NL2032727A

NL2032727A - Method for improving the quality of solanum melongena hybrid seed production by using greenhouse

Info

Publication number: NL2032727A
Application number: NL2032727A
Authority: NL
Inventors: Zhang Hongyuan; Zhang Min; Huang Shuping; Tan Jie; Chen Xia
Original assignee: Wuhan Acad Agricultural Sciences
Priority date: 2021-08-27
Filing date: 2022-08-10
Publication date: 2023-03-08
Also published as: CN113597992A; NL2032727B1

Abstract

U I T T R E K S E L A method for improving the quality of Solanum melongena hybrid seed production: 1) Greenhouse facilities: A steel—frame greenhouse field and an insect—proof net are used; 2) Planting density: the planting density of the male plants is 2,300—2,400 5 plants/mu, the female and male plants are planted in a centralized manner; 3) Pollination time. Carry out cross pollination from the "four Solanum melongena", pollinate mainly on two layers of fruits of "four Solanum melongena" and “eight Solanum melongena", continuously pollinate; 4) Pollen extraction: On the day before 10 pollination, collect flowers of a day, pick anthers with forceps, place into a pollination tube made of a transparent tube for pollination; 5) Cross pollination: Pollinate at 7—10 a.m., stretch a style after castration into the pollen tube; 6) Plant adjustment; 7) Seed harvesting: Solanum melongena can be harvested 15 when the Solanum melongena fruit skin becomes yellow—brown, and rinse with clean water; 8) Seed treatment.

Description

METHOD FOR IMPROVING THE QUALITY OF SOLANUM MELONGENA HYBRID SEED

PRODUCTION BY USING GREENHOUSE

TECHNICAL FIELD

The present disclosure belongs to the technical field of plant breeding, and specifically relates to a new method for im- proving the quality of Solanum melongena hybrid seed production.

The method can be applied to the cultivation of new varieties of

Solanum melongena.

BACKGROUND

Solanum melongena is one of the three major vegetable crops of the Solanaceae family, and is listed as the fourth largest veg- etable crop in the world by the Food and Agriculture Organiza- tion of the United Nations, with the global output of 52.3 million tons. Solanum melongena are planted all over the world, and culti- vated most in Asia. China has a long history of Solanum melongena cultivation and is the largest producer and consumer of Solanum melongena. According to statistics, in 2019, the sown area of So- lanum melongena reached 12.06 million mu in China, accounting for 53% of the world's total sown area. Hybrid Solanum melongena vari- eties have been widely used in production due to their strong het- erosis in yield, resistance and growth potential, etc.

At present, large-scale production of Solanum melongena hy- brid seeds is generally carried out by open-field cultivation in the northwest and other low-rain areas, and physical isolation is implemented. It is not allowed to plant other Solanum crops or So-

Janum melongena wild relatives within 300 m with the surrounding of the seed field as the radius. The planting density of the fe- male parent is 2,800-3,300 plants/mu. Starting from the pollina- tion of Solanum melongena, pollens are collected from the anthers by sun exposure, and after emasculation, a paper bag is used; and after pollination, absorbent cottons are used for isolation and protection, and color is applied or sepals are torn off for mark- ing. Each plant bears 4-8 fruits, topping once after pollination.

This pollination method utilizes the isolation of heterologous pellen clusters through physical distance, which cannot effective- ly guarantee the absence of cluster pollen, and it is difficult to ensure the purity of seeds. When pollinating, choosing paper bags and absorbent cotton to isolate insects is time-consuming and la- bor-intensive, and requires a high labor cost for pollination.

Smearing the color or tearing the sepals for marking is easily af- fected by high temperature and strong light and plant growth, and when the marking is not obvious in the later harvest, it is prone to cause mistaken harvesting and confusion. In addition, in recent years, due to the abnormal weather, the rainfall in the northwest region has increased, the number of diseases and insect pests has increased in the open field seed production, and the phenomenon of rotten fruits and abscission of fruits begins to increase, result- ing in a decrease in seed yield and quality.

