Author : Minguez, Lucille T.

Summary : Ralstonia solanacearum causes bacterial wilt in many plant species worldwide.Race 2 affects mostly Musa and Heliconia sp. but its invasion in root tissues and multiplication site in 'Cardaba' and 'Cavendish' remains unclear. This work provides data of morphological and histological symptoms in the two cultivars of banana. In the screenhouse, 4-month old tissue cultured 'Cardaba' and 'Cavendish' bananas were inoculated with moko and bugtok isolates of Ralstonia solanacearum Race 2. Inoculation was done by drenching 100 ml bacterial suspension standardized at 1 x 10 (9th power) cfu/ml around woulded and intact roots of bananas grown in 6 x 9 sq.in. clear plastic bag. The bacteria colonized and degraded the cell walls of the xylem vessels and intercellular spaces of 'Cardaba' and 'Cavendish' cultivars . They were abundant particularly in protoxylem vessels. The 'Cavendish' cultivar showed more colonized xylem vessels than 'Cardaba'. Regardless of root condition, the bugtok isolate was more aggressive as shown by 1.84-6.03 xylem vessels invaded per cross-section root at 14 DAI compared to moko with only .038-2.30 vessels invaded per cross-section root. The bugtok-inoculated 'Cavendish' with intact roots had the higher xylem colonization of 2.77-9.33 xylem vessels per root section at 14 DAI: however, at 28 DAI, the wounded 'Cardaba' inoculated with the same bacterial isolate had the higher xylem colonization (3.07-7.57 vessels per root). The moko isolates poorly invaded the xylem vessels and walls of both cultivars. Tyloses were however, detected in both cultivars with wounded root suggesting that wounding induced tyloses formation. In intact roots, there were no tyloses observed. Results also suggested that wilting was not only due to bacterial occlusion but more on the destruction of cell walls of xylem vessels.