Mendelian segregation in an interspecific hybrid population of tetraploid × diploid Coffea species-part 1

摘要

Mating of two parental varieties always leads to the production of genotypic admixture of both the parental traits in F_1 and on selfing the progeny exhibits the phenotypic segregation in a definite proportion in F_2. Mendel described it as "Law of Independent Assortment". It is general belief that coffee varieties do not follow the Mendel's ratios of segregation. Keeping in view the above findings and beliefs, a study was undertaken during 2008-2011 to observe the segregation pattern in the F_2 population of C. arabica cv. 'Cauvery' × (C. congensis × C. canephora var. robusta) established at Coffee Research Sub Station, Chettalli, Kodagu District, Karnataka, India in the year 2002. The results of the study revealed that coffee cultivars of commercial importance possessed two types of genetic traits known as dependent and independent characters. The dependent characters showed assortment of characters along with closely related characters and expressed varying degrees of expression. Therefore, the frequency of the occurrence of such phenotypic traits did not considerably match with the expected frequency of the same traits at high probability level and it matched at low probability. The genetic behavior of independent traits exhibited genetic segregation in accordance with the Mendel's law of independent assortment showing goodness of fit to the dihybrid ratio of 9:3:3:1 with high level of statistical confidence (P≥0.50 up to 0.95). It was observed that the genes regulating the dwarfing effect for coffee bush, thin stem and primary girth, low number of primary branches and reduced length of primary branches were dominant over tall type bush, thick main stem and primary shoot as well as higher number and length of primary shoots.