Development Of Resistant Cultivars Research Articles

Molecular identification of the causal agent of bacterial wilt in tomato plants in southwestern Paraná

Bacterial wilt, caused by phytopathogenic species of the genus Ralstonia, is one of the main diseases affecting the tomato crop. The Ralstonia solanacearum species complex occurs as a result of variants being widely diverse in terms of adaptation to different climatic conditions, host variations, and aggressiveness, which complicate disease control recommendations. In this study, we employed molecular methods to analyze 26 R. solanacearum isolates collected from tomato plants cultivated in the southwest region of Paraná, Brazil. Isolates were obtained from plants exhibiting wilt symptoms in a protected cultivation system and in an open field. The specific primers 759/760 confirmed the isolates as part of the Ralstonia solanacearum complex, and Nmult primers were used to identify the phylotype. Variability analysis using BOX-PCR with the BOX-A1R primer on 19 isolates revealed molecular diversity. All 26 isolates were confirmed as Ralstonia solanacearum, belonging to phylotype II. Comparison of genomic DNA band patterns amplified by BOX-PCR indicated molecular variability, forming eight groups at a similarity level of 0.63. These results confirm the prevalence of R. solanacearum phylotype II in southwestern Paraná. This information aids decision-making in disease management and contributes to breeding efforts aiming at the development of resistant cultivars.

Prevalence of groundnut dry root rot (Macrophomina phaseolina (Tassi) Goid.) and its pathogenic variability in Southern India.

Macrophomina phaseolina is the most devastating and emerging threat to groundnut production in India. An increase in average temperature and inconsistent rainfalls resulting from changing climatic conditions are strongly believed to aggravate the disease and cause severe yield losses. The present study aims to conduct a holistic survey to assess the prevalence and incidence of dry root rot of groundnut in major groundnut growing regions of Southern India, viz., Andhra Pradesh, Telangana, Karnataka, and Tamil Nadu. Furthermore, the pathogenic variability was determined using different assays such as morphological, cultural, pathogenic, and molecular assays. Results indicate that disease incidence in surveyed locations ranged from 8.06 to 20.61%. Both temperature and rainfall played a major role in increasing the disease incidence. The pathogenic variability of M. phaseolina isolates differed significantly, based on the percent disease incidence induced on cultivars of JL-24 groundnut and K-6 groundnut. Morphological variations in terms of growth pattern, culture color, sclerotia number, and sclerotia size were observed. The molecular characterization of M. phaseolina isolates done by ITS rDNA region using ITS1 and ITS4 primers yielded approximately 600 bp PCR amplicons, sequenced and deposited in GenBank (NCBI). Molecular variability analysis using SSR primers indicated the genetic variation among the isolates collected from different states. The present investigation revealed significant variations in pathogenic variability among isolates of M. phaseolina and these may be considered important in disease management and the development of resistant cultivars against groundnut dry root rot disease.

Antioxidant enzymes activity associated with resistance to Phytophthora melonis-pumpkin blight

