Influences of a root-lesion nematode, Pratylenchus coffeae, and two arbuscular mycorrhizal fungi, Acaulospora mellea and Glomus clarum on coffee (Coffee arabice L.)

A greenhouse experiment was conducted to investigate the effects of a root-lesion nematode, Pratylenchus coffeae, two arbuscular mycorrhizal (AM) fungi, Acaulospora mellea and Glomus clarum, and timing of inoculation on the growth and nutrition of a nematode-susceptible Arabica coffee cultivar. The late AM inoculation (added simultaneously with nematodes) did not enhance coffee tolerance to P. coffeae. In the presence of P. coffeae, late-mycorrhizal plants were P deficient during the entire experiment and their foliar P concentration remained as low as that of non-mycorrhizal plants. After 7.5 months, nematodes decreased AM colonization of late-mycorrhizal plants by half and their biomass was only 20-30% that of the controls. In contrast, early AM inoculation (4 months before nematode inoculation) with either AM species improved the tolerance of coffee to P. coffeae. Root colonization by AM was not significantly reduced by P. coffeae. Despite higher densities of nematodes, root lesions were less numerous and more localized in early AM inoculated plants than in those of non-mycorrhizal plants. In the presence of P. coffeae, early AM-inoculated plants remained P sufficient and their biomass was still 75-80% that of their nematode-free controls. This study shows that in soils with low P levels, enhanced tolerance to P. coffeae seems limited to mycorrhizal coffee plants with well established AM symbiosis and improved P status.