Submitted to: International Society for Horticultural Science Meeting
Publication Type: Proceedings
Publication Acceptance Date: 2/8/2008
Publication Date: 3/1/2009
Citation: Johnson-Cicalese, J., Vorsa, N., Polashock, J.J. 2009. Breeding for fruit rot resistance in vaccinium macrocarpon. In: Proceedings of the Ninth International Vaccinium Symposium, July 14-16, 2008, Corvallis, Oregon. p.191-195. Interpretive Summary:
Technical Abstract: The cranberry fruit rot complex can cause severe crop loss and requires multiple fungicide applications each year. To identify sources of fruit rot resistance, fungicides were withheld from our germplasm collection in 2003 and 2004 and the collection was rated for fruit rot (1-5 scale, 1=no rot, 5=nearly 100% rotten fruit). In Sept. 2003, 70% of the plots had severe rot (392 out of 562 accessions had a rating of ‘5’), while 6% showed some resistance (33 plots with a rating of ‘1’ or ‘2’). Fruit was harvested and counts ranged from 5% to 100% rotten fruit, confirming visual ratings. In 2004, several accessions continued to show resistance and there was a close correlation between the 2003 and 2004 ratings (r=0.80) and counts (r=0.70). Three of the resistant accessions had previously been used in crosses and their progeny were planted out in a large progeny evaluation trial. Fungicides were withheld in 2005-2007 and the trial was rated each year for fruit rot. In 2007, disease pressure was so severe that of the 1644 plots evaluated from 30 crosses (4 of these crosses had a resistant parent), 1085 plots had a rating of ‘5’ (nearly 100% rot), while only 13 plots had a rating of ‘2’. The families from resistant parents had a higher frequency of resistant progeny, indicating the potential for improving resistance. However, a few resistant progeny originated from susceptible parents. Fruit cultured from susceptible and resistant plots had the same species of fruit rot fungi present (primarily Phyllosticta vaccinii, Physalospora vaccinii, and Glomerella cingulata), suggesting broad-based resistance. DNA fingerprinting of resistant accessions identified several genetically-distinct types, offering potentially different sources of resistance. These fruit rot-resistant plants have now been used in 60 crosses. Molecular markers for resistance are being developed, which will allow for more efficient progeny screening.