Effects of plant growth regulators on growth and yield of pre-basic seed potato production under glasshouse condition

SAARC J. Agri., 15(1): 149-160 (2017) DOI: http://dx.doi.org/10.3329/sja.v15i1.33161 EFFECTS OF PLANT GROWTH REGULATORS ON GROWTH AND YIELD OF PRE-BASIC SEED POTATO PRODUCTION UNDER GLASSHOUSE CONDITION P. Bhattarai* National Potato Research Program, Nepal Agricultural Research Council, Khumaltar, Nepal ABSTRACT A glasshouse experiment was carried out to study the effect of Plant Growth Regulators (PGRs) on the production of pre-basic seed (PBS) potatoes, cv. Janakdev at Khumaltar, (1360 masl) Lalitpur, Nepal during autumn and spring seasons of 2014 and 2015 respectively. Four - week old virus free in vitro plantlets grown in tissue culture laboratory were planted with 20 cm distance between rows and 10 cm between plantlets under glasshouse in completely randomized design. Three growth regulators, paclobutrazol (50 ppm), daminozide (100 ppm), chlormequat chloride (Cycocel) (200 ppm) and simple water as control were used for single foliar spray 6 weeks after transplanting with four replications. Analysis showed that there were significant differences on growth parameters; plant survival, plant uniformity, plant height and yield components; number of minitubers per plant and per square meter in both the seasons. Significantly maximum number of potato minitubers was recorded in growth retardants treated plants as compared to control. Experimental results showed that maximum number of minituber 2 2 (22.9/plant and 668.2/m ) in autumn and (23.7/plant and 1185.0/m ) in spring season were gained from paclobutrazole spray, which were statistically differed from those of other growth regulators and control. Plants without PGR and treated with daminozide produced the least amount of minituber per unit area. Plant height decreased in all growth regulators over control due to their inhibiting effect on growth of the plants. paclobutrazol significantly reduced plant height but produced larger and heavier minitubers compared to other treatments. Hence, the best PGR for optimum enhancement of minituber number and size was paclobutrazol. The results suggested that paclobutrazol could be used in pre-basic seed potato production, leading to maximum minituber production which ultimately gave higher returns. The study concluded that spraying growth retarding chemicals at grand growth stage checked the excessive vegetative growth and increased the number and size of minituber. * Corresponding author email: Received: 30.04.2017 150 P. Bhattarai Keywords: Daminozide, chlormequat chloride, glasshouse, minituber, paclobutrazol, potato, plant growth regulators, pre-basic seed INTRODUCTION Potato (Solanum tuberosum L.) is one of the most important crops in Nepal. It is used as a major vegetables in terai and mid-hills and as a staple food in the high hills and mountains. According to recent statistics (ABPSD, 2015), it ranks fifth in area coverage (197,037 ha), second in quantity of production (25, 86, 287 tons) and first in productivity (13.1 t ha-1) compared with the main staple food crops of rice, maize, wheat and finger millet grown in Nepal. Despite its importance in food security and cash generation, the average productivity is very low which has been considered mainly due to unavailability of high quality seed potato tubers and several other factors. Potato, being vegetatively propagated crop, is very prone to seed degeneration as several potato viruses accumulate to the seed tubers overtimes resulting in its reduced yield potential. So far, six major potato viruses, namely PLRV, PVS, PVX, PVY, PVA and PVM had been reported to infect potato crops in Nepal (Akius and Kloos, 1990; Ranjit et al., 1994). Seed potatoes should be replaced by high quality seed potatoes at regular intervals to overcome seed degeneration (Sakha and Rai, 2004). A continuous source of high quality seed potatoes is, therefore, necessary in the country. Pre-basic seed (PBS) potatoes are disease free potato minitubers produced by transplanting pathogen free in vitro potato plantlets under protected condition in aphid-proof glasshouse and/or screen house. Since 1990, National Potato Research Program (NPRP) has been producing about 2,00,000 number of pre-basic seeds annually, out of which approximately 35% PBS were small sized (<0.5 g size), which are difficult for direct planting in the farmer's field condition (NPRP, 2016). Those farmers who are involved in potato seed production are always demanding for bigger size (>1 g size) of PBS. PBS production practice is to increase productivity by replacing old degenerated seed potatoes from the major seed potato production pocket areas of the country. PBS production per plant is very low (1:5-6), so it needs to increase at least by 1:9-10. PBS demand was about 0.4 million in the year 2011 (NPDP, 2011) while it increased up to 1 million in 2015 (NPRP, 2015). Compared to the country demand of about 1 million, supply of about 0.2 million tuberlets is far below and private seed industries are also in their infant stage. Intervention of efficient technologies to increase productivity of PBS potato minituber under glass/screen house is an urgent need to fulfil this demand. Recently minitubers productions become popular worldwide. In this system, in vitro plantlets are produced that can be used for further rapid multiplication (in vitro), SEED POTATO PRODUCTION UNDER GLASSHOUSE CONDITION 151 micro tuber production (in vitro), minituber production (in the greenhouse) (Struik and Lommen, 1990). The size of minitubers is from 5-25 mm. and their weight range is from 0.1-10 g or even more (Struik, 2007). Minitubers have the least amount of pathogens (Balali et al., 2008). Minitubers production from in vitro plantlets allows a faster multiplication rate in seed tubers (Imma and Mingo-Castel, 2006). One of the major constraints in the productivity of potato minituber is excessive growth of haulm at the cost of stolen formation, tuberization & tuber bulking under glass house condition. There is also a major challenge to increase the size of potato minituber. These twin objectives could be achieved by spraying growth retarding chemicals at grand growth phase, thereby checking the excessive vegetative growth and enhancing more translocation of photosynthates to the tuber for increasing the number and size of tuber. There are many plant growth regulators (PGRs) especially plant growth retardants used for inhibiting excessive vegetative growth of plants including potato. These PGRs can also be used for long term conservation of potato germplasms under different conditions. The PGRs are used in potato production for changing different characters of the plant such as: numbers of tubers, secondary growth in field and length time of plantlet and microtuber production in vitro (Struik and Wiersema, 1999). Some reports reported that Coumarin (EL-Sawy et al., 2007), Etephon (Mele et al., 1982) and Paclobutrazole (Davis et al., 1988) often showed inhibiting growth effect. With using oth (...truncated)