Backcross Breeding Program Research Articles

Accelerated breeding strategies for biochemical marker-assisted backcross breeding and mapping population development in bread wheat (Triticum aestivum L.)

In order to rapidly adapt to the evolving climate and sustainably nourish the growing global population, plant breeders are actively investigating more efficient strategies to enhance crop yields. In this study, we present the development of a bread wheat mapping population and backcross breeding program, serving as a valuable genetic resource for mapping the effects of different alleles on trait performance. We employed innovative methodologies to rapidly introgress traits into the bread wheat cultivar. Specifically, we utilized two parents, including Tosunbey x Tahirova2000, in a recombinant inbred line population, in addition, a backcross strategy was applied with line 148 (obtained by crossing Tosunbey x Tahirova2000 with high gluten quality) as the recipient parent of the Nevzatbey cv., known for its awnless feature. The two most important applications of the rapid breeding method are extending the light period and breaking dormancy in early harvested seeds. Both applications were successfully implemented in our study. Our vegetation periods ranging from approximately 50–60 days. Additionally, an early genotype in our developed population was harvested in 40 days. Considering that the genotype underwent a 15-day vernalization period, the generation cycle, including vernalization, drying, and refrigeration, was completed in a total of 64 days. Notably, we employed not only biochemical markers for selection but also incorporated the rapid generation advance technology known as ‘speed breeding’, allowing us to develop BC5F1 within a span of two years. We posit that this approach proves instrumental in swiftly transferring genes for multiple target traits into adapted wheat cultivars or in pyramiding desirable traits within elite breeding material.

IMPROVEMENT OF HIGH AMYLOSE CONTENT IN CH1 RICE VARIETY BY MARKER ASSISTED PSEUDO-BACKCROSS BREEDING

The objective of this research was to introgression of high amylose content into CH1 rice variety by using pseudo-backcrossing breeding. Crossing between CH1 and RD49 was performed to produce F1 progenies. After that, the progenies will backcross to CH1 to develop BC1F1 population. Then, the selected plants from the BC1F1 population were continuously selfed to develop BC1F2 and BC1F3 populations, respectively. For marker assisted selection, the OSR19 DNA marker that is specific to Wx gene was used for assisting the selection of plants with high amylose content in foreground selection to choose favorite genotype. Total 67 SSR markers used genetic background selection was done twice in BC1F1 and BC1F2 populations. The results showed that selection could be achieved for BC1F1 and BC1F2 plants having high amylose content and first highest ranking of genetic background similar to recurrent parent exhibited 91.04 and 97.76 percent, respectively. The marker assisted selection could accelerate 4 generations in backcross breeding program. The BC1F3 seeds of 6 selected lines were planted in paddy field for preliminary yield test. It was found that agronomic characters and yield of the selected lines were not statistically different from those of CH1 variety and high amylose content as donor parent.

Comparison of Blast, Bacterial Leaf Blight and Brown Plant Hopper Introgressed Lines for Yield and Morphological Traits Over Original Line

Rice as a staple food for very large population suffers from various biotic and abiotic stresses. Among the biotic stresses, Blast, Bacterial leaf blight and Brown plant hopper (BPH) are considered to most potential threats that significantly affect the rice productivity. The use of chemical usage for controlling these diseases and pest attacks is not environmentally friendly and is expensive. Using Molecular Marker assisted backcross breeding program we have improved one of our hybrid parental line with 5 genes (xa13, Xa21, Pi54, Bph20 and Bph21). We have developed 15 near isogenic lines having similar agronomical characters as of recipient parent, they are promising for their direct induction in breeding program. Our results indicated that out of fifteen lines, Six lines i.e. GK 101-12, GK 101-15, GK 101-9, GK 101-5 and GK 101-2 out-performed in all the three locations tested, they had not only have very high level of resistance to BLB, Blast and BPH but also showed significantly higher yield compared to susceptible check as well as recipient parent. These lines may be used for improvement of our existing hybrid and also for developing of new hybrids with other CMS lines. These lines are also useful for developing new set of restorer lines through (R x R) and also useful for introgression of wide spectrum of resistance to the varieties/hybrid.

