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Abstract In order to screen out the small watermelon varieties with red flesh suitable for soilless cultivation and to meet peoples requirements of highquality watermelons， comparative tests were conducted on 6 small watermelon varieties with red flesh under soilless culture conditions in 2018. Based on the data of field traits， yield traits， quality traits and commercial traits， the integrated results showed that ‘Chuanqi 2 had good quality and high yield， and the overall performance was the best.
Key words Soilless culture; Red flesh watermelon; Variety screening
Juicy and tasty watermelon is a musthave for summer heatreducing， and is deeply loved by consumers. In recent years， small watermelons have been very popular with consumers because of their higher quality and early marketing. At present， small red flesh watermelon varieties are less planted in Beijing. Mainly based on soil cultivation， there are problems of fragile melons， low sugar content， low utilization rate of land resources， low water and fertilizer utilization rate， high labor intensity， serious soilborne diseases like fausarium wilt and rootknot nematodes. Soilless cultivation is an effective method to solve the obstacles of watermelon continuous cropping， which can not only improve the water and fertilizer utilization rate， but also overcome the effects of soilborne diseases on watermelon， as well as reduce soil salinization， thereby improving watermelon yield and quality.
In order to meet demand of citizens for small red flesh watermelon， comparison tests were carried out to small red flesh watermelon varieties under soilless cultivation in Beijing Agricultural Technology Extension Station.
Materials and Methods
Test materials
The tested watermelon varieties were Chuanqi 1， Chuanqi 2， Hongyunlai and Chaoyuemengxiang， selected by Beijing Agricultural Technology Extension Station， and the varieties of Jinxiu and Jingying selected by Beijing Academy of Agriculture and Forestry were used to conduct screening tests. Chaoyuemengxiang was used as a control variety.
Test design
The planting pattern was one ridge with double rows， cultivated by hanging vines. The pruning method was "one plant each side， fruit setting on main vines". The plant spacing was 35 cm， and the planting density is 30 000 plants/hm 2. There were a total of 3 repetitions and 18 plots. Each plot had an area of 37 m 2， planted with 110 plants. In addition to the difference in varieties， the management measures for each treatment were consistent with field management， and microspraying was used. Test methods
The test was carried out in a standard steel frame greenhouse in Dongyitang Village， Panggezhuang Town， Beijing City. ① The specifications of a single greenhouse were 10 m wide from east to west and 58 m long from north to south. The shed film was the dropfree PO film produced by a regular manufacturer. The shed film could be ventilated on both sides， and a 50mesh insect net was added. In the test， seedlings were cultivated using plug tray and substrate nutrient soil， and grafting technology was adopted with Jingxinzhan 4 as the rootstock. ② The cultivation mode was soilless cultivation conducted in the form of a simple cultivation soil tank， which was made of PVC material. The tank was 45-50 cm wide at the upper end， and 30-35 cm wide at the lower with the depth of 30-35 cm. During the cultivation， a layer of plastic film was laid inside the tank to isolate soil， and another layer of thickened insect proof net was laid on the film with the substrate placing above. ③ Substrate selection： the formula for the cultivation substrate was turf∶perlite∶vermiculite = 7∶3∶4 （w/w）. When the substrates were mixed， 33 kg of chicken manure was added per square meter （organic matter content ≥ 20%; pH = 5.5-6.5; total nitrogen （in the form of N） ≥ 0.8%; total phosphorus （in the form of P2O5） ≥ 0.3%; total potassium （in the form of K2O） ≥ 0.4%）. The prepared cultivation substrate was disinfected with 800 times diluted 50% carbendazim WP， which was filled in the cultivation tank after fully mixing. ④ Water and fertilizer systems. Each cultivation tank had 2 drip irrigation zones placed parallel inside， and the irrigation zone was 15 mm in diameter and the water outlet was separated by 30 cm. the front part was equipped with precision fertilization system， so