Numerous Cucurbitaceae species are seriously threatened by the hemibiotrophic oomycetes with a severe negative impact on plant yields. In particular, Phytophthora melonis causes severe symptoms that significantly reduce cucumber productions. However, there is currently little known about the Cucurbita pepo-P. melonis interaction. This study analyzed enzymatic activity of defense-related antioxidant enzymes peroxidase (POX), superoxide dismutase (SOD), polyphenol oxidase (PPOs), catalase (CAT); hydrolytic enzymes- β-1,3-glucanase; phenylalanine ammonia-lyase (PAL) and phenolic content in two resistant pumpkin “Tanbal” and “Ghelyani” and two susceptible, “Marmai” and “Khoreshti”, in response to Phytophthora blight disease (PBD), caused by Phytophthora melonis over the time courses of 24, 48 and 72 h post inoculation (hpi). All enzymes were highly up-regulated in the resistant C. pepo accessions “Tanbal” and “Ghelyani” inoculated with P. melonis. The mean level of enzyme activity varied from 1.3 to 6-fold higher in the resistant genotypes, of which SOD was increased by 6-fold, followed by PPOs and PAL 5.3-fold in comparison to untreated controls. Conversely, the lower or negative expression of these enzymes was observed in susceptible pumpkins. The highest β-1,3-glucanases activity, marker of salicylic acid pathway, was recorded in resistant “Tanbal” with 3-fold increase, followed by 2.4-fold increase in Ghelyani 24 hpi following inoculation which shows the involvement of salicylic acid (SA)-mediated defense. Furthermore, significantly higher activities of the ROS-scavenging-defense-enzymes CAT (1.6-fold), and POX (6-fold), CAT (6-fold (, and POX (6-fold) were observed in the roots of resistant-cultivars at different-wpis, compared with non-inoculated-controls. We also analyzed the quantitative-gene-expression-changes of three-candidate-gene-markers; PR-1, POD and WRKY21 by qRT-PCR along the related time-courses revealed the considerable transcriptomic-response in the resistant-genotypes, 1.1–2.7-fold in the roots and leaves, respectively. Surprisingly, PR-1-gene-marker, basically resistant to wilting agent- Verticillium dahlia was overexpressed in resistant “Tanbal” and “Ghelyani” against P. melonis. Similar results were obtained on POD-gene-marker resistant to powdery mildew, Podosphaera xanthii that similarly modulates immunity against P. melonis. There was also a highly significant correlation between the related enzymes and gene-markers, predominantly between PPO-enzyme and PR-1, POD and WRKY21; r = 0.851**r = 0.878** and r = 0.866**, followed by PAL and SOD respectively. Thus, molecular pathways associated to P. melonis resistance may be considered as future targets for manipulation in the development of resistant cultivars.

Advances in understanding the mechanism of resistance to anthracnose and induced defence response in tea plants.

The tea plant (Camellia sinensis) is susceptible to anthracnose disease that causes considerable crop loss and affects the yield and quality of tea. Multiple Colletotrichum spp. are the causative agents of this disease, which spreads quickly in warm and humid climates. During plant-pathogen interactions, resistant cultivars defend themselves against the hemibiotrophic pathogen by activating defence signalling pathways, whereas the pathogen suppresses plant defences in susceptible varieties. Various fungicides have been used to control this disease on susceptible plants, but these fungicide residues are dangerous to human health and cause fungicide resistance in pathogens. The problem-solving approaches to date are the development of resistant cultivars and ecofriendly biocontrol strategies to achieve sustainable tea cultivation and production. Understanding the infection stages of Colletotrichum, tea plant resistance mechanisms, and induced plant defence against Colletotrichum is essential to support sustainable disease management practices in the field. This review therefore summarizes the current knowledge of the identified causative agent of tea plant anthracnose, the infection strategies and pathogenicity of C. gloeosporioides, anthracnose disease resistance mechanisms, and the caffeine-induced defence response against Colletotrichum infection. The information reported in this review will advance our understanding of host-pathogen interactions and eventually help us to develop new disease control strategies.

Mapping of leaf rust resistance genes in common wheat ‘Guinong08-6’

Wheat leaf rust (Puccinia triticina Eriks.), a devastating disease of wheat in the world, causes severe yield losses and therefore the development of resistant cultivars is very important. Here, a Chinese wheat line (Guinong08-6) showed adult-plant resistance against mixed fungal isolates of leaf rust, which is common in Guiyang region. It was crossed with a susceptible wheat line (Guinong19) to develop F1, F2, and F3 hybrids. Combined SSR and STS markers were used to map leaf rust resistance genes in Guinong08-6, and the resistance phenotype of Guinong08-6 was co-regulated by two complementary dominant genes, named LrGn08-6A and LrGn08-6B. LrGn08-6A was mapped to chromosome 2AS with markers URIC-LN2 and Xgpw2204, which flanked the gene at distances of 1.8 centimorgan (cM) and 14.83 cM, respectively. LrGn08-6B was mapped to chromosome 4DL with markers Xgpw342 and Xbarc93, which both flanked the gene at a distance of 26.57 cM. Genetic and molecular marker analyses demonstrated that LrGn08-6A, which was inherited from Aegilops ventricosa may be the resistance gene Lr37, while LrGn08-6B may be a newly discovered leaf rust resistance gene.

