Making use of conventionally produced, small size left over tubers which are of no use otherwise is another way, if the size of the tuber is increased to acceptable planting tuber size and addition of nutrients is made to give a proper kick start to plant growth under field condition. Seed pelleting, is a technique for coating seed used to increase the size of very small horticultural seeds which provides improved planting features and is a potential alternative for improving sowing efficiency. Pelleting allows the seeds not only to gain both weight and volume but also standardizes seed size. The materials used for coating seeds are classified into two groups: binder materials and bulking or coating materials with or without micronutrients or growth regulators for the invigoration of the planting material. Furthermore, the pellet's external surface is smooth and not deformed, facilitating its planting by seed drills if it is used for mechanical planting. Pelleting is mainly used for seeds which have a high market value, such as tobacco, eucalyptus, some vegetables and ornamental plants, but is uncommon for smaller seeds, such as grasses, which have a lower market value, and high volume high value crops like potato. This has been successfully practiced in many crops like chilli, groundnut, soybean etc., but, information on their effect on seed potato is scanty. Keeping the above facts in mind, a trial was initiated in two cultivars of potato (Kufri Swarna and Kufri Jyoti) during the year 2009 and 2010. Pelleting was chosen because of its advantage over priming as reported by Murata et al., (2008) in groundnut. To our knowledge, this is the first attempt which indicates the possibility of pelleting the potato tubers. Acacia nilotica leaf powder is used as a base coating material for pelleting. The use of Acacia leaf powder as pelleting agent was reported by Nargis et al (1999). Acacia species are used to treat diseases of livestock as reported by Dafallah and Al-Mustapha (1996), Shah et al. (1997), Amos et al. (1999), Gilani et al. (1999) and Hussein et al. (2000). Hence, we attempted to use the Acacia in our study.

Tuber weight loss: Tuber weights (10 tubers) were recorded prior to storage, and after every 15 days of storage. Weight loss was expressed as percentage: [(tuber weight prior to storage - tuber weight after every 15 of storage) / tuber weight prior to storage] x 100.

Length of the sprout: Tuber sprout length (10 tubers) was measured at the end of storage period in each treatment with the help of vernier caliper and expressed in millimeter.

At the end of storage, tubers were taken for field experiment. Randomised block design Design (RBD) with three replications. One row of 10 tubers each, with a spacing of 40 x 20 cm were planted. Farmyard manure and fertilizers were applied as per recommendation. One per cent urea spray was given at 45^th and 60^th days after planting on the foliage.

After maturity, tuber yield and number was recorded in three different grades (<30, 30-60 and >60 g) by grading from the row and was expressed in kg per 10 plants and number per 10 plants.

Bio chemical analysis: Reducing sugars was estimated by using the method of Nelson (1944), Total free amino acids by Roe et al., (1990) and Phenols by Sadasivam and Manickam (1992). For this purpose, three tubers were selected randomly and the analysis was carried out.

Field potential of pelleted seed tubers

Tuber yield in different grades

Tuber yield was recorded in three different grades (<30 g (small size), 30-60 g (seed size) and >60 g (large size)) by manual grading and the weight was expressed in kilogram.

Tuber number in different grades

Tuber number was recorded in three grades (<30 g (small size), 30-60g (seed size) and >60g (large size)) and it was expressed in numbers.

Statistical analysis

Data were analyzed using Analysis of Variance with mean separation by LSD Test using WASP 2, a web based software developed by ICAR research complex, Goa, India. Percentage data was arc-sin transformed before analysis. 

The rationale for seed pelleting is to make the seed perfect for planting by increasing the size as well as making the nutrition sufficient enough to give growth in the field. Selection of binder materials and bulking or coating materials is important for pelleting. Pellet forming is an artistic method combined with science.

In our experiment, vigor enhancement by way of early sprouting was noticed in SA treatments in both the cultivars by nearly 30 days over other treatments in both the cultivars. Salicylic acid (SA) is known for its defense reactions induced endogenously (Gaffney et al., 1993; Clarke et al., 2000) but effect on germination is not well defined because in some crops it inhibited the germina-tion namely, maize (Guan and Scandalios, 1995) and caused vigour enhancement in wheat (Shakirova et al., 2003) and pea (McCue et al., 2000). Vigor enhancement by the incorporation of growth regulators in pelleting might be due to increased cell division and hormonal balancing system which caused an increase in sprout growth. Many basic works have been done in Arabdiobsis to understand the role of SA on seed vigour and found that SA plays a major role from seed storage protein mobilization to protein translation which in turn increase the seed vigour. Finally, the proteomic data revealed a close interplay between abscisic (ABA) signaling and SA elicitation of seed vigor.

Abscisic acid (ABA) reduction is believed to be important for dormancy breaking which in turn leads to sprout initiation in potato. Still, this phenomenon is controversial (Ume Sonnewald, 2001) as decline of ABA did not correlate with the sprouting behavior of the tubers, ruling out the possibility that the decline of ABA content below a certain threshold level is responsible for the break of dormancy (Biemelt et al., 2000). Although, in our experiment, early sprouting has indicated that SA as growth regulator might have played some role in altering the growth promotor (GA and cytokines) and inhibition (ABA and ethylene) ratio to promote the sprouting.

