Susceptible Parent Research Articles

Identification and mapping of genetic locus conferring resistance to multiple plant viruses in soybean.

A reliable locus confers broad-spectrum resistance to multiple plant viruses in soybean under field conditions. Soybean mosaic disease (SMD) can be caused by a variety of viruses, most of which have been largely overlooked in breeding programs. Effective mitigation of the adverse of SMD might result from breeding cultivars with broad-spectrum resistance. However, reports on broad-spectrum resistance to multiple virus have been limited. To catalog viral community members behind SMD, virus samples were collected from symptomatic field plots, and pathogenicity of component strains was assessed. Preliminary ELISA and PCR detection revealed that 39.58% and 66.67% of samples contained two or more virus strains, respectively. Only three soybean accessions were completely asymptomatic, while 42% exhibited moderate or severe susceptibility, indicating that co-infection of multiple virus remains a significant threat in current soybean production systems. Further, a RIL population consisting of 150 F7:9 strains derived from two soybean genotypes with contrasting reactions to virus infection was constructed and explored for significant markers and resistance genes. QTL analysis returned a reliable locus, named GmRmv, on chromosome 13. Significance of GmRmv in imparting resistance to SMD was further confirmed in NIL lines and delimited into a 157-kb interval that contains 17 annotated genes. Among these genes, three, Glyma.13G190000, Glyma.13G190300 and Glyma.13G190400, each contained LRR domains, as well as significant variation in coding sequences between resistant and susceptible parents. Hence, these three genes are considered strong candidate genes for explaining GmRmv significance. In summary, this research opens a new avenue for formulating strategies to breed soybean varieties with broad-spectrum resistance to multiple virus associated with SMD.

Fine mapping and candidate gene analysis of gummy stem blight resistance in cucumber stem.

Two candidate genes (Csa6G046210 and Csa6G046240) were identified by fine-mapping gsb-s6.2 for gummy stem blight resistance in cucumber stem. Gummy stem blight (GSB) is a serious fungal disease caused by Didymella bryoniae, that affects cucumber yield and quality worldwide. However, no GSB-resistant genes have been identified in cucumber cultivars. In this study, the wild cucumber accession 'PI 183967' was used as a source of resistance to GSB in adult stems. An F2 population was mapped using resistant line 'LM189' and susceptible line 'LM6' derived from a cross between 'PI 183967' and '931'. By developing InDel and SNP markers, the gsb-s6.2 QTL on Chr. 6 was fine-mapped to a 34kb interval harboring six genes. Gene Expression analysis after inoculation showed that two candidate genes (Csa6G046210 and Csa6G046240) were induced and differentially expressed between the resistant and susceptible parents, and may be involved in disease defense. Sequence alignment showed that Csa6G046210 encodes a multiple myeloma tumor-associated protein, and it harbored two nonsynonymous SNPs and one InDel in the third and the fourth exons, and two InDels in the TATA-box of the basal promoter region. Csa6G046240 encodes a MYB transcription factor with six variants in the AP2/ERF and MYB motifs in the promoter. These two candidate genes lay the foundation for revealing the mechanism of GSB resistance and may be useful for marker-assisted selection in cucumber disease-resistant breeding.

Screening Technique Based on Seed and Early Seedling Parameters for Cold Tolerance of Selected F2-Derived F3 Rice Genotypes under Controlled Conditions

