Root Pruning and Auxin Application Alter Root ...

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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.

Department of Horticulture