoresis in all samples extracted from both resistant and susceptible cultivars indicated one constant sharp band, identified as Mn[sbnd]SOD with a molecular mass of 19 kDa. The intensity of this band was higher in all samples derived from the resistant cultivar than in those from the susceptible cultivar. Another superoxide dismutase (SOD) isoform, identified as CuZn[sbnd]SOD with a molecular mass of 16 kDa, was detected in all soluble proteins derived from the resistant cultivar. This isoform was not observed in the susceptible cultivar; however, following an incremental increase in the amount of loaded protein, it was illuminated as a faint band in a sample collected 3 d after inoculation, indicating insufficient production of the CuZn[sbnd]SOD isoform in the susceptible cultivar during an oxidative burst induced by the M. fragaria pathogen. Several bands were also characterized in both cultivars containing Fe and Mn as their co-factors (Fe, Mn[sbnd]SOD). Unlike in the resistant cultivar, where the activity of Fe, Mn[sbnd]SOD isoforms gradually and regularly increased and reached its highest level on the third day after inoculation, the activity of the isoforms changed irregularly over 20 days of study in the susceptible cultivar.

Response of pear cultivars to causal agent of fire blight diseases is expressed by both resistance and tolerance, however the difference of the two is not clear. To better understand the mechanisms of resistance and tolerance of pear cultivars to the disease, the necrotrophic behaviour and electrolyte leakage of resistant (Dargazi) and tolerant (Harrow Sweet) cultivars was compared with susceptible cultivar (Barttlet) after inoculation by wild type and mutant strains (hrpN-, dspA/E- and hrpW-) of the bacterium. The appearance of symptoms in reaction to wild type strains occurred after three days in susceptible and tolerant cultivars, and in seven days in resistant cultivar. However, in resistant cultivar, Dargazi, disease progress slowed down. In all cultivars, one to two days before necrosis, electrolyte leakage increased to ~70%, and with the completion of necrosis it reached to 100%. The mutant strain hrpW- did not affect incidence of necrosis and electrolyte leakage, indicating no effect of this protein on resistance mechanisms. Using strain hrpN- increased the necrosis and electrolyte leakage in resistant cultivar and delayed these indices in tolerant cultivar in comparison with susceptible cultivar. Also, dspA/E- strain accelerated necrosis and electrolyte leakage in resistant cultivar in comparison with tolerant cultivar, and had no symptoms on susceptible cultivar. Considering the dual role of HrpN in pathogencity and stimulation of host defense system, the results indicated key role of HrpN protein on acquired defense system (ADS) in relation to the pathogenic role in the resistant cultivar (Dargazi) and its inverse relationship in tolerant cultivar (Harrow Sweet). This dual behaviour can be used as a tool for deeper understanding of the fire blight resistance mechanisms in pear, and also as an index for distinctness of resistant and tolerant pear cultivars.

Bio-ecological parameters of the two-spotted spider mite (TSSM), Tetranychus urticae Koch and its predators depend on the quality of its host plants. In this study, the life table parameters of TSSM and its main predator Phytoseiulus persimilis Athias-Henriot during different generations (1st, 5th, and 10th generations) were determined on the susceptible (‘Beth-Alpha’) and resistant (‘HED’) greenhouse cucumber cultivars. The results indicated that the longest total development time of TSSM was allocated to the first generation on the susceptible cultivar, but there was no significant difference among different generations on the resistant cultivar. The total development time of the 1st and 10th generations of P. persimilis on each of the susceptible and resistant cultivars had not significant difference. Total fecundity of TSSM was higher in the 10th generation on both cultivars tested than that of the former generations. However, the total fecundity of the predator drastically reduced after long-term rearing (10 generations) on both cultivars. The intrinsic rate of increase (r) of the 1st, 5th, and 10th generations of TSSM on the susceptible cultivar was 0.178, 0.238 and 0.319 day-1, respectively, and 0.157, 0.166 and 0.168 day-1 on the resistant cultivar, respectively which indicates the significantly negative effect of the resistant cultivar on this parameter. In P. persimilis, the value of the intrinsic rate of increase in the first and tenth generations on the susceptible cultivar was 0.275 and 0.267 day-1, respectively, and on the resistant cultivar was 0.244 and 0.210 day-1, respectively. By understanding these interactions in the long term, we will be able to develop suitable strategies for biological control of TSSM on cucumber.