The cold tolerance studies were carried out in a bi-parental F2 population of a cross between tolerant and susceptible parents (SKUA-529 and HEERA, respectively). The purpose was to screen the individuals of a population for primary cold-tolerance-related attributes. The information generated has a direct application and use in identifying cold tolerance quantitative trait loci (QTLs) and further can be used for genotyping with an appropriate marker system. The screening was carried out on F2-derived F3 seeds and F3 plants for seedling and agronomic traits, respectively. Two tests measuring cold tolerance were conducted. In experiment I, seeds were germinated for 28 days at 13 °C and 7 days at 28 °C, and in experiment II, the seeds were germinated for 72 h at 28 °C, 96 h at 13 °C, and once more for 72 h at 28 °C. Coleoptile length, germination percentage, and radical reduction percentages were all measured in experiment I. The radicle and coleoptile regeneration in experiment II were measured after the cold period. The improvement in cold tolerance was achieved through radicle regrowth, as evidenced by the difference between the second and first measurements. The individual lines from the F2:3 population that recorded high germination (%) were #21, #13, #14, and #15. The percentage of coleoptile length (PERCOL %) was observed to be between the ranges of 23.33% to 53.00%. The reduction in coleoptile length (REDCOL %) was also obtained, and there was less reduction in #15, #16, and #14 and it had a range between 38.46% and 75%. Radicle regrowth (REDRAG) was high at 13 °C in #7, #11, #30, #35, and #36. Survival of the seedling range was between 33.33% and up to 100%, and the highest survival rate was observed in #16. The main objective of this rotation in temperature was to emulate field conditions where there has been a drop in temperature. The evaluations were done for primary cold stress tolerance traits, and it was found that most of these traits exhibited high variability. The mapping population developed may be utilized to generate a linkage map and locate QTLs for tolerance to cold stress in rice. Further, the identified donors for cold tolerance may be utilized for breeding programs aimed at the transfer of low-temperature stress tolerance into susceptible backgrounds. In general, a genotype with improved seedling germination rates, growth rates, and leaf yellowing scores; high seedling survival; lesser reduction in coleoptile length and in radicle development; and recovery following a cold shock at the seedling stage demonstrated its cold resistance. Genotypes with a low germination percentage, a greater number of days to germination, slow growth rate and higher leaf yellowing score, high reduction in coleoptile and radicle growth, and reduced seedling survival indicated cold susceptibility.

Transcriptome Profiling Reveals Molecular Players in Early Soybean–Sclerotinia sclerotiorum Interaction

Sclerotinia sclerotiorum causes Sclerotinia stem rot on soybean. Using RNA sequencing, the transcriptomes of the soybean host and the S. sclerotiorum pathogen were simultaneously determined at 4 and 8 h postinoculation (hpi). Two soybean genotypes were involved: a resistant oxalate oxidase (OxO)-transgenic line and its susceptible parent, AC Colibri (AC). Of the 594 genes that were significantly induced by S. sclerotiorum, both hosts expressed genes related to jasmonic acid, ethylene, oxidative burst, and phenylpropanoids. In all, 36% of the differentially expressed genes encoded genes associated with transcription factors, ubiquitination, or general signaling transduction such as receptor-like kinases, mitogen-activated protein kinase kinases, and hormones. No significant differentially expressed genes were identified between genotypes, suggesting that oxalic acid (OA) did not play a differential role in early disease development or primary lesion formation under the conditions used. Looking at pathogen behavior through its gene expression during infection, thousands of genes in S. sclerotiorum were induced at 8 hpi, compared with expression in culture. Many plant cell-wall-degrading enzymes (PCWDEs), sugar transport genes, and genes involved in secondary metabolism were upregulated and could contribute to early pathogenesis. When infecting the OxO plants, there was a higher induction of genes encoding OA, botcinic acid, PCWDEs, proteases, and potential effectors, revealing the wealth of virulence factors available to this pathogen as it attempts to colonize a host. Data presented identify hundreds of genes associated with the very early stages of infection for both the host and pathogen.

Fine Mapping and Characterization of an Aphid-Resistance Gene in the Soybean Landrace Fangzheng Moshidou.

The soybean aphid poses a severe threat to soybean quality and yield by sucking phloem sap and transmitting plant viruses. An early-maturing and highly resistant soybean landrace, Fangzheng Moshidou, with markedly reduced aphid colonization has been identified by screening of aphid-resistant soybean accessions. In a population derived from the cross of Fangzheng Moshidou with the susceptible cultivar Beifeng 9, resistance was conferred by a single dominant gene. Three linked markers, Satt114, Satt334, and Sct_033, on chromosome 13 were identified by bulked-segregant analysis. Additional simple-sequence repeat and single-nucleotide polymorphism (SNP) markers were developed for gene mapping. The resistance of Fangzheng Moshidou was fine-mapped to the interval between the SNP markers YCSNP20 and YCSNP80, corresponding to 152.8 kb in the Williams 82 assembly 2 genome. This region was near the reported loci Rag2 and Rag5 but did not overlap the interval containing them. A unique haplotype is described for Fangzheng Moshidou that distinguishes it from soybean accessions PI 587972, PI 594879, and PI 567301B in the interval containing Rag2 and Rag5. These results indicate that Fangzheng Moshidou harbors a novel gene at a tightly linked resistance locus, designated as RagFMD. Fourteen candidate genes were annotated in the fine-mapping region, including seven NBS-LRR genes, which are usually considered resistance genes in plant defense. Most of these candidate genes showed variations distinguishing the resistant and susceptible parents and some genes also showed differences in expression between the two parental lines and at several times after aphid infestation. Isolation of RagFMD would advance the study of molecular mechanisms of soybean aphid resistance and contribute to precise selection of resistant soybeans.

