THE EFFECT OF IRRIGATION PRACTICES ON THE SPATIO-TEMPORAL INCREASE OF ASIATIC CITRUS CANKER IN SIMULATED NURSERY PLOTS IN REUNION ISLAND.

Authors: PRUVOST, O. - CIRAD-FLHOR,REUNION,FRANC; Gottwald, Timothy; BROCHERIEUX, C. - CIRAD-FLHOR,REUNION,FRAN

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Asiatic citrus canker is a potentially severe disease of several citrus species and cultivars in many tropical and subtropical areas. In such areas, infected citrus nursery plants constitute an important source of primary inoculum for newly established citrus groves. This study was designed to examine how citrus canker is introduced and spread in citrus nurseries and subsequently how it enters newly established citrus plantations on infected nursery transplants. The influence of three different irrigation systems on the development of citrus canker was studied in citrus nurseries in Reunion Island, France. In overhead irrigated plots, the spread of Xac lacked directionality. Rainstorms of short duration and high intensity were apparently associated with citrus canker spread in drip irrigated plots. The results of present study indicate that less citrus canker will develop with alternative irrigation practices such as drip or mist irrigation. Therefore, alternative irrigation practices to those presently used, when integrated into a modernization scheme with other cultural practices, should minimize citrus canker increase and spread within nurseries and thus reduce the initial inoculum transferred to new groves.

Technical Abstract: Asiatic citrus canker is a potentially severe disease of several citrus species and cultivars in many tropical and subtropical areas. In such areas, infected nursery plants constitute an important source of primary inoculum for newly established citrus groves. The influence of overhead, drip, and mist irrigation systems on the development of Asiatic citrus canker was studied in simulated Mexican lime nurseries in Reunion Island. Overhead irrigation exacerbated the increase of the streptomycin resistant strain of Xanthomonas axonopodis pv. citri (Xac). The temporal development of Asiatic citrus canker for overhead irrigated nursery plots was best described by a nonlinear exponential model, because disease incidence in these plots did not reach an asymptote during the experimental period. This can be explained by the continuous production of new growth, susceptible to Asiatic citrus canker, and splash dispersal of Xac associated with overhead irrigation. Spatial autocorrelation and spatio-temporal semivariance analyses confirmed the occurrence of aggregated disease patterns irrespective of the irrigation system. In overhead-irrigated plots, the spread of Xac lacked directionality. Rains of short duration and high intensity were apparently associated with disease increase in drip irrigated plots. Our results indicate the need to improve cultivation practices in Reunion Island citrus nurseries to minimize Asiatic citrus canker incidence in nurseries and minimize introduction of Xac to new groves.