Long-Term Performance of Ten North American Pawpaw Cultivars in Missouri, USA

ABSTRACT

North American pawpaw (Asimina triloba) is an undeveloped tree fruit crop indigenous to the eastern United States. Recent breeding efforts have set the stage for successful cultivation of pawpaw, but cultivar evaluations among geographically distinct environments are needed to advance this unique specialty crop. A significant genotype by environment experiment incorporating 10 pawpaw cultivars, 350 trees, and four sites across Missouri and Oklahoma (USA) was established in 2002–03. Data across 19 years of cultivar performance, tree growth, and fruit production at the three Missouri sites were evaluated. The cultivar “PA Golden” produced the largest trees, whereas “Overleese” struggled with long-term survival, tree growth, and fruit production. “PA Golden” also tended to produce earlier crops, whereas “Sunflower” produced very high yields later into the growing seasons compared with other cultivars. “Susquehanna” consistently produced the largest fruits, averaging 184 g across the three sites and multiple years. Pawpaw trees were very productive in the Missouri environment over 19 years and show excellent promise as an economically viable specialty crop.

KEYWORDS:

• Asimina
• Annonaceae
• specialty crop
• tree fruit
• Agroforestry

Introduction

The North American pawpaw (Asimina triloba) is a widespread but little-known food-producing tree in the Annonaceae family that is native to the midwestern and eastern United States (Byers et al. 2022). Pawpaw trees are often found growing in patches along streams and as understory trees in rich, relatively moist soils. According to Pomper et al. (2008a), the tree grows in temperate woodlands or mesic hardwood forests within USDA Plant Hardiness Zones 5 to 8 (USDA, 2024). Pawpaw is closely related to several popular commercially produced tropical fruits, such as cherimoya (Annona cherimola), sweetsop (Annona squamosa), and soursop (Annona muricata), yet pawpaw’s development as a specialty food crop is nascent.

Pawpaw trees produce the largest edible fruits native to North America. The fruit has been consumed by Indigenous peoples as a nutritious, seasonal food for millennia, and it has also been used medicinally (Moerman, 1998). The fruits vary in size, shape, flavor, and color, but are generally oblong, 5–14 cm long and 5–8 cm wide, depending on the cultivar, soil conditions, and climate (Adainoo et al. 2022; Lolletti et al. 2021). Pawpaw fruits are sweet with a bright yellow or orange custard-like and sometimes juicy pulp. The pulp of the fruit has a unique flavor that is often compared with banana, mango, peach, melon, and pineapple (Brannan et al. 2012; Mcgrath and Karahadian, 1994). The fruits are best when fully tree-ripened, as they do not ripen well off the tree (Adainoo et al. 2023b) and may be presumed to be non-climacteric. Additionally, the ripe fruits are delicate, have thin skins, and deteriorate quickly after harvesting with undesirable changes in color and flavor, making them difficult to bring to fresh markets in good condition (Adainoo et al. 2022, 2023a, 2023b; Galli et al. 2008).

The pawpaw tree is a rich source of valuable nutritional and nutraceutical compounds. The twigs, leaves, bark, and roots of the tree contain potent pharmacologically active compounds, such as annonaceous acetogenins, that possess antitumor, anticancer, pesticidal, and piscicidal properties (Majrashi et al. 2018, 2021; Nam et al. 2021). Various tissues of the pawpaw tree contain phenolic compounds and other metabolites that are important for human health (Nam et al. 2017, Pande and Akoh, 2010). Thus, in addition to horticultural fruit production, harvesting and processing pawpaw leaves, twigs, bark, and roots for medicinal purposes may provide additional marketing opportunities for orchardists wishing to diversify their operations.

Many Americans are intrigued by pawpaw fruits but have very little opportunity to purchase or taste them (Cai et al. 2019). Commercial pawpaw orchards remain scarce while wild trees do not produce fruits in significant or reliable quantities. Wild pawpaw fruits are usually small with numerous seeds, and sometimes have poor flavor (Moore, 2015). Recent breeding programs have developed excellent cultivars with improved traits such as increased productivity, large and uniform fruit size, fewer seeds, precocity, excellent flavor, thicker skins (for better post-harvest handling), and superior pest and disease resistance (Okie, 2004; Pomper et al. 2008b, 2009).

