Diallel Set Of Crosses Research Articles

Resistance conferred by new gene combinations to bacterial blight of cotton

F2 families from a diallel set of crosses involving Sakel (Gossypium barbadense) strains homozygous for each of the B genes, B 1 to B 7, were screened for resistance to leaf infection by Xanthomonas malvacearum. B 2B6 was the most resistant, with B 1B4, B2B4, B3B6 and B 4B6 slightly less effective than B 2B6. Other gene combinations exhibiting additivity, but conferring intermediate resistance only, were B 1B3, B2B3, B3B4, B3B5, B4B5, B4B7, B5B6, and B 5B7. B 1 and B 4 were each transferred to the Upland variety Wilds Sus 16/1. The synthesis of normal homozygous B 1 Wilds revealed that the gene d b, one of two duplicate genes causing dwarfing, was not present in Wilds Sus 16/1. B 7 when transferred to Wilds Sus 16/1 and to Acala 4–42, both “susceptible” Uplands, was much more effective in the latter variety, emphasising the importance of genetical background on the expression of major genes for bacterial blight resistance.

The inheritance of the resistance of wheat to two races of Ustilago nuda

The inheritance of resistance to two races of Ustilago nuda was studied in a diallel set of crosses involving seven varieties of Triticum aestivum ssp. vulgare . Data from F 2 hybrid populations and F 2 plant progenies from test crosses to the variety Hybrid 46, susceptible to both races, indicate that the resistance is controlled by single dominant and independent genes. The symbol Ut is suggested to designate these genes. The major gene which controls seedling resistance of variety C.I. 12633 to Erysiphe graminis is found not to be associated with the two major genes that govern resistance to races C 1 and C 2 of U. nuda .

The genetical control of radiosensitivity

Examination of data from a set of diallel crosses between a number of inbred lines was used for analysing the genetic control of radiosensitivity in six tomato varieties. The six varities were crossed in all possible combinations, including reciprocals, and the parental and F1 seed were used in the experiments. Seeds were dried and exposed to 28,116 rad of Co60 gamma rays at a rate of 2000 rad/hr. The characters scored were the distance from the apex of one cotyledon to the apex of the other at the 12th day, and the lengths of the 1st and 2nd leaves at the 19th day after sowing. The results showed the response of tomato seeds to radiation to be genetically controlled. The nature of this control was polygeric, with evidence of additivity and dominance. The different varieties had various proportions of dominant and recessive alleles, and dominance and ambidirectional. Pronounced consistent and inconsistent maternal effects influenced the radiation response; these affected dominance values to produce a complex genetic situation. The genetic control of radiosensitivity was different from that of the simple growth characters, though there was some similarity in that both showed maternal effects. There was also evidence that the control ofmore » these characters varied according to whether they were measured in the cotyledon, first or second leaf. Relationships between spontaneous mutation and chromosome breakage, and induced mutation and breakage is discussed. It is concluded that radiosensitivity per se may not be a true character, and that what was measured may be some quite different character, which could control such factors as oxygen tension, metabolic rate, or production of radioprotective substances; and that different levels of expression of this character could result in different levels of radiosensitivity. (H.H.D.)« less

Studies on quantitative inheritance inNicotiana tabacum L

The components of genetic variation for two characters, flowering time and the number of curable leaves, which influence the gross yield, and two quality characters, grade performance and burning quality of the cured leaf, were examined in the F2 and back-cross generations of a set of diallel crosses between four flue-cured varieties selected on the degree of divergence as measured by Mahalanobis's D2 statistic. Differences in the relative proportions of D and H components were observed, in different crosses, for the same character. These differences were parallel to the degree of divergence between the parents concerned. Significant non-allelic interaction of a generalised nature was detected for each of the four characters. Additive component formed a substantial purt of the total genetic variation for the character curable leaf number only. A comparison of the degree of divergence between the parents and the heritability estimates for the characters concerned, indicated that in a majority of the cases, the use of D2 statistic for the choice of the parents would be useful for evaluating the potential of a cross. Analysis of the diallel material for Vr and Wr components confirmed the existence of a high degree of non-allelic interaction. The distribution of the desirable genes, for quality characters, over several parents, suggests the need for multiple cross for the accumulation of a maximum number of favourable genes. A contrast in the nature of gene action between quality characters and gross yield components was also indicated in the study. A variety Hicks was found to be unique in its high general combining ability and high additive variance for all the four characters, in its crosses, whereas another variety Harrison Special was a consistently poor combiner. A comparison of the components of genetic variability estimated by other workers with those of the present investigation was made with reference to the limitations of conclusions from one or few crosses. The utility of the combined use of D2 statistic, the analysis of Vr−Wr components and the partition of the components of genetic variation was discussed with reference to the future breeding work in flue-cured tobacco for the characters under study.

The F2 and backcross generations from a set of diallel crosses

THE theory and analysis of F, and parental data from a set of diallel crosses has been described and illustrated using the results of our own crosses between eight varieties of X. rustica and published work on other species (Jinks and Hayman; Jinks, 1954a, i954b, 1955; Hayman, 1954)...

Differentiation and Stability in the Development of Nicotiana rustica

Stability, or homeostasis, is that property of the organism buffering it against small random fluctuations of the environment and accidents of development. A means of measuring, within the individual, the stability of expression of one foliar and two floral characters is given. Data are presented from a set of diallel crosses among five varieties of Nicotiana rustica y derived from different populations and grown in two successive seasons. This allows stability to be examined over a number of genotypes in the parent and Fx generations, in two differing environments. The leaf characters show some change from node to node, i.e. manifesting a gradual differentiation, as well as random fluctuations which are taken as evidence of instability. Like stability, this differentiation rate varies from genotype to genotype and shows genetic control. Some attempt is made to find to what extent the different phenomena are related.