INTRODUCTION
Potato is one of the Pakistan's most valuable staple crops, ranking sixth in terms of total production after cotton, sugarcane, rice, maize, and wheat (Anonymous, 2018). It is grown on 185 thousand hectares with a total production of 4.5 million tonnes and an average yield of 24 tons/ha, which is greater than the global average (20 tons/ ha) (FAOSTAT, 2020). By the years, potato production in Pakistan has been reduced to a great extent. One of the key issues in potato seed cultivation in underdeveloped nations is insufficient supply of disease-free, high value micro seed tuber (Chiipanthenga et al., 2012). The crop's low productivity in Pakistan is attributable to a variety of biotic and abiotic stresses, but the main cause of low yields is the lack of improved seeds at proper time and at a reasonable price for the farmers. Every year, seed potato imports cost Pakistan about USD120 million for the cultivation of 15000 acres. Introduction of aeroponic technology will make Pakistan able to not only reduce the import costs but also produce high-quality seed potatoes domestically (Cheema, J.I., 2021). Now, Pakistan has less than 3% of high-quality seed in hand, and it is entirely reliant on imported seed from the Netherlands. About 15000-20000 tonnes of seed is imported annually as compared to demand of 500,000 tonnes (Ali, 2022).
Mini tuber production techniques are limited, and existing seed potato production procedures are mostly based on traditional ways. Traditional techniques have a limited potato tuber number / plant (e.g., 8-12 tubers / plant in the potato field). Moreover, production expenses has been surged with the increase in demand of labor. (Hussey and Stacey, 1981;Otazu, 2010;Chiipanthenga et al., 2012). In addition to the aeroponic approach compost is being used as an inert substrate for mini tuber production in Europe, New Zealand, and Korea. Although an enhanced seed potato multiplication rate of 8 to 13 was achieved in compost soil (Rolot & Seutin, 1999), potato yield and number of tuber/plants were seventy per cent and two hundred and fifty per cent lesser, when compared with multiplication in aeroponic system (Ritter et al., 2001). Since the application of the conventional potato culture technique in the field, agronomists and biochemists in Europe and the United States have encountered difficulties related to the nutrient requirements of the potato crop. They are also looking for a practical method that will enable them to produce potatoes in an environment that is properly controlled and offers a high degree of nutritional control. Hydroponic technology for potatoes has been developed in Europe and the United States for these reasons (Chang, 1998).
Aeroponics got popularity in recent years because of the improved mini tuber numbers per unit space and lower seed potato production costs. It is derived on the base of soilless culture, in which roots are exposed to a misty atmosphere in which nutrients circulate for a certain amount of time in a sealed compartment (Chiipanthenga et al., 2012). Aeroponics system offers various benefits over a traditional micro tuber production method including a greater seed multiplication rate, increased number of tubers/unit area, better resource usage efficiency and more uniform tubers size (Bucksetha et al. 2016). This approach permits for numerous harvests with minimum plant damage, resulting in five to twenty times higher tubers productivity per plant. A lot of research in aeroponic potato system has been published. however, in this investigation, we focused specifically on the vegetative growth and mini tuber production aspects of two cultivated varieties with varying planting intervals and planting sizes under aeroponic. The major purpose of this research is to improve Pakistan's aeroponic seed production technology.
MATERIALS AND METHODS
In fall of 2021, during planting season, all studies were conducted at the KOPIA aeroponic greenhouse experimental farm area, National Agriculture Research Center Islamabad, Pakistan. Initially, two cultivated potato varieties that are popular among farmers were tested for an aeroponic greenhouse. Lady Rosetta is a red skinned potato variety that originates in the Netherlands and was released in 1988. It is a cross between Cardinal and VTN 62-33-3. Its other advantages are early to medium maturity, medium to high resistance to PVY, common scab, and high to very high resistance to PVX. Asterix is high yielding potato variety with high dry matters and is ideal for making French fries. It is originated from the Netherlands and introduced in 1991. It is a cross of Cardinal x VE 70-9. After hardening virus-free invitro tissue culture, plantlets were transplanted into a semicontrolled net cum polythene aeroponic greenhouse. The plantlets were planted at a density of 25 cm × 25 cm and foam plugs with 3 cm diameter served as stem support. Nutrient solution is periodically sprayed onto the air hanging roots for 40 seconds every 5 minutes via nozzles. The residual nutrient solution then flows back to the reservoir tank for further nutrient recirculation. The same nutrition solution was used for all treatments. For the first month, full strength nutrition solution was used for stolen growth. Afterwards until harvesting, tuber growth solution was used for seed potato aeroponics (Table 1). Fresh nutrient solution was renewed every 14 days to reduce changes in solution EC, pH, and elemental balance. During the stolon growth stage, the photoperiod is only extended for one month, and then it is reduced from 16 to 12 hours to induce tuberization. Plantlets were shaded with white woolen fabricating cloth during the first week of transplanting. After one week, when the plantlets became stable, the cloth was rolled up. The greenhouse had side and top ventilators that could be opened to promote air circulation and passive cooling to control the interior temperature.
