Archivio Journal of Plant Pathology

Abstract:

In June 2015, crown galls were observed in a 30 day-old greenhouse crop of Aster sp. in Lecce province (southern Italy). Symptoms occurred on ca. 20% of plants and consisted of stunting and, below the soil line, white-cream spherical galls which progressively darkened. Two representative isolates, producing 5 mm-circular convex colonies with reddish center and whitish border on selective agar medium 1A, were designated DiSSPA Ag26 and DiSSPA Ag27 and subjected to biochemical assays according to Schaad et al. (2001). They were Gram-negative, oxidase positive, able to grow in 2% NaCl and in ferric ammonium citrate and produced 3-ketolactose, acidity from melezitose but not from erythritol, alkalinity from litmus milk but no alkali from malonic, L-tartaric and mucic acids and utilized citrate but not L-tyrosine. Morphological and biochemical characters of our isolates were similar to those of Agrobacterium tumefaciens species complex, formerly called A. tumefaciens biovar 1 (Costechareyre et al., 2010). In a phylogenetic tree based on the sequence of DNA gyrase subunit B gene (gyrB), constructed as per Puławska and Kałużna (2012), DiSSPA Ag26 (accession No. MF000330) and DiSSPA Ag27 (MF000331) clustered within the genomovar G1 of A. tumefaciens species complex, with the best match (99%) with Ch3 strain (HQ438217). Moreover, our isolates induced gall formation on stem of five week-old tomato cv. Marmande, tobacco cv. Samsun and on carrot disks after three weeks at room temperature from needle-inoculation of a bacterial cell suspension (108 CFU/ml). Re-isolated bacteria exhibited the same traits of the inoculated isolates. To the best of our knowledge, this is the first report of crown gall caused by A. tumefaciens species complex genomovar G1 on Aster sp. in Italy.