Japanese Plum Cultivar Evaluations in Northern and Southern Mississippi Bulletin 1042 -- April 1996 Frank B. Matta Professor, Horticulture Department of Plant and Soil Sciences Mississippi State University O. P. Vadhwa Professor, Agronomy Alcorn State University Lorman, Mississippi R. C. Sloan, Jr. Research Associate, Horticulture North Mississippi Research and Extension Center Verona, Mississippi   Published by the Office of Agricultural Communications, Division of Agriculture, Forestry, and Veterinary Medicine, Mississippi State University. Edited by Keith H. Remy, Senior Publications Editor. Cover designed by Betty Mac Wilson, Graphic Artist. Introduction       Disease has been a major factor limiting the production of plums in the southeastern United States (3). However, cultivars and hybrids of Japanese plum (Prunus salincina) are better adapted than European plum (P. domestica) and have extended the commercial season in many of the southern states (10).       Japanese plum probably originated in China. In 1870, 'Kelsey' was the first cultivar brought to the United States from Japan. Cultivars and hybrids of Japanese plums were introduced by Luther Burbank (15). Today, 'Santa Rosa' is one of the leading cultivars in California.       In 1947, horticulturists at the Mississippi Agricultural and Forestry Experiment Station recommended plum cultivars that could be successfully grown in Mississippi (12). There are now many new, better-adapted, disease-resistant, high-yielding cultivars. Plum production for the fresh market has increased in Alabama and the Southeastern United States, with extensive plantings of 'AU Producer' (7), 'Crimson,' 'Purple' (10), and limited plantings of other selections (5, 9, 2).       In addition, breeding programs in Georgia and Alabama are developing new plum cultivars for growers (11). The development of new, more desirable cultivars has prompted growers in Mississippi to seek information on adaptation of such cultivars. Plum cultivar performance results during initial tree establishment were reported in 1989 (4).       This bulletin presents results of Japanese plum cultivars evaluated from 1985 through 1991 in northern Mississippi and from 1986 through 1995 in southern Mississippi. Results are reported for each location. No attempt is made to compare locations.   Materials and Methods Pontotoc (North Mississippi)       Eleven plum cultivars on Lovell rootstock were evaluated from 1985 through 1991 at the MAFES Pontotoc Ridge-Flatwoods Branch Experiment Station (34°08'N and 89°00'W) south of Pontotoc, MS. Trees were spaced 14 feet by 20 feet in a randomized complete block design with four replications and single tree plots. Trees of 3/4-inch trunk caliper were planted February 22, 1985. Trees were trained to the modified central leader system and pruned annually. The sod-strip culture method was maintained using herbicides in a 4-foot (1.2-meter) band under tree rows and a mowed grass strip between rows.       In 1986 and 1987, trees were broadcast fertilized with 300 pounds per acre (336 kg/ha) of 13-13-13 (N-P-K). In 1988, 1989, and 1990, the trees received 3.5 oz/tree (100 g/tree) of 13-13-13 at pre-bloom, post-bloom, and June 15 for a total of 10.5 oz/tree (300 g/tree). In 1991, the trees were fertilized with ammonium nitrate at the rate of 7.88 lb/tree (225 g/tree).       Current spray schedule recommendations provided by the Mississippi Cooperative Extension Service were followed for control of insects and diseases.       