Breeding and Genomic Approaches towards Development of Fusarium Wilt Resistance in Chickpea.

Chickpea is an important leguminous crop with potential to provide dietary proteins to both humans and animals. It also ameliorates soil nitrogen through biological nitrogen fixation. The crop is affected by an array of biotic and abiotic factors. Among different biotic stresses, a major fungal disease called Fusarium wilt, caused by Fusarium oxysporum f. sp. ciceris (FOC), is responsible for low productivity in chickpea. To date, eight pathogenic races of FOC (race 0, 1A, and 1B/C, 2-6) have been reported worldwide. The development of resistant cultivars using different conventional breeding methods is very time consuming and depends upon the environment. Modern technologies can improve conventional methods to solve these major constraints. Understanding the molecular response of chickpea to Fusarium wilt can help to provide effective management strategies. The identification of molecular markers closely linked to genes/QTLs has provided great potential for chickpea improvement programs. Moreover, omics approaches, including transcriptomics, metabolomics, and proteomics give scientists a vast viewpoint of functional genomics. In this review, we will discuss the integration of all available strategies and provide comprehensive knowledge about chickpea plant defense against Fusarium wilt.

Resistencia de Tres Variedades de Tomate a la Mosca Blanca de los Invernaderos, Trialeurodes vaporariorum1

Greenhouse whitefly, Trialeurodes vaporariorum, is a polyphagous pest that causes economic loss. Management is based on constant application of synthetic insecticides. Development of cultivars resistant to insect vectors is an alternative that can reduce infestation and infection levels. In addition, it is a strategy that may be implemented effectively as part of an integrated management system. The objective of this report was to evaluate the effect of antibiosis and antixenosis of three tomato varieties on T. vaporariorum. Under laboratory and greenhouse conditions, settlement, oviposition, and nymph development were evaluated. Wild variety Solanum habrochaites was least attractive to adults in antixenosis tests, demonstrating low growth in insect nymphs in antibiosis tests compared to S. lycopersicum cv. Floradade. Variety S. pimpinellifolium showed moderate resistance in both evaluations. The high level of resistance of LA0407 can serve as a base for tomato breeding, focusing on development of resistant cultivars.

Evaluation Soybean Cultivars for Reaction to Heterodera glycines Populations HG Types 7 and 1.3.4.7 in Northeast China.

Soybean cyst nematode Heterodera glycines (SCN) is a major threat to global soybean production. Effective management of this disease is dependent on the development of resistant cultivars. Two SCN HG Types, 7 and 1.3.4.7. were previously identified as prevalent H. glycines populations in Northeast China. In order to evaluate soybean cultivars resistant to local SCN populations, 110 domestic commercial soybeans from different regions of Northeast China were assessed in the greenhouse to determine their potential as novel sources of resistance. The results suggested that cultivars responded differently to the two HG types. Of the 110 soybean cultivars evaluated, 24 accessions were classified as resistant or moderately resistant to HG Type 7, and five cultivars were classified as resistant or moderately resistant to HG Type 1.3.4.7. Among the tested cultivars, Kangxian 12 and Qingdou 13 had resistance response to both HG types 7 and 1.3.4.7. Thus, these broad-based SCN cultivars will be the valuable materials in the SCN resistance breeding program.

Selection of tomato progenies F2:3 for resistance to bacterial wilt via mixed modeling

Bacterial wilt is among the major diseases of tomatoes and is currently considered the most important in Brazil. The development of resistant cultivars is the strategy that presents greater efficiency and viability, being the mixed modeling approach allows the selection of genetic materials with major accuracy. This work defines strategies for the development and selection of segregating strains F2:3 from the estimation of genetic parameters and individual mean components using mixed models. A greenhouse experiment was conducted in a randomized complete block design with four replicates, in which the resistance of 43 progenies F2:3 segregants obtained from the F2 generation from the cross between the parents was evaluated, having as parents Yoshimatsu (Resistant) and IPA-7 (Susceptible). Components of variance and genetic parameters were estimated, followed by ranking by additive genetic values. The selection of F2:3 progenies resistant to bacterial wilt was more effective when the household information was used. Mixed model procedures for the selective accuracy of 77.98%, verified efficiency in the selection of F2:3 progenies resistant to bacterial wilt evaluated at 20 days after inoculation. A total of 240 resistant and moderately resistant individual progenies were selected with severity scores between 1 and 2.49. Families presented the new averages between 1.0 and 2.87, making 23 families F2:3 that will continue the tomato breeding program.

