4. Yellow-orange Endosperm
Studies on the genetics of the yellow-orange endosperm started at Piracicaba, Brazil, (1937), were continued at Columbia, Missouri, in 1942, through the help of a fellowship from the Guggenheim Foundation.
A deep orange endosperm from Brazil (commercial strain) was used and crossed with several white endosperm strains. These crosses gave only segregation for one pair of factors. Some were continued until F4 and the white endosperm strains checked proved to be y1 y1 Y3 Y3. Crosses with some white endosperm testers segregated again 3 colored : 1 colorless and showed independent assortment for chromosome 2 (lg 1), 4 (su 1) and 9 (df 3) indicating that the yellow gene segregating should be the Y1 in chromosome 6.
The same deep orange strain when crossed with a tester received from Dr. Jose Ma. Andres, Argentine and called A-(a1a1 B-) (Pl-y1 y1) showed a clear segregation of 9 orange : 3 yellow : 4 white. The numbers of 3 ears taken at random are the following:
|No. of the ear||Orange||Yellow||White||Total|
|40 - 12D ± 1942||156||42||61||259|
|31 - 12D ± 1942||154||56||62||272|
|Sib 49 × 17 12D 1942||137||43||49||229|
Linkage was found with the Pl gene (repulsion phase) and all yellow seeds were albescents al, the white ones segregating 3 Al: 1 al. As the al gene is probably the same as y3 or very closely linked to it, it could be said that the deep orange Brazilian strain has both Y1 and Y3. The linkage with chromosome 2 in this cross was also shown by the segregation of B. The al strain when crossed with lgl showed absolute linkage (repulsion phase). By the segregation of A it was found that chromosome 3 was not involved.
The 9 : 3 : 4 instead of a 9 : 7 ratio as found by Perry and Sprague (1936) seems to indicate the existence of another complementary gene, probably to Y1, which probably is a plant character, since its segregation was not shown in the F2 seeds. The F2 plants are now growing, but have not flowered to this moment.
The F1 of the same cross was used at Columbia, Missouri, for crossing with other Y-testers, received from Dr. H. S. Perry and the plants are growing at Piracicaba. Some unexpected ratios, were found in these crosses and will be checked in the next generation.
The deep orange Brazilian strain planted at Columbia did not flower there. So this strain could not be crossed with other testers. However, it was possible to use an Argentine strain called Coloradu Casilda and belonging to Dr. L. J. Stadler's collection. This strain has practically the same color as that of the Brazilian one and its name indicates the same variety used by Dr. J. Ma. Andres in Argentine (1939) and giving results similar to those reported here. This Argentine variety will be now crossed to the orange Brazilian strain, but to save time, it has been crossed to testers for all chromosomes. The collection of testers used was prepared at Columbia, Missouri, and includes material from Cornell (Coop) and from other corn geneticists of the States. These crosses are being checked now at Piracicaba, Brazil, where the plants are just flowering, but the situation is rather complicated since we do not know the background of the testers used with respect to the Y genes. Also, it should not be expected that we have to deal with only one sporophytic gene but several may be acting as modifiers, giving the shades found in different yellow-orange endosperm strains.
Other strains of yellow-orange corn of different origin are also being tested. Some pop-corn ears from Brazilian material showed segregation approximately of 3 white : 1 yellow-orange, and we don't know if we have here to deal with a new Y factor or only with an inhibitor of the known Y genes.
Seeds of Y4 and It received from Dr. W. R. Singleton proved to be identical with Y1 and Y3, respectively. I think also the Y2 of Dr. W. Eyster in chromosome 5 is the same as Y1; so, the general situation of the yellow-orange endosperm for the present could be simplified with only the Y1 and Y3 as complementary factors and one or more plant-character genes modifying its shade or being complementary to them. Besides this should be kept in mind, the possibility of the existence of other seed genes for yellow endosperm color, as reported by Dr. G. F. Sprague (1938).
E. A. Graner