Effect of plant density and growing containers on minituber production

Yilma, Solomon and Alvin R. Mosley

Abstract

Tissue culture derived certified greenhouse grown pre-nuclear minitubers & transplants have become standard method in the limited generation seed potato program. The production of prenuclear minitubers and transplants are costy. There is a need to increase the quality & yield of minitubers to minimize the cost of production.

 A study was conducted in the summer of 1998 to determine the effect of plant population and growing containers on minituber production of Umatilla Russet & A8495-1. In this study 5-gallon pots, and solid cell liners with 18 & 24 cells were used at plant density of 180, 360, 468, and 640 per bench (48 square feet). A randomized compelete block design with 5 replications were used for layout & analysis. The minitubers were sized in to 5 catgories such as pea size 2-4g, small 4-8g, medium 8-16g, large 16-32g & jumbo 32g. Both Umatilla & A8495-1 produced the highest total yield at 468 and 624 plants per bench in 18 & 24 cell liners, respectively as compared with lower plant density in pots. However the 5-gallon pots at 360 & 180 plants per bench produced significantly higher jumbo sized tubers as compared with higher plant population in the solid cell liners. Large sized minitubers have to be cut into pieces before planting which endanger the spread of diseases. To avoid or minimize seed cuttings at prenuclear stage there is a need to mazimize yield of less than 32 grams sized minitubers and to provide reduced price of minitubers. In Oregon seed growers prefer minituber size from 4 to 32 grams. Based on this trial the solid cell liners with 18 cells provide optimum size distribution with high yield. However this study will be repeated to warrant reasonable recommendations. Alternative methods of minituber production such as aeroponic is under investigation.

Introduction

In a limited generation program tissue culture derived disease tested plantlets are cut in greenhouse to produce certified pre-nuclear transplants & minitubers. In Oregon the Foundation Potato Seed Program provides prenuclear transplants & minitubers to Oregon certified seed growers. Minituber production is resource & labor intensive operation as the result the cost of minitubers are expensive. Potato seed growers are forced to cut even smaller minitubers for further multiplication. Cutting seeds at prenuclear stage is a high risk operation for spreading diseases. Hence there is a need to optimize quality & productivity of minitubers at relativily lower cost. Greenhouse minituber production is affected by variety, plant density, growing media, light, fertilization, irrigation, and other management practices. The purpose of this study is to asses the effect of plant density & growing containers on minituber production.

Materials & Methods

Potato clones Umatilla Russet and A8495-1 (Russet selection) were used for the experiment. The plants were grown in 5-gallon pots , solid 24, and 18 cell liners at plant density 624 , 468, 360, and 180 plants per bench (48 ft2). There are 34 benches in the greenhouse (100’ x 30’) with total production area of 1,632 square feet. Nodal cuttings were made on June 24, 1998 and transplanting were made on July 7, 1998. Harvsting was done on November 5, 1998. A randomized complete block design with five replications were used for the experiment. Standard greenhouse media ( growers best), fertiliztion, irrigation & pesticides were used in the experiment. The minitubers were size graded into pea size 2-4g, small 4-8g, medium 8-16g, large 16-32g and jumbo > 32g. The number of tubers & their weight were recorded for analyais. Analysis were made by using SAS program.

Results & conclusion

The highest total yield for Umatilla & A8495-1 was achieved with 468 plants per bench in 18 cell liners . The average weight of minitubers increases with lower plant density while the number of minitubers increases with an increase in plant density. Significantly higher yield (P=0.05) was obtained in medium (8-16 g) and large (16-32 g) size class of minitubers by using solid 24 & 18 cell liners with 624 and 468 plants per bench, respectively. Total yield of jumbo size class > 32g of minitubers increased with lower plant desity. Using 5 gallon pots at 6, 8, 12 plants produced highest number jumbo size class of minitubers as compared with the other treatments. The target of our project is to minimize jumbo size class of minitubers & optimize small, medium & large (4-32 g) minituber size classes so that seed growers will avoid or minimize cuttings of minitubers. Based on our findings solid 18 cell liners produce higher total yield with prefered minituber size classes as compared with the other treatments. Furthermore by using 18 cell liners we will reduce the total number of cuttings to15,912 as compared to using 24 cell liners which requires 21,216 transplants per greenhouse. Preliminary experiment on the use of aeropnic system is under investigation. Experiments to optimize minituber production will continue by including other factors which affects minituber production.

Table 1: The effect of plant density on mintuber production (Umatilla). 

Table 2: The effect of plant density on mintuber production (A8495-1).

Fig 1: Plant density versus number of minitubers per bench (Umatilla).

Fig 2: The effect of plant density on total yield of minitubers per bench (Umatilla).

Fig 3: Average tuber weight of minitubers as affected by plant density (Umatilla).

Fig 4: The effect of plant density on total yield of minitubers per bench (A8495-1).

Fig 5: Plant density effect on the wieght of mintubers size class per bench (A8495-1).

Fig 6: The effect of plant density on the weight of minitubers size class (Umatilla).