Testing genetic control hypotheses for Plum pox virus (sharka) resistance in apricot

The resistance/susceptibility level of 213 descendants from three different crosses between the French apricot cultivar 'Polonais' (susceptible to Plum pox virus, sharka), and the North American cultivar 'Stark Early Orange' (resistant) was evaluated during four cycles of study under controlled greenhouse conditions. Resistant:susceptible ratios were 83:17 in the case of the 'Stark Early Orange' open-pollination descendants, 62:38 in 'Polonais' × 'Stark Early Orange' descendants, and 28:72 in 'Polonais' × 'Polonais'. These ratios were checked against the expected ratios of different genetic control hypotheses, combining one, two or three genes involved in the expression of this trait and with the resistance being a dominant (Hypothesis A) or recessive trait (Hypothesis B). In addition, two other, more complex hypotheses were proposed: that the resistance is controlled by 2 independent genes, the resistance being recessive for one and dominant for the other (Hypothesis C), and another hypothesis considering the resistance to be controlled by one dominant gene and admitting a 25% error in the evaluation process (Hypothesis D). The χ2-test was applied to compare the goodness-of-fit of the proposed hypotheses. Hypothesis D seems to be the most consistent in the three apricot crosses studied.