Fruit was hand thinned to a spacing of 6 inches on fruiting limbs. Fruit thinning began soon after blossoming and was completed shortly after "June drop."       Fruit from each cultivar was harvested when maturity was indicated by changes in peel ground color. Therefore, a given tree was harvested more than once when the fruit was fully matured. Cultivar yields were subjected to analysis of variance and yield means were separated by the Duncan's Multiple Range Test. Fruit quality was determined by measuring soluble solids concentration (Abbe hand refractometer 20C) and juice pH (Accumet 925 pH meter) of five fruit/tree. The diameter of 10 fruit/tree and weights of 5 fruit/tree were determined. Fruits were sampled each year at first harvest (Table 3). The fruit flesh color, peel color, and stone freeness were determined. Bloom and harvest dates were recorded annually. Alcorn (South Mississippi)       Ten plum cultivars on Lovell rootstock were evaluated from 1985 through 1991 at Alcorn State University, Lorman, Mississipi (32°00'N and 91°00'W). Trees were spaced 14 feet by 20 feet in a randomized complete block design with four single tree replications. Trees of 3/4-inch trunk caliper were planted March 5, 1985. Tree training system and cultural practices, which included fertilization, irrigation, weed control, fruit thinning, and insect control, were identical to those at Pontotoc. The soil, however, was a Memphis silt loam with a pH of 6.5.       Procedures for harvesting and data analyses were identical to those at Pontotoc. Data collected included yield per tree, fruit flesh color, peel color, and stone freeness. Bloom and harvest dates were also recorded.   Results and Discussion Pontotoc and Alcorn       Flesh color of plums ranged from yellowish red for 'Six Weeks' to blue-black for 'Frontier' (Table 1). Skin color ranged from light red for 'Morris' to dark-red-purple for 'Methley.' All cultivars had cling stone fruit with the exception of 'Au Roadside' and 'Ozark Premier,' which had semi-cling stone fruit. 'Segundo' and 'AU Roadside' were not evaluated at Alcorn. Pontotoc       In general, full bloom dates of the plum cultivars at Pontotoc occurred from March 9 through March 20 (Table 2). Also, full bloom dates varied from year to year. This is expected because of environmental conditions.       The first potential production year was 1987 (all trees flowered profusely). A freeze of 24°F (-4.5°C) on March 31, 1987 destroyed the potential commercial crop of all cultivars. All trees were at post-bloom stage. 'Segundo,' 'Robusto,' and 'Bruce' produced some fruit, perhaps indicating some degree of hardiness to the freeze or a heavy production of blossoms, in which case some ovaries survived.       Rieger, et al. (13) reported that 'Bruce' and 'Santa Rosa' were hardy and 'Ozark Premier' the least tolerant in a freeze that occurred during bloom. On March 16, 1988, a freeze with a minimum temperature in the orchard of 23°F (-5°C), caused major crop damage to most cultivars (Table 4). However, the fruit of 'Robusto,' 'Morris,' and 'Segundo' had to be thinned to ensure fruit sizing. As indicated by average first harvest date, 'Robusto,' 'Methley,' and 'Six Weeks' were the highest producers with cumulative yield of 156.7 pounds (71.2 kg), 127.2 pounds (57.8 kg), and 117.8 pounds (53.5 kg) per tree, respectively (Table 4).       