SUMMARY

In order to overcome the above problems, an object of the present disclosure is to provide a method for improving the quality of Solanum melongena hybrid seed produc- tion by using a greenhouse. By adopting the method of sealing and isolating with the insect-proof nets in the greenhouse, the mixed pollination of insects can be avoided effectively. In addition, by using the greenhouse facilities, the effect of preventing from rain, insects and diseases has been achieved. By adjusting the techniques such as parental planting density, pollination time, pollen extraction, hybrid pollination, pollination markers, and plant adjustment before and after pollination and optimizing the pollination technology process, the fruit setting rate and seed quality of hybrid Solanum melongena are improved.

In order to achieve the foregoing object, the present disclo- sure adopts the following technical solutions:

A method for improving the quality of Solanum melongena hy- brid seed production by using a greenhouse, comprising the follow- ing steps: 1. Requirements on greenhouse facilities. A steel-frame greenhouse field is used, the top of a greenhouse is covered with a transparent plastic film, and the greenhouse is surrounded by a 40-50 mesh insect-proof net for sealing isolation.

2. Planting density.

Ditch and ridge by 1.4 m (ditch), carry out field planting on female plants in a plant distance of about

45 cm and male plants in a plant distance of about 40 cm in a row distance of about 50 cm, the planting density of the female plants is 2,000-2,100 plants/mu, the planting density of the male plants is 2,300-2,400 plants/mu, the female and male plants are planted in a centralized manner, in a total plant ratio of 1: 4-5.

3. Pollination time.

Carry out cross pollination from the "four Solanum melongena", pollinate mainly on two layers of fruits of "four Solanum melongena" and "eight Solanum melongena', gener- ally continuously pollinate for 15-20 d, then a single plant can bear more than 8 fruits on average successfully, and stop pollina-

tion when 10 fruits are born.

4. Pollen extraction.

On the day before pollination, collect flowers of a day, pick anthers with forceps, dry for 12-18h in an oven at about 30°C, collect the anthers with a mesh on the day of pollination, place in a sealed box to carry out pollen shaking,

collect anthers scattered in the box, place into a pollination tube made of a transparent tube for pollination.

5. Cross pollination.

Pollinate at 7-10 a.m., stretch a style after castration into the pollen tube, dip the stigma into the pollen sufficiently, tie the flower stalk with a red thread as a mark, the red thread is tied without falling off but not being too tight to damage the fruit stems when a fruit enlarges.

6. Plant adjustment.

The day before cross pollination, remove first flower, pair flowers and weak and useless side branches.

Af- ter the pollination, carry out topping once, while continue to re-

move the inflorescence on the female plants for a week, remove non-fruiting branches, and keep the plants ventilated.

7. Seed harvesting.

Solanum melongena can be harvested when the Solanum melongena fruit skin becomes yellow-brown completely 50-60 d after the pollination, and harvest seed fruits marked with red threads.

Place the harvested seed fruits in a cool and rain- proof place for about 7d for ripening, start to wash seeds, excise 1/3 of the seed fruits near the fruit stem, then smash the seed fruits into pulp with an Solanum melongena seed washing machine (existing equipment), and rinse with clean water. 8. Seed treatment. Dry seeds washed with the clean water in the sun for 2-3d, and bag and store when the water content of the seeds is reduced to 8%, to obtain Solanum melongena hybrid seeds.

By adopting the technical measures, the following technical problems and difficulties are solved:

In the step 1, the greenhouse facility, namely the greenhouse plastic film, is equipped with the 40-50 mesh insect-proof net for sealing isolation, playing a role of rain sheltering, heat preser- vation, insect control, disease prevention and cross-pollination prevention.

In the step 2, determining the planting density and the ratio of males plants to female plants can make full use of the land ar- ea of the greenhouse and effectively increase the seed yield per unit area.

In the step 3, pollination nodes and timing are determined, and with the combination of plant growth characteristics, the time and space are better utilized to increase the fruiting rate, thus increasing the seed yield and reducing the management cost.

In the step 4, the pollen extraction technique is clarified, avoiding the instability such as a conventional method of drying pollen in the sun.

In the step 5, the pollination time and manner of the pollen tube, as well as the red thread marking method, are clarified, thereby simplifying the pollination technology process and clear- ing pollination markings.

In the step 6, it is proposed to continue picking off flowers for a week after the end of pollination, and carry out topping, so that with the technology, nutrients can be more centralized, being beneficial to growth and development of pollinated fruits. At the same time, continue picking off flowers for a week, then self- pollinated resultant seeds can be prevented from mixing into the hybrid seeds to affect the purity of the seeds, and this is the most important cause of the low quality of conventional hybrid seeds.

