Susceptible Accessions Research Articles

Fine-Tuning Roles of Osa-miR159a in Rice Immunity Against Magnaporthe oryzae and Development

BackgroundRice blast caused by Magnaporthe oryzae is one of the most destructive diseases of rice. An increasing number of microRNAs (miRNAs) have been reported to fine-tune rice immunity against M. oryzae and coordinate with growth and development.ResultsHere, we showed that rice microRNA159a (Osa-miR159a) played a positive role in rice resistance to M. oryzae. The expression of Osa-miR159a was suppressed in a susceptible accession at 12, 24, and 48 h post-inoculation (hpi); it was upregulated in a resistant accession of M. oryzae at 24 hpi. The transgenic rice lines overexpressing Osa-miR159a were highly resistant to M. oryzae. In contrast, the transgenic lines expressing a short tandem target mimic (STTM) to block Osa-miR159a showed enhanced susceptibility. Knockout mutations of the target genes of Osa-miR159a, including OsGAMYB, OsGAMYBL, and OsZF, led to resistance to M. oryzae. Alteration of the expression of Osa-miR159a impacted yield traits including pollen and grain development.ConclusionsOur results indicated that Osa-miR159a positively regulated rice immunity against M. oryzae by downregulating its target genes. Proper expression of Osa-miR159a was critical for coordinating rice blast resistance with grain development.

A diversity of resistance sources to Fusarium oxysporum f. sp. pisi found within grass pea germplasm

Grass pea is a legume species with recognized resistance to several diseases and thus important for the improvement of related major legume crops. It is infected by the soil-borne fungus Fusarium oxysporum f. sp. pisi (Fop), known as causal agent of pea fusarium wilt. We aim to identify, among grass pea, new sources of resistance against Fop and characterize the detected resistance mechanisms. A grass pea worldwide collection of accessions was characterized under controlled conditions for response to Fop race 2. Fungal colonization dynamics and potential resistance mechanisms were studied through confocal laser scanning microscopy (CLSM) using Fop race 2 expressing green fluorescent protein (GFP). A quantitative nature of resistance to Fop, ranging from highly to partially resistant and susceptible accessions was detected, with resistance being the most frequent phenotype. Diverse colonization patterns were observed, suggesting the existence of different resistance mechanisms. In the highly resistant accessions, absence of fungal colonization in the vascular tissue was detected, while fungal progression was arrested at the level of roots both in highly resistant and partially resistant accessions. The resistant accessions identified here can be exploited in grass pea breeding for fusarium wilt resistance, and due to the phylogenetic relatedness to pea, potentially contribute to pea improvement.

Osa-miR439 Negatively Regulates Rice Immunity Against Magnaporthe oryzae

Osa-miR439 is a rice-specific microRNA family. Here we showed that Osa-miR439 acted as a negative regulator in rice immunity against blast fungus Magnaportheoryzae. Osa-miR439 differentially responded to M. oryzae between susceptible and resistant rice accessions. The accumulation of Osa-miR439 was constitutively more in the susceptible accession than in the resistant one. Transgenic lines overexpressing Osa-miR439a (OX439a) showed higher susceptibility associating with lower induction of defense-related genes and less hydrogen peroxide (H2O2) accumulation at the infection sites than the control plants. In contrast, transgenic lines expressing a target mimic of Osa-miR439 (MIM439) displayed compromised susceptibility associating with increased H2O2 accumulation. Furthermore, we found that the expression of three predicted target genes was decreased in OX439a but increased in MIM439 in comparison to control plants, and this expression was differential in susceptible and resistant accessions upon M. oryzae infection, indicating that Osa-miR439a may regulate rice blast resistance via these genes. Our results unveiled the role of Osa-miR439a in rice blast resistance and provided the potentiality to improve the blast resistance via miRNA.

