​Effect of Modified Atmosphere Storage Conditions on Seed Quality and Longevity of Kabuli Chickpea Varieties

Chickpea (Cicer arietinum L.) is a third most important pulse crop in the world after beans and peas, valued for its nutritive seed composition with high protein content and used increasingly as a substitute for animal protein and in the preparation of variety of snacks, sweets and condiments. Chickpea is classified based on seed size, shape and colour. In India, the two most commonly cultivated types are white seeded ‘Kabuli chickpea’ and brown seeded ‘Desi’ type. Globally and nationally the area, production and productivity of Kabuli chickpea is very low as compared to Desi type chickpea. However, world of chickpea is predominated by Desi type which accounts 80 per cent and Kabuli type only 20 per cent of production. India is the largest producer of chickpea contributing over 70 per cent of the world production with an area of 86.80 lakh hectares with a production of 80.90 lakh tonnes and with a productivity of 932 kg per hectare (Anonymous, 2017).

Seed deterioration is a natural process which is inevitable, inexorable and irreversible. Hence, seed storage and its quality maintenance becomes more challenging in Kabuli chickpea seeds as, they possesses thin and fragile seed coat which makes it as more susceptible to infestation of pulse beetle and storage fungi. The day by day increase in usage of chemical pesticides and on contrary the increase in health awareness among the people and their demand towards organic based products necessitates a new alternative method of storage that improves conditions and environments that cause quality deterioration then the routinely used storage methods. A low-oxygen atmosphere system for handling of chickpea seeds appears to have potential for improving storage practices. Many studies have showed that modified atmosphere of elevated carbon dioxide and depleted oxygen is an effective method against insect pests and microorganisms attack during storage. Modified atmosphere storage is one of the seed and food preservation method that maintains the natural quality of seeds and food products besides extending the storage life of seed by reducing the respiration rate (Moltos et al., 2002). Modified atmosphere storage is an alternative method to avoid chemical fumigants, which are said to cause residual effect on seed material and development of resistance by storage pest against insecticides and pesticides which help in protection of stored seed from insect pest infestations and also to slow down the seed deterioration. Besides, alternatively high carbondioxide treatment is residue free and approved by Environmental Protection Agency, USA. Carbondioxide treated seeds are also accepted in the organic market. Hence, an attempt was made to study the effect of modified atmosphere storage conditions on seed quality and longevity of Kabuli chickpea varieties.

The laboratory experiment was conducted in the Department of Processing and Food Engineering, College of Agricultural Engineering, University of Agricultural Sciences, Raichur using the Modified Atmosphere Packaging (MAP) Unit during March 2017 in order to assess the seed storability of Kabuli chickpea by subjecting to different modified atmospheric storage conditions with different concentrations combination of gases like carbon dioxide, nitrogen and oxygen. The experiment consisted of two varieties viz., V1 (BG1105) and V2 (MNK-1) and five treatments viz., C₁: Normal air (untreated control), C₂: CO₂ (80%) + N₂ (20 %) + O₂ (0%), C₃: CO₂ (75%) + N₂ (20 %) + O₂ (5%), C₄: CO₂ (70%) + N₂ (20%) + O₂ (10%) and C₅: Vaccum packing. The seeds exposed to these gas combinations were stored in 700 gauge polyethylene bags for 14 months (from March 2017 to May 2018) under ambient condition at Seed Unit, Dharwad. The experiment was carried out in Completely Randomized Design with factorial concept with four replications and observations on seed quality parameters were recorded bimonthly.

Method of modified atmosphere packaging was carried out as per the procedure given by Vasudevan et al., (2014). However, in the present study 800 g seeds of both varieties were packed in Polyethylene bag (700 gauge) with the gases like carbon dioxide, nitrogen and oxygen in different concentrations according to the treatments mentioned above.

