First Report of Acidovorax avenae subsp. citrulli as a Pathogen of Gramma in Australia

Abstract

In March 2001, a foliar bacterial disease was observed on gramma seedlings (Cucurbita moschata L.) cv. Ken Special Hybrid 864 in a commercial nursery in Bowen, north Queensland, Australia. Symptoms included chlorosis of cotyledons and angular, water-soaked lesions from the tips of the cotyledons to the petioles. Brown, angular, water-soaked lesions that were delimited by the leaf veins were also present on newly emerged true leaves. Streaming of bacterial cells from the edges of cut lesions was seen in a droplet of water with ×100 magnification. Isolations attempted on King's medium B consistently yielded a slow-growing, cream to white, gram-negative bacterium. Bacterium was identified as Acidovorax avenae subsp. citrulli based on carbon source utilization profiles (Biolog, Hayward CA) and polymerase chain reaction (PCR) using a primer pair based on the 16S-23S internal transcribed spacer region. When tested in rep-PCR with the BoxA1R primer (2), the isolate produced a banding pattern similar to other Australian A. avenae subsp. citrulli isolates previously shown to be pathogenic to rockmelon (1). Koch's postulates were completed with 20 2-week-old glasshouse-grown gramma (cv. Ken Special Hybrid 864) seedlings. Seedlings were misted until runoff with a 3 × 108 CFU/ml bacterial suspension and enclosed in plastic bags for 48 h at 23°C. Water-soaked lesions developed on cotyledons of all seedlings 6 days after inoculation, and bacterium was reisolated from symptomatic tissue. To our knowledge, this is the first report of A. avenae subsp. citrulli as a pathogen of C. moschata References: (1) R. G. O'Brien and H. L. Martin. Aust. J. Exp. Agric. 39:479, 1999 (2) J. Versalovic et al. Methods Mol. Cell Biol. 5:25, 1994.

Differences in Pathogenicity between two Genetically Distinct Groups of Acidovorax avenae subsp. citrulli on Cucurbit Hosts

“…Recent trends of devastating BFB outbreaks in melons, pumpkin, cucumber, bitter and bottle gourds in Costa Rica, Brazil, China, Australia, Nicaragua and Taiwan suggest that the host range of A. avenae subsp. citrulli has expanded (Assis et al., 1999; Langston et al., 1999; Martin and O'Brien, 1999; O'Brien and Martin, 1999; Cheng et al., 2000; Zhao et al., 2001; Martin and Horlock, 2002; Munoz and Monterroso, 2002). While the recent increase in reliance on greenhouse‐grown transplants for cucurbit production could be contributing to BFB outbreak frequency, it is more likely that increases in BFB on non‐watermelon hosts are due to changes in the population structure of the pathogen.…”

“…citroides ), prickly paddy melon ( C. myriocarpus subsp. myriocarpus ) and several types of gourds in the USA, Australia, Costa Rica, Nicaragua, Taiwan, China, Japan and Brazil (Isakeit et al., 1997, 1998; Assis et al., 1999; Langston et al., 1999; Martin and O'Brien, 1999; O'Brien and Martin, 1999; Cheng et al., 2000; Shirakawa et al., 2000; Zhao et al., 2001; Martin and Horlock, 2002; Mora‐Umana and Araya, 2002; Munoz and Monterroso, 2002).…”

Rapid and sensitive detection of Acidovorax citrulli in cucurbit seeds by visual loop‐mediated isothermal amplification assay

“…Acidovorax citrulli (Schaad et al, ; Schaad, Sowell, Goth, Colwell, & Webb, ) is the causal agent of bacterial fruit blotch (BFB), a devastating disease of watermelon and other cucurbit species crop worldwide (Martin & Horlock, ). Since the first observation in commercial production field in 1965 (Webb & Goth, ), BFB has emerged as the most serious threat to watermelon and other cucurbit crops in many regions of the world (Burdman & Walcott, ; Burdman, Kots, Kritzman, & Kopelowitz, ).…”

Genetic diversity and pathogenicity of cucurbit-associated Acidovorax

“…Since the outbreaks in commercial watermelon fields in the USA from the late 1980s to the 1990s (Black et al 1994;Evans and Mulrooney 1991;Hamm et al 1997;Jacobs et al 1992;Latin and Rane 1990;Somodi et al 1991), BFB has gained great importance. The disease has been observed in many countries and in other cucurbits such as melon (Isakeit et al 1997;Sowell 1981), squash (Langston et al 1999;Martin and Horlock 2002), and cucumber . In Japan, Shirakawa et al (2000) first reported BFB in Yamagata Prefecture in 1998, and since then, the disease has been sporadic in certain prefectures (Horita et al 2006;Ogiso et al 2005;Tomita et al 2006).…”