Evaluation of chickpea (Cicer arietinum L.) accessions for Fusarium wilt resistance

Aim: The present study was conducted to evaluate chickpea breeding lines and popular varieties for Fusarium wilt resistance through multi-location field evaluation in major chickpea growing states of India. Methodology: Forty-five chickpea accessions were evaluated for Fusarium wilt resistance in field sick plots at Kanpur, Junagadh, Sehore and Rahuri in India during 2016 and 2017. Each accession was planted in three replications in a randomized block design. The data was subjected to analysis of variance (ANOVA) for testing the significance of variation due to accessions, environments and their interaction. GGE biplots analysis were constructed from the first two principal components (PC1 and PC2) using 45 genotypes and 8 environments using statistical software R, versions 2.15. Results: The effects of genotype, environment and G x E interaction for wilt incidence were highly significant with maximum variation caused by G x E interaction effect (50.42%), followed by genotypic (46.92 %) and environmental effect (2.24%). GGE biplot analysis revealed that Rahuri and Junagadh locations were most discriminating locations and could differentiate the wilt resistant and susceptible chickpea accession, while Kanpur was least discriminating. Junagadh was most representative followed by Sehore and Kanpur while Rahuri was least representative of the average environment. On an average, the most severe wilt incidence was observed at Junagadh, followed by Sehore, Kanpur and Rahuri over the years. Interpretation: Elite chickpea accessions possessing high level of fusarium wilt resistant at each location can be utilized for region specific breeding.The accessions IPC 2008-11, H 2010-05, GNG 1581, JG 24, SCGP-WR 28, H 2010-01 and IPC 2008-69 exhibited stable resistance over locations. These possessed resistance against multiple races of Fusarium wilt prevailing in the country and can be utilized as donors for disease resistance breeding. Key words: Chickpea, Fusarium wilt, GGE biplot, Multi-location evaluation, Stable resistance

Genome-wide association study for resistance to the Meloidogyne javanica causing root-knot nematode in soybean.

A locus on chromosome 13, containing multiple TIR-NB-LRR genes and SNPs associated with M. javanica resistance, was identified using a combination of GWAS, resequencing, genetic mapping and expression profiling. Meloidogyne javanica, a root-knot nematode, is an important problem in soybean-growing areas, leading to severe yield losses. Some accessions have been identified carrying resistance loci to this nematode. In this study, a set of 317 soybean accessions was characterized for resistance to M. javanica. A genome-wide association study was performed using SNPs from genotyping-by-sequencing, and a region of 29.2kb on chromosome 13 was identified. An analysis of haplotypes showed that SNPs were able to discriminate between susceptible and resistant accessions, with 25 accessions sharing the haplotype associated with resistance. Furthermore, five accessions that exhibited resistance without carrying this haplotype may carry different loci conferring resistance to M. javanica. We also conducted the screening of the SNPs in the USDA soybean germplasm, revealing that several soybean accessions previously reported as resistant to other nematodes also shared the resistance haplotype on chromosome 13. Two SNP-based TaqMan® assays were developed and validated in two panels of soybean cultivars and in biparental populations. In silico analysis of the region associated with resistance identified the occurrence of genes with structural similarity with classical major resistance genes (NBS-LRR genes). Specifically, several nonsynonymous SNPs were observed in Glyma.13g194800 and Glyma.13g194900. The expression profile of these candidate genes demonstrated that the two gene models were up-regulated in the resistance source PI 505,099 after nematode infection. Overall, the SNPs associated with resistance and the genes identified constitute an important tool for introgression of resistance to the root-knot nematode by marker-assisted selection in soybean breeding programs.

Development of a robust hydroponic method for screening of sunflower (Helianthus annuus L.) accessions for tolerance to heat and osmotic stress

Hydroponic systems are known to provide a platform for uniform growth conditions until the reproductive stage. However, many plant species, including sunflower, show poor growth and survivability under conventional hydroponic systems due to poor nutrient availability, hypoxia and algal contamination. Thus, we tested various hydroponic systems to select a hydroponic system suitable for screening of sunflower germplasm. Sunflower accessions showed better growth and leaf gas exchange in newly-designed over conventional hydroponic systems. Selected hydroponic systems were further engaged in sunflower accession screening under heat and osmotic stress in a two-pan system (210 cm × 60 cm). Heat stress treatment was applied by growing sunflower germplasm at 42 °C and osmotic stress by adding polyethylene glycol 8000 which decreased the osmotic potential to − 0.6 MPa. There was significant variability among the sunflower accessions for their ability to survive under stress. Accessions such as C-2721 (43%), C-291 (46%) and D-14 (43%) had lower cell membrane injury percentage under osmotic stress and high seedling survivability (60‒80%) under heat stress when compared with susceptible accessions. Moreover, resistant accessions exhibited greater cuticular waxes and root length but lower transpiration losses. The newly designed hydroponic platform proved reliable for the selection of resistant sunflower accessions. Selected parental lines were validated by assessing their hybrids under field trials across two seasons under water and temperature stress during the reproductive phase (autumn). Hybrid H3 obtained by crossing drought and heat resistant parents had the highest seed yield and water use efficiency.