that each drip irrigation zone had even water distribution， and a filter device was installed to prevent the water outlet from being blocked. ⑤ Selection of fertilizers. The A， B fertilizers special for watermelon were applied. （A fertilizer： potassium nitrate∶calcium nitrate tetrahydrate = 7∶4 （w/w）; B fertilizer： ammonium dihydrogen phosphate∶magnesium sulfate heptahydrate = 1∶1 （w/w）. Trace elements were added to the two fertilizers with pH of 5.5-5.8）. ⑥ Pest control. During the vine elongation period and fruit setting period， agents such as difenoconazole， chlorothalonil and triterpene were used to control powdery mildew and starscream， imidacloprid was used cyhalothrin water aqua was used to control cotton bollworm and oriented tobacco budworm. ⑦ Field management. The test field was planted on March 12， pollinated on April 13 and harvested on May 25. Each watermelon seedlings had 2 vines left， and the fruit was set on the second female flower of the main vine. Each plant only had one melon left， and the lateral vine had the top removed after fruit setting. Determination and analysis methods
For each treatment， labels were marked on the day of female flower pollination， and the pollination date and fruit ripening period were recorded， with the average taken. During the ripening period， 10 ripe melons were randomly collected from each plot， and the average single melon weight was calculated. During the fruit ripening period， 5 representative melons were selected from each plot to measure the fruit shape index， soluble solid content， rind thickness， and the averages were taken. The taste of each melon was recorded. Each plot was harvested separately， and the actual yield was recorded. The disease resistance （divided into 5 levels of strong， medium strong， medium， medium weak and weak） of each variety was visually observed in 3 times， namely in the seedling period， fruitsetting period and fruit ripening period. The test data was analyzed by randomized block， single factor， and Ducans new multiple range method.
Results and Analysis
Comparison of main field traits
As shown in Table 1， under consistent field management measures， the fruit development period of each variety varied from 32 to 39 d. The fruit development period of Chuan 1 was the shortest， which was 32 d， followed by Chaoyuemengxiang of 34， and Chuanqi 2 and Jingying came to the third with 36 and 37 d， while Hongyunlai and Jinxiu had long fruit development period of 38 and 39 d， respectively. The whole growth period of each variety was consistent with the trend of fruit development period. The fruit setting nodes of each variety ranged from 13.3 to 17.0. Jinxiu， Jingying and Chuanqi 2 had the best fruit setting performance， with the fruit setting nodes of 13.3， 13.6 and 15.3， respectively， which were lower than those of other varieties. The fruit setting nodes of Chuanqi 1 were the highest of 17.00， which was significantly higher than those of other varieties. The intervals between female flowers in each variety ranged from 6.00 to 9.70 nodes. Among them， the female flower intervals of Chuanqi 1 was the least of 6.00， and the female flower intervals of Hongyunlai was the most， which were 9.70. The female flower intervals of the other four varieties were between 6.30 and 8.00 nodes， and there was no significant difference between different varieties. The plant growth of different varieties was not consistent. The growth vigor of Chaoyuemengxiang was weak， while Chuanqi 2 and Jingying showed vigorous growth， and the other 3 varieties had moderate growth. Comparison of yield traits
Yield
As shown in Table 2， Chuanqi 2 and Hongyunlai had high plot yields of 281.84 kg and 274.93 kg， respectively， which were significantly higher than the yields of other varieties， and the yield of Jinxiu was the lowest of 213.59 kg. The plot yields of other varieties ranged from 218.76 kg to 245.25 kg. The variation trend of output per unit area was consistent with the plot yield. Chuanqi 2 had the highest yield per unit area of 5 073.18 kg/667m 2， followed by Hongyunlai of 4 494.68 kg， and the yields of the other 4 varieties were 3 844.68 – 4 414.50 kg/667 m 2. The varieties with relatively low yields included Jinxiu， Chaoyuemengxiang and Chuanqi 1 with the yields of 3 844.68， 3 937.20 and 3 994.32 kg/667m 2， respectively， which were significantly lower than the yields of other varieties.
