Study of combining ability tests in pyrethrum (chrysanthemum cinerariaefolium vis)
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Pyrethrins yield is the most important aspect of pyrethrum breeding, which is mainiy dependent on two major components, flower yield and pyrethrins content. Other important characters are flower size, dry matter cpntent and resistance to lodging. Hybrid populations are the main source of obtaining superior clones for commercial propagation. To raise desirable hybrid populations parental clones with high general combining ability are required. -Four different combining ability test methods, namely, diallel (single crosses), top-cross with high Ylelding tester, top-cross with low yielding tester and polycross, together with parental means, were compared for their efficiency in estimation of g.c.a. for flower yield, pyrethrins content, flower size, dry matter content and lodging. -Oiallel cross method was found to be the most efficient for all the characteristics measured. _However, polycross test method was found to be equally efficient and is most practically applicable. It is therefore suggested that polycross method bE'used for screening parents for high g.c.a. and dial leI cross be limited to a few selected clones. It was also noted that the parental per se performance was a reliable measure of g.c.a. for flower yield and pyrethrins content. Based on the estimates of g.c.a. and their correlations with FI hybrid values clones P4, Ps and P6 were found to be outstanding. These clones could therefore be utilized for making .hybrids or synthetics. Crosses between clones indicated that some are better than others for a particular characteristic. The cross P4 x Ps was the best for flower yield while for pyrethrins content the cross P4 x P6 was the best. Flower yield and pyrethrins contents were found to be negatively, though insignificantly, correlated. This requires formulation of suitable selection indices to make the selection for high pyrethrins yield effective. Reciprocal Recurrent selection appears an effective selection procedure to improve the population for extracting pyrethrum clones.