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Zhongbo Ren and Jiang Lu

Non-native grape species such as V. vinifera and V. labrusca can not sustain the hot and humid environment of Florida due to their susceptibility to various diseases. Vitis rotundifolia (muscadine grapes) is native to Florida and the southeastern United States and adapted well to this climate condition. They are highly resistant to almost all grape foliage diseases and root pests such as nematode and phylloxera. Theoretically, muscadine grapes may become a valuable rootstock for bunch grapes. Unfortunately, most previous studies found that muscadine grapes were graft-incompatible with bunch grapes by normal grafting techniques. This study was to look for an alternative technique to graft V. vinifera onto muscadine rootstocks. A preliminary study indicated that bunch grape scions were successfully grafted on adult muscadine grapes. Two V. vinifera grape cultivars, `Thompson Seedless' and `Chardonnay', and two muscadine grape cultivars, `Carlos' and `Alachua', were used for this study. The muscadine grapes used as rootstocks are 6-year old field-grown vines and V. vinifera was used as scions. Using the common V-type grafting method was completely failed in more than 150 attempts. We then tried to insert the first-year buds of V. vinifera into 1- to 3-year-old muscadine canes. Surprisingly, the survival rate of the inserting buds was moderately high when `Carlos' was used as the rootstock. `Thompson Seedless'/`Carlos', `Chardonnay'/`Carlos' reached 53% and 33%, respectively. Successful grafting but lower survival rate was also obtained when `Alachua' was used as the rootstock (10% in `Thompson Seedless/`Alachua' and 3% in `Chardonny'/`Alachua'). The average survival rate of `Thompson Seedless' on the muscadine rootstocks was 36%, and `Chardonnay' was 12%. Regardless the cultivar of the scions, buds survived on `Carlos' and `Alachua' rootstocks were 44% and 5%, respectively. Results from this study indicated that V. vinifera grapes could be successfully grafted onto muscadine rootstocks. The survival rate varied depending on cultivars used for both scion and rootstock. It would be very interesting to see if resistance to certain diseases such as the Pierce's disease can be improved in those V. vinifera grape with muscadine roots and trunks derived from this preliminary study.

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Jiang Lu and Bernard Prins

The grape belongs to the genus Vitis L., which are divided into two subgenera, Euvitis Planch. and Muscadinia Planch. The Euvitis has 50 to 70 species, in which V. vinifera L. is a predominant species with hundreds of known commercial cultivars grown world wide. The Muscadinia (muscadine grapes) consists of only two to three species predominated by V. rotundifolia and only commercially cultivated in the southeastern United States. V. rotundifolia is known by its multiple resistance to almost all grape diseases and insects found on the Euvitis species, while the latter possesses good fruit characteristics that do not exist in muscadines. Attempts to produce rotundifolia-vinifera hybrids to combine good fruit quality and disease resistance of both into F1 hybrids have been made by grape breeders for many years. Limited success was reported when the V. vinifera was used as seed parents. This research extended the interspecific crosses beyond V. vinifera into other Euvitis species. Among the Euvitis species, A. aestivalis, V. cinerea, V. champinii, V. labrusca, V. monticola, V. nesbittiana, V. riparia, V. rupestris, V. thunbergii, V. quinguangularis, all with pistillate flowers, were used as female parents pollinated with V. rotundifolia pollen. Eight out of the 10 cross combinations except V. cinerea and V. thunbergii set fruits. However, most of the Euvitis-rotundifolia crosses had extremely low fruits set (<1% of pollinated flowers). The only exception was V. labrusca cv. Woodruff, which had very high percentage of fruit set (70%). Interestingly, the fruits of V. labrusca cv. Woodruff × rotundifolia were pathonocarpic that had only half size of regular fruits set from open pollination with pollen sources from other Euvitis species. In the reciprocal crosses, three pistillate V. rotundifolia cultivars, `Fry', `Higgins', `Jumbo', were used as female pollinated by pollen from Euvitis species. Limited fruit sets were found from the crosses of V. rotundifolia × V. shuttleworthii, V. cordifolia, V. rupestris, V. Piasezkii, V. quinquagularis. Results from this study indicated that hybridization between Euvitis and muscadinia species is indeed very difficult but it is possible, and some Euvitis species are cross more compatible with V. rotundifolia than the others.

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Jiang Lu and Olusola Lamikanra

Fluorescence microscopy was used to examine the unilateral intersubgeneric incongruity of muscadine grape (Muscadinia Planch.) × bunch grape (Euvitis Planch.). Pollen grains of bunch grape hydrated and germinated on the stigmas of muscadine grape. Healthy pollen tubes of the bunch grape also penetrated the stigma and entered into the style without obstacles. However, most bunch grape pollen tubes were arrested in the style near the stigma, and few bunch grape pollen tubes were found at the base of the style. Barriers to the intersubgeneric crosses apparently occurred before fertilization; abortion of pollen tubes in the style was the major cause of failure for the cross of V. rotundifolia Michx. × Euvitis.

