Study on the cultivation of seedlings using buds of potato (Solanum tuberosum L.)

Source of material and cultivation

A total of four virus-free potato varieties (Fujin, Youjin, Zhongshu 4, and Feiwuruita) were used, which were collected from the Jilin Academy of Agricultural Sciences, China. These materials yield healthy seed potatoes with excellent phenotypes, such as plant height (50∼72 cm), average number of potatoes per plant (5∼7), average potato weight (115∼151 g) and commercial potato rate (71.3%∼88%). These experimental materials were grown in a greenhouse of a practical experiment farm of Jilin Agricultural University, China. Sandy loam soil was collected and mixed with farm manure. The soil-nutrient mixture was added to pots to a depth of 30 cm. The physical and chemical properties of the soil included 1.41 g kg⁻¹ total nitrogen, 0.34 g kg⁻¹ total phosphorus, 8.9 g kg⁻¹ total potassium and 40.6 g kg⁻¹ organic matter.

Experimental design and measurements

Seed potatoes were selected on the basis of significant morphological characteristics and a lack of visual abnormalities. Three independent trials were conducted in all cases.

1. Raising of seedlings and cultivation of potato buds with different lengths: The potato buds were divided into three categories based on length: three cm ± 0.5 cm, five cm ± 0.5 cm, and seven cm ± 0.5 cm. Virus-free potato seeds of the same size and with strong dormancy were treated to promote germination under dark:light conditions. When the bud length reached three cm ± 0.5 cm (seed potato treatment for 8–9 d, T₁), five cm ± 0.5 cm (seed potato treatment for 10–11 d, T₂) and seven cm ± 0.5 cm (seed potato treatment for 12–13 d, T₃) (Fig. 1B), terminal buds were selected, and bud breaking treatment was performed. The buds were detached at the basal ends and sown into 10 cm × 10 cm nutrient pots under 20∼22  °C temperature, 60% air humidity, and a 14 h/8 h light-dark cycle. Seedlings were raised in a greenhouse beginning on March 25th, and 25-day-old seedlings were then planted in the greenhouse on April 20th.

2. Raising of seedlings and cultivation of buds from various parts of potatoes: potato buds were grouped into three treatments according to their origin on the potato tuber: terminal buds (T₄), middle buds (middle part of the seed potato, T₅) and tail bud (basal bud, T₆). When the length of the potato bud reached five cm ± 0.5 cm (seed potato treatment for 10–11 d) (Fig. 1C), bud breaking treatment was conducted on the basal part of the potato bud, and the same described in (1) above were performed.

3. Seed potato seedlings were cut and cultivated in nutrient pots (CK) (Fig. 1A). The seed potatoes were removed from the storage pit and placed in an incubator with light at 20 °C and 60% air humidity. When the bud length reached 1–2 cm, the bud was cultured under indoor scattered light for 2∼3 days. The seed potato was cut into bud blocks weighing 20 g and sown into a 10 cm × 10 cm nutrient pot, with one plant per bowl. The seedlings were raised in a greenhouse beginning on March 17th and transferred at 25 days of age on March 2nd. All seedlings were grown together.

A total of three experimental trials were performed in raised beds with a 1.2 m width, 5 m length, and 10 cm height, and a protective transparent film cover was applied. For double-row cultivation, the row spacing of border plants was 25 cm × 40 cm. The experiment was repeated three times following a randomized complete block design (RCBD). The environmental conditions were maintained at 17∼22 °C and 11∼13 h of light per day, and other environmental conditions, such as watering, air humidity, and fertilization, were flexibly adjusted according to growth stage.

Sampling and measurements

Data analysis

The recorded data were statistically analyzed by using SPSS 20.0 statistical software (SPSS Inc., Chicago, IL, USA). One-way analysis of variance (ANOVA) with post hoc tests (Tukey’s test) was used to detect differences among treatments. The mean values showing significant differences were compared with the Tukey test at a 5% level (Anita, 1988).

Effects of seedling raising on the physiological indices and growth indices of potato at the seedling stage

The chlorophyll content and net photosynthetic rate of developed seedlings with different tuber bud lengths showed the highest values for T₃, followed by T₂, and T₁ showed the lowest values, but they were significantly different from those in the CK treatment, as shown in Table 1. The potato seedlings were obtained by cultivating bud seedlings from different parts of the potato in nutrient pots, and the physiological indicators of each seedling stage were analyzed (Table 2). According to the chlorophyll content and net photosynthetic rate, the treatments ranked as follows: T₄ > T₅ > T₆ > CK. The T₄ and T₅ treatments were significantly different from T₆ and CK, respectively, but no significant difference was observed between T₆ and CK. The net photosynthetic rate was not significantly different between nursery treatments T₅, T₆ and CK. The transpiration rate and stomatal conductance decreased in turn in the four treatments of the same variety, and the tested potato varieties showed consistency.

