2.1.1. Testing for agamospermy (asexual reproduction through non-fertilized seeds)
This test will tell us whether a plant species sets seeds without pollination. If this is so, honey bees cannot contribute to seed- or fruit-set.
- Choose a given number of flower buds prior to anthesis. The number of buds may vary with availability and ease of access, but larger samples produce more reliable results.
- Protect half of these buds with pollination bags (Fig. 3) and leave the other half unbagged as a control. Pollination bags are typically made of sheer nylon or similar fine fabric that excludes insects but permits entry of air and light. They are usually semi-transparent nylon and have draw strings to secure the bag around the flower pedicel. The flower should be positioned as much as possible in the centre of the bag so that the mesh does not touch the flower, which could lead to self-pollination. To limit self-pollination further, fix a wire frame around the flower and place the bag over the frame, thus providing structural support to the bag. Identify each treatment with weather-resistant tags. Testing for agamospermy can also be done in a greenhouse without exclusion bags and is thereby easier.
- Before anther dehiscence (depending on the flower species this may happen prior to anthesis), remove the bag (Fig. 4) and emasculate the flower using a fine pair of forceps to minimize injury to floral tissue. After emasculation, replace the pollination bag on the flower to prevent undesired action of pollinating agents. The bags should remain on the flowers while the stigmas are receptive and can be removed afterwards. It is important for the investigator to become familiar with the time of day or floral morphology stage that are conducive to stigma receptivity for a given plant species.
- After ovule maturation is apparent in the pollinated treatments, check whether fruit has developed from the bagged and emasculated flowers. If none is present, one can conclude that the plant species does not exhibit agamospermy. If fruit does develop, it is necessary to wait until fruit ripening to check for seeds because some plants are parthenocarpic (produce fruits with no seeds and do not depend on pollination). If seeds are set, compare the number of fruits and seeds set per fruit from the emasculated and bagged flowers with those from the control treatment to estimate the proportion of seeds set by agamospermy in that particular plant species.
- It is important that assessments of seed- or fruit-set occur as early as possible to minimize underestimating set because of losses that occur between set and harvest.
Fig. 3. Restricted pollination treatment: a watermelon flower is bagged throughout its life to prevent honey bee visitation.
Fig. 4. Unbagging watermelon flower for hand pollination.