RFLP Mapping in Maize: Quantitative Trait Loci Affecting Testcross Performance of Elite European Flint Lines

Abstract

The dissection of quantitative traits into their underlying Mendelian factors has become possible with the aid of molecular markers. In this study, we mapped and characterized quantitative trait loci (QTL) affecting testcross performance of maize (Zea mays L.) and discussed the consistency of these QTL across environments and testers. Two homozygous flint inbred lines were crossed to produce 380 F2 individuals which were genotyped at 89 restriction fragment length polymorphism (RFLP) marker loci. By selfing the F2 plants 380 F3 lines were produced and subsequently crossed to two diverse dent inbred testers (T1 and T2). Each series of testcrosses (TC) was evaluated in field trials with two replications in four environments. Three traits were analyzed: protein content, kernel weight, and plant height. Genotypic and genotype‐by‐environment interaction variances were highly significant for all traits in both TC series and heritabilities ranged between 0.71 and 0.85. Genotypic correlations between the two TC series were 0.80 (protein content), 0.88 (kernel weight), and 0.84 (plant height). The method of interval mapping was used for characterization of QTL. Protein content was significantly affected by four QTL in TC with T1 explaining 32% of the phenotypic variance (trueσ^normalp2) and five QTL in TC with T2 explaining 42% of trueσ^normalp2. For kernel weight, eight putative QTL were found in TC with T1 and six were found for T2, explaining about 60% of trueσ^normalp2. Seven QTL explained 52% and four 60% of trueσ^normalp2 for plant height. Results from QTL mapping agreed well across environments. Highly consistent results across testers were obtained for kernel weight and plant height but not for protein content. No significant evidence for epistasis among QTL was found.

Identification of positive yield QTL alleles from exotic soybean germplasm in two backcross populations

“…Multiple regression analysis for QTL was conducted using PROC REG function with markers linked to significant QTL and epistatic interactions identified by CIM, MCIM, and SMA to determine the total phenotypic variance explained (R 2 ) by QTL and epistatic interactions. The proportion of the genotypic variance for yield explained by all significant QTL in the multivariate model was estimated from the ratio R 2 /H 2 (Schön et al 1994). To test the impact of maturity on yield QTL, yield estimates of lines in both populations were adjusted using maturity as a covariate with PROC MIXED in SAS 9.2.…”

Stacking Resistance Alleles from Wild and Domestic Soybean Sources Improves Soybean Cyst Nematode Resistance

“…The R 2 values from the multivariate models are estimates of the total phenotypic variance explained by the genes or QTL and their interactions. These R 2 values were used to estimate the proportion of the genotypic variance explained by the QTL using the ratio R 2 /H 2 (Schön et al, 1994).…”

Mapeamento de QTLs em testecrosses de milho com diferentes testadores e níveis de acidez do solo

“…A magnitude da variância genética dos testecrosses é um fator determinante no mapeamento de QTLs (SCHÖN, 1994 MIRANDA FILHO, 1988).…”

“…O mérito relativo de se utilizar mais de um testador para a avaliação das linhagens depende da correlação genética entre os testecrosses dos diferentes testadores. No mapeamento de QTLs, espera-se que a magnitude da correlação genética entre os testecrosses de diferentes testadores reflita no número e efeitos dos QTLs mapeados nos diferentes testecrosses (SCHÖN et al, 1994). Portanto, o mapeamento de QTLs com mais de um testador permite avaliar a interação QTL x testador, aplicando-se com eficiência os resultados do mapemento de QTLs nos programas de melhoramento.…”

“…Schön et al (1994) utilizaram duas linhagens elites não relacionadas (KW4115 e KW5361) como testadores e encontraram alta coincidência entre os QTLs mapeados nos testecrosses desses testadores para os caracteres peso de 1000 grãos e altura de planta. Todos os seis QTLs mapeados para peso de 1000 grãos e três dos quatro QTLs mapeados para altura de planta coincidiram com os QTLs mapeados nos testecrosses da KW5361 e os da KW4115.…”