Pyramiding Of Resistance Genes Research Articles

Comparative transcriptome analysis of canola carrying a single vs stacked resistance genes against clubroot.

Pyramiding resistance genes may expand the efficacy and scope of a canola variety against clubroot (Plasmodiophora brassicae), a serious threat to canola production in western Canada. However, the mechanism(s) of multigenic resistance, especially the potential interaction among clubroot resistance (CR) genes, are not well understood. In this study, transcriptome was compared over three canola (Brassica napus L.) inbred/hybrid lines carrying a single CR gene in chromosome A03 (CRaM, Line 16) or A08 (Crr1rutb, Line 20), and both genes (CRaM+Crr1rutb, Line 15) inoculated with a field population (L-G2) of P. brassicae pathotype X, a new variant found in western Canada recently. The line16 was susceptible, while lines 15 and 20 were partially resistant. Functional annotation identified differential expression of genes (DEGs) involved in biosynthetic processes responsive to stress and regulation of cellular process; The Venn diagram showed that the partially resistant lines 15 and 20 shared 1,896 differentially expressed genes relative to the susceptible line 16, and many of these DEGs are involved in defense responses, activation of innate immunity, hormone biosynthesis and programmed cell death. The transcription of genes involved in Pathogen-Associated Molecular Pattern (PAMP)-Triggered and Effector-Triggered Immunity (PTI and ETI) was particularly up-regulated, and the transcription level was higher in line 15 (CRaM + Crr1rutb) than in line 20 (Crr1rutb only) for most of the DEGs. These results indicated that the partial resistance to the pathotype X was likely conferred by the CR gene Crr1rutb for both lines 15 and 20 that functioned via the activation of both PTI and ETI signaling pathways. Additionally, these two CR genes might have synergistic effects against the pathotype X, based on the higher transcription levels of defense-related DEGs expressed by inoculated line 15, highlighting the benefit of gene stacking for improved canola resistance as opposed to a single CR gene alone.

Development and Validation of a Resistance Management Model for the Soybean Cyst Nematode, Heterodera glycines.

Plant-parasitic nematodes are a key yield-limiting pest of crops around the world. Deployment of plant resistance genes are an important management tactic for many economically important plant-parasitic nematodes. The selection for virulence in nematode populations is a major threat to the effectiveness of resistance gene-based management. Little research has gone into resistance management modelling despite the importance of both plant-parasitic nematodes and resistance genes for their management. In this paper, we report on a cyst nematode resistance management model created to explore the factors which are most important for determining the durability of resistance genes to this important family of plant-parasitic nematodes. The relative dominance of virulence expression, the level of inbreeding, and the number of generations per cropping season were the most important factors in predicting resistance gene durability. Aspects of cyst nematode biology that reduce the number of generations per season for a portion of the population had a much smaller effect on the durability of resistance genes. These factors included delayed hatching within a season and early dormancy. The accuracy and utility of the model was tested using the soybean cyst nematode (SCN) rhg1-mediated resistance system. The model accurately predicted the rate at which virulence to the rhg1b resistance gene developed in Iowa over a two-decade period. The model suggested resistance gene pyramids as the most durable management solution for SCN with multiple possible avenues to obtain acceptable efficacy and durability.

The Development of Multi-Resistant Rice Restorer Lines and Hybrid Varieties by Pyramiding Resistance Genes against Blast and Brown Planthopper