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Jiang Lu and Lloyd Schell

Vitis rotundifolia (Muscadine grapes), a native species characterized with multiple resistance to grape diseases and insects, are cultivated throughout the southeastern U.S. for fresh fruit and processing. However, the species falls short of consumer's expectation as fresh fruit due to its seediness and thick skin. However, Vitis vinifera, a predominant Vitis species grown worldwide possesses good fruit characteristics such as seedlessness and edible skin but is susceptible to many diseases. Attempts to produce rotundifolia-vinifera hybrids to combine good fruit quality and disease resistance of both into F1 hybrids have been made by grape breeders for many years. Limited success was only reported when the V. vinifera was used as seed parents. Pollinating seedless vinifera pollen onV. rotundifolia stigma was made in 1993 and 1994. More than 20,000 flowers from 34 cross combinations were pollinated. These crosses were made to see if there is any chance to produce hybrids when muscadine grapes were used as female parent and specifically to introgress the seedlessness from European grapes into muscadine grapes. A few hundred seeds were collected from these crosses and germinated in a greenhouse. Two seedlings were clearly distinguished from the others with morphology intermediate between muscadine and the vinifera grapes, while the rest looked straight muscadine grapes derived from possible contaminated pollination. This conclusion was further confirmed by isozyme and DNA markers. One of the seedlings produced from the cross of `Jumbo' × `Thompson Seedless' grew vigorously and has been setting fruit since 1996. Fruit are mixture of stenospermocarpic and pathonocarpic seedlessness. Fruit setting and pollen viability test indicated that this hybrid is at least partly self-fertile. Many other characteristics of the hybrid, such as leaves, stems, tendrils, time of budbreak, bloom date, and ripen date are intermediate between muscadine and bunch grapes. The hybrid is resistant to Pierce's disease, anthracnose disease, and downy mildew, which are the limited factor to growing V. vinifera in the hot and humid southeastern U.S. This is the first report of a seedless hybrid from V. rotundifolia × V. vinifera.

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Xia Xu*, Zhongbo Ren and Jiang Lu

Pierce's Disease (PD) is a major factor limiting grape production in the southeast United State. This disease is caused by a bacterium, Xylella fastidiosa Wells et al., which is transmitted to the xylem system of the grapevines primarily by glassy-winged sharpshooters (Homalodisca coagulata Say). Once it is in the xylem, the X. fastidiosa will use the xylem sap as a nutrient source to multiply, colonize, and eventually plug the xylem vessels and cause the PD in susceptible cultivars. On the other hand, symptoms of PD in tolerant cultivars do not appear until fruit maturation, and symptoms are rarely observed in PD resistant cultivars. In order to understand the correlation between X. fastidiosa and PD symptom development, a study was initialed to monitor X. fastidiosa in xylem of resistant, tolerant, and susceptible vines on a monthly basis. Presence of X. fastidiosa was detected directly from xylem sap of field-grown vines by medium culture and confirmed by polymerase chain reaction (PCR). Xylella fastidiosa was detectable throughout the growing season in PD susceptible cultivar `Chardonnay', PD tolerant Florida hybrid grape `Blanc du Bois', and muscadine cultivar `Carlos'. The bacteria were also appeared in the dormant vines with high density in cultivars `Chardonnay' and `Blanc du Bios'. Although X. fastidiosa was also found in dormant canes of `Carlos', the density decreased throughout the late fall and winter months, and they were hardly found before June. The results indicated that X. fastidiosa were carried over from previous season in cultivars `Chardonnay' and `Blanc du Bois', while in PD tolerant cultivar `Carlos', they were newly acquired from the sharpshooter feedings during the growing season.

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Zhongbo Ren*, Jiang Lu* and Xia Xu*

Muscadine grape industry in the southeastern United Sates is expanding in recent years. To provide necessary information for the growing industry, 50 muscadine grape cultivars were evaluated for vigor and fruit characteristics at Florida A&M Univ., Tallahassee, Fla. Vine vigor was measured by winter pruning weight and varied from 5.4 lb/vine to 35.7 lb/vine. Among these cultivars, Triumph, Summit, and Tara were the least vigorous, while `Carlos', `Fry Seedless', and `Gold Isle' produced the most pruning weight. Dry scar ranged from 60.6% (Darlene) to 97.7% (Dixie Red). Among the most important table grapes, `Nesbitt', `Alachua', `Jumbo', `Fry', `Triumph', and `Scarlete' showed more than 70% of dry scars. Fruit rot ranged from 0.3% (Gold Isle) to 31.8% (Dixie Land). `Noble', `Scarlet', `Nesbitt', and `Carlos' were the important cultivars with less than 5% rotted fruits. Commercial fruit index were different significantly among the cultivars, ranged from 45.5% to 96.4%. Higher commercial fruit index of table grapes were found with `Magnolia', `Rosa', `Scarlet', and `Tara', while `Dixie Land' (45.5%) was the least. Seeds per fruit varied among the cultivars, ranging from 2.4 to 4.9. Fewer fruit seeds were found in `Fry' and `Nesbitt', while `Granny Val', `Senoria', `Darlene' and `Triumph' had more seeds per fruit than the others. Seed size also differed among the cultivars. `Sugar Pop' had the largest seeds (0.144 g/seed), which was twice as the size of the smallest seeds of `Welder' (0.056 g/seed). Fruit soluble solids content (SSC) ranged from 11.7% to 16.9% among the cvs. evaluated. Higher SSCs were found in `Welder', `Fry Seedless', `Scarlet', and `Cowart', while `Senoria' and `Jumbo' had relatively low SSC.

