Jump Starting New Pawpaw Variety Production for the Industry: Developing Grafting and Top Working Approaches for Growers

Jump Starting New Pawpaw Variety Production for the Industry: Developing Grafting and Top Working Approaches for Growers

Summary

Pawpaw, a tree fruit native to the Eastern U.S., is in small-scale commercial production with its popularity on the rise. Pawpaw fruit have fresh market appeal for farmers markets and Community supported Agriculture (CSAs), and processing appeal for frozen pulp production for sale to gourmet restaurants. Many small farmers have seedling pawpaw trees or wild trees that produce small yields and low quality fruit. New commercially available pawpaw varieties are now available and new cultivars are being developed that will increase yield, fruit quality, and consumer demand.

There are over 100 limited resource farmers in Kentucky alone who have small plantings of seedling pawpaw trees or wild trees that with grafting and top working could serve as rootstock and enable rapid production from grafts of high quality and high demand pawpaw fruit. Bark inlay is a grafting technique which allows the union of a rootstock limb or trunk (at least 1 to 2 inches in diameter) that is much larger in size than the scion piece. This technique has been used by apple producers to change the variety of an existing orchard (top working), adding a branch of an untested scion cultivar to an existing tree for observation, or repairing a tree that may have had a branch broken off by storm damage or fruit overloading. This technique has not been well developed for pawpaw and represents a method for growers to change over to higher yielding and high quality fruit cultivars.

Experiments will be conducted using established seedling trees with methods to reduce negative effects of spring heating of grafts, as well as improve timing for successful spring grafting and cultivar selection to optimize this technique for farmers. The objectives of this proposal are to: 1) develop methods to optimize bark inlay grafting success by cultivar, grafting time, and heat reduction on grafts on large pawpaw seedling rootstock trees in the field at KSU and grower locations, 2) examine scion take, flowering, and fruiting response time of varieties propagated by inlay grafting, and 3) create extension bulletins and YouTube videos concerning how to successfully graft and top work pawpaws and offer to growers; hands on grafting workshops will also be offered. Grower trials will serve as demonstrations and workshop sites in coordination with the Kentucky Nut Growers Association and the Ohio Pawpaw Growers Association. This proposal will not only increase yields but will enhance high quality marketable fruit; thereby promoting a sustainable fruit production system with low inputs for limited resource farmers.

Objectives/Performance Targets

1) Develop methods to optimize bark inlay grafting success by cultivar, grafting time, and heat reduction on grafts on large pawpaw seedling rootstock trees in the field at KSU and grower locations,

2) Examine scion take, flowering, and fruiting response time of varieties propagated by inlay grafting to select for easy to propagate varieties,

3) Create extension bulletins and YouTube videos concerning how to successfully graft and top work pawpaws and offer to growers; hands on grafting workshops and “Third Thursday” workshops.

Accomplishments/Milestones

Six 17-year-old seedling trees were selected at the Kentucky State University Harold R. Benson Research and Demonstration Farm, and branches were topworked with the pawpaw selections KSU Atwood, Hi1-4, Hi4-1, and Hi7-5 via bark inlay grafting in late May 2015. Grafts were secured with rubber bands and covered with foil. None of these grafts formed a successful graft union.

Four year old rootstock trees were topworked with the pawpaw selections KSU-Atwood, Hi1-4, Hi4-1, and Hi7-5 on two dates, late-May and mid-June 2015. Chip budding was performed in May with dormant buds collected in March 2015. Whip and tongue grafts were performed in June with new green growth collected one day prior to grafting. Grafts were secured with rubber bands and/or parafilm. For chip budded trees, 66% of trees budded in May had successful graft unions. For the whip and tongue grafted trees, 75% of trees grafted in June had successful graft unions. Trees grafted with green wood showed more growth during the 2015 growing season. Trees chip budded with dormant wood healed but showed little to no growth during the 2015 growing season.

Scionwood of 14 cultivars and advanced selections was collected in March 2016 for grafting demonstrations and trials and distribution to nurseries and individuals. Travel plans were made for the grafting consultant, Neal Peterson, to perform grafting demonstrations and assist with grower trials in May 2016.

Impacts and Contributions/Outcomes

Limited resource farmers in Kentucky have small plantings of seedling trees or wild trees that with grafting and top working could serve as rootstock and enable rapid production from grafts of high quality and high demand pawpaw fruit. This project will not only increase pawpaw yields, but will enhance high quality marketable fruit from grower plantings; thereby promoting a sustainable fruit production system with low inputs for limited resource farmers.

None of the bark inlay grafts performed on older trees successfully formed graft unions. From this preliminary experiment, this method does not appear to be a feasible method for topworking pawpaw trees. Using earlier grafting dates, smaller branches, a different grafting method, or younger, more vigorous trees may improve grafting success in the future.

For chip budded trees, 66% of 4-year-old rootstock trees chip budded in May successfully formed graft unions. For the whip and tongue grafted trees, 75% of trees formed successful graft unions. Trees grafted with green wood showed more growth during the 2015 growing season. Trees chip budded with dormant wood healed; however, these buds showed little to no growth during the 2015 growing season. These grafts and buds will continue to be evaluated in 2016. Either of these grafting methods show promise for topworking smaller diameter pawpaw trees.

Collaborators: