A New Maize Heterotic Pattern Between Temperate And

A New Maize Heterotic Pattern between Temperate and Tropical GermplasmsX. M. Fan,* H. M. Chen, J. Tan, C. X. Xu, Y. M. Zhang, Y. X. Huang, and M. S. Kang ABSTRACT New heterotic groups are needed for increasing genetic diversity and productivity in maize (Zea mays L.). A study was conducted with the following objectives: (i) to determine if exotic tropical maize germplasm (TRMG) can increase diversity of Chinese maize germplasm for grain yield and five yield component traits (YCTs), namely, ear length (EL), ear diameter (ED), number of kernel rows per ear (RE), number of kernels per row (KR), and 1000-kernel weight (TKW), and (ii) to estimate general combining ability (GCA) and specific combining ability (SCA) effects to identify a possible new heterotic pattern. Twenty-five temperate maize germplasm (TEMG) from both China and the United States were crossed with four TRMG from the International Maize and Wheat Improvement Center (CIMMYT). The 100 testcrosses were evaluated in field trials for grain yield and five YCTs at three locations in Yunnan, China. Tropical lines YML146 and YML145 showed, in crosses with most of the TEMG, significant positive SCA effects for grain yield and most of the YCTs, indicating that these lines had a different genetic base from that of TEMG and could increase genetic diversity of Chinese maize germplasm. The GCA effects were more important and reliable than SCA effects for heterotic pattern classification. Exotic line YML146 (derived from Suwan1) was identified as a new heterotic group, different from Reid, Lancaster, Tangsipingtou (TSPT), and Luda Red Cob (LDRC). A new heterotic pattern of temperate × Suwan1 was postulated, which could be as important as the widely accepted fl int × dent heterotic pattern. arrow genetic base is one of the most important limiting factors for maize yield improvement and is a bottleneck in China maize breeding programs (Zeng, 1990; Wang et al., 1997; Xu, 2003). A study showed that 71% of the commercial hybrids grown in China came from four inbred lines or their derivatives, namely, Mo17, Huangzao 4, Dan 340, and Yie 478 (Zhang et al., 2000). Therefore, it is necessary to broaden the genetic base for improving maize productivity to meet continuously increasing food demand in China. An effective way to solve this problem is to introduce exotic maize germplasms and introgress some useful genes into locally adapted germplasms (Albrecht and Dudley, 1987; Abadassi and Hervé, 2000; Li et al., 2001; Fan et al., 2002a, 2002b; Reif et al., 2004). Maize heterotic patterns and heterotic groups have been extensively studied all over the world (Kauffman et al., 1982; Vasal et al., 1992; Fan et al., 2002a, 2002b; Huang and Li, 2002; Yuan et al., 2002; Menkir et al., 2004; Melani and Carena, 2005; Barata and Carena, 2006) and new heterotic patterns have been widely searched and studied in the United States (Kauffman et al., 1982; Goodman, 1985; Godshalk X.M. Fan, H.M. Chen, J. Tan, C.X. Xu, and Y.X. Huang, Institute of Food Crops, Yunnan Academy of Agricultural Sciences, Kunming 650205, Yunnan Province, China; Y.M. Zhang, Research Analyst, Parts Distribution Center, John Deere Co., Milan, IL 61264; and M.S. Kang, Vice Chancellor, Punjab Agricultural Univ., Ludhiana 141 004, India. Received 5 Sept. 2007. *Corresponding author ([email protected]). Published in Agron. J. 100:917–923 (2008). doi:10.2134/agronj2007.0298 Copyright © 2008 by the American Society of Agronomy, 677 South Segoe Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. N and Kauffman, 1995; Melani and Carena, 2005). Two new heterotic patterns, namely, Leaming × Reid Yellow Dent and Leaming × Lancaster, were found by Kauffman et al. (1982). Melani and Carena (2005) identified BS21(R)C7 × CGL(S1-S2)C5 and BS22(R)C5 × LEAMING(S)C5 as alternative heterotic patterns to Iowa Stiff Stalk Synthetic (BSSS) × Lancaster. The identification of these new heterotic groups has greatly helped in development of high grain yield maize hybrids and inbred lines with high levels of abiotic and biotic stress tolerance for the U.S. Corn Belt. Fan et al. (2002a) used a diallel mating design to evaluate the combining ability of 10 quality protein maize lines. Five of these lines were introduced from CIMMYT during 1980s and have undergone domestication and improvement for adaptation to local environment by the Yunnan