Rice blast, caused by the fungus Magnaporthe oryzae, and brown planthopper (BPH) infestation are two of the most destructive problems of rice production in China. The development of multi-resistant varieties is widely recognized as the most efficient and environmentally friendly approach to controlling crop diseases and pests. Functional molecular markers (FMMs) have been developed from functional variants in the genic region associated with trait variation, greatly enhancing the efficiency of identifying and pyramiding valuable genes in crop breeding. In this study, two FMMs and a multiplex PCR amplification system were developed for two major broad-spectrum BPH resistance genes, Bph6 and Bph9. With the assistance of FMMs in the multi-resistant rice restorer-line development pipeline, two lines (Huahui7713 and Huahui3006) with blast and BPH resistance were developed by pyramiding three resistance genes Pigm, Bph6 and Bph9. Two new hybrid rice varieties, Weiliangyou7713 and Xuanliangyou3006, derived from Huahui7713 and Huahui3006, have been developed and commercialized in China. Weiliangyou7713 and Xuanliangyou3006 exhibit enhanced resistance to both blast and BPH, while maintaining optimal yield and grain quality. The adoption of Weiliangyou7713 continues to expand, now being cultivated on a large scale, which is promising for its future role in reducing the dependence on chemical fungicides and pesticides in rice production. This suggests that the implementation of Huahui7713 and Huahui3006 in targeted breeding programs could be highly beneficial for developing rice varieties with strong resistance to blast and BPH.

Screening of Apple Cultivars for Scab Resistance in Kazakhstan

Scab, caused by Venturia inaequalis, is the most destructive fungal disease of apple worldwide. Apple scab incidence was studied in apple orchards in the south and southeast of Kazakhstan, including the Almaty, Zhambyl, and Turkestan regions, during 2022 and 2023. Disease incidence was higher in the Zhambyl region than in the Turkestan and Almaty regions in both years. The field evaluation suggested that 19 genotypes showed resistance to apple scab. Molecular screening was carried out using eight gene-specific molecular markers (AM19, CH05e03, OPL19, Hi07f02, AL07, K08, HB09, and CH02f06). The results of the molecular screening revealed that in 38 of the 45 studied cultivars, which included 11 Kazakh cultivars and 34 foreign cultivars, the Rvi (Rvi2, Rvi4, Rvi5, Rvi6, Rvi8, Rvi9, Rvi11, Rvi14, and Rvi15) resistance genes were amplified. Resistance genes such as Rvi2, Rvi4, Rvi6, and Rvi9 are still useful for breeding, but their use is recommended only in extended pyramids of multiple resistance genes. Several cultivars will be strong candidates for further breeding programs against apple scab and for the pyramiding of scab resistance genes in new cultivars.

Pyramiding of blast and bacterial blight resistance genes in premium quality rice variety, BRRI dhan63 through marker-assisted breeding approach

Pyramiding of blast and bacterial blight resistance genes in premium quality rice variety, BRRI dhan63 through marker-assisted breeding approach

Marker-assisted pyramiding of Ty-2, Ty-3, Ph-2, and Ph-3 genes for combined resistance to tomato leaf curl and late blight diseases in tomato (Solanum lycopersicum L.)

Marker-assisted pyramiding of Ty-2, Ty-3, Ph-2, and Ph-3 genes for combined resistance to tomato leaf curl and late blight diseases in tomato (Solanum lycopersicum L.)

Molecular mapping of QTL for rice black-streaked dwarf disease resistance in rice (Oryza sativa L.)

AbstractRice black-streaked dwarf disease (RBSDD) is one of the most serious crop diseases in Asia, causing serious damage to rice production. Therefore, reducing the harmful effects of RBSDD is vital to the food security of China and other Asian countries. In this study, 248 rice varieties from different countries were screened for resistance to RBSDD, and 19 varieties with high resistance to RBSDD were found. Among them, H185, an indica variety, showed stable and high resistance to RBSDD. Using an F2:3 population of H185 and Wuyujing 3 (WYJ3, a highly susceptible japonica rice variety), three QTL conferring resistance to RBSDD, namely qRBSDD2, qRBSDD7, and qRBSDD11 were identified, and they explained 53.6% of the total phenotypic variation. Among them, qRBSDD2 and qRBSDD7, with LOD scores of 4.26 and 4.25, respectively, were repeatedly detected in artificial inoculation conditions, accounting for 28.0% and 29.8% of the total phenotypic variation, respectively. Resistant alleles of the two QTL were all derived from H185, and several BC5F2 lines possessing single or two QTL of qRBSDD2 and qRBSDD7 exhibited higher resistance for RBSDD. The QTL detected in our study open new possibilities for breeding rice cultivars with RBSDD resistance through resistance gene pyramiding.