Data Collection and Analysis:
During the development of shoots, weekly records of plant's height, number of lateral stems and number of leaves per plant were kept. After the harvest of aeroponic crop, the following characteristic was noted: no. of tubers/ plant, wt. of tubers/plant, no. of tubers per square meter, and weight of tubers per square meter. We used a completely randomized design (CRD) with homogeneous experimental units. The data was statistically analyzed using the ANOVA approach by using Statistix 8.1 and the means of the treatments were assessed using the LSD test at probability 5% significant level.
Experiment 1: Comparison of Medium size plantlets of lady rosette and Asterix variety under aeroponic condition.
In this experiment, medium-sized plantlets (6 ~7 cm) of the two cultivated varieties Asterix and Lady Rosette were transplanted on the same day. In addition, 48 plantlets with three replications were selected from 144 for each of the two treatments.
Experiment 2: Effect of different Transplanting interval on growth and yielding attribute.
Normal-sized plantlets of the cultivar Lady Rosetta were transplanted twice into an aeroponic system in 2021, on October 27 and November 19, respectively. After 106 days, both treatments were harvested. The experiment's replication, number of plants per treatment, and design were all identical to those in Experiment 1.
Experiment 3: Effect of different plantlet sizes (Normal, Medium, and Small) of cultivar Lady Rosetta on growth and yield of mini tuber
On October 27, 2021, 1680 plants of normal (8~10 cm), medium (6~7 cm), and small size (4~5 cm) were transplanted separately into three aeroponic Styrofoam beds as part of the experiment. Of these, 144 plantlets were chosen for each of the three treatments, which each contained 48 plantlets with three replications. On February 10, 2022, three treatments were harvested after 106 days.
RESULT AND DISCUSSION:
Experiment 1: Comparison between Lady rosette and Asterix cultivar under aeroponic condition.
Shoot development attributes:
Between the two cultivars, there was a significant difference (p <.05) observed for shoot development attributes showed in figure 2. In Lady rosetta the maximum plant height, No. of leaves/plant, and lateral stems were recorded as being 41.31 cm, 27.13 leaves, and 18.63 lateral stems. On the other hand, the “Asterix” cultivar reached plant heights of 32.87 cm, 22.47 leaves per plant, and 14.87 lateral stems. As opposed to conventional multiplication, we typically noticed that these cultivars cultivated in aeroponic systems extended their vegetative cycle. Mbiyu et al. (2018) reported that influence of variety on plant growth, varied among kinds, and these variations were more prominent as the plants grew older. Rodríguez et al. (2012) reported that there is significant variation amongst cultivars in terms of growth responsiveness and yield in an aeroponics potato system under uniform circumstances. According to Tierno et al. (2014), aeroponic techniques produce similar results, including higher growth and a 12–36% longer vegetative cycle. Otazu (2010) showed similar one- to two- month expansions o vegetative cycles when plants were cultivated in aeroponic system. Ritter et al. (2001) documented significant finding that Variety, nutrient availability, and cycle duration are just a few of the factors that might influence on plant growth in a container. Similar findings were made by Chang et al. (2012), who found that plants develop vegetatively far more quickly in aeroponic systems than in conventional systems. According to Farran et al. (2006), early cultivar Zorba promotes vegetative development in aeroponic culture, which may be related to an unlimited supply of nitrogen. According to Masengesho et al. (2012), the genetic differences between the two cultivars were to blame for the two cultivars' markedly different plant heights, which were explained by Kinigi's more favourable growth response than Kigega's to the aeroponics situation.
