Fig. 3. Mean brix of expressed juices from mature fruits of R2 generation trees derived from original crosses of a non-transgenic pollen parents with Fig. 4. Brix measurements for expressed juices from mature fruits harvest- transgenic lines of ‘F65’ papaya. ed on different dates from R2 generation trees. papaya market where sweetness of the fruit is not an impor- four of the 17 original transgenic lines and all six of the orig- tant factor. Overall, the brix measurements declined with the inal pollen parents. onset of cooler temperatures in January and February (Fig. 4). Although resistance to PRSV was a major selection factor Literature Cited in the previous R1 generation where 24% of the plants had be- come naturally infected by the virus in the field resulting in Conover, R. A. 1964. Distortion ringspot, a severe disease of papaya in Flori- the elimination of some breeding lines, only 2 of the 1196 da. Proc. Florida State Hort. Soc. 77:440-444. Conover R. A., R. E. Litz, and S. E. Malo. 1986. ‘Cariflora’- a papaya ringspot plants of the R2 generation developed PRSV symptoms. In virus-tolerant papaya for South Florida and the Caribbean. HortScience both generations, some plants sustained substantial damage 21:1072. due to infestation by mites and were eliminated from further Gonsalves, D. 1998. Control of papaya ringspot virus in papaya: A case study. consideration. Other factors, such as uneven fruit set at differ- Ann. Rev. Phytopath. 36:415-437. Tennant, P. F., G. Fermin, M. Fitch, R. Manshardt, J. L. Slightom, and ent times of the year, fruit shape, and general vigor of the tree D. Gonslaves. 2001. Papaya ringspot virus resistance of transgenic Rain- were considerations taken into account during the selection bow and SunUp is affected by gene dosage, plant development, and coat process. Altogether, 24 individual trees were selected for fur- protein homology. Euro. J. Plant Path. 107:645-653. ther variety development efforts. These selections represent Proc. Fla. State Hort. Soc. 116:6-8. 2003. DIEBACK CAUSED BY VERTICILLIUM DAHLIAE ON BLIGHIA SAPIDA ROBERT T. MCMILLAN JR.1, W. R. GRAVES AND T. F. WOOD Additional index words. fungus, fungus inoculation, tree dieback University of Florida Tropical Research and Education Center Abstract. Akee trees (Blighia sapida K. Koenig) with wilt/dieback 18905 SW 280 St. symptoms were found in a local south Florida commercial Homestead, FL 33031 planting during the spring of 1999. A fungus, isolated from the roots onto V-8 agar, was identified as Verticillium dahliae Kleb. by the Division of Plant Industry. Twenty Akee seedlings were R. M. LEAHY transplanted into 3.85 L plastic pots and grown in a greenhouse Plant Pathology at 28 °C-day/23 °C-night temperature. When the plants were ap- Department of Agriculture, DPI proximately 25 cm in height, stabbing a 15 cm long knife, four Gainesville, FL 32608 times into the root zone, severed the roots. A standard plate of uninoculated V-8 Agar was blended with 160 mL of sterile water and 15 mL of this slurry was poured into the disturbed soil of This research was supported by the Florida Agricultural Experiment Sta- each of 10 control plants. A slurry, made and applied as above, tion, and approved for publication as Journal Series No. N-02390. using a 2-week-old culture of V. dahliae onV-8 Agar, was used 1Corresponding author. to infest the soil around the 10 treatment plants. Plants were 6 Proc. Fla. State Hort. Soc. 116: 2003. kept in the greenhouse. After 6.5 weeks, leaves of inoculated plants had symptoms of marginal leaf burn. No symptoms were seen on the control plants. Verticillium dahliae, was isolated from the roots of the inoculated plants. Young akee trees (Blighia sapida) have declined or died- back slowly in scattered areas of a grove in Miami-Dade Coun- ty, Florida. The trees were planted in soils in which vegetables had been grown previously (Conover, 1959). During the spring of 1999 discolored roots of affected trees yielded Verti- cillium dahliae Kleb (McMillan et al., 2002). The purpose of the study was to reproduce the disease in akee. Materials and Methods A fungus, isolated from the roots onto V-8 agar, was iden- tified as Verticillium dahliae Kleb. by the Division of Plant In- dustry. Twenty akee seedlings were transplanted into 3.85 L Fig. 2. Necrotic leaf symptoms of Verticillium dahliae inoculated Akee plastic pots and grown in a greenhouse at 28 °C-day/23 °C- (Blighia sapida) seedlings in the greenhouse. night temperature. When the plants were approximately 25 cm in height, stabbing a 15 cm long knife, four times into the treatment plants. Plants were kept in the greenhouse at the root zone, severed the roots. A standard plate of uninoculated above temperature setting observed daily. V-8 agar was blended