A novel method of using a heterotic group's specifi c and general combining ability (HSGCA) to assign maize (Zea mays L.) inbred lines into heterotic groups has been proposed recently. Th e objectives of this study were to (i) assign maize inbred lines to known heterotic groups using this method and (ii) compare effi ciency of this method to traditional and molecular methods relative to the percentage of high-yielding hybrids obtained across the total number of the crosses made between testers and lines. An experiment with 23 maize inbred lines crossed to four testers with known heterotic groups was conducted in 2003 and 2004. Th is study successfully established a clear procedure to classify maize inbred lines into heterotic groups. Th e HSGCA method increased maize breeding effi ciency by 16.7 to 23.6% compared with simple sequence repeat (SSR) and specifi c combining ability combined line pedigree and hybrid yield information (SCA_PY) methods, respectively. An analysis of variance showed that crosses classifi ed by HSGCA method could explain more variation in maize hybrid yield and produce more predictable yield than the other two methods. Th e superiority of HSGCA relative to the other two methods is that HSGCA includes both GCA and SCA eff ect in assigning an unknown maize line to a known maize heterotic group.

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.

Broadening the maize (Zea mays L.) genetic base is essential for improving grain yield. Suwan1, developed from a broad base of tropical germplasm in Thailand, has recently been identified as a heterotic group different from Reid and non‐Reid heterotic groups. The objectives of this study were (i) to evaluate the grain yield (GY) of crosses to see if there is value to utilizing Suwan1 as a heterotic group in maize breeding, and (ii) to investigate the general combining ability and specific combining ability to determine if Suwan1 shows good combining ability with Reid and non‐Reid heterotic groups for GY. Three testers, one from each of the three heterotic groups, were crossed with 20 elite lines collected from across China. Eighteen lines improved via introgression of exotic germplasm and two lines improved via pedigree selection were crossed with TRL02 (non‐Reid), YML46 (Suwan1), and TRL211 (Reid). Grain yield, ear length, ear diameter, kernel rows per ear, kernels per row, and 100‐kernel weight of crosses and a check were evaluated at three locations. The results suggested that the Suwan1 × temperate crossing system was a very useful heterotic pattern. Suwan1 improved all five yield components in crosses and demonstrated good combining ability for GY with Reid and non‐Reid heterotic groups. We have also determined that the appropriate percentage of introgressed germplasm should be between 6.25 and 12.5%.

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