An Investigation Of The Susceptibility Of Three Acacia Species To Viscum Articulatum Infection

ABSTRACT

Acacia species are indigenous trees which are of great importance in Zimbabwe. They can be

used for various purposes for example making pulp and tannin, as cattle feed, as fuel (charcoal

and wood) and for timber production which can be used for construction purposes. However,

Acacia species are being affected by Viscum articulatum in Zimbabwe especially in Greystone

Park, Mazowe district, Glen Lorne and some parts of Midlands province. At present, Acacia trees

affected by the Viscum articulatum are pruned to remove all the infected parts. The removed

parts are buried to control the parasite and in heavily infested cases they are cut down and burnt

as a way of controlling the Viscum articulatum parasite from spreading. A study was carried out

at Forestry Commission to investigate the susceptibility of three Acacia species (Acacia

sieberiana, Acacia polyacantha and Acacia nilotica) to Viscum articulatum infection between

mid-January 2018 and mid-February 2019. Samples of Viscum articulatum parasite were

collected from Hakuna Matata Primary School and Gaydon road in Greystone park form Acacia

hosts. Inoculation of parasite was done by watering with infected water and by means of air

layering for a period of four months. Five seedlings of each of the three Acacia species were

used. Susceptibility of the species to the infection was determined by the development of the

mistletoe and growth retardation of the seedlings. It was observed that Acacia sieberiana and

Acacia polyacantha showed greater retardation by the infection especially on the seedlings which

were inoculated by air layering compared to watering. Acacia sieberiana which was inoculated

by means of air layering developed mistletoe which grew up to a mean height of 19 μm and

recorded highest proportion (100%) of seedlings showing signs of infection after a four months

period. The controls, which were the untreated seedlings, were not affected. Findings from this

study shows that Acacia nilotica is less susceptible to Viscum articulatum whilst Acacia

sieberiana and Acacia polyacantha are susceptible, therefore growing Acacia nilotica which is

less susceptible to the infection can be a method of choice as it is environmental friendly other

than making use of chemicals.