PROBLEMS WITH INDOGAMIC LINES. I. INCREASE FROM SEED WITH TWO AND FOUR PROGENITOR PLANTS

Abstract

Three methods for calculating the inbreedíng generated with one seed increase using 2 or 4 plants from the original line to produce the basic line, and with a second seed increase from the basic line to produce the registered line, are discussed in four· types of inbred l ines of maize (Zea mays L.). Such methods are the inbreeding formula for a regular mating system, the homozygosis
coefficient, and the inbreeding formula for a synthetic variety. The types of lines are self, full-sib, half-sib, and backcross lines. lt is
shown that only with the self and backcross Lines the three methods give the same result with two seed increases, although this is only a circumstantial coincidence for the homozygosis coefficient method, ant~ that the inbreeding formula in a regular mating system requires an a posteriori reasoning in arder to be valid. With full-sib and half-sib lines, only the inbreeding formula for a
synthetic variety produces the correct results.