A Review of Botryosphaeria Stem Blight Disease of Blueberry from the Perspective of Plant Breeding

Stem blight of blueberry caused by fungal pathogens in the family Botryosphaeriaceae presents a major challenge to global blueberry production. Since its first documented outbreak in North Carolina, USA in the 1950s, Botryosphaeria stem blight has been reported in the blueberry production regions of more than nine countries across five continents. The lack of effective management strategies or resistant cultivars makes disease control especially challenging. With the goal of illuminating directions for future Botryosphaeria stem blight management, especially through resistant-cultivar development, this review summarizes the latest information on the distribution and causal pathogens of this disease, the pathogenicity of fungal species, disease resistance of blueberry cultivars, and currently recommended management practices. DNA sequencing techniques have revealed multiple fungal species that are associated with this disease. However, a lack of reliable methods to screen cultivars for stem blight resistance remains a major bottleneck for the development of resistant cultivars. Future studies should focus on at least four key areas: (1) the development and adoption of uniform and reliable screening protocols; (2) utilization of diverse and well-characterized Botryosphaeriaceae isolates for germplasm screens; (3) field evaluations of cultivar resistance and management practices; and (4) exploration of new tools for disease management and prevention.

Genotyping by Sequencing (GBS)-Based QTL Mapping for Bacterial Fruit Blotch (BFB) in Watermelon.

Watermelon (Citrullus lanatus), an economically important and nutritionally rich Cucurbitaceous crop grown worldwide, is severely affected by bacterial fruit blotch (BFB). Development of resistant cultivar is the most eco-friendly, cost-effective, and sustainable way to tackle this disease. This requires wider understanding of the genetics of resistance to BFB. In this study, we identified quantitative trait loci (QTLs) associated with BFB resistance in an F2 mapping population developed from BFB-resistant 'PI 189225' (Citrullus amarus) and -susceptible 'SW 26' (C. lanatus) genotypes based on the polymorphic markers identified by genotyping by sequencing (GSB). A linkage map covering a total genetic distance of 3377.1 cM was constructed. Two QTLs for BFB resistance, namely, ClBFB10.1 and ClBFB10.2, both located on chromosome 10 explaining 18.84 and 15.41% of the phenotypic variations, respectively, were identified. Two SNP-based high-resolution melting (HRM) markers WmBFB10.1 and WmBFB10.2 having high positive correlation with resistance vs. susceptible alleles were developed. The efficacy of the markers was validated in another F2 population derived from SW34 × PI 189225. The highest phenotypic variation was found in the locus ClBFB10.2, which also contains three putative candidate genes for resistance to BFB. These findings will accelerate the development of BFB-resistant watermelon varieties via molecular breeding.

Puccinia striiformis f. sp. tritici effectors in wheat immune responses.

The obligate biotrophic fungus Puccinia striiformis f. sp. tritici, which causes yellow (stripe) rust disease, is among the leading biological agents resulting in tremendous yield losses on global wheat productions per annum. The combatting strategies include, but are not limited to, fungicide applications and the development of resistant cultivars. However, evolutionary pressure drives rapid changes, especially in its "effectorome" repertoire, thus allowing pathogens to evade and breach resistance. The extracellular and intracellular effectors, predominantly secreted proteins, are tactical arsenals aiming for many defense processes of plants. Hence, the identity of the effectors and the molecular mechanisms of the interactions between the effectors and the plant immune system have long been targeted in research. The obligate biotrophic nature of P. striiformis f. sp. tritici and the challenging nature of its host, the wheat, impede research on this topic. Next-generation sequencing and novel prediction algorithms in bioinformatics, which are accompanied by in vitro and in vivo validation approaches, offer a speedy pace for the discovery of new effectors and investigations of their biological functions. Here, we briefly review recent findings exploring the roles of P. striiformis f. sp. tritici effectors together with their cellular/subcellular localizations, host responses, and interactors. The current status and the challenges will be discussed. We hope that the overall work will provide a broader view of where we stand and a reference point to compare and evaluate new findings.