Marker-assisted enhancement of bacterial blight (Xanthomonas oryzae pv. oryzae) resistance in a salt-tolerant rice variety for sustaining rice production of tropical islands.

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae is a major disease of rice, specially in the tropical regions of the world. Developing rice varieties with host resistance against the disease is the most effective and economical solution for managing the disease. Pyramiding resistance genes (Xa4, xa5, xa13,and Xa21) in popular rice varieties using marker-assisted backcross breeding (MABB) has been demonstrated as a cost-effective and sustainable approach for establishing durable BB resistance. Here, we report our successful efforts in introgressing four resistance genes (Xa4, xa5, xa13, and Xa21) from IRBB60 to CARI Dhan 5, a popular salt-tolerant variety developed from a somaclonal variant of Pokkali rice, through functional MABB. Both BB and coastal salinity are among the major challenges for rice production in tropical island and coastal ecosystems. Plants with four, three, and two gene pyramids were generated, which displayed high levels of resistance to the BB pathogen at the BC3F2 stage. Under controlled salinity microplot environments, the line 131-2-175-1223 identified with the presence of three gene pyramid (Xa21+xa13+xa5) displayed notable resistance across locations and years as well as exhibited a salinity tolerance comparable to the recurrent parent, CARI Dhan 5. Among two BB gene combinations (Xa21+xa13), two lines, 17-1-69-334 and 46-3-95-659, demonstrated resistance across locations and years, as well as salt tolerance and grain production comparable to CARI Dhan 5. Besides salinity tolerance, five lines, 17-1-69-179, 46-3-95-655, 131-2-190-1197, 131-2-175-1209, and 131-2-175-1239, exhibited complete resistance to BB disease. Following multilocation testing, potential lines have been identified that can serve as a prospective candidate for producing varieties for the tropical Andaman and Nicobar Islands and other coastal locations, which are prone to BB and coastal salinity stresses.

Pyramiding resistance genes for bacterial leaf blight (Xanthomonas oryzae pv. Oryzae) into the popular rice variety, Pratikshya through marker assisted backcrossing.

Bacterial leaf blight (BLB) is one of the major biotic stress in rice cultivation. Management techniques, such as the development of BLB-resistant cultivars, are required to lessen the severity of the disease attack and yield losses. Pratikshya was selected in the present investigation as the recipient parent, as it is one of the popular high-yielding rice varieties of Odisha, India, which is having excellent grain as well as cooking quality. However, Pratikshya is highly susceptible to BLB which is prevalent in Eastern Indian region. Three major BLB resistance genes xa5, xa13, and Xa21 from the donor source Swarna MAS (CR Dhan 800) were attempted to introduce into Pratikshya through a marker-assisted backcross breeding program. Those markers closely linked to the target genes were employed for foreground selection in the segregating generations till BC2F3. In each backcross generation, progenies containing all three targeted resistance genes and phenotypically more similar to the recipient parent, Pratikshya were selected and backcrossed. Screening of 1,598 plants of the BC2F2 population was conducted against BLB using Xoo inoculum and 35 resistant plants similar to Pratikshya were carried forward to the next generation. In the BC2F3 generation, 31 plants were found to possess all the three resistance genes. For background selection of plants carrying resistance genes 45 polymorphic SSR markers were employed. Evaluation of the pyramided lines at BC2F4 generation exhibited that, most pyramided lines were similar to Pratikshya in terms of morphological features and yield parameters, and some lines were superior to the recurrent parent in terms of morphological features and yield parameters. The three-gene pyramided lines showed a high level of resistance to BLB infection and are anticipated to offer a significant yield advantage over the recipient parent Pratikshya.The pyramided lines can further be used for multi-location trial, so as to be released as a variety or can be used as a potential donor for BLB resistance genes.

