Incorporating different proportions of exotic maize germplasm into two adapted populations

Abstract

Maize breeders frequently wish to use exotic germplasm in their breeding programs without losing specific characteristics of their adapted material. The objective of this study was to determine the optimal proportions of exotic germplasm to incorporate into adapted populations (F2 = 50% exotic, BC1 = 25% exotic, BC2 = 12.5% exotic and BC3 = 6.25% exotic) to form the initial foundation population and to determine the heterosis between adapted x exotics. We used six exotic populations of different origins and two adapted populations representing a Brazilian heterotic pattern. In 1993-94 and 1994-95, the parents, F1, F2, BC1, BC2, BC3 and four checks were evaluated in six environments in central Brazil using an 8 x 9 simple rectangular lattice design. Higher mean values for yield were obtained as the proportion of exotic germplasm decreased. Some backcrosses produced more than the adapted populations BR 105 (7.59 ton/ha) and BR 106 (8.43 ton/ha). The best results were obtained when incorporating 6.25 or 12.5% of exotic genes. This trend was true for root lodging, stalk lodging and ear diseases but not for plant and ear height. The midparent heterosis for yield varied from -16.1 to 40.3%. Midparent heterosis with positive and negative values were also found for the other traits. The results indicate the potential of exotic germplasm for developing good hybrids. After choosing the best exotic source, some recurrent selection might be appropriate in order to adapt and improve the exotic populations.<br>Os melhoristas de milho que utilizam germoplasmas exóticos nos programas de melhoramento têm a preocupação de não perder as características desejáveis dos materiais adaptados. Buscando atender esta demanda, o presente trabalho teve por objetivo determinar a proporção ideal de germoplasma exótico que deve ser incorporado em populações melhoradas (F2 = 50% exótico; RC1 = 25% exótico; RC2 = 12,5% exótico; RC3 = 6,25% exótico), para formar as populações base para seleção e determinar a heterose entre os germoplasmas exóticos e adaptados. Em 1993/94 e 1994/95, os parentais, F1, F2, RC1, RC2, RC3 e quatro testemunhas foram avaliados em seis ambientes da região central do Brasil, utilizando-se o delineamento em látice simples 8 x 9. De um modo geral, à medida que a proporção de germoplasma exótico decresceu, valores médios mais altos foram obtidos para o caráter peso de espigas. Alguns retrocruzamentos produziram mais que as populações melhoradas BR 105 (7.500 kg/ha) e BR 106 (8.430 kg/ha). Os melhores resultados foram obtidos quando houve a incorporação de 6,25 ou 12,5% de genes exóticos. Esta tendência foi observada para acamamento, quebramento e espigas doentes, mas não para altura de planta e de espiga. A heterose média para peso de espiga variou de -16,1 a 40,3%. Heteroses médias com valores positivos e negativos também foram encontradas para outros caracteres. Os resultados obtidos mostraram o potencial em se utilizar germoplasmas exóticos para a obtenção de híbridos. Sugere-se, após a escolha dos germoplasma, algum esque...

Use of the Suwan1 Heterotic Group in Maize Breeding Programs in Southwestern China

“…Dudley (1982) suggested that backcrossing one or more times to the elite line was useful for selecting improved offspring. Santos et al (2000) conducted a systematic study and found that the best exotic proportions were 6.25 and 12.5%. Our results from this study are highly consistent with the conclusion of Santos et al (2000).…”

“…Santos et al (2000) conducted a systematic study and found that the best exotic proportions were 6.25 and 12.5%. Our results from this study are highly consistent with the conclusion of Santos et al (2000).…”

How Many Parents Give the Highest Yield in Predicted Synthetic and Composite Populations of Maize?

“…It may be that pushing the yield of elite composites can be diffi cult through further composite formation via full crosses because the F 1 yields are often no higher than that of the elite parent and because the average parent yield is usually lower than the elite composite per se. However, dos Santos et al (2000) found that smaller proportions of exotic germplasm (12.5% vs. 50%) in a backcrossed population could signifi cantly increase the yield of elite composite populations (BR105, +15%; BR106, +4.4%) when the number of favorable alleles in the exotic populations was low. Apparently there are times when the careful addition of select alleles through backcrossing will make progress for yield of an elite composite as is often practiced with elite inbred lines used to form high yielding single cross hybrids (Troyer, 2000).…”

Genetic variability and yield potential of three semiexotic maize (Zea mays L.) populations

“…), including exotics, may be a recommended strategy for the conditions of the vast array of environments like those occurring in Brazil. Exotic germplasm has largely contributed to increase the variability and the efficiency of breeding programs for the development of cultivars REGITANO NETO et al, 1997;SANTOS et al, 2000). The development of commercial hybrids initiated with local germplasm represented by old varieties such as Cateto and Dente Paulista.…”