In the step 7, excise 1/3 of the seed fruits near the fruit stalk, and then smash the seed fruits into pulp with the Solanum melongena seed washing machine, thereby completely dissociating seeds from flesh, reducing impurities, and protecting the seed washing machine. 5 In the prior art, seed production is carried out mainly in a mode of open field cultivation in a physical distance for iscla- tion to prevent cross-pollination, and in pollination, paper bags and absorbent cotton are selected to isolate insects, being time- consuming and labor-wasting, and requiring a large pollination la- bor cost. By marking in a mode of rubbing with color or tearing sepals, plant adjustment is generally not required after pollina- tion. Such isolation does not necessarily effectively prevent cross-pollination, and the seed purity is hard to guarantee. Mean- while, due to abnormal weather with increasing rain in recent years, diseases and insects in open field seed production are in- creasing, rotten fruits are increasing, and thus the seed yield and quality can be degraded. Markings of rubbing with color or tearing sepals in pollination are prone to fade under a high tem- perature condition of sunshine at later stages, and meanwhile, the markings are unconspicuous while the plants grow flourishing at later stages, resulting in influence. Generally no plant adjust- ment is made after pollination, resulting in a certain amount of non-hybrid fruits may affect the seed purity, and events of low or even unqualified Solanum melongena seed purity happen occasional- ly.

According to the present disclosure, with the greenhouse fa- cility, namely the insect-proof net in the step 1 as an isolation measure, marking with red threads in the step 5, and topping for one week after pollination in the step 6, out-sourcing pollen can be isolated from the source, non-target hybrid seeds can be marked and distinguished in the cross pollination process, and flowers are picked off for one week after pollination to prevent authigene fruits from mixing, so that treatment from the three technical as- pects, the purity of the hybrid seeds can be ensured. Due to im- plementation of steps 2, 3, 4 and 7, the Solanum melongena plant- ing and pollination technology process are optimized, with the combination of physiological properties of Solanum melongena growth, flowering and fruiting, nutrition demands and the like, the fruiting rate of the Solanum melongena can be increased, and thus the quality and yield of Solanum melongena hybrid seed pro- duction are further improved.

Compared with the prior art, the present disclosure has the following advantages and effects:

The method sufficiently utilizes the greenhouse facility, namely the greenhouse film insect-proof net is used to play the role of rain sheltering, heat preservation, insect control and disease prevention, cross-pollination by insects is prevented, and thus the influence of adverse weather on Solanum melongena seed production is reduced. By improving the pollen extraction technol- ogy, pollination technology and optimizing pollination markings, as well as developing applicable plant adjustment methods accord- ing to the environment characteristics of the greenhouse, and clarifying technical parameters such as planting density, pollina- tion and fruiting period and number of fruits, the seed yield and quality can be improved. Specifically, with the greenhouse facili- ty, namely the insect-proof net in the step 1 as the isolation measure, marking with red threads in the step 5, and topping for one week after pollination in the step 6, out-sourcing pollen can be isolated from the source, non-target hybrid seeds can be marked and distinguished in the cross pollination process, and flowers are picked off for one week after pollination to prevent authigene fruits from mixing, so that treatment from the three technical as- pects, the purity of the hybrid seeds can be ensured. Due to im- plementation of steps 2, 3, 4 and 7, the Solanum melongena plant- ing and pollination technology process are optimized, with the combination of physiological properties of Solanum melongena growth, flowering and fruiting, nutrition demands and the like, the fruiting rate of the Solanum melongena can be increased, the seed yield is increased by 20.51%, 1.5 pollination labors are re- duced for each mu on average, insecticides for preventing and treating diseases and insects are used 8 times in the whole growth period, which are reduced by 2 times when compared with those of a conventional method. Germplasm quality testing shows that the seed emergence rate is 98.4%, the seed purity is 100%, the thousand seed weight of the seeds is increased by 0.28 g, and the seeds are full, bright in color and high in quality. By adopting the tech- nical method, the seed purity and yield of Solanum melongena hy- brid seed production are remarkably improved, the production cost and the management risk are reduced, thus improving the quality of

Solanum melongena hybrid seed production, expanding seed produc- tion area and breaking the territorial limitation of conventional seed production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a pollen collection process.