Between 1995 and 1999, a large regional pawpaw variety trial was established by The Pawpaw Foundation and Kentucky State University (Pomper et al. 1999, 2003). Locations for the study included 11 sites within pawpaw’s native range (eastern USA) and a 12th site at Corvallis, OR, USA (not in the native range). Missouri and Oklahoma (within the native range) were not included in this initial evaluation. The present study is a second-generation experiment that benefitted from data collected in the earlier study and includes several newer cultivars that had been subsequently released. The aim of this study was to determine the long-term performance of ten of the most promising pawpaw cultivars grown at four sites across Missouri and Oklahoma. Factors included tree survival and growth, fruit production, and fruit characteristics over a 19-year period.

Materials and Methods

Orchards Establishment and Management

A multi-location pawpaw research trial was established at four locations in the midwestern United States in 2002–03. The sites included the University of Missouri’s Horticulture and Agroforestry Research Farm (HARF) at New Franklin, MO (lat. 39.02479, long. −92.76736, alt. 192 m); the University of Missouri’s Southwest Research, Extension, and Education Center (SWC) at Mt. Vernon, MO (lat. 37.08586, long. −93.86714, alt. 344 m), Missouri State University’s State Fruit Experiment Station (SFES) at Mountain Grove, MO (lat. 37.15469, long −92.26568. alt. 440 m), and the Kerr Center for Sustainable Agriculture (KERR) at Poteau, OK (lat. 34.98242, long. −94.70006, alt. 145 m).

The soils at the four sites were HARF: Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs) that is deep, fertile, well-drained loess very near the Missouri River; SWC: Dapue silt loam (fine-silty, mixed, active, mesic Fluventic Hapludolls), a very deep, well drained, moderately permeable, level soil formed in silty alluvium; SFES: Viraton silt loam (fine-loamy, siliceous, mesic Typic Fragiudalfs) that is very deep and moderately well drained with a fragipan at 38–84 cm; and KERR: Cowton loam (fine, mixed, active, thermic Ultic Hapludalfs), a moderately deep, well drained, slowly permeable soil on gentle to moderate slopes (USDA-NRCS, 2023). The SWC site would be the closest to having soils similar to where pawpaw trees occur naturally in the region. Average annual rainfall at the sites is HARF: 975 mm, SWC: 1,117 mm, SFES: 1,148 mm; and KERR: 1,203 mm. Soil samples were collected at each site and evaluated prior to planting, and soil pH, P, and K adjusted according to recommendations at that time (Jones et al. 1998).

For the HARF planting, pawpaw seedlings were purchased from the Missouri Department of Conservation’s George O. White State Forest Nursery (Licking, MO). The seeds were sourced in Missouri, but were of mixed and un-tracked origin. In early spring, 2000, 50 seedlings were transplanted to the orchard site. The trees were planted in seven rows interspersed with rows of similarly aged trees of other species across a 1.2-ha site, with pawpaw trees 3.05 m apart in rows that were 6.1 m from other tree rows. In spring, 2002, the trees were grafted to 10 pawpaw cultivars (“Mango,” “NC-1,” “Overleese,” “PA-Golden,” “Prolific,” “Shenandoah,” “Sunflower,” “Susquehanna,” “Tallahatchie,” and “Wells”), with five replications each in a completely randomized design. All trees were successfully grafted; thus, this orchard was established one year prior to the other three orchards in the study.

For SWC, SFES, and KERR, all trees were produced as follows: Open-pollinated fruits from a variety of improved cultivars were harvested in 2000, with seeds provided to the project by Neal Peterson (Peterson Pawpaws, Harper’s Ferry, WV, USA), and placed into cold stratification. In early spring, 2001, seeds were germinated in a greenhouse at SFES, with resulting seedlings potted and grown in a greenhouse/nursery that summer. More than 360 seedlings resulted. Scionwood of eight promising pawpaw cultivars was provided by Peterson and Kirk Pomper (Kentucky State University) and grafted to the potted seedling trees in the greenhouse in March and April, 2002. These potted, grafted trees (along with additional similarly produced grafted and ungrafted trees for use as border trees) were maintained in a nursery, overwintered, then transplanted to all three sites 27 March 2003. The cultivar evaluations at each of these sites included 64 test trees (eight cultivars with eight replications each) arranged in a completely randomized design, planted within 36 perimeter trees to protect the main experiment from edge effects (100 trees total per site). The eight study cultivars at these three sites were “NC1,” “Overleese,” “PA-Golden,” “Shenandoah,” “Sunflower,” “Susquehanna,” “Tallahatchie,” and “Wells,” which were also among those established at the HARF site. Trees at these three sites were planted in a 10 × 10-tree configuration, with trees spaced 3.05 m apart within rows and 5.5 m apart between rows, thus occupying 0.17 ha per site.

