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Relative Values of Three Different Testers in Evaluating Combining Ability of New Maize Inbred Lines
... In addition, according to Tajwar & Chakraborty (2013), grain yield, days to 50% anthesis, days to 50% silking, ear diameter, and study of combining ability effects demonstrated significant gca effects. El-Hosary (2014) reported that σ 2 sca played the central role in determining inheritance for days to 50 % anthesis and 100-grain weight revealing that the largest part of the total genetic variability associated with these traits result of non-additive gene action. According to Dhasarathan et al. (2015), for days to 50% anthesis and plant height, the mean squares of SCA were greater than those of GCA, indicating that non-additive gene action predominates in the regulation of both traits. ...
... The practical phase of maize hybrid breeding is identification of potential inbred lines with high gca for use as parents for developing hybrids that are superior to existing ones (El-Hosary, 2014). Identification of such elite inbred lines is the major strategy adopted by most commercial plant breeders to maximize genetic gain per unit time and resources. ...
Initial evaluation of in breds for general combining ability (gca) enables plant breeders to discard undesirable ones and identify those that are potential for the production of superior hybrids. In this context, 11 parental in breds which are contrasting for Late Wilt Disease (LWD) reaction (4 LWD resistant and 7 LWD susceptible) and yielding ability were selected and were evaluated for their gca related to grain yield plant-1, its attributing traits and reaction to LWD infection. The analysis of variance revealed significant differences among the inbred lines for their per se performance as well as their gca. Similarly, the hybrids differed significantly for per se performance and their specific combining ability (sca) effects for all the traits. The non-significant correlation between per se performance and gca effects suggested that per se performance of inbred lines is not a good indicator of their gca effects for any of the traits studied including reaction to LWD infection. However, significant positive and fairly high magnitude of correlation between per se performance of hybrids and sum of parental gca effects for all the traits under study including reaction to LWD infection indicating that parental gca effect is good indicator of per se performance of hybrids. hence, parents having higher gca effects are expected to give good performing hybrids.
COMBINING ABILITY, HETEROTIC GROUPING, CORRELATION AND PATH COEFFICIENT IN MAIZE
Identifying efficient testers for separating maize (Zea mays L.) inbred lines into heterotic groups can facilitate the development of superior hybrids. Striga-resistant yellow-maize inbred lines developed at the International Institute of Tropical Agriculture (IITA) do not have well established heterotic groups. This study was conducted to identify efficient testers for classifying yellow-maize inbred lines into heterotic groups. Thirty Striga-resistant inbred lines were crossed with three testers having varying levels of resistance to Striga. A trial comprising 90 testcrosses and two hybrid checks was conducted at two locations in Nigeria for 2 years under Striga-infested and non-infested conditions. The approach that involved specific combining ability (SCA) effects and mean grain yields was found to be more efficient than the heterotic group’s specific and general combining ability (HSGCA) grouping method in separating the 30 inbred lines into three heterotic groups. The tolerant and resistant testers were highly efficient in grouping the inbred lines into heterotic groups under Striga-infested and non-infested conditions using the two approaches. Striga-resistant yellow inbred lines assigned to two of the three major heterotic groups could be used as parents for developing superior hybrids and/or synthetics and for generating source populations for developing new maize inbred lines.
Fifteen inbred lines were crossed to three testers of maize to estimate combining ability effects for maturity and yield traits. The produce 45 crosses, S.C. 168 and T.W.C. Giza 368 were evaluated across two years at the Farm of Faculty of Agriculture, Moshtohor, Benha University in RCBD with 3 replicates. Mean squares due to year (Y) genotypes (G), crosses (C), testers (T), inbred lines (L), line x tester (LxT) and interaction variance for C, L, T and LxT with (S) were significant (P>0.05) for most studied traits. Non-additive gene action (δ 2 SCA) is more pervading in determining inheritance of the most traits. The non-additive type of gene action is fluctuated by year changed more than additive. The inbred lines M. 645a (L4), M. 653 (L5), and M. 674 (L11) showed desirable ĝi for early maturity and grain yield plant-1. The crosses M.221xM.653, M.221xM.655b, M.221xM.657, M.221xM.671, M.221xM.674 and M.221xM.677 exhibited out-yielded SC 168 reached 9.96%, 11.35%, 12.53%, 8.32%, 11.80% and 4.80%, respectively across years. TWC (SC M 200xM418)xM.653 and (SC M200xM418)xM.674 showed superiority than TWC 368 being 9.11% and 3.78%, respectively. The eight superior hybrids along with SC168, SC hytech 2066, TWC 368 and TWC 352 were evaluated in 2019 year at various environments using RCBD with 3 replicates to identify suitable adapted maize hybrids. The main effects of genotypes, environments and their GxE interaction were highly significant (P<0.01). Hybrids M. 221 x M. 674, M. 221 x M. 655b, SC hytech 2066 and SC 168 were the most crosses stable phenotypically and genetically across environments.
This study was carried out during the two growing seasons 2018 and 2019 at the Agronomy Department Experimental farm, faculty of Agriculture, Assiut University using one yellow maize population (IY376, imported from India 1969) to study the effect of water stress on agronomic traits, line × tester interaction and combining ability using 100 S1-lines and two testers namely, SC162 and TWC352.
An 8x8 half diallel analysis were performed at two planting dates to study the importance of types of combining ability (GCA and SCA) and its interaction with environment in F1 of maize. Planting dates (D), crosses (Cr), GCA, SCA, CrxD, GCAxD, SCAxD were significant for all traits. GCA/SCA exceeded the unity for most traits. Non-additive seemed to be more prevalent for plant, ear heights and grain yield plant-1. P8 gave significant positive (i ĝ) effects for all studied traits. High SCA effects were exhibited by the crosses P1xP7, P1xP8, P2xP5, P3xP4, P3xP8, P4xP7, P4xP8 and P5xP6 for grain yield plant-1 across planting dates. Superiority of P2xP5 and P3xP8 over SC Hytech 2031 reached 13.84 and 6.16%, respectively. However, useful heterotic effects relative to SC 128 mean value were 21.14 and 10.22%, for the aforementioned crosses, respectively. P1xP8, P4xP8 and P5xP6 gave positive insignificant out-yielded than check hybrids. The five superior hybrids P2xP5 (G1), P3xP8 (G2), P5xP6 (G3), P1xP8 (G4) and P4xP8 (G5) along with SC10 (G6), SC 128 (G7) and SC Hytech 2031(G8) were evaluated in 2019 season at various environments using RCBD with 3 replicates to identify environments and suitable adapted maize hybrids. Stable genotypes are ranked descending for means of grain yield as follows: G1 > G8> G2> G7. G1, G8, and G2 were above average stability while genotypes G7 showed below average stability. Thus, G1 (P2xP5) and G2 (P3xP8) are promising crosses, and it's recommended to register as new varieties with high productivity and stability across environments.
Synopsis
This investigation revealed both the top cross tester parents and the segregating population influenced considerably the measurement of combining ability, but the different tester parents gave about the same relative information on lodging and ear height. The study also indicated that some single crosses were equally as effective as double crosses for measuring general combining ability.