On choosing the varietal type in consideration of the farmer's economic point of view

The choice of the varietal type that a farmer will use is the result of considering the balance between seed cost and the profit possible from using one type rather than another. This paper uses the criteria of quantitative genetics to predict the relative advantages of a population, lines extracted from this population, hybrids (3-way-, double-, and single-crosses) between such lines and their F2s. Inbreeding depression, rate of multiplication, genetic variability, the ratio of seed price to grain value constitute the main parameters of comparison. There is no single answer to the question and even the situation for one species may evolve over time and accompanying progress in selection. The F1 hybrids are the best type of variety in a large range of situations with high inbreeding depression (> 40%) and sufficient genotypic variance. In such a situation the expected superiority of single-cross hybrids over population is 20 to 35%. For cross-fertilized species, populations are to be considered only for low genetic coefficients of variation for hybrids and a relatively high seed cost. F2s and lines are obviously justified only with low inbreeding depression ( 40%) et une variance génotypique suffisante. Dans une telle situation, la supériorité attendue des hybrides par rapport à la population est de 20 à 35%. Pour les espèces allogames les populations ne sont jusitifées que si la variation génétique est faible et si le coût des semences hybrides est relativement très élevé. Les F2 et les lignées ne sont évidemment justifiées que si la dépression est faible (< 20%) et si la variation entre hybrides est faible