Characterization of a new gene for resistance to wheat powdery mildew on chromosome 1RL of wild rye Secale sylvestre.

PmSESY, a new wheat powdery mildew resistance gene was characterized and genetically mapped to the terminal region of chromosome 1RL of wild rye Secale sylvestre. The genus Secale is an important resource for wheat improvement. The Secale species are usually considered as non-adapted hosts of Blumeria graminis f. sp. tritici (Bgt) that causes wheat powdery mildew. However, as a wild species of cultivated rye, S. sylvestre is rarely studied. Here, we reported that 25 S. sylvestre accessions were susceptible to isolate BgtYZ01, whereas the other five confer effective resistance to all the tested isolates of Bgt. A population was then constructed by crossing the resistant accession SESY-01 with the susceptible accession SESY-11. Genetic analysis showed that the resistance in SESY-01 was controlled by a single dominant gene, temporarily designated as PmSESY. Subsequently, combining bulked segregant RNA-Seq (BSR-Seq) analysis with molecular analysis, PmSESY was mapped into a 1.88 cM genetic interval in the terminus of the long arm of 1R, which was closely flanked by markers Xss06 and Xss09 with genetic distances of 0.87cM and 1.01cM, respectively. Comparative mapping demonstrated that the corresponding physical region of the PmSESY locus was about 3.81 Mb in rye cv. Lo7 genome, where 30 disease resistance-related genes were annotated, including five NLR-type disease resistance genes, three kinase family protein genes, three leucine-rich repeat receptor-like protein kinase genes and so on. This study gives a new insight into S. sylvestre that shows divergence in response to Bgt and reports a new powdery mildew resistance gene that has potential to be used for resistance improvement in wheat.

Morpho-physiological Characterization of Bread Wheat Accessions for Heat Stress Tolerance under Late Sown Conditions of North-Western Plain Zone of India

Bread wheat is grown in the sub-tropical and tropical regions world-wide. Terminal-heat stress is a major abiotic stress in wheat and global warming due to climate change has negatively impacted its production and productivity. We evaluated 96 accessions of bread wheat germplasm, which included 79 indigenous and 17 exotic collections, by investigating 16 morpho-physiological and yield-related traits during two successive Rabi seasons of 2018-19 and 2019-20 under non-stressed and heat-stressed (as a delayed sown crop) environments. Heat susceptibility index (HSI) was used to classify tolerant (HSI <1.0) and susceptible (HSI >1.0) accessions. The heat-stress showed negative impact on the phenotypic expression of 14 morpho-physiological and yield related traits by reducing the traits more prominently in susceptible accessions than the tolerant. However, early ground cover showed the increased expression in the tolerant accessions and higher variability in the germplasm under the heat-stress. Grain length/width ratio (LWR) also improved in the germplasm under heat-stress, while, there was a marked increase in LWR of the susceptible accessions mainly due to relatively higher decrease of grain width in these accessions under heat-stress. The plot yield associated positively with its contributing traits namely yield per plant, number of grains per plant, number of grains per spike, grain weight per spike and plant biomass under both the non-stressed and the heat-stressed environments, but its association with chlorophyll fluorescence was only under heat-stress. The germplasm accessions IC574476 (HD2967), IC393878 (WH157), IC296383 (WR544), EC534487 (PAU351), IC519900 (HD2932) and IC539221 {EIGN-I-(04-05)/149} produced high yield and were stable across the environments. The identified bread wheat germplasm lines could be used as potential parents for bi-parental and multi-parental populations.

Screening quinoa (

Downy mildew caused by Peronospora variabilis is a major fungal disease limiting yield of quinoa (Chenopodium quinoa) around the world. Existing quinoa cultivars do not have adequate levels of resistance to the disease. In the present study, 165 quinoa accessions were screened for resistance to the disease in two consecutive years. Disease ratings were performed by using a three-leaf scoring technique. In 2018, of 70 quinoa accessions, 47.14% were moderately resistant and 18.57% were highly resistant. However, in 2019, of 95 accessions, 44.21% showed moderately resistant reaction and 26.31% highly resistant reaction to the disease. The average of AUDPC (area under disease progress curve) of all the accessions was 1293.42 in 2018, and 931.68 in 2019. The disease caused significant (P &lt; 0.01) cumulative defoliations in susceptible accessions. AUDPC was positively correlated (r = 0.796 in 2018, r = 0.896 in 2019) with defoliation rate and negatively correlated (r = –0.834 in 2018, r = –0.599 in 2019) with plant height. There were also negative correlations (r = –0.755 in 2018, r = –0.580 in 2019) between defoliation rate and plant height. The study not only revealed resistant germplasm but also showed the importance of screening downy mildew resistance by comparing disease-related agronomic characteristics.