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.

Parental polymorphism survey using rice microsatellite markers between VGD 1 and ADT 55 for marker-assisted backcross breeding program

Parental polymorphism survey using rice microsatellite markers between VGD 1 and ADT 55 for marker-assisted backcross breeding program

Ugradnja Ga1-S gena u roditeljske linije hibrida kukuruza belog zrna pomoću molekularnih markera

Maize Research Institute Zemun Polje has a marker-assisted backcross breeding (MABB) program aimed to incorporate the strong allele of incompatibility gene Ga1 into parental components of the hybrids with specific traits (white kernel). The main objective of this research was marker-assisted development of the white maize hybrid's parental lines with complete cross-incompatibility to foreign pollens. Ga1-S-tightly-linked molecular markers successfully identified heterozygous plants with a percentage of approximately 50% after all three backcrossings. Regarding the background selection, 69% of progenies had recurrent parent's genome (RPG) above the theoretical value for BC3 generation. Also, a few individuals even had 99%, the value theoretically achieved in the BC6 generation, showing that MABB made a genetic gain in RPG recovery. Foreground selection in this generation aimed to identify homozygous dominant individuals. Out of 264 BC3 F2 plants, 70 (26.5%) were dominant homozygotes, which is in accordance with the expected Mendelian ratio. Progenies of the BC3 F2 homozygous dominant plants were planted alternatively with yellow-kernel maize of the same maturity to check cross-incompatibility. Unfortunately, none of the dominant progenies had a 100% white kernel, most likely due to the presence of modifier genes that increase/decrease the effectiveness of pollen exclusion or that, alternatively, modifiers are lost during the backcrossing. It could be expected that successfully employed functional markers (developed from the sequence polymorphisms present within a functional gene(s) associated with phenotypic trait variations) would outbalance the noted impediments and enhance MABB efficiency to transfer the desired gene(s) controlling simple or complex trait(s) into cultivated varieties.

Resistance to Pythium root rot and anthracnose among Kenyan common bean genotypes and marker-assisted introgression of resistance genes

ABSTRACT Common bean (Phaseolus vulgaris L.) is an important food legume crop and major protein source in Kenya and many parts of the world. However, the yields are low due to the diseases like anthracnose caused by Colletotrichum lindemunthianum and Pythium root rots. The study, therefore, sought to screen Kenyan common bean genotypes for anthracnose and Pythium resistance and to improve the resistance of local landraces to the two diseases. Local landraces and commercial cultivars were screened for resistance under greenhouse conditions for Pythium and in vitro for anthracnose. The results showed that majority of the landraces were moderately resistant to anthracnose and Pythium root rot. The study further utilized molecular markers linked to anthracnose and Pythium resistance, respectively, to determine their potential to detect specific resistance genes among the test genotypes. None of the markers amplified the test genotypes except the control genotypes pointing toward different resistance genes. Further, cultivars G2333 and KK8 were used as donor parents for anthracnose and Pythium resistance, respectively, in a marker-assisted backcross breeding program involving three high-yielding farmer-preferred landraces. A number of lines were developed that carry both resistance genes. These lines can be advanced for release as new cultivars to enhance common bean production in Kenya.

Genotypic and Phenotypic Selection of Newly Improved Putra Rice and the Correlations among Quantitative Traits