All trees were protected with tan-colored 1-m-tall polyethylene tree tubes (Tree Pro, West Lafayette, IN, USA) for the first two years (tubes were removed in fall and replaced in spring). Drip irrigation systems were installed at all sites, and trees were irrigated when conditions were dry. Weeds were managed by hand and with glyphosate and clethodim herbicides only as needed. Vegetation within the alleys was managed through frequent mowing during the growing seasons. Trees were fertilized with 50 g 10-10-10 (N-P-K) soon after planting and again the following spring. Subsequently, N-only fertilizer (ammonium nitrate or urea) was applied each spring based on tree size, with 36 g elemental N applied per cm trunk diameter within a 1-m radius of each tree’s trunk. Insect pests and diseases were surveyed, identified, monitored, and managed as needed (see Results and Discussion). Minimal pruning was performed late each winter to encourage trees to a central leader form.

The cultivars selected for this study were chosen based on data from other on-going long-term experiments (Pomper et al. 1999, 2003), as well as promising new releases that were not included in previous trials. Five of the cultivars (“NC-1,” “Overleese,” “PA-Golden,” “Sunflower,” and “Wells”) were long-established (Brooks and Olmo, 1997), whereas “Shenandoah” and “Susquehanna” were introduced by Neal Peterson in 2004 (Okie, 2004). “Tallahatchie” is the most recent release by Peterson; note that “Tallahatchie” was evaluated as “10–35” in previous publications from these orchards (Adainoo et al. 2022, 2023a). “Mango” and “Prolific,” used only at HARF, were also older, established cultivars (Brooks and Olmo, 1997). Details on the genetic origins, horticultural attributes, yields, fruit characteristics, and flavor profiles of these cultivars have also been summarized in additional articles (Adainoo et al. 2022, 2023a; Pomper et al. 2003, 2008a, 2008b).

Long-Term Field Data

The long-term data evaluated for this study were based on individual tree performance. Number of fruits, total fruit production (fresh weight), mean individual fruit weight, and ripening period were determined on a per-tree basis each summer. Tree growth was measured during dormant seasons as trunk diameter at 30 cm above soil level (Pomper et al. 2008b). Long-term tree survival was determined, with dead or very poorly growing trees promptly replaced with new trees, and surviving rootstocks that had lost their scions re-grafted. The study was discontinued at KERR in 2005, HARF in 2013, SFES in 2015, but continued through 2022 at SWC.

Statistical Analysis

Individual, randomized trees at each site served as the experimental unit. The eight cultivars that were common among the three Missouri sites were analyzed in the form a completely randomized design per site, with five reps (trees) per cultivar at HARF and eight reps per cultivar at the SWC and SFES, with three locations (blocks), and repeated measures over time (years). Data from the 10 cultivars at HARF were also separately analyzed in a single-site comparison. The statistical differences within the data for the various cultivars were determined by one-way analyses of variance and Tukey’s test (p ≤ .05) using Minitab version 18 software (Minitab Inc., PA, USA). Hierarchical cluster analysis dendrogram, boxplots, and graphs were plotted using OriginPro 2022 version 9.9.0 software (Origin Lab Inc., Northampton, Massachusetts, USA). Data for the total number of fruits harvested per tree are presented as boxplots.

Results and Discussion

Long-Term Orchard and Tree Establishment

The establishment of the majority of trees was successful, with excellent survival initially. While tree survival at KERR during the establishment year was good (92%), the trees declined precipitously over the subsequent three years, despite what was believed to be adequate care. The site is exceptionally exposed, windy, and hot. While pawpaws are indigenous to the KERR region (commonly found growing in partially shaded, secondary bench riparian areas), the very exposed, solar-intensive site selected may not have been conducive to pawpaw cultivation. The majority of the KERR trees struggled or eventually died with very little fruit produced; thus, data from this planting are not included in this report. Tree establishment at the three Missouri sites was excellent, with significant fruit production beginning in 2008 at HARF and SFES, and 2009 at SWC.

