Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 22, 2008
Publication Date: February 27, 2008
Citation: Ramming, D.W. 2008. Breeding Table Grapes with Resistance to Powdery Mildew. In: Proceedings of San Joaquin Valley Table Grape Seminar, California Table Grape Commission, February 27, 2008, Visalia, California. Interpretive Summary: Powdery mildew is the single most important fungal disease of grapes in the world. All currently available table grapes grown in California are susceptible and can not be grown with sprays to control this disease. Resistant germplasm has been selected and is being used in a breeding program to develop seedless table grapes with resistance to powdery mildew. In 2007 11 seedless x seedless crosses produced 841 plants and 10 seeded x seedless crosses produced 2,101 seed. Twenty-seven second generation backcross selections have been made and their fruit quality is being improved over the original disease resistant types. Thirty-eight have very small, commercially acceptable aborted (seedless) seeds and berry size is nearing commercial acceptance. Inheritance and mechanism of resistance is being studied in three families. Resistance from V. romanetii appears to prevent penetration of the fungus and resistance segregates into the distinct classes of either resistant or susceptible. Resistance from M. rotundifolia and V. aestivalis shows a gradation of response from resistant to susceptible. To date 128 molecular markers have been found to segregate in these populations and will be used for mapping and determining markers for marker assisted selection in the breeding program.
Technical Abstract: Different mechanisms for resistance to powdery mildew exist in grape germplasm. M. rotundifolia and V. aesitvalis progeny show a gradation in response from resistant to susceptible, suggesting multiple resistance genes. V. romanetii progeny segregate into the distinct classes of highly resistant or highly susceptible. Its resistance appears to prevent penetration of the fungus. Molecular markers are being developed to identify resistant genes from different grape sources so they can be pyramided into one variety for durable resistance. In 2007, 11 seedless x seedless table grape crosses for powdery mildew resistance were made and produced 3,093 ovules, 1,157 embryos and 841 plants to date. Ten seeded x seedless crosses resulted in 2,101 seed. Of the 145 F1 and 170 BC1 advanced selections originating from 25 genotypes propagated in the no spray field at Parlier, 167 fruited and were evaluated in the laboratory. Based on field PM evaluations, 106 were free of mildew on the leaf, fruit and stem. Forty three were noted as potential parents based on fruit quality and resistance. Of these resistant selections 22 had small seed traces that would be commercially acceptable. An additional 16 F1, 69 BC1 and 27 BC2 advanced table and raisin powdery mildew resistant selections have been made from over 2,000 seedlings at Parlier. Of these new selections, 38 have commercially acceptable aborted seeds and 7 were rated as the best parents.