Recurrent selection

Abstract

In self-pollinated species such as soybean, the use of recurrent selection began in the 1960s, aiming to increase the frequencies of favorable alleles to the cumulative genetic progress in the desired traits over several cycles, that is, to increase additive and epistatic additive × additive genetic variances in the populations used in breeding programs. Currently, in species such as soybean, the use of the term recurrent selection is restricted to the systems that involve (a) three or more parents; (b) two or three generations of recombination, through biparental, quadruple, or octuple crosses; and (c) two or three generations of inbreeding, usually by using the single seed descent (SSD) method or a method derived from it (SHD, SHDT, MSD), in order to reduce the time of each cycle. It is also possible to reduce the time of each step by using molecular markers linked to genes that control important agronomic traits, such as seed yield and resistance to diseases and insect pests. The obtained progenies are evaluated in tests of agronomic performance, selected and used as parents in new cycle and/or released as new cultivars. In most programs, with or without the use of male sterility, it is possible to anticipate the progeny evaluation for the F3 generation, in which the plants have 75% of the loci in homozygous and 25% in heterozygosis, on average. The largest genetic gains in seed yield have been obtained from the largest numbers of genetically divergent F1 crosses. In order to enhance the genetic base, exotic and transgenic genotypes can also be used as new parents in each cycle. Although recurrent selection consumes high amount of time and labor, it should be considered as a central methodology in well-established and well-consolidated breeding programs, because it serves as the base for the creation of genetic variability to be explored in the long-term selection for various traits. In addition, it also allows the enhancement of the genetic base of the germplasm of the cultivated species and the general organization of the breeding programs in progress.