Breeding Of Resistant Varieties Research Articles

Dual Transcriptome Analysis Reveals the Changes in Gene Expression in Both Cotton and Verticillium dahliae During the Infection Process.

Cotton is often threatened by Verticillium wilt caused by V. dahliae. Understanding the molecular mechanism of V. dahlia-cotton interaction is important for the prevention of this disease. To analyze the transcriptome profiles in V. dahliae and cotton simultaneously, the strongly pathogenic strain Vd592 was inoculated into cotton, and the infected cotton roots at 36 h and 3 d post infection were subjected to dual RNA-seq analysis. For the V. dahliae, transcriptomic analysis identified 317 differentially expressed genes (DEGs) encoding classical secreted proteins, which were up-regulated at least at one time point during infection. The 317 DEGs included 126 carbohydrate-active enzyme (CAZyme) and 108 small cysteine-rich protein genes. A pectinesterase gene (VDAG_01782) belonging to CAZyme, designated as VdPE1, was selected for functional validation. VdPE1 silencing by HIGS (host-induced gene silencing) resulted in reduced disease symptoms and the increased resistance of cotton to V. dahliae. For the cotton, transcriptomic analysis found that many DEGs involved in well-known disease resistance pathways (flavonoid biosynthesis, plant hormone signaling, and plant-pathogen interaction) as well as PTI (pattern-triggered immunity) and ETI (effector-triggered immunity) processes were significantly down-regulated in infected cotton roots. The dual RNA-seq data thus potentially connected the genes encoding secreted proteins to the pathogenicity of V. dahliae, and the genes were involved in some disease resistance pathways and PTI and ETI processes for the susceptibility of cotton to V. dahliae. These findings are helpful in the further characterization of candidate genes and breeding resistant cotton varieties via genetic engineering.

Comparative genomics of Fusarium species causing Fusarium ear rot of maize.

Fusarium ear rot (FER), caused by the fungal pathogen Fusarium verticillioides, stands as one of the most economically burdensome and pervasive diseases affecting maize worldwide. Its impact on food security is particularly pronounced due to the production of fumonisins, toxic secondary metabolites that pose serious health risks, especially for livestock. FER disease severity is complex and polygenic, with few resistance (R) genes being identified for use in breeding resistant varieties. While FER is the subject of several breeding programs, only a few studies have investigated entire populations of F. verticillioides with corresponding virulence data to better understand and characterize the pathogenomics. Here, we sequenced and compared the genomes of 50 Fusarium isolates (43 F. verticillioides and 7 other Fusarium spp.) that were used to inoculate a diverse maize population. Our objectives were to elucidate the genome size and composition of F. verticillioides, explore the variable relationship between fumonisin production and visual disease severity, and shed light on the phylogenetic relationships among the isolates. Additionally, we conducted a comparative analysis of the nucleotide variants (SNPs) and the isolates' effectoromes to uncover potential genetic determinants of pathogenicity. Our findings revealed several promising leads, notably the association of certain gene groups, such as pectate lyase, with disease severity. These genes should be investigated further as putative alleles for breeding resistant maize varieties. We suggest that, beyond validation of the alleles identified in this study, researchers validate each phenotypic dataset on an individual basis, particularly if considering fumonisin concentrations and when using diverse populations. Our study underscores the importance of genomic analysis in tackling FER and offers insights that could inform the development of resilient maize cultivars. By leveraging advances in genomics and incorporating pathogen populations into breeding programs, resistance to FER can be advanced.

Mechanism of Rice Resistance to Bacterial Leaf Blight via Phytohormones.

