INFLUENCE OF THE ENVIRONMENT OF SELECTION ON THE IMPROVEMENT OF MAIZE LANDRACES BY LIMITED BACKCROSSING

Abstract

The limited use of the maize landraces in genetic improvement is mainly due to an inadequate plant archetype and limited adaptability, both being undesirable traits for modem agriculture. It is then necessary to submit the landraces to previous improvement in order to incorporate in the races the desired characteristics of plant archetype (mainly Iow plant and ear height) and wide adaptability before using them in selection and/or hybridization. In the National Center of Rescue and Improvement of Criollo Maize, a program of genetic improvement with such objective was initiated in 1992 on the fifty landraces of maize of Mexico so far documented, using the limited backcrossing method. In this method a landrace population is crossed to an improved donor population with the desired characteristics to be incorporated into the landrace population. After one generation of random mating desirable segregant genotypes are crossed to the race. From this generation on intermating is carried out using only desired plants. In this study ten landrace populations from the Pacific and the Southeast of México were submited to this methodology, advancing to the RC₁-F6 generation. The original landrace populations and their respective backcrosses were evaluated in the location where the genetic improvement was made, and in a location representative of the geographical distribution area of origin of Six of the ten landraces. It was found that the interaction of the difference between performance of the two types of populations with environments was non significant. This finding implies that the improvement by limited backcrossing can be made in a location different from the environments where the races are originated from.