1. Cross Incompatibility in Distant Cross (1) Cross incompatibility(noncrossability) Pollens not germinate pollen tubes not penetrate into the stigma Pollen tubes not reach the embryo sac Degradation of pollen nucleus in the sac The Couses Structures of floral organ: Stigma lengths Physiological disharmony: Enzymes; PH; Osmosis Genetic disharmony: Chromosome number; chrom?' Lengths; Crossability genes: eg.kr1,kr2 in wheat“ China spring”1. Cross Incompatibility in Distant Cross (1) Cross incompatibility (noncrossability) Pollens not germinate pollen tubes not penetrate into the stigma Pollen tubes not reach the embryo sac Degradation of pollen nucleus in the sac … (2) The Couses Structures of floral organ: Stigma lengths Physiological disharmony: Enzymes; PH; Osmosis Genetic disharmony: Chromosome number; Chrom’ Lengths; Crossability genes: e.g. kr1, kr2 in wheat “China spring