Rice is one of the most important food crops in the world, and its yield restricts global food security. However, various diseases and pests of rice pose a great threat to food security. Among them, bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious bacterial diseases affecting rice globally, creating an increasingly urgent need for research in breeding resistant varieties. Phytohormones are widely involved in disease resistance, such as auxin, abscisic acid (ABA), ethylene (ET), jasmonic acid (JA), and salicylic acid (SA). In recent years, breakthroughs have been made in the analysis of their regulatory mechanism in BLB resistance in rice. In this review, a series of achievements of phytohormones in rice BLB resistance in recent years were summarized, the genes involved and their signaling pathways were reviewed, and a breeding strategy combining the phytohormones regulation network with modern breeding techniques was proposed, with the intention of applying this strategy to molecular breeding work and playing a reference role for how to further improve rice resistance.

Integrated Analysis of the lncRNA-miRNA-mRNA Expression Profiles in Response to Meloidogyne incognita in Radish (Raphanus sativus L.)

Radish is an important root vegetable that is widely grown in Asia. The root-knot nematode (RKN) Meloidogyne incognita seriously affects the growth and development of radish root and causes poor appearance quality. However, the molecular mechanism of radish response to RKNs remains poorly understood. In this study, a total of 220 lncRNAs, 1144 mRNAs, 20 miRNAs and 153 proteins were differential expressed between the RKN-infected and WT samples. Correlation analysis of all DEPs compared with all DGEs showed that 8 mRNAs-DEPs showed a changed abundance. The results showed that 18 DEmiRNAs have 167 target DEGs in 220 miRNA-target modules and 29 DElncRNAs were predicted as putative targets of 16 DEmiRNAs in 37 miRNA-target modules. In all, 6 DGEs in the ABA pathway and 2 DGEs in the JA pathway were identified under RKN infection, respectively. The four regulatory networks of lncRNA-miRNA-mRNA were constructed in response to RKN infection. qRT-PCR analysis found that the expression pattern of 6 DElncRNAs, 6 DEmRNAs, 6 DEmiRNAs and 6 DEPs were consistent with sequencing results. These results provide a theoretical basis for studying the molecular mechanism of radish in response to M. incognita and breeding resistant varieties to this nematode.

Pyramiding of triple Clubroot resistance loci conferred superior resistance without negative effects on agronomic traits in Brassica napus.

Clubroot disease caused by Plasmodiophora brassicae is becoming a serious threat to rapeseed (Brassica napus) production worldwide. Breeding resistant varieties using CR (clubroot resistance) loci is the most promising solution. Using marker-assisted selection and speed-breeding technologies, we generated Brassica napus materials in homozygous or heterozygous states using CRA3.7, CRA08.1, and CRA3.2 loci in the elite parental line of the Zhongshuang11 background. We developed three elite lines with two CR loci in different combinations and one line with three CR loci at the homozygous state. In our study, we used six different clubroot strains (Xinmin, Lincang, Yuxi, Chengdu, Chongqing, and Jixi) which are categorized into three groups based on our screening results. The newly pyramided lines with two or more CR loci displayed better disease resistance than the parental lines carrying single CR loci. There is an obvious gene dosage effect between CR loci and disease resistance levels. For example, pyramided lines with triple CR loci in the homozygous state showed superior resistance for all pathogens tested. Moreover, CR loci in the homozygous state are better on disease resistance than the heterozygous state. More importantly, no negative effect was observed on agronomic traits for the presence of multiple CR loci in the same background. Overall, these data suggest that the pyramiding of triple clubroot resistance loci conferred superior resistance with no negative effects on agronomic traits in Brassica napus.

QTL mapping of downy mildew resistance in foxtail millet by SLAF‑seq and BSR-seq analysis.

