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Caitlin E. Splawski, Emilie E. Regnier, S. Kent Harrison, Karen Goodell, Mark A. Bennett and James D. Metzger

dead plant material. Many novel mulch materials remain to be investigated with regard to their ability to suppress weeds and improve crop yields. The effects of novel mulches on crop pollinators should also be studied to ensure their overall positive

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Carter M. Westerhold, Samuel Wortman, Kim Todd and Douglas Golick

Much public attention has focused on the decline of pollinating insects, in part due to european honeybee ( Apis mellifera ) colony collapse disorder. Since 2006, beekeepers have been reporting an average annual winter loss of 30% of their hives

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Matthew Arrington and Lisa Wasko DeVetter

, 2017 )]. One of the most challenging production issues for blueberry cultivation in western Washington is pollination and subsequent fruit set and reduced yields. Effective insect-mediated pollination is important for optimal fruit set and maximizing

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Thomas L. Davenport, Petra Parnitzki, Sabine Fricke and Melanie S. Hughes

Pollination was investigated in five avocado (Persea americana Mill.) cultivars during two seasons. In the first year, `Simmonds' and `Hardee' branches with inflorescences were covered with cheesecloth bags to prevent pollination by large flying insects during either or both the first (Stage I) and second (Stage II) floral openings. Adjacent, tagged branches were left open as controls. The proportion of pollinated Stage I flowers ranged from <1% in `Simmonds' to 9% in `Hardee.' Pollination rates in Stage II ranged from 15% in `Simmonds' to nearly 69% in `Hardee'. Pollination during Stage II was proportional to the number of white stigmas available during that stage. Stage II pollination rates for bagged flowers and open flowers were similar, even though large flying insects were barred from bagged flowers. In the second year, similar experiments on cultivars Simmonds, Tonnage, Tower 2, and Choquette provided results consistent with those obtained the previous year. Virtually no pollination occurred in bagged Stage I flowers in all cultivars tested, and ≈1% of the open Stage I flowers were pollinated. Pollination of bagged and open Stage II flowers was generally the same within cultivars. The percent pollination of Stage II flowers ranged from a mean of 4.3% to 35%, depending on cultivar. The results show that self-pollination during the Stage II floral opening is the primary means of pollination of commercial cultivars grown in Florida. Moreover, the presence of developing fruits on branches bagged during the flowering season demonstrated that fruit set can occur without pollination by large flying insects.

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William H. Krueger

English walnut (Juglans regia, L.) is a monoecious species bearing staminate and pistillate flowers separately on the same tree. Walnuts are generally self-fruitful, cross-compatible and dichogamous, having incomplete overlap of pollen shed and female receptivity. It is this characteristic which led to the recommendation that about 10% of the trees in a commercial planting be a cultivar with a pollen shed period overlapping pistillate flower receptivity of the main cultivar. Excessive pollen load has been implicated in the `Serr' cultivar in pistillate flower abortion (PFA), the loss of the female flowers early in the season before fruit drop due to lack of pollination. PFA can be reduced and yield improved in `Serr' orchards by reducing pollen load. This can be accomplished by pollinizer removal, or catkin removal at the beginning of pollen shed by mechanical shaking. In years of significant bloom overlap between staminate and pistillate bloom, PFA can be further reduced and yield improved by removing `Serr' catkins. PFA occurs to a lesser extent in other cultivars such as `Chico', `Chandler', `Vina' and `Howard'. This information has led to the reevaluation of pollinizer recommendations. Research focused on optimum pollinizer levels in `Chandler', a cultivar of increasing importance to the California walnut industry, has been inconclusive. Lack of pollinizers may impact yields to a greater extent in the in the northern San Joaquin Valley and Sacramento Valley than in the southern San Joaquin Valley. In any case the previously recommended 10% appears to be excessive. Two to three percent is probably adequate to limit losses due to lack of pollination without resulting in excessive PFA, and is currently being recommended by extension farm advisors and specialists. Factors to consider when determining the number of pollinators to plant include: cultivar susceptibility to PFA, walnut pollen load in the area and local pollination and fruit set experiences.

