Marker Assisted Introgression of Resistance Genes and Phenotypic Evaluation Enabled Identification of Durable and Broad-Spectrum Blast Resistance in Elite Rice Cultivar, CO 51.

Across the globe, rice cultivation is seriously affected by blast disease, caused by Magnaporthe oryzae. This disease has caused heavy yield loss to farmers over the past few years. In this background, the most affordable and eco-friendly strategy is to introgress blast-resistant genes from donors into elite rice cultivars. However, it is not only challenging to evolve such resistance lines using conventional breeding approaches, but also a time-consuming process. Therefore, the marker-assisted introduction of resistance genes has been proposed as a rapid strategy to develop durable and broad-spectrum resistance in rice cultivars. The current study highlights the successful introgression of a blast resistance gene, i.e., Pi9, into CO 51, an elite rice cultivar which already has another resistance gene named Pi54. The presence of two blast resistance genes in the advanced backcross breeding materials (BC2F2:3) was confirmed in this study through a foreground selection method using functional markers such as NBS4 and Pi54MAS. The selected positive introgressed lines were further genotyped for background selection with 55 SSR markers that are specific to CO 51. Consequently, both Pi9 as well as Pi54 pyramided lines, with 82.7% to 88.1% of the recurrent parent genome recovery, were identified and the selected lines were evaluated under hotspot. The analysis outcomes found that both the lines possessed a high level of resistance against blast disease during the seedling stage itself. In addition to this, it was also noticed that the advanced breeding rice lines that carry Pi9 + Pi54 were effective in nature and exhibited a higher degree of resistance against blast disease compared to the lines that were introgressed with a single blast resistance gene. Thus, the current study demonstrates a rapid and a successful introgression and pyramiding of two blast resistance genes, with the help of markers, into a susceptible yet high-yielding elite rice cultivar within a short period of time. Those gene pyramided rice lines can be employed as donors to introgress the blast-resistant genes in other popular susceptible cultivars.

Early flowering, good grain quality mutants through gamma rays and EMS for enhancing per day productivity in rice (Oryza sativa L.).

PURPOSE: Rice is the prominent crop of world and it frames the important component of food chain. But, long duration of highly preferred rice varieties requires more water and are prone to biotic and abiotic stresses. Short duration rice varieties serve as a promising alternative in such cases. Hence, the present study was taken up to induce early flowering mutants in popular rice variety Bapatla 2231 (BPT 2231), a long duration medium slender rice variety using gamma rays and Ethyl Methane Sulfonate (EMS) treatment combinations. MATERIALS AND METHODS: Five hundred well filled and viable grains of optimum moisture content (12%) were subjected to irradiation with 8 doses comprising 100 Gy, 200 Gy, 300 Gy, 350 Gy, 400 Gy, 450 Gy, 500 Gy and 600 Gy treatments. For combination treatments, the irradiated seeds of gamma rays were further treated with 30 mM concentrations of Ethyl Methane sulfonate (EMS). The irradiated population were raised up to M3 generation for the identification of early maturing mutants. The isolated early maturing mutants in M3 generation were characterized for phenotypic, biochemical and grain qualities. RESULTS: The frequency of desirable early maturing mutants was observed more in combination treatments than the individual treatments of gamma rays. A total of 34 early maturing mutants (M) with variation for grain quality and biochemical traits were obtained. The mutants M-1, M-3, M-5, M-32, and M-34 were high yielding with fine grain type. The mutants M-4, M-17, M-18, M-19, M-20, and M-26 were high yielding with bold grain type. The mutants M-22, M-23, M-24, M-27, and M-28 were high in nutrient content. The early mutants matured 40-50 days earlier than control. CONCLUSION: In this variety, the combination treatments showed higher mutation frequency, mutagenic effectiveness and efficiency than the gamma rays in induction of both chlorophyll and viable mutants. This study revealed that the combination treatments were more effective in inducing early mutants than the gamma ray treatments alone. The early maturing mutants can be released as variety after evaluation under different yield trials and the mutants with increased nutrient content and varied grain quality can be utilized in hybridization/heterosis breeding programs for rice crop improvement.

Marker-aided selection and validation of various Pi gene combinations for rice blast resistance in elite rice variety ADT 43.

