Medium Slender Grain Research Articles

Improvement of blast resistance of the popular high-yielding, medium slender-grain type, bacterial blight resistant rice variety, Improved Samba Mahsuri by marker-assisted breeding

Improved Samba Mahsuri (ISM) is a popular, high-yielding, bacterial blight resistant rice variety possessing medium-slender grain type. As ISM is highly susceptible to blast disease of rice, through the present study we have transferred two major blast resistance genes, Pi2 and Pi54 into the elite variety by marker-assisted backcross breeding. The two blast resistance genes were transferred to ISM through sets of backcrosses. In every backcross generation, PCR-based markers, specific for the blast resistance genes (Pi2 and Pi54) and bacterial blight resistance genes (Xa21, xa13 and xa5) were utilized for foreground selection, while a set of 144 parental polymorphic SSR markers were used for background selection and backcrossing was carried out until BC2 generation. A solitary BC2F1 plant possessing Pi2 or Pi54 along with Xa21, xa13 and xa5 and > 90% recovery of ISM genome was selected from the two sets of backcrosses were crossed and the intercross F1s (ICF1s) thus obtained were selfed to generate ICF2s. Homozygous ICF2 plants carrying all the five resistance genes were identified through markers and advanced through selfing till ICF5 generation by adopting pedigree method of selection. Three best lines at ICF5, possessing excellent resistance against bacterial blight and blast and closely resembling or superior to ISM in terms of grain quality: yield and agro-morphological traits have been identified and advanced for multi-location trials.

Marker assisted introgression of bacterial blight resistant gene into submergence tolerance rice variety BRRI dhan52

BRRI dhan52 is a uniquire submergence tolerant rice variety containing prominant genetic background of BR11, a mega rainfed lowland rice (RLR) variety of Bangladesh, but is susceptible to bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo). The variety is considerably popular in the southern part of Bangladesh due to its high yield in flash flood condition and comparatvely medium slender grain. Molecular markers linked to BB resistance genes (Xa genes) and submergence QTL (SUB1) were utilized in a marker-aided selection program to develop elite breeding lines with broad-spectrum resistance to bacterial blight. Sequence tagged site (STS) and simple sequence repeat (SSR) markers were essentially used to detect the genes for BB and submergence as well. In backcross generation, markers closely linked to Xa21 and SUB1 QTL were used to select desirable plants possessing these resistance genes (foreground selection) and microsatellite markers polymorphic between donor and recurrent parent were also used to select plants that have maximum contribution from the recurrent parent genome (background selection). In BC1F1 generation, three best plants consiquently were selected from previously selected ten double heterozygous (Xa21 and SUB1 QTL) plants. The percentage of recipient genome recovery in the best plant 1, 2 and 3 were 78.7%, 75.83% and 75.4%, respectively. Eventually this work illustrates the successful application of marker-assisted breeding for introgression of bacterial blight resistant gene into a rice variety of Bangladesh.Bangladesh J. Agril. Res. 42(3): 403-411, September 2017

Marker-assisted pyramiding of bacterial blight and gall midge resistance genes into RPHR-1005, the restorer line of the popular rice hybrid DRRH-3

Bacterial blight (BB) of rice caused by the pathogen Xanthomonas oryzae pv. oryzae and the insect gall midge (GM) (Orseolia oryzae) are two major constraints of rice production. The present study was carried out to improve RPHR-1005, a stable restorer line of the fine-grain-type rice hybrid DRRH-3, for BB and GM resistance through marker-assisted backcross breeding (MABB). Two major GM resistance genes, Gm4 and Gm8, and a major BB resistance gene, Xa21, were selected as target genes for transfer to RPHR-1005. Two sets of backcrosses were carried out to combine either Xa21 + Gm4 or Xa21+ Gm8 into RPHR-1005 using breeding lines in the genetic background of ISM possessing either Gm4 or Gm8 along with Xa21. Foreground selection was performed for Xa21, Gm4, Gm8, and the major fertility restorer genes Rf3 and Rf4 using gene-specific markers, while 61 polymorphic simple sequence repeat (SSR) markers were used for background selection and marker-assisted backcrossing was continued until BC2 generation. A promising homozygous backcross-derived plant at the BC2F2 generation possessing Xa21 + Gm4, and another possessing Xa21 + Gm8, were intercrossed to stack the target resistance genes. At ICF 4 (inter-crossed F4) , three promising lines possessing the three target resistance genes in a homozygous condition along with fine-grain type, complete fertility restoration, and better panicle exsertion than RPHR-1005 have been identified. Among these, a single line, # RPIC-16-65-125, showed better yield, was highly resistant to BB and GM, was of medium–slender grain type, and had complete fertility restoration along with better panicle exsertion and taller plant type than RPHR-1005. This is the first report of combining resistance against BB and GM in the genetic background of a hybrid rice parental line.

