1. Evaluation of Drought Tolerance of Potato Cultivars Under Greenhouse Conditions Sultan F. Alsharari and Abdullah A. Alsadon Department of Plant Production College of Food and Agricultural Sciences King Saud University P.O. Box 2460 Riyadh 11451 Saudi Arabia

2. Introduction Potato is characterized as a drought sensitive crop. Drought conditions resulted in reduced vegetative growth, leaf area and plant height. Many studies have illustrated the effect of drought treatments on low tuber yield in potatoes. Tuber quality can also be affected.

3. Fresh Tuber yield was significantly correlated to root dry mass which was reduced by drought. Proline content in the leaves is a key factor in determining drought tolerant or sensitive cultivars. Water stress in the field or greenhouse has resulted in an increase in proline content in potato tubers. From the previous studies, it is clear that drought has a major role in decreasing potato productivity and quality. Introduction

4. Objective The objective of this study was to evaluate growth and productivity of some potato cultivars in response to drought treatments under greenhouse conditions.

5. Materials and Methods Seed potatoes of seven cultivars were obtained from local agricultural companies which commonly grow them for fresh or processing purposes. These cultivars represent a selection of maturity groups and tuber characteristics (Table 1).

6. Table 1: Maturity type and tuber traits of seven potato cultivars selected in this project Long-oval, very shallow eyes, yellow smooth skin, pale yellow flesh. Early to medium- early Safrane Long-oval, shallow to rather shallow eyes, red skin, fairly yellow flesh Moderately early to moderately late Asterix Long oval, not very deep eyes, yellow skin, yellow fleshMedium-early to medium Victoria Round, shallow eyes, flaky red skin, cream to light yellow flesh Medium-lateRosetta Round to oval, moderately deep eyes, yellow medium rough skin, fairly yellow flesh Moderately early to moderately late Hermes Short oval, regular, slightly inserted eyes, yellow skin, pale yellow flesh MediumSandy Oval with long oval, regular, very shallow eyes, yellow skin, yellow flesh Medium-lateMondial Tuber TraitsMaturity typeCultivars 1- Canadian Food Inspection Agency, Plant Products Directorate, Plant Health Division, Potato Section (www.inspection.gc.ca/english/plaveg/potpom/var) 2- Nivaa Holland (www.aardappelpagina.nl/index.html)www.aardappelpagina.nl/index.html 3- Le Plant De Pomme De Terre (The French varieties) (www.plantdepommedeterre.org/eng/var.asp)www.plantdepommedeterre.org/eng/var.asp Sources:

7. Plate 1. Tuber traits of eight potato cultivars selected in this project. Hermes Mondial Sandy VictoriaRosetta SafraneAsterix

8. Materials and Methods Clonal propagation started from excised shoot apices of growing sprouts. Several multiplication cycles were carried out using single node explants. Subculture was repeated until the required number of plantlets for each cultivar was achieved to conduct the experiment. At least 200 plantlets (12-15 cm long, each with 4-5 leaves and good root system) per cultivar were transferred to the greenhouse of the Agricultural Research and Experiment Station at Dirab, near Riyadh, Saudi Arabia.

9. Plate 2. Potato sprout which is used as starting material for clonal propagation.

10. Plate 3. Potato plantlet inside a test tube.

11. Plate 4. Potato plantlet is being cut into different stem cuttings with single node.

12. Plate 5. Potato plantlet is being cut into different stem cuttings with single node.

13. Materials and Methods Plantlets of 6-8cm in length and with 4-6 leaflets were transplanted into 25 cm pots. Pots were filled with 1 : 2 peat moss : sand Acclimatization was carried out by applying mist system under plastic cover at about 10 minutes interval for 1 minute and gradually increasing time intervals until the end of second week when cover was removed. Temperature and relative humidity were set at 24 + 2 C and 70 + 5%, respectively.

14. Materials and Methods Following two weeks of acclimatization, a class A evapotranspiration pan was placed in a central location between plants. Irrigation treatments were 20, 40, 60, 80 and 100% of water depletion by evaporation (WDE). Irrigation water was added near the plant base every other day. For every cultivar, eighty pots were used (representing five irrigation treatments x 4 pots x 4 replication per treatments). The experiment was designed as split plot with four replicates each. The cultivars were assigned as main plot and irrigation treatments as sub plots.

15. Materials and Methods The first plant sample was taken at transplanting time. Destructive harvests consisting of one plant per subplot were randomly carried out 30, 60 and 90 days after treatment (DAT). Drought tolerance was evaluated based on response of vegetative growth traits (plant height, number of branches, leaf area) as well as tuber traits (number and weight). Proline content in the leaves was also evaluated. Data were analyzed using statistical SAS program. Mean separation was carried out by the least significant difference.

16. Results and Discussion Plant Height Number of Branches Leaf Area Proline content Tuber number Tuber weight

17. Table 1: Comparison of plant height between potato cultivars originated from micropropagated plantlets, grown in the greenhouse and exposed to irrigation treatments. Average plant height (cm) Cultivars Days after irrigation treatment (DAT) 9060300 158.10 a146.77 a73.46 b24.66 aMON 123.80 a126.70 c73.26 b20.66 bcSAN 135.00 c123.90 c71.26 bc19.33 cdHER 84.10 f80.45 d64.80 c23.00 abROS 151.75 b137.99 b84.06 a20.00 bcVIC 130.40 d123.05 c75.80 b16.66 dAST 82.75 f80.22 d84.00 a12.00SAF 3.6325.7936.7503.283LSD 0.05

18. Fig. 1: Effect of irrigation treatment on plant height of potato cultivars originated from micropropagated plantlets and grown in the greenhouse.

