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

Abstract

Maize (Zea mays L.) elite inbred lines developed from pedigree programs tend to be genetically related. Therefore, it is necessary to incorporate unrelated inbreds to those programs to allow the continued release of outstanding single-crosses. The objectives of this research were to compare the usefulness of a modified reciprocal recurrent selection procedure (MRRS) to improve populations to be used as sources of elite inbreds and outstanding single-crosses to integrate pedigree programs, and to investigate the effects of selection on the relative contribution of general (GCA) and specific combining (SCA) abilities to the single-crosses variation. Eight and six S 3 lines from populations IG-3-C1 and IG-4-C1, respectively, selected from the first cycle of the MRRS program were crossed in a partial-diallel mating design, and the 48 experimental and five commercial single-crosses were evaluated in six environments. Grain yield mean of the experimental singlecrosses (9.57 t ha -1 ) did not differ from the commercial single-crosses (9.86 t ha -1 ), and ten of the 48 experimental single-crosses could be released as cultivars because they compared favorably to the currently used singlecrosses. Thus, one cycle of the MRRS procedure improved efficiently the populations allowing the development of outstanding single-cross, but additional cycles of selection should be carried out since none of the experimental single-crosses outperformed the highest yielding commercial single-cross. The relative contribution of the GCA over SCA may have been affected by the MRRS, since the SCA was more important than GCA for some of the traits assessed. Key words: diallel design, maize improvement, combining ability Performance de híbridos simples de milho desenvolvidos de populações melhoradas por seleção recorrente recíproca modificada RESUMO: Linhagens elites de milho (Zea mays L.) desenvolvidas em programas genealógicos tendem a ser geneticamente relacionadas. Portanto, é necessário incorporar linhagens não relacionadas a estes programas para permitir a liberação contínua de híbridos simples superiores. Comparou-se a utilidade de um procedimento modificado de seleção recorrente recíproca (SRRM) em melhorar populações a serem utilizadas como fontes de linhagens elites e híbridos simples superiores para integrar os programas de melhoramento, e investigar os efeitos da seleção na contribuição relativa da capacidade geral (CGC) e da capacidade específica (CEC) de combinação para a variabilidade dos híbridos simples. Oito e seis linhagens S 3 obtidas das populações IG-3-C1 e IG-4-C1, respectivamente, selecionadas do primeiro ciclo de SRRM, foram cruzadas no delineamento dialelo parcial e os 48 híbridos simples experimentais (HSE) e cinco híbridos simples comerciais (HSC) foram avaliados em seis ambientes. A média geral de produção de grãos dos HSE (9.57 t ha -1 ) não diferiu significativamente dos HSC (9.86 t ha -1 ), e dez dos 48 HSE poderiam ser liberados como cultivares, pois são comparáveis aos híbridos simples comerciais. Por...

Full-sib reciprocal recurrent selection in the maize populations Cimmyt and Piranão

“…However, most seeds of maize hybrids available for commercial breeding show a reduced genetic base, mainly due to strong commercial pressures that force breeders to extract a narrow range of the elite germplasm tested (Goodman, 2005;Mikel and Dudley, 2006;Hartings et al, 2008;Fan et al, 2010;Reif et al, 2010). Moreover, elite lines developed in breeding programs are recycled repeatedly to join their favorable alleles in new inbred lines and hybrids (Bernado, 2008;Souza Jr. et al, 2010).…”

“…Although these procedures may be considered effective for the development of hybrids, in the long term, this reduced genetic variability can lead to genetic vulnerability to biotic and abiotic stresses and limited future selection gains (Smith et al, 2004;Reif et al, 2010;Souza Jr. et al, 2010;Romay et al, 2011). Therefore, the exploration of new sources of germplasm and the adoption of other breeding strategies can be considered an alternative for long-term maize breeding progress.…”

“…Furthermore, the strains developed in RRS programs are not related to the strains developed in recycling programs. Therefore, these lineages could be incorporated into these programs to maintain the rate of development and launch of new hybrids (Souza Jr. et al, 2010).…”

Changes in heterosis of maize (Zea mays L.) varietal cross hybrids after four cycles of reciprocal recurrent selection

“…These hybrids may exhibit heterosis as a consequence of genetic divergence and partial to complete dominance of genes controlling grain yield and other traits (Hallauer and Miranda 1995). When population crosses are used as commercial hybrids that can be profitable alternatives to single-cross hybrids (Carena 2005;Souza Jr et al 2010;Jenweerawat et al 2010), yield depression which occurs with the recycling of seed is lower in the former than in the latter (Paliwal 2000). Likewise, the ease of seed production and low seed price of improved varietal crosses may be of interest to small holder farmers' (Mosisa et al 2009) in remote rural areas with limited market access.…”

Genetic Parameters and Predictive Genetic Gain in Maize with Modified Recurrent Selection Method

“…In each cycle of recurrent selection a higher concentration of favorable alleles occurs in the population, with a consequent increase in the average population. This method of selection is very important in maize breeding in order to obtain cultivars and to improve the Brazilian maize populations (Pinto et al, 2003;Santos et al, 2005;Santos et al, 2007;Carvalho and Souza, 2007;Reis et al, 2009;Kist et al, 2010;Souza Jr. et al, 2010;Rovaris et al, 2011).…”