Key message Three major QTLs for resistance to downy mildew were located within an 0.78 Mb interval on chromosome 8 in foxtail millet. Downy mildew, a disease caused by Sclerospora graminicola, is a serious problem that jeopardizes the yield and quality of foxtail millet. Breeding resistant varieties represents one of the most economical and effective solutions, yet there is a lack of molecular markers related to the resistance. Here, a mapping population comprising of 158 F6:7 recombinant inbred lines (RILs) was constructed from the crossing of G1 and JG21. Based on the specific locus amplified fragment sequencing results, a high-density linkage map of foxtail millet with 1031 bin markers, spanning 1041.66 cM was constructed. Based on the high-density linkage map and the phenotype data in four environments, a total of nine quantitative trait loci (QTL) associated with resistance to downy mildew were identified. Further BSR-seq confirmed the genomic regions containing the potential candidate genes related to downy mildew resistance. Interestingly, a 0.78-Mb interval between C8M257 and C8M268 on chromosome 8 was highlighted because of its presence in three major QTL, qDM8_1, qDM8_2, and qDM8_4, which contains 10 NBS-LRR genes. Haplotype analysis in RILs and natural population suggest that 9 SNP loci on Seita8G.199800, Seita8G.195900, Seita8G.198300, and Seita.8G199300 genes were significantly correlated with disease resistance. Furthermore, we found that those genes were taxon-specific by collinearity analysis of pearl millet and foxtail millet genomes. The identification of these new resistance QTL and the prediction of resistance genes against downy mildew will be useful in breeding for resistant varieties and the study of genetic mechanisms of downy mildew disease resistance in foxtail millet.

Resistance response of yellow maize inbreds and F1 crosses against Philippine downy mildew [Peronosclerospora philippinensis (Weston) C.G. Shaw]

Maize is one of the world's most important staple crops, yet various pests and diseases impede its optimal production. Philippine maize downy mildew disease (PDM) caused by Peronosclerospora philippinensis (Weston) Shaw is one of the most devastating diseases in corn-growing areas in Asia. Breeding for resistant varieties is the most cost-effective and environmentally safe alternative for controlling the disease. In this study, we evaluated the resistance responses of yellow maize inbreds and hybrids against PDM to select promising genotypes for genetic analysis and varietal improvement. Resistance trials under greenhouse conditions were conducted to investigate the PDM resistance response of 14 selected CIMMYT lines (CMLs) and IPB Var 6 (susceptible check) to select potential parents prior to hybridization. CML 431 and CML 452 were identified to have significantly low disease incidence among the test genotypes. Subsequently, disease evaluation of the two inbred lines with putative DM resistance, four experimental hybrids derived from these inbred lines, and checks was performed in the field. Across three validation trials, inbred CML 431, and hybrid CML 452 × CML 431 showed degrees of resistance to PDM. This study's findings enabled the identification of resistant lines to downy mildew for the generation of mapping populations for genetic association studies, as well as the establishment of experimental units for transcriptomics research.

Synthetic modulation of ROS scavenging during host—Sclerotinia sclerotiorum interaction: a new strategy for the development of highly resistant plants

Sclerotinia sclerotiorum is a widespread fungal pathogen responsible for significant crop losses across the globe. The challenge of breeding resistant varieties is exacerbated by the fungus's sophisticated pathogenic mechanisms. A pivotal factor in the host-pathogen interaction is the regulation of reactive oxygen species (ROS) within both the fungi and the host plants. However, there is currently no efficient strategy to leverage this interaction mechanism for developing disease-resistant crop varieties. Here, we introduce an engineered ROS scavenging system designated as syn-ROS for impairing ROS neutralization in S. sclerotiorum while concurrently fortifying it in the host. The syn-ROS system comprises gene silencing constructs targeting the S. sclerotiorum Cu/Zn superoxide dismutase (SsSOD) and its copper chaperone (SsCCS), alongside overexpression constructs for the Arabidopsis thaliana AtSOD1 and AtCCS. Transgenic plants carrying the syn-ROS system demonstrated a marked enhancement in resistance to S. sclerotiorum. Upon infection, the expression of SsSOD and SsCCS was reduced, while the expression of AtSOD1 and AtCCS was enhanced in syn-ROS transgenic plants. Moreover, the infected syn-ROS plants showed decreased Cu/Zn SOD enzyme activity and elevated ROS concentrations within the fungal cells. In contrast, the cells of A. thaliana manifested increased Cu/Zn SOD enzyme activity and lowered ROS levels. Collectively, these findings suggest a novel and promising approach for contriving plants with robust resistance by synthetically manipulating ROS scavenging activities in the interaction between the host and S. sclerotiorum.