A promising breeding strategy for tomato resistance to Cucumber Mosaic Virus based on genetic analysis

Infection of CMV can reduce tomato yield. One of the controlling methods to solve the problem by using a resistant variety. However, the existence of resistant variety was still not available yet. Therefore, we needed the breeding program for resistance tomato to CMV to obtain a new variety. Information of previous genetic analysis results can be used to determine a promising strategy. Two tomato genotypes namely R8 51-12 as resistant and RG-57 as susceptible accession were crossed reciprocally to obtain F1, F1R, BC1.1, BC1.2, F2. Then, all of the breeding materials were inoculated by strain CMV-2 and observed on symptom disease and virus concentration. Genetic analysis results showed that there was no maternal effect and the resistance controlled by two major genes as recessive, but there was the epistatic effect on disease symptom as a selection parameter. Based on these information, the tomato’s breeding strategy were to use a susceptible genotype as female parent, while a resistant genotype as male parent. Phenotypically disease symptom selection can be conducted in the middle or late generation. However, the selection should be supported by serologically using the Elisa test. The breeding program could be addressed as a F1 hybrid variety.

Biochemical defense responses of tolerant and susceptible lettuce accessions following infection by Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is one of the most destructive lettuce diseases, restricting lettuce cultivation globally. Here, we measured the activity of three antioxidant enzymes in two contrastingly responding lettuce accessions (susceptible ML1 and tolerant Jah accessions) challenged by S. sclerotiorum. These enzymes included superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT). Moreover, we applied the 2,2-diphenylpicrylhydrazyl (DPPH) method and the malondialdehyde (MDA) assay. The activities of SOD and GPx were much pronounced in the tolerant accession than in the susceptible one. Our results indicate that MDA concentration increased significantly in the leaves of tolerant accession compared with that of the susceptible one at 1 dpi whereas MDA level was pronounced in the later time points in the susceptible accession compared with tolerant accession. Taken together, we observed that the examined biochemical markers differentially fluctuated in the applied accessions, shedding light to understand better resistance mechanisms involved in restricting this notorious fungal pathogen.

Cross-resistance to atrazine and metribuzin in multiple herbicide-resistant kochia accessions: confirmation, mechanism, and management

AbstractKochia accessions (designated as KS-4A and KS-4H) collected from a corn field near Garden City, KS, have previously shown multiple resistance to glyphosate, dicamba, and fluroxypyr. These accessions were also suspected as being resistant to photosystem II (PS II) inhibitors. The main objectives of this research were to 1) confirm the coexistence of cross-resistance to PS II inhibitors (atrazine and metribuzin) applied PRE and POST, 2) investigate the underlying mechanism of PS II-inhibitor resistance, and 3) determine the effectiveness of alternative POST herbicides for control of these multiple herbicide–resistant (MHR) kochia accessions. Results from dose-response experiments revealed that the KS-4A and KS-4H kochia accessions were 23-fold to 48-fold resistant to PRE- and POST-applied atrazine and 13-fold to 18-fold resistant to POST-applied metribuzin compared to a known susceptible kochia accession (KS-SUS). Both accessions also showed putative resistance to PRE-applied metribuzin that needs to be confirmed. Sequence analyses of the psbA gene further revealed that all samples from the KS-4A and KS-4H kochia accessions had a Ser264Gly point mutation. A pretreatment with malathion followed by a POST application of atrazine at 1,120 g ha−1 or metribuzin at 630 g ha−1 did not reverse the resistance phenotypes of these MHR accessions. In a separate greenhouse study, alternative POST herbicides, including bicyclopyrone + bromoxynil; bromoxynil + pyrasulfotole; paraquat alone or in combination with atrazine, metribuzin, 2,4-D, or saflufenacil; and saflufenacil alone or in combination with 2,4-D effectively controlled the KS-4H accession (≥97% injury). To our knowledge, this research reports the first case of kochia accessions with cross-resistance to PRE-applied atrazine and POST-applied metribuzin. Growers should adopt diversified weed control strategies, including the use of competitive crops, cover crops, targeted tillage, and harvest weed seed control along with effective alternative PRE and POST herbicides with multiple sites of action to control MHR kochia seedbanks on their production fields.