Mini tuber production attributes:
According to Figure 3, cultivars vary considerably (p <.05) in terms of mini tuber production attributes. In Lady Rosetta, the larger no. of tubers/plant, no. of tubers/m2, weight of tubers/plant, and weight of tubers/m2 were 57.50, 920 Tuber/per m2, 60.55 gram/plant, and 968.73 gram/m2. In contrast, for the Asterix cultivar, the figures for tubers per plant, tubers per m2, weight of tubers/plant, and weight of tubers/m2 were 16.76, 257, and 547.20 grams/m2, respectively. The most important characteristic in aeroponics, according to Rykaczewska et al. (2016), is the quantity of mini tubers produced per plant, which is largely controlled by the cultivar. The literature describes a wide range in the size of the individual mini tuber yields produced in aeroponic systems, depending on the cultivar and harvest interval (Chang et al., 2012). According to Chang et al. (2011), cv. Superior had an average of more tubers per plant than cvs. Jayoung and Haryeong. Mateus-Rodriguez et al. (2013) claim that cultivar-specific care may be necessary to achieve a multiplication rate of 1 ratio 45. Additionally, our results are consistent with those of Khalil & Hamed, (2020), which demonstrate that significant variations existed between the three cultivars (LR, Diamant & Spunta). The most minitubers per plant were generated by Lady Rosetta, followed by Diamant and Spunta.
Experiment 2: Effect of different Transplanting interval on growth and yielding attribute
Shoot development attributes:
Figure 4 shows a significant difference (p <.05) in shoot development features between the two transplanting intervals. In “27 Oct 2021,” the maximum plant height, no of leaves/plant, and no of lateral stems were 44.94 cm, 31.25 leaves, and 21.08 lateral stems, respectively. In contrast, the plant height, no of leaves/plant, and number of lateral stems noted on “19 Nov 2021” transplanting date were 31.19 cm, 23.38, and 16.38, respectively. The condition in the aeroponic greenhouses was monitored closely to ensure beneficial growing environmental condition and to intervene whenever needed. At the time of the first trans- planting in the last week of October, the average daily mean temperature inside the passively controlled greenhouse was 27 degrees Celsius, which was almost ideal for growing potatoes. After that, the temperature significantly decreased every week until the second transplanting time, when it was 20 degrees Celsius in the third week of November (Fig. 1a). Rykaczewska, (2016) found the similar results that the period available for growth phase was observed to be function of the date of planting and the phase of tuber formation, earlier planting provided a longer period for vegetative development than late planting. This was further enhanced by the provision of extra nutrients during the growth period for plants from early planting. Early planting resulted in increased plant growing phase and delayed tuberization because to the abundant nitrogen availability and long photoperiod during early days. Modisane, (2007) found the similar results, that plants grew faster and taller at high temperatures (27/17°C) than at low temperatures (22/14°C). The formation of larger stem length at high temp. was also proven by (Dawes et al., 1983;Khedher & Ewing, 1985;Tadesse et al., 2001;El-Beltagy et al., 2002;Thongam et al., 2017;Chandra et al., 2019).According to Benoit et al. (1983), planting time produce similar results in the growth stages first and second, the maximal rate of vegetative growth occurs at 31.3 and 27.4 degrees Celsius, while the maximum rates of leaf area expansion occur at 24.7, respectively. The findings are in line with previous research found that temperatures higher than optimal level accelerated the growth and development of aboveground parts (Bodlaender, 1963;Struik et al., 1989a;Gawroska et al., 1992;Kooman and Haverkort, 1995;Van Dam et al., 1996;Rykaczewska, 2013b). 10 potato varieties were studied in Peru using an aeroponic system, and the results revealed a considerable improvement in vegetative growth development at high temperatures but a decrease in tuberization (Chuquillanqui et al., 2010).
