). Oils applied to corn can damage the plant tissues if applied in a high enough dose ( Hazzard, 1998 ). The efficacy of oil treatments has been demonstrated in some experiments, but phytotoxicity or damage to the developing ear from reduced pollination
Tori Lee Jackson, Mark G. Hutton, and David T. Handley
Laura C. Merrick, Frank Drummond, Constance Stubbs, and Rhonda Weber
Managed and feral honey bee (Apis mellifera) colonies have declined dramatically in the past decade due largely to parasitic mites, pesticide contamination, and severe weather. Squash (Cucurbita spp.) is one of many agricultural crops whose production may be negatively effected by decline of these pollinators. A study was conducted on a set of nine farms in Maine to assess the relationship between bee abundance and fruit set of summer and winter squash. The organic and conventional farms targeted in the study included farms with and without the presence of honey bees. With winter squash, fields with more bees tended to exhibit higher fruit set. The average fruit set was slightly higher for farms with honey bees (42%) vs. those without (35%), but both types of farms were similar to that found in controlled hand pollinations (31% on average). In contrast, fruit set for summer squash averaged 95% to 96% for all farms, regardless of the relative abundance of censused bees. Bumble bees (Bombus spp.) were the most abundant wild bees found pollinating squash. Farms with honey bees on average had higher numbers of bees in squash flowers than farms without honey bees, although a difference in preference for floral sex type was detected for bee taxa. Honey bees were much more likely to be found in female flowers, while bumble bees were more abundant in male flowers. Significantly more native bees were found in squash flowers on farms without honey bee hives, although native bees were still present to some extent on farms that were dominated by Apis mellifera.
Todd P. West and Thomas W. McCutcheon
The objective of this study was to investigate the use of hornfaced bees (Osmia cornifrons Radoszkowski) as a successful sustainable alternative for pollination of commercial highbush blueberry (Vaccinium corymbosum L.). The hornfaced bee is native to Japan and introduced to the United States in 1977 by the USDA. Hornfaced bees have been shown to be 300× more efficient in pollinating apples than honey bees. Hornfaced bees are active for 4–6 weeks (April to June), and then the adults die. The rest of the year (10 months), dormant hornfaced bees exist inside nest cells located in cardboard straws stored away from berry production areas. Currently, there are no reports on hornfaced bee use available for blueberry farmers. Five pollinator treatments were compared in 2005 including: hornedfaced bees; honey bees; bumble bees; natural pollinators; and no pollinators. Enclosed pollination cages were constructed around mature field-grown highbush blueberry plants to prevent mixing of pollinator treatments. Each cage contained a single pollinator treatment except for the natural pollinator treatment. The five pollinator treatments were replicated three times inside separate netted cages on the farm. Three branches per plant were randomly selected that had a minimum of five fruiting buds and blossom number recorded. After pollination occurred the cages were removed to allow the berries to ripen. Ripe fruit were picked weekly over the season (July to August), with the fruit from each sample being counted and weighed. Blossom number was compared to fruit number and weight to determine efficiency of pollination as a result of the pollinator treatments. The results showed that hornfaced bees pollinated blueberries as well as or better than the other pollinators.
Maria Victoria González, Manuel Coque, and Maria Herrero
The effective pollination period was determined in kiwifruit [Actinidia deliciosa (Chev.) Liang and Fergusonl and the factors affecting it were evaluated. The effective pollination period, measured as the capability to set fruit after hand-pollinating flowers of different ages, was 4 days; 5 days after anthesis fruit set decreased and 2 days later it was nil. Pollen tube growth did not appear to he a limiting factor since pollen tubes grew quickly and reached the base of the style 2 days after pollination and reached the ovules 1 day later. Ovules appeared viable for the 7 days following anthesis, and visibly degenerated within the following 3 days. Stigmatic receptivity was determined by the ability to sustain pollen germination after hand pollinating flowers of different ages. The duration of stigmatic receptivity closely fit the effective pollination period determined through fruit set. Thus, it appears that stigma receptivity is the main factor responsible for the short effective pollination period.
Cheryl R. Hampson, Anita Nina Azarenko, and Al Soeldner
Scanning electron microscopy was used to describe pollen-stigma interactions during compatible and incompatible pollinations of hazelnut (Corylus avellana L.), a species possessing sporophytic self-incompatibility. The stigmatic surface is of the dry type and was covered with elongated, rounded papillae. Compatible and incompatible pollen hydrated within 2 hours of pollination. Compatible pollen tubes emerged by 4 hours and grew into the style by 12 hours after pollination. Penetration of stigmatic papillae appeared to be intracellular in some cases. In incompatible pollinations, however, pollen tube emergence was delayed until at least 8 hours. The pollen tubes were distorted and did not penetrate the stigma.