Academy of Agriculture Science (YAAS). The other five lines were domestic elite quality protein maize lines selected from across China. Based on the SCA effects and mean grain yields of 45 crosses, these10 quality protein maize lines were classified into four heterotic groups with CIMMYT germplasms being classified into groups different from China local maize lines, indicating different genetic base of CIMMYT lines from that of China local lines. Huang and Li (2002) evaluated 45 maize inbred lines from China, U.S. Cornbelt, and tropical regions with 44 restriction fragment length polymorphism (RFLP) markers equally distributed on all 10 chromosomes of maize. The 45 inbred lines Abbreviations: AFLP, amplified fragment length polymorphism; BSSS, Iowa Stiff Stalk Synthetic; CIMMYT, International Maize and Wheat Improvement Center; YAAS, Yunnan Academy of Agriculture Science; ED, ear diameter; EL, ear length ; GCA, general combining ability; GS, genetic similarity; KR, number of kernel per row; LDRC, Luda Red Cob; RFLP, restriction fragment length polymorphism; RE, number of kernel row per ear; SCA, specific combining ability; SSR, simple sequence repeat; TEMG, temperate maize germplasm; TKW, thousand kernel weight; TRMG, tropical maize germplasm; TSPT, Tangsipingtou; YCT, yield component traits. A g r o n o my J o u r n a l • Vo l u m e 10 0 , I s s u e 4 • 2008 917 Corn RE. (2004) used two testers representing the flint and dent heterotic patterns to test 38 tropical maize inbred lines. respectively. to develop inbred lines and hybrids. respectively.. For effective utilization. 1988.S. Minnesota #13. YML145 and YML146. 2002. Fan et al. namely. Two of the four tropical inbred lines. MATERIALS AND METHODS Experimental Materials The sources. These can then be effectively used to synthesize populations. 2002a). high yield. This result further suggested that TRMGs might be genetically different from TEMGs originating from both China and the U. Agronomy Journal • Volume 100. The study showed that heterotic groups of genetically similar germplasms could not be identified accurately and reliably with molecular markers even when the available germplasm was diverse. The tropical lines YML145 and YML146 had been introduced and improved for adaptation. Significant GCA and SCA effects for grain yield were detected in tested inbred lines. Germplasm sources and main characters of 29 maize inbred lines. 2002). and China local germplasms. Corn Belt. Therefore.. they recommended that the marker-based grouping techniques might only serve as the basis to design and carry out combining ability studies in the field to establish clearly defined heterotic groups with a greater GS within groups. Huang and Li. Corn Belt) and CIMMYT. The other two tropical inbred lines..S. were selected from tropical populations of Tuxpeno and Suwan1. (2002) employed 51 simple sequence repeat (SSR) markers to analyze 134 maize inbred lines from both temperate regions (China and U. Yuan et al. BSSS. CML171 and CML166. are improved inbred lines originally introduced from CIMMYT by YAAS (Fan et al.were grouped into six heterotic groups: of which three heterotic groups were related to Mo17. whereas CML166 and YML145 are tropical dent inbred lines.. Corn Belt were placed into the remaining eight clusters. contrary to what had previously been suggested. ED. 2002). In addition. Menkir et al. 2002a. 2005). B73. The objectives of this study were to (i) evaluate the combining ability of grain yield and five YCTs. 2002b.. Genetic diversity is a basis for maize breeding program to achieve success (Hallauer and Miranda. 2002. the heterotic group. Yuan et al.S. (ii) analyze the patterns of GCA and SCA effects to see if a new heterotic pattern between tropical and temperature maize can be established. Golden Glow pedigree and all the 13 North Dakota inbred lines were screened with 49 SSR markers. two groups were classified into two China local heterotic groups. Northwester Dent. 2000. inbred lines representing Lancaster Sure Crop. EL. Thus. they suggested that extensive field evaluation was needed to classify unrelated maize inbred lines into a heterotic group.