Compared Fruit Set Research Articles

Outcrossing effects on the reproductive performance of Hypericum cumulicola, an endangered Florida scrub endemic1

Abstract Trager, M. D. (Dept. of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32601), E. S. Menges (Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862), P. F. Quintana-Ascencio (Dept. of Biology, University of Central Florida, Orlando, FL 32816), and C. W. Weekley (Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862). Outcrossing effects on the reproductive performance of Hypericum cumulicola, an endangered Florida scrub endemic. J. Torrey Bot. Soc. 132: 204–213. 2005.—We investigated the effects of self-fertilizing and within-population outcrossing in two populations of Hypericum cumulicola, a perennial herb endemic to xeric scrub habitats on central Florida's Lake Wales Ridge. To examine the relationship between pollen source and reproductive performance, we compared fruit set, seed set, percent germination and net fertility (mean number of seedlings produced per flower within a pollination treatment) of hand-pollinated selfed and outcrossed flowers....

Effects of natural rates of geitonogamy on fruit set in Asclepias speciosa (Apocynaceae): evidence favoring the plant's dilemma

The role of geitonogamy in the evolution of inflorescence design is not well understood. The plant's dilemma hypothesis proposes that evolution of larger inflorescences is driven by selection for greater pollinator attraction, but constrained by higher rates of geitonogamy experienced by larger inflorescences. Here we investigate the role of geitonogamy on fruit set in natural populations of Asclepias speciosa. We compared fruit set from three pollination treatments: (1) inflorescences bagged before and after receiving 6 hand outcross pollinia (Bag), (2) inflorescences unbagged and receiving 6 hand outcross pollinia (Open), and (3) naturally pollinated inflorescences (Control). The Bag and Open treatments initiated significantly more fruits than the Control. Bag aborted significantly fewer fruits than Open or Control. Fruit set was significantly higher in Bag than Open, and Open had significantly higher fruit set than Control. From these results, we conclude that (1) high rates of geitonogamy significantly increase fruit abortion and reduce fruit set in natural populations of A. speciosa and (2) natural populations are compatible pollen limited. Both findings are consistent with the plant's dilemma hypothesis.

Influence of Compatibility System and Life Form on Plant Reproductive Success

Abstract: We studied the compatibility system and the autonomous selfing capacity of 32 native species from the Chaco Serrano forests (central Argentina), and compared fruit set, considering plant life form and compatibility status to evaluate: (i) the extent of the association between life form and compatibility system, (ii) the influence of the life form and/or of the compatibility system on natural fruit set, and (iii) the preemergent reproductive advantages provided by self‐compatibility and autonomous self‐pollination. Ca. 60 % of the species were self‐compatible (SC). Natural fruit set of SC species triplicate those of self‐incompatible (SI) species. Almost all SC species have autonomous selfing capacity. Nevertheless, on average, SC species produce more than twice as many fruits through natural pollination in comparison to autonomous selfing, and fruit set obtained after autonomous selfing was significantly lower than hand‐selfed fruit set. Most SC species received insufficient pollen from themselves via autonomous selfing, and natural fruit set was mostly pollinator‐mediated. Thus, the reproductive assurance provided by autonomous selfing is relatively low in comparison with that provided by pollinators. We supplemented our data with published results from different sites in South America, to assess how general are the associations between life form and compatibility system and between natural fruit production and the self compatibility index. There is a differential distribution of SC and SI species according to life form, with a skew towards incompatibility among woody plants and towards compatibility in herbs. On the other hand, regression analysis showed there is a general positive trend between natural fruit set and the self compatibility index of the species.

Effect of Sterol-demethylation Inhibiting Fungicides on Apple Fruit Set, Fruit Size, Total Yield, and Gross Returns

Effects of three sterol-demethylation inhibiting (DMI) fungicides and a contact fungicide were compared over two years at each of two locations to determine if fungicide treatments had differential effects on productivity, fruit size and shape, or gross returns for `Empire' apples (Malus ×domestica Borkh.). Treatments were applied four to five times per year during the primary apple scab season. Effects of treatments were assessed by comparing fruit set efficiencies, number of fruit per tree, total harvested fruit weight, and fruit length: diameter ratios at harvest. No significant differences were noted among individual treatments in any of the four trials. However, when treatments were contrasted by grouping individual treatments, significantly larger fruit size was noted for triflumizole treatments vs. combined fenarimol and myclobutanil treatments in one of the four trials and for captan or mancozeb compared to fenarimol and myclobutanil treatments in two trials. None of the DMI fungicides compared in these trials had any consistent adverse affect on fruit size, total yield, or estimated gross return per hectare. We conclude that the plant growth regulator effects of DMI fungicides are inconsistent and are unlikely to have significant economic impact on commercial apple production.

Pollination requirements of loquat (Eriobotrya japonicaLindl.), cv. `Algerie'

Introduction. Loquat shares with other pomes, such as apple (Malus domestica ) and pear (Pyrus communis ), flowering habits, but, in contrast with them, the tree is considered a self-compatible species. However, when planted in solid blocks under mesh, low fruit set and small fruit size are often reported. To explore in which way restrictions of bee activity and/or impediments for cross-pollination can be responsible for low productivity and poor fruit quality, we carried out controlled pollination on flowers of loquat cv. Algerie. Materials and methods. A first experiment checked cross-pollination response by comparing fruit set and quality from self-, open-, and cross-pollinated flowers. A second experiment explored poor pollination effects by modifying the number of stigmas being hand cross-pollinated. Results. Cv. Algerie loquat flowers cross-pollinated with pollen of cvs. `Tanaka' and `Golden Nugget' loquat flowers produced more fruits of higher quality (larger, heavier and more precocious) than flowers under self-pollination. Benefits of cross-pollination can be explained by an earlier and higher level of fertilization. Observations under microscopy showed, however, that self-incompatibility of cv. Algerie flowers is not complete, and a certain level of self-fertilization occurs. The second experiment demonstrated that limiting the number of stigmas pollinated resulted in a significant reduction in the number of seeds formed that, in turn, affected fruit size and shape. Flowers with only one stigma pollinated seldom formed more than two seeds while flowers with all five stigmas pollinated produced fruit with an average of four seeds. Conclusion. Our results emphasize a dependence of cv. Algerie flower pollination on both adequate activity of pollinator insects and appropriate placement of pollinizers.

