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The reproductive biology of Grevillea robusta growing underexotic conditions in Kenya and Australia is reported. The speciesshowed both protandry and a self-incompatibility mechanism.The stigma was wet and papillate with a distinct groove in themiddle. The anthers dehisced prior to anthesis, when the perianthopened. Stigmatic receptivity began 1 d after anthesis, withthe greatest pollen germination rates and longest pollen tubesobtained 2 d after anthesis. Nectar secretion commenced withpollen dehiscence and was abundant at anthesis. Most stigmaticgrooves opened widely 12 d after anthesis and stigmasshowed taller papillae and abundant secretion. Controlled pollinationsgave a greater fruit set from cross-pollination (5.9% in Apriland 17.5% in July) than open-pollination (0.1% in April and3.3% in July). No fruit set from self-pollination was obtainedin April, and very few fruit set for geitonogamous (two outof 1622; 0.1%) or for autogamous (one out of 2707 flowers; 0.04%)pollination treatments in July. Following self-pollination,growth of pollen tubes was poorer than in other treatments,and was generally arrested in the upper style. Cross-pollinatedflowers produced normal and straight pollen tubes, while self-pollentubes had growth abnormalities. Most of the open-pollinatedflowers were found without pollen or with only self-pollen ontheir stigmas indicating that the amount of cross-pollen reachingthe stigma under open-pollination may be a factor limiting seedproduction. Flowers shed soon after the fertilization phasewere those with ungerminated pollen or no pollen. Although avery low rate of selfing may occur, G. robusta presents a self-incompatibilitysystem and allogamy is its primary breeding behaviour.Copyright2000 Annals of Botany Company Grevillea robusta, silky oak, Proteaceae, protandry, controlled pollinations, receptivity, pollen-tube growth, self-incompatibility, pollination 相似文献
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Roeland Kindt Antoine Kalinganire Mahamane Larwanou Mamounata Belem Joseph Marie Dakouo Jules Bayala Maguette Kairé 《Biodiversity and Conservation》2008,17(8):1883-1905
Although farmers have managed west African parkland savanna systems for 1,000 of years, concerns have been raised about the
sustainability of these agro-ecosystems due to human population growth, shortening of fallow periods, droughts, desertification
and new orientations towards cash generation away from subsistence farming. We conducted a tree diversity survey in 16 villages
from Burkina Faso, Mali, Niger and Senegal, recording total species composition for 300 quadrats (mainly 50 × 20 m2) that were randomly sampled from the main landuse categories of parklands of village fields (VF), bush fields (BF), sylvopastoral
zone (SP) and forest reserves (FR). About 110 tree species were encountered, including 100 indigenous species. The results
from balanced species accumulation curves (based on randomized subsampling of the same number of quadrats from each village)
showed that the accumulated number of species was smallest in VF, largest in FR and almost equal in BF and SP, whereas classical
(unbalanced) species accumulation curves yielded different results. Although there was a significant within-village reduction
in species richness with increasing diameter class [averaging 8.5–13.1 more species in the smallest (<5 cm) compared to the
largest diameter class (>80 cm)] for the different landuse categories, new species were also encountered in larger diameter
classes (2.7–7.2 species). The evidence for tree regeneration problems (including problems in FR) suggest that farmer-managed
tree regeneration should be further explored and that advances in domestication and marketing of indigenous tree species may
be crucial to tree conservation in parkland systems. 相似文献
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The floral visitors of silky oak, Grevillea robusta A. Cunn. ex R.Br., their foraging behaviour and their effects on fruit‐set were studied at Malava, western Kenya. Grevillea robusta is a popular tree for farm plantings in the eastern and central African highlands. Yield of seed has been disappointingly low in some areas and a lack of appropriate pollinators has been suggested as a possible cause. Investigations involved the monitoring of visitors on active inflorescences, assessment of the rewards available to potential pollinators, and exclusion experiments to establish the effects of various visitors on fruit‐set. The flowers are visited mainly by birds and insects. The likely pollinators of G. robusta are sunbirds (Nectarinia amethystina, N. cyanolaema, N. olivacea, N. superba and N. venusta) and white‐eyes (Zosterops kikuyuensis and Z. senegalensis). Very little aggressive behaviour between birds was recorded. No nocturnal pollinators were observed. Nectar was the major floral reward for pollinators, but is likely depleted by ants and honey bees, the foraging behaviour of which confirmed them to be nectar‐robbers. These insects hardly ever touched stigmas during their visits. Eighty‐nine per cent of bird visits were in the morning (07.00–10.00 hours) when nectar volume was highest. Inflorescences bagged to exclude birds set no fruits, and unmanipulated flowers and flowers bagged with self‐pollen set no fruits, indicating a self‐incompatibility mechanism. Control cross‐pollinated flowers displayed greatly increased fruit‐set (25.1%) compared with natural open‐pollination (0.9%). All these findings confirm the importance of cross‐pollen transfer to flowers and the necessity of pollinators for fruit‐set. Effective seed production requires activity of pollinators for self‐pollen removal and cross‐pollen deposition. Seed production stands for G. robusta should be established where flowering is prolific and bird pollinators are abundant. 相似文献
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