-originated maize germplasms and the TRMGs were genetically different from both U. and grain texture of 25 TEMGs and four elite TRMGs used for this study are listed in Table 1. and Oh43. and one group was identified as tropical group. The two testers classified 23 of the 38 tested inbred lines into two heterotic groups based on SCA effects and testcross’s mean grain yields. disease resistance and other stress resistances in the last decade by our institution (Fan et al. Corn Belt heterotic groups and evaluated the consistency between SSR grouping and testcross data analysis. 2002a.S. They found that most of the inbred lines from CIMMYT were assigned to one major cluster whereas all inbred lines that originated from both China and U.S.. KR. Melani and Carena. CML171 and YML146 are tropical flint inbred lines. Yuan et al.. Issue 4 • 2008 † CML and YML refer to the inbred lines of CIMMYT Maize Line and Maize Line from Yunnan Academy of Agricultural Sciences.S. Previous studies have shown that genetic base of TRMGs was different from that of TEMGs (Fan et al. 918 . Code no. This study suggested that the China local maize germplasms were genetically different from U. Barata and Carena (2006) attempted to classify some elite North Dakota maize inbred lines into current U. Thirteen North Dakota maize inbred lines representing diverse genetic background were crossed in a diallel mating design in 2000. 2002b. Huang and Li. Diversity analysis of all 40 maize inbred lines using amplified fragment length polymorphism (AFLP) and SSR markers classified the tested lines into different heterotic groups obtained by mean grain yield and SCA Table 1. These 25 TEMGs are the major parental lines for the commercial maize hybrids currently grown in China. the classification and determination if the new introduced TRMGs belongs to a new alternative heterotic group becomes critical in our maize breeding programs. and TKW using a line × tester mating design from four TRMGs and 25 TEMGs to see if TRMGs can increase the genetic diversity of China local maize germplasm. 2003). These lines had been classified into different heterotic groups in previous studies (Zhang et al. The 134 maize inbred lines were grouped into nine clusters according to genetic similarity (GS) values between the inbred lines. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Inbred line† CML171 CML166 YML145 YML146 81515 Qi319 Yuzi87–1 P138 X178 Shen136 543 Tie7922 Ye107 Luyuan92 Zheng58 DS01 Yun147 Liao3180 K22 Lai3189 Mo17 13247 Zi330 Tie9010 Dan340 Zong3 Xi502 K1218 Huangzao4 Heterotic Source group Pool25QPM Tropical Pop66QPM Tropical Improved yellow Tuxpeno Tropical Suwan1 Population of Thailand Tropical Huangzao4 × TSPT (HuaFeng100 × Ai C103) Pioneer78599 Reid Hybrid 87001 from US Reid Pioneer78599 Reid Pioneer78599 Reid Double cross hybrid from US Reid Pioneer78599 Reid Pioneer3382 Reid Foreign Hybrid XL80 Reid Yuanqi123 × 1137 Reid Mutation of Ye 478 Reid Hybrid CM190 from US Reid Hybrid from US Reid Foreign Hybrid Reid K11 × Ye478 Reid 5003 × U8112 TSPT C103 × 187–2 Lancaster 1324 × Ye478 Lancaster OH43 × Keli 67 Lancaster Kang1 × Dan340 LDRC λ irradiation mutant LDRC Baizhoulu9 × Pod corn synthetic cultivar N/A Dan340 × Huangzao4 TSPT Variation of K12 TSPT Tangsipingtou TSPT Grain texture Flint Dent Dent Flint Flint Flint Middle Flint Flint Flint Flint Dent Semi-dent Semi-dent Middle Dent Flint Flint Flint Flint Semi-dent Middle Dent Middle Middle Dent Dent Flint Flint effects. 7 m and length of 5 m. Zi330.9 Previous crop wheat corn oil crop Soil texture loam loam loam Planting date 3 May 2 July 12 June Fertilizer applied at planting 20 kg 40 kg 20 kg (NPK-21–6-13) per mu† Fertilizer applied at seedling 9. SCA.66** 48 1903.01.06** 6 567.72** 144 750. MGCA: general combining ability for male parent. The locations. 919 . the 25 TEMG’s were used as female parents and were crossed with the four TRMG. °C 14.62** 599.23 m and the population density was approximately 60.38** 34.2 kg stage (N by urea) per mu 9. and fertilizer application for the three locations is presented in Table 2. eijkl = residual effect.42** 68. MGCA × Loc.60.97** 72 779.1 (StatSoft.49 257. Information on elevation. Issue 4 • 2008 between ith F1 hybrid and lth location.1 Mean annual rainfall. Yun147. Luyuan92.14** 1.8 kg Fertilizer applied at ear development (N by urea) per mu †. and DS01 had significantly positive GCA effects. ED.58** 198 2135.12** 5. 2006) and Microsoft Excel 2003.33** 22.67 3.74 2. Location name Parameter/cultural practice Kunming Dehong Linchang Elevation.56** 29.92** 1.21** 1. RE.70** 594 82.38** 4. 