Effects of seedling raising on the growth indices and quality of potato plants at the seedling stage

There were significant differences in the plant height, stem diameter, and compound leaf number of potato at the seedling stage among the treatments with different lengths of potato buds (Table 3). Seedling cultivation with seven cm potato buds was significantly longer than that with five cm and three cm buds; however, overall, the values in the three treatments were much higher than those in the CK treatment.

The T₃ treatment increased plant height, stem diameter and leaf number in the ‘Fujin’ variety by 49.63%, 60.94% and 58.81%, respectively, compared with those in CK. It increased these parameters in ‘Youjin’ by 21.80%, 57.83% and 43.61%, respectively, compared to those in CK; those in ‘Zhongshu 4’ by 49.12%, 51.09% and 40.93%, respectively; and those in ‘Feiwuruita’ by 37.38%, 44.7% and 35.69%, respectively. In terms of the quality of potato seedlings at the seedling stage (i.e., aboveground dry weight, belowground dry weight, root activity, and seedling index), the different potato bud length treatments were ordered T₃ > T₂ > T₁ > CK. Most of the measured indicators in T3 were significantly different from those in CK (Table 4).

Furthermore, buds from different parts of the tuber were used for seedling cultivation in nutrient pots, and the results at the seedling stage are shown in Table 5. Within varieties, treatments ranked in terms of plant height, stem diameter and compound leaf number as T₄ > T₅ > T₆ > CK, with terminal buds yielding significantly higher values than observed in the CK treatment. All the tested varieties showed the same performance, with the indices of plant height, stem diameter and leaf number of ‘Fujin’ increasing by 32.10%, 43.94% and 35.29%, respectively, those of “Youjin” increasing by 11.01%, 48.44% and 22.95%, respectively, those of ‘Zhongshu 4’ increasing by 31.40%, 35.62% and 20.37%, respectively, and those of ‘Feiwurita’ increasing by 20.00%, 27.85%, and 17.24%, respectively, compared with those in the CK treatment.

The effects of bud source on potato seedling quality are shown in Table 6. The aboveground dry weight in the seedling raising treatments was higher than that in the CK treatment, and the four varieties showed consistent results. The dry weight of aboveground parts and the dry weight of belowground parts of seedlings derived from terminal buds were significantly different from those in the CK treatment. In terms of root activity and the seedling index of all tested varieties, the treatments were ordered T₄ > T₅ > T₆ > CK, with all varieties showing the same performance trend.

Effect of seedling cultivation on potato plants in the greenhouse

By comparing the plant growth of potatoes grown from potato buds of different lengths during the tuber expansion stage, it was found that the three growth indicators plant height, stem diameter, and leaf area in each treatment and within the varieties were different, showing the order T₃ > T₂ > T₁ > CK. The treatments were significantly different, and the performance trends of the four experimental varieties were consistent.

Plant height increased by a maximum of 23.90% in the T₃ treatment for the ‘Feiwurita’ variety, and the stem diameter and leaf area increased the most in the T₃ treatment for ’Feiwurita’, with increases of 37.32% and 16.84%, respectively (Table 7). The comparison of plant growth between potato buds collected from distinct positions during the expansion period of potato tubers is shown in Table 8. In the potato tuber expansion period, the three growth indicators plant height, stem diameter, and leaf area showed the following treatment order in each variety: T₄ ≥T₅ > T₆ ≥CK. The greatest plant height of 69.52 cm was observed for seedling cultivation from terminal buds of the variety ‘Youjin,’ the maximum stem diameter was 15.99 mm for ‘Zhongshu 4’, and the leaf area of ‘Zhongshu 4’ was the greatest at 6810 cm². The largest increases in stem diameter compared with that in the CK treatment were observed for the cultivation of ‘Fujin’ seedlings from terminal buds, which were 24.31%, 31.28%, and 13.55% (Table 8).

During the expansion stage of potato tubers, the dry matter distribution rate in different tissues and organs was the highest, and the order of organs from large to small was tubers, stems, leaves, roots and stolons. The distribution rate of dry matter showed the following order among the treatments with potato buds of different lengths: T₃ > T₂ > T₁ > CK. Within varieties, the distribution rates of tissues and organs (tubers, stems and leaves) in T₁ and T₂ were generally the same, with minor differences, but significantly higher than those in the T₃ and CK treatments. In the T₁ treatment, the percentage of tubers among varieties was approximately 33%, and the percentage of stems and leaves was approximately 64% (Fig. 2A). The percentage of ‘Zhongshu No. 4’ tubers was the highest (34.12%), and the proportion of stems and leaves was 63.01%. The stem and leaf accounted for the largest percentage in CK, with the highest percentage observed for ‘Youjin’: 80.87%.