Marker-assisted improvement of the elite restorer line of rice, RPHR-1005 for resistance against bacterial blight and blast diseases.

This study was carried out to improve the RPHR-1005, a stable restorer line of the popular medium slender grain type rice hybrid, DRRH-3 for bacterial blight (BB) and blast resistance through marker-assisted backcross breeding (MABB). Two major BB resistance genes, Xa21 and Xa33 and a major blast resistance gene, Pi2 were transferred to RPHR-1005 as two individual crosses. Foreground selection for Xa21, Xa33, Pi2, Rf3 and Rf4 was done by using gene-specific functional markers, while 59 simple sequence repeat (SSR) markers polymorphic between the donors and recipient parents were used to select the best plant possessing target resistance genes at each backcross generation. Backcrossing was continued till BC2F2 and a promising homozygous backcross derived line possessing Xa21+ Pi2 and another possessing Xa33 were intercrossed to stack the target resistance genes into the genetic background of RPHR-1005. At ICF4, 10 promising lines possessing three resistance genes in homozygous condition along with fine-grain type, complete fertility restoration, better panicle exertion and taller plant type (compared to RPHR-1005) were identified.

Marker-assisted introgression of the major bacterial blight resistance gene, Xa21 and blast resistance gene, Pi54 into RPHR-1005, the restorer line of the popular rice hybrid, DRRH3

The elite Indian rice hybrid, DRRH3 is highly susceptible to two major diseases, bacterial blight (BB) and blast, which limit its productivity significantly. In the present study, we have introgressed two major genes, viz., Xa21 and Pi54 conferring resistance against BB and blast, respectively into RPHR-1005, the male parent of DRRH3 through marker-assisted backcross breeding (MABB) and analyzed the backcross derived plants for their resistance against BB and blast. RPBio Patho-2 was used as a donor for both the resistance genes. Gene-specific markers were used for the foreground selection of Xa21 and Pi54 at each stage of backcrossing and markers specific for the major fertility restorer genes, Rf3 and Rf4 were used only at BC1F1 generation for foreground selection. Background selection was done using 62 polymorphic SSR markers and marker-assisted backcrossing was continued till BC3 generation. At BC3F4, through intensive phenotype-based selections 15 promising lines (ABLs) possessing high level of resistance against BB and blast, high yield, fine-grain type, complete fertility restoration along with better panicle exsertion and taller plant type as compared to RPHR-1005 were identified and test crossed with APMS 6 A, the female parent of DRRH3. The newly derived hybrids (i.e. improved versions of DRRH3) were observed to possess high level of resistance against BB and blast along with medium-slender grain type and yield level better than or equivalent to that of DRRH3. Our study exemplifies the utility of MABB for targeted improvement of multiple traits in hybrid rice.

Evaluation of drought tolerance in backcross inbred lines of rice genotypes based on selection indices

Drought tolerant lines of Improved White Ponni (IWP) were developed by marker assisted back crossing of IWP with Apo. Three drought tolerant backcross inbred lines (BILs), developed by introgressing the drought tolerance QTLs from Apo were evaluated for drought tolerance along with their parents based on drought indices. Twenty drought indices were calculated based on grain yield under drought and irrigated conditions. Yield in drought and irrigated conditions were significantly and positively correlated with mean productivity index, harmonic mean, geometric mean of productivity and stress tolerance index. Ranking method and three dimensional plot discriminated IWP-4-2 as the most drought tolerant genotype, which was placed in group A (Genotypes, which performed good under drought and irrigated conditions), and outperformed the drought tolerant parent, Apo. IWP-4-2 possessed medium slender grains similar to the recurrent parent, IWP. Based on its drought tolerance and grain type IWP-4-2 can also be used as donor parent for developing climate resilient rice variety suitable to conditions obtaining in Tamil Nadu.

