CROP DEMAND TRIALS
4 Guidelines for Selected Crops
4.2 Fruit vegetables
4.2.6 Watermelon
By Pedro Gomez
Botanical name: Citrullus lannatus Common names: Watermelon
General crop requirements
Watermelon is a herbaceous, annual plant with a prostrate growth habit. It is cultivated as an annual crop under climatic conditions warmer than 20°C. Nowadays, most varieties are triploids producing seedless fruit, without pollen, and need to be grown together with diploid varieties with fertile pollen. In the Mediterranean region, greenhouse plants are grown in soil with sand as a mulch. The fruit has a smooth hard rind, usually green with dark green stripes or yellow spots, and a juicy, sweet interior fl esh, often deep red to pink.
Experimental design
Recommended replicates: at least three. For trial purposes it is best to erect barriers to stop the foliage form adjacent plots becoming mixed. If conditions in the greenhouse are homogenous it is possible to use only 2 replicates but with more plants per replicate. This minimizes the expense on plot separation (see Figure 4.12). Where triploid varieties are grown a diploid pollinator is needed in the row is one after every three plants.
Figure 4.12 Watermelon trial - showing the separation system between cultivars.
Table. 4.24
Typical watermelon plant spacing and number of plants needed for trials.
North & Central Unheated
Mediterranean Unheated (frost-free)
Minimum number of plants/ core plot 5 5 - 20*
Minimum size core plot (m²) 5 5*
Plant density / m² 1 1
Row distance (cm) 200 200
Distance within the row (cm) 50 50
*The plants require plenty of space to grow. Depending on the heterogeneity of the group to be tested, the core size can be increased in order to avoid differences of variation.
Table 4.25
Typical watermelon sowing and harvesting dates.
Region
- Production type*
Sowing at Planting at Start of Harvest
End of harvest Remarks
North & Central
- Unheated April May July September
Mediterranean
- Short cycle Spring Dec Jan Apr May Grafted crops
Mediterranean
- Short cycle Autumn Feb Feb May Jun Grafted crops
*Watermelons are not usually grown using heated production (seasonal) or in Mediterranean long cycle production.
Table 4.26
Temperatures required for the production of watermelon seedlings and
Region Germination temperature °C Day / Night Days until germination Temperature for seedlings in °C Day / Night
Pot size Weeks until planting
North & Central 20 - 25 / 20 5 - 10 18 - 25 / 16 - 20 10 cm 2 - 4 Mediterranean 17 - 30 / 15 7 - 15 17- 30 / 10
Ventilation from 20 - 25
10 cm 3 - 4
Table 4.27
Optimal temperatures for watermelon growth and fruit production in the Mediterranean.
Day (°C) Night (°C) Ventilation from (°C)
Planting in February / harvest end April 18 - 27 10 - 14 20 - 25
Table.4.28
Watermelon plant nutrient requirements.
Yield expectation (kg/m2)
N (g/m²) P(g/m²) K(g/m²) Mg (g/m²)
5 12 3 15 3
10 17 6 23 5
Source: adapted from various sources, see Appendix B. Leaf nutrient contents are given in Appendix C.
Crop management
Pruning is advisable in order to control the architecture of the plant. The main shoot is cut before growth exceeds 5 - 6 leaves, to encourage 4 - 5 secondary shoots.
Pollination by Apis mellifera, is recommended, introducing 2 - 4 beehives / ha. Triploid watermelons need diploid watermelons with viable pollen as pollinators. It is important to establish a ratio of 25-30% pollinator diploid cultivars amongst triploid cultivars.
Disease and pest infestation, physiological disorders and other abiotic damage
Diseases:
• Powdery mildew - Sphaerotheca fuliginea. • Gummy Stem Blight - Didymella bryoniae. • Fusarium - Fusarium oxysporum.
• MNSV (Melon Necrotic Spot Virus). • ZYMV (Zucchini Yellow Mosaic Virus). • WMV-2 (Watermelon Mosaic Virus-2). • CMV (Cucumber Mosaic Virus).