Single fruit weight
As shown in Table 2， the average single fruit weight of different watermelon varieties ranked from high to low was in the order of Chuanqi 2 （2.57 kg） > Hongyunlai （2.53kg） > Jingying （2.25kg） > Chuanqi 1 （2.04 kg） = Chaoyuemengxiang （2.04 kg） > Jinxiu （1.99 kg）. Among them， the single fruit weight of Chuanqi 2 was the highest， while the single fruit weight of Chuanqi 1， Chaoyuemengxiang and Jinxiu was low， which indicated poor yielding ability. The fruit setting rates of different varieties ranged from 96.50% to 98.70%. Among them， Chuanqi 2 and Jingying had high fruit setting rates of 98.70% and 98.10% respectively， while the fruit setting rate of Chaoyuemengxiang was the lowest of 96.6%， and there was no significant difference in the fruit setting rates among different varieties.
Comparison of fruit commercial traits
As shown in Table 3， the tested 6 varieties all had ellipse shape， green rind covered with dark green stripes. The fruit shape indexes were between 1.10 and 1.38. Chuanqi 1 and Chaoyuemengxiang had relatively higher fruit shape indexes of 1.37 and 1.38， while the fruit shape index of Hongyunlai was the lowest of 1.10. Comprehensive comparison on fruit traits showed that Chuanqi 2 and Jingying had bright green rind， clear and ordered stripes and hotpink flesh， which suggested good commercial characters， and the rind hardness could also reach 12.8 kg/cm 2 and 12.9 kg/cm 2.
Agricultural Biotechnology2018
Comparison of fruit quality
As shown in Table 4， Chuanqi 2 had the highest central soluble solids， reaching up to 13.40， which was significantly higher than that of other varieties， followed by Jingying， which had the central soluble solids content of 12.40. The central soluble solids content of Chaoyuemengxiang reached over 12%， indicating it was a small watermelon variety with high sugar content， and the central soluble solids content of Hongyunlai， Jinxiu and Chuanqi 1 was 11.40%， 11.50 and 11.80%， respectively. Hongyunlai had the smallest difference in the soluble solids between the center and side， which was 1.8%， and the largest difference was found in Chuanqi 2， which was 3.6%. Chuanqi 2 and Chaoyuemengxiang had good flesh and flavor. The rind thicknesses of the 6 varieties were between 0.55 and 0.75 cm. Chuanqi 1 had the thinnest rind of 0.55 cm， while Jingying had the thickest rind of 0.75 cm， and both showed significant differences in the rind thickness from other varieties. Discussion and Conclusion
The conventional facility watermelon planting in Beijing is mainly based on soil cultivation， which has the problems of low utilization rate of land resources， low water and fertilizer utilization rate， high labor intensity， serious soilborne diseases like fausarium wilt and rootknot nematodes. Soilless cultivation is an effective method to solve the problem of continuous cropping of facility watermelon. The comparative tests on the small watermelon varieties with red flesh under soilless cultivation show that Chuanqi 2 is a midearly maturing variety which has cracking resistance and fine flesh， and it also has stable performances in field traits， yield traits， quality traits and commercial traits. Moreover， Chuanqi 2 is the most juicy variety with sweet and refreshing taste， making it suitable for planting under soilless cultivation.
References
[1] ZENG JB， ZHU L， LI L， et al. Summary of the current status of watermelon and melon cultivation techniques in Beijing[J]. China Cucurbits and Vegetables， 2014， 27（5）： 68-70.
[2] LI T， ZENG JB， CHEN YL， et al. Cultivation techniques of small fruit watermelon in the autumn greenhouse in Beijing[J]. China Cucurbits and Vegetables， 2013， 26（6）： 52-53.
[3] MA C， ZENGG JB， ZENG X， et al. Close hanging planting and early harvesting cultivation techniques of small greenhouse watermelon in spring in Beijing[J]. China Vegetables， 2014（1）： 83-85.
