ORIGINAL AND ADAPTED POPULATIONS OF MAIZE. I: LOCAL TEMPERATE VARIETIES x TROPICAL VARIETIES

Abstract

In México, few maize (Zea mays L.) breeding programs have adapted and incorporated exotic germplasm to increase the genetic base of their materials and to incorporate favorable genes. In this paper we considered grain yield as an indicator of genotypic adaptation to the central highlands of México, and it is proposed that genes for adaptation increase their frequencies by selection and are dominant over the genes that cause inability to adapt. Eight parents and 15 of their 28 F₁ crosses were evaluated. From these 15 crosses, 12 were generated from the mating among one variety of Chalqueño race (original and improved versions) with three original exotic varieties and with three selected (adapted) exotic varieties of the tropical landraces Tabloncillo, Tepecintle and Comiteco; and three of the crosses resulted from the mating between the original and the selected (adapted) exotic landraces. Thus, the crosses evaluated were of three types: local original variety by original and adapted exotic varieties, improved local variety by original and adapted exotic varieties, and original exotic variety by its adapted version. Grain yield, plant height and days to male flowering were recorded. The adapted exotic populations generally surpassed their original versions in grain yield; and they also matured earlier and formed higher plants. Most contrasts for grain yield among the crosses were significant and had values in favor of the adapted exotic populations. These results support our assumption that F₁ crosses have a higher frequency of favorable genes from the adapted parent, and those genes dominate over the genes from the original parent. Crosses between varieties of Chalqueño with Tepecintle landraces showed the higher heterosis, thus showing a new heterotic pattern.