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Zhongbo Ren, Jiang Lu and Xia Xu

`Pam' is a popular muscadine grape (Vitis rotundiforia) used for the fresh fruit market. It is characterized with large berry, nice appearance, good texture and flavor, and high disease resistance. This cultivar, however, requires pollinators because it is pistillate. To select a better pollinator for this pistillate cultivar, a 2-year study was conducted at Florida A&M University in 2003 and 2005. Fresh pollen of muscadine grape `Alachua', `Nesbitt', and `Noble' was used for pollination. `Nesbitt' pollen resulted in 100% of the pollinated clusters setting fruits in both years, while pollination with `Alachua' yielded 70% (2003) to 87% (2005) of fruiting clusters, and `Noble' pollen yielded 72% (2003) and 97% (2005) fruiting clusters, respectively. Fruit numbers per fruiting cluster also varied among pollen sources. `Alachua' pollen resulted in 7.2 (2003) and 8.1 (2005) fruits per cluster, while `Nesbitt' produced 10.1 (2003) to 10.5 (2005) fruits per cluster, and `Noble' produced 8.3 (2003) and 9.0 (2005) berries per cluster. Open pollinated `Pam' had 100% clusters set fruits, averaging about 11 fruits per cluster in both seasons. No difference of berry size was observed among fruits produced from different pollen sources. Both sugar contents and acids levels were a little bit higher in 2005 than that in 2003. However, no differences of sugar content and acid level were found among the fruits derived from different controlled pollen sources. These data suggested that `Nesbitt' is a better pollinator than `Alachua' and `Noble' for `Pam' muscadine grape.

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Jiang Lu, Olusola Lamikanra and Stephen Leong

Gibberellic acid (GA3), a plant growth regulator used routinely in the production of seedless bunch grapes, was sprayed on the seeded muscadine grape cultivar Triumph. GA3 at 100, 200, and 300 mg·L-1 was sprayed on the leaves and fruit clusters at late bloom; a second spray followed 1 week later. The sprayed vines produced more than 20% seedless berries and the size of the berries with seeds increased significantly. GA3 application in commercial muscadine grape production may have potential benefits.

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Jiang Lu, Elvis Clarke and Zhong-bo Ren

Although some of the American native Vitis species and their hybrids, particularly those originated from the southeastern United States, have been known for resistance to Pierce's disease (PD), their resistant status against the glassy-winged sharp shooter [GWSS, Homalodisca coagulata (Say)], the vector transmitting PD pathogen (Xylellafastidiosa Well), has not been reported. To determine GWSS feeding preferences on different grape species/cultivars and correlations of feeding to Pierce's disease development, a survey was conducted at Florida A&M University, Tallahassee. The feeding preference of GWSS on different species/cultivars was evaluated in two different ways: 1) count the number of GWSS on different grapevines in the field; and 2) determine the feeding preference by measuring the excretion of the GWSS feeding on difference grape species/cultivars, including highly susceptible V. vinifera cultivars, native American grape species and hybrids, and muscadine grapes. Results from this study indicated that the frequency of GWSS visits on different grapevines varied among the species/cultivars investigated. For example, PD-resistant grape V. rotundifolia (muscadine grape) had significantly fewer GWSS visits than did the PD-susceptible V. vinifera grape. The frequency of GWSS visits to V. labrusca, the native American grape susceptible to PD, was intermediate between those found on V. rotundifolia and V. vinifera. Similarly, the GWSS sucked more xylem sap when they fed on PD-susceptible grapevines than on PD-resistant ones. Overall, there is a positive correlation between the GWSS visits/feeding and the status of grapevine resistance/susceptibility to Pierce's disease.

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Xia Xu, Jiang Lu and Zhongbo Ren

Ploidy level in grapevines varies, especially since in vitro techniques are employed in the breeding process and after plants are treated with either chemicals or radiation. Detection of ploidy level in grapevines by microscopic chromosome counting is complicated by their high number and the small size of chromosomes. Flow cytometry provides an accurate and rapid method in determining the ploidy level in plant tissue by measuring the nuclear DNA content in living cells and thus is a very useful tool in plant breeding or genetic studies. The objective of this research was to analyze the ploidy level of a selected group of muscadine vines that were different from normal diploid vines in morphology. These grapes were derived from either chemical treatment of known varieties or from controlled/open pollinations. Among the 26 grapevines investigated, 8 were found to be diploids, 11 were tetraploids, and 7 were chimeric aneuploids. Results of this study indicate that flow cytometry is a quick, reliable tool for determining ploidy levels of grapevines.