Questions such as the following often arise: “Should reciprocal crosses be included in a diallel?” and “Would their inclusion in a diallel impact grain yield (GY), estimates of general (GCA) and specific combining ability (SCA) effects, and heterotic group classification in maize (Zea mays L.)?” We evaluated a 12‐parent maize diallel cross (Griffing's Method 3 and Method 4) in three environments to determine (i) if reciprocal crosses impact GY of crosses and GCA and SCA effects, (ii) if reciprocal crosses influence the GCA and SCA and residual variance estimates in a diallel analysis, and (iii) if reciprocal crosses impact maize heterotic group classification. The results showed that inclusion of reciprocal crosses in a diallel greatly impacted GY and estimates of GCA and SCA effects. Under the assumption of a random‐effects model, the inclusion of reciprocal crosses caused the residual and GCA variances to decrease and the SCA variances to increase as the number of parental lines increased in a diallel cross. Because inclusion of reciprocal crosses impacted GY and SCA estimates, reciprocal crosses would have great impact on maize heterotic group classification. The maize heterotic groups might be classified differently with and without the inclusion of reciprocal crosses. Based on our dataset from southwest China, three heterotic groups seemed to be an ideal number for improving maize‐breeding efficiency.

ReseaRchD iallel mating design is often used by plant and animal breeders to generate genetic information that can be used for devising breeding strategies. Crop breeders would like to know if genetic parameters or statistics obtained from different diallel methods developed by Griffing (1956) and Gardner and Eberhart (1966) and from the diallel experiments with different numbers of parental lines yield the same, similar, or different results. Such information would not only be useful for researchers in selecting the most appropriate diallel method, but it would also be valuable in determining if the results from other diallel studies with different numbers and different sets of parental lines could be used as reference in our own crop breeding programs.Several key studies relate to diallel mating designs (e.ABSTRACT Diallel analyses, although popular, raise key questions: (i) Do genetic statistics from different diallel methods with same and different sets of lines offer the same or similar information? and (ii) Would lack of information on reciprocal (REC) and maternal (MAT) effects in certain diallels put breeding programs at risk? To answer these questions, general (GCA) and specific combining ability (SCA), MAT, and REC effects were calculated from diallels with 12, 10, 8, 6, and 4 maize (Zea mays L.) parents. We found that with the same lines, the signs and magnitudes of GCA effects were similar and highly correlated among Griffing's Methods 1, 2, 3, and 4 and identical between Griffing's Method 4 and Gardner and Eberhart analysis III (G&EIII). The SCA effects from Griffing's Methods 1 to 4 were correlated. Griffing's Method 4 produced SCA effects identical to G&EII and G&EIII; SCA effects from Griffing's Methods 1 and 2 were upwardly biased because of inclusion of parental lines. Griffing's Method 3 (no parents included) was the best method among all six methods; it gave unbiased SCA estimates and information on MAT and REC effects. With different numbers of lines in diallel crosses, genetic statistics could serve as references across breeding programs because the signs of GCA and SCA effects were mostly same; however, caution must be exercised because some effects with opposite signs were detected. A diallel method that does not provide REC and MAT information could miss identifying superior hybrid(s). Because Methods 1 and 2 provided upwardly biased estimates of GCA and SCA effects, they are not recommended for estimation of GCA and SCA effects. We also concluded that Method 3 was the best diallel method; it provided unbiased estimates of SCA effects and also provided crucial REC and MAT effects, which are useful for proper selection of male and female parents in hybrid development.

A tropical gray leaf spot (GLS)-resistant line, YML 32, was crossed to a temperate GLS-susceptible line, Ye 478, to produce an F2:3 population for the identification of quantitative trait loci (QTL) associated with resistance to GLS. The population was evaluated for GLS disease resistance and flowering time at two locations in Yunnan province. Seven QTL using GLS disease scores and six QTL using flowering time were identified on chromosomes 2, 3, 4, 5, and 8 in the YML 32 × Ye 478 maize population. All QTL, except one identified on chromosome 2 using flowering time, were overlapped with the QTL for GLS disease scores. The results indicated that QTL for flowering time in this population strongly corresponded to QTL for GLS resistance. Among the QTL, qRgls.yaas-8-1/qFt.yaas-8 with the largest genetic effect accounted for 17.9 to 18.1 and 11.0 to 21.42% of variations for GLS disease scores and flowering time, respectively, and these should be very useful for improving resistance to GLS, especially in subtropical maize breeding programs. The QTL effects for resistance to GLS were predominantly additive in nature, with a dominance effect having been found for two QTL on the basis of joint segregation genetic analysis and QTL analysis.

The development of resistant lines and hybrids is an economical way to control disease and improve yield stability. The objectives of this study were (i) to investigate if differences in resistance to gray leaf spot (GLS, caused by Cercospora zeina) exist among recombinant inbred lines (RILs) with and without the quantitative trait locus encompassing the resistance‐carrying GZ204/IDP5 DNA segment (RDNAS) and to determine its effect on grain yield, and (ii) to determine general combining ability and specific combining ability effects for grain yield and GLS scores (GLSS). Four RILs (three with RDNAS [RL1_1, RL1_2, and RL2_1] and one without RDNAS [RL2_2]) were developed via marker‐assisted selection from a cross between YML32 and Q11—an elite line susceptible to GLS. The four RILs and the susceptible parent (Q11) were crossed as testers with 13 maize (Zea mays L.) lines of known heterotic groups (Suwan1, Reid, and non‐Reid). The three RDNAS‐carrying RILs showed reduced GLSS and improved grain yield stability, but grain yield itself was not significantly increased. These three RILs also showed negative general combining ability effects for GLSS. RL2_1 was the best line for improving GLS resistance. The RILs possessing the RDNAS in crosses with lines from the Suwan1 heterotic group had lower GLSS than those from Reid and non‐Reid heterotic groups, suggesting that resistance genes or quantitative trait loci, in addition to RDNAS, might be present in Suwan1.

Capability to intercept and utilize sunlight is important in maize {Zea mays L.) for its growth and dry matter accumulation. Little research has been conducted on the combining ability of maize physiological traits related to photosynthesis, such as light saturation point (LSP), light compensation point (LCP), apparent quantum efficiency (AQE), maximum photosynthesis (Pmax), total protein content (PRO), and activity of phosphoenolpyruvate carboxylase (PEPC) and ribulosebisphosphate carboxylase (RuBPC). The five photosynthesis-related traits and two key enzymes were examined for their combining abilities using a six-parent diallel design. The objectives were to (i) evaluate general combining ability (GCA) and maternal (MAT) effects of the six maize lines and specific combining ability (SCA) and nonmaternal (NMAT) effects for crosses and (ii) determine if GCA effects were different among three maize heterotic groups. Results revealed that the additive gene effects were more important than nonadditive effects for LSP, LCP, Pmax, PRO, PEPC, and RuBPC. Maternal effects for LCP, PRO, and RuBPC were significant and positive for some lines, which could be used as female parents in hybrid development. Information on means of parental lines, combining ability, and heterosis values suggested that RUBPC, PEPC, and PRO might be the key traits that make the Suwan 1 heterotic group different from the Reid and nonReid groups and should be explored fully in future hybrid maize breeding programs.