Correlation between seed coat colour and longevity of seeds in sorghum genotypes

Introduction

Sorghum is the fifth most important cereal in the world followed by maize, rice, wheat and barley. It is a cultivated diploid (2n = 20) tropical cereal C 4 grass plant, belonging to Poaceae family. It is an important grain and forage crop of semiarid regions due to its high adaptability and suitability to rain-fed low input agriculture (Anagholi et al., 2000) [3] . One of the unique features of sorghum seed is its variation in seed colour. Seed coat colour is simple and excellent indicator of seed quality parameters. The colour of seed coat is most obvious physical characteristic which varies widely with white, cream, red, black etc. Differences in seed coat colour have been associated with differences in the composition of chemical compounds in the seed coats or the presence of phenolic compounds in the seed coats. The actual colour is determined primarily from three variables: seed coat (pericarp) colour and thickness, the presence or absence of a sub-layer beneath the pericarp called the testa and the endosperm colour and texture. Phenolic compounds in seed coat play important role in seed longevity contributing to seed hardness, inhibition of microorganism growth and also help in defence system of seeds that are exposed to oxidative damage by many environmental factors such as light, oxygen, free radicals and metal ions. Pigmented seed coats have a prolonged storage life because of presence of phenolic compounds. The main purpose of seed storage is to secure the supply of good quality seed for a planting programme whenever needed. Seed storage and retention of seed viability is an important post-harvest operation that decides the success of seeds in the next generation. So seed coat is having the central role in seed longevity as it is the primary defence against adverse environmental condition.

Substantial research has been conducted to know the effect of seed coat colour on longevity of sorghum genotypes. With that overall goal, the focus of this research paper was to compare different seed coat colour sorghum genotypes with respect to their seed quality characters and to find the correlation of seed coat colour with longevity of sorghum genotypes.

Materials and Methods

Seed materials

A laboratory experiment was conducted in Department of Seed Science and Technology, College of Agriculture, Raichur during 2021-22, to know influence of seed coat colour on longevity of sorghum. The experiment was laid in a completely randomised design. There were 20 genotypes, white (G 1, G 2, G 3 ), pearly white (G 4 , G 5 ), chalky white (G 6 ), whitish purple (G 7 ), purple(G 8 ), yellow (G 9 ), red (G 10 , G 11 ), light red (G 12 , G 13 , G 14 ), light brown (G 15 , G 16 ), dark brown (G 17 , G 18 ), black (G 19 , G 20 ). The seeds were harvested during February 2021. They were dried at 10 per cent moisture level and kept for storage under ambient condition in the month of August. These seeds were used for testing seed quality parameters.

Moisture content

Moisture content was determined according to the method described by ISTA., 2013 [9] . The five gram of seed material is added to the cup. The samples were incubated in hot air oven at high constant temperature at 130ºC for one hour. After completion of drying period, the moisture cups are removed and kept in desiccators with silica gel for 15-20 minutes and then the weight was taken (M 3 ). The moisture percentage was calculated using below mentioned formula

Where M 1 = weight of the container + lid (g), M 2 = weight of the container + lid+ seed before drying (g), M 3 = weight of the container + lid + seed after drying (g)

One hundred seeds from each replication were taken from each treatment. They were kept for germination and number of germinated seeds was counted as per the formula Seed Germination (%) = Number of normal seedlings × 100 Total number of seeds

Seedling vigour index (SVI-I)

The seedling vigour index -I was calculated as per the method followed by Abdul-Baki and Anderson (1973) [1] .

SVI-I = Germination (%) x Seedling length (cm)

Seedling vigour index (SVI-II)

The seedling vigour index-II was worked out by multiplying the per cent seed germination and mean seedling dry weight (Abdul-Baki and Anderson, 1973) [1] .

