Wounding During Harvest
Other pages about wound healing:
- The Process of Wound Healing
- Healing Factors
- Cutting Seed Tubers
- Handling Seed Pieces
- Wounding at Harvest
- Healing in Storage
There are a number of factors that affect susceptibility to bruising during harvest. The physical condition of the soil such as type is important, but the key controllable factor is soil moisture. For minimum risk of bruising, soil moisture at harvest should be between 60 and 80% of field capacity (FC). Possibly the most critical factors in the tendency to bruise and type of bruising are tuber hydration and maturity. Hydrated tubers (turgid) are firm and less susceptible to black spot but more susceptible to shatter and cracking while dehydrated tubers (flaccid) susceptibilities are the reverse. Tuber temperature as well as soil moisture affects tuber dehydration, so it is best to harvest when tubers are between 45 and 65o F with 50 to 60o F being optimal. The temperature as discussed in earlier issues is the key factor affecting wound healing as well. Immature tubers easily show skinning. And, different potato cultivars show differing propensities to bruising and the type of bruising that occurs.
Another and obvious major factor for bruising is the harvesting and piling operations themselves, such as chain speeds and heights. For the discussion on these influences, I recommend the videos listed in the references section and "Bruise-Free Potatoes: Our Goal" edited by Kleinschmidt and Thornton, 1991.
For a brief review, note that a break in the skin allows tubers to loose water or dehydrate, and entry of pathogens into the tuber causing storage rots. The wound healing process involves the formation and cross-linking of lignin and pectin between the cells below the damage and slow water loss. This is followed by suberization in cell walls thereby inhibiting bacterial rots. Finally, a new skin, the phellogen layer, is formed via cell division and this inhibits fungal rots and controls movement through the skin. This process is highly affected by temperature, and additionally affected by relative humidity and air quality.
Videos available on bruise prevention from the Univ. of Idaho, College of Agriculture:
- The Harvester, Tape # 275
- Harvester Chain Adjustment, Tape # 471
- Handling, Tape # 586
Kleinschmidt, G. and Thornton, M. (Eds.) 1991. Bruise-Free Potatoes: Our Goal. Univ Idaho Coop. Ext. Bull. # 725.
Smittle, D.A., R.E. Thornton, C.L. Peterson, and B.B. Dean. 1974. Harvesting potatoes with minimum damage. Amer Potato J 51:142-164.
Thornton, M. and Bohl, W. (Eds.) 1998. Preventing Potato Bruise Damage. Univ. Idaho Coop. Ext. Bull. 725 (revised).
Thornton, R.E., Smittle, D.A., and Petterson, C.L. 1981. Reducing Potato Damage During Harvest. Washington St. Univ. Extension Bull. # 646.