Effects Of Plant Density, Growing Season And Seed Source On Minituber Production Of Potatoes

Virus-free seed potato is an effective measure to reduce yield loss resulted from virus infection. A shorter seed potato production system is of most importance in China’s agrisystem to ensure seed quality. The minituber efficiently produced under protected conditions has been proved capable to rapid seed potato propagation. However, obvious differences in minituber production efficiency have been reported widely. To look into the factors influencing number of tubers formed and tuber size, impacts of growing methods and plant density were investigated in spring and autumn seasons. The main results are as follows.1. Tuber size distribution of minitubers follows a negative exponential curve. With4potato varieties which were grown from microtubers and tip-cuttings of the microtuber plants under protected conditions of spring and autumn seasons, the number of tubers formed and tuber weight were investigated at plant densities of200,400and600microtubers or plants/m2. The results showed that number of tubers decreased as tuber weight category increasing, which could be represented as y=N(e-λbn-1-e-λbn)(where, y is the number of tubers of weight category n, N is total number of tubers per unit area, λ stands for the reciprocal of mean tuber weight, bn and bn-1are upper and lower limit of tuber weight category n, respectively, and e is the natural constant2.71828). The distribution pattern is determined by two parameters, total number of tubers and mean tuber weight.2. Plant density is a main factor controlling number of tubers per unit area. In different growing seasons, it was observed that tuber formed per plant was decreased in each variety tested as plant density increased, the maximum difference was about0.5tubers/plant. However, the total number of tubers formed per unit area was about2folds between the highest and lowest densities, suggesting that the minitubers produced largely related to the plant density.3. Competition between tubers for photoassimilates, which is elevated as plant density increasing, is causal for mean tuber weight. The results demonstrated that, for all the experimental treatments, there was a linear relationship between plant dry weight and accumulated radiation interception of the crop, which followed a formular of y=a+bx (where, y is plant dry weight while x stands for accumulated radiation interception). The dry matter partitioning rates among the varieties tested were between75-85%with a genotype-dependent feature, but no obvious difference existed between plant densities. Consequently, similar relationship was established between tuber dry weight and accumulated radiation interception in present research. The results also showed that the relationship between leaf area index and percentage of radiation interception fitted well to the Beer’s Law. The higher plant density had a larger radiation interception in early stage of plant growth in comparison with the lower plant density. However, a smaller value of the slope, calculated for the correlation between mean tuber weight and accumulated radiation interception, was accompanied with higher plant density suggesting a less amount of photoassimilates transmitted to the tubers of higher plant density than that to the tubers of lower one.4. Microtubers are super over tip-cuttings for improving the production efficiency of the minitubers. The number of minitubers harvested, tubers per plant and mean tuber weight were higher in the crop grown from microtubers than the crop of tip-cuttings for all the varieties investigated. It is feasible, therefore, to produce minitubers mainly with microtubers and complemented with tip-cuttings for the sake of enhancing productivity and minimizing the production cost.5. The findings of present research are informative for optimal minituber production. Based on the tuber size distribution model reconfirmed and the relationships established between plant density and tuber formation, radiation interception and tuber weight, an optimal plant density for specific variety can be estimated by given a desired tuber weight to produce more sized minitubers with reasonably lower production cost.