English

Soil salinity is one of the most significant stressors limiting plant productivity in the world's irrigated and cultivated agricultural lands. Plants have a wide range of adaptations and mitigation strategies to overcome salinity effects. It is possible to mitigate the effects of salt stress by the development of resistant cultivars and more efficient use of available resources. However, these methods are time-consuming and costly. Solutions to salinity issues need to be developed that are both straightforward and inexpensive, as they will likely only be implemented temporarily. In this study, the effects of the different salinity levels (Control, 20mM, 40mM, 60mM, 80mM, and 100mM) on citrus rootstocks were determined. In the citrus growing regions, the sour orange, trifoliate orange, and Carrizo citrange were the three most popular rootstocks. As a result of the present study, the sour orange was found to have the lowest decline in plant height (13.36%), leaf area (31.19%), and root length (8.13%), while the trifoliate orange had the lowest decrease in fresh weight of the plant (6.82%) and root (4.42%). Trifoliate orange was shown to have the highest levels of catalase activity, whereas superoxide dismutase and peroxidase activities were found to be highest in Carrizo citrange and sour orange, respectively. The highest concentration of plant nutrients was found in the Carrizo citrange. Therefore, sour orange was discovered to be more salinity tolerant in terms of morphological traits, physiological qualities, biochemical composition, and plant nutrition than trifoliate orange and Carrizo citrange. For areas with high salt levels, growing citrus on sour orange rootstock may be a viable alternative

Time-Series Monitoring of Transgenic Maize Seedlings Phenotyping Exhibiting Glyphosate Tolerance

Glyphosate is a widely used nonselective herbicide. Probing the glyphosate tolerance mechanism is necessary for the screening and development of resistant cultivars. In this study, a hyperspectral image was used to develop a more robust leaf chlorophyll content (LCC) prediction model based on different datasets to finally analyze the response of LCC to glyphosate-stress. Chlorophyll a fluorescence (ChlF) was used to dynamically monitor the photosynthetic physiological response of transgenic glyphosate-resistant and wild glyphosate-sensitive maize seedlings and applying chemometrics methods to extract time-series features to screen resistant cultivars. Six days after glyphosate treatment, glyphosate-sensitive seedlings exhibited significant changes in leaf reflection and photosynthetic activity. By updating source domain and transfer component analysis, LCC prediction model performance was improved effectively (the coefficient of determination value increased from 0.65 to 0.84). Based on the predicted LCC and ChlF data, glyphosate-sensitive plants are too fragile to protect themselves from glyphosate stress, while glyphosate-resistant plants were able to maintain normal photosynthetic physiological activity. JIP-test parameters, φE0, VJ, ψE0, and M0, were used to indicate the degree of plant damage caused by glyphosate. This study constructed a transferable model for LCC monitoring to finally evaluate glyphosate tolerance in a time-series manner and verified the feasibility of ChlF in screening glyphosate-resistant cultivars.

Gene Expression, Histology and Histochemistry in the Interaction between Musa sp. and Pseudocercospora fijiensis.

Bananas are the main fruits responsible for feeding more than 500 million people in tropical and subtropical countries. Black Sigatoka, caused by the fungus Pseudocercospora fijiensis, is one of the most destructive disease for the crop. This fungus is mainly controlled with the use of fungicides; however, in addition to being harmful to human health, they are associated with a high cost. The development of resistant cultivars through crosses of susceptible commercial cultivars is one of the main focuses of banana breeding programs worldwide. Thus, the objective of the present study was to investigate the interaction between Musa sp. and P. fijiensis through the relative expression of candidate genes involved in the defence response to black Sigatoka in four contrasting genotypes (resistant: Calcutta 4 and Krasan Saichon; susceptible: Grand Naine and Akondro Mainty) using quantitative real-time PCR (RT–qPCR) in addition to histological and histochemical analyses to verify the defence mechanisms activated during the interaction. Differentially expressed genes (DEGs) related to the jasmonic acid and ethylene signalling pathway, GDSL-like lipases and pathogenesis-related proteins (PR-4), were identified. The number and distance between stomata were directly related to the resistance/susceptibility of each genotype. Histochemical tests showed the production of phenolic compounds and callosis as defence mechanisms activated by the resistant genotypes during the interaction process. Scanning electron microscopy (SEM) showed pathogenic structures on the leaf surface in addition to calcium oxalate crystals. The resistant genotype Krasan Saichon stood out in the analyses and has potential for use in breeding programs for resistance to black Sigatoka in banana and plantains.