Mini tuber production attributes:
In terms of tuber production parameters, Figure 5 shows that transplanting intervals varied considerably (p<.05). The maximum no. of tubers/plant, tubers/m2, weight of tubers/plant, and weight of tubers/m2 in “27 Oct 2021” were 79.75, 1276 Tuber/per m2, 77.41 gram/plant, and 1238.57 gram/m2. For the “19 Nov 2021” transplanting interval, the no. of tubers/plant, no. of tubers/m2, weight of tubers/plant, and weight of tubers/m2 were 73.74, 1155.55 Tubers/per m2, 41.88, and 547.20 gram/m2, respectively. Furthermore, after 50-55 days (19 to 23 December 2021) after transplanting, tuberization was initiated, and the temperature in the screenhouse at that time was (18-20°C). Early planting resulted in increased plant growing phase and delayed tuberization because to the abundant nitrogen availability and long photoperiod during early days (Rykaczewska, 2016). According to Vandam et al., (1996), tuber commencement is best at temperatures between 15 and 19°C. Our findings are consistent with those published by (Balali et al., 2008) who founded that early planting time could boost tuber production if the amount of radiation for plant growth is sufficient. As it is probable that the total quantity of radiation sunlight at the initial planting time may decrease the amount of endogenous gibberellic acids, resulting in the increase the number of mini tubers. Moreover, showed that the overall minituber yield of potato cv Cara was considerably higher from the initial planting date than from successive planting dates. The overall quantity of radiation received throughout the growing season influenced plant growth and tuber yields. The key factors that influence tuber formation in potato plants are temperature and photoperiods (Struik et al., 1989b). Subsequently, tuberization yield is reduced by more than 50% because of extreme day (32°C) and nighttime Temperature (20°C) (Rykaczewska, 2004). Temperatures over 25°C cause delayed in tuberization up to 21 days (Levy and Veilleux 2007). Additionally, according to Xu et al., (1998) Such circumstances result in the activation of a transmissible signal that causes cell proliferation and elongation in the sub-apical area of the stolon to form tuber initials.
Experiment 3: Effect of different planting size on growth and yielding attribute.
Figure 6 shows the ascribed shoot development and tuber production. demonstrates that planting size varied significantly (p<.05). Plant length (cm), no. of leaves per plant, and no. of lateral stems were all substantially larger in “Normal size plantlets” than in “Medium size” or “Small size plantlets.” Furthermore, in “Normal size plantlets,” the maximum no. of tubers/plant and tubers per m2 were 79.75 and 1276 Tuber/per m2, respectively. The no. of tubers/plant and the no. of tubers/m2 for the “Medium size plantlet” were 57.50 and 920 Tubers/per m2, 41.88 and 547.20 gram/m2, and 39.70 and 622 Tubers/per m2 for the “Small size plantlet,” respectively. This might be due to increased or enhanced biomass, resource accumulation, and better water relation in the plants. Smaller seedlings had less biomass and less food storage in aspects of solutes molecules required for cell expansion, resulting in less growing extension, while larger seedlings were sufficiently developed, limiting vegetative cell extension. (Shukla et al., 2011). Montano-Mata and Nunez (2003) utilized larger plantlets for optimal production and obtained nearly com- parable results. Several studies (Hasandokht and Nosrati, 2010) founded vegetable grown from larger seedling considerably give higher yields. These findings contradict with the results of (Choudhari and More, 2001). The variations in size are due in part to changes in the tuber formation date and development rate. However, it is widely assumed that the rate of development of each individual tuber varies (Gray, 1973.; Ahmed and Sagar, 1981.; Stroik et al., 1988). The size and physiology of the tuber had a major influence on plant growth, affecting both directly and indirectly on stolon and tuber formation (Choi et al., 1994;Lommen & struik, 1994;Ranalli et al., 1994)
CONCLUSION
After conducting series of experiments the results showed that amongst the two famous cultivars of potato, Lady Rosetta and Asterix under aeroponics production system confirmed that Lady Rosetta was the best assessed cultivars in terms of shoot develop and mini tuber production attributes. Consequently, for both early and late planting dates, Lady Rosetta performed very good vegetative growth and productivity in early plantings as compared to late planting. Moreover, in different planting sizing at the time of transplanting (Normal, Medium, and small size) Normal size plantlets of Lady Rosetta showed best results as compared to other planting size. Overall concluded that Normal size plantlets (8-10 cm) of Lady Rosetta cultivar at optimum time showed best results in aeroponic system at NARC, Islamabad Pakistan. Further studies on EC, Ph value and planting date are needed to be optimized to increase the size and weight of tuber per plant in aeroponic seed system in Pakistan.