4.73** 25.74. China.25** 31. consequently. vij = F1 hybrid effect = gi + g j + sij [where gi = general combining ability (GCA) for the ith parental line. As the variances of crosses and crosses-by-locations interaction were significant. Thus.56** 24 3200. m 1960 913 1750 Longitude 102°27´0˝ 98°20´60˝ 100°1´12˝ Latitude 25°1´12˝ 24°15´36˝ 23°25´12˝ Mean annual temperature.64. † Loc.01 probability level for all traits studied.000 plants ha–1.56** 273735. h 2054 2385 2115. respectively. which yielded 100 testcrosses. Graphs were made using Statistica 7. crosses. latitude.91** 5. temperature. the crosses variation was further partitioned into GCA and SCA and the interaction variation was further partitioned into GCA × location and SCA × location interactions.62** 140. RE. Only replication was considered to be a random factor.24** 4006. Because the three locations selected for this experiment were not a random sample of all possible locations within Yunnan.82** 0.7 20. 5.81 108.06** 177. The tropical inbred lines YML146 and YML145 had significantly positive GCA effects for grain yield. EL: ear length. Distance between two adjacent plants was 0. 4.86** 5.): replications under each location. Experimental field location.56. Yunyou 21.† Sources Loc. ED. previous crop.17** 2.88 99 2392. experiment error term was used (Table 3). g j = GCA effect of jth tester. Zheng58.2 Mean temperature in 2005. soil properties.57** 45. and TKW are 6. Rep(Loc. General Combining Ability Analysis The GCA effects for grain yield and the five YCTs for the 25 TEMGs and four TRMGs are listed in Table 4.91** 9.06** 1. A widely grown commercial hybrid.92** 2132. Dan340. Hybrid or cross effect and. For all other significance tests. After harvest. The GCA and SCA were analyzed via a specific SAS program developed by our team. CV for Yield. was employed as a check. The GCA. μ = population mean. and KR were recorded from each harvested ear.2 kg 9.: location. GCA × locations. sij = specific combining ability (SCA) for the ijth F1 hybrid]. At maturity.35** 0. Error Yield DF plant–1 EL ED RE KR TKW 2 22920. KR: number of kernel per row. SCA × Loc. and weather information. Mean square from ANOVA analysis of 100 test-crosses for yield and yield components under three environmental conditions of Yunnan province in 2005. A randomized complete-block design with three replications was used at all locations. rainfall.52** 2.2 kg 9. FGCA × Loc. Tie 7922.Table 2.75** 0.9 19. with all TEMGs.85** 2227. RE: number of kernel row per ear.45** 9.97.57** 17. Among the TEMGs. In 2005.) Crosses MGCA FGCA M × F.08** 6. and crosses × locations sources of variation were significant at the 0. When these two lines were crossed with all TEMGs. αl = location effect.09** 2. TKW: thousand kernel weight.27** 31. the kernels were air-dried until constant moisture of 130 g kg–1 was achieved. RESULTS AND DISCUSSION Analysis of Variance of the 100 Testcrosses for Grain Yield and Yield Component Traits The data on grain yield and the five YCTs from the three locations were subjected to an ANOVA (Table 3). Table 3. Statistical Model and Analyses The following statistical model was used for the data analysis: Yijkl = μ + αl + bkl + vij + (αυ)ijl + eijkl vij = gi + g j + sij where Yijkl = observed value from each experimental unit.16** 3 34632. sunshine. 2002). Experimental Design for Field Trial In 2004. °C 16. mm 1031 1653 1750 Mean rainfall for 2005. 2. which had significantly negative GCA effects. The hybrid seeds were hand-planted at the three locations. Data collected from the trials were first analyzed via the GLM procedure of SAS 9. The EL.84** 0.60** 39.53** 259.19** 457.39** 0.6 16.46 0. preparation.02 0.01** 0. we treated locations as a fi xed factor. and 5. and SCA × locations were also significant for all traits analyzed (Table 3). whereas Lai3189. the 100 testcrosses were fieldtested for grain yield and five YCTs at three locations in Yunnan. at Kunming.2 kg 13. longitude. ED: ear diameter. Mo17. KR. DF: degree of freedom.00** 11550. Rep(Loc. GCA and SCA effects were regarded as fi xed effects. Tie9010.21** 12477.09 0.02 0. 1 mu = 1/6 acre. Liao 3180. 