with 160 mL of sterile water and 15 mL of this slurry was poured into the disturbed soil and damaged Results and Discussion roots of each of 10 control plants. A slurry, made and applied as above, using a 2-week-old culture of V. dahliae on V-8 agar, One or more branches died and the leaves became was used to infest the soil and damaged roots around the 10 brown, but most of the leaves remained attached to the dead branches (Fig. 1). Wood (Fig. 3) and roots of affected plants showed brown discoloration typical of the Verticillium wilt disease in woody trees (Marlatt and Goldweber, 1969; Marlatt et al., 1970). Forty-six days after inoculation, a few leaves on the 10 in- oculated trees dried slowly from their tips to their petioles. The affected leaves did not hang loosely, but twisted slightly as they dried (Fig. 2). Since these plants were grown in the greenhouse at the temperatures listed in the materials and methods section, dead leaves were a tannish-brown. No symp- toms were observed on the control plants. V. dahliae was recovered from the discolored roots only from the inoculated trees. The Akee grove is visited periodi- cally and this disease continues to spread from infected trees to healthy trees. In 1999 only five trees out the grove of 40 trees were showing decline and to date 20 trees are affected. Fig. 1. Verticillium dahliae infected Akee (Blighia sapida) tree showing ter- Fig. 3. Discolored vascular tissue caused by Verticillium dahliae of Akee minal dead branches, leaf necrosis. (Blighia sapida) tree in the infected grove. Proc. Fla. State Hort. Soc. 116: 2003. 7 Literature Cited Marlatt, R. B., R. J. Knight, Jr., and S. Goldweber. 1970. Verticillium wilt of mango (Mangifera indica) in Florida. Plant Dis. Rptr. 54:569-571. Conover, R. A. 1959. Verticillium wilt of tomato in Dade County, Florida. McMillan, R. T., Jr., W. R. Graves, and T. F. Wood. 2002. First Report of Die- Proc. Florida State Hort. Soc. 72:199-201. back Caused by Verticillium dahliae on Blighia sapida in the United States. Marlatt, R. B. and S. Goldweber. 1969. Verticillium wilt of avocado (Persea Plant Disease. 86:74. americana) in Florida. Plant Dis. Reptr. 53:583-594. Proc. Fla. State Hort. Soc. 116:8-10. 2003. MUSCADINE VINE DIEBACK: EMERGING PROBLEM AND POSSIBLE CONTROL MEASURES ZHONGBO REN AND JIANG LU1 Florida A&M University Center for Viticulture and Small Fruit Research 6505 Mahan Drive Tallahassee, FL 32317 Additional index words. Vitis routondifolia, shoots, leaves, infec- tion, vine survival Abstract. Increasing numbers of muscadine dieback incidents have been found in north Florida and south Georgia vineyards in recent years. Symptoms such as dying of new shoots (one or both arms), or entire vines were observed. A case survey in a north Florida commercial vineyard with five cultivars indicat- ed that the disease is a new threat to muscadine grapes (Vitis routondifolia Michx or Vitis routondifolia Small). Up to 100% of vine infection that resulted in 17% mortality, was observed in some important cultivars. The possible treatments for prevent- Fig. 2. Stunted shoot growth (right) in comparison of a healthy shoots ing this disease are discussed. (left). Muscadine grapes (Vitis routondifolia Michx or Vitis routon- found in a few new shoots, one arm or an entire plant (Fig. 5), difolia Small) are generally known to have a high degree of re- randomly distributed in the vineyard. Shoots growing from the sistance or tolerance to pests and diseases commonly found in lower portion of unaffected area are healthy. bunch grapes (Olien, 1990). However, studies have indicated This disease is believed to be caused by the fungus Botry- that several diseases exist on muscadine grapes, such as osphaeria (Fusiccocum spp.). If left untreated, the fungus will Pierce’s Disease (PD), black rot, angular leaf spot, ripe rot, bitter rot, and macrophoma (Chen et al., 2000). Among them, dieback or dead arm has been found in increasing numbers of muscadine vineyards in the north Florida and south Georgia area. The disease appears in spring when new shoots grow out. The typical symptom is necrosis and dying back from the tips of new shoots (Fig. 1). Weak and stunted shoots with shortened internodes may easily be seen among the affected plants at the beginning of growth (Fig. 2). The leaves usually are small, mis- shaped and distorted at first. As the disease advances, necrosis will appear on the leaves, and shoots eventually die back from the shoot tips (Fig. 3). Dark, wedged-shaped cankers develop- ing in the woody vascular tissue (Fig. 4) is an important diag- nostic symptom. This may be easily observed from the cross cutting surface of an affected arm or branch. Symptoms may be This research is funded in part by Florida Viticulture Advisory Council.