Cultivar Productivity

Figure 1 provides a snapshot of fruit yields among 10 cultivars in a single year (2011) at a single site (HARF). The pawpaw trees at that site had a statistically similar range of total number of fruits harvested per tree for all 10 cultivars. Although “Shenandoah” had a lower range in the total number of fruits harvested per tree, it was similar to the fruit yield of all the other cultivars except for “NC-1” (p = .042). Further, some “Shenandoah” trees had more than 200 fruits per tree within the harvest season, making them outliers from the range as represented by the diamond dot in Figure 1. Similarly, some “NC-1” trees bore more fruits than the overall range for that cultivar in the 2011 harvest season.

Figure 1. Boxplots showing range of total number of fruits per tree for the ten pawpaw cultivars at the HARF site in 2011.

Boxplots with the same letters are statistically similar for the respective cultivars at p ≤ .05.

Figure 2 shows the range of total number of fruits harvested per tree for eight cultivars at the SFES site in 2006, 2008–10, and 2013. The plots show that among all the cultivars at the SFES site, the trees had the highest total number of fruits in 2009. The total number of fruits per tree (within cultivars) among all the other years were statistically similar at p ≤ .05. Among the cultivars grown at the SFES site, only “Overleese” trees had statistically similar numbers of fruits per tree across all the years (including 2009) at the site.

Figure 2. Boxplots showing range of total number of pawpaw fruits per tree for the eight cultivars at the SFES site in 2006, 2008–10, 2013.

Boxplots with the same letters are statistically similar for the respective cultivars at p ≤ .05.

Boxplots representing the range of total number of fruits harvested per tree for all eight pawpaw cultivars at the SWC site in 2009, 2012–17, and 2019–22 are presented in Figure 3. Pawpaw trees can sometimes produce initial fruit crops about 3 years after planting and grafting (Blake et al. 2015). Many of the trees at this site produced sporadic crops during those early years, but consistent fruit production did not begin until 2009. In the figure, it is evident that, while a fruit crop among all cultivars was produced in 2009 (six years after planting and grafting), significant production began in 2012. The data show that among all the cultivars at the SWC site, there were higher ranges of total number of fruits harvested in the 2015 harvest season for most cultivars. The fruit yields in 2022 for “Sunflower,” “Susquehanna,” and “Wells” were similar to the 2015 fruit yield. The numbers of fruits within cultivars varied significantly (p < .0001) from year to year at this site. Overall, “Tallahatchie” and “Sunflower” trees had more fruits per tree than all other cultivars at the site, while “Overleese” trees bore relatively fewer fruits per tree across the study period. This poor performance of “Overleese” may have been due to its lower tree survival (48.8%) throughout the study period as shown in Table 1, which summarizes long-term tree survival among the eight cultivars at SWC. The cultivars “Sunflower” and “Susquehanna” showed greater long-term tree survival (86.9% and 81.3% respectively), although their survival was not statistically greater than some of the other cultivars.

Figure 3. Boxplots showing range of total number of fruits per tree for the eight pawpaw cultivars at the SWC site in 2009, 2012–17, and 2019–22.

Boxplots with the same letters are statistically similar for the respective cultivars at p ≤ .05.

Table 1. Percentage (%) tree survival per year for eight cultivars of the North American pawpaw at the SWC site.

Year	Tallahatchie	NC-1	Overleese	PA Golden	Shenandoah	Sunflower	Susquehanna	Wells
2003	62.5	75.0	75.0	62.5	75.0	100.0	75.0	50.0
2004	62.5	100.0	87.5	75.0	75.0	100.0	75.0	62.5
2005	62.5	100.0	75.0	75.0	87.5	100.0	75.0	62.5
2006	62.5	100.0	75.0	75.0	87.5	100.0	87.5	62.5
2007	62.5	100.0	37.5	75.0	87.5	87.5	75.0	62.5
2008	87.5	100.0	37.5	87.5	87.5	87.5	75.0	62.5
2009	87.5	100.0	50.0	87.5	100.0	75.0	62.5	75.0
2010	87.5	87.5	62.5	75.0	100.0	62.5	75.0	87.5
2011	87.5	87.5	75.0	62.5	100.0	87.5	75.0	87.5
2012	100.0	100.0	87.5	62.5	100.0	87.5	87.5	87.5
2013	100.0	100.0	75.0	62.5	100.0	87.5	87.5	87.5
2014	87.5	100.0	50.0	75.0	100.0	100.0	87.5	87.5
2015	87.5	100.0	50.0	75.0	100.0	100.0	100.0	87.5
2016	87.5	87.5	62.5	87.5	87.5	100.0	100.0	87.5
2017	87.5	87.5	50.0	62.5	87.5	100.0	100.0	87.5
2018	62.5	37.5	0.0	50.0	50.0	87.5	87.5	87.5
2019	62.5	37.5	0.0	50.0	37.5	75.0	87.5	87.5
2020	37.5	37.5	0.0	12.5	12.5	75.0	75.0	62.5
2021	37.5	37.5	12.5	12.5	12.5	62.5	75.0	50.0
2022	37.5	37.5	12.5	12.5	12.5	62.5	62.5	50.0
Average	72.5^ab	80.6^ab	48.8^c	61.9^bc	75.0^ab	86.9^a	81.3^ab	73.8^ab
95% CI	(62.5, 82.5)	(70.6, 90.6)	(38.8, 58.8)	(51.9, 71.9)	(65.0, 85.0)	(76.9, 96.9)	(71.3, 91.3)	(63.8, 83.8)

