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## Cultivar, Rootstock, and Training Method Influence Flower Bud Production in Pawpaw Kirk Pomper, Sheri Crabtree, and Jeremiah Lowe* Kentucky State University Desmond Layne Clemson University ===== PAGE 2 ===== ## Introduction: What is Pawpaw?

Pawpaw: Asimina triloba (L.) Dunal. Native tree fruit in the southeastern U.S. Tropical-like flavor mixture of banana, mango, and pineapple. Early stages of commercial production.

===== PAGE 3 ===== ## Pawpaw Flowering and Harvest Flower on 1 year old wood Cross-pollinate Pollinated by flies and beetles Ripe fruit should yield when squeezed and give way with a gentle tug Color change not a reliable indicator of ripeness Fruit may be harvested from the same tree over several weeks

NC-1 ===== PAGE 4 ===== ## Pawpaw Propagation and the Nursery Industry Historically, pawpaw has been a difficult tree species to propagate Seed stratification needed Desiccation sensitive ## Commercial clonal propagation is via chip budding Seedling rootstock No clonal rootstocks available

===== PAGE 5 ===== ## Pawpaw Propagation and the Nursery Industry High tree prices are limiting development of an industry Seedlings $5-$10 Grafted trees $15-$30

Our goal is to identify seedling rootstocks that would enhance scion growth, improve tree establishment, and promote precocity. ===== PAGE 6 ===== ## Pawpaw Training and Pruning Tend to form narrow-angled weak branches at the trunk. Therefore, pawpaws are prone to wind damage. A central leader training system would develop a strong framework and a desirable form for harvesting. Will pruning dwarf a young tree and delay bearing in pawpaw? Will fruit suffer sunburn? ===== PAGE 7 ===== ## Objective To determine if cultivar, rootstock, and training method would influence early flower bud production in pawpaw

===== PAGE 8 ===== ## Materials and Methods The rootstock trial was planted on May 10, 2004. Rootstocks: 5 seedling rootstocks Scions: 'Sunflower' and 'Susquehanna' Two pruning systems: minimal pruning versus central leader 8 replicate blocks with each treatment combination for a total of 160 trees (2 x 5 x 2 x 8 = 160).

===== PAGE 9 ===== ## Why Did We Choose These Selections? Scions: Sunflower Noted to flower and produce fruit in 4^{th} year in Princeton, KY trial. Susquehanna' Slow to flower and to come into production. ## Seedling rootstocks: Cultivars vigorous: Sunflower and PA-Golden Cultivars lack vigor: Susquehanna and K8-2 Commercial mixed seed: RVT Studies with seedlings in containers Seed size and genetic background important ===== PAGE 10 ===== ## End of 2004

9/21/04 ===== PAGE 11 ===== ## End of 2005

3/03/06 ===== PAGE 12 ===== ## End of 2006

===== PAGE 13 ===== ## End of 2007

KENTUCKY STATE UNIVERSITY 1/28/08 ===== PAGE 14 =====

Central leader 3/23/07 Minimal pruning ===== PAGE 15 =====

Central leader 1/28/08 Minimal pruning ===== PAGE 16 ===== ## After 2005 Growing Season

Scion	Survival %	TCA (cm2)	% of trees flowering	Number of flower buds per tree	Flower density (Tot flw tr/TCA)
Susquehanna	63	3.4	8% b	0.4 b	0.09 b
Sunflower	71	3.5	51% a	3.7 a	0.93 a
Significance	0.37 NS	0.75 NS	0.0000***	0.001**	0.006**
Rootstock	Survival %	TCA	% of trees flowering	number of flower buds per tree	Flower density (total flowers/TCA)
RVT	77% a	3.4	40%	2.1 ab	0.50
Sunflower	90% a	3.2	25%	2.2 ab	0.70
PA-Golden	84% a	3.9	36%	3.4 a	0.74
K8-2	77% a	3.3	21%	0.8 b	0.14
Susquehanna	52% b	3.4	33%	1.7 ab	0.51
Significance	0.004**	0.40 NS	0.63 NS	0.58 NS	0.71 NS

TCA=Trunk Cross-sectional Area ===== PAGE 17 ===== ## After 2006 Growing Season

scion		survival	TCA	% of trees flowering
Susquehanna		68%	6.4 b	62% b
Sunflower		82%	8.5 a	83% a
Significance		0.06 NS	0.006**	0.002**
rootstock	Survival	TCA	% of trees flowering	number of flower buds/tree	Flower density
RVT	77% a	7.4 ab	78%	11 b	1.09
Sunflower	90% a	9.0 a	75%	11 b	0.95
PA-Golden	84% a	9.0 a	74%	21 a	1.57
K8-2	73% a	6.7 ab	60%	8 b	0.89
Susquehanna	52% b	5.1 b	82%	11 b	0.98
Significance	0.005**	0.01*	0.33 NS	0.03*	0.07 NS

===== PAGE 18 ===== ## After 2007 Growing Season

Scion	Survival %	TCA	Percent of Trees\nFlowering	Flower Density\n(Tot flw tr/TCA)
Susquehanna	68%	14.3	94% b	1.6 b
Sunflower	82%	14.3	100% a	6.0 a
Significance	0.06 NS	0.64 NS	0.04*	0.0000***

Rootstock	Survival %	TCA	Percent of Trees\nFlowering	Flower Density\n(Tot flw tr/TCA)
RVT	77% a	13.8	96%	3.8
Sunflower	90% a	14.0	96%	4.2
PA-Golden	84% a	15.7	100%	4.1
K8-2	73% a	14.0	95%	3.5
Susquehanna	52% b	13.7	100%	4.7
Significance	0.005**	0.32 NS	0.63 NS	0.13 NS

===== PAGE 19 ===== ## After 2007 Growing Season

Training Method	Survival %	Percent of Trees Flowering		Number of Flower Buds Per Tree	Flower Density (Tot flw tr/TCA)
Training Method	Survival %	TCA	Flowering	Tree	Flower Density (Tot flw tr/TCA)
Minimal Pruning	72%	17.4 a	98%	63 a	3.8
Central Leader	79%	11.5 b	97%	50 b	4.3
Significance	0.20 NS	0.0000***	0.63 NS	0.015 *	0.18 NS

===== PAGE 20 ===== ## Conclusions Genetic background of seedling rootstock did not influence scion precocity or growth. Survival of Susquehanna seedling rootstock was poor. Sunflower was more precocious than Susquehanna. Central leader training tended to reduce vigor (TCA) and the number of flowers/tree. ===== PAGE 21 =====

## Questions?