Archivio Journal of Plant Pathology

Abstract:

In the late summer of 2014, two weeks after a heavy rain, severe soft rot symptoms, especially in flooded areas, were observed on cauliflower (Brassica oleracea L. var. botrytis) cultivars Littoral F1 (Clause) and Terzolo F1 (Enza Zaden) grown in a 5 ha-field located in Potenza province (Basilicata, Southern Italy). Symptoms consisted of a progressive yellowing and withering of basal leaves, dark green to brown and then white creamy soft rot of pith followed by totally hollow stem and wilting of the whole plant. Three of the bacterial isolates that produced typical deep cup-shaped cavities on crystal violet pectate (CVP) agar medium were designated DiSSPA 42, DiSSPA 45 and DiSSPA 46 and identified by biochemical and physiological assays (Schaad et al., 2001). They were Gram-negative, oxidase-negative, able to degrade pectin and to produce reducing substances from sucrose, acids from α-methyl-glucoside, sorbitol, D-arabitol, palatinose and maltose but not from acetic acid, D,L- lactic acid and dextrin. They utilized citrate, but did not produce indole, and induced hypersensitive reaction on tobacco leaves. Species identification of one isolate, DiSSPA 42, was also confirmed by multi-locus sequence analysis (MLSA) using the genes Glyceraldehyde-3-phosphate dehydrogenase A (gapA; primers gapA326F/gapA845R) and Malate dehydrogenase (mdh; primers mdh2/mdh4) (Onkendi and Moleleki, 2014). MLSA indicated DiSSPA 42 belonging to Pectobacterium carotovorum subsp. odoriferum. Its nucleotide sequences were deposited in GenBank under accession Nos. KX346907 and KX346908. The three isolates incited stem soft rot symptoms at 26 ±1°C three days after inoculation on four weeks old cauliflower plants cv. Littoral F1. To the best of our knowledge, this is the first report of stem soft rot on cauliflower in Italy, and Europe, caused by P. carotovorum subsp. odoriferum.