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 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

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

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