Pyramiding Fusarium head blight resistance QTL from T. aestivum, T. dicoccum and T. dicoccoides in durum wheat

Key messageFHB resistance of durum wheat was improved by introgression of Fhb1 and resistance genes from emmer wheat and by selection against adverse alleles of elite durum wheat.Durum wheat is particularly susceptible to Fusarium head blight (FHB) and breeding for resistance is impeded by the low genetic variation within the elite gene pool. To extend the genetic basis for FHB resistance in durum wheat, we analyzed 603 durum wheat lines from crosses of elite durum wheat with resistance donors carrying resistance alleles derived from Triticum aestivum, T. dicoccum and T. dicoccoides. The lines were phenotyped for FHB resistance, anthesis date, and plant height in artificially inoculated disease nurseries over 5 years. A broad variation was found for all traits, while anthesis date and plant height strongly influenced FHB severities. To correct for spurious associations, we adjusted FHB scorings for temperature fluctuations during the anthesis period and included plant height as a covariate in the analysis. This resulted in the detection of seven quantitative trait loci (QTL) affecting FHB severities. The hexaploid wheat-derived Fhb1 QTL was most significant on reducing FHB severities, highlighting its successful introgression into several durum wheat backgrounds. For two QTL on chromosomes 1B and 2B, the resistance alleles originated from the T. dicoccum line Td161 and T. dicoccoides accessions Mt. Hermon#22 and Mt. Gerizim#36, respectively. The other four QTL featured unfavorable alleles derived from elite durum wheat that increased FHB severities, with a particularly negative effect on chromosome 6A that simultaneously affected plant height and anthesis date. Therefore, in addition to pyramiding resistance genes, selecting against adverse alleles present in elite durum wheat could be a promising avenue in breeding FHB-resistant durum wheat.

Characterization of tomato yellow leaf curl virus resistance genes and genetic variability in commercial tomato F1 hybrids

Tomato (Solanum lycopersicum L.) resistance to Tomato Yellow Leaf Curl Virus (TYLCV) is a major objective of breeding programs. Tomato breeders are now interested in the subsequent introgression of many resistance genes to increase resistance levels, expand resistance spectrum, and prolong the longevity of resistant cultivars. Many F1 hybrids are now multigene resistant. To select the best breeding materials, 15 commercial F1 tomato TYLCV-tolerant hybrids were evaluated for TYLCV resistance and productivity during the 2018 and 2019 fall seasons. Resistance genes were identified using gene-based molecular markers. Most hybrids have multiple heterozygous resistance genes. ‘Brivio’, ‘Dania’, ‘SV8320’, and ‘Tyrmes’ comprised resistance genes Ty-1/Ty-3, Ty-2, Ty-4, and ty-5. Thus, F1 hybrids exhibited moderate to mild symptoms, and viral replication was detected in their symptomless plants by PCR and qt-PCR. Genetic variability among hybrids, hybrid relationships, and inter-trait correlations were estimated based on phenotypes of TYLCV-tolerance, productivity, and fruit quality. Most traits had high estimates of genetic variance, genotypical coefficient of variance, and heritability. Genetic variability sufficed in selecting the best genotype. Based on multivariate analyses of principal components and hierarchical clusters, hybrids were highly diversified and divided into three clusters. Clusters 1 and 3 were better at TYLCV tolerance, yield, and fruit quality. Positive genotypical correlations were found between tolerance, total yield, and fruit quality (firmness, equatorial diameter, and TSS content). The use of ‘Brivio’, ‘Dania’, ‘SV8320’, and ‘Tyrmes’ will be very useful in TYLCV resistance breeding programs to pyramiding resistance genes by marker-assisted selection technique.