Phenotypic Screening of F3 Rice (Oryza sativa L.) Population Resistance Associated with Sheath Blight Disease

The experiment was conducted during July–December, 2019 in the Agricultural Research Farm Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India. One hundred and twenty-two F3 rice populations from the cross made between IC277332 (susceptible parent)×IC277275 (moderately resistant parent) were evaluated against sheath blight disease under field conditions. The area under disease progress curve (AUDPC) values categorized rice population into four groups viz., moderately resistant (24), moderately susceptible (38), susceptible (40), and highly susceptible (20). A moderate resistance level to the disease was identified during the study in 24 lines (19.6%) with a mean Percentage Disease Index (PDI) of 12.22%−36.6%. Furthermore, 38 individuals showed moderate susceptibility with AUDPC values (1012−1446 day-1). The maximum PDI and AUDPC value were 76.11 and 2325.56, and the minimum PDI and AUDPC values were 22.78 and 622.22, respectively. The principal component (PCA) biplot analysis showed 71.62% and 12.05% variation, respectively. Unweighted Pair Group Method of Arithmetic Means (UPGMA) cluster analysis grouped the 122 individuals into two major clusters, A and B and sub-clusters. These findings indicated that no rice line resistant to sheath blight had been identified. However, few population lines exhibited moderate resistance, which can be utilized as donor lines to generate sheath blight-resistant rice cultivars. These findings will provide a solid basis for our future breeding and screening activities at the institution.

Late Blight Resistance Conferred by Rpi-Smira2/R8 in Potato Genotypes In Vitro Depends on the Genetic Background

Potato production worldwide is threatened by late blight, caused by the oomycete Phytophthora infestans (Mont.) de Bary. Highly resistant potato cultivars were developed in breeding programs, using resistance gene pyramiding methods. In Sárpo Mira potatoes, five resistance genes (R3a, R3b, R4, Rpi-Smira1, and Rpi-Smira2/R8) are reported, with the latter gene assumed to be the major contributor. To study the level of late blight resistance conferred by the Rpi-Smira2/R8 gene, potato genotypes with only the Rpi-Smira2/R8 gene were selected from progeny population in which susceptible cultivars were crossed with Sárpo Mira. Ten R8 potato genotypes were obtained using stepwise marker-assisted selection, and agroinfiltration of the avirulence effector gene Avr4. Nine of these R8 genotypes were infected with both Slovenian P. infestans isolates and aggressive foreign isolates. All the progeny R8 genotypes are resistant to the Slovenian P. infestans isolate 02_07, and several show milder late blight symptoms than the corresponding susceptible parent after inoculation with other isolates. When inoculated with foreign P. infestans isolates, the genotype C571 shows intermediate resistance, similar to that of Sárpo Mira. These results suggest that Rpi-Smira2/R8 contributes to late blight resistance, although this resistance is not guaranteed solely by the presence of the R8 in the genome.

Genome-based high-resolution mapping of fusarium wilt resistance in sweet basil

Fusarium wilt of basil is a disease of sweet basil (Ocimum basilicum L.) plants caused by the fungus Fusarium oxysporum f. sp. basilici (FOB). Although resistant cultivars were released > 20 years ago, the underlying mechanism and the genes controlling the resistance remain unknown. We used genetic mapping to elucidate FOB resistance in an F2 population derived from a cross between resistant and susceptible cultivars. We performed genotyping by sequencing of 173 offspring and aligning the data to the sweet basil reference genome. In total, 23,411 polymorphic sites were detected, and a single quantitative trait locus (QTL) for FOB resistance was found. The confidence interval was < 600 kbp, harboring only 60 genes, including a cluster of putative disease-resistance genes. Based on homology to a fusarium resistance protein from wild tomato, we also investigated a candidate resistance gene that encodes a transmembrane leucine-rich repeat – receptor-like kinase – ubiquitin-like protease (LRR-RLK-ULP). Sequence analysis of that gene in the susceptible parent vs. the resistant parent revealed multiple indels, including an insertion of 20 amino acids next to the transmembrane domain, which might alter its functionality. Our findings suggest that this LRR-RLK-ULP might be responsible for FOB resistance in sweet basil and demonstrate the usefulness of the recently sequenced basil genome for QTL mapping and gene mining.