• CVYV (Cucumber vein yellowing virus).
Pests:
• Red mite - Tetranychus spp.
• Whitefly - Trialeurodes vaporariorum, Bemisia tabaci. • Aphids - Aphis gossypii , Myzus persicae.
• Thrips - Frankliniella occidentalis.
• Leaf miner - Liriomyza trifolii, Liriomyza strigata, Lyriomyza bryoniae. • Green worm - Spodoptera exigua.
• Nematodes - Meloidogyne spp. (roots nodules), M. javanica, M. arenaria, M. incognita.
Physiological disorders
• Fruit breakage (caused by excess relative humidity and temperature changes, conductivity changes, poor ventilation etc.).
• Fruits abort (caused by excessive vigour or plant auto-regulation).
• Root anoxia, resulting in adventitious roots and wilting with high soil water content (caused by a lack of oxygen in the soil).
Assessments made during growth
These include: Missing plants, number of pollinator plants, uniformity of crop, number of stems and vigour, regeneration capacity, number of fruits per stem, leaf size, root resistance: (Fusarium and nematodes), physiological damage caused by salininty. Many of these can best be assessed on a 1 to 9 scale when measurements are not possible (1 = very low, 3 = low, 5 = medium, 7 = high, 9 = very large / high). Assessments made at harvest
Watermelons are non-climacteric fruit, harvested in maturity, when fruits have developed at least 12o Brix sugar
content. After harvest, plants can be left to regenerate a second crop. Fruits should be sorted into marketable and unmarketable categories according to recognised quality standards. Unmarketable fruits should be categorised according to the reasons for rejection. The acceptable size depends on the cultivar.
Quality parameters include: • Total soluble solids (oBrix).
• Fruit size (diameter).
• Width of stripes (very narrow to very broad).
• Skin ground colour (yellow to very dark green) - based on UPOV watermelon DUS guidelines. • Colour of flesh (white to dark red) - based on UPOV watermelon DUS guidelines.
• Seediness.
• Flesh texture and firmness. • Symmetry.
Overall value
This takes into account all the criteria for the cultivation and marketing of a variety, based on expert opinion as evaluated by researchers using information from farmers, wholesalers and consumers (1 = very low, 3 = low, 5 = medium, 7 = high , 9 = very high).
References and further information
UPOV Guidelines for the conduct of tests for distinctness, uniformity and stability. Watermelon (TP/142/2). www.upov.int
Reche J. 1997
4.2.7
Melons
By Pedro Gomez
Botanical name: Cucumis melo
Common names: muskmelon, honeydew melon, cantaloupe melon.
General crop requirements
Melon plants are herbaceous, annual plants, with a prostrate habit. The crop is grown under warm climatic conditions with optimal temperatures higher than 20°C. Nowadays, most varieties are hybrids, harvested when they reach maturity, and usually very sweet. In Mediterranean greenhouses plants are grown in soil with sand as a mulch. In experimental crops of melon, where varieties are being evaluated, the most productive method of growing is to stake plants. Fruit shape depends of cultivar, from long to round and skin colour can vary from green, yellow or white. Fruit skin is strong, and flesh acquires variable colour from white to orange.
Experimental design
Recommended replicates: at least three.
Table 4.29
Typical melon plant spacing and number of plants required for trials.
North & Central Heated
Mediterranean Unheated (frost-free)
Minimum number of plants / core plot 7 6*
Minimum size core plot (m²) 5 3*
Plant density / m² 1.3 2
Stem density / m² 1.3 - 2.6 4
Row distance (cm) 150 150 - 200
Distance within the row (cm) 50 50 - 100
*The plants require plenty of space to grow. Depending on the heterogeneity of the group to be tested, the core plot size can be increased in order to avoid too much variation.
Table 4.30
Typical melon sowing and harvesting dates.
Region
- Production type
Sowing at Planting at Start of harvest
End of harvest
Remarks
North & Central*
- Unheated April May July September Vertical string trained (recommended) or along the soil. Mediterranean
- Long cycle November December April May - Short cycle
Spring December January May June
Table 4.31
Conditions required for the production of melon seedlings and plants.
