MULTIPLE ALLELES AND THE CONTROL OF LEAF ZONATION PATTERNS IN ZONAL PELARGONIUMS

The expression of four red zonation leaf patterns, and the absence of zonation, was studied by a matrix of crosses between one plant representative of each pattern and two zoneless plants. The patterns were defined by their position on the leaf and by the leaf zone index - the ratio of zone width to leaf length. The zonation was determined by multiple alleles of one gene, Zo/zo. Individual alleles determined the expression zoneless, Zo(l), narrow peripheral zone, Zo(p), medium middle zone, Zo(mm), narrow middle zone, Zo(nm), and wide basal zone, Zo(b). All four zone patterns were dominant over zoneless. Within the zoned patterns, the middle zoned types were dominant over the peripheral and basal zones in determining zone position, but the effects of the four zoned alleles were additive with respect to zone index. The zoneless allele appeared not to share these additive properties; instead the two zoneless plants behaved as if they had the middle phenotype, dominant for position but recessive for its expression.