Comparative Epidemiology of Citrus tristeza virus in Plantings of Various Citrus Species in Costa Rica, and Long Distance Spread by the Brown Citrus Aphid

Abstract

Five 400-tree plots were established to compare the virus increase and spread of Citrus tristeza virus (CTV) among grapefruit, orange and lemon plots in San Carlos and Nicoya citrus producing areas of Costa Rica. Tree disease status was assayed semiannually over a 5-yr period via DAS-I ELISA using a monoclonal mixture to detect all CTV isolates, and MCA13 to identify more severe isolates. Aphid population dynamics and species prevalence/diversity were monitored using yellow and green water traps to estimate flying aphid populations. Spatial and spatio-temporal analyses were conducted to determine the dynamics of virus spread. Virus increase was most rapid in the orange plot, much slower in the grapefruit plot and even slower in the lemon plots. Both grapefruit and orange plots in Boca de Arenal demonstrated some tree to adjacent tree associations of CTV-infected trees but none at the scale of groups of trees. This was reversed for the grapefruit plot in Nicoya for which no association existed among adjacent trees but aggregation did exist within groups of trees. Groups of trap trees were planted and maintained every 0.1 km along roadsides radiating away from the edges of a commercial citrus production area in San Carlos to detect long distance spread by events vector. Brown citrus aphid, Toxoptera citricida, colonies formed multiple times in the trap trees, and CTV-infected trap trees were found as far as 4.6 km from the nearest commercial source trees, indicating the ability of T. citricida to traverse and transmit CTV over considerable distances.