Knock-out of BnHva22c reduces the susceptibility of Brassica napus to infection with the fungal pathogen Verticillium longisporum

Verticillium longisporum (Vl43) is a soilborne hemibiotrophic fungal pathogen causing stem striping on oilseed rape (OSR) and severe yield losses. Breeding for resistant varieties is the most promising approach to control this disease. Here, we report the identification of Hva22c as a novel susceptibility factor and its potential for improving OSR resistance. Hva22c is a member of the Hva22 gene family, originally described for barley (Hordeum vulgare). Several Hva22 members have been located at the endoplasmic reticulum. Hva22c is up-regulated in response to Vl43 in both Arabidopsis and OSR. We demonstrate that knock-out of Hva22c in OSR by CRISPR/Cas9 and its homolog in Arabidopsis by T-DNA insertion reduced plants’ susceptibility toVl43infection and impaired the development of disease symptoms. To understand the underlying mechanism, we analysed transcriptomic data from infected and non-infected roots of hva22c knock-out and wild type plants. We identified a homozygous mutant with frame-shifts in all four BnHva22c loci displaying a vastly altered transcriptional landscape at 6 dpi. Significantly, a large set of genes was suppressed under mock conditions including genes related to the endomembrane systems. Among the up-regulated genes we found several defense-related and phytohormone-responsive genes when comparing mutant to the wild type. These results demonstrate that Hva22c is functionally required for a fully compatible plant-fungus interaction. Its loss of function reduces plant susceptibility, most likely due to endoplasmatic reticulum and Golgi dysfunction accompanied by additionally activated defense responses. These findings can help improve OSR resistance to V. longisporum infection.

Elucidating the role of monoacetylphlorogulcinol in the pathogenicity of Pseudomonas 'gingeri' against Agaricus bisporus.

Agaricus bisporus is a globally important edible fungus. The occurrence of ginger blotch caused by Pseudomonas 'gingeri' during A. bisporus growth and post-harvest stages results in significant economic losses. The biotoxin monoacetylphloroglucinol (MAPG) produced by P. 'gingeri' is responsible for inducing ginger blotch on A. bisporus. However, the understanding of the toxic mechanisms of MAPG on A. bisporus remains limited, which hinders the precise control of ginger blotch disease in A. bisporus and the breeding of disease-resistant varieties. Integrating transcriptomic, metabolomic, and physiological data revealed that MAPG led to an increase in intracellular superoxide anion (O2 -) levels and lipid peroxidation in A. bisporus. MAPG changed the cellular membrane composition of A. bisporus, causing to damage membrane permeability. MAPG inhibited the expression of genes associated with the 19s subunit of the proteasome, thereby impeding cellular waste degradation in A. bisporus. Unlike melanin, MAPG stimulated the synthesis of flavonoids in A. bisporus, which might explain the manifestation of ginger-colored symptoms rather than browning. Meanwhile, the glutathione metabolism pathway in A. bisporus played a pivotal role in counteracting the cytotoxic effects of MAPG. Additionally, enhanced catalase activity and up-regulation of defense-related genes, including cytochrome P450s, Major Facilitator Superfamily (MFS), and ABC transporters, were observed. This study provides comprehensive insights into MAPG toxicity in A. bisporus and uncovers the detoxification strategies of A. bisporus against MAPG. The findings offer valuable evidence for precise control and breeding of resistant varieties against ginger blotch in A. bisporus. © 2024 Society of Chemical Industry.

Mno-miR164a and MnNAC100 regulate the resistance of mulberry to Botrytis cinerea.