A Brief Comparative Effectiveness Research (CER) about Conventional and Homeopathic Treatment of Type 2 Diabetic Patients

A Brief Comparative Effectiveness Research (CER) about Conventional and Homeopathic Treatment of Type 2 Diabetic Patients Bacterial leaf blight (BB) disease caused by Xanthomonas oryzae pv. oryzae is one of the most severe diseases effecting Basmati rice production in India. CSR-30 is widely grown in Haryana and is extremely popular amongst rice farmers and consumers because of its salt tolerance, aroma, high yield, medium slender grains and excellent cooking and eating qualities. CSR-30 lacks tolerance to BB. The present investigation was therefore planned to introgress BB resistance genes (xa5, xa13 & Xa21) from IRBB-60 to CSR-30. The pyramided BC3 F1 genotypes were evaluated for BB incidence under artificial field inoculation. Scoring of inoculated plant was done 14 days after inoculation. The triple and double resistance genes pyramided genotypes provided enhanced resistance as expressed by smaller mean lesion length in comparison to genotypes with individual genes...

Evaluation of Pyramided Rice Genotypes Derived from Cross Between CSR-30 and IRBB-60 Basmati Variety against Bacterial Leaf Blight

Evaluation of Pyramided Rice Genotypes Derived from Cross Between CSR-30 and IRBB- 60 Basmati Variety against Bacterial Leaf Blight Bacterial leaf blight (BB) disease caused by Xanthomonas oryzae pv. oryzae is one of the most severe diseases effecting Basmati rice production in India. CSR-30 is widely grown in Haryana and is extremely popular amongst rice farmers and consumers because of its salt tolerance, aroma, high yield, medium slender grains and excellent cooking and eating qualities. CSR-30 lacks tolerance to BB. The present investigation was therefore planned to introgress BB resistance genes (xa5, xa13 & Xa21) from IRBB-60 to CSR-30. The pyramided BC3 F1 genotypes were evaluated for BB incidence under artificial field inoculation. Scoring of inoculated plant was done 14 days after inoculation. The triple and double resistance genes pyramided genotypes provided enhanced resistance as expressed by smaller mean lesion length in comparison to genotypes with individual genes.

Assessment of adaptability of recently released salt tolerant rice varieties in coastal regions of South Bangladesh

Productivity of rice is adversely affected by salinity and water logging stresses in coastal zones, and affected areas are progressively expanding as consequences of climate change and overexploitation of natural resources to meet the needs of increasing populations. Several varieties were developed and commercialized in this region in recent years, including some salt and stagnant flood (SF, medium deep, 25–50cm water depth) tolerant varieties. However, suitability of these varieties based on adaptation to local conditions across the region and farmers’ preferences have not been sufficiently evaluated. Genotype by environment analysis leads to identification of varieties with stable performance, or suitability to specific regions. Two frequently used statistical analyses are additive main effects and multiplicative interaction (AMMI); and the genotype main effects and genotype×environment interaction effects (GGE). These models were used in this study to identify stable rice varieties for the wet and dry seasons in South Bangladesh. Experiments were conducted at six sites over four years (2010–2013) in coastal Bangladesh, using eight and five varieties for wet and dry season, respectively. The trials were laid in a randomized complete block design (RCBD) with three replications. Genotypic contribution was much higher than the environmental effect on grain yield in the wet season, while the environmental contribution was much higher than genotypic effect during the dry season. SF stress affected yield of wet season rice; but in the dry season, salinity stress had major effect on grain yield. The variety BRRI dhan54 was identified as the most suitable genotype with wider adaptability in the region during the wet season, followed by BRRI dhan40 and BRRI dhan53, while BRRI dhan47 was the most stable variety followed by BRRI dhan61 and BINA dhan8 for the dry season across all sites. However, when these varieties were evaluated based on farmers’ preferences in participatory varietal selection, BRRI dhan53; a short duration variety with medium slender grains was the most preferred, followed by BRRI dhan54 and BRRI dhan40 for wet season, and in the dry season BRRI dhan47 was the most popular variety followed by BRRI dhan61, which agreed with ranking based on yield. Modern varieties were far superior over traditional varieties based on grain yield and farmers’ preferences, and should be targeted for large-scale seed production and dissemination.