This experiment was conducted to genotypically and phenotypically select new rice lines pyramided with blast and bacterial leaf blight disease resistance genes after a marker-assisted backcross breeding programme. The inter-relationship among agro-morphological characteristics and their effect on yield was also studied. The polymorphic functional and microsatellite markers Xa21FR and pTA248 (Xa21), Xa13prom (xa13), RM21 (xa5), MP (Xa4), RM6836 (Pi2, Pi9 & Piz) and RM8225 (Piz) were first confirmed for the target genes. The selected markers were used for foreground selection of BC2F2 homozygous progenies with the target genes. Plants that had homozygous IRBB60 alleles for these markers were evaluated for their recovery of the recurrent parent genome. IRBB60 was used as the donor parent for bacterial blight resistance genes while Putra-1 served as a recipient/recurrent parent with background blast-resistance genes and high yield. After the foreground selection, 79 polymorphic simple sequence repeat markers identified from the marker polymorphism survey were used for marker-assisted background selection to determine the percentage recovery of the recurrent parent genome. In order to make a selection on a phenotypic basis, 14 agro-morphological traits were measured and recorded. The result obtained from the study showed that 16 lines received the seven resistance genes in sufficiently varied numbers and were selected. The distribution of yield per hectare showed that about 50% of the selected lines had yields as high as 5 t/ha and above. Some of the lines produced as high as 8.4 t/ha. These lines demonstrated the potential of recording uniform 8t/ha upon recombination at BC2F2. The study also indicated that the number of panicles per hill correlated strongly, significantly and positively with the number of tillers (r = 0.962 **), total grain weight per hill (r = 0.928 **) and yield per hectare (r = 0.927 **). It was concluded that the newly improved resistant lines which were selected have the capability to compete with Putra-1 in terms of its productivity and yield. The newly developed lines would be useful in future breeding programmes as donors for bacterial leaf blight and blast resistance genes. These lines are recommended for release to farmers in Malaysia and other rice-growing agro-ecologies for commercial cultivation.

Wheat breeding for early heading: Does it improve grain yield under drought stress and well-watered conditions?

Terminal drought stress strongly affects wheat grain yield under Mediterranean conditions. Therefore, developing early-heading bread wheat cultivars in these conditions is an important breeding strategy. In the present research, earliness was transferred from the Australian cultivar, Excalibur, to three Iranian cultivars, Roshan, Kalheydari and Mahdavi, in separate backcross (BC) breeding programs from 2012 to 2018. The earliest and latest heading genotypes of each BC 3 population, were selected as near-isogenic lines (NILs). NILs and their parents were assessed under diverse field conditions including rain-fed, moderate drought stress and well-watered conditions in three locations, Kerman, Sepidan and Semirom, during two growing seasons, 2018–2019 and 2019–2020. Breeding for early heading significantly improved earliness in all genetic backgrounds and increased grain yield by 36.4% and 9.6%, in the rain-fed and moderate drought stress conditions, respectively. Whereas, grain yield was not significantly affected by early heading under well-watered conditions. Results showed that breeding for early heading, a highly heritable trait, is an appropriate method to increase grain yield and reduce water consumption under drought stress and well-watered conditions, respectively. Based on these findings, we recommend transferring early heading to high yield late heading commercial cultivars using backcrossing. • For the first time, near isogenic lines of early heading were developed. • Breeding for early heading increased grain yield by 36.4% in rain-fed conditions. • Early heading increased grain yield by 9.6% in moderate drought stress conditions. • Early heading did not affect grain yield under well-watered conditions in Kerman.

Microsatellites based parental polymorphism survey for moisture stress in Rice (Oryza sativa L.) between the parental genotypes HUR-1309 and CR Dhan 801

The present investigation was conducted during Rabi 2018-19. The parental polymorphism research was done at the Molecular Drought Breeding Laboratory (Department of Genetics and Plant Breeding), Institute of Agricultural Sciences, BHU, and the Crop Improvement Division, ICAR-NRRI, Cuttack. The purpose of this research was to identify the parental polymorphism markers, analyze their chromosomal distribution, and determine the repetitive motifs. The polymorphic markers will be helpful to introgress the drought tolerant yield QTLs (qDTY) from the donor CR Dhan 801 into the background of HUR-1309, a popular aromatic short duration variety through marker-assisted backcross breeding program. Polymerase chain reaction (PCR), agarose gel electrophoresis, and genomic DNA separation were carried out according to standard procedures. A total of 510 microsatellites were used for evaluation of the parental polymorphism and 90 markers showed polymorphism among the parents and the rest 420 markers are monomorphic for the studied QTLs (qDTY1.1, qDTY2.1, and qDTY3.1). The parental polymorphism in the present study ranged between 11.43% to 30.61%. Considering the 12 chromosomes of rice, the average polymorphism was observed 17.65%. Out of 90 polymorphic markers, 59 were dinucleotide repeats, 24 were trinucleotide repeats and 4 were tetra nucleotide repeats. The dinucleotides were highly present on chromosomes 1 (12), 2 (9), and 3 (9) and repeated 12, 9, and 9 times respectively. The markers which are found to be polymorphic can be used in the marker-assisted backcross breeding (MABB) program for grain yield under moisture stress.