10 ears were harvested from 10 consecutive plants in the middle of each row.01** 69. (αv)ijl = interaction effect Agronomy Journal • Volume 100. the average grain yield from these crosses was significantly higher than the yields from the crosses of CML166 and CML171.1 (SAS Institute. Climatic Parameters for the Three Locations Three locations with different climatic and geographical conditions were selected to test grain yield and other differences among hybrids developed by crossing local lines with CIMMYT lines.28** 44997.34** 4504. K1218. mm 976 1405 1588 Annual sunshine. bkl = block or replication effect within each location.8 kg 13.77** 0. FGCA: general combining ability for female parent.01 significance probability level.22** 114.01** 227869. and then TKW and grain yield per plant were determined. significance of location variance was tested against replication-within-location entity.67** 6 37249. Inc. Each experimental unit was a single row plot with a row spacing of 0. X178.98 ** Refers to 0.1 17. SCA Cross × Loc. EL. 76** –14.20** 132.68 –7.16** –30.30** 3.23 –13.65 111.58** –3. Thus.23** –0.18** 134.60 –16.77 3.51** 1.13** –0.66** 0.56** –0. The two other tropical lines.62 –19.40** 1.92** and negative SCA effects did not show any 6 Qi319 140.36 118.13** 0. RE.71** 3.29** –10.72 –0.02** 104.69** –4.02 –0.51* 7.40** –0.46** 136.37 1.36** 18.34 8.74 151.54** 1.02** Shen136.49 7.34** 1.70 –12.65** 147.32** 1.03** –13. CML166.28** –7.75 * Refers to 0.71 –1.59** 8 P138 132.39** –0.47** –1.60 –6. EL.67 4.48 –21. 6.37 5.06 –2.29** –8.17** 0. indicating that the direction and 14 Luyuan92 126.25* 0.06* 0.19 125.12 9.04** 142.81 120.24** 14. KR.58** 0.23** –0. that is. Specific Combining Ability Analysis The SCA effects of the crosses of 25 TEMGs with four TRMGs for grain yield are given in Table 5.01 0.36 144.93** 2.45 –14.34** 162.34 –11.83 20. A line which had significantly positive GCA effect for grain yield.46** 0.19** 0.67 137.8 130.37** magnitude of SCA effect of a cross could 15 Zheng58 144.45** 0.95 9.88 6.29** –0.86** 190.17 14.46** 0. for the four tropical lines of YML146.59 153.41* –11.78 13 Ye107 139.66 164.81 –3.54** –0.99** –1.38** 0. 8. respectively.04 159. had usually more YCTs showing significantly positive GCA effects.90 16.53 162. numbers of crosses with significantly positive SCA effects ** Refers to 0.41 131.86 3.19 132.94 10.5 0.29 148.43** the parental lines.29** –1.05 significance probability level.28** –1.48** –0.93** –0.57 136.48 109.97* –8. General combining ability (GCA) effects of grain yield and yield component traits of 25 temperate inbred lines and four tropical testers.54** 28.54 131.42** 4.32** 114.51 139.73 –1.90** 5.91 –5.34** –4.62 131. RE: number of kernel row per ear.87 3.09** 0.28** 0.61** –19.09 –0.77** –20.93 –3.41** –0.82** 144. These results suggested that grain yield was closely related to the YCTs and for the development of an inbred line having higher positive GCA effect for grain yield.87 –10.61 2.89 157. it is best to improve all of its YCTs.65** 140.01 significance probability level.11 146.74** 0.21** 1.05 significance probability level.65** 4.55** –23.00 125.64** –21.25** –7.52** 137.48 –3.40 146.19 9.26 104.89 6.66** 2.88 132.89** 1. Grain yield and specific combining ability (SCA) effects of all crosses.91** 142.62 –6.89 159.08** 8. ** Refers to 0.05** 5.14** 0. and CML171 were Yield Yield Yield Line Inbred Yield SCA plant–1 SCA plant–1 SCA plant–1 SCA no. Because these two lines had significantly positive GCA effects for most of the YCTs as well as for grain yield.97** 2.77 160.59** 5.01 10.41 149.39 8.10** –0.35 117.98 g plant–1) were crosses between the two tropical exotic • Volume 100.06** TKW 10.25** –0.18** –44.25** 162.94** 0.52* 1.62 137.77** –4. respectively.24 0.38 –3. It shows that most of the crosses with grain yield higher than the check (average yield for the check was 141.20** 0.61** 115.66** not be predicted from the GCA effects of 16 DS01 141.03 7.06 115.95 1.36 9.56** –0.05 111.71** 1.84 –2.74 –0.09** –0.65** KR –0. Whereas those with significantly negative GCA effect for grain yield generally had more YCTs showing significantly negative GCA effects (Table 4). had significantly positive GCA effects for ED.14** –2.50** –0.00 –11.69** 3.17** –14.01 –0. and P138 had significantly negative GCA effects.55 9.07 0.11* 148.25** –0.54 122.23** 0.08 140.44** 0.41** RE –1.03 –0.73** –0.39** 2.27 –8.64* –6.21 –3.45** 0.01 –0.59 154.38** –0.01 0.07** 0.81 –16.15 1.81 –5.79** 147.82 1.36** 3.92 127. The GCA effects for the five YCTs are also listed in Table 4.82** –0.23** –4. TKW: thousand kernel weight.79 168. CML166. This result suggested that though 9 X178 117.38** 1.79 148.13 –1.48 8. RE.69** 0.08** 0.87** –0.52* –2.79 statistical