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Improving the cooking and eating quality of grain has always been an important consideration in most rice (Oryza sativa L.) breeding programs. In this study, an established rice doubled-haploid (DH) population consisting of 219 lines from anther culture of the F1 of indica variety PSB Rc10 and japonica variety Nippon-bare was used to identify the quantitative trait loci (QTL) for amylose content (AC), gel consistency (GC), and gelatinization temperature (GT). Two hundred five simple sequence repeat (SSR) markers were used to construct a genetic linkage map covering the 12 chromosomes. A total of 13 QTLs were identified--three for AC and five each for GC and GT. Eight QTLs had major effects from which seven coincided with the most important loci identified in previous reports. All QTLs for AC were shown to have major effects on GC and GT. The QTL with the largest effect, which accounted for 74% of the AC variation corresponded to the waxy (Wx) locus while the other two QTLs were located above and below this region. The significant phenotypic correlations of these traits may underlie the colocalization of their QTLs. A major QTL specifying GT was detected within the alkali degeneration (AIk) locus. Other minor QTLs were identified for GC in chromosomes 2 and 8 and for GT in chromosome 2. Utilization of a homozygous DH population with relatively large sample size might have increased the accuracy of mapping these QTLs. The results thus obtained are valuable in breeding rice varieties with better grain quality.

Molecular markers have been successfully used in rice breeding however available markers based on Oryza sativa sequences are not efficient to monitor alien introgression from distant genomes of Oryza. We developed O. minuta (2 n = 48, BBCC)-specific clones comprising of 105 clones (266-715 bp) from the initial library composed of 1,920 clones against O. sativa by representational difference analysis (RDA), a subtractive cloning method and validated through Southern blot hybridization. Chromosomal location of O. minuta-specific clones was identified by hybridization with the genomic DNA of eight monosomic alien additional lines (MAALs). The 37 clones were located either on chromosomes 6, 7, or 12. Different hybridization patterns between O. minuta-specific clones and wild species such as O. punctata, O. officinalis, O. rhizomatis, O. australiensis, and O. ridleyi were observed indicating conservation of the O. minuta fragments across Oryza spp. A highly repetitive clone, OmSC45 hybridized with O. minuta and O. australiensis (EE), and was found in 6,500 and 9,000 copies, respectively, suggesting an independent and exponential amplification of the fragment in both species during the evolution of Oryza. Hybridization of 105 O. minuta specific clones with BB- and CC-genome wild Oryza species resulted in the identification of 4 BB-genome-specific and 14 CC-genome-specific clones. OmSC45 was identified as a fragment of RIRE1, an LTR-retrotransposon. Furthermore this clone was introgressed from O. minuta into the advanced breeding lines of O. sativa. [ABSTRACT FROM AUTHOR]

Accessions of Oryza longistaminata and O. glaberrima, two rice species from Africa, and O. sativa were screened to identify sources of resistance to Meloidogyne graminicola. An initial population of 6000 J2/plant was inoculated to cuttings of the African rice species and 5-day-old seedlings of O. sativa. Root nematode densities were estimated 60 days after the last inoculation. O. sativa entries were all susceptible to the rice root-knot nematode. One accession of O. longistaminata represented by two individuals (WL02-2 and WL02-15) and three accessions of O. glaberrima (TOG7235, TOG5674 and TOG5675) were resistant to M. graminicola. DL01-1, an O. longistaminata accession, was susceptible to the rice root-knot nematode. Identification de sources de resistance a Meloidogyne graminicola chez Oryza longistaminata et O. glaberrima - Plusieurs accessions d'Oryza longistaminata et d'O. glaberrima, deux riz africains, et d'O. sativa ont ete criblees pour trouver des sources de resistance a Meloidogyne graminicola. Des inoculums de 6000 J2 par plante ont ete inocules sur des boutures des deux riz africains et sur des plantules de 5 jours d'O. sativa. Les populations presentes dans les racines ont ete evaluees 60 jours apres l'inoculation. Toutes les varietes testees d'O. sativa etaient sensibles. Une accession d'O. longistaminata, representee par deux individus (WLO2-2 et WLO2-15), et trois accessions d'O. glaberrima (TOG7235, TOG5674 et TOG5675) etaient resistantes. [ABSTRACT FROM AUTHOR]

Abstract: Anther culture (AC)-derived doubled haploid (DH) lines from the F1 of indica (PSB Rc10) and japonica (Nipponbare) cultivars were evaluated for different agronomic traits under field conditions. These lines were also characterized using simple sequence repeat (SSR) markers. Significant variation was observed among the 73 DH lines for different characters namely; plant height, tiller number, panicle number, panicle length, days to heading, and % seed fertility. For all traits, the phenotypic variance within each DH line was comparable to the mean phenotypic variance of parents indicating that the plants within lines were uniform and did not exhibit plant-to-plant variation. SSR analysis of the DH population showed an expected 1:1 ratio of indica and japonica alleles. It revealed homozygosity for 99.84% of the total marker loci in the 141 lines evaluated suggesting that the AC-derived plants originated from the F1 pollen. Heterozygosity was observed in only 10 DH lines for one or three marker loci out of 107 polymorphic SSR markers. Absence of non-parental bands in the DH lines is indicative of the purity of the DH lines and that no variation at the DNA level occurred during the in vitro process. Agronomic and molecular data support DH lines generated to be quite suitable and useful in rice breeding and many other areas of research such as genetics, genomics, QTL analysis and mapping for different agronomic traits including grain quality characteristics. [Copyright &y& Elsevier]