1. Corn Breeding in the Tropics. Perhaps a few observations on corn breeding in Venezuela, latitude N 12, would be of interest to geneticists in other parts of the world.
A preliminary survey of the existing corn varieties in Venezuela made in September, 1939, revealed that all of them were of inferior productive capacity with a tendency to grow extremely tall and set the ear high on the stalk. Most varieties had white seeds, primarily because the people depend to a large extent on "arepa", ground corn in the form of a small, thick pancake, for food. Yellow "arepas" are preferred in some regions of the country, but white "arepas" are more commonly used. For years, negative selection has been going on in corn because the people eat the best seeds and plant the leftovers.
Some of the best varieties and hybrids from the United States and from many tropical and subtropical countries, including Cuba, Puerto Rico, Santo Domingo, and Colombia, were collected and planted together with the Venezuelan varieties in three different experiment stations. The types from the United States were vigorous in the seedling stage but they came into flower too early, as was expected, due to the difference in length of day. They became weak and were attacked by many diseases and insects. A Puerto Rican variety, Mayorbella, obtained from Dr. Arturo Roque, was vigorous in the seedling stage, then became weak, and later vigorous again and produced relatively large ears. The Venezuelan varieties gave their usual rank plant growth but did not set desirable ears. A yellow seeded type from Cuba with sturdy stalk of medium height set two ears at the proper distance from the ground. This type outyielded the others by at least 100 per cent. In further tests it has made the unusual performance of giving relatively high yields all over Venezuela from altitudes of 40 feet to 4,000 feet. In three years in which six generations of mass selection have been made, it has become the most popular variety in the country in spite of its color.
Its origin is interesting. A representative from this government collected two varieties from Cuba in 1938, but the seeds of the two were mixed in handling. About two years later several hundred sound seeds were salvaged from a bag of weevil-eaten material, and from these seeds the present selection has been developed. This selected type is being distributed in this country and in other neighboring countries under the name of VENEZUELA-1.
The main project is the development of hybrid corn adapted to the climatic conditions of Venezuela. Six generations of inbreeding of the heterogeneous material has resulted in approximately 300 selected lines, some of which have a desirable appearance and have done well in topcrosses and single crosses. The first double crosses are now being tested.
It is interesting to note that most of the varieties collected from Venezuela and other countries of this latitude degenerate rapidly with intensive inbreeding. Outcrossing followed by sib crossing has been accepted as the best practice for utilizing these varieties.
The Cuban type is a striking exception to this rule. Selfing has resulted in a multitude of types, but most of them are relatively vigorous and some are exceptionally impressive.
Inbreeding has resulted in the usual number of hidden recessives and the isolation of new mutations. Male sterile, barren stalk, brown midrib, virescents, white seedlings, zebra, tassel seed, cuzcoid, and many others have been observed.
A small but important change in breeding technique has been necessary due to the larvae of an octitud fly, Euxesto stigmatia Loew. It is not advisable to cut back the husks of the ear shoot to obtain a uniform brush of silks because the insects enter and destroy the ear. It is better to wait as long as possible for the silks to come out naturally before pollinating.
There can be no doubt that in the near future hybrid corn will be available for distribution in a country which has no seed companies and little knowledge of seed improvement. In the meantime, however, the type VENEZUELA-1, improved by mass selection, has been widely distributed.