9. Unpaired row‑number.
In 1946 a nine‑rowed ear of corn was found by I. W. Hepperly and reported (Jour. Hered. 40: 62‑64, 1949). Seed was obtained from this source for studies of the inheritance and developmental morphology of this character.
Hepperly described the type as odd‑rowed. This is only partly true, since the condition is caused by the failure of one spikelet of each pair to develop from branch primordia which normally produce two spikelets. This results in an ear with half the number of rows normally expected; i.e., a normally 18‑rowed ear would be 9‑rowed, a normally 16‑rowed ear would be 8-rowed. The unpaired condition of the spikelets also occurs in the tassel.
Inheritance of the unpaired spikelet condition was originally believed to be controlled by a single recessive gene. My studies have shown that inheritance is more complex. F1 populations between the unpaired‑spikelet type and Roman's translocation testers T.B.‑1a (9‑70 B 1‑1), T.B.‑4a (9‑72A‑1), and T.B.‑9b (8‑193‑2) have been grown. F1's from crosses with testers 4a and 9b had unpaired rows, but the F1 with 1a tester had unpaired rows only on the tips of the ears.
Other F1 populations showing unpaired spikelets were those from crosses of an unpaired‑row selection with multiple testers from Stadler and Mangelsdorf individual chromosome testers 1 and 2. No ears with unpaired rows were found in the F1 between the unpaired‑row selection and Mangelsdorf's chromosome 9 tester.
Wesley C. Wilcox