PLANT-TO-SEED TRANSMISSION OF CURTOBACTERIUM FLACCUMFACIENS pv. FLACCUMACIENS IN A DRY BEAN CULTIVAR

Bacterial wilt is a disease that causes serious bean crop losses in Brazil, and its causal agent, the bacterium Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), is seed transmitted. Recommendations for managing the disease in the field include the use of pathogen-free seed, crop rotation, and resistant cultivars of dry bean. Transmission of Cff from plant to seed was evaluated in three assays with six different dry bean cultivars (IAC Carioca, IAC Carioca Arua, IAC Carioca Akyta, IAC Carioca Pyata, IAC Carioca Tybata, and Perola). Plants of these cultivars were inoculated with a Cff isolate by stem puncture and the disease symptoms were evaluated using a scale. To assess bacterial transmission to seeds, three assays were made analysing in each 500 seeds of the cultivars IAC Carioca, IAC Carioca Arua, IAC Carioca Akyta, IAC Carioca Pyata, and IAC Carioca Tybata respectively, whereas for the cv. Perola 46, 155, and 87 seeds were analysed in the first, second, and third assay, respectively. These seeds were macerated individually in distilled and sterilized water, and soaked for 24 h at 5°C. The resulting suspension was streaked on Petri dishes containing semi-selective medium for Cff, and incubated at 28°C for 96 to 120 h. Typical colonies for Cff were purified on 7% NSA+NaCl medium, after which Gram staining, KOH, and pathogenicity tests were conducted. Isolates from the first and second assays were characterized by Microlog2TM, and those of the third assay with PCR. Results showed that on cvs IAC Carioca Arua, IAC Carioca Akyta, IAC Carioca Pyata, and IAC Carioca Tybata low levels of disease developed, indicating resistance to bacterial wilt, whereas cvs Perola and IAC Carioca were highly susceptible in all the assays. With respect to transmission of Cff from plants to seeds, cvs IAC Carioca Akyta, IAC Carioca Pyata, and IAC Carioca Tybata showed no transmission, whereas IAC Carioca Arua showed a 5.5-14.8% level of transmission. Cvs IAC Carioca and Perola showed the highest levels of transmission, namely 10.4-70% and 32.61-74.2%, respectively.