95% CI = 95% confidence interval.

Averages with the same letters are statistically similar for the respective cultivars at p ≤ .05.

The average weights of fruits harvested from the SWC, SFES and HARF sites are summarized in Table 2. The table shows analysis of the fruit weights among cultivars within site, and within cultivar across the three sites. The results show that there were no statistically significant differences in the weights of “Overleese,” “Sunflower,” “Susquehanna,” “Tallahatchie,” and “Wells” fruits among the three sites. This suggests that the growth conditions at the three study sites did not significantly influence the weight of the fruits produced by these cultivars, and therefore the fruit size is largely genetically controlled. However, “NC-1” (p = .022), “PA Golden” (p = .002) and “Shenandoah” (p < .001) fruits were statistically different in terms of their weights among the three sites, suggesting that environment and management decisions may have some impact on fruit size. Further, within the respective study sites, there were statistically significant differences in the fruit weights among the cultivars. Overall, “Susquehanna” fruits were consistently heavier (184 ± 56 g) than fruits from other cultivars, whereas “Wells” fruits were lighter (96 ± 31 g). It is evident that “Susquehanna” produces heavier fruits than the other cultivars studied but the average weight of “Wells” fruits over the years was significantly lower than what had been previously reported (Adainoo et al. 2022).

Table 2. Average fruit weights (g) of pawpaw cultivars grown at the SWC, SFES, and HARF sites from 2006–2022.

Site	Tallahatchie	NC-1	Overleese	PA Golden	Shenandoah	Sunflower	Susquehanna	Wells	Mango	Prolific	p-value
SWC	133 ± 30^Abc	135 ± 26^Bbc	137 ± 19^Ab	102 ± 7^Bcd	137 ± 20^Bb	133 ± 11^bc	202 ± 31^Aa	94 ± 14^Ad	–	–	<0.001
SFES	124 ± 31^Aab	163 ± 25^Aab	95 ± 87^Ab	122 ± 13^Aab	178 ± 23^Aa	140 ± 36^ab	165 ± 76^Aab	104 ± 40^Aab	–	–	0.01
HARF	107 ± 23^Abcd	132 ± 11^Bb	83 ± 27^Ad	131 ± 21^Abc	92 ± 8^Cbcd	107 ± 25^bcd	193 ± 31^Aa	88 ± 26^Acd	99 ± 11^bcd	100 ± 14^bcd	<0.001
Mean*	124 ± 30^bcd	146 ± 28^b	107 ± 58^cd	116 ± 18^bcd	140 ± 38^bc	129 ± 28^bcd	184 ± 56^a	96 ± 31^d	99 ± 11^bcd	100 ± 14^bcd	<0.001
p-value	0.330	0.022	0.180	0.002	<0.001	0.116	0.385	0.648	–	–	–

Upper case superscripts show statistical differences within cultivars among the different sites (columns); lower case superscripts show statistical differences among cultivars within each site (rows) at p ≤ .05.

Means with the same letters are statistically similar at p ≤ .05.

*The mean values were not included in the ANOVA analysis that yielded the p-values at the bottom of the table.

