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

Three commercially available pawpaw cultivars with large, high quality fruit and high yields were selected: ‘KSU-Atwood’, ‘Sunflower’, and ‘Susquehanna’. Three trees of each cultivar were grafted on two dates, early vs. late May, at two locations, the Kentucky State University H.R. Benson Research and Demonstration Farm, and a local commercial grower’s site located in Versailles, KY. The average trunk diameter of grafted trees was 4.7 cm, and the range was from 1.6 cm – 9.4 cm. Trees grafted using the bark inlay method in early May (May 3) had a success rate of 91%, whereas trees grafted in late May (May 23) had a success rate of 67%. Growth was similar between the two dates, with scions grafted in early May growing an average of 0.78 m, while scions grafted in late May grew an average of 0.76 m. There was not a significant correlation between diameter and graft take, or diameter and scion growth. Due to a higher success rate, early May appears to be preferable to late May for performing bark inlay grafting of pawpaw trees. This experiment will be repeated in May, 2017.

Videos were recorded of the grafting process in May, 2016 with Mr. Neal Peterson demonstrating the bark inlay method. A demonstration video was created and was presented at the 2016 Fourth International Pawpaw Conference in September, 2016. Over 130 people participated in the Conference and saw the video. The video is being edited and will soon be placed on YouTube for the public to view.

Scionwood of 14 cultivars and advanced selections was collected in March 2017 for grafting demonstrations and trials and distribution to nurseries and individuals. Travel plans were made for the grafting consultant, Neal Peterson, to perform additional grafting demonstrations and assist with grower trials in May 2017.

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.

Trees grafted using the bark inlay method in early May had a success rate of 91%, whereas trees grafted in late May had a success rate of 67%. Growth was similar between the two dates, with scions grafted in early May growing an average of 0.78 m, while scions grafted in late May grew an average of 0.76 m. There was not a significant correlation between diameter and graft take, or diameter and scion growth. Due to a higher success rate, early May appears to be preferable to late May for performing bark inlay grafting of pawpaw trees by Kentucky farmers. However, this experiment will be repeated in May, 2017. 

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