The effect of soil chemical properties and plant nutrition on the growth of banana (Musa acuminata L.A. Colla) plants infected with Fusarium wilt

Abstract

Fusarium wilt of banana, which is caused by the soil-borne fungus Fusarium oxysporum f.sp. cubense (Foc), is a serious threat to continued banana production in Kiepersol (Mpumalanga), South Africa. Some farmers have lost up to 50% of the area originally planted to bananas due to this disease. Although several control strategies have been investigated internationally, no effective control strategies exist as yet. The objectives of this study were twofold. The first was to determine the effect of liming and nitrogen fertilisation on the growth of banana plants infected with Foc. The second was to determine the soil chemical properties of selected sites of three fields with soils that are suppressive or conducive to Fusarium wilt of banana in Kiepersol, in order to find possible differences between these soils and to provide basic data for future research. A soil pot trial and a hydroponic pot trial were conducted simultaneously. Banana plants were grown in the pots with a 2 x 3 x 3 factorial combination of pH, N-level and N-source used in both growth mediums. In the soil pot trial, the interaction of liming, N-levels and N-source applications yielded significant differences in plant growth, despite the infection of plants with Fusarium wilt. When no lime was applied, the application of low N-levels as a combination of both NO3- and NH4+ was most beneficial to both plant growth and nitrogen uptake. On the other hand, high N-levels, primarily in the form of NO3-, were only effective in promoting plant growth and nitrogen uptake when it was combined with liming. Liming did not significantly affect the soil pH and the observed effect thereof, in conjunction with N-application, could therefore be ascribed to the affect of the added Ca itself to the soil. In the hydroponic trial, the low pH treatments resulted in distinctly lower plant growth than the high pH treatments. Due to the constant mixing of the nutrient solutions in the hydroponic trial, less significant and conclusive results were generally obtained. The statistical analysis also showed that nitrogen source did not contribute to the observed results, compared to that of the soil pot trial. This indicates that the rhizosphere in the soil environment could play an important role in the observed results in the soil pot trial and this possibility needs to be investigated and quantified in further studies. Analysis of the three field soils yielded conclusive evidence that chemical differences may occur between suppressive and conducive soils. The chemical analysis of soil samples showed varied results between the three fields in terms of Ca, K, Mg, Na, P, NO3-, NH4+ and pH(H2O), while the levels of Cu, Fe, Mn and Zn in the 0-30mmsoil layer were higher in the suppressive soils compared to the conducive soils in all three fields. Overall, results indicated that the effective management of soil chemical properties and fertilisation may aid in the manipulation of Fusarium wilt of banana in the field. These results justify further field research in order to develop an integrated management strategy for the control of Fusarium wilt of banana and also serve as a basis for such research.