Cultivar Phenology

In addition to the variations in fruit yield among the cultivars, the ripening periods also varied. Figure 4 shows the total number of fruits harvested for each of the cultivars in 2009 and 2012–22 at SWC according to the weeks in which the fruits were harvested. The total number of fruits harvested in the week of August 1–7 was summed up to obtain the first point in the graph, with the same procedure repeated for each of the weeks indicated in the graph until the week of the latest harvest October 12–18. This graph shows the ripening period for each of the cultivars and could guide farmers in developing orchard design strategies for maximizing harvest efficiency as well as processing and marketing efficiencies. For example, according to Moore (2015) and Pomper et al. (2009), “Susquehanna,” “Wabash,” and “Potomac” pawpaw fruits ripen late in the harvest season, while “Rappahannock” and 10–35 (“Tallahatchie”) ripen mid-season, and “Allegheny” and “Shenandoah” ripen early. Figure 4 shows that all the cultivars had a relatively similar pattern in terms of fruit yield with respect to time. The main difference among the cultivars was in the total number of fruits harvested over multiple seasons; some cultivars yielded many more fruits than others. From the figure, it is clear that over multiple years, there was an initial stage of limited, early fruit ripening followed by a brief hiatus before fruit ripening rapidly intensified. The reason for this consistent initial surge in fruit production is unclear but may be related to an early flush of flowers in early spring that precedes full-scale anthesis (long-term personal observations). The data show that “PA Golden” is a consistently early-ripening cultivar, whereas “Sunflower” and “Wells” hold and ripen much of their fruit later in the season. In the week of September 13–19, “Wells” reached its peak fruit yield with “Sunflower” peaking the week after. The total fruit number data also demonstrate that “Sunflower” is a prolific producer of fruits, however its fruits tend to be smaller than other cultivars [Table 2 and Adainoo et al. (2022)]. “Overleese” had the lowest long-term fruit yield, likely due to the low tree survival throughout the study period (Table 1). While “Overleese” may perform well in other environments, its poor tree and fruit yield performance in this study suggest that it may not be well-suited to Missouri production.

Figure 4. Ripening period chart showing the total number of harvested pawpaw fruits each week for the respective cultivars in 2009 and 2012–22 at the SWC site.

Figure 5 shows a similar plot as Figure 4; however, the ripening period chart is based on the total fruit weight for each of the cultivars according to the weeks in which the fruits were harvested. The figure shows that “Susquehanna” fruits weighed more than “PA-Golden” and “Tallahatchie” fruits even though more fruits of the “PA-Golden” and “Tallahatchie” cultivars were harvested as shown in Figure 3 and Table 2. Previous studies also showed that “Susquehanna” fruits were heavier than “PA-Golden,” “Tallahatchie,” and “Sunflower” fruits (Adainoo et al. 2022). However, from Figure 4, it can be seen that over the years, the total cumulative weight of the “Sunflower” fruits produced was higher than the total weight of “Susquehanna” fruits. The weights of the all the other cultivars (“NC-1,” “Shenandoah,” “Wells,” and “Overleese”) corresponded with the total number of fruits harvested as shown in Figures 4 and 5.

Figure 5. Ripening period chart showing the total fruit weight of harvested pawpaw fruits for the respective cultivars in 2009 and 2012–22 at the SWC site.

Cultivar Uniformity

Hierarchical cluster analysis can provide specific details about observations in terms of how similar they are to one another (Tullis and Albert, 2013). The dendrogram that results from the analysis shows that observations that cluster together earlier are more comparable to one another than data that cluster together later with reference to the similarity axis. The dendrogram in Figure 6 compares the 10 cultivars across the three Missouri sites in terms of their fruit yields. The dendrogram shows that “Susquehanna” and “Shenandoah” cultivars have a 63.8% similarity. “Wells” and “Sunflower” have a similarity of 44.3%, and “NC-1” has a similarity of 54.6%. Further, “Prolific” and “PA-Golden” are similar in terms of fruit yield (similarity = 16.7%), as are “Mango” and “Overleese” (similarity = 18.9%). Among cultivars, “Tallahatchie” recorded a 100% similarity to all the cultivars studied in terms of fruit yield over the study period. The “Tallahatchie” cultivar’s high similarity to the other cultivars’ fruit yield may be as a result of its genetic similarity to the other cultivars studied (Huang et al. 2003).

Figure 6. Hierarchical cluster analysis dendrogram showing the similarity of pawpaw cultivars across all the sites based on their fruit yields over the years.

