Abstract
The objectives of this study were to evaluate dry matter (DM) yield and seed yield of six leafed and semi-leafless pea (Pisum sativum L.) genotypes, and to compare them for these traits. Evaluation of genotype x environment (G x E) interaction, stability and cluster analysis were also carried out at eight diverse locations with typical Mediterranean and Mediterranean-type climate during the 2001-2002 and 2002-2003 growing seasons. Significant differences were found among the pea genotypes for DM and seed yield on individual years and combined over years, and in all locations. All interactions which related to G x E interaction showed significance (P>0.001) for DM and seed yield. The highest yield (4789 kg/ha) was obtained from the leafed genotype 'Urunlu'. However, stability analysis indicated that for DM yield, the leafed genotypes 'Golyazi' and 'Urunlu' should be grown in low yielding and high yielding environments, respectively. Cluster analysis, based on grouping locations, showed that P101 was the preferred variety in low yielding environments, and P98, in high yielding ones. It was suggested that the use of both stability and cluster analyses might give better results. Comparison of Cluster and stability analyses showed that the stability analysis fails to recommend cultivars to different regions where yield potential showed significant differences. It seems, however, that Cluster analysis could be a powerful tool to examine G x E interaction. If the number of environments was sufficient, a separate stability analysis could be run in each Cluster.
Highlights
Peas (Pisum sativum L.) are grown for hay, pasture or silage production, alone or mixed with cereals, in different parts of the world (McKenzie and Spooner, 1999)
The highest and lowest average dry matter (DM) yields were obtained from the leafed varieties Urunlu (4789 kg ha-1) and P101 (3840 kg ha-1), respectively
Significant genotype × location (G × L) interaction shows that the same genotype might not give the highest yield in all locations
Summary
Peas (Pisum sativum L.) are grown for hay, pasture or silage production, alone or mixed with cereals, in different parts of the world (McKenzie and Spooner, 1999). Genotypes selected in a breeding program should be tested at various locations for several years, and analyzed appropriately to determine the extent of the genotype × environment (G × E) interaction before being released as cultivars. To determine the extent of the G × E interaction, a simple regression of cultivar mean on the experiment mean was proposed This technique became extensively used after the studies of Finlay and Wilkinson (1963) and Eberhart and Russell (1966). This method is based on regression analysis of stability parameters for cultivars by analyzing experiments conducted over years and/or locations. Eberhart and Russell (1966) proposed to consider two parameters: the first one is the regression coefficient (bi) to compare relative responsiveness of a particular cultivar to the mean of all cultivars (environmental index), the second one is the deviation from the regression mean square (S2d) for measuring how well the predicted response compares with the observed response
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