A BREEDING STRATEGY FOR IMPROVING RESISTANCE TO STRAWBERRY BLACK SPOT (COLLETOTRICHUM ACUTATUM) IN THE UNITED KINGDOM

Two aggressive isolates (32008 and 32043) were selected to screen for resistance in the East Malling Research (EMR) germplasm collection and, over two years, 84 genotypes were tested. These included named cultivars, advanced selections and breeding lines from EMR and other programmes. A standardised procedure was used for 11 separate experiments but it was not possible to achieve a uniform disease pressure. Consequently, most genotypes were tested on two or more occasions and in most cases the results were consistent enough for a firm classification. Nine genotypes were identified that showed strong resistance: ‘Addie’, ‘EM1235’, ‘EM1315’, ‘EM1326’, ‘EM1395’, ‘Honeoye’, ‘Senga Sengana’, ‘US070’ and ‘US159’. Ten genotypes, ranging from very susceptible to highly resistant, were selected to use as parents in a crossing programme to investigate the inheritance of resistance. These were inter–crossed in a pattern of five overlapping 4 x 4 half-diallels, including selfs. The progenies were screened for resistance as young seedlings during four experiments. Two EMR lines (‘EM1326’ and ‘EM1395’) demonstrated good general combining ability for resistance. These lines are unrelated and have had good yield and fruit quality in EMR trials. They will thus be very valuable as parents for resistance in the commercial breeding programme.