Pollens are collected after drying in an oven at about 30°C for 16 hours. The quantity of pollens is large, the quality is good and the technology is stable and controllable.

FIG. 2 is a schematic diagram of a red line mark of hybrid pollination.

The marks are clear and will not be lost, which facilitates the later fruit picking and ensures the homozygosity of hybridiza- tion.

FIG. 3 is a schematic diagram illustrating the growth situa- tion in the late stage of seed production.

The Solanum melongena grows vigorously, the fruit setting rate of a single Solanum melongena is high, and the seed yield is high.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make the technical characteristics and the object of the present disclosure to be clearer, the present disclosure will be further described in detail in conjunction with specific embodiments. The specific embodiments are only used to explain ra- ther than limit the present disclosure.

Seed production of hybrid Solanum melongena variety “Yingchun

No.1”

Example 1:

A method for improving the quality of Solanum melongena hybrid seed production by using a greenhouse, including the following steps:

1.Requirements for seed production plots:

The steel frame greenhouse is used, with a width of 8 meters and a length of 40 meters. The roof of the greenhouse is covered with a transparent plastic film, and a 40-mesh insect-proof net is used for isolation around the greenhouse. The planting field re- quires sandy lcam and loam soil, and no solanaceous vegetables have been planted therein in 2-3 years. The terrain is flat, the drainage and irrigation are convenient, the soil texture is loose, and the soil layer is deep and fertile. 2. Sowing time:

In Wuhan, the seedlings are sown from middle-later December to early January of the following year, and the male parent is sown 5 days earlier than the female parent. 3. Sowing and raising seedlings:

The seeds are scalded with warm water at 60°C for 30 minutes, soaked at room temperature for 8 hours, and then scrubbed to pro- mote germination. The treated seeds are placed in a mesh bag and wrapped with a wet towel to keep them moisturizing, and germina- tion is accelerated at a constant temperature of 30°C. When more than 70% of the seeds are germinated, seeds are taken out for sow- ing in trays, 1 seed per hole. 4. Field planting:

Field planting is carried out from March 25. The female par- ent plant spacing is about 45 cm, the male parent plant spacing is about 40 cm, and the row spacing is about 50 cm. The male and fe- male parents are planted in a ratio of male plant to female plant of 1:5 in a centralized way. 5. Plant adjustment:

Cross-pollination starts from Four eggplants. The first flow- er and pair flowers and weak side branches are removed in time be- fore pollination. After pollination, flowers are picked and top- ping is carried out in one week, to remove the non-fruiting branches and keep the plants ventilated. The old leaves and yellow leaves at the middle and lower parts of the plant are removed. 6. Hybrid seed production: 6.1 Isolation protection:

Before pollination, the insect nets are checked for the in-

tegrity, to ensure that there are no breakage and leaks. Pesti- cides are sprayed twice before pollination, focusing on the con- trol of aphids, yellow tea mites and thrips. 25% thiamethoxam wa- ter dispersible granules or 3% acetamiprid EC or 10% nitenpyram WP are sprayed by 2,000-fold alternatively. 6.2 Removal of miscellaneous plants:

The miscellaneous plants are removed in a centralized way be- fore pollination. All miscellaneous plants with inconsistent plant shape, leaf shape and fruit shape are removed, to ensure that there are no miscellaneous plants in both parents for seed produc- tion before pollination. 6.3 Collection of male parent pollens:

The flowers are collected one day before pollination. The an- thers are picked with tweezers and dried in an oven at 30 °C for 16 h. On the day of pollination, the pollens are shaken with gauze on the day of pollination, and the collected pollens are placed into the pollination tube for pollination. 6.4 Emasculation of female parents:

Emasculation is started in the afternoon one day before pol- lination. The main flower buds that will flower on the next day are selected, and petals are gently poked with tweezers, and then the tweezers are inserted into the inner base of the petals to clamp the anthers to remove, to ensure that each flower is com- pletely emasculated. The tweezers cannot damage the styles and ovaries. After emasculation, a red thread is placed on the leaves near the flowers as a mark. 6.5 Hybrid pollination:

Pollination is started at 7:00 am and finished before 10:00 am. The emasculated styles are placed into the pollen tube, so that the stigma is fully dipped in pollens. A red thread is tied to the flower stalk as a mark, to keep the thread not to fall off.