[4] MA C， ZENG JB， MU SQ， et al. The study on the different cultivation density of small fruit watermelon under the conditions of "two vines and one line" in spring greenhouse[J]. Chinese Horticulture Abstract， 2014（7）： 19-20.
Key words Soilless culture; Red flesh watermelon; Variety screening
Juicy and tasty watermelon is a musthave for summer heatreducing， and is deeply loved by consumers. In recent years， small watermelons have been very popular with consumers because of their higher quality and early marketing. At present， small red flesh watermelon varieties are less planted in Beijing. Mainly based on soil cultivation， there are problems of fragile melons， low sugar content， low utilization rate of land resources， low water and fertilizer utilization rate， high labor intensity， serious soilborne diseases like fausarium wilt and rootknot nematodes. Soilless cultivation is an effective method to solve the obstacles of watermelon continuous cropping， which can not only improve the water and fertilizer utilization rate， but also overcome the effects of soilborne diseases on watermelon， as well as reduce soil salinization， thereby improving watermelon yield and quality.
In order to meet demand of citizens for small red flesh watermelon， comparison tests were carried out to small red flesh watermelon varieties under soilless cultivation in Beijing Agricultural Technology Extension Station.
Materials and Methods
Test materials
The tested watermelon varieties were Chuanqi 1， Chuanqi 2， Hongyunlai and Chaoyuemengxiang， selected by Beijing Agricultural Technology Extension Station， and the varieties of Jinxiu and Jingying selected by Beijing Academy of Agriculture and Forestry were used to conduct screening tests. Chaoyuemengxiang was used as a control variety.
Test design
The planting pattern was one ridge with double rows， cultivated by hanging vines. The pruning method was "one plant each side， fruit setting on main vines". The plant spacing was 35 cm， and the planting density is 30 000 plants/hm 2. There were a total of 3 repetitions and 18 plots. Each plot had an area of 37 m 2， planted with 110 plants. In addition to the difference in varieties， the management measures for each treatment were consistent with field management， and microspraying was used. Test methods
The test was carried out in a standard steel frame greenhouse in Dongyitang Village， Panggezhuang Town， Beijing City. ① The specifications of a single greenhouse were 10 m wide from east to west and 58 m long from north to south. The shed film was the dropfree PO film produced by a regular manufacturer. The shed film could be ventilated on both sides， and a 50mesh insect net was added. In the test， seedlings were cultivated using plug tray and substrate nutrient soil， and grafting technology was adopted with Jingxinzhan 4 as the rootstock. ② The cultivation mode was soilless cultivation conducted in the form of a simple cultivation soil tank， which was made of PVC material. The tank was 45-50 cm wide at the upper end， and 30-35 cm wide at the lower with the depth of 30-35 cm. During the cultivation， a layer of plastic film was laid inside the tank to isolate soil， and another layer of thickened insect proof net was laid on the film with the substrate placing above. ③ Substrate selection： the formula for the cultivation substrate was turf∶perlite∶vermiculite = 7∶3∶4 （w/w）. When the substrates were mixed， 33 kg of chicken manure was added per square meter （organic matter content ≥ 20%; pH = 5.5-6.5; total nitrogen （in the form of N） ≥ 0.8%; total phosphorus （in the form of P2O5） ≥ 0.3%; total potassium （in the form of K2O） ≥ 0.4%）. The prepared cultivation substrate was disinfected with 800 times diluted 50% carbendazim WP， which was filled in the cultivation tank after fully mixing. ④ Water and fertilizer systems. Each cultivation tank had 2 drip irrigation zones placed parallel inside， and the irrigation zone was 15 mm in diameter and the water outlet was separated by 30 cm. the front part was equipped with precision fertilization system， so that each drip irrigation zone had even water distribution， and a filter device was installed to prevent the water outlet from being blocked. ⑤ Selection of