Development of Rice Variety With Durable and Broad-Spectrum Resistance to Blast Disease Through Marker-Assisted Introduction of Pigm Gene.

Rice blast, caused by Magnaporthe oryzae (M. oryzae), is one of the most destructive diseases threatening rice production worldwide. Development of resistant cultivars using broad-spectrum resistance (R) genes with high breeding value is the most effective and economical approach to control this disease. In this study, the breeding potential of Pigm gene in geng/japonica rice breeding practice in Jiangsu province was comprehensively evaluated. Through backcross and marker-assisted selection (MAS), Pigm was introduced into two geng rice cultivars (Wuyungeng 32/WYG32 and Huageng 8/HG8). In each genetic background, five advanced backcross lines with Pigm (ABLs) and the same genotypes as the respective recurrent parent in the other 13 known R gene loci were developed. Compared with the corresponding recurrent parent, all these ABLs exhibited stronger resistance in seedling inoculation assay using 184 isolates collected from rice growing regions of the lower region of the Yangtze River. With respect to panicle blast resistance, all ABLs reached a high resistance level to blast disease in tests conducted in three consecutive years with the inoculation of seven mixed conidial suspensions collected from different regions of Jiangsu province. In natural field nursery assays, the ABLs showed significantly higher resistance than the recurrent parents. No common change on importantly morphological traits and yield-associated components was found among the ABLs, demonstrating the introduction of Pigm had no tightly linked undesirable effect on rice economically important traits and its associated grain weight reduction effect could be probably offset by others grain weight genes or at least in the background of the aforementioned two varieties. Notably, one rice line with Pigm, designated as Yangnonggeng 3091, had been authorized as a new variety in Jiangsu province in 2021, showing excellent performance on both grain yield and quality, as well as the blast resistance. Together, these results suggest that the Pigm gene has a high breeding value in developing rice varieties with durable and broad-spectrum resistance to blast disease.

Genome-Wide Association Study of Leaf Rust and Stem Rust Seedling and Adult Resistances in Tetraploid Wheat Accessions Harvested in Kazakhstan.

Leaf rust (LR) and stem rust (SR) are diseases increasingly impacting wheat production worldwide. Fungal pathogens producing rust diseases in wheat may cause yield losses of up to 50–60%. One of the most effective methods for preventing such losses is the development of resistant cultivars with high yield potential. This goal can be achieved through complex breeding studies, including the identification of key genetic factors controlling rust disease resistance. The objective of this study was to identify sources of tetraploid wheat resistance to LR and SR races, both at the seedling growth stage in the greenhouse and at the adult plant stage in field experiments, under the conditions of the North Kazakhstan region. A panel consisting of 193 tetraploid wheat accessions was used in a genome-wide association study (GWAS) for the identification of quantitative trait loci (QTLs) associated with LR and SR resistance, using 16,425 polymorphic single-nucleotide polymorphism (SNP) markers in the seedling and adult stages of plant development. The investigated panel consisted of seven tetraploid subspecies (Triticum turgidum ssp. durum, ssp. turanicum, ssp. turgidum, ssp. polonicum, ssp. carthlicum, ssp. dicoccum, and ssp. dicoccoides). The GWAS, based on the phenotypic evaluation of the tetraploid collection’s reaction to the two rust species at the seedling (in the greenhouse) and adult (in the field) stages, revealed 38 QTLs (p < 0.001), comprising 17 for LR resistance and 21 for SR resistance. Ten QTLs were associated with the reaction to LR at the seedling stage, while six QTLs were at the adult plant stage and one QTL was at both the seedling and adult stages. Eleven QTLs were associated with SR response at the seedling stage, while nine QTLs were at the adult plant stage and one QTL was at both the seedling and adult stages. A comparison of these results with previous LR and SR studies indicated that 11 of the 38 QTLs are presumably novel loci. The QTLs identified in this work can potentially be used for marker-assisted selection of tetraploid and hexaploid wheat for the breeding of new LR- and SR-resistant cultivars.

