Differences in mycorrhizal infection and P uptake of sweet potato cultivars (Ipomoea batatas L.) during their early growth in three soils

Mycorrhizal infection in the roots of 10 sweet potato cultivars was assessed 7 weeks after planting in three soils collected from Ibadan, Fashola and Onne in southern Nigeria, three soils which contained 21.0, 7.8 and 54.8 mg P kg−1, respectively. Mycorrhizal infection averaged 17% in the soil from Ibadan, 24% in the soil from Fashola and 7% in the acid soil from Onne. The plants grown in the Fashola soil contained the same percentage of P as plants grown in the Onne soil. Although the percentage of P in sweet potato was lowest in the Ibadan soil, shoot dry weights were 35% higher in this soil than in the other two soils. There was no correlation between the level of mycorrhizal infection and plant dry weight in the partially sterilized soil from Ibadan. Sweet potato inoculated in this soil with infected roots of Leucaena leucocephala showed a higher level of mycorrhizal infection than uninoculated plants. Dry-matter production was, however, the same for all treatments. The sweet potato cultivars differed in their level of mycorrhizal infection and in their response to applied P. Cultivars TIS 2498 and TIS 70357 consistently showed the lowest percentage of infection; and TIb 4, TIS 8441 and TIS 8524 showed infection levels above 20% in the Fashola and Ibadan soils. When the low-yielding cultivar, TIb 4, and an improved clone, TIS 9265, were grown in the presence of 50 and 100 mg single superphosphate per kg soil, TIb 4 produced more dry matter in the presence of P fertilizer than it did without the fertilizer. Growth and mycorrhizal infection of TIS 9265 were not affected by the fertilizer.