Long-Term Tree Growth

Long-term trends in tree growth (based on trunk diameter) among cultivars at SWC and SFES are shown in Figure 7. At both sites, it is evident that “PA-Golden” trees recorded the highest growth in trunk diameter compared with all the other cultivars. The “PA-Golden” trees at SWC had statistically larger trunk diameters only in 2013 (p = .01), whereas “PA-Golden” trees at the SFES site had statistically greater growth at all time points (p = .004). This was followed at both sites by “NC-1,” “Shenandoah,” and “Susquehanna” trees. “Overleese” and “Wells” trees recorded the lowest trunk diameters among the cultivars at both sites. While these cultivar growth patterns were similar at both sites, the trees at SFES had significantly greater trunk diameter (p = .004) by the last trunk diameter measurement (2011) compared with those at the SWC site in 2013 (p = .010). This growth difference is difficult to explain as the soil at SWC would be considered superior to that at SFES for pawpaw growth (USDA-NRCS, 2023), but it may point to the responsiveness of pawpaw trees to different degrees of management; despite efforts at equitable management across sites, it is possible that the SFES trees received more water and had less weed pressure.

Figure 7. Trend graphs showing (a) SWC and (b) SFES pawpaw tree trunk diameter at 30 cm above soil level, by cultivar.

Pest and Disease Incidence

Very few significant insect or disease pests were encountered (data not shown), and little intervention was needed. The most important pest was a leaf-rolling caterpillar, sometimes called the Asimina webworm moth (Omphalocera munroei). During intermittent years, larvae appeared in late summer and caused defoliation, especially of younger trees, along with occasional fruit rind damage. Infestations were allowed to develop to a threshold of about 10% defoliation before intervention with either Bacillus thuringiensis, carbaryl, or Mustang Maxx. The leaf-eating larvae of the zebra swallowtail butterfly (Eurytides marcellus) was frequently present but never caused sufficient foliar damage to merit intervention at any of the sites. Fungal leaf spots, generally identified as belonging to the Asperisporium, Phyllosticta, and Septoria genera (P. Tian, unpublished data), appeared intermittently toward the ends of the growing seasons, but did not segregate by genotype (data not shown) and was not severe enough to warrant intervention.

Conclusion

Except at the Oklahoma site, all the pawpaw cultivars studied thrived and produced significant numbers of high-quality fruit crops over many years. While “Overleese” seemed to struggle with tree establishment and fruit production in the long-term, its fruit quality was nevertheless excellent (Adainoo et al. 2022, 2023a). Fruits harvested from this study at SWC were used in other studies (Adainoo et al. 2022, 2023a) that elucidated, for example, the exceptional quality of “Shenandoah” and Susquehanna’ fruits. The present study indicates that those were not the highest yielding cultivars, but were long-lived trees and may be excellent choices for the region. “PA Golden” consistently produced larger trees and an earlier crop compared with other cultivars, however its fruit quality was not as high. “Sunflower” produced abundant numbers of high quality but somewhat smaller fruit and would also be an excellent late-season choice for the region.

Long-term data from this study indicate that pawpaws can be very productive in a full-sun orchard setting in Missouri’s temperate environment. However, the trees seem to have a productive life span of 12–15 years at which point they decline, mainly in the form of bark deterioration on trunks and large lower branches. This decline does not appear to be related to any specific disease or pest, but may be a result of long-term full-sun winter exposure of the thin bark in trees that normally grow in more shaded settings. This seems consistent with long-term observations of wild pawpaw “patch” communities, where large, dominant individual trees are rarely encountered; rather, within the community, older trees are regularly replaced with vigorous young suckers. Experiments to develop methods to protect the bark and prolong tree life are warranted and might be beneficial, but the authors recommend a strategic regimen of replacing pawpaw orchard trees on a 15-year cycle (similar to peaches, blackberries, and other fruit crops). Despite their short-lived nature, pawpaw trees can be very productive in the region, and offer promise as a unique specialty crop for producers wishing to diversify their enterprises.

Acknowledgments

We gratefully acknowledge support for this project from The Kerr Center for Sustainable Agriculture (Poteau, OK, USA), the Missouri Department of Agriculture through a USDA Specialty Crop Block Grant, The Pawpaw Foundation, Kentucky State University, and the University of Missouri Center for Agroforestry through cooperative agreements (58-6020-6-001 and 58–6020-0-007) with the USDA/ARS Dale Bumpers Small Farm Research Center.

Disclosure Statement

No potential conflict of interest was reported by the author(s).