EVALUATION OF INOCULATION TECHNIQUES TO SCREEN FOR BACTERIAL CROWN ROT RESISTANCE IN DIFFERENT BREEDING LINES OF CARICA PAPAYA
F.M. Dela Cueva, A.F. Waje, P.M. Magdalita, V.P. Justo, N. Pathania, L. Vawdrey
Bacterial crown rot (BCR) is considered as the most destructive disease of papaya in the Philippines. The use of resistant cultivars with acceptable horticultural traits remains the most effective and economical strategy to manage the disease. This study was conducted to develop a rapid and effective inoculation technique that could be used to screen for BCR resistance in a papaya breeding program. Furthermore, papaya breeding lines and germplasm collections were evaluated using the inoculation technique to identify promising materials that can either be released as commercial cultivars or used as parental lines. Different isolates of Erwinia mallotivora collected from Luzon and Mindanao, Philippines were pathogenicity tested to papaya seedlings cv. ‘Solo’. The most aggressive and virulent isolate was identified and used in the evaluation of various inoculation techniques. The leaf abrasion technique proved to be the most effective of the five inoculation techniques that were assessed namely: a) stem injection, b) pricking, c) leaf clipping, d) drenching and e) leaf abrasion. This technique was able to differentiate levels of resistance/susceptibility of the different breeding lines and cultivars. Fiftynine of the eighty parentals/inbreds/lines that exhibited resistance in the field with high BCR incidence were further evaluated using the leaf abrasion technique in the screen-house. Of these, nine parental lines, six inbred lines and five accessions exhibited resistance to BCR. These materials are now being grown in the field for horticultural trait evaluation.