Estimation of genotype x environment interaction for yield in Ethiopia maize (Zea mays L.)

Abstract

English: The study was undertaken to assess the performance of 10 maize genotypes across 15 maize growing environments of Ethiopia. The study was conducted from 1999 to 2001. The grain yields of these genotypes were analyzed using different statistical procedures to determine their G X E interactions and grain yield stability. The main objective of this study was to investigate the G X E interactions and stability performance of genotypes in various environments by applying different statistical methods of analysis in order to make useful recommendations for future utilization. Separate and combined analyses of variance across locations and years and five types of stability parameters were performed, using the AGROBASE 2000 program. In order to perform the stability analyses, data of 10 maize genotypes tested across five locations and three years were analyzed using the procedures of Finlay and Wilkenson (1963), Eberhart and Russel, (1966) for the joint regression, Wricke (1962) for ecovalence, Shukla (1972) for stability variance and (Gauch and Zobel, 1988) for the AMMI stability model. Separate trial analyses for the three years showed highly significant (P<0.01) differences among genotypes and locations for grain yield. In the year 1999, BH-670 was the best performer, followed by (A-7016 x G-7462) x 142-1-e and (A-7032 x G-7462) x 142-1-e with average yields of 9.59, 9.51 and 9.14 t ha" respectively. This ranking changed during 2000 and 2001, due to the presence of interactions. Across locations and years, (A-7032 x F-7215) x 144-7-b ranked first, followed by (A-7032 x G-7462) x 142-1-e and BH-670. All are three-way hybrids with mean yields of 8.93, 8.79 and 8.74 t ha" respectively. Among the locations the highest yield of 8.80 t ha" was obtained from Awassa, followed by Bako and Jimma over the three years, indicating the high potential of these sites for maize production. The results also showed yield variations over locations and years, confirming the presence of G X E interactions. The average of ANOV A components over the three years indicated that about 42% of the total variance was accounted for by genotypes and 13% by blocks. This confirmed variability between genotypes in their response to environmental factors. Combined analyses of variance across locations found highly significant (P<0.01) differences among locations (L) and genotypes (G) for grain yield. There was a .differential response of genotypes over locations, mainly due to edaphic and climatic factors. About 34% of the variance components were attributed to locations, while 16% of the variance components were attributed to genotypes and 12% to their interactions over the three years. This confirms the effect of environmental factors and thus the necessity of stability analyses for the appropriate genotypes. The combined analyses across locations, years and their interaction indicated highly significant differences (P<0.01) among the genotypes for grain yield, which suggests differential responses of genotypes to their environments. Significant G X E interaction makes the genotype selection processes difficult, which create problems in cultivar characterization. Stability analyses with appropriate statistical methods are therefore required to overcome this problem. Most of these interactions were highly significant due to abiotic and biotic factors, which need in-depth studies for better understanding. Generally, when G X E interaction is mainly caused by unpredictable environmental factors, breeing efforts should be aimed at the development of stable varieties with a relatively good performance under a range of environments. When the interaction is however due to predictable environmental factors the aim should be to develop either different varieties for different environments or broadly adapted varieties for a range of environments. The joint regression model for grain yield indicated highly significant differences between the genotypes. The joint regression model identified (A-7032 X G-7462) X 142- l-e as the most stable genotype, followed by (A-7032 X F-7215) X 144-7-b and (A-7033 X F-7189) X 142-1-e. These last two genotypes were the best yielders across all environments and both are three-way hybrids. Wricke's (1962) ecovalence considered BH-660 (one of the popular hybrids) as the most stable genotype, followed by (A-7033 X F-7189) X 142-1-e and Gibe-l (an openpollinated variety). BH-660 is the most popular hybrid currently under production in the country and Gibe-l is a newly released open-pollinated variety (OPV). (A-7032 X G- 7462) X 142-1-e and (A-7032 X F-7215) X 144-7-b were categorized as intermediate in stability, unlike Kulani and BH-140, which were found to be unstable according to this stability measurement. According to Shukla's stability variance (1972), BH-660 followed by (A-7033 X F-7189) X 142-I-e and Gibe-l were the most stable genotypes, whereas Kulani and BH-140 were considered as the least stable genotypes. BH-660, the popular three-way hybrid was the most stable genotype as measured by both ecovalence and the stability variance. Joint regression was also in agreement with these results with only slight differences. Additive main effects and multiplicative interactions (AMMI) stability values, and scores of the interaction principal component analysis (lPCA) showed that BH-660 was the most stable genotype followed by (A-7032 X F-7215) X 144-7-b and (A-7033 X F-7189) X 142-1-e, whereas Kulani and BH-140 were considered to be unstable. AMMI gave the same results as the ecovalence and Shukla in identifying the stable genotypes.

