Acidovorax anthurii (Gardan et al., 2000), the causal organism of BLS of anthurium (A. andraeanum Linden ex André), was first reported by Prior et al. (1985) in the French West Indies and later in Trinidad (Dilbar, 1992; Saddler et al., 1995). It is regarded as one of the major contributors to the demise of the anthurium industry in the Caribbean region (Saddler et al., 1995), along with bacterial blight disease caused by X. axonopodis pv. dieffenbachiae (Elibox and Umaharan, 2007). Cultural control methods have proven to be inadequate in controlling BLS and it is generally believed that breeding for resistance is the only means of sustainable management of the disease. Since the first report in 1992, there have not been any follow-up studies to determine the prevalence and geographical distribution of BLS in Trinidad, although anecdotal reports indicate a widespread distribution and a significant negative impact on the industry. Furthermore, there have been no studies on the pathogenic variation of A. anthurii.
The causal agent of BLS enters the vascular system of anthurium leaves via natural openings (stomata and hydathodes) or wounds (Prior et al., 1985). Early foliar symptoms are small, angular, greasy spots on the lower surface of leaves near veins and leaf margins, and on spathes (Prior et al., 1985). These lesions develop rapidly resulting in large, black necrotic spots which become grey-black on older leaves often deforming the infected leaves (Prior et al., 1985). Necrotic spots are surrounded by greasy margins and narrow, bright chlorotic halos (Dilbar and Gosine, 2003; Prior et al., 1985). Under conditions of high humidity, bacterial slime oozes from the leaf margins. On spathe tissues, black or brown necrotic spots surrounded by violet halos usually develop (Dilbar and Gosine, 2003; Prior et al., 1985). Both leaf and spathe infections may progress into veins causing a soft rot with eventual abscission of the petiole and peduncle. Infections can become systemic resulting in a general yellowing of the entire leaf lamina and occurrence of typical black, necrotic lesions progressing from the leaf petioles into the major veins (Prior and Rott, 1989). Systemic infections lead to eventual plant death (Prior et al., 1985).
The A. anthurii isolates collected in the French West Indies have been characterized both morphophysiologically and biochemically (Gardan et al., 2000; Prior and Sunder, 1987; Prior and Rott, 1989; Saddler et al., 1995). All isolates were gram-negative motile rods (0.2 to 0.7 × 1.0 to 5.0 µm), with a single polar flagellum. They produced creamy white, circular, raised colonies with entire margins on Kelman’s medium without tetrazolium chloride and amended with 1 g/L yeast extract (KY), King’s medium A (KMA), King’s medium B (KMB) and yeast dextrose agar (YDA) media. Some isolates produced a brown diffusible pigment when grown at 41 °C on solid KY medium and all isolates elicited a hypersensitivity reaction on the tobacco variety, ‘Samsun NN’ (Prior et al., 1985). Furthermore, all isolates were strictly aerobic; positive for catalase; used arginine and asparagine as the sole source of carbon and nitrogen; produced hydrogen sulfide from cysteine; were tryptophan deaminase positive; showed urease activity; hydrolyzed cellulose; grew on YDA amended with 2% NaCl; produced acids from galactose, arabinose, glycerol; and used acetate, formiate, and citrate (Prior and Rott, 1989). Isolates were shown to be variable for production of acid from trehalose and glucose as well as for the utilization of d-tartrate and l-tartrate (Prior and Rott, 1989). They were positive for oxidase, nitrate reductase (Saddler et al., 1995), dl-5-aminobutyrate, d(-) tartrate, and azelate (Gardan et al., 2000). Schaad et al. (2001) reported that some Acidovorax species use d-glucose and ethanol.
All isolates from the French West Indies were also negative for production of fluorescent pigment on KMA or KMB and did not show turbidity after 10 d at 4 °C or 41 °C in liquid KY medium (Prior et al., 1985). Furthermore, all isolates were negative for indole, levan, acetoin production; aesculin and casein hydrolysis; DNAse activity; pectinolysis; potato soft rot; growth on YDA amended with 5% NaCl; production of acid from inositol, sorbitol, mannose, sucrose, cellobiose, rhamnose; utilization of propionate and benzoate (Prior and Rott, 1989); arginine dihydrolase; starch hydrolysis; gelatin liquefaction (Saddler et al., 1995); trehalose; caprylate; d-ribose; d-glucose; N-acetylglucosamine; l-arginine; saccharose; inositol; sarcosine; itaconate; d-xylose; l-tryptophan; and mannitol (Gardan et al., 2000).
Dilbar (1992) observed that the A. anthurii isolates from Trinidad produced a brown pigment when grown on nutrient agar (NA) for 48 h, but to date the morphological and biochemical variation or aggressiveness of isolates of A. anthurii have not been investigated. We do so in this paper as this information is important for breeding resistance to BLS in anthurium. We also report the status and distribution of A. anthurii in Trinidad 12 years after it was first reported, the extent of morphophysiological and biochemical variation and differences in aggressiveness among the native isolates. A more recent unpublished survey (2014) showed that all of the anthurium farms save one have collapsed due to the effects of either BLS, bacterial blight disease or both.
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