fertilizers. The A， B fertilizers special for watermelon were applied. （A fertilizer： potassium nitrate∶calcium nitrate tetrahydrate = 7∶4 （w/w）; B fertilizer： ammonium dihydrogen phosphate∶magnesium sulfate heptahydrate = 1∶1 （w/w）. Trace elements were added to the two fertilizers with pH of 5.5-5.8）. ⑥ Pest control. During the vine elongation period and fruit setting period， agents such as difenoconazole， chlorothalonil and triterpene were used to control powdery mildew and starscream， imidacloprid was used cyhalothrin water aqua was used to control cotton bollworm and oriented tobacco budworm. ⑦ Field management. The test field was planted on March 12， pollinated on April 13 and harvested on May 25. Each watermelon seedlings had 2 vines left， and the fruit was set on the second female flower of the main vine. Each plant only had one melon left， and the lateral vine had the top removed after fruit setting. Determination and analysis methods
For each treatment， labels were marked on the day of female flower pollination， and the pollination date and fruit ripening period were recorded， with the average taken. During the ripening period， 10 ripe melons were randomly collected from each plot， and the average single melon weight was calculated. During the fruit ripening period， 5 representative melons were selected from each plot to measure the fruit shape index， soluble solid content， rind thickness， and the averages were taken. The taste of each melon was recorded. Each plot was harvested separately， and the actual yield was recorded. The disease resistance （divided into 5 levels of strong， medium strong， medium， medium weak and weak） of each variety was visually observed in 3 times， namely in the seedling period， fruitsetting period and fruit ripening period. The test data was analyzed by randomized block， single factor， and Ducans new multiple range method.
Results and Analysis
Comparison of main field traits
As shown in Table 1， under consistent field management measures， the fruit development period of each variety varied from 32 to 39 d. The fruit development period of Chuan 1 was the shortest， which was 32 d， followed by Chaoyuemengxiang of 34， and Chuanqi 2 and Jingying came to the third with 36 and 37 d， while Hongyunlai and Jinxiu had long fruit development period of 38 and 39 d， respectively. The whole growth period of each variety was consistent with the trend of fruit development period. The fruit setting nodes of each variety ranged from 13.3 to 17.0. Jinxiu， Jingying and Chuanqi 2 had the best fruit setting performance， with the fruit setting nodes of 13.3， 13.6 and 15.3， respectively， which were lower than those of other varieties. The fruit setting nodes of Chuanqi 1 were the highest of 17.00， which was significantly higher than those of other varieties. The intervals between female flowers in each variety ranged from 6.00 to 9.70 nodes. Among them， the female flower intervals of Chuanqi 1 was the least of 6.00， and the female flower intervals of Hongyunlai was the most， which were 9.70. The female flower intervals of the other four varieties were between 6.30 and 8.00 nodes， and there was no significant difference between different varieties. The plant growth of different varieties was not consistent. The growth vigor of Chaoyuemengxiang was weak， while Chuanqi 2 and Jingying showed vigorous growth， and the other 3 varieties had moderate growth. Comparison of yield traits
Yield
As shown in Table 2， Chuanqi 2 and Hongyunlai had high plot yields of 281.84 kg and 274.93 kg， respectively， which were significantly higher than the yields of other varieties， and the yield of Jinxiu was the lowest of 213.59 kg. The plot yields of other varieties ranged from 218.76 kg to 245.25 kg. The variation trend of output per unit area was consistent with the plot yield. Chuanqi 2 had the highest yield per unit area of 5 073.18 kg/667m 2， followed by Hongyunlai of 4 494.68 kg， and the yields of the other 4 varieties were 3 844.68 – 4 414.50 kg/667 m 2. The varieties with relatively low yields included Jinxiu， Chaoyuemengxiang and Chuanqi 1 with the yields of 3 844.68， 3 937.20 and 3 994.32 kg/667m 2， respectively， which were significantly lower than the yields of other varieties.