High-Density Linkage Mapping and Identification of Quantitative Trait Loci Associated with Powdery Mildew Resistance in Flowering Dogwood (Cornus florida)

Flowering dogwood (Cornus florida L.) is a popular, spring-blooming ornamental tree native to the eastern United States. The species is in general very susceptible to powdery mildew caused by Erysiphe pulchra, which disfigures leaves, decreases growth, and negatively affects flowering. Breeding for resistance has been recognized as an ideal strategy for controlling the disease in C. florida, but efforts have been hindered by the rarity of PM resistance in available germplasm and knowledge of its genetic control. In this study, we mapped quantitative trait loci (QTL) associated with PM resistance/tolerance in two full sibling populations segregating for PM response: Rutgers H4AR15P25 (P25) × Rutgers H4AR15R28 (P28) (n = 195) and Rutgers H4AR15R25 × Rutgers H4AR15P35 (P35) (n = 83). High-density genetic linkage maps were constructed for the mapping populations using double digest restriction-site associated DNA sequencing-derived single nucleotide polymorphisms (SNPs) and simple sequence repeats (SSRs). The P25 × P28 map consisted of 2265 markers, spanning 1520 cM and 11 linkage groups (LGs) with an average marker spacing of 0.69 cM. The P25 × P35 map was constructed with 1788 markers, spanning 1256 cM and 11 LGs, with an average marker spacing of 0.72 cM. The maps had 604 markers in common and exhibited excellent collinearity. Through multiple QTL model mapping, one major QTL (LOD = 11.36 and R2 = 58.9%) was identified in P25 × P35. Furthermore, a minor QTL (LOD = 3.30 and R2 = 7.8%) was detected in P25 × P28. Due to their proximity onLG3, these QTL may be designating the same locus or tightly linked loci. The negative additive effects of both QTL signify that the PM susceptible male parents were contributing susceptibility alleles to the progeny. This is the first report of QTL associated with PM response on LG3 in C. florida and lays the groundwork for the development of marker-assisted selection for PM resistance in C. florida breeding programs.

Bruchid Resistance Study through Bulked Segregant Analysis: Used as a Preliminary Step for Next-Generation Sequencing

Seed beetles, commonly known as bruchids, are serious insect pests of Indian pulses inflicting high damage during storage. Earlier, a bruchid resistant rice bean landrace (TNAU Red) from Manipur and a susceptible mung bean variety (VRMGg1) from Tamil Nadu were reported and their inter-specific cross was made in Tamil Nadu Agricultural University. In the present study, seeds from the segregating populations (recombinant inbred lines, RILs) of VRM (Gg)1 and TNAU Red were evaluated for bruchid Callosobruchus maculatus Fabricius resistance following standard methods under laboratory conditions. Bulked segregant analysis (BSA) is an efficient method for quick identification of molecular markers linked to any specific gene or genomic region. BSA significantly reduces the scale and cost by simplifying the procedure compared to conventional method of analyzing the entire population. BSA was carried out using 3 marker systems with an attempt to identify markers associated with the present trait of interest. Two DNA bulks namely resistant bulk (RB) and susceptible bulk (SB) were grouped by pooling equal amount of DNA from 5 each of resistant and susceptible RILs based on bruchid responses such as seed damage (%), mean developmental days (MDP) and adult emergence from seeds. Marker analysis carried out with 41 polymorphic SSRs showed skewed segregation distortion towards the susceptible parent. However, out of 9 RAPDs and 10 ISSRs, 2 RAPD (OPB08 and OPX04) and 1 ISSR (UBC810) primers amplified an allele at 200 - 300 and 300 - 400 bp, respectively, in resistant parent and resistant bulk but not in susceptible parent and susceptible bulk. The amplification of resistant parent allele in resistant bulk may indicate the presence of bruchid resistant gene(s) in the resistant RILs. This experiment was aimed at verifying the presence of bruchid resistant lines carrying resistant gene(s) prior to further association mapping or QTL mapping studies. Further, such type of study can be applied as a preliminary step in NGS technology.&#x0D; HIGHLIGHTS&#x0D; &#x0D; Bruchids are the most damaging storage insect in pulses and other legumes causing great economic losses&#x0D; Bulk segregant analysis (BSA) conducted using three marker systems in an attempt to identify markers associated with bruchid resistance&#x0D; Categorization of RILs based on bruchid responses such as seed damage (%), mean developmental days (MDP), adult emergence from seeds and scoring done&#x0D; Marker analysis using BSA useful for verification of the presence of bruchid resistant lines carrying resistant gene(s) prior to further advanced studies such as QTL mapping, NGS, etc.&#x0D; &#x0D; GRAPHICAL ABSTRACT

