Potencial discriminatório de três testadores em "topcrosses" de milho

Abstract

Resumo -O objetivo deste trabalho foi determinar o potencial de três testadores endogâmicos elites a fim de avaliar e classificar 15 materiais genéticos para a síntese de híbridos. Quarenta e cinco híbridos mais quatro testemunhas foram avaliados em cinco ambientes, no ano agrícola 2000/2001, utilizando delineamento em blocos ao acaso, com três repetições. Foram avaliados os caracteres peso de grãos corrigido, altura de planta e altura de espiga. As estimativas de capacidade geral e específica de combinação foram obtidas pelo modelo de Griffing, adaptado por Vencovsky e Barriga, para análise em delineamento genético fatorial. O rendimento médio obtido entre os cinco ambientes variou de 8,97 t ha -1 a 12,21 t ha -1 . Vinte e sete tratamentos superaram a média geral absoluta da melhor testemunha. A análise de variância conjunta revelou efeitos significativos de ambientes, capacidade geral de combinação dos parentais e testadores, capacidade específica de combinação e das interações ambiente x capacidade geral de combinação dos parentais e testadores. Os testadores promoveram uma classificação diferenciada para a base genética avaliada, com destaque para os cruzamentos entre parentais HS1, HS2, HS5 e HT4 com o testador LF e parentais L10 e HS5 com o testador L05.Termos para indexação: Zea mays, progênie, híbrido, capacidade combinatória, germoplasma. Screening potential of three maize topcross testersAbstract -The objective of this work was to assess the potential of three elite inbred testers to evaluate and rank fifteen genetic materials for hybrid synthesis. Forty-five hybrids and four controls were evaluated in five different environments in the 2000/2001 growing season using a randomized complete block design with three replications. The main agronomic traits were assessed, including the corrected grain yield and plant and ear height. Estimates of general and specific combining ability were obtained using Griffing's method adapted by Vencovsky and Barriga. The average yield in the five environments ranged from 8.97 ton ha -1 to 12.21 ton ha -1 . Twenty seven treatments outperformed the mean yield of the best control. The analysis of variance over environments revealed significant main effects of environments, general combining ability of the parents and testers, specific combining ability and significant interactions, such as environment x general combining ability of parents and also environment x general combining ability of testers. The testers allowed ranking and screening of the assessed genetic basis, suggesting as best combinations the crosses that included the HS1, HS2, HS5 and HT4 parents with the LF tester and the L10 and HS5 parents with the L05 tester.

Performance of testers with different genetic structure for evaluation of maize inbred lines

“…DUARTE et al (2003) found significant difference in the GCA for testers with high values, suggesting that the higher frequency of favorable alleles for improving the GY was in testers than lines. However, if a tester is used only to evaluate the combining abilities of lines, negative GCA estimate for this tester can be more interesting because the better expression of the favorable alleles from different lines depends on the frequency of unfavorable alleles form the testers (BARATA & CARENA, 2006).…”

Use of testers for combining ability and selection of papapya hybrids

“…The SCA values are related with the genetic distance between the tester and the line and show the importance of non-additive interactions, characterized by complementarity in relation to the allele frequency in loci with some dominance among parents (Duarte et al 2003), i.e., SCA is linked to the dominance effects.…”

“…In breeding programs for high performance with great potential, elite lines are used whenever possible. For this reason, in most cases, the testers used are also elite, by which genotypes with market potential can be obtained, besides a prediction of the performance of potential hybrids (Duarte, et al 2003) From a practical point of view, the main purpose of the use of testers is to eliminate lines with unsatisfactory performance from the selection process. In this way, the hybrid development program can be rationalized and becomes more efficient (Elias et al 2000).…”

“…However, a high genetic divergence does not necessarily increase the expression of heterosis. It is therefore important to use methods that can identify the best combinations (Duarte et al 2003).…”

“…For Hallauer (1975) however, the ideal tester should allow genetic gain maximization. In general, for any program of hybrid development, the tester must comply with the following criteria: ease of use, generate information that classifies the potential for the crossings correctly, and genetic gain maximization (Duarte et al 2003).…”