Circular 301
February 1990
Alabama Agricultural Experiment Station
Lowell T. Frobish, Director
Auburn University
Auburn, Alabama
First Printing 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 Respectively, Professor, Research Associate, former Associate Professor, and Technician of Horticulture |
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.
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.
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).
Fruits of AU-Rubrum have dark red (scarlet red, HCC 44A)1 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.
The cultivar has been in trials as Crimson M-l 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.
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.
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 varieties 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.
1 Horticulture Color Chart; Royal Horticulture Society, London.