Genomic regions linked to reniform nematode (Rotylenchulus reniformis) resistance in castor

Reniform nematode (Rotylenchulusreniformis) infects castor and makes it vulnerable to vascular wilt and root rot diseases. In this study, a population consisting of 92 recombinant inbred lines (RILs) derived from the cross between reniform nematode resistant line JC-12 and susceptible line 48-1 was used to identifythe genomic regions linked to reniform nematode resistance. The parents, F1 and RILs were screened against reniform nematode in pot culture with artificial inoculation of nematodes. The scoring for nematode resistance was done on the basis of number of nematodes extracted from the soil at 60 days after inoculation. The mean nematode count in 48-1 and JC-12 was 215.0±9.1 and 77.8±4.8 nematodes/ml of soil wash, respectively. The F1 reaction (217.3±13.2 nematodes/ml of soil wash) was similar to the susceptible parent indicating that nematode resistance in JC-12 is recessive in nature. The nematode count in RILs ranged from 43.8 to 327.3. QTL mapping using a linkage map consisting of 1,090 SNP markers resulted in the identification one QTLeach on chromosome-6 and chromosome-8, linked to resistance. This is the first report on mapping of genomic regions linked to reniform nematode resistance in castor, which form the basis for furthering the research on genetic and molecular biology of nematode resistance in castor.

SNP Discovery Using BSR-Seq Approach for Spot Blotch Resistance in Wheat (Triticum aestivum L.), an Essential Crop for Food Security.

The pathogenic fungus, Bipolaris sorokiniana, that causes spot blotch (SB) disease of wheat, is a major production constraint in the Eastern Gangetic Plains of South Asia and other warm, humid regions of the world. A recombinant inbred line population was developed and phenotyped at three SB-prone locations in India. The single nucleotide polymorphism (SNP) for SB resistance was identified using a bulked segregant RNA-Seq-based approach, referred to as “BSR-Seq.” Transcriptome sequencing of the resistant parent (YS#24), the susceptible parent (YS#58), and their resistant and susceptible bulks yielded a total of 429.67 million raw reads. The bulk frequency ratio (BFR) of SNPs between the resistant and susceptible bulks was estimated, and selection of SNPs linked to resistance was done using sixfold enrichments in the corresponding bulks (BFR >6). With additional filtering criteria, the number of transcripts was further reduced to 506 with 1055 putative polymorphic SNPs distributed on 21 chromosomes of wheat. Based on SNP enrichment on chromosomal loci, five transcripts were found to be associated with SB resistance. Among the five SB resistance-associated transcripts, four were distributed on the 5B chromosome with putative 52 SNPs, whereas one transcript with eight SNPs was present on chromosome 3B. The SNPs linked to the trait were exposed to a tetra-primer ARMS-PCR assay, and an SNP-based allele-specific marker was identified for SB resistance. The in silico study of these five transcripts showed homology with pathogenesis-related genes; the metabolic pathway also exhibits similar results, suggesting their role in the plant defense mechanism.

