Genetical control of amylose content in selected crosses of indica rice

Models of Pooni et al. (1992) were employed to investigate the genetic control of amylose content in 10 rice crosses produced by the pairwise crossing of five varieties representing almost the whole range of amylose levels from 0 to 28 per cent. Analyses of the first-degree statistics revealed an important role of the additive and the dominance effects in determining the genetic variability in all the crosses. Epistasis and cytoplasmic effects were also observed to contribute significantly to the variability among the generation means of most crosses. Dominance was generally towards the higher score and its effects were enhanced by a complementary dominance x dominance interaction in several sets of basic generations. The predominantly additive nature of the genetic variability was further revealed by the analyses of second-degree statistics. Component D was detected significant in all the crosses while components H1 and H2 were non-significant throughout. Significance of the covariance components F' and F", however, showed indirectly that dominance contributed significantly to variability at the variance level. Higher levels of transgression and considerable increases in the phenotypic ranges displayed by the segregating generations of various crosses, also pointed to their potency for yielding superior recombinants with diverse levels of amylose

A comprehensive model for disomically inherited metrical traits expressed in triploid tissues

A biometrical genetic model is presented for the analysis of quantitatively varying diploid inherited traits which are expressed in a triploid phase. It shows that gene dispersion and ambidirectionality influences virtually all the components of means and at least four components of variances. Consequently, separate parameters are needed to describe the genetic variation among the second-degree statistics of the selfing and the backcrossing series. It is further shown that the effects of maternal/cytoplasmic inheritance can be separated from those of the nuclear genes both by the scaling tests and by the weighted least squares method. The applicability of the model to experimental data is demonstrated by analysing the amylose content of the generations derived from a cross between two pure breeding lines of rice

Mapping the gene for aroma in rice(Oryza sativa L.) by bulk segregation analysis via RAPD markers

The sensory qualities of food such as aroma, taste, and texture are the most important criteria for distinguishing Basmati type rices from non-Basmati types. To map the gene(s) controlling aroma, bulked segregant analysis (BSA) using Random Amplified Polymorphic DNA (RAPD) markers was applied in an F2/F3 population of Basmati 370 (aromatic) and IR36 (non-aromatic). DNA samples from homozygous aromatic and homozygous non-aromatic plants identified on the basis of progeny tests were bulked and used for BSA. A total of 550 random primers were used and the primers, AG8 and AN1, produced polymorphism between aromatic and non-aromatic types. Association of AG8-AR, AN1-AR1, and AN1-AR2 with a gene for aroma was determined by surveying F2 individuals. The three RAPD markers AG8-AR, AN1-AR1, and AN1-AR2 were found to be linked to the gene for aroma with a distance of 6.9, 8.9 and 16.4 cM, respectively. Southern analysis with AG8-AR as a probe with 125 F2 individuals confirmed linkage between AG8-AR and the gene for aroma. AG8-AR was mapped on chromosome 8 flanked by two tightly linked markers, RZ617 and RG978, at 2.1 and 1.7 cM distances, respectively, indicating that this gene in Basmati 370 is located on chromosome 8

A general method of detecting additive, dominance and epistatic variation for metrical traits. V. Triple test cross analysis of disomically inherited traits expressed in triploid tissues

The applicability of the triple test cross design to the genetic analysis of metrical traits that subscribe to disomic inheritance but are expressed in a trisomie state has been investigated both theoretically and experimentally. Theory has shown that the standard sets of triple test cross families (L1i etc.) do not provide unambiguous tests of the additive, dominance and epistatic effects when reciprocal crosses are analysed separately. Analysis of the backcross families also suffers from similar problems but only in respect of the additive component and the tests of dominance and epistasis are not biased by the parentage of the families. Selfs of the standard families, on the other hand, do not display reciprocal differences (of heritable kind) and therefore provide umambiguous tests of the additive, dominance and epistatic effects, but the dominance component is now detected with reduced reliability as the level of heterozygosity is halved due to selfing. Theory further shows that biases of the various tests are eliminated rather easily by including the reciprocal families in the analysis. This is confirmed to a large extent by the analysis of amylose content in rice which also reveals that it is controlled by genes that display both interallelic (additive and dominance) and nonallelic interactions. Furthermore, dominance is shown to be partial but the dominance ratio seems to be high for both the ha1 and ha2 types of non-additive effects

Genetical control of amylose content in a diallel set of rice crosses

Models proposed by Gale and Pooni, Kumar and Khush are applied to study the inheritance of amylose content in a diallel set of crosses produced from seven elite inbred lines of indica rice representing all the major rice consuming regions of the world. In theory, the standard (Hayman's and Griffing's) analyses of diallel tables and the Wr/Vr relationship are found to apply even though the trait under investigation is expressed in a triploid state. It is further revealed that reciprocal effects can only be detected unambiguously in the F2 diallel and the additive and non-additive effects cannot be separated in the B1 and B2 diallels when they are analysed separately. Analysis of the experimental data reveals that additive and dominance effects are the main sources of variation among the 21 crosses of the 7 times 7 diallel. Comparisons of the B1 and B2 diallels also show that the single dosage dominance (ha1 type) effects differ significantly from the double dosage dominance (ha2 type) effects. In addition, cytoplasmic control of amylose content is confirmed unambiguously and a large proportion of the heritable variation is shown to be controlled by a series of multiple alleles with large effects

