ew Early Season Plum Developed I AU-Rubrum Cultivar combines high yielding ability with disease resistance and excellent fruit quality *0 Circular 301 February 1990 Alabama Agricultural Experiment Station Lowell T. Frobish, Director Auburn University Auburn University, Alabama Information contained herein is availableto all without regard to race, color, sex, or national origin. FIRST PRINTING 4M, FEBRUARY 1990 NEW EARLY SEASON PLUM DEVELOPED AU-Rubrum Cultivar Combines High Yielding Ability with Disease Resistance and Excellent Fruit Quality J.D. Norton, G.E. Boyhan, D.A. Smith, and B.R. Abrahams' INTRODUCTION AU-RUBRUM is a new plum cultivar developed by the Alabama Agricultural Experiment Station, Auburn University, for growing in areas receiving at least 700 hours of chilling temperature below 45°F. It was developed to meet the needs for disease-resistant cultivars. Such resistance is particularly important in the Southeast where prevalence of certain diseases and susceptibility of commercial varieties had discouraged plum production. CULTIVAR DESCRIPTION Trees of AU-Rubrum are spreading with dark green leaves. In test orchards in Alabama, the trees were vigorous, disease resistant, and long lived. The plant is self-fruitful, flowers profusely, and sets a heavy crop. The cultivar has proved its ability to produce high yields of excellent quality fruit where certain fruit and tree disease problems occur. It is an early maturing cultivar that produces fruit of excellent size and quality. Disease Resistance AU-Rubrum is highly resistant to bacterial canker (Pseudomonas syringae, Van hall), bacterial fruit spot [Xanthomonas pruni E. F. Smith), Dows], bacterial leaf spot (X. pruni), and black knot [Apisporina morbosa (Schw.) Ark.], table 1. Trees are tolerant to plum leaf scald (Xylella fastidiosa). 'Professor, Research Associate, Associate Professor, and Technician of Horticulture. TABLE 1. DISEASE RESISTANCE OF PLUM CULTIVARS IN EXPERIMENTAL PLANTINGS AT AUBURN AND SHORTER, ALABAMA Cultivar Bacterial Bacterial Disease index' Bacterial Black Brown Plum leaf fruit spot AU-Rubrum .... AU-Amber ..... AU-Producer ... AU-Roadside ... Bruce ......... Crimson ....... Homeside ...... Methley ....... Morris......... leaf spot 0 0 0 0 0 0 0 5 2 canker 1 0 0 0 0 0 1 5 2 knot 0 5 1 0 0 0 1 5 5 rot 2 2 2 2 4 1 3 3 2 scald 1 0 1 1 4 3 1 4 2 0 0 0 0 0 0 0 3 1 Ozark Premier .. Purple......... Santa Rosa ..... 0 O 5 1 0 5 1 0 5 1 0 3 3 3 4 5 5 'Disease index: 0 = 0, 1 = 1-10, 2 = 21-40, 3 = 41-60, 4 = 61-80, and 5 = 81-100 percent of fruit, leaves, and trees infected. Ratings were taken in years when injury from disease was severe on susceptible cultivars. Fruit Quality Fruits of AU-Rubrum have dark red (scarlet red, HCC 44A) 2 skin and flesh. Fruit quality is excellent for fresh market, which makes AU-Rubrum adaptable for home, roadside, and local markets. Fruits were rated acceptable in canned fruit tests, table 2. Fruit have adequate firmness for handling, packing, and shipping to commercial markets, table 5. Maturity date is about 1 week after Methley, table 6. 2Horticulture Color Chart; Royal Horticulture Society, London. TABLE 2. MEAN QUALITY EVALUATIONS' OF 12 CANNED PLUM CULTIVARS Cultivar AU-Rubrum ................ AU-Amber ................. AU-Producer ............... AU-Roadside ............... Crimson ................... Giant Cherry ............... Methley ................... Morris ..................... Ozark Premier .............. Red June ................... Sapa ........................ Color 8 8 8 8 8 5 8 8 7 6 10 Texture 8 8 8 8 8 6 8 8 7 8 8 Flavor 8 8 8 8 8 7 8 7 6 8 8 2 Overall quality 8.0 8.8 8.0 8.0 8.0 6.0 8.0 7.7 6.7 7.4 8.6 Starking Delicious ............ 8 7 5 6.7 'Numerical scores as follows: 9 or 10 = highly acceptable, 7 or 8 = acceptable, 5 or 6 = barely acceptable, and below 5 = unacceptable. Mean scores of an expert panel (3-4 panelists) were obtained on the canned plums after at least 6 weeks warm-storage. 2Overall ratings are the means of all the panelists' three quality ratings. [4] Yields The cultivar has been in trials as Crimson M-1 at two locations in the Alabama Agricultural Experiment Station System and in grower trials. It compares favorably with other cultivars in yield. Production has been highest in central Alabama, table 3. Average yields of marketable fruit per tree were 50 pounds, 102 pounds, and 115 pounds, respectively, from 3-, 4-, and 5-year-old trees. TABLE 3. YIELD OF FRUIT OF AU-RUBRUM AT AUBURN AND SHORTER, ALABAMA 3 4 5 6 ........................................ ........................................ ........................................ ........................................ 'Reduced crop from late frost injury. Auburn Lb. 53 108 120 501 Fruit yield per tree Shorter Lb. 47 96 110 401 Average Lb. 50 102 115 45 Storage Fruits of AU-Rubrum store as well as Crimson, AU-Producer, and Santa Rosa and better than AU-Roadside, AU-Amber, Homeside, and Methley, table 4. TABLE 4. PERCENT MARKETABLE PLUM FRUIT AFTER STORAGE AT 32 ° F SCultivarMarketable, Cultivar 3 Pct. 100 95 100 95 20 100 95 95 100 90 100 100 6 Pct. 85 70 90 70 5 90 65 70 90 65 85 80 by weeks of storage 9 12 Pct. 65 20 65 20 0 65 15 20 65 15 55 45 Pct. 10 0 30 0 0 30 0 0 30 0 25 20 14 Pct. 5 0 15 0 0 15 0 0 15 0 8 5 AU-Rubrum ........................ AU-Amber ......................... AU-Producer ....................... AU-Roadside ........................ Bruce ............................. Crimson ........................... Homeside........................... Methley ........................... Morris.............................. Ozark Premier ...................... Purple.............................. Santa Rosa ......................... OUTSTANDING CHARACTERISTICS Tree vigor and tolerance to plum leaf scald are the primary improvements of AU-Rubrum. Trees of AU-Rubrum are vigorous and show only traces of plum leaf scald, whereas trees of susceptible va[5] TABLE 5. FRUIT CHARACTERISTICS OF PLUM CULTIVARS Cultivar Fruit set Flesh color Skin color Size In. Shape Flavor Firmness Ston freeness e Texture Soluble solids Pct. AU-Rubrum .......... AU-Amber ........... AU-Producer ......... AU-Roadside ......... 5' 5 5 5 5 5 5 5 .5 5 5 .4 dark red yellow dark red dark red orange to red crimson red cream dark red light red cream cream red dark red dark red dark red to purple dark red orange to red crimson red orange to light red dark red to purple light red red to purple dark red to purple dark red to purple 21/4-21/2 13/4-2 13/4-2 2-21/4 13/4-2 11/2-13/4 21/4-2/2 1-11/4 13/4-21/4 2-21/4 13/4-2 11/4-12 51 5 5 5 5 5 5 5 4 5 5 5 51 5 5 5 3 5 5 5 3 5 5 5 51 4 5 4 2 5 4 3 5 4 5 5 cling cling free semi-cling cling cling cling cling cling semi-cling semi-cling cling 51 5 5 5 3 5 5 5 5 5 4 5 15.6 19.2 16.5 17.2 9.4 16.3 18.8 18.5 13.4 15.7 14.8 16.7 Bruce ............... Crimson ............. Homeside ............ Methley .............. Morris ............... Ozark Premier ........ Purple ................ Santa Rosa ........... 'Rating index: 5 = excellent, 4 = good, 3 = fair, 2 = poor, and 1 = very poor. rieties grow much more slowly and show obvious symptoms of plum leaf scald. Tree vigor is a primary selective criterion in the Southeast, and the relationship of plum leaf scald to phony peach makes resistance important. Two other characteristics, ripening date and skin color at maturity, may be taken collectively as another important advantage of AU-Rubrum. Its fruit ripens 7 days later and is more fully colored at any comparable stage of maturity than Methley, tables 5 and 6. Another improvement of AU-Rubrum is increased tree longevity. In test orchards at two locations in Alabama, trees of AU-Rubrum remained in extremely vigorous condition for 10 years. TABLE 6. BLOOM AND HARVEST DATES AND YIELD OF PLUM CULTIVARS Variety Auburn Bloom date Harvest date Yield' 3-22 3-17 3-20 3-22 3-20 3-22 3-20 3-22 3-22 3-20 3-24 3-24 6-19 5-30 6-27 7-4 6-29 7-14 7-5 6-10 6-17 7-10 7-20 7-5 5 5 5 5 2 5 5 3 5 4 5 3 Headland Bloom date Harvest date Yield' 3-24 3-18 3-21 3-22 3-22 3-22 3-20 3-24 3-22 3-23 3-28 3-26 6-16 5-27 6-24 6-29 6-26 7-5 7-1 6-7 6-14 7-5 7-15 7-1 5 5 5 5 3 5 5 5 5 5 5 5 AU-Rubrum ......... AU-Amber .......... AU-Producer ........ AU-Roadside . ........ . . 2 . . . . . . . . . . . Bruce Crimson ............ Homeside . ............ . . . . . 3 . . . . Methley Morris .............. Ozark Premier ...... Purple ............... . . . . . . 4 . . . Santa Rosa 2 Trees 3 Trees 4 'Yield index: 0 = short lived short lived Trees short lived 0, 1 = very low, 2 = low, 3 = fair, 4 = good, and 5 = excellent. due to ring spot virus. due to black knot and bacterial canker. due to bacterial canker. [7] tabala s Agricultural Expermicnit Stationi System AUBURN UNIVERSITY With an agricul tural research unit in every major s( il area, Auburn University serves the needs of field crop, livestock, forestry, and horticultural producers in each region in Alabama. Every citi zen of the State has a stake in this research program, since any advantage from new% and more economical ways of produc ing and handling farm products directly benefits the consuming public. 1- IR O a _ 10 1 1 8" Q ® 16_ 1J. - Research Unit Identification ® Main Agricultural Experiment Station, Auburn. ~ E. V. Smith Research Center, Shorter. Tennessee Valley Substation, Belle Mina. Sand Mountain Substation, Crossville. North Alabama Horticulture Substation, Cullman Upper Coastal Plain Substation, Winfield. Forestry Unit, Fayette County. Chilton Area Horticulture Substation, Clanton. Forestry Unit, Coosa County. Piedmont Substation, Camp Hill. Plant Breeding Unit, Tallassee Forestry Unit, Autauga County Prattville Experiment Field, Prativille. Black Belt Substation, Marion Junction. The Turnipseed-Ikenberry Place, Union Springs Lower Coastal Plain Substation, Camden. Forestry Unit, Barbour County Monroeville Experiment Field, Monroeville Wiregrass Substation, Headland. Brewton Experiment Field, Brewton. Solon Dixon Forestry Education Center, Covington and Escambia counties. 20. Ornamental Horticulture Substation, Spring Hill. 21. Gulf Coast Substation, Fairhope. 1. 2. 3. 4. 5. 6. 7. 8. 9 10 11. 12. 13. 14. 15. 16 17 18 19.