difference for the four tropical 7 Yuzi87–1 135.59 1.56 128. CML171 CML166 YML145 YML146 YML145.90 143.25 0. K22.01 significance probability level.33** –2.78** –1. and CML171 were 7. and TKW.50** –1.91 –0.7 0.28 12.92* 134.75 110.55 2.50 0.83 0.62** –0.81** 1.12 –2.87 6. The number of g g g g crosses with both significantly positive 5 81515 142.84** –0. The GCA effects for grain yield did not reach significant level for remainder of the TEMGs.44** line seemed not to be related to the SCA 12 Tie7922 135.98 115.97** 9.40 113.22** 1.59* the GCA effects for the four lines were 10 Shen136 125.49** 0.99** 10.41 7.11** 31.38 123.24** 1.13** 1.51** –1.16** 0. KR: number of kernel per row.39** 10.49 11.03 134.63** 2.13 125.82** –0.36** –7.14 155.91 –16.09** –0.26 139.36 –2.64 115.58 –8. and TKW. SCA effects and the numbers of crosses Temperate Tropical inbred lines with significantly negative SCA effects inbred lines for the four tropical lines of YML146.31 –8.89 124.34 –6. ED: ear diameter. respectively.87** –1. CML166 and CML171. YML145. Twenty-nine testcrosses showed significantly negative Table 5.57 12.49** 0.32** 0.18* effects. and TKW.10** 0.23** –10. The YML146 had significantly positive GCA effects for all YCTs except KR and YML145 showed significantly positive GCA effects for three of the five YCTS.40 4.65** –1.82 EL† –0.38** 1.24** 0.27** –0.82 29.14* 115.55 –5.66 3.44** –1.59 152.32 –12.33** 157.96** 0.83 –1.47 –8.30 160.80** 147.72** 2.74** 141.19 140.61 –0.23* –0.05** –0.66 –7.31** 21. 7.24** ED –0. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Inbred lines CML171 CML166 YML145 YML146 81515 Qi319 Yuzi87–1 P138 X178 Shen136 543 Tie7922 Ye107 Luyuan92 Zheng58 DS01 Yun147 Liao3180 K22 Lai3189 Mo17 13247 Zi330 Tie9010 Dan340 Zong3 Xi502 K1218 Huangzao4 Yield plant–1 –4.50 –2.07 0.05 –0. Twenty-seven testcrosses showed significantly positive SCA effects and the * Refers to 0.56** 146.65* 18 19 20 21 22 23 24 25 26 27 28 29 Liao3180 K22 Lai3189 Mo17 13247 Zi330 Tie9010 Dan340 Zong3 Xi502 K1218 Huangzao4 143.34 different (Table 4).44** –5.30 –9.85* 12.02 –0.66 121.02** 24.13** 32.32** 0. † EL: ear length.12* 3.33** 0. and 5.64 9.84** –1.57 –18.79** 140.06** 1.60 2. lines plant–1 9.04** –2.83** lines.08 122.21** –8.02 1.40 –6.Table 4.52** –0. respectively.40** –1.31 3. Dent × Flint Heterotic Pattern in the Crosses between Tropical Maize Germplasms and Temperate Maize Germplasms Grain yields of all crosses are represented in a scatter plot (Fig. and 6.61** 0.27 –2.11** –0. Issue 4 • 2008 920 Agronomy Journal .99 147. 17 Yun147 134.54 0.00** 0.67** –2.82** –1.42 –4.51** 152.45** 0. the GCA effect of a 11 543 127.46 149.22** –0.87** –2. these two tropical lines might be used in maize hybrid development programs directly.27 0.75** –0.83** 2.38 1. Code no.42** –1.27 9.32 116.24** 19. 1). the tropical lines CML166 and CML171 could be used for line or population improvement for ED. 8.55 130.93* 170. Fig. 2. different from the current heterotic groups. Fig. 1. which is flint. with flint Reid The GCA effect of a line would be different when evaluated lines all had positive SCA effects except with line Qi319. X178. Thus.. brown. Qi319. were crossed with the The SCA effects and mean grain yield have been widely lines from different sets of heterotic groups. 2006). On the basis of Griffing’s (1956) model. combining ability analyses between the two tropical lines and 1982. we had conducted used for classifying maize heterotic group (Kauffman et al. Combing abilities of YML145 with lines belonging to different heterotic groups. the crosses between YML145. To analyze the interaction patterns of the two tropical lines (YML 146 and YML 145) with the four current maize heterotic groups of the 25 TEMGs. and K22) are flint. 2005. 2004. YML146 and YML145. 