Marker-assisted introgression of bacterial blight and blast resistance into DRR17B, an elite, fine-grain type maintainer line of rice

DRR17A is a stable wild-abortive cytoplasmic male sterile line with medium-slender grain type. DRR17A and its maintainer line DRR17B are highly susceptible to two of the major rice diseases, bacterial blight (BB) and blast. To improve DRR17B for resistance against BB and blast, we have introgressed a major dominant gene each conferring resistance against BB (Xa21) and blast (Pi54) into the maintainer line through marker-assisted backcross breeding using RP-Bio-Patho-2 (a near-isogenic line of Samba Mahsuri possessing Xa21 and Pi54) as the donor parent. PCR-based molecular markers tightly linked to Xa21 and Pi54 were used for foreground selection of the resistance plants at each backcross generation, while molecular markers tightly linked to the major fertility restorer genes, Rf3 and Rf4, were used for negative selection (i.e. selection of plants possessing non-fertility-restoring alleles at the two loci) at BC1 generation. After foreground selection for the target genes at each backcross generation, the ‘positive’ plants were screened with parental polymorphic markers for identifying backcross plants possessing maximum recovery of DRR17B genome. Marker-assisted backcrossing was continued till BC3 generation, and a single BC3F1 plant possessing the target genes with ~94 % recovery of recurrent parent genome was identified and selfed to generate BC3F2s. A total of six homozygous BC3F2 plants were identified and advanced. At BC3F5, six promising, stable, backcross-derived lines possessing high level of resistance against BB and blast, high yield, short plant stature, fine-grain type, have been identified; their maintenance ability and heterotic potential validated through test crosses and these lines are being converted to CMS lines through marker-assisted breeding.

Molecular mapping of rice blast resistance gene Pi-1(t) in the elite indica variety Samba mahsuri

Samba mahsuri (BPT 5204) is a cultivar of the medium slender grain indica variety of Oryza sativa grown across India for its high yield and quality. However, this cultivar is susceptible to several diseases and pests including rice blast. The analysis of near isogenic lines indicated the presence of a resistance gene, Pi-1(t) in the donor cultivar C101LAC which is highly resistant to the rice blast fungus Magnaporthe grisea (M. grisea). C101LAC was crossed with susceptible indica rice cultivar (BPT 5204) to generate the mapping population. A mendelian segregation ratio of 3:1 for resistant to susceptible F2 plants using bulk segregation analysis confirmed the presence of a major gene pi-1(t) by simple sequence repeats marker RM224 to the highly virulent blast isolate DRR 001.

Marker assisted introgression of bacterial blight resistance in Samba Mahsuri, an elite indica rice variety

Samba Mahsuri (BPT5204) is a medium slender grain indica rice variety that is very popular with farmers and consumers across India because of its high yield and excellent cooking quality. However, the variety is susceptible to several diseases and pests, including bacterial blight (BB). We have used PCR based molecular markers in a backcross-breeding program to introgress three major BB resistance genes (Xa21, xa13 and xa5) into Samba Mahsuri from a donor line (SS1113) in which all the three genes are present in a homozygous condition. At each backcross generation, markers closely linked to the three genes were used to select plants possessing these resistance genes (foreground selection) and microsatellite markers polymorphic between donor and recurrent parent were used to select plants that have maximum contribution from the recurrent parent genome (background selection). A selected BC4F1 plant was selfed to generate homozygous BC4F2 plants with different combinations of BB resistance genes. The three-gene pyramid and two-gene pyramid lines exhibited high levels of resistance against the BB pathogen. Under conditions of BB infection, the three-gene pyramid lines exhibited a significant yield advantage over Samba Mahsuri. Most importantly, these lines retain the excellent grain and cooking qualities of Samba Mahsuri without compromising the yield as determined in multi-location trials. This work demonstrates the successful application of marker-assisted selection for targeted introgression of multiple resistance genes into a premium quality rice variety.