Plum yields in Alabama have ranged from 39 to 149 pounds (17.7 to 67.7 kg) per tree depending on cultivar (6). The low cumulative yields for most cultivars reported in this publication (Table 4) were primarily caused by the March 16, 1988 freeze. It is interesting to note that 'Robusto' and 'Segundo' produced both years (measurable yields in 1987 and a commercial crop in 1988).       On March 18, 1989, a minimum temperature of 23°F (-5°C) was recorded and resulted in a crop loss of 'Explorer,' 'AU Roadside,' and 'Frontier.' All trees were in full bloom. The remaining cultivars did not apparently suffer damage. The temperature in the orchard dropped to 24°F (-4.5°C) on April 10 when fruits were 5-12 mm in diameter, resulting in complete crop loss. A crop load rating was taken after the damage, indicating that all cultivars except 'Explorer,' 'AU Roadside,' and 'Frontier' would have produced an adequate crop if the April 10 freeze had not occurred (Table 2).       It is evident that late spring freezes severely limit plum production in this climate since the bloom period for all cultivars occurred in early to mid-March. Results indicate and are in agreement with Rieger, et al. (13) that certain cultivars are hardier or produce an abundance of blossoms and, therefore, are able to produce a crop consistently.       In 1990, yields ranged from 6.5 pounds (3.0 kg) per tree for 'AU Roadside' to 41.4 pounds (18.8 kg) per tree for 'Methley.' 'Methley,' 'Frontier,' and 'Morris' were the highest producers followed by 'Robusto' and the remaining cultivars. In 1991, 'Methley' and 'Morris' were again the highest producers followed by 'AU Producer.' 'Frontier,' a high producer in 1990, did not produce a crop in 1991. Greater cumulative yield with time is a good indicator of consistency in production. 'Robusto,' 'Morris,' 'Segundo,' and 'Methley' had greater cumulative yields indicating that these cultivars were more consistent producers (Table 3).       Fruit juice pH, based on a 4-year average, ranged from 3.7 for 'AU Producer' to 3.1 for 'Segundo' (Table 5). The remaining cultivars had an average pH of 3.4 to 3.2 except for 'Morris,' which had a pH of 3.6. Soluble solids ranged from a 14.2 for 'Robusto' to 10.9 for 'Segundo.' Fruit diameter varied from 1.9 inches (4.9 cm) for 'Methley' and 'Ozark Premier' to 1.44 inches (3.7 cm) for Morris. Fruit weight (five fruit/tree) did not differ among cultivars and ranged from 1.2 pounds (500.8 g) for 'Methley' to 0.42 pound (192.1 g) for 'AU Producer.'       The climate in Mississippi is characterized by long, hot, humid summers, mild winters, periods of heavy rainfall, and late spring freezes (Wax et al., 1987). 'Robusto,' 'Morris,' 'Segundo,' and 'Methley' were the best adapted cultivars as indicated by yield. Resistance or tolerance of the various cultivars to black knot, bacterial canker, bacterial fruit spot, and plum leaf scald was not monitored. However, disease pressure seemed to be minimal in this orchard, perhaps attesting to the disease resistance developed in these cultivars. Alcorn       In general, full bloom dates of the plum cultivars occurred from February 25 through March 7 (Table 6). Full bloom date varied from year to year and was expected because of environmental conditions. Bloom period was approximately 2 weeks earlier at Alcorn than at Pontotoc. The first potential production year was 1987 (all trees flowered profusely). However, as in Pontotoc, late spring freezes in March of 1987, 1988, 1989 destroyed the crop. In addition to the freezes that occurred in northern Mississippi, two additional freezes occurred at Alcorn in 1990 and 1991, which also destroyed the plum crop. Therefore, the first production year at Alcorn was 1992.       