Raúl De la Rosa, Angjelina Belaj, Antonio Muñoz-Mérida, Oswaldo Trelles, Inmaculada Ortíz-Martín, Juan José González-Plaza, Victoriano Valpuesta, and Carmen R. Beuzón
pollinations and pollen tube germination ( Bradley and Griggs, 1963 ; Breton and Bervillé, 2012 ). Current information indicates that the compatibility system in olive might be of the sporophytic type ( Breton and Bervillé, 2012 ; Collani et al., 2012
Thomas L. Davenport
Individual avocado (Persea americana Mill.) flowers are perfect, opening two times to display two distinct reproductive stages on consecutive days. Stage 1 focuses on presentation of pistils and Stage 2 on presentation of pollen. The Stage 1 opening offers the greatest opportunity for outcrossing due to the absence of available pollen in that stage. Stage 2 flowers, however, are self-pollinated within flowers in direct proportion to the number of white stigmas present at the time of pollen dispersal. The potential success of these self-pollination events was examined in orchard trees of seven commercial Florida cultivars: Booth 7, Brooks Late, Choquette, Monroe, Simmonds, Tonnage, and Tower 2 and compared with hand-pollinations from complementary cultivars (cross pollination) and from flowers of the same cultivar (close pollination). The furthest advancement of pollen tubes down styles and into the ovaries on their way to the egg apparatus was noted in hundreds of individual flowers 24 and 48 h after pollen deposition on receptive white stigmas of the Stage 2 flowers. Virtually none of the seven cultivars exhibited pollen tubes reaching the egg apparatus by 24 h after deposition. By 48 h, however, pollen tubes had reached the egg apparatus in 25% to 85% of the pollinated flowers, depending upon cultivar. Pollen source was inconsequential. The results demonstrate the success of self-pollination in avocados. It is especially important for cultivars growing in humid climates, which display a high proportion of receptive white stigmas in Stage 2.
Zhongbo Ren, Jiang Lu, and Xia Xu
`Pam' is a popular muscadine grape (Vitis rotundiforia) used for the fresh fruit market. It is characterized with large berry, nice appearance, good texture and flavor, and high disease resistance. This cultivar, however, requires pollinators because it is pistillate. To select a better pollinator for this pistillate cultivar, a 2-year study was conducted at Florida A&M University in 2003 and 2005. Fresh pollen of muscadine grape `Alachua', `Nesbitt', and `Noble' was used for pollination. `Nesbitt' pollen resulted in 100% of the pollinated clusters setting fruits in both years, while pollination with `Alachua' yielded 70% (2003) to 87% (2005) of fruiting clusters, and `Noble' pollen yielded 72% (2003) and 97% (2005) fruiting clusters, respectively. Fruit numbers per fruiting cluster also varied among pollen sources. `Alachua' pollen resulted in 7.2 (2003) and 8.1 (2005) fruits per cluster, while `Nesbitt' produced 10.1 (2003) to 10.5 (2005) fruits per cluster, and `Noble' produced 8.3 (2003) and 9.0 (2005) berries per cluster. Open pollinated `Pam' had 100% clusters set fruits, averaging about 11 fruits per cluster in both seasons. No difference of berry size was observed among fruits produced from different pollen sources. Both sugar contents and acids levels were a little bit higher in 2005 than that in 2003. However, no differences of sugar content and acid level were found among the fruits derived from different controlled pollen sources. These data suggested that `Nesbitt' is a better pollinator than `Alachua' and `Noble' for `Pam' muscadine grape.
Kenna E. MacKenzie
The effects of pollination treatments on fruit set and five berry characteristics [mass, diameter, number of apparently viable seeds (well-developed, plump with dark seed coat), total seed number (includes apparently viable and partially developed seeds), and harvest date] were examined on three highbush blueberry cultivars. Pollination treatments included unpollinated, open pollinated, emasculated, and three hand pollinations that used pollen from the same flower, from the same cultivar, or from a different cultivar. Berries matured earliest and were smallest with the most apparently viable seeds in `Northland', `Patriot' had the greatest fruit set and smallest seed number, and `Bluecrop' matured the latest. Fruit set was greater, berry size larger, seed number smaller, and maturation later in 1990 than 1991. For all three cultivars, berries were generally smallest, latest maturing, and had the fewest seeds when pollination was prevented and were largest with the most seeds and earliest maturing in open visitation. Emasculation resulted in berries similar to those from unpollinated flowers. For berry characteristics, cross-pollination was of benefit for `Patriot' and possibly `Northland' but not `Bluecrop'. Thus, commercial highbush blueberry planting designs must be based on the pollination requirements of the particular cultivar. `Northland' berries almost always had seeds, while `Patriot' showed high levels and `Bluecrop' low levels of parthenocarpy.
J.R. Schupp, S.I. Koller, and W.D. Hosmer
This study was undertaken to test the efficacy of a power duster for supplemental pollination of `McIntosh' apple trees, where lack of nearby pollinizing cultivars was thought to be a limiting factor to productivity. The pollen duster was ineffective in increasing fruit set, fruit size, or seed number in fruits on limbs that were covered with spun-bonded rowcover material prior to bloom. Applying supplemental pollen to open-pollinated `McIntosh' trees had no effect on fruit set, yield, fruit size, or seed number, regardless of pollen dose, timing, or number of applications. Dispersal of supplemental pollen with a power duster appears to be an inefficient method of pollinating apple trees.