Meta-analysis and validation of genomic loci governing seedling and reproductive stage salinity tolerance in rice.

Identification of concurrent genomic regions contributing tolerance to salinity at the seedling and reproductive stages were done using 45 quantitative trait loci (QTL) mapping studies reporting 915 individual QTLs. The QTL-data were used to perform a meta-analysis to predict, validate and analyze the Meta-QTLs governing component traits contributing to salinity tolerance. We predicted a total of 65 and 49 Meta-QTLs distributed across the genome governing seedling and reproductive stage salinity tolerance, respectively. Salinity stress (EC ~10.0dSm-1 ) was evaluated in a set of 32 genotypes grown hydroponically, from these eight extreme (highly tolerant and highly susceptible) genotypes were selected for validation of significant Meta-QTLs. Another set of eight previously known and reported (highly tolerant and highly susceptible) genotypes were evaluated under saline micro plot conditions (EC ~8.0dSm-1 ) and used for validation of significant Meta-QTLs for reproductive stage salinity tolerance. The microsatellite marker "RM5635" linked to MSQTL4.2 (~295.43 kb) was able to clearly differentiate contrasting genotypes for seedling stage salinity tolerance, whereas at the reproductive stage, none of the markers were able to validate the predicted Meta-QTL for salinity tolerance. Earlier reported, gene expression studies were used for candidate gene analysis of validated MSQTL4.2, which indicated the down regulation of Os04g0423100, a gene encoding Mono-oxygenase-FAD binding domain containing protein. The traits associated with this Meta-QTL were root and shoot sodium and potassium concentration and leaf chlorophyll content. The identified and validated genomic region assumes a great significant role in seedling stage salinity tolerance in rice, and it can be used for marker-assisted backcross breeding programs.

Comprehensive speed breeding: a high-throughput and rapid generation system for long-day crops.

Breeding cycle time largely determines the efficiency of crop genetic improvement. To accelerate the generation progress, Watson et al. (2018) proposed a concept of 'speed breeding (SB)' by extending the photoperiod and increasing the light intensity during plant growth. However, there have been few reports on the successful application of SB in semi-winter and winter long-day crops. Here, we propose a comprehensive speed breeding (CSB) system for the rapid generation and high-throughput culture of long-day crops, which can accomplish 4.5 generations for both semi-winter canola and winter wheat per year. With the aid of extra far-red light, three and 5.5 generations can be accomplished for the typical winter and semi-winter type canola. CSB also exhibits high efficiency in spring type canola, and can achieve up to 6.5 and 5.5 generations with or without extra far-red light, respectively. This strategy is expected to greatly accelerate gene pyramiding of superior alleles, screening of recombinants for QTL mapping and functional genomics research by rapid purification of multiple mutated alleles.

Breeding of High Cooking and Eating Quality in Rice by Marker-Assisted Backcrossing (MABc) Using KASP Markers.

The primary goals of rice breeding programs are grain quality and yield potential improvement. With the high demand for rice varieties of premium cooking and eating quality, we developed low-amylose content breeding lines crossed with Samgwang and Milkyqueen through the marker-assisted backcross (MABc) breeding program. Trait markers of the SSIIIa gene referring to low-amylose content were identified through an SNP mapping activity, and the markers were applied to select favorable lines for a foreground selection. To rapidly recover the genetic background of Samgwang (recurrent parent genome, RPG), 386 genome-wide markers were used to select BC1F1 and BC2F1 individuals. Seven BC2F1 lines with targeted traits were selected, and the genetic background recovery range varied within 97.4–99.1% of RPG. The amylose content of the selected BC2F2 grains ranged from 12.4–16.8%. We demonstrated the MABc using a trait and genome-wide markers, allowing us to efficiently select lines of a target trait and reduce the breeding cycle effectively. In addition, the BC2F2 lines confirmed by molecular markers in this study can be utilized as parental lines for subsequent breeding programs of high-quality rice for cooking and eating.