19. Table 2: Comparison of number of branches between potato cultivars originated from micropropagated plantlets, grown in the greenhouse and exposed to irrigation treatments. Average number of branches Cultivars Days after irrigation treatment (DAT) 9060300 4.65 b3.85 b2.53 b1MON 3.65 c3.00 d3.13 b1SAN 3.55 c3.40 c3.00 b1HER 5.35 a4.50 a4.26 a1ROS 2.70 d2.60 e2.46 b1VIC 3.60 c3.45 c2.93 b1AST 1.75 e1.75 f2.40 b1SAF 0.2840.2120.775N/SLSD 0.05

20. Fig. 2: Effect of irrigation treatment on number of branches/plant of potato cultivars originated from micropropagated plantlets and grown in the greenhouse.

21. Table 3: Comparison of leaf area between potato cultivars originated from micropropagated plantlets, grown in the greenhouse and exposed to irrigation treatments. Average leaf area (cm 2 ) Cultivars Days after irrigation treatment (DAT) 9060300 2072.62 b4250.80 b2213.10 ab128.18 aMON 1462.42 c2939.30 e1877.60 bc75.42 bSAN 929.20 e5383.90 a2610.00 ab127.90 aHER 0.00 f3638.20 d2669.00 a106.87 aROS 1156.36 d3142.10e1438.10 c105.00 aVIC 2470.88 a3993.40c2387.90 ab73.49 bAST 0.75 f777.30f1899.20 bc30.85 cSAF 114.11236.4473.6628.03LSD 0.05

22. Fig. 3: Effect of irrigation treatment on leaf area of potato cultivars originated from micropropagated plantlets and grown in the greenhouse.

23. Table 4: Comparison of proline content between potato cultivars originated from micropropagated plantlets, grown in the greenhouse and exposed to irrigation treatments. Average proline (mg/g) Cultivars Days after irrigation treatment (DAT) 9060300 2.81 b2.18 bc1.80 a0.52MON 0.57 fc2.42 bc1.46 ab0.49SAN 1.97 e1.48 c1.43 ab0.50HER 4.01 a3.66 a1.26 ab0.53ROS 2.69 c2.83 ab1.50 ab0.47VIC 2.28 d2.04 bc1.47 ab0.55AST 2.90 b2.24 bc1.20 b0.48SAF 0.1190.9530.549LSD 0.05

24. Fig. 4: Effect of irrigation treatment on proline content of potato cultivars originated from micropropagated plantlets and grown in the greenhouse.

25. Table 5: Comparison of tuber number between potato cultivars originated from micropropagated plantlets, grown in the greenhouse and exposed to irrigation treatments. Average tuber number Cultivars Days after irrigation treatment (DAT) 9060300 2.90 f1.40 e0.70 d0MON 12.70 b9.90 b1.05 cd0SAN 10.90 c9.45 b2.15 b0HER 13.35 a12.20 a7.05 a0ROS 4.45 e1.10 e0.50 d0VIC 2.65 f2.15 d1.25 bcd0AST 6.20 d3.40 c1.75 bc0SAF 0.6350.6440.924N/SLSD 0.05

26. Fig. 5: Effect of irrigation treatment on tuber number of potato cultivars originated from micropropagated plantlets and grown in the greenhouse.

27. Table 6: Comparison of tuber weight between potato cultivars originated from micropropagated plantlets, grown in the greenhouse and exposed to irrigation treatments. Average tuber weight (gm) Cultivars Days after irrigation treatment (DAT) 9060300 27.30 d17.43 e1.83 cd0MON 130.55 a31.25 c1.15 d0SAN 110.80 b36.14 b2.99 cd0HER 131.43 a89.03 a15.63 a0ROS 19.10 e2.90 f0.90 d0VIC 32.20 d21.92 d3.81 bc0AST 89.75 c35.42 b5.36 b0SAF 6.1693.0922.278N/SLSD 0.05

28. Fig. 6: Effect of irrigation treatment on tuber weight of potato cultivars originated from micropropagated plantlets and grown in the greenhouse.

29. Conclusion Significant differences have been reported among cultivars and between irrigation treatments in most traits. In general, as water stress increased, vegetative growth and tuber yield decreased. Proline content increased as water stress increased.

30. Conclusion Significantly higher tuber weight was measured in Rosetta plants at 60 DAT. Whereas after 90 DAT, both Rosetta and Sandy plants had higher tuber weight followed by Hermis, Safrina Asterix and Mondial plants, respectively. Accordingly three cultivars have been selected based on their tuber weight response at the 20 % WDE. These cultivars were : Rosetta (drought tolerant), sandy ( moderately drought tolerance ) and Asterix ( drought sensitive ).

31. Acknowledgment Authors wish to thank King Abdulaziz City for Science and Technology for providing financial support through Graduate Student funding program (No. GR- 10-24). Thanks are also due to Research Center of the College of Food and Agricultural Sciences.