4. Segregation for sucrose storage in corn stalks.
In last yearÕs News Letter (No. 23) we reported refractometer readings for segregating progenies between C103 and T1. In 1949 readings were made on segregating progenies of crosses of C103 with the following inbreds: C 22(su), C102, R 4, Hy, 38‑11, Os420, I 159, Oh 40B, CI 7, DT 21, I 205, WF9, and 1188 a rd field corn line. The C102¥103 F2 progeny showed the narrowest range of refractometer readings from 10.75 to 16.75 in one progeny, while in a second progeny the range was from 6.25 to 16.75 with an indication of a bi‑modal curve for this progeny. At least three of the progenies C103¥38‑11, C103¥W7 and C103¥Hy gave distinctly bi‑modal curves with approximately 25% of the readings centered around a low mode 3.25 for 38‑11, 6.25 for WF and 6.25 for Hy with the respective high modes of 11.5 for 38‑11, 10.75 for WF and Hy. These data indicate that true low sucrose behaves as a recessive. Readings will be made on the F3 generation this summer.
Inbreds show marked differences in the way they maintain total solids in the stalks as the grain is filling. Two weeks after pollination WF has almost as high a refractometer reading as C103 (more than 12%) but 50 days later the percentage for WF9 has dropped to about 4%, while 103 has gone up to 15% and then back to 12. Inbred 38‑11 shows a similar pattern to C103, but in a lower range, going from 6‑1/2% to 8‑1/2% and then falling to 4% as the grain matured. C102 showed considerable variation from plant to plant, but in a lower range than C103. C102 is a Lancaster Surecrop line as is C103.
The genetic picture for sucrose storage is still obscured by other factors that affect amount of sucrose present in the stalk when the grain is mature. One of these factors is the size of ear produced. An incompletely filled ear will have a higher reading than one completely filled, although high readings have been obtained on some plants having well filled ears.
Time of sampling is another factor influencing solids present in stalk juice since some lines lose solids very fast as they mature while for others such as C103 the solids present remain fairly constant.
Possibly amount of sunlight a plant receives affects total solids stored. In 1948 at Mt. Carmel, Connecticut, there was a tendency for end plants on the south end of the row to havo a higher reading than plants in the row. It is also probable that soil fertility will have some influence.
All of these variable factors must be controlled as well as possible before accurate genetic analysis can be made.
W. Ralph Singleton and Robert Van Reen