Relationship between heterosis and genetic distances as revealed by AFLP markers in intervarietal F1 hybrids of bunching onion (Allium fistulosum)

Heterosis for seedling growth in bunching onions (Allium fistulosum L.) were evaluated using 11 cultivars belonging to Senju, Kaga, Kujo and Okunegi groups and 40 of their intervarietal F-1 progenies. For fresh weight of seedlings at four weeks after transplanting, heterosis over the mid-parent (the mean of the parents) ranged from - 3 to 70% with an average of 21%, whereas heterosis over the better parent ranged from - 10 to 46% with an average of 10%. High heterosis among F, hybrids occurred most frequently in the inter-group crosses of Senju X Kujo, whereas high heterosis for practical use was also exhibited by some F, hybrids of intra-group crosses within the Senju group. Although significant heterosis for root number, plant height and relative growth rate (RGR-fw) occurred, the degrees of response were less than that for fresh weight. The 11 parental cultivars were assayed for DNA polymorphism by using 128 AFLPs to estimate genetic distances (GDs). Cluster analysis of the parents, based on GDs, accorded with the traditional classification, based on morphological and ecological characteristics. The GDs based on AFLPs correlated significantly with heterosis over the mid-parent for each seedling trait at four weeks after transplanting, but the GDs were not correlated with heterosis over the better parent. Consequently, these correlations are not applicable for predicting heterosis.