Evaluation of coconut-citrus intercropping systems in the context of lethal yellowing disease of coconut in Ghana

Abstract

Global coconut production is under the devastating threat of lethal yellowing diseases endemic in East and West Africa. The most practical solution to the disease problem lies in the development of resistant or tolerant coconut planting materials. Malayan Yellow Dwarf (MYD) crossed (x) Vanuatu Tall (VTT) coconut hybrid was identified in a resistance screening work to have moderate tolerance to the disease. Consequently, the hybrid was recommended for replanting of coconut fields devastated by lethal yellowing in Ghana. To stimulate a greater replanting effort however, there was the need to develop a more efficient coconut intercroppingsystems involving other economic tree crops that are capable of providing insurance against total crop failure and loss of income since the MYD x VTT coconut hybrid was only moderately tolerant to lethal yellowing. Four cropping systems involving the tolerant MYD x VTT coconut hybrid and Late Valencia sweet orange were evaluated in a randomized complete block design with three replicates. The cropping systems were: 1. Sole coconut (Coconut planted at 8.5m triangular spacing at 160 palms ha-1) 2. Sole citrus (Citrus planted at 6m square spacing at 277 trees ha-1) 3. Coconut-citrus intercrop I (Coconut planted at 9.5m triangular spacing at 128 palms ha-1 and intercropped with citrus at 100 trees ha-1) 4. Coconut-citrus intercrop II (Coconut planted at 10.5m triangular spacing at 105 palms ha-1 and intercropped with citrus at 80 trees ha-1). Citrus was planted at the convergence point of any two diagonal lines linked with four adjacent coconut palms. The MYD x VTT coconut hybrid planted at 9.5m triangular provided optimal spacing for citrus intercropping. The intercroppingsystem did not hinder the optimal growth and yield of coconut or citrus. It enabled a more efficient use of land and generated higher productivity by fitting more trees (coconut/ citrus) to a unit area of land as compared with sole cropping. The costbenefit ratio of the intercropping came next to sole coconut planting. Nevertheless, intercropping enjoyed 26% of fruit income as insurance against lethal yellowing disease while sole coconut planting had no insurance cover.