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Comparison of the crop species Brassica napus and wild B. rapa: characteristics relevant for building up a persistent seed bank in the soil
- Tom J. de Jong, Maria Tudela Isanta, Elze Hesse
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- Journal:
- Seed Science Research / Volume 23 / Issue 3 / September 2013
- Published online by Cambridge University Press:
- 11 June 2013, pp. 169-179
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Can seed characters be used for predicting the presence of a persistent seed bank in the field? We address this question using ten cultivars of the crop Brassica napus, ten feral B. napus accessions originating from seeds collected in the field and nine accessions of the closely related ruderal species Brassica rapa. When buried for a year in the field, seeds of the wild B. rapa displayed, as expected, much higher survival fractions than those of domesticated B. napus at two different locations in The Netherlands. Compared to B. napus, B. rapa produces relatively small seeds with high levels of aliphatic glucosinolates and a thick seed coat. However, within each species none of these characters correlated with seed survival in the soil. At low temperatures, B. rapa seeds had lower and more variable germination fractions than those of B. napus; a small fraction (4.6%) of the B. rapa seeds showed primary dormancy. Rather surprisingly, B. napus displayed genetic differences in germination at low temperature, and germination fractions at 5°C correlated negatively with seed survival in the soil. Our comparisons between and within the two species suggest that foregoing germination at low temperatures is an important character for developing a persistent seed bank. We discuss our results in light of environmental risk assessment of genetically modified B. napus.
2 - Pollination crisis, plant sex systems, and predicting evolutionary trends in attractiveness
- Edited by Sébastien Patiny, Université de Mons-Hainaut, Belgium
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- Book:
- Evolution of Plant-Pollinator Relationships
- Published online:
- 05 January 2012
- Print publication:
- 08 December 2011, pp 28-43
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Summary
Introduction
Since publication of The Forgotten Pollinators by Buchmann and Nabhan (1997), the term pollination crisis has gained widespread currency. Catchy phrases like “silent springs” and “fruitless falls” have been adopted in both the scientific literature and newspapers. Sub-optimal pollination of crops incurs an economic cost; less pollination may also lead to profound changes in the species composition of ecosystems all over the world. However, Aizen et al. (2008) have recently challenged the related idea that colonies of honeybees are generally on the decline (Jacobsen 2008). Analyzing data obtained from the FAO, they noted a downward trend in the number of bee colonies in Europe and North America, but an upward trend in non-industrialized countries that more than compensated for the decline. While this is good news, it is not the whole story. Aizen et al. (2008) also noted a trend in the crops that are being grown. Traditionally, wind-pollinated grains (rice, maize, wheat, rye) make up most of the world’s food supply. Now, insect-pollinated crops are on the rise – crops like Brazil nut, cocoa bean and oil palm. This creates a need for more honeybee colonies or other alternative pollinators, which is a challenge for the future. In this context it is useful to reflect on the likely effects of reduced pollination levels on natural ecosystems. Here I shall focus on plant sex systems and plant attractiveness in the context of reduced pollinator visitation, approaching the problem in the context of what is known about the evolutionary ecology of plants.
Expected effects of reduced pollination: dioecy and gynodioecy
The great majority of angiosperm species have perfect flowers. These flowers have both male parts that bear pollen, and female parts that receive pollen and later produce fruits and seeds. Combining the two sexes into a single flower is economic, sharing the costs of pollinator attraction and reward over the two sex functions. The proximity of the male and female organs has dual consequences, however. In plants that are self-compatible (SC), when pollinators are in short supply, selfing provides reproductive assurance, and this can be positive. Proximity may also be negative, though, when self-pollen on the stigma prevents outcrossing and reduces seed set, even in self-incompatible (SI) species (Webb and Lloyd 1986; Bertin 1993). These negative effects are known as pollen–stigma interference or pollen–pistil interference.
Chapter 17 - Sex ratios in dioecious plants
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- By Tom J. de Jong, Institute of Evolutionary and Ecological Sciences, University of Leiden, The Netherlands, Peter G.L. Klinkhamer, Institute of Evolutionary and Ecological, Sciences, University of Leiden, The Netherlands
- Edited by Ian C. W. Hardy, University of Nottingham
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- Book:
- Sex Ratios
- Published online:
- 06 August 2009
- Print publication:
- 13 June 2002, pp 349-364
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Summary
Summary
Some seeds of dioecious plants develop into male plants and others become females. Brothers and sisters can grow close together in the seed shadow of the maternal plant, which promotes sib-mating, and classical sex-allocation theory predicts a slight female bias among the seeds produced. We describe different ways of examining seed sex ratios and some of the pitfalls involved. The available direct (seed sex ratio) and indirect (proportions of male and female plants in the field) evidence suggests that the seed sex ratio is often close to 0.5, despite the fact that there is genetic variation in the seed sex ratio in some cases. The combination of significant sib-mating and an unbiased seed sex ratio is at odds with classical sex-allocation theory. Genetic conflict theory might provide new insights and should be a central theme in future research. The adult sex ratio can also become male or female biased due to sexually differential mortality, but this does not influence the seed sex ratio.
