| Fusarium basal rot (FBR) caused by Fusarium oxysporum f. sp. cepae and pink root (PR) caused by Pyrenochaeta terrestris are two of the most important diseases that affect onion production resulting in yield losses. The use of resistant varieties provides the most effective control of FBR and PR, thus, the need to develop onion varieties with FBR and PR resistance. Publically available onion germplasm accessions resistant to FBR or PR were identified using seedlings in a controlled environment. FBR and PR selections were effective in increasing FBR and PR survival. Based on the performance of testcrosses, FBR resistance in W440B showed specific combining ability and dominance and PR resistance in W446B showed general combining ability and dominance. An annual seed to seed method which bypassed the bulb stage was successfully used to develop ten B5351C x W440B families segregating for FBR and eight B5351C x W446B families segregating for PR. Two segregating populations DehyA x B5351C and DehyA x SkiMsMs were used to map PR resistance. In DehyA x B5351C, one QTL for PR resistance was mapped to chromosome 4 at position 71.5 cM with a LOD score of 8.03, additive and dominant effects of -2.05 and 0.35, respectively, and explained 27.6% of the variation for PR phenotype. In DehyA x SkiMsMs, one QTL was also identified at chromosome 4 at position 65.1 cM with a LOD score of 10.05, additive and dominant effects of -2.33 and -0.32, respectively, and explained 35.2% of the variation for PR phenotype. In both cases, PR resistance was from the DehyA parent. This is the first report of mapping a major QTL controlling PR resistance in onion. Information on sources, combining ability, and effectiveness of selection to increase FBR and PR resistance will be valuable to develop FBR- and PR-resistant cultivars. Mapping of PR resistance will also be useful in breeding for PR-resistant cultivars and continue future research to understand the genetic mechanisms of PR resistance. |
