To study the genetic diversity of Iranian onion landraces, seeds of twenty landraces and two hybrids were planted using a randomized complete block design (RCBD) with three replications in Agricultural and Natural Resources Center of East Azarbayjan for two years. Onion yield per plant, onion dry weight, percentage of onion dry matter, bulb diameter, bulb length, soluble solids, number of centers, shape index, number of leaves, leaf length and number of edible layers were measured. Analysis of variance showed significant differences for all attributes. Cluster analysis, using Ward`s method, grouped the entries under study, into four clusters. Grouping based on morphological attributes showed no correspondence with the geographical pattern. In principal component analysis, the first three principal components accounted for 83.42% of the total phenotypic variation. In the first principal component, onion dry weight, bulb diameter, leaf length, onion yield per plant, number of leaves, soluble solids and dry matter percent of onion showed positive while shape index showed negative effect. In the second principal component, bulb length, number of edible layers, shape index and number of leaves had positive while soluble solids and dry matter percent of onion had negative contributions. Therefore, cultivars having larger values for the first principal component would have higher onion yield per plant and the cultivars having higher values for the second principal component would be marketable and more suitable for the fresh-market. Path analysis showed that bulb diameter have largest positive direct effect on yield of onions. Indirect effects of length and number of leaves on onion yield through bulb diameter were also considerable. Selection of plants with larger leaf length, bulb length and diameter could be therefore suitable. For breeding onion for higher yield. Due to the low-dry matter percentage, the landraces under study are not suitable for industry and must be used in fresh-market.
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