Although microRNAs (miRNAs) regulate the defense response of a variety of plant species against a variety of pathogenic fungi, the involvement of miRNAs in mulberry's defense against Botrytis cinerea has not yet been documented. In this study, we identified responsive B. cinerea miRNA mno-miR164a in mulberry trees. After infection with B. cinerea, the expression of mno-miR164a was reduced, which was fully correlated with the upregulation of its target gene, MnNAC100, responsible for encoding a transcription factor. By using transient infiltration/VIGS mulberry that overexpressed mno-miR164a or knocked-down MnNAC100, our study revealed a substantial enhancement in mulberry's resistance to B. cinerea when mno-miR164a was overexpressed or MnNAC100 expression was suppressed. This enhancement was accompanied by increased catalase (CAT) activity and reduced malondialdehyde (MDA) content. In addition, mno-miR164a-mediated inhibition of MnNAC100 enhanced the expression of a cluster of defense-related genes in transgenic plants upon exposure to B. cinerea. Meanwhile, MnNAC100 acts as a transcriptional repressor, directly suppressing the expression of MnPDF1.2. Our study indicated that the mno-miR164a-MnNAC100 regulatory module manipulates the defense response of mulberry to B. cinerea infection. This discovery has great potential in breeding of resistant varieties and disease control.

Screening of Sugarcane Proteins Associated with Defense against Leifsonia xyli subsp. xyli, Agent of Ratoon Stunting Disease

Sugarcane is the most important sugar crop and one of the leading energy-producing crops in the world. Ratoon stunting disease (RSD), caused by the bacterium Leifsonia xyli subsp. xyli, poses a huge threat to ratoon crops, causing a significant yield loss in sugarcane. Breeding resistant varieties is considered the most effective and fundamental approach to control RSD in sugarcane. The exploration of resistance genes forms the foundation for breeding resistant varieties through molecular technology. The pglA gene is a pathogenicity gene in L. xyli subsp. xyli, encoding an endopolygalacturonase. In this study, the pglA gene from L. xyli subsp. xyli and related microorganisms was analyzed. Then, a non-toxic, non-autoactivating pglA bait was successfully expressed in yeast cells. Simultaneously the yeast two-hybrid library was generated using RNA from the L. xyli subsp. xyli-infected sugarcane. Screening the library with the pglA bait uncovered proteins that interacted with pglA, primarily associated with ABA pathways and the plant immune system, suggesting that sugarcane employs these pathways to respond to L. xyli subsp. xyli, triggering pathogenicity or resistance. The expression of genes encoding these proteins was also investigated in L. xyli subsp. xyli-infected sugarcane, suggesting multiple layers of regulatory mechanisms in the interaction between sugarcane and L. xyli subsp. xyli. This work promotes the understanding of plant–pathogen interaction and provides target proteins/genes for molecular breeding to improve sugarcane resistance to L. xyli subsp. xyli.

Hyperspectral imaging detects biological stress of wheat for early diagnosis of crown rot disease

Crown rot, caused by a stubble-soil fungal pathogen, threatens wheat production, leading to significant yield losses. The challenge lies in the absence of early visible symptoms for timely detection and management. While hyperspectral imaging technologies have been successfully applied to improve screening for some plant health indicators and diseases, they have not yet been successfully used for crown rot disease detection. This study endeavoured to harness hyperspectral imaging technologies for early-stage, high-throughput, accurate, economical, and non-destructive detection of crown rot disease. Four common Australian commercial wheat varieties with different resistance levels were chosen for study, including Aurora, Yitpi, Emu Rock and Trojan. Three different hyperspectral cameras, covering various wavelength ranges, were tested from both side-view and top-view. Four types of input data for support vector machine classification were tested, including reflectance and the other three derived forms namely hyper-hue, standard normal variate, and principal components. The experimental results showed that hyperspectral imaging technologies can successfully diagnose infected plants in a greenhouse approximately 30 days after infection when there were no visible symptoms on shoots, and the hyper-hue and standard normal variate data transformation methods achieved high F1 scores above 0.75. By discovering key wavelengths, we found that hyperspectral imaging achieved early detection by uncovering biological stress related to photosynthetic activities, and limited absorption of water, protein and starch synthesis. These findings represent a critical advance towards establishing a hyperspectral imaging system for crown rot detection, thereby facilitating disease management and breeding resistant varieties.