Identification and genetic mapping of novel resistance gene, Rvn4, for pear scab in Chinese pear

Pear scab, caused by Venturia nashicola, is one of the most harmful diseases of pears, especially of Japanese and Chinese pears. The breeding of new cultivars resistant to pear scab has long been an aim of the Asian pear breeding programs. Although loci for pear scab disease resistance have been identified in Japanese and European pears, information on the genes controlling scab resistance in Chinese pears is limited. Genetic control of scab resistance in Chinese pear is reported to involve a single dominant gene. Here, we reaffirmed the scab resistance in the Chinese pear ‘Hong Li’ controls a single dominant gene and identified the exact location of a scab resistance gene, Rvn4. We first mapped Rvn4 at the top of linkage group (LG) 7 and then used public genome sequences to develop novel simple sequence repeat (SSR) markers to enrich the target region. Using these novel SSRs and the previously published SSR markers, we constructed a LG 7 of ‘Hong Li’ with an average marker density of 1.4 cM per marker. The novel SSR marker Pbr.chr07.20 had a significant linkage to Rvn4, with a genetic distance of 1.3 cM. The identification of the precise locus of Rvn4 in Chinese pear, together with previous studies in Japanese and European pear, will enhance our understanding of the mechanisms of pear scab resistance. DNA markers linked to the novel gene may also allow efficient selection of scab-resistant seedlings in pear breeding programs and the pyramiding of multiple resistance genes.

Pyramiding of Multiple Genes to Improve Rice Blast Resistance of Photo-Thermo Sensitive Male Sterile Line, without Yield Penalty in Hybrid Rice Production.

Rice blast caused by pathogenic fungus Magnaporthe oryzae is one of the most serious diseases in rice. The pyramiding of effective resistance genes into rice varieties is a potential approach to reduce the damage of blast disease. In this study, combinations of three resistance genes, Pigm, Pi48 and Pi49, were introduced into a thermo-sensitive genic male sterile (PTGMS) line Chuang5S through marker-assisted selection. The results showed that the blast resistance of improved lines increased significantly compared with Chuang5S, and the three gene pyramiding lines (Pigm + Pi48 + Pi49) had higher rice blast resistance level than monogenic line and digenic lines (Pigm +Pi48, Pigm + Pi49). The genetic backgrounds of the improved lines were highly similar (>90%) to the recurrent parent Chuang5S by using the RICE10K SNP chip. In addition, agronomic traits evaluation also showed pyramiding lines with two or three genes similar to Chuang5S. The yields of the hybrids developed from improved PTGMS lines and Chuang5S are not significantly different. The newly developed PTGMS lines can be practically used for the breeding of parental lines and hybrid varieties with broad spectrum blast resistance.

Marker assisted pyramiding of major brown plant hopper resistance genes in an elite culture CBMAS14065

Marker assisted pyramiding of major brown plant hopper resistance genes in an elite culture CBMAS14065

Pyramiding of Adult-Plant Resistance Genes Enhances All-Stage Resistance to Wheat Stripe Rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases in wheat production. Pyramiding of adult-plant resistance (APR) genes is a promising strategy to increase durability of resistance. The stripe rust resistance (R) genes Yr18, Yr28, and Yr36 encode different protein families which confer partial resistance to a broad array of P. striiformis f. sp. tritici races. Here, we developed BC3F5 wheat lines representing all possible combinations of Yr18, Yr28, and Yr36 in a genetic background of the highly P. striiformis f. sp. tritici-susceptible wheat line SY95-71 that is widely used in stripe rust analysis. These lines enabled us to accurately evaluate these genes singly and in combination in a common genetic background. The adult plant resistance experiments were analyzed in the field, where stripe rust epidemics occurred frequently. The field results indicated that these partial R genes act additively in enhancing the levels of resistance, and a minimum of two-gene combinations can generate adequate stripe rust resistance. The Yr28 + Yr36 and Yr18 + Yr28 + Yr36 combinations also showed adequate resistance at the seedling stage, implying that APR gene pyramiding can achieve all-stage resistance. Meanwhile, the three genes were simultaneously introduced into elite wheat lines through gene-based marker selection. Elite lines exhibited strong all-stage resistance to stripe rust. This work provides valuable insights and resources for developing durable P. striiformis f. sp. tritici-resistant varieties and for elucidating the regulation mechanism of partial R gene pyramiding.