Effects of Habitat Fragmentation on Pollinator Diversity and Plant Reproductive Success in Renosterveld Shrublands of South Africa

Abstract: We examined the effects of habitat fragmentation on the pollinator diversity and reproductive success of seven perennial plant species in renosterveld shrublands in South Africa. We sampled pollinators in small (0.5–2 ha), medium (3–10 ha), and large (>30 ha) habitat fragments during the peak flowering period in spring and summer. We also compared fruit set and seed set in the seven plant species on different‐sized fragments. Hand‐pollinated controls were used to determine pollination deficits in three species. Seed‐germination studies were done on two species to determine the effect of reduced seed set on reproductive output. Overall, the species richness of bees, flies, and butterflies did not vary significantly among different‐sized fragments. However, the abundance of particular species of bees and monkey beetles (Scarabaeidae: Hopliini) was significantly affected by fragment size, together with other factors such as vegetation cover and the ratio of grass to shrubs. Fragment size and distance to large remnants of vegetation had a significant influence on seed or fruit set in four of the seven plant species examined. One species failed to set any seed in small‐ and medium‐sized fragments. Comparisons of fruit and seed set among hand‐pollinated and naturally pollinated plants confirmed that seed set was pollinator‐limited in the orchid Pterygodium catholicum. Our results suggest that perennial plant species respond in different ways to fragmentation, and that populations on small fragments do not always experience pollination deficits. Existing classifications of pollination systems, in relation to their vulnerability to fragmentation, do not adequately explain our results. We argue that there needs to be a greater focus on the habitat requirements of pollinators to predict the effects of habitat fragmentation on pollination systems and plant reproductive success.

REPRODUCTIVE CHARACTERISTICS OF A STABLE-DUNE THEROPHYTE COMMUNITY IN DOÑANA (SOUTHERN SPAIN)

ABSTRACT Aspects of the reproductive biology of 22 annual taxa inhabiting stabilized sand dunes at the Donana National Park (southern Spain) were studied. In most instances, growth and reproduction of the plants took place during winter, with seedlings appearing mostly in January. The highest number of species in bloom was detected in March, while flowering and fruiting had ceased by June. Dependence on pollination vectors (insects or wind) for reproduction was ascertained by caging plants of the studied species with either mesh or acetate exclosures and comparing fruit set with that of uncaged individuals. Caging had little or no effect on the reproduction of most species. Facultative autogamy was widespread, and cleistogamy was detected in one species (Tuberaria inconspicua). Only two taxa (Andryala arenaria and Ononis broterana) showed zero fruit set when pollination vectors were excluded. Pollen-to-ovule (P:O) ratios were usually low (the median for the whole sample was 238), which is consistent with ...

Pollen-Limited Fruit Set in Isolated Patches of Maianthemum canadense Desf. in New Jersey

WORTHEN, W. B. AND E. W. STILES (Department of Biological Sciences and Bureau of Biological Research, Rutgers-The State University of New Jersey, Piscataway, NJ 08855-1059). Pollen-limited fruit set in isolated patches of Maianthemum canadense Desf. in New Jersey. Bull. Torrey Bot. Club 115: 299-305. 1988.-We examined the effects of pollen addition and raceme density on fruit set in seven isolated patches of Maianthemum canadense Desf. (Liliaceae; False Lily-of-the-Valley) in central New Jersey. We removed racemes from two of four quadrants in each patch to create distinct high and low density sectors. We hand pollinated all the racemes in four 1-m quadrats (1/quadrant) within each patch, and compared fruit set in these quadrats with fruit set in eight naturally pollinated control quadrats (2/quadrant). We recorded the percentage of racemes that bore fruit and the mean number of fruits/infructescence in each quadrat, and analyzed these data with three-factor analyses of variance (patch, density, and pollination-treatment effects). There was a significant effect of pollen addition on fruit set. In four patches, hand pollination significantly increased both the percent of racemes that bore fruit and the number of fruits/infructescence. We conclude that fruit set in these patches of M. canadense was pollen limited. A previous study reported that fruit set in M. canadense was resource limited, but our results suggest that fruit set in different patches may be limited by different factors. The clonal architecture of a patch and the relatedness and distance between mating plants may influence these patterns. There were no significant density effects, in any patch, on fruit set in hand pollinated or naturally pollinated quadrats. Although this suggests that plant density (and inferentially, competition for resources) did not limit fruit set, clonal growth patterns may confound this conclusion.

Pollen Limitation in a Monocarpic Species, Ipomopsis Aggregata

(1) We tested whether seed production in the perennial monocarpic plant Ipomopsis aggregata (Polemoniaceae) was pollen-limited by adding outcross pollen to open stigmas of plants on three occasions at weekly intervals. We compared fruit set and seed set per fruit with a set of adjacent, untreated plants of the same average height and flower number. (2) Experimental pollination doubled the number of flowers producing seed after each occasion and increased the average seed set per fruit for the first one. (3) Plants treated with pollen showed correlations between seed production and height and aborted seed production consistent with resource limitation, but untreated, naturally pollinated plants did not.