The Grapevine Transcription Factor VvTGA8 Enhances Resistance to White Rot via the Salicylic Acid Signaling Pathway in Tomato

White rot, caused by Coniella vitis, is a devastating disease in grapevine (Vitis vinifera) that seriously affects yield and quality. Breeding resistant grapevine varieties is a highly economical, environmentally friendly, and effective strategy to protect against the disease; however, this strategy requires a comprehensive understanding of the genes and pathways related to resistance. In this study, we sequenced the transcriptome of V. vinifera L. cv. GF, a highly resistant variety, at six time points after C. vitis inoculation. A transcriptome analysis showed that the salicylic acid (SA) signaling pathway was activated in response to C. vitis. Transient silencing of the VvTGA8 gene in the cv. GF greatly increased susceptibility to C. vitis. Subcellular localization studies showed that the VvTGA8 gene is localized in the nucleus. Heterologous expression of VvTGA8 in Solanum lycopersicum improved resistance to C. vitis and increased levels of the SA signaling pathway marker genes SlPR1 and SlPR2 significantly. To explore the mechanism by which VvTGA8 mediates disease resistance, we silenced SlICS1, a key gene in the SA synthesis pathway, through virus-induced gene silencing to inhibit SA synthesis in a VvTGA8 overexpression line, resulting in significantly weakened resistance to C. vitis and decreased expression levels of SlPR1 and SlPR2. We conclude that VvTGA8 is involved in SA signaling pathway, which activates the expression of pathogenesis-related genes in the nucleus, thereby mediating resistance to C. vitis in grapevine. This study provides an excellent target gene for disease-resistant breeding and gene editing in grapevine.

Phosphate deficiency induced by infection promotes synthesis of anthracnose-resistant anthocyanin-3-O-galactoside phytoalexins in the Camellia sinensis plant

Abstract Tea (Camellia sinensis) is a well-known beverage crop rich in polyphenols with health benefits for humans. Understanding how tea polyphenols participate in plant resistance is beneficial to breeding resistant varieties and uncovering the resistance mechanisms. Here, we report that a Colletotrichum infection-induced ‘pink ring’ symptom appeared outside the lesion, which is highly likely to occur in resistant cultivars. By identifying morphological feature-specific metabolites in the pink ring and their association with disease resistance, and analysis of the association between metabolite and gene expression, the study revealed that the accumulation of anthocyanin-3-O-galactosides, red phytotoxin compounds resistant to anthracnose, plays a pivotal role in the hypersensitive response surrounding infection sites in tea plants. The results of genetic manipulation showed that the expression of CsF3Ha, CsANSa, CsUGT78A15, CsUGT75L43, and CsMYB113, which are involved in anthocyanin biosynthesis, is positively correlated with anthracnose-resistance and the formation of the pink ring. Further phosphorus quantification and fertilization experiments confirmed that phosphate deficiency caused by anthracnose is involved in the occurrence of the pink ring. Genetic manipulation studies indicated that altering the expression levels of Pi transporter proteins (CsPHT2-1, CsPHT4;4) and phosphate deprivation response transcription factors (CsWRKY75-1, CsWRKY75-2, CsMYB62-1) enhances resistance to anthracnose and the formation of the pink ring symptom in tea plants. This article provides the first evidence that anthocyanin-3-O-galactosides are the anthracnose-resistant phytoalexins among various polyphenols in tea plants, and this presents an approach for identifying resistance genes in tea plants, where genetic transformation is challenging.

