1. Breeding program.
Brazil may not yet be ready for large‑scale introduction of hybrid corn and premature widespread use might lead to a loss of valuable genetical and breeding material in the numerous local populations. In view of these considerations, I have tried since 1937 the following program of establishing homogeneous self-propagating populations.
(a) Selection of the initial material which may either consist of plants of local populations or hybrids combining desired characters.
(b) Selfing during three to four generations and elimination of all pedigree lines which contain undesirable characters.
(c) Sib and between‑line crosses during about three generations; selecting the most vigorous combinations, eliminating any hybrid showing undesirable characters; and maintaining all families separately (pedigree).
(d) Thus, the final stage is reached after abort seven to eight generations and all the selected families are united into one population which is maintained by open pollination and simple mass selection for stock seeds.
Final results have been obtained by this method in establishing new sweet corn varieties: Piracicaba white P678, P18, orange P9, etc. Satisfactory, though only preliminary results have been obtained also with hard orange flint (cateto) and with yellow dent. After having essentially solved the question of producing sweet corn for our climate, we are now concentrating on the hard orange flints.
The theoretical basis of the process "controlled pollination-pedigree-breeding" is easily explained. It consists in producing a population essentially homozygous for all desired characters, such as color and texture, ear size and form, plant height and relative position of ear (slightly above the middle of the plant); and heterozygous for the main factors giving vigor. That such a combination of homozygosis and heterozygosis is possible, was proved in indigenous corn which is on the one side very homogeneous for many seed and plant characters, but at the same time extremely susceptible to close inbreeding.
In Piracicaba sweet corn which is a new synthetic variety we have started the routine work of selfing in order to produce ultimately hybrid seeds.