Single fruit weight
As shown in Table 2， the average single fruit weight of different watermelon varieties ranked from high to low was in the order of Chuanqi 2 （2.57 kg） > Hongyunlai （2.53kg） > Jingying （2.25kg） > Chuanqi 1 （2.04 kg） = Chaoyuemengxiang （2.04 kg） > Jinxiu （1.99 kg）. Among them， the single fruit weight of Chuanqi 2 was the highest， while the single fruit weight of Chuanqi 1， Chaoyuemengxiang and Jinxiu was low， which indicated poor yielding ability. The fruit setting rates of different varieties ranged from 96.50% to 98.70%. Among them， Chuanqi 2 and Jingying had high fruit setting rates of 98.70% and 98.10% respectively， while the fruit setting rate of Chaoyuemengxiang was the lowest of 96.6%， and there was no significant difference in the fruit setting rates among different varieties.
Comparison of fruit commercial traits
As shown in Table 3， the tested 6 varieties all had ellipse shape， green rind covered with dark green stripes. The fruit shape indexes were between 1.10 and 1.38. Chuanqi 1 and Chaoyuemengxiang had relatively higher fruit shape indexes of 1.37 and 1.38， while the fruit shape index of Hongyunlai was the lowest of 1.10. Comprehensive comparison on fruit traits showed that Chuanqi 2 and Jingying had bright green rind， clear and ordered stripes and hotpink flesh， which suggested good commercial characters， and the rind hardness could also reach 12.8 kg/cm 2 and 12.9 kg/cm 2.
Agricultural Biotechnology2018
Comparison of fruit quality
As shown in Table 4， Chuanqi 2 had the highest central soluble solids， reaching up to 13.40， which was significantly higher than that of other varieties， followed by Jingying， which had the central soluble solids content of 12.40. The central soluble solids content of Chaoyuemengxiang reached over 12%， indicating it was a small watermelon variety with high sugar content， and the central soluble solids content of Hongyunlai， Jinxiu and Chuanqi 1 was 11.40%， 11.50 and 11.80%， respectively. Hongyunlai had the smallest difference in the soluble solids between the center and side， which was 1.8%， and the largest difference was found in Chuanqi 2， which was 3.6%. Chuanqi 2 and Chaoyuemengxiang had good flesh and flavor. The rind thicknesses of the 6 varieties were between 0.55 and 0.75 cm. Chuanqi 1 had the thinnest rind of 0.55 cm， while Jingying had the thickest rind of 0.75 cm， and both showed significant differences in the rind thickness from other varieties. Discussion and Conclusion
The conventional facility watermelon planting in Beijing is mainly based on soil cultivation， which has the problems of low utilization rate of land resources， low water and fertilizer utilization rate， high labor intensity， serious soilborne diseases like fausarium wilt and rootknot nematodes. Soilless cultivation is an effective method to solve the problem of continuous cropping of facility watermelon. The comparative tests on the small watermelon varieties with red flesh under soilless cultivation show that Chuanqi 2 is a midearly maturing variety which has cracking resistance and fine flesh， and it also has stable performances in field traits， yield traits， quality traits and commercial traits. Moreover， Chuanqi 2 is the most juicy variety with sweet and refreshing taste， making it suitable for planting under soilless cultivation.
References
[1] ZENG JB， ZHU L， LI L， et al. Summary of the current status of watermelon and melon cultivation techniques in Beijing[J]. China Cucurbits and Vegetables， 2014， 27（5）： 68-70.
[2] LI T， ZENG JB， CHEN YL， et al. Cultivation techniques of small fruit watermelon in the autumn greenhouse in Beijing[J]. China Cucurbits and Vegetables， 2013， 26（6）： 52-53.
[3] MA C， ZENGG JB， ZENG X， et al. Close hanging planting and early harvesting cultivation techniques of small greenhouse watermelon in spring in Beijing[J]. China Vegetables， 2014（1）： 83-85.
[4] MA C， ZENG JB， MU SQ， et al. The study on the different cultivation density of small fruit watermelon under the conditions of "two vines and one line" in spring greenhouse[J]. Chinese Horticulture Abstract， 2014（7）： 19-20.