The thread cannot be tied tightly, to prevent the fruits from en- larging and damaging the fruit stems. Generally after pollination for 18 days, when there are more than 8 fruits set in a single plant, the pollination is stopped. 6.6 Hybrid pollination test

Experiments are set up with different treatments.

The pollen extraction method includes: 1. Sun exposure; 2.

Oven.

Marking methods: 1. tearing the sepals; 2. coloring the fruit stems; 3. tying a red thread.

Isolation measures: 1. Covering the paper bag with cotton; 2.

Isolating with insect nets.

Plant adjustment treatments: 1. Topping only once; 2. Picking flowers for one week and removing new leaves for topping.

The test results show that: 1. By adopting the present dis- closure and using the oven to dry the anthers to obtain the pol- lens, the quality of the pollens is high, and the conditions are controllable, avoiding the defects that the pollens extraction with sun exposure is greatly affected by the weather changes, the conditions are uncontrollable, and the quality of the pollen is not high. 2. The red thread will not be fallen off when a red thread method is used, and the fruits are easy to distinguish in the later stage, which are not affected by the plant growth and high temperature, and the marks are conspicuous. By using the ex- isting method of tearing the sepals and applying red paint to the fruit stems, the fruit stems fade to varying degrees 50 days after pellination, and the color of the fruit stems is uneven after the fruits are enlarged. After the fruit is ripe, the sepals them- selves have notches, which need to be carefully observed to dis- tinguish the marks. In the later stage of growth, the plants are closed, and there are many branches and leaves, and it is not easy to observe the color of the fruit stems and the fruit sepals. The fruit picking speed is slow, and the technical problem of mixing non-hybrid seeds is also prone to occur. 3. The use of insect- proof net isolation method does not need to be isolated again dur- ing pollination. It takes 3 labors to complete the pollination per mu every day, which saves 1.5 labors compared to the conventional method of using paper bags and cottons. 4. Through the technical means of continuous flower picking and topping, the plant growth is adjusted, and the nutrition is controlled to the growth of the target hybrid fruits. The test results show that the 1000-grain weight of the seeds increases by 0.28g, the seeds are plump, the color is bright, and the quality is high. By adopting the technol-

ogy of the present disclosure for hybrid seed production of Sola- num melongena, the yield of seeds per mu reaches 21.15 kg, while the yield of seeds produced by the conventional method is 17.55 kg. The yield of seed production is increased by 20.51% in the present disclosure. 7. Seed harvesting: 7.1 Fruit picking: 55 days after pollination, the Solanum melongena fruits can be harvested when the skin turns yellow-brown completely. The fruits marked with red threads are harvested, and those that are not clearly marked and fallen off are removed in time. 7.2 Seed washing:

The harvested seeds are placed in a cool and sheltered place and then washed about 7 days after maturity. After cutting off the seed fruits near 1/3 of the fruit stem, the Solanum melongena is smashed into pulp with a seed washing machine, and rinsed with clean water. 7.3 Drying:

The seeds washed with clean water are placed in well- ventilated items such as plastic gauze and canvas, then dried in the sun for 2 or 3 days, and frequently turned. Placing seeds di- rectly on the cement floor or drying them for a long time under direct sunlight at noon should be avoided, which may reduce the germination rate. When the moisture content is reduced to 8%, seeds can be stored in bags.

Through the above specific technical measures, after adjust- ing the techniques such as parental planting density, pollination time, pollen extraction, hybrid pollination, pollination markers, and plant adjustment before and after pollination and optimizing the pollination technology process, the fruit setting rate and the seed quality of hybrid Solanum melongena are improved.