Fine-mapping of a candidate gene for web blotch resistance in Arachis hypogaea L.

Peanut (Arachis hypogaea L.) is a globally important oil crop. Web blotch is one of the most important foliar diseases affecting peanut, which results in serious yield losses worldwide. Breeding web blotch-resistant peanut varieties is the most effective and economically viable method for minimizing yield losses due to web blotch. In the current study, a bulked segregant analysis with next-generation sequencing was used to analyze an F2:3 segregating population and identify candidate loci related to web blotch resistance. Based on the fine-mapping of the candidate genomic interval using kompetitive allele-specific PCR (KASP) markers, we identified a novel web blotch resistance-related locus spanning approximately 169 kb on chromosome 16. This region included four annotated genes, of which only Arahy.35VVQ3 had a non-synonymous single nucleotide polymorphism in the coding region between the two parents. Two markers (Chr.16.12872635 and Chr.16.12966357) linked to this gene were shown to be co-segregated with the resistance of peanut web blotch by 72 randomly selected recombinant inbred lines (RIL), which could be used in marker-assisted breeding of resistant peanut varieties.

Сравнително изпитване устойчивостта на образци фасул към склеротинийно гниене (Sclerotinia sclerotiorum) чрез директен и индиректен метод

White mold, caused by Sclerotinia sclerotiorum, is a key disease of common beans in temperate and subtropical climates. For the climatic conditions of Bulgaria, the infection occurs mainly as a result of mycelogenic development of the sclerotia, which is why the disease is observed mostly in varieties with a prostrate type of the habitus. Due to the wide range of hosts of the pathogen and long-term preservation of sclerotia in the soil, agrotechnical measures have little effect in controlling the fungus. Therefore, breeding resistant varieties are the most effective measure to prevent the disease. The selection of appropriate and verified methods for testing the source and breeding materials is of primary importance for the success of breeding programs to increase resistance to the pathogen. The present study aimed to compare the response of bean accessions to S. sclerotiorum, by applying a direct and indirect evaluation method with a view to their parallel use in the breeding process. The studies were conducted under greenhouse conditions, and 29 bean accessions were included in them. The accessions were grown in pots (45x30x10 cm) with a soil-sand mixture. In the first trifoliate leaf, the stem was cut at 3 cm from the node of the primary leaves (STAW test). A single-sided closed plastic straw containing an agar disc from the periphery of 3-day-old cultures of four isolates cultivated on PDA medium (five plants per isolate), was placed on the cut. The reaction of the accessions was recorded 7 days after inoculation on a 9-point scale. The cut plant parts (stem and trifoliate leaf) were immersed in oxalic acid solution (20 mM brought to pH=4.0 with 1N NaOH), five plants per sample. The cut plant parts immersed in sterile water adjusted to pH=4.0 with 1N HCl were used for the control. The reaction of the accessions was recorded after 19h on a 9-point scale. The data were processed with the SPSS stat. ver. 19 software. Significant differences were observed in the response of the accessions concerning the isolates used. Weak positive or negative correlations were found between the oxalate test and the STRAW test, and the direction was related to the aggressiveness of the isolates. It was established that for accessions A195, ‘GTB Scythia’, ‘Izabel’, ‘Rhodopeia’ and ‘Pirina’ the results of the oxalic test are comparable to those of the STRW-test. The obtained results give us reason to recommend the application of the oxalate test in the initial generations of the breeding materials, after a preliminary comparative analysis of the parental forms by both methods.

Integrated genome-wide association study and QTL mapping reveals qSa-3A associated with English grain aphid, Sitobion avenae (Fabricius) resistance in wheat.