In general, calcium is amended as a nutrient in the soil to enhance the quality of potato because of its direct correlation with post-harvest quality and to enhance the drought tolerance in potato cultivation. Calcium is impor-tant for the growth of sprout in potato and to have the apical dominance, which arrests the lateral branches. Dark storage creates calcium deficiency and causes sub-apical necrosis followed by death (Dyson and Digby, 1975(a)). In pelleting, the tubers are covered by pelleting material and a dark condition is created for the tuber. Calcium Sulphate was added in one of the treatments to understand and to avoid the formation of sub-apical necrosis.

Calcium sulphate pelleted tubers were able to sprout within 60 days after storage in both the cultivars when compared with control (45 days) showing its ability to overcome the sub-apical necrosis. In all the treatments sub-apical necrosis was not noticed. The sprouting was delayed by 15 days in CS when compared with control. This shows that some physiological activities either dormancy breaking or sprout initiation was modified. Arrest of physiological ageing through calcium application is tested by Dyson and Digby (1975b). Further, Booth (1963) showed that lateral branching is due to poor interaction between auxin and gibberellin.

Tri-iodo-benzoic acid (TIBA) was added to the experiment to understand the role of an inhibitor in the pelleting process. TIBA was identified as auxin inhibitor by Kuse (1953) when he found that auxin moving from the leaf did not pass the point where the TIBA was applied in a band of lanolin paste on the petiole. In this paper, these deductions have been tested by direct methods. Further this was confirmed by Muller (1999) in wild type peas. Ana Rincon et al. (2001) hypothesized that TIBA prevented fungal IAA transport towards the root Laccaria bicolor. In our experiment, tubers pelleted with TIBA took 60-75 days for sprouting when it is only 45 days in control. Sprout growth was inhibited by TIBA for 15 to 30 days. This might be due to the alteration in the auxins level. Though auxins did not play a direct role in the sprouting but played a major role in the dormancy breaking mechanism which is a pre request for the sprout initiation.

The sprouting percent was affected by Acacia leaf powder    pelleting. It took 90 days to start sprouting    which    is 45 days later than control. The highest total extractable phenolics and total extractable tannin values were recorded in A. nilotica (168.36 and 176.15 mg g^-1 DM, respectively) (Mtui Dorah, 2008). Pelleted with acacia leaf powder delayed germination might be due to the less accessibility to oxygen by the sprouts.

Many phenolic compounds are reported in the potato tubers (Uppal and Verma, 1982; Ghanekar et al., 1984). These compounds are the substrates of polyphenoloxidase enzyme and are involved in enzymatic browning of peeled potatoes (Mapson et al., 1963), in resistance of potatoes to diseases (Tripathi and Verma, 1975) and further reported that a decrease in the content of total phenols in the peels and pulp of two varieties of potatoes stored under ambient conditions. In the present investigation, the there is significant change in the phenol content among the treatments and between varieties. The chemistry of A. nilotica leaf extracts has shown the presence of phenol (Table 2) which played a role when it is coated over the tubers especially giving good health in the field by avoiding the diseases. Though there is a significant difference among the treatments in the free sugars and total free amino acids, a definite correlation could not be arrived.

The early achievement of 50% germination in the field by control (without coating) which is one of the vigour indicating factors may be due to non-hindrance by coating. Reduced emergence due to pelleting is possible when clay is applied over sugar beet seeds (Durant and Loads, 1986) but macronutrient solution immersed seeds yielded with more in cereals (Woomer et al., 2003) and nutrient pelleted seeds accelerated growth and develop-ment (Konstantinov, 1983) which has not happened in our experiment with potato. There is a significant difference between A. nilotica pelleting alone with that of added nutrients treatments. The performance of pelleted seed with other growth regulators might have affected the chemical transformation in the plant system. Further, Razzaque et al. (2004) reported that the application of TIBA had reduced the height of tomato plants. The increase in the tuber number and the total yield by A. nilotica coating is due to its antimicrobial activity, disease resistance is due to high phenol content and non-hindrance with other nutrients during growth period which facilitated the good source to sink movement during the bulking stage, a crucial period in potato growth.

Potato seed tuber which acts as a mother, supplies the food to growing sprout till it starts photosynthesis. This feeding results in vigorous and rapid crop growth during early growth stages, which probably leads to higher tuber yields. The vigorous sprout growth is due to the availability of external nutrients applied to the acacia leaf powder and suppression of tannins and phenols available in the acacia leaf powder. Acacia leaf powder alone is having the potential to prolong the shelf life of very    small left over tubers in the field and to give little lesser than the normal potato yield when it is planted in the field without much extra care. Hence, very small potato seeds which or otherwise waste in the field can be used as potato seed by modifying its size by pelleting where the seed cost is very high depending upon the labour availability.

The authors have not declared any conflict of interest.

Thanks are due to The Director, CPRI, Shimla for providing facilities for this study. We also thank Dr. Hari. K. Principal Scientist, Sugar cane Breeding Institute, Coimbatore, India and Dr. Sundralingam, Assoc. Prof, Department of Seed Technology, TNAU for their help in the Biochemical analysis.