An evaluation of cultivar stability in ARC maize trials over a six year period

[摘要] English: 1. This study was undertaken to compare various statistical methods of analysis todetermine the most suitable procedure to evaluate maize genotype performanceunder the variable production conditions in South Africa, as well as to assess thesuitability of these statistical procedures for characterizing yield stability. Themain objective of this study was to recommend the most appropriate statisticalprocedure(s) to estimate maize genotype performance and stability more accuratelyand to investigate the GxE interaction and stability performance of genotypes invarious environments by applying different statistical methods of analysis in orderto make useful recommendations for future utilization.2. Ninety four genotypes were planted at 80 localities in South Africa for the period1998 to 2003. These trails, which were done by the Agricultural ResearchCounsel, were divided into six research regions. Three of these regions were usedfor the purpose of this study. Twenty four cultivars were planted at three sitesunder irrigation for the Irrigation research region, 24 cultivars at six sites for theEastern region and 21 genotypes at five sites for the Western region for the periodof 2001 to 2003. Both the Eastern and Western region are dryland maizeproduction regions. Grain yield was determined and genotypes were evaluated forperformance and yield stability in all three regions according to eight statisticalprocedures, which were (i) Combined Analysis of Variance, (ii) CultivarSuperiority Measure (Pi), (iii) Wi-Ecovalence (Wi), (iv) Shukla's procedure ofstability variance, (v) Stability Variance with Locality as Covariate, (vi) Rankdifferences (S1) and Variance differences (S2), (vii) Eberhart and RussellRegression Model, (viii) Additive Main Effects and Multiplicative Interaction(AMMI). The procedure proposed by Purchase (1997) to determine the absolutestability measure for the AMMI model was used as well. Comparisons betweenresults from all statistical procedures as well as recommendations from Phurcase(1997) were used to determine the best suited procedure.3. The combined analysis of variance ranked cultivars according to their mean grainyield measured in ton ha-1. CRN3505, CRN3549, PAN6844, Phb30H22 andCRN3760 indicated good mean yield over all three different regions. On the otherhand QS7608, SC405, LS8508 and SC401 delivered the lowest mean yield valuesover all three regions. This procedure is no indication of the stability for yield ofthe genotypes.4. Lin and Binns cultivar superiority measure indicated good yield stability,according to their definition and procedure, for especially the genotypesCRN3505, CRN3549, SNK2472, PAN6146. The worst performers werePAN6777, QS7608 and SC401. There was considerable correspondence in theperformance of the genotypes over the Irrigation and Eastern regions as well as theEastern and Western (dryland condition) regions.5. Wricke's ecovalence, Shukla's stability variance and stability variance withlocality as covariate procedures had approximately the same results. They showeddifferent genotypes to be more stable in different regions. These three proceduresfound SNK2472, LS8508, SNK2778 and Phb30G03 to be the most stable cultivarsand Phb30H22 and PAN6777 to the most unstable cultivars in the Irrigationregion. For the eastern region PAN6757, CRN3549, SNK2778 and SNK2969 werethe most stable genotypes while PAN6777 and SC405 were the unstablegenotypes. Phb3442, SNK2472, PAN6615 and PAN6043 were the most stablecultivars in the western region with PAN6734 and SC401 the most unstable ones.6. Rank difference and variance difference procedure correlated the best with theAMMI model. This procedure found SNK2472, LS8508, SNK2778 and NS2900as the most stable genotypes in the irrigation region, while QS7608 and CRN3505were the unstable genotypes. These results were very much the same as theprevious three procedure's results. But for the eastern region the results weredifferent for the previous three procedures. PAN6777, SNK2472, PAN6757 and CRN3549 were the most stable cultivars and Phb30H22 and LS8508 were theunstable genotypes. In the western region, PAN6615, PAN6043, QS7608 andPhb30H22 were the most stable genotypes while SNK2900 and SC401 were themost unstable genotypes.7. The Eberhart and Russel procedure, based on deviation from the regression inregression analysis, showed exactly the same results as Stability variance withlocality as covariate and therefore had exactly the same rankings for all threeregions as Wricke's ecovalence, Shukla's stability variance and stability variancewith locality as covariate.8. For the AMMI method, a procedure combining the IPCA1 and IPCA2 scores wasused to determine an absolute AMMI value. According to this analysis, Phb30H22,PAN6740, QS7608 and CRN3604 were the most stable genotypes in the irrigationregion. This differs totally from the results found by the other procedures.PAN6568 and CRN3505 were the most unstable genotypes. For the eastern regionSC405, LS8508, QS7608 and SNK2472 were the most stable cultivars andPhb30H22 and PAN6777 were the most unstable cultivars. In the western regionPAN6734, PAN6146, Phb30H22 and Phb3442 were the most stable genotypes andPAN6043 and PAN6479 were the most unstable genotypes.9. Wricke's ecovalence, Shukla's stability analysis and Eberhart and Russel'sprocedures correlated highly significantly. However, no correlation was found inthe pair wise comparison of Lin and Binns' (Cultivar Superiority Measure)procedure with the other procedures and very little correlation was found in thepair wise comparison of the AMMI model and the other procedures. The moreholistic approach of AMMI is particularly effective in clarifying GxE interactions.Using the IPCA1 and IPCA2 scores to determine an AMMI stability value,superiority ranking of genotypes can easily be done. The AMMI model cansummarize patterns and relationships of genotypes and environments successfullyand offers a valuable prediction assessment. For this reason, it is recommended that this model is used for analyzing GxE interaction of maize genotypes in SouthAfrica. The Lin and Binns procedure appears to be more of a cultivar performancemeasure than a stability measure which explains its correlation with the mean yieldof the genotypes. The Eberhart and Russel, Wricke's ecovalence and Shukla'sstability analysis showed highly significant correlation and are recommended to beused to describe genotype stability of maize genotypes rather than to be used todescribe GxE interactions, due to the limitations of these techniques.10. There were six genotypes and three localities that were common over the six yearperiod for the irrigation region and six genotypes with six localities for the easternregion and seven genotypes with five localities for the western region. Wricke'sstability parameter was used to determine the most stable cultivars over all sixyears over all localities for all three regions. SNK2778 was the most stablegenotype for the irrigation maize production region in South Africa for a six yearperiod. In the eastern region, Phb3442 was the most stable cultivar with the lowestWi value, while NS9100 was the most stable cultivar in the western region. Thegenotypes planted in the western region are different from those planted in theeastern and irrigation regions. This is due to the difference in climatic conditions.The western region is much dryer and warmer and therefore needs genotypes thatare more stable under these extreme conditions. PAN6479 had one of the lowestmean yields throughout all three regions and was found to be relatively unstable inall the analyses. CRN3760 had a good mean yield and intermediate stabilitythroughout all three regions over the period 1998-2003.11. In the yield progress study, no significant progress was visible. Eighty cultivarsplanted for a six year period at Cradock were used for this analysis. Year 1998 hadthe lowest mean yield and 2000 the highest mean yield. The cultivars that weretested in the later part of the period 1998-2003, had overall higher mean yield,which proves that progress has been made by breeding companies in genotypeyield increase.

[发布机构] University of the Free State