Harvest date ranged from May 27 through June 28 (Table 7) depending on cultivar and year. As indicated by harvest date, 'May Ripe,' 'Methley,' and 'Six Weeks' were early producers. 'Morris,' 'Frontier,' and 'Explorer' were late producers (Table 2). 'AU Producer,' 'Methley,' and 'May Ripe' were the highest producers with cumulative yields of 178.7, 138.9, and 95.8 lb/tree (81, 63, and 43.5 kg/tree), respectively (Table 8). The remaining cultivars produced between 73.2 pounds (33.2 kg) per tree and 30.0 pounds (13.6 kg) per tree. 'Ozark Premier' was the lowest producer with 16.3 pounds (7.4 kg) per tree.       Plum cultivar yields in northern Mississippi ranged from 8.4 pounds (3.8 kg) per tree to 52.2 pounds (23.7 kg) per tree based on a 3-year average. At Lorman, yield ranged from 4.1 to 44.6 pounds (1.8 to 20.2 kg) per tree based on a 4-year average. The 3-year average yield per tree for all cultivars at Pontotoc was 24.9 pounds (11.6 kg). At Lorman, the 4-year average yield per tree for all cultivars was 19.3 pounds (8.75 kg). Results indicate that, in general, the cultivars were equally productive at both growing sites. However, some cultivars performed better in northern Mississippi and others in southern Mississippi.   Conclusion       Results illustrate yield of Japanese Plums in northern and southern Mississippi. Based on cumulative yield, 'Robusto,' 'Morris,' 'Sunglo,' and 'Methley' are recommended for northern Mississippi. 'AU Producer,' 'Methley,' and 'May Ripe' are recommended for southern Mississippi.       Japanese Plums, as indicated by bloom period, were very susceptible to late spring freezes. Bloom period at Alcorn was approximately 2 weeks earlier than at Pontotoc and perhaps rendered buds more susceptible to freeze injury. 'Segundo,' 'Robusto,' and 'Bruce' indicated some degree of hardiness to late spring freezes or perhaps a heavy production of blossoms in northern Mississippi resulting in yield. As would be expected, because of higher day/night temperatures and earlier bloom, cultivars matured earlier in southern Mississippi (Lorman).       On the basis of yield date and other performance characteristics presented in this bulletin, the production of Japanese plum in northern and southern Mississippi is possible. However, spring freezes during Japanese plum tree bloom severely limit plum yields and annual production in Mississippi.   Acknowledgments       Appreciation is extended to all the technical staff, support staff, and graduate students for their valuable contributions to this research. Special thanks are extended to those from each research station who made this research possible, and to Dr. Patrick D. Gerard, Assistant Professor/ Statistician, for his review of the manuscript for statistical accuracy.   Literature Cited   Climatological Data. 1993. Department of Geology and Geography, Mississippi State University. Hughes, Morris B. 1974. Wade: A new plum for the South. Clemson Univ. (SC) Agr. Exp. Sta. Cir. 171.  Latham, A. J., and J. D. Norton. 1980. Incidence of plum leaf scald. Auburn Univ., Alabama Agr. Exp. Sta. Bulletin 525:1-15. Matta, F. B., O. P. Vadhwa, F. Raspberry, and S. N. Little. 