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One hundred and ninety three parental lines obtained from 26 countries for an international rice molecular breeding program were evaluated using 101 well-distributed simple sequence repeat (SSR) markers. An overall genetic diversity of 0.68 and an average of 6.3 alleles per locus were revealed, indicating a high level of genetic variation in these lines. Cluster analysis of the 193 accessions showed three major groups and nine subgroups. Group I corresponded to the classical indica subspecies, whereas groups II and III belong to the japonica subspecies. Indica and japonica differentiation accounted for only 6.5% of the total variation in the entire sample and 93.5% was due to within-subspecies diversity. Differentiation among eco-geographic regions accounted for 24% of the diversity within the subspecies. Larger amounts of the eco-geographical differentiation were resolved within japonica than within indica. The largest indica-japonica differentiation based on the single locus level was detected by markers on chromosomes 9 and 12, while the smallest differentiation was detected by markers on chromosomes 4 and 8. Furthermore, genetic differences at the single-locus and two-locus levels, as well as components due to allelic and gametic differentiation, were revealed between indica and japonica and among the main geographic regions. The multilocus analysis in genetic diversity showed a higher proportion of variation caused by predominant non-random associations of different loci within and among the classified subspecies and geographic subdivisions. The results suggest that selection for eco-geographical adaptation on multilocus associations was largely responsible for the maintenance of the extensive variation in the primary gene pool of rice.

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The species specificity of the Candida krusei DNA fingerprinting probe CkF1,2 has been investigated. A total of 149 pathogenic and nonpathogenic fungal and bacterial DNAs were screened with CkF1,2. The probe was cold labeled with peroxidase, and its specificity was assessed by using Southern blot, dot blot, and colony blot hybridization. Its sensitivity was determined by dot blot hybridization. The CkF1,2 probe proved to be species specific. It hybridized with DNA for the 112 C. krusei strains studied, whereas it failed to hybridize under low-stringency conditions to 37 DNAs from 27 different yeast species, including Candida albicans, Candida glabrata, Candida norvegensis, Candida inconspicua, Candida tropicalis, Candida valida, Candida zeylanoides, and Yarrowia lipolytica, as well as DNAs from the filamentous fungi and bacteria tested. However, CkF1,2 hybridized strongly with DNA of the yeast species Issatchenkia orientalis, the putative ascogenous perfect state of C. krusei. Amounts as small as 60 to 120 ng of C. krusei target DNA were detected by dot blot hybridization with CkF1,2. It permitted the direct screening of colony blots for early identification. The CkF1,2 probe has potential value as a diagnostic reagent for identifying C. krusei.