Electrophoretic variation of isozymes in plumules of rice (Oryza saliva L.) - a key to the identification of 76 alleles at 24 loci

A simple and efficient method has been developed for studying isozyme variation in rice. It involves starch gel electrophoresis of crude rice plumule extracts, followed by staining of 13 enzymes. It permits monitoring the variation at 24 polymorphic loci distributed on at least 8 chromosomes. Technical procedures are described, and the zymograms obtained from materials containing all known alleles are shown. A total of 76 alleles can be readily identified

Inheritance of resistance to bacterial blight in 21 cultivars of rice

Genetic analysis for resistance to bacterial blight (Xanthomonas oryzae pv. oryzae) of 21 rice (Oryza sativa L.) cultivars was carried out. These cultivars were divided into two groups based on their reactions to Philippine races of bacterial blight. Cultivars of group 1 were resistant to race 1 and those of group 2 were susceptible to race 1 but resistant to race 2. All the cultivars were crossed with TN1, which is susceptible to all the Philippine races of X. oryzae pv. oryzae. F1 and F2 populations of hybrids of group 1 cultivars were evaluated using race 1 and F1 and F2 populations of hybrids of group 2 cultivars were evaluated using race 2. All the cultivars showed monogenic inheritance of resistance. Allelic relationships of the genes were investigated by crossing these cultivars with different testers having single genes for resistance. Three cultivars have Xa4, another three have xa5, one has xa8, two have Xa3, eight have Xa10, and one has Xa4 as well as Xa10. Three cultivars have new, as yet undescribed, genes. Nep Bha Bong To has a new recessive gene for moderate resistance to races 1, 2, and 3 and resistance to race 5. This gene is designated xa26(t). Arai Raj has a dominant gene for resistance to race 2 which segregates independently of Xa10. This gene is designated as Xa27(t). Lota Sail has a recessive gene for resistance to race 2 which segregates independently of Xa10. This gene is designated as xa28(t)

Genetics of amylose content in rice (Oryza sativa L.)

Inheritance of amylose content was studied in crosses involving very low-, intermediate-, and high-amylose parents. The single-grain analysis of parents, F1, F2, B1F1, and B2F1 seed from a single-season harvest, showed that the parental mean difference of 14-17% in IR37307-8/BPI 121-407 or IR37307-8/IR24632-34 and about 20% in the cross IR37307-8/IR8 were controlled by a single gene with major effect, along with some minor genes and/or modifiers. The appearance of segregants in between the two parents was attributed to gene dosage effects in the endosperm. The results indicate that selection for amylose level can effectively be done in early segregating generations. Selection for intermediary segregants would be ineffective because the dosage effects would dissipate in further generations

Field performance of Xa21 transgenic indica rice (Oryza sativa L.), IR72

Based on the characterization of the resistance phenotype and molecular analysis, several homozygous lines carrying Xa21 against the bacterial blight (BB) pathogen were obtained from previously transformed indica rice, IR72. The homozygous line, T103-10, with the best phenotype and seed-setting, was repeatedly tested under normal field conditions to evaluate its levels of resistance to the BB pathogen in Wuhan, China, in 1998 and 1999. The isolates of Xanthomonas oryzae pv oryzae (Xoo) used in this experiments were PXO61, PXO79, PXO99 and PXO112 isolated from the Philippines, T2 isolated from Japan, and Zhe173 isolated from China. The results demonstrated that the transgenic homozygous line expressed the same resistance spectrum, but with a shorter lesion length to each inoculated isolates as the lesion length of the Xa21 donor line IRBB21. The non-transformed control IR72 carrying Xa4 was resistant to PXO61, PXO112, Zhe173 and T2, but susceptible to PXO99 and PXO79. The negative control variety IR24 was susceptible to all isolates under field conditions. The results demonstrated clearly that the Xa21 transgene led to an excellent field performance of the introduced bacterial blight resistance trait on the recipient plants. The yield performance of this transgenic homozygous line, T103-10, is comparable with that of the control under field conditions

Primary trisomic of rice: orgin, morphology, cytology and use in linkage mapping

Twelve primary trisomics of Oryza sativa L. were isolated from the progenies of spontaneous triploids and were transferred by backcrossing to the genetic background of IR36, a widely grown high yielding rice variety. Eleven trisomics can be identified morphologically from one another and from diploids. However, triplo 11 is difficult to distinguish from diploid sibs. -The extra chromosome of each trisomic was identified cytologically at pachytene stage of meiosis, and the chromosomes were numbered according to their length at this stage. The major distinguishing features of each pachytene chromosome were redescribed. -The female transmission rates varied from 15.5% for triplo 1, the longest chromosome, to 43.9% for triplo 12, the shortest chromosome. Seven of the 12 primary trisomics transmitted the extra chromosome through the male. The low level of chromosomal imbalance tolerated by rice and other evidence are interpreted to indicate that this species is a basic diploid. -Genetic segregation for 22 marker genes in the trisomic progenies was studied. Of a possible 264 combinations, involving 22 genes and 12 trisomics, 120 were examined. Marker genes for each of the 12 chromosomes were identified. The results helped establish associations between linkage groups and cytologically identifiable chromosomes of rice for the first time. Relationships between various systems of numbering chromosomes, trisomics, linkage groups and marker genes are described, and a revised linkage map of rice is presented