Abstract
Summary Homozygous and heterozygous lines containing the alleles S5, S7, S15, S22, S29, S36 and S61 gave evidence that old flowers have increased levels of pollen-tube counts in styles compared with young flowers. Flowers developing late on the inflorescences were also found to have higher pollen-tube counts in incompatible matings than those formed early. Two alleles, S22 and S29, were identified which condition uniformly high levels of pollen-tube-inhibition in incompatible crosses at all times and under all conditions. The evidence suggests that the use of genotypes containing consistently efficient 5 alleles in inbred lines, and the selection of areas which minimize pseudocompatible fertilizations for the production of hybrid seed, would reduce the level of contamination of hybrid varieties by inbred seedlings.