3 for YML146 and YML145. The temperate Reid group includes 14 inbred lines and eight of them (i. The average GCA and SCA effects of the crosses of yield consisted of both SCA and GCA effects. Liao3180. a dent line. GCA YML146 and of YML145 with the four different sets of inbred Fig. The SCA effects of YML146. effects with a set of lines from a current maize heterotic group. different heterotic groups) with results indicated that the heterotic pattern between dent and different genetic base. average GCA and SCA effects of all crosses were plotted and are shown in Fig. Grain yield for all crosses between 25 temperate and four tropical lines. Combining abilities of YML146 with all 25 tested lines. Combining abilities of YML145 with all 25 tested lines. Yun147. suggesting that the exotic lines YML146 and YML145 had genetic base different from that of the 25 TEMGs.. with six out of the eight flint Reid lines were significantly negative. Agronomy Journal • Volume 100. Combing abilities of YML146 with lines belong to different heterotic groups. All Fig.e. respectively. Specific Combining Ability Effects for To see the difference of GCA and SCA effect when the two Heterotic Group Classification tropical lines. On the other effects can also be used in classifying maize heterotic groups. green. They most likely belong to a maize heterotic group different from the heterotic groups that the 25 TEMGs belong to. Red. These with a different set of lines (i.lines. and CML171. 543. 4. CML166. P138.. YML146 and YML145. 5. 2 and Fig.. Menkir et al. Melani and Carena. 3. it could suggest that this line might belong to a new heterotic General Combining Ability and group. Fig. tive except with Yuzi87–1.e. Fan et the lines belonging to each of the four sets of known heterotic al. mean grain groups. which had a grain texture in-between that of flint and Dent. If a line generally has high positive GCA flint also exits in the crosses between TRMGs and TEMGs. hand. respectively. Issue 4 • 2008 921 . and TEMGs.. and blue circles represent yields of all crosses between 25 crosses of YML146 with other Reid lines were posi.temperate lines with YML146. YM L145. Shen136. Zhang et al. Further studies are needed to find which maize agronomic traits are responsible for high GCA effects between YML146/YML145 and TEMGs. Huang Bihua (Dehong Institute of Agricultural Science of Yunnan province) and Prof. 2002b). Giauffret et al. that is. but also the relative sizes of SCA and GCA effects had changed. Agronomy Journal • Volume 100. it indicates that the new line’s additive genes are complementary to the lines from the heterotic group and the new line might belong to an alternative heterotic group. and the crosses between these tropical lines and TEMGs had higher grain yield than the crosses among TEMGs. TSPT and LDRC. disease resistance and planting-to-silking duration. Based on the average GCA values of YML146. 4). Issue 4 • 2008 . such as high disease resistance. 14 of them were from CIMMYT and 13 of them from China. 3 and Fig. and TSPT. Lancaster. but was significantly negative with another Reid dent line luyan92. 2 and Fig. Comparing the GCA and SCA effects between Fig. was distinguished from other tropical lines and might belong to a new heterotic group. For example. the SCA effect of YML145 with the Reid dent line Yuzi87–1 was significantly positive. A new heterotic pattern can be defined as temperate × Suwan1. strong root system. Yield variation was also related to emergence duration or early growth. this tropical line seemed to belong to a heterotic group different from the Reid. And the SCA effect of YML146 with Reid flint line P138 was significantly negative. high resistance to drought and other stresses. thus. Figures 4 and 5 also revealed that the SCA effects of the crosses between YML146/YML145 and the lines from the same heterotic group could be quite different. and from the two major China local heterotic groups. 4 and between Fig. A new heterotic pattern of temperate × Suwan1 was demonstrated by the crosses of temperature inbred line × YML146 in this study.lines are shown in Fig. Reid and Lancaster. 4 and Fig. respectively. Lancaster. Further systematic studies on temperate × Suwan1 heterotic pattern are warranted to be able to exploit this new heterotic pattern. We did not collect data on disease resistance and other important agronomic traits. Suwan1 might be classified as a new heterotic group different from the four heterotic groups. That difference could cause different levels of gene expression in Reid flint. If the average GCA effect is significantly positive. 