Estimation of genetic parameters in barley (Hordeum vulgare L.) : I. full, half and quarter diallel analysis

Four exotic and four indigenous strains of barley were used for making diallel crosses. The sets of parents and crosses making full, half and quarter diallel were analysed in a randomized block design for plant height, number of effective tillers, ear length, grain yield per plant, 100 grain weight and number of grains per ear.The three alternatives of diallel were similar with respect to the estimates of degree of dominance, general combining ability and specific combining ability, indicating that all these three methods of diallel were equally efficient. However, as the number of entries are minimum in quarter diallel, it would be economical in terms of cost, time and labour to estimate genetic parameters by this method. Average degree of dominance was found in the range of overdominance. The ranking of parents on the basis of their array mean was similar to the ranking based on gca effects. Similarly, the ranking of crosses on the basis of per se performance was similar to the ranking based on sca effects. This suggests that the selection of best general combiner or best cross combinations may be easier and more effective through array mean for per se performance rather than through high gca and sea effects, respectively. From among 56 crosses, IB-226 X X C-164 was the one which showed superiority for maximum number of characters followed by AB-12/59 X PTS-57. High sea effect for plant height, ear length, grain yield, 100 grain weight and number of grains per ear was the result of cross between parents having high X low general combining ability, indicating additive X dominance type of gene interaction. For number of effective tillers, high sca was produced by low x low general combiners, indicating dominance x dominance gene interaction.

Combining ability studies in Pearl millet (Pennisetum typhoides (Burm.) S.& H.)

A line x tester analysis of combining ability involved five male-sterile lines from different sources and 10 inbreds of Pearl millet developed at Hissar (India). Additive x additive and additive x dominance types of gene interaction were found to predominate in the material under study. A high degree of association was found between general combining effects and the mean performance of lines and testers over crosses but no association was observed betweenper se performance of the crosses and their specific combining ability effects. Among the male sterile lines, L-110 proved to be the best general combiner, whereas H-297, followed by H-198, was the best of the inbreds. The crosses L-110 x H-440, L-110 x H-406, 18D2A x H-297, 18 A x H-198 and L-110 x H-297, were superior to the released variety, Hybrid-1, used as control.

Effect of various parameter combinations on genetic gain in computer simulated two-character selection

In a simulation study, the effect of various parameter combinations such as linkage, dominance, heritability, and economic weights on the individual trait means was investigated using additive genetic, genotypic and the phenotypic index of Elston (1963). The characters responded differently to these indices under various parameter combinations, indicating favourable and unfavourable effects of the mentioned parameters. Linkage was found to reduce the rate of progress through selection. Depression of genetic gain was greater where the genes governing a character showed dominance and/or heritability coefficients were low. It was, however, noticed that depression of genetic gain due to low heritability of a character could be avoided by assigning higher economic weight to that character. This suggests that desirable changes in the means of characters available for selection can be manipulated by choosing appropriate economic weights. The additive genetic index, where only the additive genetic variances and covariances go into its construction, does not seem to be affected by intra-allelic interactions since they add to variances and covariances due to dominance deviations and these have nothing to do with the additive genetic variances and covariances. It seems that from such studies, if conducted extensively incorporating still more parameters, conclusions may be drawn on the most suitable selection model for simultaneous selection under a given set of parameters available in real biological systems.

A comparison of different stability models in wheat

Eight different varieties of wheat, namely S-308, WG-377, K-227, PV-18, HD-1941, HD-1949, C-306 and C-281, were tested under twenty-four environments over two successive years. The models of Eberhart and Russell (1966), Perkins and Jinks (1968a), and Freeman and Perkins (1971) were applied to study genotype-environment interactions. The correlations between different environments were also determined and the partitioning of sum of squares due to genotype X environment interaction attributable to each variety was done as suggested by Wricke (1962). The term 'ecovalence' was used to signify this parameter. The major findings of the study were as follows: (i) The models of Eberhart and Russell, and Perkins and Jinks, produced similar results with respect to both responsiveness (b) and stability [Formula: see text]. The pattern of b-values in Freeman and Perkins' model was also similar to its pattern using these two models. (ii) The pattern of correlations between environments (r) for various genotypes showed high similarity with the pattern of b-values obtained in various models. The varieties having high b-values were found to have high environmental correlations and vice versa. (iii) Ecovalence and Freeman and Perkins' model were quite similar to each other for determining the stability of a genotype, but the rank correlations between ecovalence and Eberhart and Russell's model were low. It was, however, observed that the most stable varieties could be detected by using any of these models. Keeping in view the computational convenience, the use of correlation between environments (r) and ecovalence was suggested for predicting responsiveness and stability of genotypes, respectively.

