6. Linkage Tests
A small number of linkage testers, of Cornell origin, was brought over from England and some others from Cornell. It was soon evident that these North-American strains are difficult to grow in Brazil. They were all rather small and weak, so that it was necessary to plant them in especially prepared beds. They seem to grow and produce reasonably well when planted in the first part of summer, that is, during the period when the length of the day is still increasing. For crossing purposes, it was always advisable to make several successive plantings, with the hope that sometimes the flowering period of the strains to be crossed may coincide.
Crosses between these imported lines and local lines, such as Cateto, or with native Indian corn (Diamantino III) Chavantes, etc. were carried out and the extracts from these hybrids, are promising.
F. G. Brieger
A good collection of recessive and dominant genes in all chromosomes was organized at Columbia, Missouri with material received from Cornell (Coop) and from Drs. L. J. Stadler, H. Roman, L. F. Randolph, H. S. Perry, C. R. Burnham, R. A. Brink, W. R. Singleton and others. The plants are now at Piracicaba, Brazil, and they are growing very reasonably. After some experience we think it possible to grow in Brazil some of the American strains in the months of November to January, when we have the maximum of light, about 15 hours a day. Plants sown in December are flowering in 50 days as compared with the same strains in Columbia, Missouri, flowering in 55 days.
The problem of genetical tests for Brazil consists in the transference of the genes to late Brazilian strains, but we don't think this solution satisfactory since some segregating plants will be so late as to make our work difficult.
The principal-genes in all chromosomes were crossed in Columbia with an Argentine strain and the hybrids look good for our conditions. We think it will be possible to isolate the segregating genes in this background and in plants not too late and promising for Piracicaba.
Deficiency testers produced by X-ray in chromosomes 3, 4, 5, 6, 9 and 10 were introduced into our collection from material of Dr. L. J. Stadler. The deficiency in chromosome 5 is linked with Pr, in chromosome 6 with Y1 and in chromosome 9 with I. The deficiencies in chromosome 3, 4, and 10 were crossed respectively with Rg, Tu and Og in order to get these dominant genes linked with them.
Translocation-B testers from Dr. H. Roman for chromosomes 1, 4, and 7 were also brought to Brazil. The Tb-4 test has been useful in checking the su gene in many of our experiments.
A collection of trisomics from Cornell will be crossed with the respective recessives in order to facilitate its conservation without the necessity of cytological work.
The use of all these tests was started at Columbia, Missouri, in checking new mutants and will be continued at Piracicaba, Brazil.
E. A. Graner