Responses to reciprocal recurrent selection and changes in genetic variability in IG-1 and IG-2 maize populations

Abstract

This paper reports the effects of three cycles of reciprocal recurrent selection (RRS) on the means, genetic variances, and on the genetic correlations for several traits in the IG-1 and IG-2 maize (Zea mays L.) populations. Interpopulation full-sib progenies from cycle zero (C 0 ) and from cycle 3 (C 3 ) of RRS were evaluated in two locations. RRS was highly effective to improve the traits according the objectives of the program: grain yield and prolificacy increased significantly, while plant height, ear height, and ear placement decreased significantly. Genetic variances for all traits decreased significantly from C 0 to C 3 , but the genetic correlations did not change consistently across the cycles of selection. The expected responses to the fourth cycle of RRS and the probability of selecting double-crosses from C 3 that outperform those from C 0 showed that the decreases in the genetic variances were not great enough to limit the continued improvement of the populations as well as the use of the improved populations as sources of inbred lines to develop commercial hybrids. However, if the magnitudes of the genetic variances continue to decrease, new sources of improved germplasm should be incorporated into both populations to allow the continued improvement of the interpopulation by RRS.

Seleção recorrente recíproca na obtenção de híbridos interpopulacionais de milho-pipoca

“…Portanto, a seqüência no processo de melhoramento dessas populações, visando o aumento de capacidade de expansão, pode enfrentar problemas no futuro em razão da reduzida variabilidade para essa variável. Santos et al (2005), em três ciclos de SRR para milho, observou redução de variabilidade para todas as características avaliadas. Segundo os autores, caso a variabilidade continue a decrescer ao longo dos próximos ciclos de seleção, é indicado que novas fontes de germoplasma sejam inseridas nas populações para que seja possível a continuação do processo de melhoramento.…”

“…Esses autores observaram ainda que os ganhos realizados com seleção para rendimento de grãos representaram 25 a 50% do ganho predito. Ao utilizar famílias de irmãos-completos das populações IG-1 e IG-2, Santos et al (2005) avaliaram o efeito de três ciclos de SRR sobre as médias, as variâncias genéticas e as correlações de várias características. Para produção de grãos foram observados ganhos de 4,07% por ciclo.…”

Diversidade genética em seleção recorrente de maracujazeiro-amarelo detectada por marcadores microssatélites

“…Essa perda na variação genética ao longo dos diversos ciclos de seleção, recombinação e avaliação pode ser mensurada com as estimativas dos componentes de variância genética (Santos et al, 2005).…”

Performance of maize single-crosses developed from populations improved by a modified reciprocal recurrent selection

“…One cycle of the modified (MRRS) procedure designed by Rezende and Souza Jr. (2000) increased grain yield by 16.7% and reduced significantly plant and ear heights. In a per cycle basis, this MRRS procedure increased grain yield at a higher rate than the 6.0% to 7.0% reported for standard RRS programs where 10% to 20% as selection intensity and S 1 lines for recombination were used (Eyherabide and Hallauer, 1991;Santos et al, 2007;Santos et al, 2005;Souza Jr. and Pinto, 2000). Then, the MRRS procedure was highly effective in improving the population cross performance in only one cycle of selection.…”

“…Reciprocal recurrent selection (RRS) is a long-term cyclical breeding procedure outlined to improve population crosses, and reported results have shown that RRS has been very effective (Eyherabide and Hallauer, 1991;Souza Jr. and Pinto, 2000;Santos et al, 2005), and also the improved populations have been sources of elite inbreds and outstanding single-crosses Betrán and Hallauer, 1996). The elite inbred lines from the RRS programs are unrelated to the inbreds developed from the recycling programs, and then they could be incorporated to these programs to maintain the rate of the development and release of new hybrids.…”