Varieties of corn grown in the Northeast and in the Middle West at the same latitude are noticeably taller in the East. Several environmental conditions are involved in this growth difference, principally light intensity and temperature. Plants of many species, including maize, grown under tobacco shade cloth are significantly taller and broader in leaf than plants from the same lots of seed grown in full sunlight. Under the cloth shade the temperature is the same as outside but the humidity is higher and the light intensity is lower. The same effect is noticed in the field where short-stalked varieties of corn are grown in single rows between taller varieties. Where there is a wide alley between ranges the plants at the ends of the rows are shorter than those in the center of the rows, the plants graduating in height. Here humidity and temperature are the same but light intensity varies.
Some corn seedlings started in the greenhouse and set outdoors were shorter at maturity than plants from the same seed started outdoors. This indicated that temperature in the early stages of growth had an effect. To test this, seeds of a uniform, vigorous, first generation hybrid (Wf9 × P8) were germinated in an incubator at about 30° C. until the shoots and roots were from one fourth to one half inch long. Three different lots of sprouted seedlings were held at 40, 50 and 60° C. for one hour. They were then planted in pots and left in the greenhouse until it was certain the plants would grow. They were then set in the field alongside plants from the same lot of seed sown in the open ground at the same time the treated seedlings were started in the incubator. Some of the treated seedlings died but enough were started in each lot and later thinned to give an even stand of plants in the field.
All three lots of heat-treated seedlings were shorter in height, less vigorous in growth throughout the season and later in flowering than the treated plants. All lots grew to full maturity and were measured after growth had ceased. The results are: Control 101: 40° C. 87; 50° C. 89; 60° C. 93 inches in height. The differences between the three temperature treatments are small. All three averaged 90 compared to 101 inches in height for the control.
The result that was not anticipated was the pollen sterility in all treated lots. Normal tassels were produced with well-developed florets but the anthers were small and shriveled and for the most part remained enclosed in the glumes. In view of the fact that high temperatures sterilize the male germ cells in animals, from amphibians to mammals, these results are highly significant. This influence on growth is an anti-vernalization effect and may have wide usefulness in the production of hybrid seed especially if shown by other plants as well as maize.
D. F. Jones