Relations Between Biomass Accumulation and Infection by Vesicular-Arbuscular Mycorrhizal Fungi in Cassava as Affected by Planting Date

Roots of 12, 3-month-old, field-propagated clones of cassava (Manihot esculenta Crantz) were more heavily mycorrhizal in the dry (Jan.–March and Oct.–Dec.) (39–83 %) than in the wet season (April–Sept.) (20–71%). Mean dry weights (biomass) of roots and shoots in the wet season (3.8–7.9 and 9.7–19.1 g/plant) were higher (P = 0.01) than in the dry season (2.1–5.9 and 5.4–12.8 g/plant, respectively). Clones with symptoms of the African cassava mosaic disease (ACMD) were less mycorrhizal, (20–69%) than mosaic symptom-free clones (51–83%). Higher colonization of roots of the clones by indigenous fungal symbionts and lower biomass accumulation in the dry season are attributed mainly to soil moisture and other effects, while reduced infections in cassava with ACMD symptoms may be due to ACMD-induced reductions in carbohydrate levels.