Previous experiments have demonstrated that the performance of asexual propagules of Allium vineale is greater with genetically identical than with unrelated neighbors. This growth chamber experiment tested whether the benefit to identical neighbors is due to arbuscular mycorrhizal fungi. Five genotypes were used as focal plants, and each focal plant had two neighbors that were either genetically identical to the focal plant, from the same population, or from a different population. These combinations were then replicated in mycorrhizal and non-mycorrhizal soil (created by applying Benomyl, a fungicide). Plants growing in non-mycorrhizal soil had significantly lower bulb mass, regardless of their neighbor type. More importantly, plants growing in mycorrhizal soil with siblings or neighbors from the same population were significantly larger than those growing with neighbors from a different population. Pots with neighbors from a different population also had higher variance in performance in mycorrhizal soil than those with more similar neighbors. Thus mycorrhizae affect intraspecific competition in A. vineale, favoring plants with more similar neighbors. A field experiment has demonstrated local adaptation to the fungal soil community in this A. vineale population at a scale of 10 m, giving further evidence for specificity in this plant-mycorrhizal interaction. The effect of the soil fungal community differed among genotypes. All genotypes performed equally poorly in Benomyl-treated soil, but genotype B showed little benefit when grown without Benomyl. Genotype B also differed from the other four genotypes in that those plants with genetically identical neighbors had the lowest bulb mass. During the final harvest it was noted that pots without Benomyl containing genotype B were infected with a fungal pathogen, indicating that the co-occurance of both mycorrhizal and pathogenic soil fungi may further alter intraspecific interactions in A. vineale.

Key words: Allium vineale, asexual reproduction, intraspecific competition, local adaptation, mycorrhizae, pathogen