1. Stress Management

2. Outline l What is stress and how does it affect potato plants? l How does stress impact external tuber quality? l How does stress impact internal tuber quality? l How can you avoid or manage stress?

3. What is Stress? l Any condition (moisture availability, temperature, fertility, etc.) that is above or below the optimum for plant growth and tuber production l The “ideal” temperature for growing potatoes is 77 o F in the day and 54 o F at night. “ Therefore, potatoes grown in all regions experience temperature stress every year”

4. What is Stress? l The impacts of stress tend to be cumulative - 10 days of heat stress is more damaging than 5 days - Two stresses together (ex. heat and water stress) tend to cause more damage than a single stress

5. Moisture Stress and High Soil Temperatures Combine to Cause Damage Source: Kleinkopf, 1988 Hot Soil No Stress Heat cables increase soil temperature by 6 to 9 F

6. Environment (uncontrollable) Heat/cold/frost Drought/excess rainfall Hail/lightening Air pollution Sources of Stress

7. Management (controllable) Soil moisture deficits or excesses Nutrient deficits or excesses Poor stand establishment Compaction/root pruning Physical damage to tubers Sources of Stress

8. Water Stress l Low moisture availability l High demand (heat, wind, excess N) l Low capacity (poor root system)

9. Heat and Water Stress Occur Together l As temperatures increase, so does water use by the plant

10. Effect of ET rate on level of soil moisture that can be used before development of stress Low High Data for a sandy soil in Egypt

11. Stress–related problems External Tuber size Malformation Second growth Chain tubers Growth cracks Greening Enlarged lenticels Heat sprouts Internal Hollow heart / Brown center Internal brown spot (IBS) Sugar ends Vascular discoloration Black heart *Blackspot /shatter bruise Low starch High sugars *Frost *Chilling injury Pressure bruise *Immediate

12. From Hiller, WCS 19:169

13. Stress-related problems Requirements for Expression Susceptible variety + Stress conditions Weather or environment Management mistakes

14. Russet Burbank Common DefectsTriggers MalformationsHeat, drought Growth cracksMoisture stress, erratic growth Sugar endsHeat Hollow heartCold soil, low tuber set Stem end?? Low solidsHeat, early death Net necrosisPLRV

15. Outline l What is stress and how does it affect potato plants? l How does stress impact external tuber quality? l How does stress impact internal tuber quality? l How can you avoid or manage stress?

16. l During stress low availability of sugars and the imbalance in top/tuber growth can temporarily stop tuber growth. When growth resumes, it occurs at the site of most active cell growth. The end result is malformed tubers that may have knobs Around the eyes and bud end is where growth resumes

17. 1. How does stress affect sugar development - Energy production and use l The temperature optimum for Photosynthesis (energy production) is around 65 o to 75 o F, Respiration (energy use) continues to increase with temperature Source: Winkler, 1961

18. Plants Continue to Produce Sugars on Hot Days l There is a period during the morning where photosynthesis reaches the optimum, even on very hot days Temperature (F) 6182 93 86 “Mid-day depression” Source: Dwelle, 1983

19. Dry matter partitioning – two temps APJ 69:653 Harvest Index =.5 to.7 Harvest Index =.2 to.7

21. Outline l What is stress and how does it affect potato plants? l How does stress impact external tuber quality? l How does stress impact internal tuber quality? l How can you avoid or manage stress?

22. l During stress there is less sugar available, and the tuber has a harder time converting sugar into starch. The tuber becomes a weaker sink, and the end result is lower specific gravity and more sugar ends Stems StarchSugar

23. Carbohydrate metabolism in potato tubers During normal tuber growth, metabolism is driven towards the production of starch. Stress (in-season or in-storage) changes enzyme activity and membrane function

24. Effect of temperature on specific gravity of potatoes Air Temperature ( o F) Cool (77/54)Hot (100/82)

25. Comparison of soil temperatures at Oakes, ND High sugar ends

26. Kincaid et al., 1993 “Soil temperature was directly related to percentage of sugar end tubers” R 2 = 0.42 Irrigation Frequency

27. WE 75.7% 36.6%50.4% 63.4% 0” 8” 4” Percentage of 10 Tuber Sample with Sugar Ends Impact of row orientation on Russet Burbank quality

28. Row Width Can Influence Sugar Ends Source: Shock, 1988

29. End of stress Harvest Storage at 48 F The damage that occurs to the starch production system early in the season is permanent – The symptoms usually develop when the tubers are exposed to cold Source: Sowokinos

30. Effect of a single water stress event on the incidence of disorders in Russet Burbank Source: Shock, OSU

31. Pattern of hormone changes during tuber growth and storage Stress event High or erratic N availability

32. Outline l What is stress and how does it affect potato plants? l How does stress impact external tuber quality? l How does stress impact internal tuber quality? l How can you avoid or manage stress?

33. Principles of Stress Avoidance and Management Maintain uniform and optimal conditions throughout the plant growth and tuber bulking growth phases Minimize environmental stress Avoid added management stress Plant resistant varieties

34. Don’t Contribute to Environmental Stress with Management Stress! l Poor root development –Compaction and late cultivation l Poor vine development –Erratic stands and early stress l Excess vine development - Too much N l Disease

35. Plant root systems 21 days after emergence extracted from: compacted soil (left) uncompacted soil (right)

37. 1 ft Source: Modified from Weaver (1926) 2 ft 3 ft By row closure a healthy potato root system extends more than 3 feet down and across the entire furrow Compact layer Root Pruning

38. How does a stand like this impact row closure and soil temperature?

39. Excess Nitrogen Fertility Can Lead to an Imbalance in Vine and Root Growth Vines with too much N Roots with too much N

40. Stress (water, heat, nutrients, pests) can lead to premature plant death

41. Impact of Resistance on Stress Management Intensity of Management Required Resistance LevelInput Level HighLowModerate LowHigh

42. Sugar End Susceptibility by Variety Parma, ID - 1994

44. Varieties With Stress Resistance Heat and Drought Stress Ranger Russet Gem Russet Russet NorkotahClearwater Russet Umatilla Russet

45. Water Use Efficiency (WUE) 15 cwt/ in of water 18 cwt/ in of water

46. Varieties With Stress Resistance Defoliation Stress Ranger Russet Alturas Gem RussetBannock Russet Summit Russet Russet Norkotah (affects yield)

47. Varieties With Stress Resistance Stresses Conducive to Hollow Heart Ranger RussetAlturas ShepodyUmatilla Russet

48. Ask questions – gain some wisdom!