1989. Plum cultivar performance during initial tree establishment. Mississippi Agr. and For. Exp. Sta. Res. Report Vol. 14, No. 11. Norton, J. D. 1984. AU Roadside: An excellent quality plum for home use and local markets. Auburn Univ., Alabama Agr. Exp. Sta. Circular 271. Norton, J. D. Et al. 1982. Effect of leaf scald disease varies among plum varieties. Highlights of Agricultural Research. 29:4. Auburn Univ., Alabama Agr. Exp. Sta. Norton, J. D. 1978. AU Producer: A high quality plum for the commercial market. Auburn Univ., Alabama Agr. Exp. St. Cir. 240. Norton, J. D. 1976. Bruce 12-4: A disease-resistant and cold hardy plum seedling (For use in breeding). Auburn Univ., Alabama Agr. Exp. Sta. Circular 230. Norton, J. D. 1975. Homeside: An excellent quality plum for home and roadside market. Auburn Univ., Alabama Agr. Exp. Sta. Cir. 218. Norton, J. D. 1973. Crimson and Purple: two disease-resistant plums for the commercial market. Auburn Univ., Alabama Agr. Exp. Sta. Leaf 85. Okie, W. R. 1988. New plum varieties. Amer. Fruit Grower. 108(5) 46-47. Ragland, C. H., and J. P. Overcash. 1947. Orchard and small fruit culture in Mississippi. Mississippi State College Agr. Exp. Sta. Bulletin 450. Rieger, Mark, Shaoli Lu, and Mike Duernmel. 1991. Frost tolerance of some peach and Japanese plum cultivars. Fruit Var. J. 45(1):3-6. Wax, C. L. , F. P. Raspberry, and Frank B. Matta. 1987. A climatological assessment: Late freezes in Mississippi and their influence on peach crop damage. Mississippi Agr. and For. Exp. Sta. Tech. Bulletin 148. Westwood, M. E. 1993. Temperate-zone pomology. 3rd Edition. Timber Press, Portland, Oregon. Table 1. Fruit characteristics of eleven plum cultivars grown at Pontotoc Ridge-Flatwoods Branch Experiment Station, Pontotoc, MS, 1985-1991. Table 1. Fruit characteristics of eleven plum cultivars grown at Pontotoc Ridge-Flatwoods Branch Experiment Station, Pontotoc, Mississippi, 1985-1991. Cultivar Flesh Color Skin Color Stone Freeness AU Producer Dark Red Dark Red Cling AU Roadside Dark Red Dark Red Semi-Cling Bruce Orange-Red Orange-Red Cling Explorer Dark-Purple Dark-Purple Cling Frontier Blue-Black Dark-Purple Cling Methley Reddish-Purple Dark-Red-Purple Cling Morris Light Red Light Red Cling Ozark Premier Bright Red Red-Purple Semi-Cling Robusto Red Bright Red Cling Segundo Orange-Red Red Cling Six Weeks Yellowish-Red Red Cling Table 2. Full bloom dates of plum cultivars grown at Pontotoc Ridge-Flatwoods Branch Experiment Station, Pontotoc, Mississippi, 1988-1991. Year Cultivar 1988 1989 1990 1991 March Full Bloom Date AU Producer 15 16 17 15 AU Roadside 13 10 16 13 Bruce 11 12 19 16 Explorer 13 13 20 18 Frontier 14 12 18 16 Methley 17 16 20 17 Morris 12 12 15 13 Ozark Premier 9 11 20 18 Robusto 14 12 15 14 Segundo 14 13 18 17 Six Weeks 18 17 19 18 Table 3. First harvest dates of plum cultivars grown at Pontotoc Ridge- Flatwoods Branch Experiment Station, Pontotoc, Mississippi, 1988-1991. Year Average First Cultivar 1988 1990 1991 Harvest First Harvest Date (month/day) AU Producer 6/23 6/22 6/20 6/22 AU Roadside 6/23 6/15 6/11 6/16 Bruce 6/17 6/16 6/20 6/18 Explorer 6/27 6/22 7/7 6/29 Frontier 6/27 6/22 6/20 6/23 Methley 6/9 6/6 6/20 6/12 Morris 6/23 6/22 6/20 6/22 Ozark Premier 7/5 7/5 7/6 7/5 Robusto 6/9 6/1 6/20 6/10 Segundo 6/23 6/6 6/20 6/16 Six Weeks 6/1 5/21 6/11 6/11 Table 4. Yield of plum cultivars grown at Pontotoc Ridge-Flatwoods Branch Experiment Station, Pontotoc, Mississippi, 1988-1991. Year Cumulative1 4-yr Cultivar 1988 1989 1990 1991 Yield Avg. Yield (lb/tree) AU Producer 30.7c2 5.03 16.1bcd 34.0a 80.0c 26.6 AU Roadside 13.8d 0 6.5cd 5.1c 25.4d 8.4 Bruce 16.2d 3.3 9.7bcd 19.6b 45.5d 11.3 Explorer 1.8d 0 13.6bcd 1.2c 29.7d 9.9 Frontier 18.3d 0 34.3a -- 52.6cd 17.5 Methley 17.3d 4.0 41.4a 45.4a 104.1b 84.7 Morris 57.4b 2.8 31.0ab 38.8a 127.2ab 42.4 Ozark Premier 27.0c 5.0 9.3cd 12.7c 49.0cd 16.3 Robusto 115.4a 5.0 24.5abc 16.8c 156.7a 52.2 Segundo 74.5b 2.0 16.1bcd 27.2b 117.8ab 39.2 Six Weeks 26.0c 5.0 13.7bcd 7.0c 46.7d 15.5 1Cumulative of 3 years. 