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The phylogenetic relationships among members of the family Comamonadaceae and several unclassified strains were studied by direct sequencing of their PCR amplified 16S rRNA genes. Based on the 16S rRNA gene sequence analysis, members of the family formed a coherent phylogenetic group. The closest relatives are species of the Rubrivivax subgroup: Leptothrix discophora, Ideonella dechloratans, and Rubrivivax gelatinosus. The genus Hydrogenophaga formed two subclusters, as did the species of Acidovorax, whereas the five generically mis-named species of Aquaspirillum were polyphyletic. Comamonas acidovorans was phylogenetically distant from the type species of Comamonas, Comamonas terrigena. On the basis of this work and previous studies, Comamonas acidovorans is removed from the genus Comamonas, and renamed as Delftia acidovorans gen. nov., comb, nov A description of the new genus Delftia is presented.Using the BIOLOG system, combined with additional phenotypic and genotypic characterisations and pathogenicity tests on millet, melon and sugarcane, Australian isolates from millet and sugarcane were identified as A. avenae subsp. avenae, and isolates from melon were identified as A. avenae subsp. citrulli. The North Queensland sugarcane isolates and qPseudomonas calatheaq strains were identified as A. avenae.A rep-PCR analysis using the BOXA1R primer showed that 78 strains of A. avenae and A. konjaci were very diverse in their genetic profiles. Cluster analysis of BOX-PCR fingerprinting divided the 77 strains of A. avenae and 1 strain of A. konjaci into 33 clusters at a similarity of 75 %. The 13 Australian millet strains of A. avenae subsp. avenae were distributed in 8 clusters. The American melon strains have slightly different patterns from the Australian melon strains. Among Australian melon strains, South Queensland strains were different from North Queensland strains in their BOX- PCR banding patterns.Pathogenicity tests revealed that there were two distinct groups within A. avenae. The first group consists of strains of A. avenae subsp. avenae, which are pathogenic on millet and sugarcane but not on melons. The second group contains strains of A. avenaensubsp. citrulli from melons, which are pathogenic on melons, but not on millet and sugarcane. Strains identified as A. avenae subsp. avenae from maize, sugarcane, millet, teosinte, canna, rice, Vaseygrass, and sorghum were pathogenic on millet, despite their diverse geographic origin. Symptoms on millet consist of stripe, streak, spot, and blight, and strains could be classified into five groups based on symptoms. Strains of A. avenae subsp. citrulli from watermelon and rockmelon differ in their virulence on cultivars of rockmelon. Rockmelon strains were not always more virulent on rockmelon, and some strains from watermelon were more virulent than the rockmelon strains on rockmelon.This study has developed a reproducible and quick bioassay to assess resistance in future tests. In a screening of 23 commercial millet accessions with 3 strains of A. avenae subsp. avenae, Setaria italica (Italian millet) accession TS108073 was the most resistant millet germplasm and Panicum miliaceum (French millet) accession SP109138 was the most susceptible.n n n n n n n n |