MAIZE CULTIVARS WITH NATIVE INSECT RESISTANCE – POTENTIAL, ADVANCES, AND CHALLENGES

The development of resistant cultivars is one of the strategies applied in pest control. The method has the advantages of reduced cost and the lack of unwanted effects on the environment. Over the past decades, significant effort has been made toward developing the natural maize resistance to pests by evaluating germplasm and cultivar selection. This review highlights a maize breeding program, potential, advances, and challenges in addressing these characteristics. Also, it describes the main components and procedures applied in the mass rearing of insect pests of maize, artificial diets, techniques of artificial infestation employed in genotype selection, and methods to evaluate the mechanisms and causes of resistance. Studies on the inheritance of resistance, the breeding methods, and the potential for integrating classical and transgenic resistance are also emphasized.

Analysis of Fhb1 gene and resistance to Fusarium head blight in 3,177 diverse wheat accessions

Fusarium head blight (FHB), elicited mainly by the fungal pathogen Fusarium graminearum (Fg), causes serious damages to global wheat production. Development of resistant cultivars is the most efficient measure for controlling FHB, which requires efficient identification and utilization of the wheat germplasm carrying FHB resistance genes. Because the Fhb1 gene recently cloned from the wheat cultivars Sumai 3 and Wangshuibai, designated here as Fhb1-R, confers type II resistance to FHB, we investigated the presence of Fhb1-R in 3,177 wheat accessions from different countries of the world. By PCR screening with a functional molecular marker amplifying a part of Fhb1 genomic sequence, Fhb1-R was detected in 33 of the 3,177 accessions. Through two independent inoculation tests with Fg under greenhouse conditions, eight Fhb1-R carrying lines were found to exhibit relatively high levels of type II resistance to FHB, seven of which were newly identified in this work. Remarkably, a substantial proportion of Fhb1-R carrying accessions were actually susceptible to Fg infection, highlighting the fact that the presence of Fhb1-R is not always associated with type II FHB resistance. Further analysis of representative Fhb1-R carrying accessions led to the finding of one Fhb1-R carrying, but FHB susceptible, wheat accession showing moderate resistance to Fusarium crown rot (FCR), another serious disease caused mainly by Fusarium pseudograminearum (Fp). Our work provides insight into the presence of Fhb1-R in a large set of diverse wheat germplasm lines and new genetic resources likely useful for improving wheat resistance to FHB or FCR in the future.

Genetic Insight Into the Insect Resistance in Bread Wheat Exploiting the Untapped Natural Diversity.

Climate change is an undeniable threat to sustainable wheat production in the future as an increased temperature will significantly increase grain loss due to the increased number of generations per season of multivoltine species that are detrimental to plants. Among insects, orange wheat blossom midge (OWBM), yellow wheat blossom midge (YWBM), saddle gall midge (SGM), thrips, and frit fly (FF) are important wheat pests in the European environments, which can be managed by the development of resistant cultivars. This involves the identification, confirmation, and incorporation of insect resistance sources into new high-yielding cultivars. We used two diverse and unrelated wheat [winter wheat (WW) and spring wheat (SW)] panels to associate single-nucleotide polymorphism (SNP) markers with the mentioned pests using the tools of association mapping. All in all, a total of 645 and 123 significant associations were detected in WW and SW, respectively, which were confined to 246 quantitative trait loci. Many candidate genes were identified using the BLAST analysis of the sequences of associated SNPs. Some of them are involved in controlling the physical structures of plants such as stomatal immunity and closure, cuticular wax in leaf blade, whereas others are involved in the production of certain enzymes in response to biotic and abiotic stresses. To our knowledge, this is the first detailed investigation that deals with YWBM, SGM, thrips, and FF resistance genetics using the natural variation in wheat. The reported germplasm is also readily available to breeders across the world that can make rational decisions to breed for the pest resilience of their interest by including the resistant genotypes being reported.