2Means in columns separated by Duncan's Multiple Range Test with significance level 0.05. 3Crop load rating: 0=no commercial crop, 1=low crop, no thinning, 2=commercial crop, light thinning, 3= commercial crop moderate thinning, 4=commercial crop, heavy thinning, 5=commercial crop, very heavy thinning.   Table 5. Fruit quality characteristics of plum cultivars grown at Pontotoc Ridge-Flatwoods Research Branch Experiment Station, Pontotoc, Mississippi, 1985-1991. Soluble Fruit Fruit Cultivar pH1 Solids2 Diameter3 Weight (%) (cm) (g/5 fruit) AU Producer 3.7a 11.7bc 3.9bcd 192.1a AU Roadside 3.2d 12.5b --- 343.7a Bruce 3.2cd 12.3b 4.5ab 438.2a Explorer 3.2c 11.2c 4.5ab 277.4a Frontier 3.4a-d 12.9b 4.7a 341.6a Methley 3.2cd 11.0c 4.9a 500.8a Morris 3.6ab 12.4b 3.7cd 263.4a Ozark Premier 3.4a-d 13.5a 4.9a 333.8a Robusto 3.4a-d 14.2a --- 335.6a Segundo 3.1d 10.9c 4.3abc 307.3a Six Weeks 3.2d 11.4c 4.6ab 421.3a 1Means in Columns separated by Duncan's Multiple Range Test with significance level 0.05. 2Mean pH values and soluble solids concentration of fruit from four replications and 4 years. 3Mean of 10 fruit per tree from four replications and 4 years.   Table 6. Full bloom dates of plum cultivars grown at Alcorn State University, Lorman, Mississippi, 1989-1995. Year Cultivar 1992 1993 1994 1995 AU Producer March 2 March 4 February 28 March 2 Methley March 5 March 7 March 4 March 5 May Ripe March 1 March 3 February 27 March 1 Morris February 28 March 3 March 2 February 27 Robusto March 1 March 2 March 5 March 1 Explorer March 2 February 28 March 1 March 3 Frontier March 2 March 4 March 4 March 7 Six Weeks March 5 March 7 March 3 March 4 Bruce February 26 February 28 March 1 February 28 Ozark Premier February 25 February 28 March 1 February 26 Table 7. First harvest dates of plum cultivars grown at Alcorn State University, Lorman, Mississippi, 1989-1995. Year Cultivar 1992 1993 1994 1995 AU Producer May 29-June 17 June 5-25 June 8-27 May 31-June 26 Methley May 27-June 2 June 1-14 June 3-22 May 31-June 5 May Ripe May 27-May 29 June 1-10 May 18-23 May 31-June 5 Morris June 5-10 June 1-14 June 8-22 May 31-June 12 Robusto May 29-June 5 June 1-17 June 1-9 May 31-June 12 Explorer June 23-26 June 25-July 1 June 8-22 -- Frontier June 15-26 June 25-28 June 9-27 -- Six Weeks May 27-June 5 June 1-7 May 18-23 May 31-June 5 Bruce May 27-June 8 June 1-17 June 1-17 May 31-June 5 Ozark Premier June 10-15 June 17-22 June 17-20 June 9-16 Table 8. Yield of Japanese plum cultivars grown at Alcorn State University, Lorman, Mississippi, 1989-1995. Year Cultivar 1992 1993 1994 1995 Cumulative 4-yr Avg AU Producer 71.15a 17.15b 84.88a 5.58a 178.76a 44.6 Methley 18.68b 53.45a 66.65b 0.13a 138.91b 34.7 May Ripe 7.53c 29.9b 56.45b 2.01a 95.89c 23.9 Morris 0.5c 16.58b 54.9b 1.28a 73.26d 18.3 Robusto 29.83b 30.53b 5.0d 4.41a 69.77d 17.4 Explorer 2.4c 2.18c 55.73b 1.25a 61.56d 15.3 Frontier 10.93c 2.5c 42.03b 1.0a 56.46d 14.1 Six Weeks 2.3c 19.33b 29.4c 0.83a 151.86df 12.9 Bruce 6.33c 14.7bc 7.73d 1.3a 30.06fg 7.5 Ozark Premier -- 3.75c 12.35d 0.25a 16.35g 4.09

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