First Report of Anthurium Blight Caused by Xanthomonas axonopodis pv. dieffenbachiae in Reunion Island.

Xanthomonas axonopodis pv. dieffenbachiae is the causal agent of Anthurium blight, a severe systemic disease of Anthurium. Bacterial blight has been reported in most of the areas where Anthurium is cultivated, especially in Hawaii, California, Guadeloupe, Martinique, Jamaica, and Venezuela. This pathogen is also described on many genera of the Araceae family, e.g., Dieffenbachia, Syngonium, Philodendron, Caladium, Aglaonema, and Colocasia. In Reunion Island, Anthurium blight was first observed in 1997 during routine inspections in two nurseries on Anthurium andreanum plants imported from the Netherlands. Lesions consisted of water-soaked spots at the leaf margins surrounded by chlorotic or necrotic zones. Several necrotic lesions had coalesced to form large, dark patches that covered a large portion of the leaf. Some plants showed symptoms of systemic decay. The disease rapidly spread to other Anthurium plants in the nurseries, causing severe damage. Bacteria, which were consistently isolated from infected plants, were gram negative, yellow-pigmented, and mucoid. Carbon source utilization patterns (Biolog, Hayward, CA) were consistent with Xanthomonas sp. and the bacteria responded positively to monoclonal antibodies raised against X. axonopodis pv. dieffenbachiae (Agdia) in an enzyme-linked immunosorbent assay. Between 1997 and 1999, 114 isolates were collected from three main locations: the two primary infected nurseries and another one found contaminated later. Pathogenicity tests were performed on 8-month-old plants of A. andreanum cv. Carré by infiltrating the leaves with a suspension of bacteria (105 CFU/ml) using a syringe. Each strain was inoculated onto three young leaves (four inoculation points per leaf) on two plants. Control plants received sterile Tris solution. Plants were maintained in a growth chamber at 28°C (±1°C) with 95% (±5%) relative humidity and a photoperiod of 12 h. All 114 strains caused typical symptoms on Anthurium with the development of water-soaked spots near the inoculation point after 9 days, evolving into chlorotic and then necrotic areas after 20 to 24 days. No symptoms developed on control plants. Koch's postulates were completed by reisolating, from all the inoculated plants, bacteria that were again serologically identified as X. axonopodis pv. dieffenbachiae. Since 1997, control measures were adopted, consisting of the destruction of the infected plants and quarantining the contaminated nurseries, as well as surveillance intensification at the ports of entry to prevent new introductions.

First Report of Tomato Yellow Leaf Curl Virus in Réunion Island.

In September 1997, stunting, reduced leaf size, leaf curling, and yellow margins were observed on tomato plants on a farm on the south coast of Réunion, a French island belonging to the Mascarenes archipelago. To our knowledge, these symptoms appeared to be characteristic of a tomato yellow leaf curl virus (TYLCV) infection. Diseased plants gave positive reactions with a triple antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA), using ADGEN antibodies specific for begomoviruses (1). The serological results were confirmed by polymerase chain reaction (PCR) with a pair of degenerate primers-MP16, 5'-CCTCTAGATAATATTAC(C/T)(G/T)(G/A)(A/T)(T/G)G(G/A)CC-3' and MP82, 5'-CGGAATTC(T/C)TGNAC(C/T)TT(G/A)CANGGNCC(T/C)T C(G/A)CA-3'-designed by Malla Padidam (ILTAB, San Diego, CA) to amplify a region of the A component of begomoviruses, between the intergenic conserved nonanucleotide sequence (TAATATTAC) and the first 5' quarter of the capsid protein gene. A 500-bp PCR product was obtained from a symptomatic plant but not from a healthy looking one. After cloning the PCR product in a pGEM-T Easy vector (Promega, Madison, WI) and sequencing it with plasmid-specific primers (SP6, T7), the sequence was compared with the sequences of the NCBI data base, with the use of BLAST. Nineteen sequences among those producing the highest scoring segment pairs were compared with each other and with the 500-bp PCR product from Réunion by the Clustal method of MegAlign (DNASTAR, London). The Réunion sequence (AJ010790) was at least 94% similar to sequences of TYLCV isolates from the Dominican Republic (AF024715), Cuba (AJ223505), and Israel (X15656, X76319 for the mild clone). Based on these results, it appeared that the analyzed tomato plant was infected by a geminivirus isolate belonging to the Israeli species of TYLCV. A preliminary survey was carried out from December 1997 to April 1998 in both outdoor and protected tomato crops. Infected plants were detected by TAS-ELISA in 52 of the 123 locations visited. Severe economic losses were observed: 14 locations with 60 to 100% yield reduction and 11 locations with 40 to 60% yield reduction. All the infected samples were collected in the leeward coast, which is the driest region of the island. Although Bemisia tabaci (Gennadius) has been recorded since 1938 in Réunion (2), it has been observed on tomato crops only since 1997 and population levels were low compared with those of Trialeurodes vaporariorum Westwood. During the first six months of 1998, B. tabaci was found on Euphorbia heterophylla L., Lantana camara L., Solanum melongena L., S. nigrum L., and Phaseolus vulgaris L. These host plants often occur near infected tomato crops. References: (1) S. Macintosh et al. Ann. Appl. Biol. 121:297, 1992. (2) L. Russell and J. Etienne. Proc. Entomol. Soc. Wash. 87:202, 1985.

Evaluation of the Biolog Substrate Utilization System To Identify and Assess Metabolic Variation among Strains of Xanthomonas campestris pv. Citri.

Metabolic fingerprints of 148 strains of Xanthomonas campestris pv. citri originating from 24 countries and associated with various forms of citrus bacterial canker disease (CBCD) were obtained by using the Biolog substrate utilization system. Metabolic profiles were used to attempt strain identification. Only 6.8% of the studied strains were correctly identified when the commercial Microlog 2N data base was used alone. When the data base was supplemented with data from 54 strains of X. campestris pv. citri (40 CBCD-A strains, 8 CBCD-B strains, and 6 CBCD-C strains) and data from 43 strains of X. campestris associated with citrus bacterial spot disease, the percentage of correct identifications was 70%. Thus, it is recommended that users supplement the commercial data base with additional data prior to using the program for identification purposes. The utilization of Tween 40 in conjunction with other tests can help to differentiate strains associated with CBCD and citrus bacterial spot disease. These results confirmed the separation of X. campestris pv. citri into different subgroups (strains associated with Asiatic citrus canker [CBCD-A], cancrosis B [CBCD-B], and Mexican lime canker [CBCD-C]). The utilization of l-fucose, d-galactose, and alaninamide can be used as markers to differentiate strains associated with these groups. A single strain associated with bacteriosis of Mexican lime in Mexico (CBCD-D) was closely similar to CBCD-B strains.