Non-disjunction in presence of interchanges involving B-type chromosomes in maize, and some phenotypical consequences of meaning in maize breeding

Summary

By using appropriately interchanges between A and B chromosomes in maize it has been possible to reach the following conclusions, chiefly on the basis of genetical experiments:

• 1. non-disjunction of B^A chromosomes in the second microspore mitosis is greatly influenced by environmental conditions;

• 2. different B^A chromosomes undergo different rates of non-disjunction: B¹⁰, B⁴ and B⁹ chromosomes show, under the same field conditions, decreasing values of such event;

• 3. following non-disjunction in the above mentioned mitosis, the “directed fertilization”, that is the tendency of the hyperploid sperm to unite with the egg nucleus rather than with the polar nuclei, is greater for B⁴ and B¹⁰, as compared with B⁹;

• 4. while non-disjunction in the mentioned mitosis may occur in 70% of the generative nucleus of microspore or more; according to genotype and environmental conditions, as mentioned above, the same phenomenon, although at a very much lower rate, does occur both in endosperm and sporophyte tissues;

• 5. the presence in the nucleus of B chromatin may not only result in nondisjunction of B^A chromosomes, but also may cause non-disjunction of other A chromosomes;

• 6. kernels differing in B^A chromosome endowment may greatly differ in endosperm size, as well as in the size of the plant derived from them;

• 7. the points (5) and (6) are specifically discussed respectively from the point of view of basic mechanisms of genetic control of nuclear behavior and of application in maize breeding.