Rice blast caused by fungal pathogen Pyricularia oryzae has a major impact on reducing yield potential of rice. In this study, homozygous plants were selected using microsatellite markers from the BC3F2 population pyramided with four major genes in elite rice variety ADT 43. Background and selected lines with various blast resistance gene combinations were screened under natural conditions to study the effects of various gene combinations. Upon inspection of lines with different gene combinations, the three-gene pyramided line Pi54+Pi33+Pi1 was found to be highly resistant with the score of 3.3 followed by other three-gene pyramided lines Pi54+Pi2+Pi1 and Pi33+Pi2+Pi1, with the scores of 3.9 and 3.8, respectively. Two-gene pyramided lines Pi54+Pi1, Pi33+Pi1 and Pi2+Pi1 were found to be moderately resistant with a mean score of 4.0 each. In the case of monogenic lines, positive plants for Pi54 performed almost equal to three-gene pyramided lines with a mean score of 3.6. Lines with Pi and Pi1 were found to be moderately resistant and moderately susceptible with the mean scores of 4.1 and 4.5, respectively.

Effectiveness of selection, parent-offspring correlation and regression in bacterial blight resistance genes introgressed rice segregating population / Efetividade da seleção, correlação pais-prole e regressão nos genes de resistência à ferrugem bacteriana introgressaram a população segregante de arroz

ABSTRACT: The effectiveness of early generation selection was practiced in bacterial blight resistance genes introgressed F2 and F2:3 population of the cross CB 174 R × IRBB 60 in rice. F2 Selection have been proved to be robust and effective tool in crop improvement program. Selection differential was positive for all studied traits. Selection response was high for number of grains, thus indicating the effectiveness of selection for these character. Realized heritability was found high for number of grains and thousand grain weight, suggested that direct selection was effective. Expected selection response and predicted genetic gain was high for number of grains. Parent-offspring correlation showed low but significance association for number of productive tillers (r=0.47**, P<0.01), single plant yield (r=0.35**, P<0.01) and (r=0.30*, P<0.05) panicle length in F2 and F2:3 generation indicates that selection was fruitful in early generation. Statistically regression coefficient was not significant linear dependence of the mean of F2 and F2:3 generation.

RESUMO: A eficácia da selecção das primeiras gerações foi praticada na população F2 e F2: 3 de CB 174 R × IRBB 60 do gene bacteriano. A seleção foi positiva para todos os caracteres estudados. A resposta de seleção foi alta para o número de grãos. A herdabilidade realizada foi encontrada alta para o número de grãos e mil grãos de peso, sugeriu que a seleção direta foi eficaz. A resposta à seleção esperada e o ganho genético previsto foi elevado para o número de grãos. A correlação entre pais e filhos mostrou forte associação com o número de latifundiários produtivos (r = 0,47**, P<0,01), produção única de planta (r = 0,35**, P<0,01) e (r = 0,30*, P<0,05) Comprimento em F2 e F2:3 geração indica que a seleção foi frutífera. O coeficiente de regressão estatística não foi dependência linear significativa da média de F2 e F2:3 geração.

Analysis of Population Structure and Genetic Diversity in Rice Germplasm Using SSR Markers: An Initiative Towards Association Mapping of Agronomic Traits in Oryza Sativa.

BACKGROUND: Genetic diversity is the main source of variability in any crop improvement program. It serves as a reservoir for identifying superior alleles controlling key agronomic and quality traits through allele mining/association mapping. Association mapping based on LD (Linkage dis-equilibrium), non-random associations between causative loci and phenotype in natural population is highly useful in dissecting out genetic basis of complex traits. For any successful association mapping program, understanding the population structure and assessing the kinship relatedness is essential before making correlation between superior alleles and traits. The present study was aimed at evaluating the genetic variation and population structure in a collection of 192 rice germplasm lines including local landraces, improved varieties and exotic lines from diverse origin. RESULTS: A set of 192 diverse rice germplasm lines were genotyped using 61 genome wide SSR markers to assess the molecular genetic diversity and genetic relatedness. Genotyping of 192 rice lines using 61 SSRs produced a total of 205 alleles with the PIC value of 0.756. Population structure analysis using model based and distance based approaches revealed that the germplasm lines were grouped into two distinct subgroups. AMOVA analysis has explained that 14 % of variation was due to difference between with the remaining 86 % variation may be attributed by difference within groups. CONCLUSIONS: Based on these above analysis viz., population structure and genetic relatedness, a core collection of 150 rice germplasm lines were assembled as an association mapping panel for establishing marker trait associations.