The Pollination and Fruit Quality of Two Kiwifruit Cultivars (Actinidia chinensis var. chinensis ‘AU Golden Sunshine’ and ‘AU Gulf Coast Gold’) (Ericales: Actinidiaceae) Grown in the Southeastern United States

Abstract

Kiwifruit is a new emerging crop for the southeastern United States that requires cross-pollination to set fruit. However, the pollination requirements for varieties grown in the southeastern United States are unknown. Through insect surveys and a bagging experiment, we assessed the pollination requirements of two female kiwifruit cultivars (Actinidia chinensis var. chinensis ‘AU Golden Sunshine’ and A. chinensis var. chinensis ‘AU Gulf Coast Gold’). For each, fruit quantity (fruit set) and fruit quality (weight, size, seed count, firmness, soluble solid content, and dry matter) were compared among three pollination treatments (wind, insect, and artificial pollination). Low abundances of insects were observed visiting female flowers of both kiwifruit cultivars, and therefore likely minimally influenced kiwifruit pollination. Artificial pollination resulted in the greatest percentages of fruit set and marketable fruits, followed by insect and wind pollination. Artificial pollination resulted in fruits that were greater in weight, size, and contained more seeds, than insect- and wind-pollinated fruits. Firmness and soluble solid content did not vary greatly between pollination treatments, yet were greater in ‘AU Golden Sunshine’. Dry matter content did not vary greatly between pollination treatments or between each cultivar. To maximize yields and optimize fruit quality, these results suggest that kiwifruit producers should place more effort into artificial pollination compared to wind and insect pollination. Future research should explore the use of managed bees (e.g., honey bees and bumble bees) within kiwifruit orchards to determine ways to utilize them as a secondary source for pollination needs.

Artificial pollination of kiwifruit (Actinidia chinensis Planch. var. chinensis) (Ericales: Actinidiaceae) results in greater fruit set compared to flowers pollinated by managed bees (Apis mellifera L. (Hymenoptera: Apidae) and Bombus impatiens Cresson (Hymenoptera: Apidae))

“…In kiwifruit, inefficient pollination due to either pollen (inadequate quantity or quality of pollen) or pollinator (fewer pollinator visits or less pollen deposited per visit) limitation (Ashman et al 2004) can result in low fruit set and unsatisfactory size, shape, and uniformity (Tacconi et al 2016). For this reason, kiwifruit growers demand efficiently pollinated female flowers to ensure economic viability (Ferguson 1990, Costa 1999, Abbate et al 2021).…”

“…It is thought that kiwifruit pollination is mainly provided by insects, and to a lesser degree, wind (Testolin et al 1991, Miñarro and Twizell 2015). Studies have documented wind pollinated kiwifruit flowers produce similar-sized fruits compared to insect-pollinated flowers (Bellini et al 1989); however, most evidence suggests pollination via wind is ineffective in producing kiwifruits of marketable size (Donovan and Read 1991, Costa et al 1993, Vaissière et al 1996, Gonzalez et al 1998, Morley-Bunker and Lyford 1999, Howpage et al 2001, Pomeroy and Fisher 2002, Abbate et al 2021). Honey bees and bumble bees are considered the most important pollinators of kiwifruit (Palmer-Jones and Clinch 1974, Matheson 1991a, 1991b, Vaissière et al 1996, Howpage et al 2001); however, their contribution to kiwifruit pollination has been debated (Clinch 1984, Read et al 1989, Donovan and Read 1991, Costa et al 1993, Pomeroy and Fisher 2002, Cnaani et al 2006, Hanley et al 2008, Miñarro and Twizell 2015, Somme et al 2015, Abbate et al 2021).…”

“…Studies have documented wind pollinated kiwifruit flowers produce similar-sized fruits compared to insect-pollinated flowers (Bellini et al 1989); however, most evidence suggests pollination via wind is ineffective in producing kiwifruits of marketable size (Donovan and Read 1991, Costa et al 1993, Vaissière et al 1996, Gonzalez et al 1998, Morley-Bunker and Lyford 1999, Howpage et al 2001, Pomeroy and Fisher 2002, Abbate et al 2021). Honey bees and bumble bees are considered the most important pollinators of kiwifruit (Palmer-Jones and Clinch 1974, Matheson 1991a, 1991b, Vaissière et al 1996, Howpage et al 2001); however, their contribution to kiwifruit pollination has been debated (Clinch 1984, Read et al 1989, Donovan and Read 1991, Costa et al 1993, Pomeroy and Fisher 2002, Cnaani et al 2006, Hanley et al 2008, Miñarro and Twizell 2015, Somme et al 2015, Abbate et al 2021). Studies argued honey bees are inefficient pollinators of kiwifruit due to a lack of attraction to the nectar-lacking blooms (Donovan and Read 1991, Costa et al 1993, Pomeroy and Fisher 2002), and because they forage on concurrently flowering non-kiwifruit plants, often collecting as little as 2–4% kiwifruit pollen (Ford 1971, Blanchet et al 1990).…”

“…Studies argued honey bees are inefficient pollinators of kiwifruit due to a lack of attraction to the nectar-lacking blooms (Donovan and Read 1991, Costa et al 1993, Pomeroy and Fisher 2002), and because they forage on concurrently flowering non-kiwifruit plants, often collecting as little as 2–4% kiwifruit pollen (Ford 1971, Blanchet et al 1990). Similarly, bumble bees ( Bombus impatiens and Bombus terrestris L. (Hymenoptera: Apidae)) have been evaluated as potential pollinators of kiwifruit (Read et al 1989, Miñarro and Twizell 2015, Abbate et al 2021), yet have been shown to be greatly influenced by accessible non-kiwifruit floral blooms collecting as little as 21% kiwifruit pollen (Pomeroy and Fisher 2002). Within the United States, no studies have evaluated the foraging preferences and contribution of A. mellifera and B. impatiens to kiwifruit pollination while stocked within a commercial kiwifruit orchard.…”

“…We predicted that the amount of kiwifruit pollen collected by both managed honey bees and bumble bees would differ due to a difference in attraction between kiwifruit blooms and concurrently flowering non-kiwifruit plants (Pomeroy and Fisher 2002). We also predicted that artificial pollination would result in the greatest fruit set, fruit size, and seed counts compared to wind and insect pollination because more pollen grains would be deposited on the stigma of female flowers than the other pollination methods (Costa et al 1993, Gonzalez et al 1994, 1998, Abbate et al 2021). The results of this research will assist orchard managers within the United States develop a science-backed pollination management plan for the kiwifruit industry.…”