The estimation of hybrid rice seed purity is done conventionally by the grow out test (GOT), which is based on the assessment of morphological and floral characteristics in plants grown to maturity. For seed companies, large amounts of capital are locked up in the form of hybrid seed stock while awaiting the results of the GOT. With the objective of replacing the GOT with DNA based assays, cytoplasmic male sterile (CMS), restorer, and hybrid lines have been screened by means of microsatellite and sequence tagged site (STS) polymorphisms. A simple procedure for detecting heterozygosity and purity has been standardized and uses 6‐d‐old rice (Oryza sativa L.) seedlings, which could be used for detection of off‐types in hybrid seed lots. The extent of heterozygosity within parental lines of rice hybrids was assessed and the results suggest that a single, appropriately chosen microsatellite marker should be sufficient for assessing hybrid seed purity.
Xanthomonas oryzae pathovar oryzae causes a serious disease of rice in India and is endemic in all of the major rice-growing areas of the country. Sixty-seven X. oryzae pv. oryzae strains, collected mostly in 1994 and 1995, from 18 locations in India were analyzed by DNA fingerprinting methods using two separate repeat element probes from the X. oryzae pv. oryzae genome. These results show that strains belonging to a single pathogen lineage can be isolated from 16 of the 18 locations sampled; many of these locations are separated from each other by hundreds of kilometers and represent ecologically diverse rice-growing areas. Pathotyping analysis indicated that the strains in this lineage belong to pathotype 1b of X. oryzae pv. oryzae.
Three exopolysaccharide (EPS)- and virulence-deficient mutants of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight of rice, were isolated by Tn5 mutagenesis. These insertions are not located within the gum gene cluster. A 40-kb cosmid clone that restored EPS production and virulence to all three mutants was isolated, and the three transposon insertions were localized to contiguous 4.3- and 3.5-kb EcoRI fragments that are included in this clone. Sequence data indicate that two of the transposon insertions are in genes that encode a putative sugar nucleotide epimerase and a putative glycosyl transferase, respectively; the third insertion is located between the glycosyl transferase gene and a novel open reading frame (ORF). A 5.5-kb genomic region in which these three ORFs are located has a G+C content of 5-1.7%, quite different from the G+C content of approximately 65.0% that is typical of X. oryzae pv. oryzae. Homologues of this locus have not yet been reported in any other xanthomonad.
Xanthomonas oryzae pv. oryzae is the causal agent of bacterial leaf blight, a serious disease of rice. Spontaneous loss of virulence in X. oryzae pv. oryzae is associated with mutants that produce reduced levels of extracellular polysaccharide. Evidence is presented that these mutants accumulate in long-term stationary phase cultures but are not obtained from exponentially growing cultures. A number of independent spv (stationary-phase variation) mutants have been isolated and characterized. These mutants differ from each other with respect to the stability of the mutant phenotype, extent of loss of virulence, ability to outcompete wild type cells in stationary-phase cocultures, and hypersensitivity to hydrogen peroxide.Key words: stationary-phase variation, spontaneous loss of virulence, Xanthomonas oryzae.
Xanthomonas oryzae pv. oryzae causes bacterial leaf blight, a serious disease of rice. We have collected leaf blight-affected samples from wild rice (Oryza nivara) plants growing naturally at 22 locations in five revenue districts (Nalgonda, Ranga Reddy, Medak, Nizamabad, and Adilabad) in the Telangana Region of Andhra Pradesh, India. Pathotype analysis on a set of differential rice cultivars and DNA fingerprinting with two multilocus restriction fragment length polymorphism probes indicated that the X. oryzae pv. oryzae strains from the O. nivara plants belonged to a pathotype and lineage previously widely distributed among cultivated rice in India. This suggests that the lineage may be native to wild rice and may have been transferred subsequently to cultivated rice plants.
Ensuring the genetic purity of parental lines and hybrids is a prerequisite to realize their full potential. The cytoplasmic male sterile (CMS) lines that are utilized for developing the popular “three‐line” hybrids, often get contaminated with their isonuclear maintainer lines during CMS line multiplication. Use of such CMS lines in hybrid seed production results in the production of genetically impure hybrid seed. We report the identification of a DNA sequence that is homologous to rice mitochondrial DNA but unique to the Wild Abortive (WA) cytoplasmic male sterile lines of rice (Oryza sativa L.). In a polymerase chain reaction (PCR) using total genomic DNA as a template, oligonucleotide primers based on this unique DNA sequence could amplify a fragment from CMS lines of rice and their hybrids but not from their cognate maintainer lines. In tests on mixed samples of plants containing both CMS and Maintainer lines, this PCR assay was used to correctly predict the genotypes of these plants indicating that it can be used to detect the mixture of maintainer lines in the seed stocks of the CMS line.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.