POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
6
1. BACKGROUND TO POLLINATORS,
POLLINATION AND FOOD PRODUCTION
pollination are often complex, such as in wild figs. The
books by Proctor et al. (1996) and Willmer (2011) describe
and explain those pollination relationships.
1.2.2 Plant mating and breeding
systems
Pollination is a precursor to the sexual union of gametes.
Following pollination pollen grains germinate on the stigma
and the resulting pollen tubes grow through the tissues of
the stigma to the ovule. The ovule develops into the seed
and the ovary into the fruit. Even so, pollination alone does
not assure sexual union (e.g. self-pollination on a plant that
is self-infertile often occurs, but does not result in seed
set). Pollination is crucial for reproduction, fruit and/or seed
set in flowering plants whether they be crops, weeds or
natural vegetation. Inadequate pollination may result from a
shortage of viable pollen or limited pollinator activity.
Many plants have special mechanisms, some physiological
and others morphological, that prevent or reduce the
chances of self-pollination. An extreme strategy to avoid
self-fertilization in plants is dioecy, the presence of male
and female flowers on separate individuals. Some flowering
plants that need to reproduce sexually cannot produce
seeds without cross-pollination. Other plants readily selfpollinate
and are self-fertile, and may rely on self-pollination
and self-fertilization for seed production. Plant mating
systems, as described and discussed in detail by Richards
(1997) are defined in terms of a plant’s form of reproduction
(self-fertile to self-sterile) (Figure 1.2).
FIGURE 1.1
Plant breeding systems, of which there are many, explain the
mechanisms that promote or dictate the particular mating
system of a species of plant, or individual plant. They, like
plant mating systems are an integral part of understanding
pollination (see Proctor et al., 1996; Richards, 1997;
Willmer, 2011).
There are four common mating systems that apply to
plants that require pollinators for optimal fruit production.
Obligate xenogamy (as in pome fruits, e.g. apples and
pears) requires that the fruit/seed-bearing plant receives
pollen from and is fertilized by pollen from an individual
that is genetically different from the plant that receives the
pollen. Self-pollination and self-fertilization can take place
in two ways. In autogamy, pollen moves within the same
flower whereas in geitonogamy the pollen moves between
different flowers of the same plant. Pollen may move
spontaneously or through pollinator activity. Facultative
xenogamy, geitonogamy and autogamy together (Mixed
mating systems) occur to various degrees in, and may
differ among cultivars. The modern literature contains
little information on the mating systems (and pollination
requirements) that contribute to optimal yields for many
important crop varieties. Even so, in several economically
important crop cultivars capable of autogamy, such as
sunflower (Helianthus annuus) (Carvalheiro et al., 2011),
oil seed rape (Brassica napus) (Bartomeus et al., 2014),
strawberries (Fragaria vesca) (Klatt et al., 2014), coffee
(Coffea spp.) (Roubik, 2002) and soybean (Glycine max)
(Milfont et al., 2013), significant yield boosts and improved
quality have been documented when pollinators are involved
(Garibaldi et al., 2013b).
A section of a flower showing the different parts (modified from Pixabay Creative Commons Deed (2012).
Connective
Stigma
Pollen
Anther
Style
Filament
Petal
Sepal
Floral axis
Nectary
Articulation
Ovule
Pedicel
Mature flower
Ovary
Stamen