Molecular Marker-Assisted Backcrossing of Anthracnose Resistance Genes into Common Beans (<i>Phaseolus vulgaris</i> L.) Varieties

Anthracnose, caused by Colletotrichum lindemuthianum, is a major disease of common bean and results in high yield loss. Due to the high degree of pathogenic variability of the fungus and the continual emergence of new races, genetic resistance in the host is not durable. Gene pyramiding using Marker Assisted Selection (MAS) is proposed as a viable approach to improve the durability of major genes conditioning resistance to anthracnose. In this study a common bean line Urugezi x AND 1062 susceptible to anthracnose but already improved for Pythium root rot resistance was improved for anthracnose resistance through a backcross breeding program. Genotypic selection was done in Rubilizi laboratory in Kigali, Rwanada whereas phenotypic selection was conducted in an anthracnose hotspot at Rwerere, a research Centre of the Rwanda Agricultural and Animal Resources Development Board (RAB). Analysis of variance for effect of bean varieties and anthracnose isolates on disease expression showed significant differences (p 2F1 plants were 41% of them resistant and 59% susceptible to anthracnose. However, the observed proportion of 26 resistants and 37 susceptible in BC2F1 plants didn’t fit the goodness of fit of the expected proportion of 75 resistants to 25 susceptible. Only 41% of BC2F1 plants inherited the resistance genes and were phenotypically resistant. Presence of SCAR-markers, SAB3 and SBB14, in the developed resistant lines h suggested successful resistance transfer of anthracnose resistance genes.

Pyramiding Ty-1/Ty-3, Ty-2, ty-5 and ty-6 genes into tomato hybrid to develop resistance against tomato leaf curl viruses and recurrent parent genome recovery by ddRAD sequencing method

Tomato leaf curl virus (ToLCV) is a begomovirus transmitted by whitefly (Bemisia tabaci) and causes Tomato (yellow) leaf curl disease (TYLCD/ToLCD) in many parts of India and rest of the world resulting in huge economic losses. Many Ty genes identified either from wild and/or cultivated tomato, which confers various levels of resistance to ToLCV. The current study aimed at stacking four important resistant genes (Ty-1/Ty-3, Ty-2, ty-5, and ty-6) in parental lines of a commercial tomato hybrid JKTH811 with the aid of the marker-assisted backcross breeding program. As a donor source, two pre-breeding lines, CLN3125K (Ty-1/Ty-3 and Ty-2) and FLA456 (ty-5 and ty-6) was used. Crossed population screened by using tightly linked Ty genes specific markers for foreground selection and attempted the fastest recovery of recurrent parental genome through NGS based ddRAD sequencing approach. Ty genes introgressed parental lines as well as the resulting F1 hybrids were tested for their bio-efficacy against ToLCNDV (New Delhi var.) under greenhouse and field conditions. Disease severity of Ty genes pyramided female lines and F1 hybrids were found as significantly lower when compared to original parental lines and hybrid. This report demonstrates the efficiency of Ty genes pyramiding from different donors in a hybrid against ToLCV and recovery of the recurrent genome using the ddRAD-seq platform in the minimum generations possible.

