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Cultivated rice is a high-volume, low-value cereal crop providing staple food to more than 50% of the world populace. A small group of rice cultivars, traditionally produced on the Indo-Gangetic plains and popularly known as Basmati, have exquisite quality grain characteristics and are a prized commercial commodity. Efforts to improve the yield potential of Basmati have led to the development of several crossbred Basmati-like cultivars. In this study we have analysed the genetic diversity and interrelationships among 33 rice genotypes consisting of the traditional Basmati, improved Basmati-like genotypes developed in India and elsewhere, American long-grain rice and a few non-aromatic rice using a DNA marker-based approach - fluorescent-amplified fragment length polymorphism (f-AFLP). Using a set of nine primer-pairs we scored a total of 10,672 data points over all of the genotypes in the size range of 75-500 bp. The scored data points corresponded to a total of 501 AFLP markers (putative loci/genome landmarks) of which 327 markers (65%) were polymorphic. The f-AFLP marker data, which were analysed using different clustering algorithms and principal component analysis, indicate that: (1) considerable genetic variability exists in the analysed genotypes; (2) traditional Basmati cultivars could be distinctly separated from the crossbred Basmati-like genotypes as well as from the non-aromatic rice; (3) the crossbred Basmati-like cultivars from the subcontinent and elsewhere are genetically very distinct; (4) f-AFLP-based clustering, in general, conforms to the putative pedigree of the improved genotypes. Moreover, analysis to ascertain the scope of AFLP as a technique suggests that the polymorphism revealed by three selective primer-pair combinations is sufficient to obtain reliable estimates of genetic diversity for the type of material used in this study. However, its utility to identify group-specific DNA markers was discounted due to a low frequency of observed group-specific discrete markers.

The rapid progress in rice genotyping must be matched by advances in phenotyping. A better understanding of genetic variation in rice for drought response, root traits, and practical methods for studying them are needed. In this study, the OryzaSNP set (20 diverse genotypes that have been genotyped for SNP markers) was phenotyped in a range of field and container studies to study the diversity of rice root growth and response to drought. Of the root traits measured across more than 20 root experiments, root dry weight showed the most stable genotypic performance across studies. The environment (E) component had the strongest effect on yield and root traits. We identified genomic regions correlated with root dry weight, percent deep roots, maximum root depth, and grain yield based on a correlation analysis with the phenotypes and aus, indica, or japonica introgression regions using the SNP data. Two genomic regions were identified as hot spots in which root traits and grain yield were co-located; on chromosome 1 (39.7–40.7 Mb) and on chromosome 8 (20.3–21.9 Mb). Across experiments, the soil type/ growth medium showed more correlations with plant growth than the container dimensions. Although the correlations among studies and genetic co-location of root traits from a range of study systems points to their potential utility to represent responses in field studies, the best correlations were observed when the two setups had some similar properties. Due to the co-location of the identified genomic regions (from introgression block analysis) with QTL for a number of previously reported root and drought traits, these regions are good candidates for detailed characterization to contribute to understanding rice improvement for response to drought. This study also highlights the utility of characterizing a small set of 20 genotypes for root growth, drought response, and related genomic regions.