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Different genotypes of marigolds, representing different vegetative and flowering habits, were evaluated for colonization and responsiveness to inoculation by different arbuscular mycorrhizal (AM) fungi under low soil P conditions. Cultivars included were Tagetes erecta ‘Jubilee’, ‘Perfection’, ‘Antigua’, ‘Inca’, and ‘Discovery’ as tall and compact forms of the African-type; Tagetes patula ‘Aurora’, ‘Disco’, ‘Nema-gone’, and ‘Lemon Drop’ as French-types with single or double flowers; and Tagetes tenuifolia ‘Ursula’ as a fine-leaf Mexican-type. Considerable variation occurred in shoot and root biomass response depending on the cultivar and AM fungus used. Most cultivars responded minimally, but positively to inoculation with AM fungi (1–22% increase in total plant biomass compared to the non-AM controls); however, some responded in reduced growth (1–12% decrease compared to the non-AM controls). Cultivars varied in their pattern of partitioning biomass into roots or shoots, with some partitioning more into roots than others with similar shoot biomass. Flower number or plant height did not vary between AM and non-AM plants. Stem diameter, measured only on ‘Jubilee’ and “Nema-gone’, was increased only on ‘Jubilee’, compared to the non-AM controls. There was also great variation in the extent of AM colonization, ranging from under 10% in ‘Ursula’, ‘Antigua’, ‘Inca’, and Perfection’, to over 70% in ‘Jubilee’ and ‘Aurora’, by Glomus intraradices, Glomus mosseae, and Glomus deserticola; and notably, Gigaspora albida did not colonize any marigold cultivar. Intraradical colonization intensity ratings (arbuscules, vesicles, and internal hyphae) varied significantly among cultivars and AM fungal inoculants, as did extraradical hyphal development. These results document the potential variation in responsiveness that can occur depending on host genotype and AM fungal endophyte combination, and indicates the need for caution in predicting benefit from inoculating with mycorrhizal fungi under any set of conditions when different genotypes are grown. |
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