Afrikaans: Die studie is onderneem om te toets hoe 10 mielie genotipes In 15 verskillende omgewings in Etiopië sou presteer. Die studie is uitgevoer vanaf 1999 tot 2001. Die graanopbrengs van die verskillende genotipes is ge-analiseer deur verskillende statistiese metodes te gebruik om hul G x E interaksie en opbrengs stabiliteit te bepaal. Die hoofdoel van die studie was om die G x E interaksies en stabitliteitsprestasies van genotipes in verskillende omgewings te bepaal deur van verskillende statistiese metodes gebruik te maak, sodat nuttige voorstelle vir gebruik in die toekoms gemaak kon word. Afsonderlike en gekombineerde analises van variansie oor omgewings en jare en vyf verskillende stabiliteits parameters is gedoen met behulp van die AGROBASE 2000 sagteware. Die data van 10 mielie genotipes oor vyf omgewings en drie jare is gebruik in die analises van die modelle van Finlay en Wilkenson (1963), Eberhart en Russel (1966) vir die gesamentlike regressie, Wricke (1962) vir ekovalensie, Shukla (1972) vir stabiliteitsvariansie en Gauch en Zobel (1988) vir die AMMI stabiliteitsmodel. Afsonderlike proef analises vir drie jaar het hoogs betekenisvolle verskille (P<0.01) tussen genotipes en gebiede vir graan opbrengs gevind. In 1999, het BH-670 die beste presteer, gevolg deur (A-7016 x G-7462) x 142-1-e en (A7032 x G7462) x 142-1-e met gemiddelde opbrengste van 9.59, 9.51 en 9.14 t ha" respektiewelik. Die rangordes het egter verander gedurende 2000 en 2001, as gevolg van die teenwoordigheid van interaksies. Oor gebiede enjare het (A-7032 x F-7215) x 144-7-b die hoogste rang gehad, gevolg deur (A7032 x G7462) x 142-I-e en BH-670. AI drie is drie-rigting basters met gemiddelde opbrengste van 8.93, 8.79 en 8.74 t ha-l respektiewelik. Tussen die gebiede is die hoogste opbrengs gekry in Awassa, gevolg deur Bako en Jimma oor die drie jare. Dit dui op die hoë potensiaal van hierdie gebiede vir mielie produksie. Die resultate toon ook opbrengsverskille oor gebiede en jare, wat weer op G x E interaksies dui. Die gemiddelde van die ANOV A komponente oor die drie jare toon dat ongeveer 42% van die totale variansie was as gevolg van die genotipes, terwyl 13% die gevolg van blokke was. Dit bevestig die variasie tussen genotipes in hul reaksies tot omgewingsfaktore. Gekombineerde analises van variasie oor gebiede toon hoogs betekenisvolle verskille (P<0.01) tussen gebiede (L) en genotipes (G) vir graanopbrengs. Daar was 'n differensiële respons van genotipes oor gebiede, hoofsaaklik as gevolg van klimaatsfaktore. Ongeveer 34% van die variansie komponente was as gevolg van gebiede, terwyl 16% toegeskryf kon word aan die genotipes en 12% aan die interaksies oor die drie jare. Dit bevestig die effekte van omgewingsfaktore en dus die noodsaaklikheid van stabiliteitsanalises om die belangrikste genotipes te bepaal. Die gekombineerde analises oor gebiede, jare en hul interaksie toon hoogs betekenisvolle verskille tussen die genotipes vir hulopbrengste, wat dui op die verskillende reaksies van genotipes teenoor die omgewing. Betekenisvolle G x E interaksies bemoeilik die seleksie van genotipes en veroorsaak probleme in die karakterisering van kultivars. Om hierdie probleem te oorkom, is stabiliteitsanalises met behulp van gepasde statistiese metodes dus nodig. Meeste van die interaksies is hoogs betekenisvol as gevolg van biotiese en abiotiese faktore. In diepte studies is egter nodig om dit beter te verstaan. Oor die algemeen as G x E interaksies die gevolg is van onvoorspelbare omgewingsfaktore, moet telers poog om stabiele variëteite te ontwikkel wat goed presteer in verskillende omgewings. As die G x E interaksies egter die gevolg is van voorspelbare omgewingsfaktore, moet spesifiek aangepasde variëteite vir spesifieke gebiede of wyd aangepasde variëteite vir 'n wye reeks gebiede ontwikkel word. Die gemeenskaplike regressie model vir graanopbrengs het hoogs betekenisvolle verskille tussen genotipes gewys. Hierdie model het gevind dat (A7032 x G7462) x 142- 1-e die mees stabiele genotipe was, gevolg deur (A-7032 x F-7215) x 144-7-b en (A-7033 x F-7189) x 142-1-e. Laasgenoemde twee genotipes het die hoogste opbrengste oor al die omgewings gehad en altwee was drie-rigting basters. Die ekovalensie van Wricke (1962) het gevind dat BH-660 ('n baie populêre baster) die mees stabiele was, gevolg deur (A-7033 x F-7189) x 142-1-e en Gibe-l ('n oopbestuiwende variëteit). BH-660 is die mees gewildste baster tans onder produksie in die land, terwyl Gibe-l is nuut vrygestelde oop-bestuiwende variëteit is. (A7032 x G7462) x 142-1-e en (A-7032 x F-7215) x 144-7-b het intermidiêre stabiliteit, terwyl Kulani en BH-140 as onstabiel geklassifiseer word. Shukla's se stabiliteits variansie (1972) het gevind dat BH-660, gevolg deur (A-7033 x F-7189) x 142-1-e en Gibe-l stabiel was, terwyl Kulani en BH-140 as onstabiel geklassifiseer is. Ekovalensie sowel as die stabiliteits variansie het gevind dat BH-660 was die mees stabiele genotipe. Die gesamentlike regressie het ongeveer dieselfde resultate gehad as laasgenoemde twee. Die stabiliteits waardes van additiewe hoofeffekte en vermenigvuldige interaksies (AMMI) en rangordes van die interaksie hoofkomponent analises (IPCA) het ook gevind dat BH-660 die mees stabiele genotipe was, gevolg deur (A-7032 x F-721~) x 144-7-b en (A-7033 x F-7189) x 142-1-e, terwyl Kulani en BH-140 as onstabiel geklassifiseer is. AMMI het dieselfde resultate as die ekovalensie en Shukla gehad ten opsigte van die mees stabiele kultivars.