Evaluation of selection indices under various parameter combinations in simulated genetic populations

In a simulation study, the efficiency of some selection indices was tested under various parameter combinations. For the purpose of such comparison a criterion, named as 'evaluation coefficient' was developed. In the evaluation coefficient both the total genetic gain and the relative gains obtained in the individual traits, as a measure of harmony, were taken into consideration.The results have indicated that the genotypically constructed selection indices were more efficient than the phenotypically constructed selection index of Elston (1963). Furthermore, the effectiveness of selection indices, irrespective of the model used, was found to be decreased in case of tight linkage as compared to that of loose linkage. It was, however, observed that the genotypically constructed indices were more sensitive to linkage and the reduction in their performance was relatively greater if characters included in the index had varying heritability coefficients. The efficiency of the indices was also reduced when the characters incorporated in the index possessed different economic weights. The results, however, suggested that relatively faster rate of improvement in the character having low heritability could be obtained by assigning higher economic weights to that character. This would mean that, manipulation of economic weights may help in bringing about the harmonical improvement in all the characters to be selected simultaneously.

Combining ability studies in tomato (Lycopersicon esculentum Mill.)

Diallel analysis was carried out involving eight diverse varieties of tomato, namely Pusa Early Dwarf, Sl-1, S-12, Punjab Tropics, Sl-120, HS-101, Pusa Ruby and Sl-73-1, to characterize the gene action involved in the inheritance of some of the quantitative traits and to correlate array mean and per se performance with general combining ability (gca) and specific combining ability (sca) effects, respectively.The results indicated that the variance component due to general combining ability was higher than that due to specific combining ability for yield and number of fruits, showing preponderance of an additive type of gene action. On the other hand, all other characters - height, number of branches, locule number, T.S.S., acidity and ascorbic acid content - were found to have a high variance component due to specific combining ability, which means excess of non-additive type gene action. In such cases, heterosis breeding, or any other breeding plan which makes use of specific combining ability effects, would be more effective. High correlation between parental array means and gca effects and between per se performance of the crosses and the sca effects was observed. The implications of the results are discussed.

Carotenoid biosynthesis in Rhodopseudomonas spheroides. S-adenosylmethionine as the methylating agent in the biosynthesis of spheroidene and spheroidenone

[methyl-(14)C]Methionine and S-adenosyl[methyl-(14)C]methionine were incorporated into the methoxycarotenoids spheroidene and spheroidenone by Rhodopseudomonas spheroides. The incorporation was greatly enhanced in the presence of lysozyme. On degradation of labelled spheroidene by hydriodic acid, the (14)C label was recovered in methyl iodide. Degradation of spheroidenone by reduction and allylic dehydration and demethylation of the reduction product gave a mixture of unlabelled carotenoid hydrocarbons, including 3,4-didehydrolycopene and 3,4-didehydro-7',8'-dihydrolycopene. The label from [methyl-(14)C]methionine and S-adenosyl[methyl-(14)C]methionine was located specifically in the methoxy group of spheroidene and spheroidenone. The biosynthesis of methoxycarotenoids in Rps. spheroides involves methylation of the tertiary hydroxyl groups of intermediates with S-adenosylmethionine.

Biosynthesis of spheroidene and hydroxyspheroidene in Rhodopseudomonas species: experiments with nicotine as inhibitor

Neurosporene replaces spheroidene and hydroxyspheroidene as the main carotenoid in Rhodopseudomonas spheroides and Rhodopseudomonas gelatinosa grown in the presence of nicotine. On removal of the nicotine, spheroidene and hydroxyspheroidene are formed at the expense of the accumulated neurosporene. This shows that nicotine inhibits introduction of the C-1 tertiary hydroxyl groups, and supports the postulated pathway neurosporene-->spheroidene-->hydroxyspheroidene.

Problems of generalization of selection indices

The present investigation was undertaken to study the problem of generalization of the selection index in plant breeding. It was found that specific selection indices brought about the maximum genetic advance, provided that they were used for selection in the specific populations. If these indices were used as "foreign indices" the gain was negligible. The general selection indices, which were based on corrected pooled information from different experiments, were found to be as efficient as the specific indices. The problems of sampling, specific populations and base population of a crop species, and the application of general indices in a practical breeding programme have been discussed in detail.