Epistasis in Maize (Zea mays L.) III. Comparison of Single and Three‐Way Crosses for Forage Traits

Abstract

The importance ol epistasis for forage performance and quality traits was studied in early maturing European maize {Zea mays L.) breeding materials. Sixty-six three-way crosses {3W), 33 of the flint X (dent -dent) and 33 of the dent x (flint • flint) type, were compared with the mean of their respective non-parental single crosses (2W) using data obtained in six environmenis. For each of the 11 traits examined, at least 6 out of the 66 three-way crosses displaved significant (P < 0.05) epistatic deviations, calculated as 2W -3W. Averaged over crosses and environments, epistatic deviations were highly significant (P < 0.01) for 8 traits, but of minor importance except for grain yield, ln general, the variance ot epistatic deviations was appreciably smaller than the variance of genotype X environment interactions. Highly significant correlations occurred among epistatic deviations for silking date, dry matter content of ear. and dry matter yield ot grain and stover. .The reliability of predicting the performance of rhree-way cros.ses from 2W as opposed to assessing them directly was investigated as a function of the number of test environments. Disturbmg effects of epistasis on prediction only became important under intense testing (> 3 or 4 environments). With fewer test environments, both procedures were almost equivalent, due to a smaller influence of genotype X environment interaction on the 2W values. Epistasis is concluded to be of minor importance with regard to the optimum type of hybrid for forage use.Key words: 2ea mays -forage maize -epistasisgenotype X environment interaction -hybrid prediction -type oi hybrid During the last decade, the acreage of forage maize production in Centra) and Western Europe has increased dramatically. Most of the hybrids currently used for forage maize production in this area arc thrcc-way crosses, whereas the majority of hybrids for grain production are single crosses.Epistasis IS one of several important aspects when contrasting the advantages and disadvantages of the two types of hybrids {for detailed discussion, see HAELAUHR and MIRANDA 1981). Eirstly, epistasis might cause differences in the average performance level of single and threeway crosses. Secondly, epistasis might impair the precision of three-way cross prediction and, consequently, increase the time and cost requirements for breeding new varieties of this type compared with single crosses.Investigations about epistasis m grain maize comparing balanced sets ot different types of hybrids according co BAUMAN'S (1959) method have been reviewed by SCHNELL (1975) and more recently by MELCHINGER (1984 a). Concerning the average performance level, most experiments with selected hnes established epistatic effects to the advantage of single crosses for grain yield, but differences were generally small. As to the prediction of three-way crosses, several authors (STUBER et al. 1973, STUBER and MOLL 1974, MEECHINGER et al. 1986) have reported that epistasis becomes more important than genotype X environment interaction...

Reciprocal differences for forage traits in single and three‐way crosses of maize

“…Examination of variance components in Table 2 revealed highly signiflcant variances among crosses for reciprocal differences for all traits except MEC of stover and forage. In agreement with previous studies on maize for grain usage (Mann 1979, Melchinger et al 1985, the variance of reciprocal differences was small for most traits compared with the variance among crosses and their interactions with environments. Exceptions were DMY and MEY for forage, for which a-, amounted to more than one quarter of al.…”

“…Considering the positive (DMY, MEC) and negative (DMC) economic weights of these three traits in a selection index for forage maize (Utz et al 1993), there are no clear advantages in employing flint seed parents in crosses between flint and dent inbred lines for forage use. This is in contrast to the conclusions of Mann (1979) and Melchinger et al (1985), who both recommended the use of flint seed parents in the production of flint x dent hybrids for grain usage, if the breeder refrains from testing for reciprocal differences. Examination of variance components in Table 2 revealed highly signiflcant variances among crosses for reciprocal differences for all traits except MEC of stover and forage.…”

“…Mann et al (1981) reported signiflcant reciprocal differences for dry-matter yield of grain and stover, and suggested that they should be considered in applied breeding programmes. For interpool crosses, both Mann and Pollmer (1981) and Melchinger et al (1985) found greater grain yield for hybrids produced on flint inbreds ( = seed parent) as compared with their reciprocal crosses produced on dent inbreds. For three-way crosses, Schnell and Singh (1978) observed sizeable reciprocal differences to the advantage of hybrids produced on single-cross seed parents as compared with their reciprocal forms produced on the parental inbred.…”

“…Three-way crosses produced on singles exhibited greater DMC (3%) and DMY (5%) of the ear, metabolizable energy content (MEC) of stover (1%), and DMC and DMY of forage (2%) than their reciprocal forms produced on lines. Based on this study, because of their minor importance, routine testing for reciprocal difl"erences among 2W hybrids is not recommended.Differences between reciprocal crosses have been reported by several investigators for various agronomic characters in different types of maize {Zea mays L.) materials for grain usage (review: see Melchinger et al 1985). However, there is Httle consensus in the literature concerning the relative importance and systematic exploitation of these effects in practical breeding programmes.…”

“…Differences between reciprocal crosses have been reported by several investigators for various agronomic characters in different types of maize {Zea mays L.) materials for grain usage (review: see Melchinger et al 1985). However, there is Httle consensus in the literature concerning the relative importance and systematic exploitation of these effects in practical breeding programmes.…”