Backcross breeding for improvement of heat tolerance at reproductive phase in Thai rice (Oryza sativaL.) varieties

AbstractHeat stress during the reproductive and grain-filling stages leads to severe yield losses in rice, especially in irrigated areas during the dry season in Thailand. Thus, breeding for heat-tolerant rice is one of the strategies for developing rice crops adapted to the effects of high temperature in major growing regions. M9962, a fast neutron-induced mutant, was identified as a heat-tolerant line that was then used as a donor parent and crossed with the Phisanulok 2 (PSL2) cultivar (the recurrent parent) in a backcross breeding programme. Heat tolerance scoring under controlled greenhouse and field conditions was based on the percentage of spikelet fertility. Yield trials for the BC2F7and BC3F6lines were subsequently conducted under field conditions at three locations and under controlled greenhouse conditions during the dry season of 2019 (DS2019). In the early generation, 210 plants of the BC1F1population and 440 plants of BC2F1population were evaluated for their heat tolerance, and the spikelet fertility distribution within the BC1F1, BC2F1and BC3F1populations showed a skewed-right pattern. In addition, most rice plants in every generation were heat sensitive. Finally, compared with PSL2, the four-candidate heat-tolerant lines exhibited a high percentage of spikelet fertility and high yield. In addition, the one candidate line, BC2F7-6-5-4-1-1-21 was most similar to PSL2 in terms of genetic background, plant type and grain quality. Thus, backcross breeding programmes via the spikelet fertility can be used as an indirect trait to select for heat tolerance.

Identification of QTLs for high grain yield and component traits in new plant types of rice.

A panel of 60 genotypes comprising New Plant Types (NPTs) along with indica, tropical and temperate japonica genotypes was phenotypically evaluated for four seasons in irrigated situation for grain yield per se and component traits. Twenty NPT genotypes were found promising with an average grain yield varying from 5.45 to 8.8 t/ha. A total of 85 SSR markers were used in the study to identify QTLs associated with grain yield per se and related traits. Sixty-six (77.65%) markers were found to be polymorphic. The PIC values varied from 0.516 to 0.92 with an average of 0.704. A moderate level of genetic diversity (0.39) was detected among genotypes. Variation to the tune of 8% within genotypes, 68% among the genotypes within the population and 24% among the populations were observed (AMOVA). This information may help in identification of potential parents for development of transgressive segregants with very high yield. The association analysis using GLM and MLM models led to the identification of 30 and 10 SSR markers associated with 70 and 16 QTLs, respectively. Thirty novel QTLs linked with 16 SSRs were identified to be associated with eleven traits, namely tiller number (qTL-6.1, qTL-11.1, qTL-4.1), panicle length (qPL-1.1, qPL-5.1, qPL-7.1, qPL-8.1), flag leaf length (qFLL-8.1, qFLL-9.1), flag leaf width (qFLW-6.2, qFLW-5.1, qFLW-8.1, qFLW-7.1), total no. of grains (qTG-2.2, qTG-a7.1), thousand-grain weight (qTGW-a1.1, qTGW-a9.2, qTGW-5.1, qTGW-8.1), fertile grains (qFG-7.1), seed length-breadth ratio (qSlb-3.1), plant height (qPHT-6.1, qPHT-9.1), days to 50% flowering (qFD-1.1) and grain yield per se (qYLD-5.1, qYLD-6.1a, qYLD-11.1).Some of the SSRs were co-localized with more than two traits. The highest co-localization was identified with RM5709 linked to nine traits, followed by RM297 with five traits. Similarly, RM5575, RM204, RM168, RM112, RM26499 and RM22899 were also recorded to be co-localized with more than one trait and could be rated as important for marker-assisted backcross breeding programs, for pyramiding of these QTLs for important yield traits, to produce new-generation rice for prospective increment in yield potentiality and breaking yield ceiling.

Pyramiding Bacterial Blight Resistance Genes in Tainung82 for Broad-Spectrum Resistance Using Marker-Assisted Selection.