The seeds obtained from each treatment were evaluated for the seed quality parameters in the Seed Quality and Research Laboratory, Seed Unit, University of Agricultural Sciences, Dharwad. Germination test was conducted as per procedure given by ISTA (2014). The speed of germination was calculated by using the formula given by Maguire (1962). Ten normal seedlings were selected randomly in each treatment from all the replications on 8^th day. The root length was measured from the tip of the primary root to base of hypocotyl and mean root length was expressed in centimeter (cm) while, the shoot length was measured from the base of the primary leaf to the base of the hypocotyl and mean shoot length was expressed in centimeter (cm). Seedling dry weight (Evans and Bhatt, 1977) and seedling vigour index Abdul-Baki and Anderson (1973) were calculated by using the formula as suggested by Abdul-Baki and Anderson (1973), Electrical conductivity of seed leachate was measured as per procedure given by Presley (1958). The data collected from the experiment were analyzed statistically by the procedure prescribed by Gomez and Gomez (2010).

Influence of varieties on seed quality
 
Seed quality differs among the varieties in a crop. Among the varieties, significantly higher seed germination (99.10%) (Table 1), speed of germination (57.07) (Table 2), root length (22.09 cm) (Table 3), shoot length (16.33 cm) (Table 4), seedling dry weight (163 mg) (Table 5), seedling vigour index (3813) (Table 6) and lower electrical conductivity (0.299 dSm^-1) (Table 7) were recorded in variety V₁ (BG1105) as compared to variety MNK^-1 (98.15%, 38.44, 19.35 cm, 12.95 cm, 81 mg, 3173 and 0.520 dSm^-1, respectively). However, there was gradual decrease in seed quality with the advancement of storage period.















Similar trend was observed throughout the storage period, whereas at the end of fourteen months of storage V1 (BG1105) recorded significantly highest seed germination (91.40%), speed of germination (55.01), root length (16.96 cm), shoot length (10.87 cm) seedling dry weight (116 mg), seedling vigour index (2546) and lower electrical conductivity (1.068 dSm^-1) as compared to MNK^-1 (V2) (90.10%, 36.26, 14.60 cm, 7.57 cm, 59 mg, 2000 and 1.255 dSm^-1, respectively). This may be attributed to genotypic response of varieties, where V₁ (BG1105) was superior over MNK^-1 (V₂). Similar varietal response was reported by Merwade (2000), Gnyandev (2009) and Sushma (2013) in chickpea.
 
Influence of modified gaseous on seed quality in Kabuli chickpea genotypes
 
The present study of modified atmospheric storage conditions exhibited significant effect on seed germination of chickpea seeds. The seeds which were stored with the gaseous combination of CO₂ (80%) + N₂ (20%) + O₂ (0%) (C₂) showed better germination throughout the storage period followed by the gaseous combination of vaccum packing (C₅) and CO₂ (75%) + N₂ (20%) + O₂ (5%) (C3) and lowest was in control (C₁). The seed germination per cent due to concentrations of modified atmospheric gases varied significantly at all the month of storage period except for initial month. From second month of storage period significantly higher seed germination (99.88%) was recorded in C₂ (80% CO₂ + 20% N₂ + 0% O₂) treated seeds and it was followed by C₅ (vaccum treated seeds) (99.38%), while the lower (95.75%) was recorded in untreated seeds (control) (C₁). At the end of fourteen months of storage period the highest seed germination was recorded in C₂ (92.38%) and it was followed by C₅ (91.63%) and the lowest was recorded in control (C₁)(88.75%). Whereas, in the initial month numerically highest germination was recorded (99.88%) in C₂ and the lowest (96.63%) in control (C₁) (Table 1).

Modified atmosphere storage of seeds devoid of oxygen recorded higher seed viability for an appreciable period. Higher seed viability and vigour were maintained with modified atmospheric storage particularly in carbon dioxide and vacuum packaged condition. The probable reason for differences in longevity of seeds in the modified atmospheric storage conditions might be due to the variation in the gas concentrations, where the treatments C₂ and vaccum packing having gas combination of higher CO₂ with zero per cent of oxygen concentration i.e., low oxygen atmosphere and also the seeds stored under vacuum condition showed better germination as reported by Meena et al., (2017). Whereas, germination was reported to decrease in peas with increase in oxygen level (Roberts and Abdalla, 1968).