EVALUATION OF THE EFFICIENCY OF GENOMIC SELECTION APPROACH FOR PREDICTING SHEATH BLIGHT RESISTANCE IN RICE (ORYZA SATIVA L.) USING BAYESIAN MODELS

sheath blight (ShB) is one of the most serious fungal diseases caused by Rhizoctonia solani, instigating significant yield losses in many rice-growing regions of the world. Intensive studies indicated that resistance for sheath blight is controlled possibly by polygenes. Because of complex inheritance, it’s very difficult to exploit and tap all the genomic regions conferring resistance using classical approaches of quantitative trait loci (QTL) mapping, it’s very important to have a planned strategy to harness such resistance mechanism. One of the most promising approach is genomic selection (GS). The research was undertaken with an objective to validate genomic selection approach for predicting sheath blight resistance involving 1545 Recombinant inbred lines (RILs) derived from eleven bi-parental populations from crosses between resistant and susceptible parents. Where, Jasmine 85, Tetep and MTU 9992 were resistant parents and TN1, Swarna Sub1, II32B, IR54 and IRBB4 were susceptible parents. During rainy season (2020) the F7 recombinant inbred lines (RIL) were screened for their reaction to sheath blight in two hot spot locations. The genotyping was done with Illumina platform having 6564 SNP markers. Three Bayesian models were used, Bayesian A, Bayesian B and Bayesian CPi to train the statistical model for calculation of marker effects and genomic estimated breeding values (GEBV). The prediction accuracy of training set across models ranged from 0.69 to 0.72, lowest and highest prediction accuracies were observed with Bayesian A and Bayesian B models respectively and the average prediction accuracy of tenfold cross validation with different models was 0.60. Bayesian B model exhibited higher prediction accuracies compared to other models studied. The results are lucrative, all in all, higher prediction accuracies across the models studied suggest genomic selection as a promising breeding strategy for predicting sheath blight resistance in Rice.

Evaluation of F2:3 rice population resistant to Rhizoctonia solani Kuhn inciting sheath blight disease

Rice sheath blight caused by the soil-borne fungal pathogen Rhizoctonia solani Kuhn is an economically important disease in rice resulting in enormous yield losses worldwide. In the present investigation, a population constituting F3 lines resulted from the cross made between IC277332 (susceptible parent) and Tetep (resistant parent) were evaluated for sheath blight resistance and other agronomic traits over a season. The rice population lines were categorized into four groups viz., moderately resistant (11), moderately susceptible (63), susceptible (24), and highly susceptible (8), based on area under disease progress curve (AUDPC) values. During the study, nine moderate resistant lines showed, less AUDPC values in comparison to Tetep. Furthermore, 63 individuals (60%) exhibited moderate susceptibility with AUDPC values (677-987 per day). The principal component biplot analysis PC1 and PC2 showed 47.08% and 13.19% variation, respectively. The employment of Unweighted Pair Group Method of Arithmetic Means (UPGMA) cluster analysis led to the grouping of the 106 individuals into 2 major clusters A and B. The results suggested that none of the rice lines was resistant to sheath blight disease. However, few lines showed moderate resistance to the disease which can be exploited for the development of sheath blight-resistant cultivars.

Combining Ability and Gene Action Controlling Chocolate Spot Resistance and Yield Traits in Faba Bean (Vicia faba L.)

Chocolate spot disease devastatingly impacts faba bean growth and productivity. Thenceforth, genetic study of chocolate spot resistance and yield traits is crucial to conceive appropriate strategies for breeding and sustaining faba bean production particularly under abrupt climate change and fast-growing global population. The current study was performed to identify promising resistant and high-yielding progenies, to study the mode of inheritance for chocolate spot resistance and yield traits using half diallel mating design, and to investigate the association between seed yield and its attributes traits under conditions of chocolate spot disease.Two resistant (Nubaria-1and Sakha-1) and two susceptible (Tribe-White and Camolina) parents previously characterized were used to generate six F1 hybrids which were selfed to produce F2 progenies. The parents and their F1 and F2 were evaluated at hot-spot location for chocolate spot disease. Significant variation was detected for chocolate spot resistance and yield traits among the evaluated parents and their cross combinations in both generations. The general (GCA) and specific (SCA) combining ability effects were highly significant for chocolate spot severity and yield traits in both generations. From the results, it is noteworthy that the cross combinations of P1(Nubaria-1)×P2(Sakha-1), P1×P4(Camolina) and P2×P3(Tribe-white) displayed constant performance through both generations (F1 and F2) with high-yielding and resistance to chocolate spot. Consequently, these crosses could be promising combinations for increasing seed yield, and resistance to chocolate spot in breeding programs of faba bean. The additive gene effect was predominant for chocolate spot resistance, plant height, days to flowering, number of branches per plant and 100-seed weight in both generations. Accordingly, selection could be effective to improve these traits in early generations. By contrast, the non-additive gene effects were preponderant for seed yield per plant, number of seeds per plant and number of pods per plant. This suggests the importance of transgressive segregation for improving these traits through breeding programs. While selection for improving these traits could be less effective in the segregated generations which should be postponed to advanced generations. A strong positive association was identified between seed yield per plant and each of number of branches per plant, 100-seed weight, plant height, days to flowering, number of pods per plant and number of seeds per plant. This signifies their significance as vital attributes for indirect selection, especially in the early generations due to their ease of evaluation in comparison with seed yield. On the contrary, linear regression analysis revealed a steeply inverse relationship between seed yield and chocolate spot disease in both generations.

