Reverse germ orientation mutants
--Jackson, JD

In the course of studies with the Laughnan cms-S restorer genes, a mutation was observed in an RfVI strain. This new trait conditions the germ orientation of embryos causing them to face the base of the ear as opposed to the tip. Genetic analysis indicates it is a simply inherited trait and is inherited as a maternal plant character. Similar mutations were reported previously by Brieger (MNL 22:55, 1948) and Joachim (MNL 29:53, 1955; MNL 30:84-85, 1956; Proc. Minn. Acad. Sci. 24:37-43, 1956). Brieger reported an abnormality in which development of the second flower was observed. Joachim concluded that the so-called "reverse germ" in her studies is due to the development of only the lower florets in an earshoot as opposed to the usual condition of only the upper florets functioning. The name "reversed germ" was common in the literature (reviewed in Joachim, Proc. Minn. Acad. Sci. 24:37-43, 1956) and no other name was suggested. Reversed germs are found in the sweet corn variety Country Gentleman in which both the upper and lower florets function causing crowding and uneven rows (Kiesselbach, Am. Jour. Bot. 13:35-39, 1925).

A reversed germ mutation was recovered by Sachan and Sarkar (MNL 52:119-120, 1978) in the course of a mutagenesis study. They proposed the three letter symbol rgo for the trait and their mutant is now designated rgo1 (see following article). I have designated my new mutation rgo*-VI. A similar trait has been recovered by Frances Burr. It showed up as a sector on a selfed ear carrying y1-m261::dSpm. This rgo stock was crossed to rgo*-VI for allelism and gave a positive result. The relationship of these mutations to rgo1 is under study. 


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