Characterization of interspecific hybrids and backcross progenies from a cross between Oryza minuta and Oryza sativa.

Oryza minuta, a tetraploid wild relative of cultivated rice, is an important source for the genetic improvement. Interspecific hybrids were obtained from the cross of O. sativa L. (IR24) and O. minuta (Acc. No. 101133) with 5.58% crossability, which ranged from 0.11% to 1.62% in the backcross generations. The chromosome numbers of the backcross progenies were 24 to 48. Seven yield-related traits of the parents, hybrid F(1), and backcross progenies were evaluated. Simple sequence repeat markers analysis showed that the polymorphism ratio of SSR bands between IR24 and Acc. No. 101133 was 93.2%. The average donor segment number, length, donor genome size, and percentage of donor genome of 92 BC(3)F(1) plants (2n=24) were 24.1, 17.8 cM, 438.4 cM and 26.2%, respectively. They were complex variation and uneven among the chromosomes. These introgression lines could be used to identify the favorable genes of O. minuta and provide a new platform for the genetic improvement of cultivated rice.

[Relationship of activation of Tos17 and rice adult plant resistance to bacterial blight].

to investigate whether rice adult plant resistance (APR) is related to activation of long terminal repeat (LTR) retroelements, polymorphism of LTR retroelemnts Tos17 are studied using SSAP (Sequence-Specific Amplification Polymorphism) in seedlings and adult plants of rice cultivar Wase Aikoku 3 inoculated with Xanthomonas oryzae pv. Oryzae, water and those untreated. Of 2000 fragments detected, 9 and 2 are activated in seedlings and adult plants induced by development, respectively; each 3 fragments are activated in seedlings and adult plants induced by pathogen, respectively. The number of activated Tos17 induced by development is more in seedlings than that in adult plants while it is equal due to pathogen induction in seedlings and adult plants, suggest that the activation of Tos17 induced by development probably associate with rice APR to bacterial blight.

[Effect of temperature on the fertility restoration of different two-line hybrid rice].

On the basis of the fertility observation of hybrids from Pei'ai 64S and Nongken 58S crossed with an indica variety Nanjing11 and japonica marker line FL235, respectively, The plant growth chambers were employed to expose the F2 plant individuals to such different day mean temperature as 24 degrees C, 27 degrees C and 30 degrees C during natural long hour daylight from July to August in Wuhan (30 degrees 27' N), with a view to analyzing the difference in the temperature sensitivity of fertility between the two kinds of different fertility-restoring genes for two years running. The results showed that, whether it was under long daylight and high temperature or under long daylight and middle temperature, the mean natural seed-set percent of F1 was higher than 68.75%, suggesting that Nanjing11 could completely restore the fertility of Pei'ai 64S. And however, under natural high temperature condition, N58S x FL235 F1 could set seed naturally with 21.93%-26.75%, the mean natural seed set percent of F1 was 46.36%-48.38% in natural middle temperature condition, ability of FL235 to restore the fertility of N58S was affected by high temperature. Further analysis proved that temperature could not alter the inheritance mode of F2 but affect the extent of fertility genes expression in Nanjing11. On the other hand, the expression of fertility-genes of FL235 was sensitive to high temperature, whose the putative critical temperature was 27 degrees C, and high temperature influenced not only the genetic interactions but also the segregation modes in F2 generations.

Genetic analysis of the low critical sterility temperature point in photoperiod-thermo sensitive genic male sterile rice.

It has been a long haul but photoperiod- and thermo-sensitive genic male sterile (PTGMS) rice has not been freely used in hybrid rice production because there are two perplexing problems corresponding to the critical sterility temperature point (CSTP): the uncertainty of the CSTP segregating pattern and the instability of CSTP for every originally useful line. N5088S, the most widely commercialized japonica-type PTGMS line in China, also saw that its CSTP variants have been isolated but with all other agronomic characteristics unchanged. In this report we analyzed the genetic basis of CSTP, by employing the iterated expectation and conditional maximization (IECM) algorithm on four tiller-splitting-formed sets of seven generations from N5088S and its CSTP-variant H5088S, each set treated with one temperature regime. The main results indicated that there are two dominant major genes and polygene, as well as their respective epistasis conditioning the CSTP in the 23.5 degrees C regime. Based on the results obtained, the strategy for breeding of PTGMS lines with stable low CSTP was outlined.

Localizing the Bacterial Blight Resistance Gene, Xa22(t), to a 100-Kilobase Bacterial Artificial Chromosome.

ABSTRACT The rice bacterial blight resistance gene, Xa22(t), provides resistance to a broad spectrum of Xanthomonas oryzae pv. oryzae isolates. Here, we localize the gene to a small 100-kb fragment of chromosome 11 by a combination of genetic recombination analysis and physical mapping. Mapping was done with two F(2) populations from the cross between Zhachanglong and Zhenzhuai. The first population consisted of 248 random individuals and 404 highly susceptible individuals selected from an F(2) population of more than 2,000 individuals and was used to construct a linkage map around the Xa22(t) locus. For the second F(2) population, 7,680 plants were examined with simple sequence repeat markers flanking the Xa22(t) locus to identify recombinants useful for fine-genetic mapping. Two large-insert bacterial artificial chromasome (BAC) libraries (from cvs. Teqing and Minghui63) were screened with a marker (R1506) which cosegregated perfectly with Xa22(t) in the first population. Restriction mapping of the resulting BAC clones enabled a physical map of the area to be constructed, and subclones from the BAC clones provided additional restriction fragment length polymorphism probes which could be placed on the fine-structure genetic map using the recombinants from the second mapping population. The Xa22(t) locus was mapped to a approximately 100-kb interval delimited by the R1506 marker and a subclone from the M3H8 BAC clone.

Cloning and expression of VB12-independent methionine synthase gene responsive to alkaline stress in rice.

VB12-independent methionine synthase is present in higher plants, and catalyzes the methylation of C-homocysteine to form methionine, which is very important for methylation reactions and syntheses of polyamines and ethylene. Under the alkaline condition, using cDNA-RAPD method, a new VB12-independent methionine synthase gene has been cloned and characterized for the first time in rice in this study. The results exhibited that, the cDNA gene entailed 2740 bp, had single copy in the rice genome and encoded peptide of 765 amino acids, the peptide showed 92% and 83% identity with that from Mesembryanthemum cystallinum (U84889) and Cathararanthus roseus (X83499), respectively. It enhanced the transcription more greatly after sodium carbonate treatment for 12 h and 24 h than that of sodium chloride treatment, and then obviously reduced in 48 h later, suggesting that it is related to this stress tolerance in rice.