2004.S. no significantly positive GCA effects were found between YML145 and the lines from the Lancaster group. This phenomenon may be due to some different genetic bases between YML146 and YML145. YML145. we could not relate the difference of the GCA effects to any maize agronomic traits. Suwan1 was identified as a new heterotic group different from the current heterotic groups of Reid.. SUMMARY AND CONCLUSIONS This study had shown that both GCA and SCA played a role in maize heterotic classification with GCA effects being more important and reliable than SCA effects. These results suggested that Suwan1 population. the GCA effects of YML145 with the Reid flint lines were significantly positive. (2000) studied a diallel with five temperate and five tropical maize lines and found that the best crosses with high grain yield were between temperate and tropical lines and the grain yield variation was related to two major adaptation factors. TSPT. The authors would like to give great thanks to Prof. the GCA effects of YML146 with Lancaster and both Reid flint and Reid dent lines were significantly positive (Fig. Fan et al. Their results showed that the GCA effects of the CIMMYT populations were generally higher than those of domestic populations. Further evidence is needed to ascertain to which heterotic group YML145 belongs. Furthermore. Li Xuezhi (Lincang Institute of Agricultural Science of Yunnan province) for their help in data collection for this study. The way to use GCA effects to classify a new germplasm into a current heterotic group is to see if a line’s average GCA effect is significant when it crosses with several lines from the same heterotic group. 5. in crosses with lines from the four known heterotic groups. 922 They found that the GCA effects of the inbred lines from population Suwan1 and Pob28 were much higher than those of other inbred lines. 5. Another tropical line. ACKNOWLEDGMENTS The authors express their sincere appreciation for the support from Yunnan Provincial Key Foundation (2004C0011Z) and Yunnan Key Science and Technology Development Project Foundation for 11th 5-Year Plan (2006NG06). the parent population of YML146. Because YML146 had a positive average GCA with all lines from the two major temperate heterotic groups in the U. but not significant with the Reid Dent lines and Lancaster lines. These two figures showed that when a line was crossed with different sets of maize germplasms grouped by the four heterotic groups. (2002b) employed four testers to evaluate 25 inbred lines from five tropical and subtropical populations. we found that not only the absolute values. not only the SCA effects of its crosses but also its GCA effects varied. etc. For instance. China. LDRC. A New Heterotic Group: Suwan1 YML146 was selected from tropical maize population Suwan1 (Table 1). It seemed that the high combining abilities between YML145 and the lines from Reid groups were caused by the dent and flint heterotic pattern only. Because YML146 was derived from Suwan1 population. The new heterotic pattern may be as important as the widely accepted heterotic pattern of flint × dent. YML145 might belong to either Reid dent or Lancaster group based on GCA effect. Reid dent. Fan et al. and Lancaster lines for controlling key agronomic traits.. Some studies on heterosis between its derived lines with TEMGs have previously been done (Zhang et al. had higher GCA effects with flint lines but no significant GCA effect was detected when it was crossed with dent lines from Reid dent lines (Fig. 5). Figures 4 and 5 revealed that the average GCA effects of YML146 and YML145 were clearly different when they crossed with lines from the four known heterotic groups. Thus. and LDRC. The results from this study suggested that TRMG had a genetic base different from that of TEMG. These results strongly suggested that GCA effects should be considered in maize heterotic group classification. Corn Belt. Thus. GCA effect is a reliable criterion and better than SCA effect for classifying new germplasms into current heterotic groups because it gave more consistent results. In contrast. (2004) using four testers evaluated maize grain yield of 27 maize populations. but was significantly positive with another Reid flint line Shen136. Agric. Iowa State Univ. 8th Asian Regional Maize Workshop: New Technologies for the New Millennium. Li. Srinivasan et al (ed. Yang. Classification of heterotic groups among maize germplasms in China using molecular markers. and temperate Germplasm by SSR Markers. Derieux.D. Cary. D. Corn Breeders School 18:6–39. D. Sin. Classification of North Dakota maize inbred lines into heterotic groups based on molecular and testcross data. Sci.S. Alternative maize heterotic pattern for the northern corn belt. 2008).W. Maize Sci. 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