Vol. 75 No: 5

Title:
Reduction in 'Marsh' grapefruit tree size infected with citrus tristeza virus populations

Authors:
S.P. VAN VUUREN and J.V. DA GRAÇA

pp: 542-545

Abstract:
'Marsh' grapefruit trees on 'Troyer' citrange rootstock were bud-inoculated with different populations of citrus tristeza virus (CTV) prior to planting in the field. Selected CTV populations GFMS 2, GFMS 10, GFMS 12, GFMS 19, GFMS 25, GFMS 27 and GFMS 35, free of citrus viroids, were used for inoculation. A severe population (GFSS 1) and plants left virus-free served as controls. Tree size, production, fruit size and tree health were determined. Fifteen years after planting, canopy volumes of trees with three populations, GFMS 2, GFMS 19 and GFMS 25, were significantly smaller than those of the control trees and trees with populations GFMS 10, GFMS 12 and GFMS 35. Trees with population GFMS 19 had a larger diameter than those with populations GFMS 2 and GFMS 25 and together with the slightly higher yield efficiency of GFMS 19 trees, this resulted in a cumulative yield equal to that of the control and the GFMS 12 trees. Considering fruit size and their value, the performance of trees with population GFMS 19 equalled that of the larger trees. Tree health was also similar, making this population suitable for use in high density plantings. A projection was made which showed that the production and crop value of trees with population GFMS 19 were similar to those of trees with populations GFMS 10, GFMS 12 and GFMS 35. However, benefits such as easier and better spray application and easier harvesting can increase profits when trees with population GFMS 19 are planted. The cumulative yield, crop value and tree health where populations GFMS 2 and GFMS 25 were inoculated were similar to those of the severe population which had an unacceptable crop. However, decline and reduction in fruit size of the trees with the severe population were more drastic than those of trees with population GFMS 2.

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