2. Corn Grass - a possible ancestral type of maize.


In the 1947 Maize News Letter #21 we reported on a second "Teopod" mutation, that was also grown under the name of Corn Grass. Since the strain is quite distinct from Teopod, we prefer the original name of Corn Grass and are using the gene symbol CG since it is a dominant character. So far this stock has been maintained in the heterozygous condition although we expect to have a homozygous stock soon since it is being selfed in the greenhouse this winter.


Corn Grass plants respond markedly to different day lengths. In the field when grown during long days the plants tiller profusely and make a plant that resembles some of the native grasses much more that Corn. (The differences between Corn Grass and normal corn are so great that students in taxonomic botany have failed to recognize Corn Grass as a relative of corn.) When Corn Grass is grown in the greenhouse with no supplemental light the plants assume a more upright position, produce fewer tillers and sometimes produce a tassel with functional pollen. Sowings at intervals of two weeks, beginning on August 15th, have demonstrated that the change in tillering takes place at the November 1st sowing. We expect to establish the date of sowing at which the normal Corn Grass type of growth will be resumed.


Corn Grass plants can be propagated asexually. In 1947 one clump was divided into four parts and the plants made good vegetative growth. In 1948 Herbert Everett at the Connecticut Station divided one clump of Corn Grass into 16 different plants which then continued to make a good growth. We are maintaining clonal lines of Corn Grass in the greenhouse at this Laboratory.


Attempts were made in 1948 to cause Corn Grass to mutate back to normal. Germinating seeds were X-rayed (75-600 r) and grown for a few days in a medium containing P32. No vegetative mutants were observed. Higher dosages will be given in 1949; also Corn Grass plants will be grown in an area receiving continuous gamma rays, in an effort to change Corn Grass to normal. This character behaves as a monogenic dominant. It could be due to a small chromosomal deficiency, or duplication. If it is a deficiency it will not be possible to secure a back-mutation; otherwise the chances of success seem fairly good.


Corn Grass has several of the characteristics that are required of an ancestral type.


A. It can be vegetatively propagated. Plants of such a type as Corn Grass could haver been grown and propagated for centuries before mutating to a normal corn plant. In warm climates, perhaps it would be perennial.


B. The seeds are produced in "ears" varying from one seed in a place to ears having a hundred seeds or more. (The larger ears are always produced in the greenhouse.) Most "ears" contain from one to ten seeds. Seeds fron such plants would be easily dispersed and would give rise to a very few seedlings in one place. Hence, they would have wider dispersal than an ear of normal corn. Germinating seedlings would not crowd each other as is the case with a normal ear of corn.


C. A single gene change (at the most a change in a short chromosomal segment) is all that is necessary to make the step from Corn Grass to normal corn. It is rather remrkable that the difference between Corn Grass and corn can be due to a single gene, but the genetic evidence indicates this is so. Since the whole change from a grass-like ancestor to normal corn can be made at one "jump", is it necessary to postulate so many steps in the building up of an ear of corn?