Influence of Soil Water Regimes on VA Mycorrhiza

A greenhouse trial was conducted with cassava inoculated with seven different VAM fungal species, i.e. Acaulospora longula, A. myriocarpa, Entrophospora colombiana, Glomus fasciculatum, G. manihotis, G. occultum and Scutellospora heterogama. A wet and a dry soil water regime was established to study the effect of water stress on performance of these fungi with a drought tolerant cassava clone. At harvest, N, P and K concentration was analysed in leaves, petioles, stems and roots.
In unstressed plants, five endophytes were effective whereas in stressed plants only three fungi improved growth beyond the non-mycorrhizal control. These were E. colombiana, G. manihotis and G. occultum which were most effective for P uptake under stress. Differential effects of VAM fungal species on root length and K. uptake were found. A. myriocarpa caused the greatest increase in length of feeder roots and G. occultum was one of the most effective for K uptake under both water regimes even though these fungi were not the most effective for dry matter production. Under each water regime, the concentration of N, P and K in leaves, petioles, stems and roots was influenced by the fungal species. Mycorrhizal endophytes differed in tolerance to dry soil conditions as found by root infection ratings. From the results it can be concluded that in addition to the improved P nutrition the enhanced root length and K uptake by VAM fungi may be important for drought tolerance of cassava.