Analysis of the test results: By adopting the technical solu- tions of the present disclosure, the hybrid seed production of So-

Janum melongena "Yingchun No. 1" is completed. The test results are as follows: 1. The method of pollen extraction by sun exposure is direct- ly related to the intensity and temperature of the sun. Under the conditions of strong light and high temperature, the anthers can be dried in the sun for 6-8 hours, and it is easy to disperse pol- lens and the amount of pollen is sufficient. However, in the case of rainy weather and high humidity, it is difficult to extract pollens and difficult to disperse the pollens, and the amount of pollen is insufficient. When dried in an oven 18 hours, the an- thers are dry, the pollens are completely scattered, the pollens are easy to scatter, and the amount of pollens is sufficient. 2. The marking method of tearing the sepals and painting the red paint on the fruit stems is used. The fruit stems fade to var- ying degrees 50 days after pollination, and the color of the fruit stems 1s uneven after the fruits are enlarged. After the fruit is ripe, the sepals themselves have notches, which need to be care- fully observed to distinguish the marks. In the later stage of growth, the plants are closed, and there are many branches and leaves, and it is not easy to observe the color of the fruit stems and the fruit sepals. The fruit picking speed is slow. Using the method of tying the red thread, the red thread also fades to a certain extent, the red thread will not fall off, and it is easy to distinguish. 3. Isolation measures. Using the method of paper bags and cottons, the isolation is thorough and there is no mixing. It takes 4.5 labors to complete the pollination per mu every day. The insect-proof net isolation method is adopted, and there is no need to isolate again during pollination, and it takes 3 labors to com- plete the daily pollination work.

Overall evaluation: using the technology of the present dis- closure for hybrid seed production of Solanum melongena, the yield of seeds per mu reaches 21.15 kg, while the yield of seeds pro- duced by the conventional method is 17.55 kg. The yield of seed production is increased by 20.51% in the present disclosure. Three pollinators are required per mu per day, the average pollination time is 19 days, and the average number of pollinators per mu is reduced by 1.5. During the whole growth period, 8 times of pesti- cides are used for pest control, which is 2 times less than the conventional method. One thousand seeds are randomly selected and divided into 5 groups on average. Each group is independently tested for seed quality.

The results show that the seed germina- tion rate is 98.4%, the seed purity is 100%, the 1000-grain weight of the seeds increases by 0.28g; the seeds are plump, bright in color and high in quality.

Claims

CONCLUSIONS

A method of improving the quality of Solanum melongena hybrid seed production by using a greenhouse, comprising the following steps: 1) Greenhouse facilities: a steel frame greenhouse field is used, the top of a greenhouse is covered with a transparent plastic film and the greenhouse is surrounded by a 40 to 50 mesh insect repellent net for sealing insulation; 2) Planting density: ditch and ledge with 1.4m, carry out field planting on female plants at about 45cm planting distance and male plants at 40cm planting distance with 50cm row spacing, the planting density of the female plants is

2,000 to 2,100 plants/mu, the planting density of the male plants is 2,300 to 2,400 plants/mu, the female and male plants are planted centrally, in a total planting ratio of 1: (4 to 5); 3) Pollination time: carry out cross-pollination of the "four Solanum melongena", mainly pollinate on two layers of fruit of "four So-Janum melongena" and Macht Solanum melongena", continuously pollinate for 15 to 20 d, and when a single plant averages more than bears 8 fruits successfully, stop pollination; 4) Pollen extraction: On the day before pollination, collect flowers of one day, pluck anthers with tweezers, dry in an oven at about 30 °C for 12 to 18 hours, collect the anthers with a gauze on the day of pollination, place in a sealed box to shake pollen, collect anthers scattered in the box, place in a pollination tube made of a transparent tube for pollination; 5 ) Cross-pollination: pollination at 7 to 10 am, stretch a style after castration into the pollination tube , dip the stigma enough in pollen, tie the flower stem with a red thread as a mark, making the red thread tied up without falling out; 6) Plant adaptation: The day before cross-pollination, remove the first flower, few flowers and weak and useless side branches, after pollination, top once, while continuing to remove the inflorescence on the female plants for a week, remove non-fruit-bearing branches, and keep the plants ventilated; 7) Harvesting Seed: Solanum melongena can be harvested when the

Solanum melongena fruit rind turns completely yellow-brown 50 to 60 days after pollination and harvest seed fruits marked with red threads; place the harvested seed fruits in a cool and rainproof place for 7 days to ripen, start by washing the seeds, cut away 1/3 of the seed fruits at the fruit stem, and crush the seed fruits into a pulp with a Solanum melongena- seed washer and rinse with clean water; 8) Seed treatment: dry the seeds washed with clean water in the sun for 2 to 3 days, and put them in a bag and keep them when the water content of the seeds is reduced to

8%, to obtain Solanum melongena hybrid seeds.