Maize silage is a significant energy source for animal production operations, and the efficiency of the conversion of forage into animal mass is an important consideration when selecting cultivars for use as feed. Fiber and lignin are negatively correlated with digestibility of feed, so the development of forage with reduced levels of these cell-wall components (CWCs) is desirable. While variability for fiber and lignin is present in maize germplasm, traditional selection has focused on the yield of the ear rather than the forage quality of the whole plant, and little information is available concerning the genetics of fiber and lignin. The objectives of this study were to map quantitative trait loci (QTLs) for fiber and lignin in the maize stalk and compare them with QTLs from other populations. Stalk samples were harvested from 191 recombinant inbred lines (RILs) of B73 (an inbred line with low-to-intermediate levels of CWCs) x De811 (an inbred line with high levels of CWCs) at two locations in 1998 and one in 1999 and assayed for neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL). The QTLs were detected on nine chromosomes, mostly clustered in concordance with the high genetic correlations between NDF and ADF. Adjustment of NDF for ADF and ADF for ADL revealed that most of the variability for CWCs in this population is in ADF. Many of the QTLs detected in this study have also been detected in other populations, and several are linked to candidate genes for cellulose or starch biosynthesis. The genetic information obtained in this study should be useful to breeding efforts aimed at improving the quality of maize silage.

Quantitative trait loci for cell-wall components in recombinant inbred lines of maize (Zea mays L.) I: stalk tissue.

Estimating and Interpreting Heritability for Plant Breeding: An Update

A unified presentation, a synthesis, and an evaluation of the methods employed in the estimation of heritability in plants are presented. Asexual, cross‐fertilizing, and self‐fertilizing diploid species, as well as annual and perennial ones, are considered. All broad‐ and narrow‐sense heritabilities are defined on individual and family bases for prediction of response to selection for a target population of environments in space and time. Narrow‐sense heritabilities are defined in cross‐fertilizing species for expected response to variations of mass, half‐sib, and full‐sib family selection for the next generation and the long term, and similarly in self‐fertilizing species. The use of both collateral and lineal relatives to estimate heritability is discussed, and the biases present in the estimators are given. Many departures and variations of the common procedures are discussed. The standard errors of heritability estimators and confidence intervals are presented.

Estimation of heritability and prediction of selection response in plant populations

The efficiency of marker-assisted selection (MAS) depends on the power of quantitative trait locus (QTL) detection and unbiased estimation of QTL effects. Two independent samples N = 344 and 107 of F2 plants were genotyped for 89 RFLP markers. For each sample, testcross (TC) progenies of the corresponding F3 lines with two testers were evaluated in four environments. QTL for grain yield and other agronomically important traits were mapped in both samples. QTL effects were estimated from the same data as used for detection and mapping of QTL (calibration) and, based on QTL positions from calibration, from the second, independent sample (validation). For all traits and both testers we detected a total of 107 QTL with N = 344, and 39 QTL with N = 107, of which only 20 were in common. Consistency of QTL effects across testers was in agreement with corresponding genotypic correlations between the two TC series. Most QTL displayed no significant QTL x environment nor epistatic interactions. Estimates of the proportion of the phenotypic and genetic variance explained by QTL were considerably reduced when derived from the independent validation sample as opposed to estimates from the calibration sample. We conclude that, unless QTL effects are estimated from an independent sample, they can be inflated, resulting in an overly optimistic assessment of the efficiency of MAS.

https://www.genetics.org/content/genetics/149/1/383.full.pdf

Quantitative Trait Locus (QTL) Mapping Using Different Testers and Independent Population Samples in Maize Reveals Low Power of QTL Detection and Large Bias in Estimates of QTL Effects

Soybean [Glycine max (L.) Merr.] yield, when regressed on water needed to replenish 0 to 100% seasonal evapotranspiration (ET), generates an estimate of season-specific water-use efficiency (WUE). The impact of unpredictable water deficits might be lessened if high-yielding genotypes had a smaller beta. Our objective was to determine the genetic basis of beta and carbon isotope discrimination (CID), a theorized indicator of transpiration efficiency (TE). A Minsoy' Noir I' population of 236 recombinant inbred lines (RILs), genotyped at 665 loci, was evaluated in six water treatements (100, 80, 60, 40, 20, and 0% ET) for 2 yr. Water stress was mild in 1994, but high temperatures and no rainfall in 1995 led to a drought so severe that the 100% ET treatment required 41 cm of irrigation. The 1995 yield-to-water regression was highly linear (28 kg ha -1 cm -1 ), Genotype × water (G × W) interaction was due to genotypic heterogeneity in beta. The CH) vs. beta correlation was low (r = 0.26), so selection for better leaf TE may not improve crop WUE, Selection of low beta (less sensitivity to drought) will be difficult, given the yield beta vs. yield correlation (r = 0.71). The major quantitative trait loci (QTL) for yield beta, yield, and CID were coincident with maturity and/or determinancy QTLs. except for a CID QTL in linkage group U09-C2. but it had no effect on beta. Genetic improvement of soybean yield performance under drought would be better achieved by coupling a high-yield grand mean with a high- (not low-) yield beta.

Soybean response to water : A QTL analysis of drought tolerance

Heritability (H) on a progeny mean basis is frequently estimated in recurrent selection experiments for the purpose of estimating the expected progress from family selection; however, appropriate measures of precision have been developed for only a few heritability estimators. The objective of this research was to develop a measure of precision for H for certain balanced linear models. Exact confidence intervals for H were derived and are not restricted to a specific experimental design. The confidence intervals were applied to sorghum [Sorghum bicolor (L.) Moench] half-sib family data.

An exact confidence interval for heritability on a progeny mean basis

Exact Confidence Intervals for Heritability on a Progeny Mean Basis1

The emphasis of variance component and heritability estimation experiments has been on point estimation. Minimal attention has been given to confidence interval estimation. Our research was motivated by the limited use of confidence intervals and the importance of interval estimation to the statistical inference process. Our objectives were to evaluate variance component and heritability estimate precision from confidence interval estimate data and to describe the effects of experiment size and point estimate magnitude on interval estimate width. Point and interval estimates (1 - α = 0.90) for the family variance component and heritability on a family mean basis were obtained from half-sib, full-sib, or S1 family selection experiments in four sorghum [Sorghum bicolor (L.) Moench.] populations. Agronomic traits were measured on 200 families per population grown on a Typic Argiudoll soil at Mead, NE, in 1981 and 1982 in a replications-in-incomplete blocks experimental design. Confidence interval estimate widths (widths) were functions of F =(family mean square)/(family ✕ year mean square) Mf/Mfy and tabled F-values determined by degrees of freedom for Mf (dff) and Mfy (dffy) and the confidence coefficient (1 - α). Ratios of widths point estimates (ratios) decreased at a decreasing rate as F increased for fixed F-values. Widths and ratios decreased at a decreasing rate as dff and dffy increased for fixed F. Ratios for drf= dfy = 190 for variance components were 0.32 for F = 10.0 and 4.27 for F = 1.11, and for heritability were 0.05 for F = 10.0 and 4.05 for F = 1.11. Our data demonstrated the problems of wide interval estimates for large experiments and variation in precision among point estimates for experiments of fixed size.

S. J. Knapp

Papers

An exact confidence interval for heritability on a progeny mean basis

Exact Confidence Intervals for Heritability on a Progeny Mean Basis1

Precision of Genetic Variance and Heritability Estimates from Sorghum Populations 1