Response of traditional cultivars of Fagioli di Sarconi beans to artificial inoculation with common bacterial blight agents

Cultivars of the Fagioli di Sarconi are a pool of high value common bean (Phaseolus vulgaris L.) traditional cultivars selected from various landraces. These cultivars are protected by the European Union (Reg. CEE n° 1263/96) with the mark PGI (Protected Geographical Indication) and are cultivated in Basilicata (southern Italy) for the production of dry seeds. Fagioli di Sarconi cultivars are susceptible to common bacterial blight (CBB), a disease caused by the varieties fuscans and non-fuscans of Xanthomonas axonopodis pv. phaseoli. Five Fagioli di Sarconi cultivars (Tondino bianco, Verdolino, Cannellino, Tabacchino and Ciuoto) were artificially inoculated with two virulent strains of this bacterium, representative of 59 recently characterized strains of both the fuscans and non-fuscans varieties, with the aim to evaluate the susceptibility of these cultivars to the pathogens. Four CBB–resistant breeding–lines were used for comparison. Suspensions of the bacterium were injected into the first trifoliate leaflets of bean plants and produced typical CBB symptoms on the Fagioli di Sarconi cultivars, and hypersensitive necrotic lesions on the CBB–resistant breeding–lines. When cultivars were inoculated with the strain of the variety fuscans, Tondino bianco, Verdolino and Cannellino were more susceptible than Tabacchino and Ciuoto, whereas when they were inoculated with the non–fuscans strains, Tondino bianco, Tabacchino and Verdolino were more susceptible than Ciuoto and Cannellino. The tolerant cultivars appeared good candidates for the introgression of CBB–resistance characters in a breeding programme. The varying response of the traditional Fagioli di Sarconi bean cultivars to artificial inoculation suggests that several plant and pathogen factors are involved in the interaction between X. a. pv. phaseoli varieties and the bean cultivars