In general, ageing is manifested by decrease of metabolic activity and an increase of catabolic processes. In particular, an oxidative stress might be reduced in oxygen free storage atmospheres (Justice and Bass, 1978; Benson, 1990). It should be noted that seed deterioration during storage could result in marked changes in the content and activity of enzymes capable for degrading the stored reserves (Priestley, 1986; Wilson and McDonald, 1986; Walters, 1998). The advantage of higher seed reserve utilization efficiency in seeds stored in low oxygen concentration and vacuum packing, provide energy for a faster growing rate of the seedlings. In the present study also maximum speed of germination (48.83 and 46.40) was noticed in seeds stored in C₂ (80% CO₂+ 20% N₂ + 0% O₂) and C₅ (vaccum treated seeds) (Table 2), respectively compared to control (C1) (42.15) at the end of fourteen months of storage. The similar results were also reported by Guillaumin (1928), Rathi et al., (2000) and Bera et al., (2008).

The root length and shoot length of Kabuli chickpea seeds were decreased gradually with the advancement in storage period. However, highest root length (17.99 cm) was recorded in C₂ (80% CO₂ + 20% N₂ + 0% O₂) treated seed followed by C₅ (vaccum treated seeds) (16.53 cm), while lowest was recorded in control (C₁) (13.64 cm) at the end of fourteen months of storage period (Table 3). At the end of fourteen months of storage period, highest shoot length (9.93 cm) was recorded in C₂ (80% CO₂ + 20% N₂ + 0% O₂) followed by C₅ (vaccum treated seeds) (9.32 cm), while lowest shoot length (8.72cm) was recorded in control (C₁) (Table 4). The decline in root and shoot length might be due to the damage caused by fungi and insects and also toxic metabolites which might have hindered the seedling growth. Similar findings were reported in onion (Shivappa, 2011) and groundnut (Shrishail, 2011). Deterioration in seed quality associated with decrease in root and shoot length with the passage of time had been confirmed by earlier workers in many crops.

In the present study, highest vigour index was recorded in C₂ (80% CO₂ + 20% N₂ + 0% O₂) treated seed (2581) followed by C₅ (vaccum treated seeds) (2367), while lowest was recorded in control (C₁) (1988) respectively (Table 6) at the end fourteen months of storage period. Gradual decline in seedling vigour index was noticed due to age induced decline in germination and decrease in seedling length.

The significant difference due to modified atmospheric storage conditions on seedling dry weight was recorded throughout the storage period. At the end of fourteen months of storage period, highest seedling dry weight was recorded in C₂ (80% CO₂ + 20% N₂ + 0% O₂) treated seed (99 mg) followed by C₅ (vaccum treated seeds) (88 mg), while lowest was recorded in control (C₁) (79 mg) (Table 5). This gradual decline in seedling dry weight may be due to deterioration of seed.

Whereas, at the end of fourteen months of storage period, lowest electrical conductivity (0.941 dSm^-1) of seed leachate was recorded in C₂ (80% CO₂ + 20% N₂ +0% O₂) treated seed followed by C₅ (vaccum packing) (1.096 dSm^-1). This might be due to the better maintenance of membrane integrity while, the highest electrical conductivity (1.427 dSm^-1) was recorded in control (C₁) (Table 7). Increase in electrical conductivity as the storage period advanced may be due to increased membrane permeability and decreased integrity of seed coat resulted in excess release of electrolytes which caused higher electrical conductivity. Such of these findings were also reported by Shivappa (2011) in onion and Shrishail (2011) in groundnut.

The results revealed that seeds stored in gaseous combination of CO₂ (80%)+N₂ (20%)+O₂ (0%) [C₂], followed by Vaccum Packing [C₅] by using 700 gauge polyethylene bags can be stored for 14 months under ambient condition by maintaining seed quality and its storability above the Indian minimum seed certification standards. Hence, these modern techniques of modified atmospheric storage can play an important role in future days as it is simple and easily adaptable and cost effective, particularly beneficial in the absence of cold storage facility whereas, vacuum packaging can help in maintenance of better seed quality for nucleus, breeder and organically produced seed and can be replaced with the laborious and hazardous fumigation process as it is eco-friendly. However, there is still large scope for depth research study with respect to biochemical and molecular basis of storability under these MAP conditions.

The authors wish to sincerely acknowledge faculty of Department of Processing and Food Engineering, College of Agricultural Engineering, University of Agricultural Sciences, Raichur, Karnataka [India] for providing facility of using Modified Atmospheric packaging Unit for research purpose.