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S.H. Jalikop and Ravindra Kumar

constraint limiting commercial production of annonaceous fruits is low flower to fruit ratio resulting from inadequate pollination ( Gazit et al., 1982 ; Peña et al., 2002 ). Neither self- nor cross-pollination takes place effectively. Self-pollination is

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Carlos G. Vaz, Domingos de Oliveira and Orlando S. Ohashi

Cowpea, Vigna unguiculata (L.) Walp., is a very important legume in the diet of the population of the Amazon. Although it is autogamous, this species has a cross-pollination rate of ≈10%. Over several years, the mean productivity of cowpea has declined. We suggest that this is linked to a decrease in or an absence of pollinating insects in the fields. The objective of this study is to ascertain the pollinator contribution to cowpea production, as well as to determine the pollination type of the `BR3-Tracuateua' cultivar. In an experimental design, four treatments were compared: no pollination, with flowers in cages to prevent insect visits; open-pollination, with flowers exposed to all visiting insects; self-pollination, with flowers pollinated with their own pollen; and cross-pollination, with emasculated flowers being pollinated manually with pollen from another plant. We observed higher fruit set in the presence of pollinators (83%) than in their absence (77%, caged flowers). However, cross-pollination reduced both the number of seeds per pod and fruit set relative to self-pollination. This result suggests that pollinators have a complementary role in the yield of cowpea, by creating a mixed pollination system where self-pollination dominates.

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R. Paul Baker, Karl H. Hasenstein and Michael S. Zavada

In order to characterize the self-incompatibility system in Theobroma cacao, the levels of ethylene, indole-3-acetic acid (IAA), and abscisic acid (ABA) were determined after pollination with compatible and incompatible pollen and in unpollinated flowers. Pollen tube growth rates after incompatible and compatible pollinations were identical, and the majority of the pollen tubes reached the ovules between 12 and 20 hours after pollination. ABA levels rose in incompatibly pollinated flowers, and fell in compatibly pollinated flowers, prior to pollen tube—ovule contact. Ethylene evolution remained stable in compatibly pollinated flowers and rose in incompatibly pollinated flowers. IAA concentrations increased in compatibly pollinated flowers, and remained stable in incompatibly pollinated flowers after pollination and subsequent to pollen tube—ovule contact.

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M.S. Stanghellini, J.T. Ambrose and J.R. Schultheis

The effectiveness of bumble bees, Bombus impatiens Cresson, and honey bees, Apis mellifera L., on the pollination of cucumber, Cucumis sativus L., and watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai, was compared under field conditions. Comparisons were based on fruit abortion rates and seed set as influenced by bee type (honey bee or bumble bee) and the number of bee visits to treatment flowers (1, 6, 12, and 18 bee visits), plus two controls: a no-visit treatment and an open-pollinated (unrestricted visitation) treatment. For both crops, an increased number of bee visits had a strong positive effect on fruit and seed set. All cucumber and watermelon flowers bagged to prevent insect visitation aborted, demonstrating the need for active transfer of pollen between staminate and pistillate flowers. Bumble bee-visited flowers consistently had lower abortion rates and higher seed sets in the cucumber and watermelon studies than did honey bee-visited flowers when compared at the same bee visitation level. Only slight differences in fruit abortion rates were detected between bee types in the watermelon study. However, abortion rates for bumble bee-visited flowers were consistently less than those for honey bee-visited flowers when compared at equal bee visitation levels, with one exception at the 12 bee visit level. As the number of honey bee colonies continues to decline due to parasitic mite pests and based on the data obtained, we conclude that bumble bees have a great potential to serve as a supplemental pollinator for cucumbers, watermelons, and possibly other vine crops, when honey bees available for rental are in limited supply.

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M.S. Stanghellini, J.T. Ambrose and J.R. Schultheis

The number of honey bees (Apis mellifera L.) continues to decline due to parasitic mite pests and other factors. Honey bees and bumble bees (Bombus impatiens Cresson) were therefore compared for their effects on the seed set of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in a 2-year field experiment. The experiment was a 2 x 4 + 2 factorial, comparing bee type (honey bee or bumble bee) at four visitation levels (1, 6, 12, and 18 bee visits) to pistillate flowers, with two controls: a no-visit treatment and an open-pollinated treatment. Bee visitation level had a strong positive influence on seed set (P ≤ 0.0001). All flowers bagged to prevent insect visitation aborted, demonstrating the need for active pollen transfer between staminate and pistillate watermelon flowers. Flowers visited by B. impatiens consistently contained more seed than those visited by A. mellifera, when compared at equal bee visitation levels (P ≤ 0.0001). We conclude that bumble bees have great potential to serve as a supplemental pollinator for watermelon when honey bees available for rental are in limited supply.