Genetic improvement of pyrethrum : 4. Selective divergence, heterosis and potential hybrid clones

Pyrethrum (Chrysanthemum cinerariefolium), an important paramedicinal plant is a potential source of pyrethrins, which have a long history of safe uses against mosquito larvae - a carrier of malarial parasite. It was introduced in India from Kenya in 1931. Considerable genetic diversity has been generated over the years. Repeated clonal selection could lead to isolation of a number of divergent clones representing selective divergence. Planned hybridization among some of the chosen clones could further enlarge the spectrum of variation as measured by multivariate analyses (D(2)-statistic and canonical analysis). The resulting hybrids manifested a variable degree of heterosis which was found to be, by and large, positively associated with the degree of divergence between the two constituent parents of a hybrid. However, the choice of the potential hybrid clone(s) for commercial exploitation was most viable when parents for hybridization were short-listed on the basis of parental divergence coupled essentially with per se performance for specific traits. The latter criterion assumes greater significance since low x low or medium x low parental hybrids also tended to register high heterosis for both the pyrethrins content and yield. Four hybrids: 234xL, 8xL, 326×395 and 319xL were identified to be the most promising for clonal selection.