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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.
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
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
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.
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?
Objective
To determine if cultivar, rootstock, and training method would influence early flower bud production in pawpaw
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).
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
KENTUCKY STATE UNIVERSITY
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
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 |
After 2007 Growing Season
| Scion | Survival % | TCA | Percent of Trees Flowering | Flower Density (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 Flowering | Flower Density (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 |
After 2007 Growing Season
| Training Method | Survival % | Percent of Trees Flowering | Number of Flower Buds Per Tree | Flower Density (Tot flw tr/TCA) | |
|---|---|---|---|---|---|
| TCA | Flowering | Tree | |||
| 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 |
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.