Investigation of malformation symptoms in (Searsia lancea)

The common karee (Searsia lancea, Anacardiaceae) is a common, widely distributed tree in South Africa. Popular as a garden and street ornament, its fruit and foliage serve as a source of food for many animals and humans. It also has applications in the leather tanning industry and phytoremediation. Disease symptoms on S. lancea were reported that resemble malformations of the closely related mango (Mangifera indica, Anacardiaceae). This disease was named karee malformation disease (KMD). Formal investigation was conducted to determine whether malformation symptoms on the two separate genera of the Anacardiaceae family share a causal agent, namely Fusarium spp. A pilot study and review of literature identified other relevant aspects worthy of study including insect associations, and differences in phytohormone and nutrient concentrations between healthy and affected trees. It was determined that Fusarium spp., which cause malformation of M. indica, does not cause malformation of S. lancea. It is also unlikely that the dominant fungal group, Alternaria alternata, causes S. lancea malformations. However, this study identified interesting fungal and insect associations with healthy and malformed tissues of S. lancea. It is possible that the dominant insect group, namely Psyllidae, causes malformations of S. lancea directly, or indirectly by acting as a vector of another pathogen. Lower concentrations of the phytohormones gibberelic acid and jasmonic acid, and higher concentrations of salicylic acid were noted in malformed compared to healthy tissues of S. lancea. However, only the differences for salicylic acid were significant. Higher concentrations of the mineral nutrients nitrogen and potassium were noted for malformed tissues, while the phosphorus concentration was the same for both conditions of S. lancea.