Combining ability

Combining ability, GCA and SCA, Features and Procedure of GCA and sca

1. Parvati Tamrakar M.Sc. FGR 3 rd Sem G.G.V. Bilaspur COMBINING ABILITY

2. Certain inbreed lines will display hybrid vigor when crossed. These vigor lines are said to have favorable combining ability. Combining ability is the capacity of an individual to transmit superior performance to its offspring. It is the phenomenon with which the inbreed lines when crossed give rise to hybrid vigor. It is examined by progeny testing. INTRODUCTION

3. Two types of combining ability, general (GCA) and specific (SCA), have been recognized in quantitative genetics. The concepts of general combining ability ( GCA) and specific combining ability (SCA) were first introduced by in relation to corn breeding and have been expanded into animal breeding by others. Certain inbreeds which have the ability to combine well with testers have general combining ability (GCA ). The inbreeds combines well only in certain crosses have specific combining ability (SCA) . TYPES OF COMBINING ABILITY

4. The term GCA is used to designate the average performance of an inbred line in hybrid combinations. Featues of GCA: GCA is due to genes which are largely additive in their effects. It is due to additive genetic variance and additive x additive gene interaction. It denotes combining ability of genotype especially with other testers. It helps in identification and selection of best genotype to use it in hybridization as a parent. It is estimated by half-sib mating. It have relationship with Narrow sense Heritability. GENERAL COMBINING ABILITY

5. First Year Superior plants for the character under improvement are selected from the base population. The selected plants are selfed and also crossed with heterozygous tester having broad genetic base. The selfed seed is kept storage. Second Year The crossed seed is sown and the combining ability selected plants is evaluated and plants with good GCA are identified. PROCEDURE FOR ESTIMATING AND UTILIZING GCA

6. Third Year The progeny of selected plants with good GCA are grown from their selfed seed is kept in cold storage. These progenies are inter mated in all possible combinations and their crossed seed is composited to form a new source of population for further selection. This complete original selection cycle. Many such cycles may be made to obtain desired results. Main features of this method to use for genetic improvement of quantitative characters in which selection is made or the basis of test crosses performance. This method also used for providing good of population and required three season or year

7. SCA is used to designate those cases in which certain combinations do relatively better or worse than would be expected on the basis of the average performance of the lines involved . SCA is due to genes with dominance or epistatic effect. Features of SCA: It represents deviation from gca . It is due to dominance genetic variance and all the three types of gene interactions. It helps into identification and hence the selection of best cross combinations i.e. those with the desired output. SPECIFIC COMBINING ABILITY

8. When we see that a inbred line combines well in any cross, it is due to specific combining ability. It is estimated by full sib mating. It have a relationship with heterosis . Contd …

9. First Year Several plants are selected and selfed . The selected plant (male ) are also crossed to an tester (female). Second Year R.Y.T is conducted using test cross progeny. Outstanding progenies are identified. Third Year Selfed seeds from the progeny are planted in separate progeny row in a crossing block. All possible inter cross are made by hand among progeny. Equal amount of seed is composited. T his complete the original selection cycle. PROCEDURE FOR ESTIMATING AND UTILIZING SCA

10. Fourth Year The combination seed is planted and operation of 1st year repeated. Fifth Year Second year operation repeated. Sixth Year Third year operation repeated. Contd …