Registration of 64 soybean germplasm lines with all combinations of five soybean aphid resistance genes in two genetic backgrounds

AbstractSoybean aphid is a serious pest in North America, and infestations can cause economically significant losses. Aphid resistance genes have been identified and mapped with genetic markers, and the deployment of cultivars with pyramids of these genes could offer durable resistance. There is a need, however, for soybean [Glycine max (L.) Merr.] lines with different gene pyramids to be developed and tested to improve our understanding of what combinations provide the most resistance across aphid biotypes. We backcrossed the resistance genes Rag1, Rag2, Rag3, Rag4, and Rag6 into the background of two soybean cultivars, and lines with all 32 combinations of these five genes were developed in each background. These lines, LD19‐APH01–LD19‐APH64 (Reg. no. GP‐459–GP‐522, PI 701410–PI 701473), were evaluated for agronomic traits in the field and lines from one background were evaluated for resistance to four soybean aphid biotypes. There were significant differences among the performance of the backcross lines for agronomic traits; however, yield performance for most of the backcross lines did not significantly differ from the recurrent parent. Those lines with the Rag6 resistance gene and many gene pyramids showed a high level of resistance to all four aphid biotypes. Because these lines have the resistance genes in a mostly uniform background, they will be a useful source of germplasm for researchers studying soybean aphid isolates and the interaction between resistance genes and aphid isolates, as well as for breeders who are developing germplasm with resistance gene pyramids.

Marker-Assisted Recurrent Selection for Pyramiding Leaf Rust and Coffee Berry Disease Resistance Alleles in Coffea arabica L.

In this study, marker-assisted recurrent selection was evaluated for pyramiding resistance gene alleles against coffee leaf rust (CLR) and coffee berry diseases (CBD) in Coffea arabica. A total of 144 genotypes corresponding to 12 hybrid populations from crosses between eight parent plants with desired morphological and agronomic traits were evaluated. Molecular data were used for cross-certification, diversity study and resistance allele marker-assisted selection (MAS) against the causal agent of coffee leaf rust (Hemileia vastatrix) and coffee berry disease (Colletotrichum kahawae). In addition, nine morphological and agronomic traits were evaluated to determine the components of variance, select superior hybrids, and estimate genetic gain. From the genotypes evaluated, 134 were confirmed as hybrids. The genetic diversity between and within populations was 75.5% and 24.5%, respectively, and the cluster analysis revealed three primary groups. Pyramiding of CLR and CBD resistance genes was conducted in 11 genotypes using MAS. A selection intensity of 30% resulted in a gain of over 50% compared to the original population. Selected hybrids with increased gain also showed greater genetic divergence in addition to the pyramided resistance alleles. The strategies used were, therefore, efficient to select superior coffee hybrids for recurrent selection programs and could be used as a source of resistance in various crosses.

Advances in Durable Resistance to Diseases in Staple Food Crops: A Review

Background: At all stages of their development, plants are in permanent contact with causative agents of various diseases. Mechanisms of disease resistance and its durability in crops largely depend on the pathogen’s lifestyle, namely the nutrition mode and host range. Objective: The objective of this review is to consider the main advances in the production of genotypes with durable disease resistance in the globally important food crops, wheat, rice, and potato, as well as barley. Results: In wheat, durable resistance could be provided by the employment of various adult plant resistance genes against biotrophic pathogens, whose action commonly does not involve hypersensitivity response, as well as major quantitative genes, including mutants of susceptibility alleles, against necrotrophs via marker assisted selection (MAS). In barley, the most prominent example is the gene mlo conferring durable powdery mildew resistance, but it is compromised by higher susceptibility to some necrotrophic fungi. A few genes for broad-spectrum resistance against the rice blast and bacterial blight pathogens confirmed their effectiveness for decades, and they could be combined with effective R genes via MAS. Resistance to late blight of potato is mainly provided by R genes introgressed from wild potato species, which could be pyramided with quantitative trait loci. Genes for extreme resistance to potato viruses derived from related species provide durable and broad-spectrum resistance and could be effectively deployed in potato breeding using MAS. Silencing susceptibility genes by genome editing technologies is the most promising approach to produce plants with durable resistance to many pathogens in the crop species. Genetic transformation with genes for resistance-associated proteins or constructs providing silencing via RNA interference is an effective biotechnological method to generate plants with durable resistance against pathogens, especially viruses. Conclusion: Main advances in the production of crop plants with durable resistance are based on studies of molecular mechanisms of plant immunity and its special features for pathogens with different lifestyles via the use of biotechnological approaches such as MAS for pyramiding of monogenic quantitative resistance genes or qualitative R genes, changes in expression of certain genes associated with resistance, the introduction of transgenes, mutagenesis and genome editing aimed at silencing susceptibility genes.

