among seedlings, has limited the use of hickories (Carya Nuttall). We examined effects ... Carya ovata K. Koch (shagbark hickory), and Carya tomentosa Nuttall.
Root Pruning and Auxin Application Alter Root Development of Hickories Brandon M. Miller and William R. Graves Background and Objectives
40
A
100
35
A
90
Primary Lateral Roots
30
Stem Length (cm)
Diversification of taxa is an important goal of those who manage urban landscapes. Some otherwise desirable species have not been promoted for use due to reports of challenges associated with their production or establishment. A reputation for being difficult to transplant due to coarse root systems with dominant tap roots, and for slow shoot development among seedlings, has limited the use of hickories (Carya Nuttall). We examined effects of root pruning and auxin on root and shoot development of seedlings of five species of hickory that are adapted to diverse natural habitats.
Mean Count of Lateral Roots Across Treatments
Mean Stem Length Across Treatments
25 B
20 15
C
C
C
10 5
80 70
A
A
60
B
B
0 C. aquatica C. cordiformis C. laciniosa
C. ovata
50 40 30 20 10
0 C. aquatica C. cordiformis C. laciniosa
C. ovata
C. tomentosa
Above: Seedlings of Carya laciniosa at treatment initiation
C. tomentosa
Species
Species
Means with the same letter are not significantly different according to Tukey-Kramer HSD test (P ≤ 0.05).
Our objectives were to • quantify root branching and shoot development of five species of hickory, and • determine effects of root pruning and auxin on lateral root formation and shoot growth.
Above: Carya ovata seedling
Above: Carya aquatica seedling
Carya aquatica
We questioned whether the reputation of coarse root systems was warranted for the entire genus, and whether root pruning and auxin could overcome the phenomenon in species that might otherwise have potential for horticultural use.
Above: Carya laciniosa seedling
Carya laciniosa
Left to right within images: Control, Root Pruned, Root Pruned and Auxin
Conclusions
Treatment Effects on Primary Lateral Roots 120
Representative seedlings of Carya tomentosa. Left: Control treatment Right: After root pruning and application of auxin
Methods • Species studied: Carya aquatica Nuttall (water hickory), Carya cordiformis K. Koch (bitternut hickory), Carya laciniosa Loudon (kingnut hickory), Carya ovata K. Koch (shagbark hickory), and Carya tomentosa Nuttall (mockernut hickory) • Treatments: control, two-thirds of tap root removed shortly after germination (root pruned), and tap-root removal followed by auxin (IBA) application (root pruned and auxin) • N = 180 (36 plants/species, 12 plants/treatment) • Plants were cultured singly in 15-centimeter-diameter standard containers with a commercial soilless medium in a greenhouse for 75 days • Completely randomized block design
Mean Number of Lateral Roots
A 100
A B
A B
A B A B
80
A B C
A B C 60
B C D
B C D
40
B C D B C D
B C D
B C D
C D D
20
0 Control
Root Root Control Prune Prune & Auxin
water hickory C. aquatica
Root Root Control Prune Prune & Auxin
bitternut hickory C. cordiformis
Root Root Control Prune Prune & Auxin
kingnut hickory C. laciniosa
Root Root Control Prune Prune & Auxin
shagbark hickory C. ovata
Root Root Prune Prune & Auxin
mockernut hickory C. tomentosa
Species by Treatment
Means with the same letter are not significantly different according to Tukey-Kramer HSD test (P ≤ 0.05).
• The genus Carya is collectively dismissed for horticultural use due to poor root branching, but root development of the five Carya we studied varied, suggesting that some Carya may be better suited to nursery production and transplanting than others. Across treatments, Carya laciniosa, Carya tomentosa, and Carya aquatica on average formed 69% more lateral roots than did Carya ovata and Carya cordiformis. The entire genus should not be dismissed based only on root development of the most familiar species, Carya ovata. • At least with young seedlings, beneficial effects of root pruning on lateral root development can be achieved without reducing shoot development.
Acknowledgements
• Compared to the control group, root pruning combined with the application of auxin increased the number of primary lateral roots of C. aquatica We thank the J. Frank Schmidt Family Charitable Foundation and C. laciniosa. Both species merit further for funding and Byron Carmean and Coreen Robinson for investigation. assistance with the collection of seeds.
