Verbeterde metodes vir miniknol produksie by aartappels (Solanum tuberosum L.)

[摘要] ENGLISH ABSTRACT:Potatoes is the fourth most important food source in the world. To provide in the everincreasing demand by the growing world population for this staple food, alternativeways will have to be found to produce a cheaper and a healthier end product. Thetubers mainly consist of carbohydrates and starch, although 9% of the dry weight ofthe tubers consist of proteins. In its natural state the potato tuber is low in sodium andhigh in potassium and vitamin C. These proteins can provide in all the amino-acidrequirements of humans and make it an outstanding balanced diet.The most important factor by which the production and quality of potatoes can beincreased, is to provide better propagation material to producers. Minituberproduction is a relatively new method of producing better quality propagation materialfor producers. It is, however, very expensive because of the high capital investmentneeded. By producing more tubers per plant, or more tubers per square meter, the unitprice per tuber may be lowered. The system commonly used for minituber productionis where in vitro plants are planted in a greenhouse, usually in a vermiculite/peatmixture as medium. As in a hydroponic system, nutrients are added to the irrigationwater.As possible strategy to increase the production of mini-tubers, the effect of nutritionwas investigated. No significant differences were found in tuber production withsmall deviations in phosphorous and calcium nutrition. Researchers who reportedsignificant differences in tuber production with nutrition, either corrected extremeshortages or induced it.By subjecting the root and tuber medium of potato plants to a pH-shock (nutrientsolution with a pH of 3.5 for 10 hours), large amounts of tubers were initiated. A newproduction technique was developed where plants were grown in a hydroponic waywithout any root medium. In this way the right sized tubers could be removed withoutdamaging the plant. Potato plants do not initiate tubers easily where stolons are notsubjected to mechanical resistance. This problem was solved with the help of a pHshock,where significantly more tubers were formed per plant.The action of the pH-shock could be explained by a temporary inaccessibility ofnutrients to the plant. Both calcium and magnesium absorpsion are hampered at a lowpH, but calcium is also poorly translocated in the plant. Considering that a nutrientsolution without calcium produced the same results as the pH-shock treatment in thisstudy, one may make the assumption that an induced calcium shortage may beresponsible for the low pH effect. The same effect may even be induced by giving theplants clean water for some time. Such a treatment was, however, not tested butshould receive attention in further studies.The correct timing for a low pH-shock may need more research. A precise number ofdays after transplanting can not be prescribed since many factors such as lightintensity, daylength and cultivar difference affect plant growth and tuber initiation.Environmental conditions, the physiological age and the biomass of the plant mayaffect the timing of the shock. A low pH-shock could not at any stage induce tubers inpotato plants where unfavorable environmental conditions occurred. It seems as if theplants need to be ready for tuber initiation before the pH-shock can be successfullyapplied. By removing/harvesting the tubers at the required weight, the burden on theplant may be relieved enabling more tubers to form.It was experienced that the reproductive system of the potato plant is complex with anumber of factors affecting it. The new production system has potential, but moredevelopmental work is still needed.

[发布机构] Stellenbosch University