In terms of the dry matter distribution rate in the tuber expansion stage, the treatments including plants from potato buds of different positions were ordered as followed: T₄ > T₅ > T₆ > CK. The four tested varieties showed the same performance. The highest material distribution rate was 34.12%, and the lowest rate was 16.30%, which was observed for direct seeding of ‘Youjin’ buds. The stem dry matter distribution rate and leaf dry matter distribution rate of each variety were the highest in CK (Fig. 2B).

In the potato tuber expansion stage, the physiological indices (chlorophyll content and photosynthetic indices) of potato sprouts from buds of different lengths in the nutrient pots were the highest in the T₃ treatment, followed by the T₂ > T₁ treatments and then CK. The maximum photosynthetic rate was 20.9 µmol CO₂ m⁻² s⁻¹ in ‘Feiwurita’ under the T₁ treatment, and the highest chlorophyll content was found in ‘Zhongshu 4’ under the T₃ treatment, which was 4.26 mg g⁻¹. The seedling chlorophyll content of the four tested potato varieties, “Fujin, Youjin, Zhongshu 4 and Feiwuruita”, increased dramatically, measuring 32.97%, 49.57%, 51.06% and 37.93%, respectively, and the photosynthetic rate increased by 23.33%, 23.81%, 22.22% and 15.47%, respectively (Table 9).

During the expansion period, potato tubers showed significant differences in the chlorophyll content, photosynthetic rate, and transpiration rate depending on bud position (Table 10). Specifically, among treatments the photosynthetic rate and transpiration rate of potato during the expansion stage showed the order T₄ > T₅ > T₆ > CK, and T₄ and T₅ were significantly different from T₆ and CK, respectively. The performance trends of all varieties were similar. ’Zhong Shu No. 4’ had the highest chlorophyll content of 3.89 mg g⁻¹, and the highest photosynthetic rate was observed in ‘Feiwurita’ at 20.1 µmol CO₂ m⁻² s⁻¹. The stomatal conductance of plants derived from buds at different positions was not obviously different during the expansion period. The chlorophyll content of ‘Zhongshu 4’ seedlings derived from terminal buds was the highest. Compared with that in CK, the photosynthetic rate of plants from these buds increased most obviously, by 37.94% and 16.67%.

Effects of seedling cultivation methods on the earliness and yield of potato

The planting dates of the treatments were the same, and the harvest time and growth days in the shed were different. Within varieties, the earliest maturity was observed in T₃, followed by T₂, T₁ and CK. Compared with the CK, the T₃ treatment advanced harvest by 13 days, and the difference in harvest time between the T₃ and T₂ treatments was small, only 1–2 days (Table 11).

The yield composition of all tested potato varieties derived from potato buds of different lengths was as follows: in terms of average weight per potato and average plot yield, the difference between T₂ and T₃ was small, but it was significantly larger than that between T₁ and CK. In terms of average yield, the treatments ranked T₃ > T₂ > T₁ > CK, the difference between T₂ and T₃ was not significant, but there was a significant difference from T₁ and CK. Each treatment increased the yield by more than 10%, and the T₃ treatment of ‘Zhongshu 4’ had the highest yield, reaching 3506.41 kg/667 m², an increase of 46.35% (Table 12).

The yield of cultivated potato sprouts derived from buds at various positions was measured for each variety, and it was found that compared with those in CK, the average weight per potato and average plot yield were different (Table 13). In all varieties, the indices was maximal under the T₄ treatment, followed by T₅ and T₆, and they were minimal in CK. The yields of ’Zhongshu 4’ and ’Youjin’ under the T₄ treatment reached 3,439.29 kg/667 m² and 3,366.53 kg/667 m², representing increases of 43.55% and 41.53%, respectively. Yield did not significantly increase in the T₆ treatment for any variety. For example, production increased by only 1.29% in ‘Zhongshu 4’.

Effects of seedling cultivation methods on potato quality

The postharvest potato quality measurements of plants from potato buds of different lengths and positions grown in nutrient pots are shown in Tables 14 and 15. The reducing sugar, starch, crude protein, and L-Vc contents did not differ between treatments in the same potato variety. However, there were significant differences in the reducing sugar and crude protein contents among the tested varieties. There was no difference in starch between ‘Youjin’ and ‘Zhongshu 4’, but there were significant differences between ‘Fujin’ and ‘Feiwurita’. There was no difference in the content of L-Vc between ’Fujin’ and ‘Youjin’, but it differed significantly different from that in ‘Zhongshu 4’ and ‘Feiwurita’, respectively. In terms of the commercial potato rate, the treatments were ordered T₃ > T₂ > T₁ > CK and T₄ > T₅ > T₆ > CK, and all tested varieties exhibited the same trend. In the experiment of seedlings from buds of different lengths and positions, the commercial potato variety that increased the most was the ‘Zhongshu 4’. That in seedlings from seven cm buds increased by 5.4% compared with that in the CK, and that in the seedlings from terminal buds increased by 4.9% compared with that in the CK.