Muhammad Roman, Zeeshan Arif Wahla, Maria Riaz
Department of Seed Science & Technology University of Agriculture Faisalabad
Hybrid Seed Production in Tomato (Solanum Lycopersicum L.)
Botanical name: Solanum Lycopersicum L.
Chromosome no: 2n=24
Origin: Peruvian and Mexican region
Hybrid tomato varieties have many advantages compared to open-pollinated varieties. Hybrids usually produce higher yields. They generally mature earlier and more uniformly. Many hybrids have better fruit quality and disease resistance. With all of these advantages, many farmers prefer to sow hybrid seeds in spite of the higher seed costs. The demand for hybrid tomato seeds can open a new market for growers interested in seed production. Hybrids have almost 5-7 times higher yields than open pollinated varieties. Hybrid tomato seed production is not simple. First, it is laborious process. Fortunately, this is not a problem in developing countries where affordable labor is available. Second, it requires the mastery of special skills and a close attention to detail. This publication will teach these skills.
For hybrid seed production we have to provide a certain temperature range for day and night periods as 15-20 Ċ and 20-28 Ċ respectively
- Selecting Parents
Hybrid seed production involves the crossing of a female line to a male line. Either line can be the female or male parent, but normally the best seed yielder is selected as the female parent. Both parents should be pure, preferably being self-pollinated for more than six generations (this is called inbreeding). The inbred parents are selected for their desirable traits (e.g., high yields, disease resistance, fruit quality, earliness, etc.).
It is important to have plenty of pollen available for making hybrid crosses. Since tomato vines bloom profusely, a ratio of one male for every four female plants is recommended.
Self-pollination cannot be allowed in hybrid seed production. The female flower must be pollinated by the pollen from the male line. To prevent self-pollination, remove the stamens from the flower buds of the female line before they shed their pollen and this process is called emasculation.
Emasculation begins about 55-65 days after sowing. Flower buds from the second cluster which will open in two to three days are chosen for emasculation. Petals will be slightly out of the flower bud but not opened, and the corolla color is slightly yellow or even paler. Flowers from the first cluster are removed. Sterilize the forceps, scissors and hands by dipping them in 95% alcohol before emasculation is started. If gloves are used, these should also be dipped in 95% alcohol to prevent pollen contamination. Use sharp-pointed forceps to force open the selected buds. Then, split open the anther cone. Carefully pull the anther cone out of the bud, leaving the calyx, corolla and pistil .To help identify the hybrid fruits from self-fruits at the time of harvest, cut the corolla and calyx (all or two sepals)
Emasculation of Tomato: selection of buds, removal of anther cone, and cutting of petals
- Pollens Collection
Collect flowers from the male parent to extract pollen. The best time for pollen collection is during the early morning before the pollen has been shed. Avoid pollen collection on rainy days.
Remove the anther cones from the flowers and put them in suitable containers, such as glassine, cellophane, or paper bags. Dry the anther cones by placing them 30 cm below a 100-watt lamp for 24 hours. The lamp creates a drying temperature of about 30°C. Pollen can also be sun-dried, but avoid drying at midday when temperature is very high. Put the dried anther cones in a plastic pan or cup.
Cover the cup with a fine mesh screen (200-300 mesh) and then seal it with a similar tight-fitting cup, serving as a lid. Shake the cup about 10-20 times so that the pollen is collected in the “lid” cup. Transfer the pollen into a small convenient-to handle container for pollination. Fresh pollen is best for good fruit-set. It can be kept for one day at moderate room temperature. When weather conditions are not suitable for pollination, dried or dehydrated pollen can be stored in a sealed container (capsule or vial) and kept in the freezer for about a month. Without freezing, the pollen can be kept in an ordinary refrigerator for two to three days without any significant loss in viability. The pollen should be taken from the freezer or refrigerator and kept closed until the container warms to room temperature. This will prevent the pollen from getting wet due to condensation.
Emasculated flowers are generally pollinated one to two days later. Try to avoid pollination on rainy days. The corolla of the emasculated flower turns bright yellow, signaling that the stigma is ready for pollination. Dip the stigma into the pool of pollen in the pollen container or pollinate by touching the stigma with the tip of the index finger dipped in the pollen pool Pollination is usually done three times weekly over a three to five week period. Successful pollinations are easily seen within one week by the enlargement of the fruit.
Pollination of Emasculated Flowers
- Fruit Production
The number of hybrid fruits produced per plant depends on the fruit size of the maternal parent. As a rule of thumb, maintain the following: 30 fruits for large-fruited parent; 40 fruits for medium- fruited parent; and 50 or more fruits for small-fruited parent. Hybrid fruits are easily recognized by their cut sepals. Remove the naturally-pollinated (non-hybrid) fruits, if any, from the female plants. This removal will prevent the accidental mixture of non-hybrid with hybrid fruits. Furthermore, non-hybrid fruits will steal nutrition away from the ripening hybrid fruit
Tomato fruits ripen about 50-60 days after pollination, but may take longer if temperatures are cool. Keep the fruits on the vine until they are fully mature, preferably to the pink or red ripe stage. This enables the seed to develop normally and fully. If fruits are harvested at an earlier stage, place them in a covered, cool dry place for three or four days until they become red ripe. Be sure to check for the clipped sepal before harvesting fruit. Collect fruits in nonmetallic containers, such as nylon net bags, plastic buckets, or crates. Metal containers may react with acids in the tomato juice and affect seed viability. Hence, they should not be used.
- Tomato Seed Extraction:
The work on tomato seed extraction and storage contains lot of care. For the storage of tomato seeds, the seeds were dried.
- Seed drying:
The fully ripped fruits like fully red tomatoes are selected for collection of seed and then their seed are extracted manually. For the extraction the tomatoes are placed in shopping bags by putting some water in it and remain it for one day. The next day seeds are extracted by shaking of shopping bags and washed with water. The seeds are dried in sun shine till 8 am to 1 pm and stored in packet. It’s a cheap and manual way of collecting seed. But it needs a lot of labor and it’s a time consuming task as well. Environment also affects this process, some time there is sun shine sometimes not.
In Pakistan we have to import hybrid seeds of vegetable crops. But now we started to produce our own hybrids mainly in tomato i.e. Salar. This is leading towards a satisfactory level. These hybrids are meeting with the nutritional and economic prospects of farmers and breeders.