Cutting of seed
In many countries seed cutting is practiced, especially if the seed size is large.
This is done to:
- economize on seed costs,
- stimulate sprout growth if seed is still dormant,
- increase stem number if seed is still in the early apical stage.
Either plant cut seed directly in moist soil and cover immediately or cut seed prior to planting and store a few days under conditions favourable for suberization (temperature about 15 C, relative humidity 85% and a sufficiently high oxygen content of the air.
Seed pieces, either freshly cut and planted or properly healed before planting, can be just as productive and healthy as whole small seed tubers.
The desired seed piece size from the stand point of productivity and planter performance is:
> 28 g and < 56 g.
Soil conditions at planting are frequently favourable for suberization or healing of the cut surface so that freshly-cut seed pieces can be planted directly after cutting. This requires that the cutting operation and the planting operations be synchronized to avoid holding unplanted cut seed pieces an extended length of time.
It is safe to cut seed tubers some time ahead of planting if storage conditions promote healing of the cut surfaces.
Wound healing is best accomplished by:
1) holding the cut seed pieces 3 to 5 days at temperatures of 13-18 C,
2) maintaining a relative humidity of at least 85 percent, and
3) providing good ventilation.
Failure to provide any of these conditions can lead to seed piece decay.
Seed cutting (drawing)-----Seed cutting
Risks
The percentage emergence may be lower if cut seed is used (due to seed piece decay). In general the percentage of emergence is inversely proportional to the size of the cut tuber pieces.
Another disadvantage of cutting may be the transmission of certain diseases by means of the knife: PVX, PVS, ring rot (Corynebacterium sepedonicum), brown rot
(Pseudomonas solanaecearum), blackleg (Erwinia carotovora var. atroseptica).
The following measures are relevant to reduce risks:
- do not cut seed when there is a risk transmitting of dangerous diseases (contaminated lots).
- periodically disinfect cutting tools in a 1% solution of calcium hypochlorite.
- do not cut physiologically old seed.
- do not use cut seed when soil temperature is high (e.g. 25 C).
- do not cut seed of varieties susceptible to Fusarium and which are slow in wound healing.
- cut seed pieces should not be exposed to hot sun or wind for even a short time or they will severely shrivel and may decay (keep cut seed in the shade).