Abstract
Mycorrhizal symbiosis is important for growth of coffee (Coffea arabica), but differences among coffee cultivars in response to mycorrhizal interactions have not been studied. We compared arbuscular mycorrhizal (AM) extraradical hyphae in the soil and diversity of AM fungi among three coffee cultivars, Caturra, Pacas, and Borbón, at three farms in Puerto Rico. Caturra had significantly lower total extraradical AM hyphal length than Pacas and Borbón at all locations. P content did not differ among cultivars. Extraradical hyphal lengths differed significantly among locations. Although the same morphotypes of mycorrhizal fungal spores were present in the rhizosphere of the three cultivars and total spore density did not differ significantly, frequencies of spore morphotypes differed significantly among cultivars. Spore morphotypes were typical of Glomus and Sclerocystis. Levels of soil nutrients did not explain differences in AM colonzation among cultivars. The cultivar Caturra is a mutant of Borbón and has apparently lost Borbón’s capacity to support and benefit from an extensive network of AM hyphae in the soil. Widespread planting of Caturra, which matures earlier and has higher yield if fertilized, may increase dependence on fertilizers.
Highlights
Mycorrhizae play an important role in growth and development of wild and cultivated plants
All of the Glomus spore morphotypes were recovered from soil beneath each of the three coffee cultivars
Five spores with typical Glomus morphology were assigned to Glomus group A as defined by Schwarzott et al [28] on the basis of nuclear ribosomal ITS sequences, grouping with G. sinuosum and G. manihotis
Summary
Mycorrhizae play an important role in growth and development of wild and cultivated plants. Genetic variation within plant species can influence both the degree of root colonization by mycorrhizal fungi and the response of the plant to mycorrhizal symbiosis [1]. Most classic studies on interactions between cultivars and AM fungi used colonization of mycorrhizal fungi within the root to quantify the fungal part of the symbiosis. Miller et al [7] found that mycorrhizal root colonization was poorly correlated with plant growth, whereas extraradical hyphal length in the soil around plants was a good predictor of plant growth. Extraradical hyphal length is recognized as an important aspect of the symbiosis [8, 9] and has become a common measure of AM mycorrhizal colonization [10]
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