Region Germination temperature °C Day / Night Days until germination Temperature for seedlings in °C Day / Night
Weeks until planting
North & Central 20 - 25 / 20 5 - 10 18 - 25 / 16 - 20
Mediterranean 20 - 25 / 12 5 - 10 25 - 30 / 15 1.5 - 2
Table 4.32
Melon plant nutrient requirements.
Yield expectation (kg/m2)
N (g/m²) P(g/m²) K(g/m²) Mg (g/m²)
4 18 2 19 2
7 21 4 29 4
Source: adapted from various sources, see Appendix B. Leaf nutrient contents are given in Appendix C.
Crop management
Staking the plants increases productivity and improves fruit quality. Pruning is recommended to leave two stems per plant. For cultivars with prostrate growth, it is advisable to cut the primary stem to encourage several secondary stems to develop which will carry the fruit. One stem will produce 2- 4 fruits depending of the fruit size of the cultivar.
The most effective way of pollination is by Apis melliphera (2 hives/ha) and Bombus terrestris (2-4 hives/ha). If only a smaller area of melons are being grown the number of hives will need to be maintained.
Disease and pest problems, physiological disorders and other abiotic damage Diseases:
• Powdery mildew - Sphaerotheca fuliginea. • Gummy Stem Blight - Didymella bryoniae. • Botrytis - Botrytis cinerea.
• ZYMV (Zucchini Yellow Mosaic Virus). • WMV-2 (Watermelon Mosaic Virus-2). • CMV (Cucumber Mosaic Virus).
• CVYV (Cucumber vein yellowing virus). • ToLCNDV (Tomato Leaf Curl New Delhi Virus). • CYSDV (Cucumber Yellow Stunt Disorder Virus).
Pests:
• Thrips - Frankliniella occidentalis.
• Whitefly - Trialeurodes vaporariorum, Bemisia tabaci. • Aphids - Aphis gossypii , Myzus persicae.
• Red mite - Tetranychus spp.
• Leaf miner - Liriomyza trifolii, Liriomyza strigata, Lyriomyza bryoniae. • Green worm - Spodoptera exigua.
Physiological disorders
Sudden wilt (associated to some cultivars at certain growth stages during some climatic conditions). Excessive vegetative growth resulting in a reduction of flowering.
Fruits abort (due to insufficient pollination or plant auto-regulation).
Assessment during growth
These include: Missing plants, uniformity of crop, vigour, number of faults, number of female flowers per plant, number of fruits per stem, leaf size, virus resistance and salinity responses. When counting is not possible these can be scored on a scale (1 = very low, 3 = low, 5 = medium, 7 = high, 9 = very large / high).
Assessments at harvest
It is very important to determine the correct moment for harvest. Fruit must reach the appropriate °Brix level according to the type of cultivar. There are several characteristics that alter during ripening (e.g. skin colour, aroma). Cracks at the stem base as well as a sweet smell from the fruit indicate ripeness. Fruits are usually picked on a weekly basis. The crop should be harvested into marketable and unmarketable according to recognised standards and the reasons for rejection recorded (broken fruit, twisted fruit, incorrect size etc.). Scores (on a 1-9 scale) or measurements can be made of fruit parameters including:
• Colour and skin characteristics. • Flesh texture and firmness. • Colour of flesh.
• Diameter. • Shape.
Overall value score
This is particularly appropriate for variety trials. It takes into account all the criteria for cultivation and marketing, based on expert opinion as evaluated by researchers using information from farmers, wholesalers and consumers (1 = very low , 3 = low, 5 = medium, 7 = high , 9 = very high).
References and further information
UPOV Guidelines for the conduct of tests for distinctness, uniformity and stability. Melons (TP/104/2). www.upov.int
Reche J. 1997
Cultivo de melón en Invernadero (Spanish). Ed Consejeria de Agricultura y Pesca Maynard, D. N. and G. J. Hochmuth. 2007.