Development of a dense genetic map and QTL analysis for pod borer Helicoverpa armigera (Hübner) resistance component traits in chickpea (Cicer arietinum L.).

Genetic enhancement for resistance against the pod borer, Helicoverpa armigera is crucial for enhancing production and productivity of chickpea. Here we provide some novel insights into the genetic architecture of natural variation in H. armigera resistance in chickpea, an important legume, which plays a major role in food and nutritional security. An interspecific recombinant inbred line (RIL) population developed from a cross between H. armigera susceptible accession ICC 4958 (Cicer arietinum) and resistant accession PI 489777 (Cicer reticulatum) was evaluated for H. armigera resistance component traits using detached leaf assay and under field conditions. A high-throughput AxiomCicerSNP array was utilized to construct a dense linkage map comprising of 3,873 loci and spanning a distance of 949.27 cM. Comprehensive analyses of extensive genotyping and phenotyping data identified nine main-effect QTLs and 955 epistatic QTLs explaining up to 42.49% and 38.05% phenotypic variance, respectively, for H. armigera resistance component traits. The main-effect QTLs identified in this RIL population were linked with previously described genes, known to modulate resistance against lepidopteran insects in crop plants. One QTL cluster harbouring main-effect QTLs for three H. armigera resistance component traits and explaining up to 42.49% of the phenotypic variance, was identified on CaLG03. This genomic region, after validation, may be useful to improve H. armigera resistance component traits in elite chickpea cultivars.

The soybean gene GmHsp22.4 is involved in the resistance response to Meloidogyne javanica in Arabidopsis thaliana

BackgroundSmall heat shock proteins (sHSPs) belong to the class of molecular chaperones that respond to biotic and abiotic stresses in plants. A previous study has showed strong induction of the gene GmHsp22.4 in response to the nematode Meloidogyne javanica in a resistant soybean genotype, while repression in a susceptible one. This study aimed to investigate the functional involvement of this small chaperone in response to M. javanica in Arabidopsis thaliana. First, it was evaluated the activation of the promoter region after the nematode inoculation, and the occurrence of polymorphisms between resistant and susceptible re-sequenced soybean accessions. Then functional analysis using A. thaliana lines overexpressing the soybean GmHsp22.4 gene, and knocked-out mutants were challenged with M. javanica infestation.ResultsHigh expression levels of the GFP gene marker in transformed A. thaliana plants revealed that the promoter region of GmHsp22.4 was strongly activated after nematode inoculation. Moreover, the multiplication of the nematode was significantly reduced in plants overexpressing GmHsp22.4 gene in A. thaliana compared to the wild type. Additionally, the multiplication of M. javanica in the A. thaliana mutants was significantly increased mainly in the event athsp22.0–2. This increase was not that evident in the event athsp22.0–1, the one that preserved a portion of the promoter region, including the HSEs in the region around − 83 bp. However, structural analysis at sequence level among soybean resistant and susceptible genotypes did not detect any polymorphisms in the whole gene model.ConclusionsThe soybean chaperone GmHsp22.4 is involved in the defense response to root-knot nematode M. javanica in A. thaliana. Specifically, the promoter region covering until − 191 from the transcriptional start site (TSS) is necessary to promoter activation after nematode infection in Arabidopsis. No polymorphisms that could explain these differences in the defense response were detected in the GmHsp22.4 gene between resistant and susceptible soybean genotypes. Therefore, further investigation is needed to elucidate the triggering factor of the plant’s defense mechanism, both at the sequence level of the soybean genotypes presenting contrasting reaction to root-knot nematode and by detecting cis-elements that are essential for the activation of the GmHsp22.4 gene promoter.