SVI-II = Germination (%) x Seedling dry weight (mg)

Electrical conductivity (dSm -1 ) Seeds were soaked overnight by keeping in an incubator maintained at 25°C ± 1 for twelve hours. The seed leachate was collected and measured in digital conductivity bridge with a cell constant 1.0 and the mean values were expressed in deci Siemens per meter (dSm -1 ) as described by Milosevic et al., 2010 [13] .

Total dehydrogenase activity (OD value)

Twenty five seeds from each treatment were pre conditioned by soaking in water overnight at room temperature. The half cut seeds was steeped in 0.25 per cent solution of 2, 3, 5-triphenyl tetrazolium chloride and kept in dark for 2 hours at 40°C for staining. The stained seeds was then soaked in 10 ml of 2 methoxy ethanol and kept overnight for extracting the red colour formazan. The intensity of red colour was measured using spectrophotometer using blue filter at 620 nm wave length and methyl cellosolve was used as a blank. The OD value obtained was reported as dehydrogenase activity (Kittock and Law, 1968) [10] .

Data analysis

The mean data of the laboratory experiments was statistically analyzed by adoting appropriate statistical methods as outlined by Panse and Sukhatme (1985) [15] . The critical differences were calculated at one per cent level of probability wherever 'F' test was found significant.

Results and Discussion

Results and discussion for the present laboratory experiment on "correlation between seed coat colour and longevity of seeds in sorghum genotypes" were analyzed using standard statistical methods, which are presented and discussed below. Among the 20 sorghum genotypes of different seed coat colour, black seed coat colour genotype recorded lowest moisture content (10.24% and 9.94%) at the beginning and at the end of the storage period compared to all other genotypes and the highest was noticed by white seed coat colour genotype (10.58% and 10.18%) at initial and after ten months of storage respectively. Seed coat colour exhibited negative correlation with seed moisture content (-0.249 and -0.077).

The highest moisture content in white seed coat colour genotype may be due to thinner seed coat. Similar results were explained by Mokashi (2017) [14] coated that unpigmented seed having thinner seed coat absorbs more moisture than pigmented seeds. Giang and Gowda (2007) [6] reported that the fluctuation in moisture content may be due to the hygroscopic nature of the seeds which absorb or desorbs moisture from the environment. Since cloth bag is moisture and vapor pervious in nature, the moisture content of seeds showed more fluctuation and greater loss of seed quality. The lowest seed germination in white seed coat genotype might be due to the presence of some various phenolic compounds in unpigmented seed. Similar results were noticed by Mokashi (2017) [14] in cowpea. He stated that, some phenolic compounds present in unpigmented genotype hinders the metabolism preparatory to germination and prevent the access of oxygen to embryo and release of carbonic acid which make it deteriorate faster than the pigmented genotypes. Abdullah et al. (1988) [2] [16] , Anuradha et al. (2009) [4] in chickpea, Mokashi (2017) [14] in cowpea.

Dehydrogenase enzyme played crucial role in the transfer of electrons during the respiratory process. The black seed coat colour sorghum genotype recorded significantly highest total dehydrogenase activity both at initial and at the end of storage period (0.208 OD value and 0.200 OD value respectively). While the lowest was found in white seed coat colour genotype (0.179 OD value and 0.145 OD value) at beginning and after end of storage month. Seed coat colour showed positive significant correlation with dehydrogenase enzyme activity (0.701 and 0.807).

The least dehydrogenase activity in white seed coat genotype might be due to its highest moisture content. Mokashi (2017) [14] studied different seed coat coloured cowpea genotypes and suggested that unpigmented genotypes have thin seed coat and absorbs more moisture from the environment during storage which inturn reduces all the seed quality parameters and thus the cotyledon of the seeds fails to stain 2, 3, 5-tri phenyl tetrazolium chloride. These findings are also in accordance with Saxena and Maheswari (1980) [17] in soybean. Significantly lowest electrical conductivity was recorded by black seed coat colour genotype at the beginning and at the end of storage period (0.10 dSm -1 and 0.24 dSm -1 ) whereas white seed coat colour genotype recorded significantly highest electrical conductivity at initial and at the end of storage period (0.15 dSm - 1 and 0.39 dSm -1 ). Seed coat colour exhibited negative correlation with electrical conductivity (-0.855 and -0.868).

