Screening Test of Small Seedless Watermelon Varieties in Beijing Area

Shengqi MU, Xuesong YOU, Ying ZHANG, Yanli CHEN, Chao MA, Jin XU

Abstract ［Objectives］ This study was conducted to select small seedless watermelon varieties with excellent quality and high yield suitable for planting in Beijing.

［Methods］ Under the conditions of facility cultivation in Beijing， a screening test was conducted on seven small seedless watermelon varieties for growth process， field traits， yield traits， fruit quality， and disease resistance.

［Results］ Varieties Mitong， Motong and Tianbao Xiaowuzi had a short growth period and relatively stable growth， and bore fruit easily， and their female flowers were closely spaced. Their yields exceeded 60 000 kg/hm2， ranking in the top three among all varieties. The fruit had a thin skin， a bright red flesh color， and a high mass fraction of soluble solids in the center. The flesh was tight or crispy， and tasted good. They also showed good disease resistance. Overall， they showed excellent comprehensive agronomic traits， and are thus suitable for facility cultivation in Beijing and its surrounding areas.

［Conclusions］ This study provides a theoretical basis for the upgrading of varieties and the increase in production and farmers income in the suburbs of Beijing.

Key words Small seedless watermelon; Variety screening; Beijing area; High yield; high quality

Received： January 28， 2023  Accepted： March 29， 2023

Supported by Special Crop Innovation Team of Beijing （BAIC04-2022）.

Shengqi MU （1983-）， male， P. R. China， senior agronomist， devoted to research about watermelon breeding and cultivation technique promotion.

*Corresponding author. E-mail： cnrxu@126.com.

With the improvement of peoples living standards and the increasing miniaturization of families， traditional big seeded watermelons no longer meet the needs of peoples lives， and small seedless watermelons has become a new favorite in peoples eyes. Small seedless watermelons have a beautiful appearance， moderate size， convenient consumption， and high nutritional value， and are highly popular among consumers. They are widely planted throughout the country［1-10］.   At present， there are few small seedless watermelon varieties in Beijing area， and there is no main variety for production. To address this issue， Beijing Agricultural Technical Extension Station introduced new and high-quality small seedless watermelon varieties both from abroad and at home， and conducted a variety screening test. Small seedless watermelon varieties with excellent quality and high yield suitable for planting in Beijing were selected by comparing various factors such as quality， yield， and disease resistance of the tested varieties， providing assistance for variety upgrading and increase in production and farmers income in the suburbs of Beijing.

Materials and Methods

Test materials

A total of seven new watermelon varieties were tested， including ‘Mitong and ‘Motong （provided by Syngenta Investment Co.， Ltd.）， ‘Tianbao Xiaowuzi， ‘Jiamei， ‘Tianbao 3， ‘Tianbao 4 （provided by our unit）， and ‘Jinlan Wuzi （provided by Zhengzhou Fruit Research Institute）.

Test methods

Test design and planting

The test was conducted in the spring of 2020 in a greenhouse with sandy loam soil in Shunyi District， Beijing. The greenhouse had a steel frame structure， with a length of 60 m， a width of 10 m， and an area of 600 m2. The test was carried out in randomized block arrangement， and repeated three times. Each plot had an area of 31.76 m2 and set with guard rows around. The tested varieties were all sown on February 20， and nurtured through nutrient bowl grafting. The seedlings were planted at 38 days old with a plant and row spacing of 0.4 m×1.0 m. Vine-hanging cultivation was adopted. Each plot was planted with 79 plants， equivalent to 24 900 plants/hm2.   Pruning was performed to reserve two vines. Pollination began from the second female flower， and one fruit was left per plant. The base fertilizer was applied in bulk with 90 m3/hm2 of decomposed chicken manure， ternary compound fertilizer （15：15：15） 750 kg/hm2， and carbendazim 45 kg/hm2. For each crop， when the fruit was in the size of an egg and the fruit was harvested， top application was performed with water with 150 kg/hm2 of high-potassium water soluble fertilizer. Other field management and pest control measures were the same as local conventional watermelon production.

Trait investigation

During the test， the main growth process of various watermelon varieties was investigated， including fruit development period and full growth period. During the ripening period， 10 pieces of mature fruit were randomly selected from each plot and the average single fruit weight was measured; and five representative pieces of fruit were selected from each plot to measure fruit shape indexes， soluble solid contents and peel thicknesses， the average values of which were calculated， and the taste was evaluated and recorded. Various plots were harvested， separately， and the actual yields were recorded. The resistance to powdery mildew and viral diseases in each variety was visually tested in three stages during the first female flower opening stage， fruit setting stage， and fruit ripening stage （divided into five levels： strong， moderately strong， moderate， moderately weak， and weak）. The experimental data were analyzed for significance of differences by the new multiple range test method.

Data processing

The experimental data was processed and analyzed using Excel spreadsheet and DPS 3.01 software.

Results and Analysis

Comparison of main field traits

The test results are shown in Table 1. The growth periods of varieties Mitong， Motong， Tianbao Xiaowuzi， and Jiamei were relatively short， not exceeding 120 d， and their fruit development periods all did not exceed 40 d. Among them， Tianbao Xiaowuzi had the shortest growth period， which was 115 d. Varieties Tianbao 3， Tianbao 4 and Jinlan Wuzi had a longer growth period of 121-124 d， and a fruit development period of 41-43 d.