High Concentrations of Very Long Chain Leaf Wax Alkanes of Thrips Susceptible Pepper Accessions (Capsicum spp)

The cuticular wax layer can be important for plant resistance to insects. Thrips (Frankliniella occidentalis) damage was assessed on 11 pepper accessions of Capsicum annuum and C. chinense in leaf disc and whole plant assays. Thrips damage differed among the accessions. We analyzed the composition of leaf cuticular waxes of these accessions by GC-MS. The leaf wax composition was different between the two Capsicum species. In C. annuum, 1-octacosanol (C28 alcohol) was the most abundant component, whereas in C. chinense 1-triacotanol (C30 alcohol) was the prominent. Thrips susceptible accessions had significantly higher concentrations of C25-C29n-alkanes and iso-alkanes compared to relatively resistant pepper accessions. The triterpenoids α- and ß-amyrin tended to be more abundant in resistant accessions. Our study suggests a role for very long chain wax alkanes in thrips susceptibility of pepper.

Resistance Screening and Influence of Fruit Physico-biochemical Properties of “Carabao” and Other Mango Varieties Against Oriental Fruit Fly, Bactrocera dorsalis (Diptera: Tephritidae), in the Philippines

The Philippines is one of the major exporters of fresh and dried mangoes in the world, with “Carabao” (Mangifera indica L.) as its flagship variety. Among the most damaging pests that attack this cultivar is the oriental fruit fly, Bactrocera dorsalis Hendel, which limits the country’s export potential drastically. The control and management of this pest have been developed, however, the search and use of resistant cultivars have not been explored in the Philippines. In this study, a total of 33 mango accessions consisting of “Carabao” and other varieties were evaluated for resistance against B. dorsalis over a period of four years (one trial per year) through ‘choice’ tests. Repeated trials showed that accessions 12-209 (“Carabao” – Tree 203), 12-127 (“Carabao” – Tree 30), 12-103 (“Farrales”), and 16-010 (GES 77 NSIC Carabao variety) exhibited promising resistance ratings (i.e. no damage to moderately susceptible) against oriental fruit fly. Overall correlation analysis of fruit physico-biochemical properties revealed that insect visit is moderately affected by flesh flavonoid content. Meanwhile, adult emergence correlated to peel physicobiochemical properties, especially peel firmness, which considerably affected insect reproduction. Comparison between the most resistant and most susceptible accessions suggests that, apart from high flesh flavonoids and peel firmness, high flesh phenolics and low pH (acidic) levels may also play a defensive role in mango against oriental fruit fly. The accessions characterized can be used as stop-gap varieties or as parental lines for the breeding of resistant “Carabao” mango.

Influence of Wounding and Temperature on Resistance of Maize Landraces From Mexico to Aflatoxin Contamination.

Maize is a staple for billions across the globe. However, in tropical and sub-tropical regions, maize is frequently contaminated with aflatoxins by Aspergillus section Flavi fungi. There is an ongoing search for sources of aflatoxin resistance in maize to reduce continuous exposures of human populations to those dangerous mycotoxins. Large variability in susceptibility to aflatoxin contamination exists within maize germplasm. In Mexico, several maize landrace (MLR) accessions possess superior resistance to both Aspergillus infection and aflatoxin contamination but their mechanisms of resistance have not been reported. Influences of kernel integrity on resistance of four resistant and four susceptible MLR accessions were evaluated in laboratory assays. Wounds significantly (P < 0.05) increased susceptibility to aflatoxin contamination even when kernel viability was unaffected. Treatments supporting greater A. flavus reproduction did not (P > 0.05) proportionally support higher aflatoxin accumulation suggesting differential influences by some resistance factors between sporulation and aflatoxin biosynthesis. Physical barriers (i.e., wax and cuticle) prevented both aflatoxin accumulation and A. flavus sporulation in a highly resistant MLR accession. In addition, influence of temperature on aflatoxin contamination was evaluated in both viable and non-viable kernels of a resistant and a susceptible MLR accession, and a commercial hybrid. Both temperature and living embryo status influenced (P < 0.05) resistance to both aflatoxin accumulation and A. flavus sporulation. Lower sporulation on MLR accessions suggests their utilization would result in reduced speed of propagation and associated epidemic increases in disease both in the field and throughout storage. Results from the current study should encourage researchers across the globe to exploit the large potential that MLRs offer to breed for aflatoxin resistant maize. Furthermore, the studies provide support to the importance of resistance based on the living host and maintaining living status to reducing episodes of post-harvest contamination.

