Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Peter A. Peterson


Self-incompatibility has never been reported in maize but some cases of unidirectional cross-incompatibility have been reported in the literature. One such case of unidirectional cross-incompatibility was noticed in the maize cytogenetics nursery Ames, Iowa during 1975. In this case, the crosses between the derivatives of a particular line am(pa-pu)/a1 sh2 and a specific male parent al et/al et resulted in reduced seed setting (<25 seeds/ear). The reciprocal crosses between the same parents gave normal seed setting (NSS). It was also observed that this unidirectional cross-incompatibility was heritable and the factors controlling this incompatibility were different from the known unidirectional cross-incompatibility locus ga1.;The present investigations were made to study the genetics of this unidirectional cross-incompatibility and the mechanism involved in the rejection of the incompatible pollen. It was found that this cross-incompatibility system is not controlled by cytoplasmic factors but nuclear genes are involved in the incompatibility reaction. The results showed that this system is controlled by three recessive loci. One locus named cif (cross-incompatible female) controls the incompatibility reaction in the female parent (called RSS female) and the other two, cim1 and cim2 (cross-incompatible male), are controlling the incompatibility reaction in the male parent (called RSS male). The cross will be incompatible only when the female parent has the cif locus in homozygous recessive form and the male parent has the cim1 as well as cim2 locus also in homozygous recessive form. The reciprocal cross between the same parents will be compatible.;The cytological studies on the in vivo pollen germination and pollen tube growth showed that there was no difference between the compatible and the incompatible pollen tube growth during first 6 hours of pollination. The incompatibility reaction occurs between 6 and 12 hours of pollination as the tips of the pollen tubes in the incompatible pollinations appeared swollen to a considerable extent compared with the tips of the pollen tubes in the compatible crosses. It was also observed that sometime between 18 and 24 hours of pollination, the swollen tips of the pollen tubes burst and the pollen tube growth is stopped.



Digital Repository @ Iowa State University,

Copyright Owner

Abdul Rashid



Proquest ID


File Format


File Size

114 pages