Das Zahlenverhältnis [0.5] kann aber nur dann rein herauskommen, wenn eine ganze Reihe von Bedingungen erfüllt sind.
The ratio [0.5] can, however, only emerge, when a whole range of conditions is satisfied.
(Correns 1928)Introduction
Like most animals, but unlike the great majority of plant species, dioecious plants have separate male and female individuals. Both male and female organs develop in each of their flowers, in separate floral whorls, but the development of one type is halted before maturity (Grant et al. 1994), with the timing of the arrest differing between species.
Chapter 16 - Sex allocation in hermaphrodite plants
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- By Peter G.L. Klinkhamer, Institute of Evolutionary and Ecological, Sciences, University of Leiden, The Netherlands, Tom J. de Jong, Institute of Evolutionary and Ecological Sciences, University of Leiden, The Netherlands
- Edited by Ian C. W. Hardy, University of Nottingham
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- Book:
- Sex Ratios
- Published online:
- 06 August 2009
- Print publication:
- 13 June 2002, pp 333-348
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Summary
Summary
The flowers of hermaphrodite plants have both male and female parts. Hermaphrodite plants can change their allocation to both sexual functions in various ways, such as by changing the production ratios of pollen grains to ovules within flowers and of flowers to fruits. We discuss the problems involved in measuring sex allocation, trade-offs and fitness gain curves and present a simple model for the evolutionary stable allocation to fruits and flowers. The model provides an explanation for the low fruit-to-flower ratio found in many species and for the increasing allocation to female function with increasing selfing rate. Theoretical models predict that evolutionary stable sex allocation depends on plant size and this prediction is supported by literature data on monocarpic hermaphrodites and on monoecious species.
Introduction
By far the most common mode of plant reproduction is through hermaphrodite flowers. Although such flowers serve both male and female functions, this does not mean that hermaphrodites are invariant in their sexual behaviour. Substantial variation in intraspecific sex allocation has been found and related to environmental conditions or plant size. A large body of theoretical literature is now accumulating that predicts how allocation to male and female reproduction should vary with a variety of factors such as pollination type, resource status, selfing rate, selective abortion, population structure, dispersal mechanisms, etc. Unfortunately empirical evidence lags far behind, mostly because the required measurements are notoriously difficult to collect and the methods full of pitfalls.
Is the threshold size for flowering in Cynoglossum officinale fixed or dependent on environment?
- TOM J. DE JONG, LEENTJE GOOSEN-DE ROO, PETER G. L. KLINKHAMER
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- Journal:
- The New Phytologist / Volume 138 / Issue 3 / March 1998
- Published online by Cambridge University Press:
- 01 March 1998, pp. 489-496
- Print publication:
- March 1998
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In the monocarpic perennial Cynoglossum officinale L. the probability of flowering is related to the size of the plant. In previous work it was observed that this relation varies between years. We hypothesized that variable conditions during the winter, the period of vernalization, explain this variation.
We collected plants from the field in autumn and placed these under different simulated winter conditions in a climate room. In contrast to our hypothesis, the probability of initiating flowering at a given size was not affected by: (a) the temperature during the cold period, (b) the duration of the cold period, or (c) the application of a plant hormone (GA3) or an inhibitor of gibberellin synthesis (paclobutazol) during the cold period. Winter cold is not necessary for floral initiation, and is only required for elongation of the inflorescence. It is unlikely that winter temperature affects the fraction of plants flowering.
Subsequent morphological investigation of flower development in material collected in the field showed that large plants had primordial inflorescences well before vernalization, sometimes as early as August. In plants grown from seeds under constant conditions in a climate room, the probability of initiating the inflorescence differed for plants grown at various temperatures (34·1% at 15°C, 100% at 20°C, and 95% at 25°C). Our results suggest that environmental conditions in August and September, up to 10 months before actual flowering, could affect the fraction of flowering plants.