Сцепленное наследование микросателлитного локуса ORS 822 с геном Plarg, контролирующим устойчивость к ложной мучнистой росе, у подсолнечника

Resistance to the downy mildew pathogen Plasmopara halstedii (Farl.) Berlese et de Toni in sunflower is controlled by the resistance gene Pl. The Plarg gene is currently promising in breeding for resistance as it is effective against all known races of the pathogen. This gene is introgressed from the wild species Helianthus argophyllus. Molecular markers and, in particular, simple microsatellite repeats (SSRs) allow to control the transfer and pyramiding of disease resistance genes. However, validation of the molecular marker is needed to prove its reliability. The microsatellite marker ORS 822 was tested to identify the Plarg gene. We conducted the research on a hybrid combination of a susceptible sunflower line of VNIIMK's breeding VK 925 and a resistant line RHA 419, a donor of the Plarg gene. We es-tablished that these lines differ from each other by the allelic state of this locus. Molecular analysis of the F1 generation showed that the microsatellite locus is inherited codominantly. We obtained the F2 generation by self-pollination and made a phytopathological evaluation of resistance to P. halstedii. Split analysis by ph-notype showed that the actually observed segregation corresponded to the theoretically expected 3:1 model for monogenic inheritance of the trait. Based on the obtained data, we determined that the Plarg gene and microsatellite locus ORS 822 are linked with a recombination frequency of 0.26. As a result of this research, we concluded that this marker can be used to select homozygous resistant sunflower plants for resistance to downy mildew in marker-assisted selection (MAS).

Pyramiding of Four Broad Spectrum Bacterial Blight Resistance Genes in Cross Breeds of Basmati Rice.

Pyramiding of major resistance (R) genes through marker-assisted selection (MAS) is a useful way to attain durable and broad-spectrum resistance against Xanthomonas oryzae pv. oryzae pathogen, the causal agent of bacterial blight (BB) disease in rice (Oryza sativa L.). The present study was designed to pyramid four broad spectrum BB-R genes (Xa4, xa5, xa13 and Xa21) in the background of Basmati-385, an indica rice cultivar with much sought-after qualitative and quantitative grain traits. The cultivar, however, is susceptible to BB and was therefore, crossed with IRBB59 which possesses R genes xa5, xa13 and Xa21, to attain broad and durable resistance. A total of 19 F1 plants were obtained, some of which were backcrossed with Basmati-385 and large number of BC1F1 plants were obtained. In BC1F2 generation, 31 phenotypically superior genotypes having morphological features of Basmati-385, were selected and advanced up to BC1F6 population. Sequence-tagged site (STS)-based MAS was carried out and phenotypic selection was made in each successive generation. In BC1F6 population, potentially homozygous recombinant inbred lines (RILs) from each line were selected and evaluated on the bases of STS evaluation and resistance to local Xanthomonas oryzae pv. oryzae (Xoo) isolates. Line 23 was found pyramided with all four BB-R genes i.e., Xa4, xa5, xa13 and Xa21. Five genotypes including line 8, line 16, line 21, line 27 and line 28 were identified as pyramided with three R genes, Xa4, xa5 and xa13. Pathological study showed that rice lines pyramided with quadruplet or triplet R genes showed the highest level of resistance compared to doublet or singlet R genes. Thus, line 23 with quadruplet, and lines 8, 16, 21, 27, and 28 with triplet R genes, are recommended for replicated yield and resistance trials before release as new rice varieties. Further, traditional breeding coupled with MAS, is a solid way to attain highly effective BB-resistant rice lines with no yield cost.