The English grain aphid, Sitobion avenae (Fabricius), is a devastating pest impacts yield and quality in wheat (Triticum aestivum L.). Breeding resistant wheat varieties and detecting resistance genes are important strategies to control aphid. In this study, we evaluated the number of aphids per spike, the rate of thousand kernel weight decrease and aphid index based on three classic resistance mechanisms (antibiosis, tolerance and antixenosis), and detected SNPs/QTLs for resistance to S. avenae in a natural population of 163 varieties with 20,689 high-quality single-nucleotide polymorphism (SNP) markers and recombinant inbred line (RIL) population of 164 lines with 3,627 diversity arrays technology (DArT) markers. Results showed that 83 loci significantly associated with S. avenae antibiosis and 182 loci significantly associated with S. avenae tolerance were detected by genome-wide association study (GWAS), explaining 6.47-15.82% and 8.36-35.61% of the phenotypic variances, respectively. The wsnp_Ku_c4568_8243646 detected in two periods was localized at 34.52 Mb on chromosome 3AS. Then, we confirmed a stable QSa.haust-3A.2 explained 11.19-20.10% of the phenotypic variances in two periods with S. avenae antixenosis in the physical interval of 37.49-37.50 Mb on chromosome 3A in the RIL population. Therefore, a narrow region in the physical interval of 34.52-37.50 Mb on chromosome 3AS was named as qSa-3A, which was a new locus between wsnp_Ku_c4568_8243646 and QSa.haust-3A.2 associated with S. avenae resistance. We found qSa-3A was a new locus associated with S. avenae resistance. The results could be applied in gene cloning and genetic improvement of S. avenae resistance in wheat.

Combined analysis of metabolome and transcriptome of wheat kernels reveals constitutive defense mechanism against maize weevils.

Sitophilus zeamais (maize weevil) is one of the most destructive pests that seriously affects the quantity and quality of wheat (Triticum aestivum L.). However, little is known about the constitutive defense mechanism of wheat kernels against maize weevils. In this study, we obtained a highly resistant variety RIL-116 and a highly susceptible variety after two years of screening. The morphological observations and germination rates of wheat kernels after feeding ad libitum showed that the degree of infection in RIL-116 was far less than that in RIL-72. The combined analysis of metabolome and transcriptome of RIL-116 and RIL-72 wheat kernels revealed differentially accumulated metabolites were mainly enriched in flavonoids biosynthesis-related pathway, followed by glyoxylate and dicarboxylate metabolism, and benzoxazinoid biosynthesis. Several flavonoids metabolites were significantly up-accumulated in resistant variety RIL-116. In addition, the expression of structural genes and transcription factors (TFs) related to flavonoids biosynthesis were up-regulated to varying degrees in RIL-116 than RIL-72. Taken together, these results indicated that the biosynthesis and accumulation of flavonoids contributes the most to wheat kernels defense against maize weevils. This study not only provides insights into the constitutive defense mechanism of wheat kernels against maize weevils, but may also play an important role in the breeding of resistant varieties.

Plant resistance to pests and diseases: potency in coconut

Plant resistance to pests and diseases help avoid, tolerate or recover from an injury that would cause greater damage to plants of the same species under similar environmental conditions. In coconut, resistant traits are generally acquired traits against pests and diseases in conventional breeding programs and indirectly through the application of nutrients. The paper provides a list of existing resistant or tolerant coconut varieties reported against key pests and diseases. The use of resistant coconut varieties as part of the integrated pest management toolbox is considered to be an effective medium to long-term strategy. Thus, it is anticipated that resistant varieties will become increasingly important as a component of the IPM toolbox as we encounter invasive species and face the vagaries of climate change. This strategy may also be helpful for managing diseases caused by phytoplasmas. The paper alluded to a number of challenges faced in breeding resistant coconut varieties and the strategies for deploying them. The future projects interesting prospects for resistant variety development that are underpinned by the use of biotechnological tools such as Resistance Gene Analogues (RGAs) and Eco-TILLING and supported by advances in tissue culture and micropropagation that could be used to expedite conventional breeding programs.