There was a slight difference in growth among different watermelon varieties. The leaf areas of the four varieties， namely Mitong， Motong， Tianbao Xiaowuzi and Jiamei， were all less than 440 cm2， and their overall growth was moderate or weak. Among them， Tianbao Xiaowuzi had the smallest leaf area， which was 378.15 cm2， and its overall growth was the weakest. Varieties Tianbao 3， Tianbao 4 and Jinlan Wuzi all had a leaf area exceeding 530 cm2 and grew vigorously.  Among them， Tianbao 4 had the largest leaf area and the most vigorous growth. Varieties such as Mitong， Motong， Tianbao Xiaowuzi and Jiamei bore fruit easily with a lower fruit setting node ranging from 11.1 to 13.7 nodes and a female flower spacing ranging from 4.5 to 5.1 nodes. Among them， Jiamei had the lowest fruit setting node at 11.1 nodes， while Mitong had the densest female flower spacing at 4.5 nodes; and varieties Tianbao 3， Tianbao 4 and Jinlan Wuzi had a higher fruit setting node ranging from 14.6 to 15.7 nodes and a female flower spacing between 5.7 and 6.2 nodes. Among them， Tianbao 3 had the highest fruit setting node at 15.7 nodes， while the female flowers were fewest with a female flower spacing at 6.2 nodes.

Yield comparison

The yield traits of various varieties are shown in Table 2. There were significant differences in single fruit weight among different varieties. Jiamei had the smallest single fruit weight of 2.3 kg， while Motong， Tianbao 4， and Jinlan Wuzi had the largest single fruit weight of 2.8 kg. There were also significant differences in fruit setting rate among different varieties. Jinlan Wuzi had the lowest fruit setting rate， only 0.79， while Tianbao Xiaowuzi had the highest fruit setting rate， reaching 0.98. Mitong， Motong and Tianbao Xiaowuzi had the highest yield， with an equivalent yield of over 60 000 kg/hm2， which was significantly different from other treatments. Among them， Motong had the highest yield， reaching 64 839.6 kg/hm2. The yields of varieties Jiamei， Tianbao 3， Tianbao 4 and Jinlan Wuzi were relatively low， all less than 60 000 kg/hm2. Among them， Jiamei had the lowest yield， only 52 115.7 kg/hm2， which was 24.41% lower than Motong.

Comparison of fruit quality

From Table 3， it can be seen that the peel hardness of varieties Mitong， Motong， and Tianbao 3 was relatively high， all exceeding 50 kg/cm2; the peel hardness of varieties Jiamei and Jinlan Wuzi was moderate， at 42.8 and 44.6 kg/cm2， respectively; and varieties Tianbao Xiaowuzi and Tianbao 4 had the lowest peel hardness， both below 30 kg/cm2. Varieties such as Mitong， Tianbao Xiaowuzi and Jiamei had thinner skin， with skin thickness less than 0.6 cm; and varieties Motong and Tianbao 3 had moderate skin thickness， at 0.63 to 0.62 cm， respectively. The central soluble solid mass fractions of varieties Mitong， Motong， Tianbao Xiaowuzi and Jiamei were the highest， all exceeding 12%， and Mitong among them exhibited the highest value， reaching 12.9%; and the central soluble solid mass fractions of varieties Tianbao 3， Tianbao 4 and Jinlan Wuzi were relatively low， all below 12%， and Tianbao 4 among them showed the lowest value of only 11%. The flesh of varieties Mitong and Motong was tight and crispy， and the flesh of Tianbao Xiaowuzi was loose and crisp， and that of the variety Jiamei was crispy. They all had a good taste. Variety Tianbao 3 has hard flesh， while Tianbao 4 has soft flesh， and the flesh of Jinlan Wuzi was crispy. The three had a moderate taste.

Comparison of disease resistance

Powdery mildew and viral diseases are the main diseases in the entire growth period of watermelon. According to Table 4， the tested varieties had good disease resistance during the fruit setting stage， most reaching moderately strong to strong. Varieties Mitong， Motong and Tianbao Xiaowuzi had good resistance to powdery mildew during the harvest stage， all reaching moderately strong. Other varieties had poor resistance， ranging from weak to moderately weak， and Jiamei and Tianbao 3 had the worst resistance. Varieties Mitong and Motong had the best resistance to viral diseases during the harvest stage， both at the strong level， and the resistance of Tianbao Xiaowuzi and Jinlan Wuzi was acceptable， both at the moderately strong level. Varieties Jiamei， Tianbao 3 and Tianbao 4 had poor resistance， ranging from weak to moderately weak. Varieties Mitong， Motong， Tianbao Xiaowuzi and Jinlan Wuzi had good stress resistance， with a ratio of wilted plants below 5%; and varieties Jiamei， Tianbao 3 and Tianbao 4 had poor stress resistance， with a ratio of wilted plants exceeding 8%.

Conclusions

Varieties Mitong， Motong and Tianbao Xiaowuzi had the best overall performance. They had a short growth period and relatively stable growth， and bore fruit easily， and their female flowers were closely spaced. Their yields exceeded 60 000 kg/hm2， ranking in the top three among all varieties. The fruit had a thin skin， a bright red flesh color， and a high mass fraction of soluble solids in the center， exceeding 12%. Among them， Motong had a unique skin color， which was black. The peel of Motong and Mitong was tough， with a hardness of over 50 kg/cm2， and their flesh was tight and crispy. Tianbao Xiaowuzi had crispy skin with a skin hardness of only 27.6 kg/cm2， and loose and crisp flesh.

Shengqi MU et al. Screening Test of Small Seedless Watermelon Varieties in Beijing Area

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