Strategic spatial patterning of crop species and cultivars could make agricultural landscapes less vulnerable to plant disease epidemics, but experimentation to explore effective disease-suppressive landscape designs is problematic. Here, we present a realistic, multiscale, spatiotemporal, integrodifference equation model of potato late blight epidemics to determine the relationship between spatial heterogeneity and disease spread, and determine the effectiveness of mixing resistant and susceptible cultivars at different spatial scales under the influence of weather. The model framework comprised a landscape generator, a potato late blight model that includes host and pathogen life cycles and fungicide management at the field scale, and an atmospheric dispersion model that calculates spore dispersal at the landscape scale. Landscapes consisted of one or two distinct potato-growing regions (6.4-by-6.4-km) embedded within a nonhost matrix. The characteristics of fields and growing regions and the separation distance between two growing regions were investigated for their effects on disease incidence, measured as the proportion of fields with ≥1% severity, after inoculation of a single potato grid cell with a low initial level of disease. The most effective spatial strategies for suppressing disease spread in a region were those that reduced the acreage of potato or increased the proportion of a resistant potato cultivar. Clustering potato cultivation in some parts of a region, either by planting in large fields or clustering small fields, enhanced the spread within such a cluster while it delayed spread from one cluster to another; however, the net effect of clustering was an increase in disease at the landscape scale. The planting of mixtures of a resistant and susceptible cultivar was a consistently effective option for creating potato-growing regions that suppressed disease spread. It was more effective to mix susceptible and resistant cultivars within fields than plant some fields entirely with a susceptible cultivar and other fields with a resistant cultivar, at the same ratio of susceptible to resistant potato plants at the landscape level. Separation distances of at least 16 km were needed to completely prevent epidemic spread from one potato-growing region to another. Effects of spatial placement of resistant and susceptible potato cultivars depended strongly on meteorological conditions, indicating that landscape connectivity for the spread of plant disease depends on the particular coincidence between direction of spread, location of fields, distance between the fields, and survival of the spores depending on the weather. Therefore, in the simulation of (airborne) pathogen invasions, it is important to consider the large variability of atmospheric dispersion conditions.

Strawberry plants are subjected to many pathogens. Fungal diseases of strawberries are important worldwide and occur in all parts of the plant, including leaves, crowns, and fruits. The results of the bio-agent experiment indicated that Trichoderma harzianum was the most effective in reducing the growth of Alternaria alternata and Botrytis cinerea in vitro, the main causes of leaf spots in strawberry plants. The inhibition zone was observed and mycelium of T. harzianum invaded the colony of the tested pathogens. The importance of the biochemical study of defense reaction in the physiology of disease resistance was accepted. The activity of total, free, and conjugated phenols as well as peroxidase, polyphenol oxidase, and catalase enzyme activities were determined in resistant and susceptible strawberry cultivars. All the total, free, and conjugated phenols increased in resistant cultivars (Fortuna and Winter Star) and decreased in susceptible cultivar (Festival). Oxidative enzymes, like the increased activity of enzymes that appear mince of new polypeptide protein, have become models in the study of plant disease resistance. The higher content of peroxidase, polyphenol oxidase, and catalase enzymes in resistant cultivars, were noticed compared with those in susceptible ones. It was found also that, the chemical inducers increased total phenols in resistant and susceptible cultivars i.e., potassium di-phosphate, ferrous sulphate, and oxalic acid. Inducer resistance also caused an increase of free phenols than the control. However, conjugated phenols accumulated faster after using chemical inducers in the leaves of the resistant cultivars, than the susceptible ones.