Molecular Characterization of Genomic Regions for Adult Plant Resistance to Stem Rust in a Spring Wheat Mapping Population.

Adult plant resistance (APR) to wheat stem rust has been one of the approaches for resistance breeding since the evolution of the Ug99 race group and other races. This study was conducted to dissect and understand the genetic basis of APR to stem rust in spring wheat line 'Copio'. A total of 176 recombinant inbred lines (RILs) from the cross of susceptible parent 'Apav' with Copio were phenotyped for stem rust resistance in six environments. Composite interval mapping using 762 genotyping-by-sequencing markers identified 16 genomic regions conferring stem rust resistance. Assays with gene-linked molecular markers revealed that Copio carried known APR genes Sr2 and Lr46/Yr29/Sr58 in addition to the 2NS/2AS translocation that harbors race-specific genes Sr38, Lr37, and Yr17. Three quantitative trait loci (QTLs) were mapped on chromosomes 2B, two QTLs on chromosomes 3A, 3B, and 6A each, and one QTL on each of chromosomes 2A, 1B, 2D, 4B, 5D, 6D, and 7A. The QTL QSr.umn.5D is potentially a new resistance gene and contributed to quantitative resistance in Copio. The RILs with allelic combinations of Sr2, Sr38, and Sr58 had 27 to 39% less stem rust coefficient of infection in all field environments compared with RILs with none of these genes, and this gene combination was most effective in the U.S. environments. We conclude that Copio carries several genes that provide both race-specific and non-race-specific resistance to diverse races of stem rust fungus and can be used by breeding programs in pyramiding other effective genes to develop durable resistance in wheat.

Genetic dissection of the powdery mildew resistance in wheat breeding line LS5082 using BSR-Seq

Powdery mildew of wheat is a destructive disease seriously threatening yield and quality worldwide. Comprehensive dissection of new resistance-related loci/genes is necessary to control this disease. LS5082 is a Chinese wheat breeding line with resistance to powdery mildew. Genetic analysis, using the populations of LS5082 and three susceptible parents (Shannong 29, Shimai 22 and Huixianhong), indicated that a single dominant gene, tentatively designated PmLS5082, conferred seedling resistance to different Blumeria graminis f. sp. tritici (Bgt) isolates. Bulked segregant RNA-Seq was carried out to map PmLS5082 and to profile differentially expressed genes associated with PmLS5082. PmLS5082 was mapped to a 0.7 cM genetic interval on chromosome arm 2BL, which was aligned to a 0.7 Mb physical interval of 710.3–711.0 Mb. PmLS5082 differs from the known powdery mildew (Pm) resistance genes on chromosome arm 2BL based on their origin, chromosome positions and/or resistance spectrum, suggesting PmLS5082 is most likely a new Pm gene/allele. Through clusters of orthologous groups and kyoto encyclopedia of genes and genomes analyses, differentially expressed genes (DEGs) associated with PmLS5082 were profiled. Six DEGs in the PmLS5082 interval were confirmed to be associated with PmLS5082 via qPCR analysis, using an additional set of wheat samples and time-course analysis post-inoculation with Bgt isolate E09. Ten closely linked markers, including two kompetitive allele-specific PCR markers, were confirmed to be suitable for marker-assisted selection of PmLS5082 in different genetic backgrounds, thus can be used to detect PmLS5082 and pyramid it with other genes in breeding programs.

