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- Author or Editor: O. Lamikanra x
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Angular leaf spot is a common but rarely studied disease of muscadine grapes (Vitis rotundifolia Michx.) in the southeastern United States. During 1994 and 1995, we performed two field evaluations of angular leaf spot on 30 muscadine cultivars. Based on disease severity data, no cultivar was immune to angular leaf spot; however, `Albermarle', `Doreen', `Higgins', `Noble', `Regale', `Scuppernong', `Southland', and `Summit' showed high degrees of resistance. `Alachua', `Darlene', `Dixie Red', `GA-3-9-2', `Jane Bell', `Janet', `Jumbo', `Pam', and `Rosa' were susceptible.
Gibberellic acid, a plant growth regulator commonly sprayed for seedless bunch grape cultivars, was used to spray on the seeded muscadine grape cultivars `Carlos', `Fry', `Higgins' and `Triumph'. GA3 at 100 to 300 ppm were sprayed on leaves and fruit clusters before and after anthesis. The flower/fruit clusters also were dipped into a much higher concentration (1000 ppm) in addition to the sprayed concentration of GA3. Berry weight significantly increased in all the sprayed vines, with a maximal increase up to 50%. Early and more uniform ripening was observed in the cultivar `Triumph'. More than 20% of seedless berries also were found on the GA3-sprayed `Triumph' vines. However, the latter two responses (early ripening and seedlessness) did not occur in other cultivars tested. Similar results also were obtained in the dipping treatments. The results indicated that the seeded muscadine grapes responded well to the GA3 treatments in general, but genotype variation is obvious.
Low frequency of in vitro regeneration has hampered the adoption of genetic engineering technique for improving the quality of muscadine grape. This study is to develop a straightforward method for high-frequency regeneration of muscadine grapes in vitro. Leaves, petioles, and immature ovules of muscadine grapes were cultured on various media. Embryogenic callus, somatic embryos were formed after 9 weeks inoculated on embryo rescue (ER) medium. The somatic embryos were isolated and subcultured on fresh medium to promote enlargement and increase the number of uniformly sized somatic embryos. Of the medium tested (MS, NN, and ER), the ER medium was the best for somatic embryo growth and multiplication. The somatic embryogenic lines were maintained by transferring the embryos to the fresh ER medium every 4 weeks. Germination was achieved by transferring these embryos to woody plant medium or NN medium. The frequency of somatic embryogenesis of embryo germination appeared to be genotype dependent. The establishment of the somatic embryogenesis system in this study should be a step forward in directly transferring a foreign gene into muscadine grape.
Resistance to grape anthracnose [Elsinoë ampelina (de Bary) Shear] was evaluated in 13 known Vitis species and five taxonomically undescribed grapes native to China. One hundred and eight clones of Chinese Vitis species were tested under field conditions between 1990 and 1992. Berry infection did not occur in these species. Leaves displayed strong resistance to anthracnose, although intraspecific variations were observed. There was no relationship between anthracnose resistance and geographical origin of the species. Results from this study indicate that oriental grape species are useful for disease-resistance breeding.
The grape is an important horticultural crop that is grown worldwide. Breeding a new grape cultivar by conventional means normally will take several generations of backcross, at least 15 years. The efficiency and speed of selection can be accelerated if genetic markers are available for early screening. This project is designed to generate RAPD markers linked to viticulturally important traits, including seedlessness and pistillate genes. A F1 population with 64 progenies of V. vinifera was used for the RAPD analysis. Bulked Segregant Analysis (BSA) method was used for RAPD primer screening. Three-hundred primers were screened between the two pairs of pooled DNA samples, seeded and seedlessness, pistillate and perfect flowers. At least 10 primers produced one polymorphism each between the pools. Further analysis revealed that one of these RAPDs cosegregated tightly with the seedlessness trait, while the others either had loose linkage or no linkage to the traits. To make the RAPD marker useful for breeding selection, an attempt was made to convert it into SCAR marker. The results demonstrated that the RAPD marker may be useful for grape breeding and interpreting inheritance of a particular trait in grapes.