Tainung82 (TNG82) is one of the most popular japonica varieties in Taiwan due to its relatively high yield and grain quality, however, TNG82 is susceptible to bacterial blight (BB) disease. The most economical and eco-friendly way to control BB disease in japonica is through the utilization of varieties that are resistant to the disease. In order to improve TNG82’s resistance to BB disease, five bacterial blight resistance genes (Xa4, xa5, Xa7, xa13 and Xa21) were derived from a donor parent, IRBB66 and transferred into TNG82 via marker-assisted backcrossing breeding. Five BB-resistant gene-linked markers were integrated into the backcross breeding program in order to identify individuals possessing the five identified BB-resistant genes (Xa4, xa5, Xa7, xa13 and Xa21). The polymorphic markers between the donor and recurrent parent were used for background selection. Plants having maximum contribution from the recurrent parent genome were selected in each generation and crossed with the recipient parent. Selected BC3F1 plants were selfed in order to generate homozygous BC3F2 plants. Nine pyramided plants, possessing all five BB-resistant genes, were obtained. These individuals displayed a high level of resistance against the BB strain, XF89-b. Different BB gene pyramiding lines were also inoculated against the BB pathogen, resulting in more than three gene pyramided lines that exhibited high levels of resistance. The five identified BB gene pyramided lines exhibited yield levels and other desirable agronomic traits, including grain quality and palatability, consistent with TNG82. Bacterial blight-resistant lines possessing the five identified BB genes exhibited not only higher levels of resistance to the disease, but also greater yield levels and grain quality. Pyramiding multiple genes with potential characteristics into a single genotype through marker-assisted selection can improve the efficiency of generating new crop varieties exhibiting disease resistance, as well as other desirable traits.

Morphological characterization of Katarni rice (Oryza sativa L.) derived backcross population for yield and its contributing traits

The aim of backcross breeding is the introgression of a certain trait of interest in a popular variety from a suitable donor variety. Morphological characterization of backcross derived line is a crucial step in backcross breeding programme. Present investigation was framed for the morphological characterization of advance backcross population, developed to introgress semi-dwarf and early maturing traits of Rajendra Sweta and BPT5204 into the background of tall, late maturing scented Katarni rice. The results indicated a significant decrease in the plant height and days of 50 % flowering in the backcross derived lines with respect to Katarni rice. Higher values of phenotypic coefficient of variation (PCV) than the genotypic coefficient of variation (GCV) for all character indicated environmental influence in the development of all characters. High heritability with high genetic advance as percent of mean was observed for 1000 grain weight and plant height. Highly significant and positive correlation with yield per plant was exhibited by traits like 1000 grain weight and leaf aroma. Result of path coefficient analysis indicated direct positive effect of characters like L/B ratio, kernel length and 1000 grain weight on grain yield per plant.

DNA Fingerprinting and Diversity Analysis of Some Aus Rice Landraces

Objective: The allelic diversity and relationship among 48Aus rice landraces were determined through SSR markers. A total of 11 SSR markers were used to characterize all Aus rice genotypes. Methods/Findings: All of them were polymorphic showing different chromosome numbers. The number of alleles per locus varied from 3 alleles (RM234 and RM277) to 15 alleles (RM493). A total number of 72 alleles were detected with an average number of 8.91 alleles per locus. The polymorphic information content (PIC) values ranged from 0.19 (RM277) to 0.90 (RM493) with an average 0.70. The highest PIC value was obtained in RM493 (0.89) followed by RM526 (0.85) and The highest genetic dissimilarity (1.00) was found among the nineteen Aus genotypes combinations viz., Kalojira TAPL-68, Busmoti-sufoid, Hatisail, Sakharkhara, Khasa, Black, Ukinmodhu, Fulkari, Porbotjira, Straw THPL-554, Kalonunia, China IRRI, Mehedhan, Tulsimoni, Meny, Tilkapur, Nunia, Lalmota and Tapu. This material may be selected as potential parents for crop improvement for their distinctive characters. Whereas lowest genetic dissimilarity was found between Chini sagor-1 vs Malshira and Kalijir TAPL74 vs Kalojira (0.18) followed by three other pairs (0.28). Application: The genetic distance-based results seen in the Unweighted Pair Group Method of Arithmetic means (UPGMA) revealed six genetic groups. These landraces will be useful for the selection of diverse parents, background selection during backcross breeding programs and assist in broadening germplasm-based rice breeding programs in the near future. Keywords: DNA Fingerprinting, Genetic Diversity, Landraces, Microsatellites.