葫蘆科的授粉特性 Pollination of Cucurbitacea
Cucurbitaceae is geitonogamy, meaning that pollen is applied from a flower to another flower on the same plant for propagation. This is one form of cross-pollination, which is developed in many plant species for diversity. Self-incompatability in the brassica family, which was featured in one of our earlier post - is another form.
Flowering of cucurbitaceae is highly affected by sunlight. Shorter length of day actually benefit the flowering of female flowers. Cucurbitaceae depends on insects, in particular bees for pollination. Isolation is needed to avoid inbreeding and to save seeds that are high in purity.
There are two kinds of isolation. Spatial isolation of keeping a 1000m distance within crops, or physial isolation of setting up nettings. Plant enough to maintain genetic diversity, enabling higher chance for characteristics to be passed onto next generation. It is suggested that 10-20 plants is sufficient for cucurbitaceae. Cut unnecessary vines to concentrate nutrients.
However, netting may decrease exposure to sunlight, worsen ventilation, and highten temperature. It will also require hand pollination.
授粉及篩選 Pollination and Selection
Select early flowering and vigorous plants for seed saving. Hand-pollinate female flowers at 10-20 nodes of the plant and remove deformed fruits. Theoretically, pollination in early morning when flowers are most energetic allows higher germination. Label your pollinated fruits and record the date. Ensure the plant and fruits are not affected by viruses or bacteria such as fruit rot. Any infected plant are not suitble for seed saving, and should be removed before flowering. Choose a sunny day that is not too humid to harvest.
為授粉後的果實套上膠紙牌等記號以作識別，並標示授粉日 / Label your pollinated fruit and record the date
葫蘆科雌花，授粉前花柱為白色 / The style of cucurbitacea female flower remains white before pollination
雄花花藥内藏花粉 / Pollen is hidden within anthers of male flower
採種及保存 Harvesting and Storage
Here are some seed harvesting timing for different species:
- Wax gourd and pumpkin: allow an extra 1-2 weeks maturation. Fruits should be kept in shade 2-4 weeks after harvest for after-ripening, but too long may result in seed germinating. Cut fruit to obtain seeds
- Cucumber: Let the fruit ripen to brown, or harvest fruit that has turned yellow and keep in shade for 10 days. Wash away jelly in a non-metalic container
- Ridge Gourd (Luffa)：Let fruit dried, harvest when you can hear the seeds while shaking the gourd
- Bitter Gourd: Similar to cucumber, let fruit turn orange-yellow, or harvest fruit that has turned yellow and keep in shade for 10 days. Bitter gourd seeds are wrapped in a red jelly-texture aril, leave them in a container and avoid water, wash after 24 hours
- Watermelon: After-ripen for 7-14 days. Leave seeds with flesh in a container to fermentate for 2-3 days, then wash away the jelly
老黃瓜盛載種子 / Harvest seeds in yellow old cucumber
果實完全成熟轉爲橙黃色 / Ripening bitter gourd can be kept in shade for 10 days before obtaining seeds
苦瓜的種子有紅色膠囊包裹 / Red jelly-texture aril coating bitter gourd seeds
You'd have heard that high quality seeds should be plump and relatively bigger. Vigor, moisture content, physical purity and genetic purity are all standards for high quality seed. Let us close up to moisture content this time so you know the basic to store the seed you saved!
After drying the harvested seeds, their moisture content should be 7-8%. How do we know without the help of appliances? If it is a thin seed, try break it with your hands. If it is a thick seed, use a hammer. If your seeds can be broken into pieces easily, it is basically dried.
Seeds stored in a refrigerator without humidity contol can still germinate before you want them to. The famous Harrington Rule of Thumb proposed in 1963 suggested that, 'The arithmetic sum of percent relative humidity and the temperature in Fahrenheit should not exceed 100 [50 in celcius], with not more than half of that contributed by temperature'. When we store seeds at home, it is better to keep them in a sealed foil bag with descicant packets, then store in refrigerator. Remember to mark down seed information such as species, time of harvest, spot of harvest for your next sow!
Stay tuned with our SEED BLOG as we open a new topic next time!
Source other than Clover Seed: AVRDC, 種籽保典