Iron (Fe) toxicity is a major abiotic stress which severely reduces rice yield in many countries of the world. Genetic variation for this stress tolerance exists in rice germplasms. Mapping of gene(s)/QTL controlling the stress tolerance and transfer of the traits into high yielding rice varieties are essential for improvement against the stress. A panel population of 119 genotypes from 352 germplasm lines was constituted for detecting the candidate gene(s)/QTL through association mapping. STRUCTURE, GenAlEx and Darwin softwares were used to classify the population. The marker-trait association was detected by considering both the Generalized Linear Model (GLM) and Mixed Linear Model (MLM) analyses. Wide genetic variation was observed among the genotypes present in the panel population for the stress tolerance. Linkage disequilibrium was detected in the population for iron toxicity tolerance. The population was categorized into three genetic structure groups. Marker-trait association study considering both the Generalized Linear Model (GLM) and Mixed Linear Model (MLM) showed significant association of leaf browning index (LBI) with markers RM471, RM3, RM590 and RM243. Three novel QTL controlling Fe-toxicity tolerance were detected and designated as qFeTox4.3, qFeTox6.1 and qFeTox10.1. A QTL reported earlier in the marker interval of C955-C885 on chromosome 1 is validated using this panel population. The present study showed that QTL controlling Fe-toxicity tolerance to be co-localized with the QTL for Fe-biofortification of rice grain indicating involvement of common pathway for Fe toxicity tolerance and Fe content in rice grain. Fe-toxicity tolerance QTL qFeTox6.1 was co-localized with grain Fe-biofortification QTLs qFe6.1 and qFe6.2 on chromosome 6, whereas qFeTox10.1 was co-localized with qFe10.1 on chromosome 10. The Fe-toxicity tolerance QTL detected from this mapping study will be useful in marker-assisted breeding programs.

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-Genetic diversity in thirty Indian

The cytophotometric estimation of 4C DNA content, and karyotypic and somatic chromosome number analyses were carried out in 30 genotypes comprising seven cultivars and 23 advanced breeding lines of Solanum tuberosum. Detailed karyotype analysis revealed genotype specific chromosomal characteristics and structural alterations in chromosomes of the genome, with a rare phenomenon of aneusomatic (2n = 4x + 2 = 50) condition in cv.K. Chandramukhi. The origin of this variation could be attributed to mitotic non-disjunction in the shoots giving rise to aneusomatic roots. Highly significant variations in the genome length, volume and total form percentage were noted at the cultivar level. The total chromosome length varied from 84.56 microm in cv.K. Pukhraj to 127.62 microm in MS/89-60, with an average value of 100.94 microm +/- 1.82. Total chromosome volume varied from 57.22 microm3 in MS/92-1090 to 132.64 microm3 in JW-160. Significant variations in the 4C DNA content (7.28-15.83 pg) were recorded at the cultivar level, with an exceptionally high DNA content (22.24 pg) in cv.K. Chandramukhi. This could be due to the aneusomatic condition of this genotype. Correlation studies revealed interdependence between the chromosomal and nuclear parameters of the genotypes. Structural alterations in the chromosomes, as well as loss or addition of highly repetitive sequences in the genome, caused variations in DNA content at the cultivar level. Variations in genomic structure and nuclear DNA content of the 48-chromosome genotypes suggest a genetic drift during microevolution, leading to the development of new cultivars.

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