Genetic variance and heritability estimation of hybridized pepper plants (Capsicum annuum L.) F2 progeny for begomovirus resistance in growth stage

Pepper is widely cultivated as a condiment and cash crop in Indonesia. However, Pepper yellow leaf curl disease (PepYLCD) caused by begomovirus is currently seriously affect the domestic pepper production. Breeding for begomovirus resistance material by crossing is currently necessary to overcome the constraint. The present study is aimed to determine the resistance of pepper (C. annuum) plants F2 progenies to begomovirus infection in the growth stage. Two local C. annuum accessions, BaPep-5 as a resistance donor for pepy-1 begomovirus resistance gene (locally called Perintis) and BaPep-4 as a susceptible parent (locally called Kencana) were crossed to generate F2 progenies. The research was conducted in Agricultural Extension Training Centre (BLPP) Saree and Horticulture Laboratory of Syiah Kuala University from February to July 2020. 500 F2 progenies were transplanted to the field along with 15 plants of each parent as control. The result suggested that plant height and crown width had the highest broad sense heritability value, whereas the dichotomous height, stem diameter, secondary branch, and tertiary branch had the lowest broad sense heritability value. Coefficient of genetic variance and coefficient of phenotypic variance from overall characteristics were relatively low which suggest the narrow sense to slightly narrow sense heritability.

Inheritance of resistance to damping-off (Rhizoctonia solani) in watermelon

This study aimed to find sources of resistance to damping-off and to determine the inheritance of resistance in watermelon. Firstly, 72 watermelon accessions were inoculated with CMM 1053 isolate of Rhizoctonia solani. Only two accessions (BGH 29 and BGH 76) were considered moderately resistant to the disease. The inoculated plants without symptoms from accession BGH-29 identified as resistant were self-fertilized and the inbred line S1 was used for the crosses. The reaction to R. solani after inoculation of the segregating populations of the cross and backcrosses between susceptible cultivar Crimson Sweet and the inbred line BGH-29 was evaluated. In other experiment eight S1 lines of watermelon were inoculated with six different isolates of R. solani and the reaction was evaluated by partial diallel analysis using the Griffing’s method IV to obtain estimates of general resistance ability (GRA), general aggressiveness ability (GAA), and specific interaction ability (SIA). According to ratings of the susceptible and resistant parents, generations F1, F2, BC1 (F1 × P1) and BC2 (F1 × P2), resistance to damping-off was conferred by at least nine genes with additive effect and low heritability which indicates polygenic inheritance. The results of the diallel analysis corroborate with the analysis of segregating population, indicating inheritance of resistance was horizontal, since 46.1% of the total sum of squares of the variation observed in the crosses was due to GRA, while the SIA corresponded to only 20.39% of variation. This is the first report about inheritance of resistance to damping-off caused by R. solani in watermelon.

Identification and Fine-Mapping of a Novel QTL, qMrdd2, That Confers Resistance to Maize Rough Dwarf Disease.

Maize rough dwarf disease (MRDD) is caused by a virus and seriously affects maize quality and yield worldwide. MRDD can be most effectively controlled with disease-resistant hybrids of corn. Here, MRDD-resistant (Qi319) and -susceptible (Ye478) parental inbred maize lines and their 314 recombinant inbred lines (RILs) that were derived from a cross between them were evaluated across three environments. A stable resistance QTL, qMrdd2, was identified and mapped using best linear unbiased prediction (BLUP) values to a 0.55-Mb region between the markers MK807 and MK811 on chromosome 2 (B73 RefGen_v3) and was found to explain 8.6 to 11.0% of the total phenotypic variance in MRDD resistance. We validated the effect of qMrdd2 using a chromosome segment substitution line (CSSL) that was derived from a cross between maize inbred Qi319 as the MRDD resistance donor and Ye478 as the recipient. Disease severity index of the CSSL haplotype II harboring qMrdd2 was significantly lower than that of the susceptible parent Ye478. Subsequently, we fine-mapped qMrdd2 to a 315-kb region flanked by the markers RD81 and RD87, thus testing recombinant-derived progeny using selfed backcrossed families. In this study, we identified a novel QTL for MRDD resistance by combining the RIL and CSSL populations, thus providing important genetic information that can be used for breeding MRDD-resistant varieties of maize.