Prediction of Heterosis 2

Prediction of Heterosis:

Prediction of Heterosis AK CHHABRA Professor Genetics & Plant Breeding

Crops where heterosis has been exploited:

Crops where heterosis has been exploited Cross-pollinated crops Self-pollinated crops Maximum in Maize What is prediction? Calculating the performance of a plants in a generation using the observations of its preceding / other generations.

Assumptions:

Assumptions Prediction methods are based on following assumptions: Diploid segregation No preferential fertilization Hardy-Weinberg equilibrium Linkage Equilibrium Negligible epistasis Situation that should exist in a population undisturbed by selection, migration, etc., in which all possible combinations of linked genes should be present at equal frequency. The situation is no more common than are such undisturbed populations.

Prediction of inbred progenies:

Prediction of inbred progenies Mather (1949): developed prediction methods for self-fertilized crops Mather and Jinks (1971): gave formula for inbreds in CP crops FOR ANY QUANTITATIVE TRAIT: Where P 1 , P 2 are the inbred lines and F 1 is the cross between them Example: P1 = 40, P2 = 60, F1 = 90 F2 = {(40+60+(2X90)}/4 = 240/4 = 60

Prediction of F3 to Fn progenies:

Prediction of F 3 to F n progenies Mean values of other advanced generations: F 3 = 1/8( 3P 1 +3P 2 +2F 1 ) F n = ½ { 1-(1/2) n-1 }(P 1 +P 2 )+(1/2) n-1 F 1 where n th generation is obtained after n-1 generation of selfing (Mather 1949)

Prediction of BACKCROSS progenies:

Prediction of BACKCROSS progenies Mean values of Back Cross generations can also be predicted as: BC 1 = [1/2] (P 1 + F 1 ) BC 2 = [1/2] (P 2 + F 1 )

Prediction of Double Cross Hybrids :

Prediction of Double Cross Hybrids Double cross hybrids are between two parents, where the parents are the two single crosses (F 1 s). Jenkins (1934) was the first person to propose the prediction method for double crosses based upon the single cross data. This has been followed a standard method in maize over the years.

Prediction of Double Cross Hybrids :

Prediction of Double Cross Hybrids P 1 X P 2 F 1 P 3 X P 4 *F 1 x Double Cross Jenkins’ Prediction Methods Symbols used S 1.2 X S 3.4 D 12.34 S 1.2 means P 1 X P 2= F 1 S 3.4 means P 3 X P 4= *F 1 D 12.34 means F 1 X *F 1

Prediction of Double Cross Hybrids :

Prediction of Double Cross Hybrids Suggested 4 methods: Mean performance of 6 possible single crosses among any set of 4 inbred lines. Mean performance of 4 non-parental single crosses. Mean performance of 4 inbred lines over a series of single crosses. Mean performance of 4 inbred lines over a series of top crosses.

Prediction of Synthetic varieties::

Prediction of Synthetic varieties: Y 2 = Y 1 (Y 1 -Y 0 ) n - Lonquist (1961): defined Synthetics as “Open Pollinated Populations” derived from the intercrossing of selfed plants or lines and subsequently maintained by routine mass selection procedures from isolated plantings. Write (1922) stated that “ A random-bred stock derived from n inbred families will have (1/n)th less superiority over its inbred ancestry than the first cross or a random bred stock from which inbred families might have been derived without selection……IT APPLIES TO THE SYNTHETIC VARIETIES. The formula based on this statement to predict the performance of synthetics is c/a Wright’s Formula cited by Kinman and Sprague (1945) is:

Slide 11:

Y 2 = Y 1 (Y 1 -Y 0 ) n - Wright’s Formula Mean of synthetic variety obtained by intercrossing all possible single crosses among a set of n inbred lines. Av. Performance of all single crosses among n inbred lines Av. Performance of n parental inbred lines Gilmore (1969) has indicated that the above formula can be used: At lines of any stage of selfing (S1, S2, S3 etc.) Parental lines need not be inbred lines. Gene freq should be 0.5 or 1.0 i.e each locus should be in Hardey -Weinberg Equilibrium

Prediction of Composite varieties::

Prediction of Composite varieties: The mean performance of composites represents the expression of inter-varietal heterosis. To maximize heterosis, parents for the composites are chosen on the basis of a varietal cross diallel in the same way as for hybrid. Composite means can be predicted from the diallel cross data. It was first suggested by Eberhart et al. (1967) which was somewhat similar to Wright’s’s Formula: Y co = Y c (Y c -Y v ) n - r Predicted mean of a quantitative trait for a composite obtained from random mating Av. of all possible intervarietal crosses among n parental varieties Mean of the parental varieties N is the number of varieties.

Prediction of Synthetic varieties::

Prediction of Synthetic varieties: itre du document / Document title On the meaning of Busbice's prediction formula Auteur(s) / Author(s) SAHAGUN CASTELLANOS J. (1) ; VILLANUEVA VERDUZCO C. (1) ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s) (1) Depto . de Fitotecnia , Universidad Autónoma Chapingo Km 38.5 Carretera México- Texcoco , 56230 Chapingo , MEXIQUE Résumé / Abstract Synthetic varieties (SVs) of maize ( Zea mays L.) and other species are important because they are grown in large areas of several regions of the world (Latin America, for example) and possess advantages particularly attractive for low-income farmers (stability of performance, cheap seed, and low-input requirements). In a plant breeding program, however, to identify the best of the numerous SVs that can be derived plant breeders have to resort to prediction. A formula that describes the genotypic mean of a SV (Y 2 ) is BUSBICE'S (1970): Y 2 = A + (1-F 2 )B, where F 2 is the inbreeding coefficient of the SV; and relative to A and B, although defined, estimators for them were not provided. The objective of this work was to investigate the usefulness of A and B for prediction purposes, and the existence, or the possibility of the derivation of estimators for them that enable the breeder to predict the genotypic mean of a SV derived from m individuals of each of n parents. On the basis of the expected genotypic array and mean of the SV it was found that A stands for the expected mean of the genotypes formed with two identical-by-descent genes, and if the expected mean of the values of the remaining genotypes of the SV is H e , B = He - A. It was found, however, that only when the parents are fully inbred and unrelated can A and B be properly estimated on the basis of experimental data. Despite this limitation, based on the meaning of A and B, it is possible to express Y 2 of BUSBICE'S (1970) formula as linear combinations of the expected means of subpopulations of the SV that can be experimentally evaluated and thus the expected mean (Y 2 ) of the SV can be predicted. All derived prediction equations from BUSBICE'S (1970) formula, however, can be obtained from the genotypic array of the SV as well. Revue / Journal Title Maydica ISSN 0025-6153 CODEN MYDCAH Source / Source 2007, vol. 52, n o 2, pp. 145-150 [6 page(s) (article)] (1/4 p.)