QTL mapping of qSCN3-1 for resistance to soybean cyst nematode in soybean line Zhongpin 03-5373

Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most economically destructive pathogens. The soybean line Zhongpin03-5373 (ZP), which combines resistance genes from several donors, is highly resistant to SCN race 3 (SCN3). In our previous study, two QTL (rhg1 and GmSNAP11) were identified in a population of recombinant inbred lines derived from a cross between ZP and the susceptible parent Zhonghuang 13. The two QTL explained around one-third of the resistance, suggesting the presence of further QTL contributing to SCN resistance. In the present study, we used an improved version of the genetic map comprising the previously applied 1062 molecular markers and 47 newly developed InDel (insertion-deletion) markers. The improved map revealed a novel locus contributing to SCN3 resistance: qSCN3-1, flanked by InDel marker InDel1-7 and SNP marker Map-0047, explained 4.55% of the phenotypic variance for resistance to SCN3 and was not involved in digenic epistatic interaction with rhg1 and GmSNAP11. Haplotypes of Map-0047_CAPS (a CAPS marker developed for Map-0047) and InDel1-7 were significantly associated with SCN3 resistance in a panel of 209 resistant and susceptible accessions. Using further allele-combination analysis for three functional markers representing three cloned resistance genes (rhg1, Rhg4, and GmSNAP11) and two markers flanking qSCN3-1, we found that adding the resistance allele of qSCN3-1 greatly increased soybean resistance to SCN, even in diverse genetic backgrounds. The qSCN3-1 locus will be useful for marker-assisted polygene pyramid breeding and should be targeted for the future identification of candidate genes.

BdWRKY38 is required for the incompatible interaction of Brachypodium distachyon with the necrotrophic fungus Rhizoctonia solani.

SUMMARY Rhizoctonia solani is a soil‐borne necrotrophic fungus that causes sheath blight in grasses. The basal resistance of compatible interactions between R. solani and rice is known to be modulated by some WRKY transcription factors (TFs). However, genes and defense responses involved in incompatible interaction with R. solani remain unexplored, because no such interactions are known in any host plants. Recently, we demonstrated that Bd3‐1, an accession of the model grass Brachypodium distachyon, is resistant to R. solani and, upon inoculation with the fungus, undergoes rapid induction of genes responsive to the phytohormone salicylic acid (SA) that encode the WRKY TFs BdWRKY38 and BdWRKY44. Here, we show that endogenous SA and these WRKY TFs positively regulate this accession‐specific R. solani resistance. In contrast to a susceptible accession (Bd21), the infection process in the resistant accessions Bd3‐1 and Tek‐3 was suppressed at early stages before the development of fungal biomass and infection machinery. A comparative transcriptome analysis during pathogen infection revealed that putative WRKY‐dependent defense genes were induced faster in the resistant accessions than in Bd21. A gene regulatory network (GRN) analysis based on the transcriptome dataset demonstrated that BdWRKY38 was a GRN hub connected to many target genes specifically in resistant accessions, whereas BdWRKY44 was shared in the GRNs of all three accessions. Moreover, overexpression of BdWRKY38 increased R. solani resistance in Bd21. Our findings demonstrate that these resistant accessions can activate an incompatible host response to R. solani, and BdWRKY38 regulates this response by mediating SA signaling.

Comparative Transcriptome Analysis Revealing the Different Germination Process in Aryloxyphenoxypropionate-Resistant and APP-Susceptible Asia Minor Bluegrass (Polypogon fugax).

Herbicide-resistant mutations are predicted to exhibit fitness cost under herbicide-free conditions. Asia minor bluegrass (Polypogon fugax) is a common weed species in the winter crops. Our previous study established a P. fugax accession (LR) resistant to aryloxyphenoxypropionate (APP) herbicides, which also exhibited germination delay relative to the susceptible accession (LS). A comparative transcriptome was conducted to analyze the gene expression profile of LS and LR at two germination time points. A total of 11,856 and 23,123 differentially expressed genes (DEGs) were respectively identified in LS and LR. Most DEGs were involved in lipid metabolism, carbohydrate metabolism, amino acid metabolism, and secondary metabolites biosynthesis. Twenty-four genes involved in carbohydrate and fatty acid metabolism had higher relative expression levels in LS than LR during germination. Nine genes involved in gibberellin (GA) and abscisic acid (ABA) signal transduction showed different expression patterns in LS and LR, consistent with their different sensitivity to exogenous hormones treatments. This study first provided insight into transcriptional changes and interaction in the seed germination process of P. fugax. It compared the differential expression profile between APP herbicides resistance and susceptible accessions during germination, which contributed to understanding the association between herbicide resistance and fitness cost.