Fruit abortion in the Chihuahuan-Desert endemic cactus <Emphasis Type="Italic">Opuntia microdasys</Emphasis> |
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Authors: | Hugo H Piña Carlos Montaña María del Carmen Mandujano |
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Institution: | (1) Departamento de Biología Evolutiva, Instituto de Ecología A.C., Km 2.5 carretera antigua a Coatepec, Apartado Postal 63, 91000 Xalapa, Veracruz, Mexico;(2) Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Apartado Postal 70-275, 04510 México, D.F., Mexico |
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Abstract: | Resource and pollen limitation, as well as pollen/ovule incompatibility, have been proposed as causes to explain fruit abortion.
To assess whether abortion in Opuntia microdasys was due to resource and/or pollen limitation and could therefore be reversed fruit set and seed set were studied using controlled
pollination experiments on 60 plants that had been randomly assigned a combination of watering and fertilization treatments.
On the other hand, to test whether fruit abortion was irreversible, due to pollen/ovule incompatibility, we examined the reproductive
biology of the species. This included observations on floral phenology, nectar production, flower visitors, numbers of pollen
grains and ovules, and self-pollination experiments. Results showed that O. microdasys is a fully self-incompatible species and its floral biology and the activity of the main pollinator allow constant deposition
of incompatible pollen onto stigmas, which may contribute to fruit abortion. Reproductive success was limited by nutrients
and pollen, but the fruit set increased only by 58%, compared to 47% of the control, after the experimental addition of pollen,
nutrients and water. The magnitude of pollen and resource limitation suggests that similar levels of abortion will be present
in good as well as in bad years. Selfing as well as incompatibility between ramets from the same clone and between closely
related plants seem plausible candidates to explain the large proportion of fruit abortion, and experimental cross pollination
between genotypes identified through molecular markers are necessary to fully understand the considerable abortion rate that
remains unexplained after pollen and resource addition. Interestingly, the possible reason why the abortion of energetically
expensive fruits has not been eliminated by natural selection is that the aborted fruits are propagules able to root and produce
new plants with the same genotype of the mother. Abortion would have a dramatic effect on cross-fertilized genotypes because
they result in zero fitness, but it would have a positive effect on the fitness of the maternal genotype because a clonal
offspring is produced. Evidently, the exact fitness consequences to the maternal plant will depend on the differences in survival
and reproduction of these different offspring types. |
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Keywords: | Breeding system Bunny-ears prickly pear Floral biology Fruit and seed production Nutrient and pollen limitation Self-incompatibility |
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