The highest electrical conductivity in white or unpigmented genotypes was attributed to thinner seed coat. Similar findings were recorded by Capeleti et al. (2005) [5] and Kumar et al. (2020) [11] in soybean. They suggested that thinner seed coat in white seed coat colour genotype leads to water uptake into the outer cells of cotyledons that might disrupts the cell membranes and resulting in high solute leakage from the embryo.

Correlation study between seed coat colour and seed longevity

Seed coat colour exhibited positive significant association with germination (0.710 and 0.674), seedling vigour index-I (0.855 and 0.834), seedling vigour index-II (0.706 and 0.615) and total dehydrogenase activity (0.701 and 0.807), alpha amylase activity (0.734 and 0.184), Protien (0.587 and 0.802), Starch (0.361 and 0.519), Iron (0.795 and 0.805), Zinc (0.749 and 0.788), Crude fibre (0.588 and 0.144), Tannin (0.771 and 0.779) at initial and at the end of storage respectively but it is significantly negatively correlated with electrical conductivity (-0.855 and -0.867). Whereas initially, seed moisture content exhibited negative significant correlation with seed coat colour (-0.249) but at the end of the storage month, non significantly negative correlation was found between seed moisture content and seed coat colour (-0.077).

References

1. Abdul-Baki AA, Anderson JD. Vigor determination in soybean seed by multiple criteria. Crop Science. 1973;13(6):630-633.
2. Abdullah WD, Powell AA, Matthews S. Association of differences in seed vigour in long bean (Vigna sesquipedalis) with testa colour and imbibition damage. Journal of Agricultural Science. 1991;116(2):259-264.
3. Anagholi A, Kashiri A, Mokhtarpoor H. The study of comparison between inside forage sorghum cultivars and speed feed hybrids. Agricultural Science and Natural Resources Journal. 2000;7(4):73-83.
4. Anuradha C, Gaur PM, Pande S, Gali KK, Ganesh M, Kumar J, et al. Mapping QTL for resistance to botrytis grey mould in chickpea. Euphytica. 2011;182(1):1-9.
5. Capeleti I, Bonini EA, Ferrarese MLL, Teixeira ACN, Krzyzanowski FC, Ferrarese-Filho O. Lignin content and peroxidase activity in soybean seed coat susceptible and resistant to mechanical damage. Acta Physiologiae Plantarum. 2005;27(1):103-108.
6. Giang PL, Gowda R. Influence of seed coating with synthetic polymers and chemicals on seed quality and storability of hybrid rice. Omonrice. 2007;15:68-74.
7. Hacisalihoglu G, Settles AM. Natural variation in seed composition of 91 common bean genotypes and their possible association with seed coat color. Journal of Plant Nutrition. 2013;36(5):772-780.
8. Atis I, Atak M, Can E, Mavi K. Seed coat color effects on seed quality and salt tolerance of red clover (Trifolium pratense). International Journal of Agriculture and Biology. 2011;13(3).
9. International Seed Testing Association. International rules for seed testing. Seed Science and Technology. 2013;27:2530.
10. Kittock DL, Law AG. Relationship of seedling vigor to respiration and tetrazolium chloride reduction by germinating wheat seeds. Agronomy Journal. 1968;60(3):286-288.
11. Kumar SJ, Kumar A, Ramesh KV, Singh C, Agarwal DK, Pal G, et al. Wall bound phenolics and total antioxidants in stored seeds of soybean (Glycine max) genotypes. Indian Journal of Agricultural Sciences. 2020;90:118-122.
12. Mavi K. The relationship between seed coat color and seed quality in watermelon Crimson Sweet. Horticultural Science. 2010;37(2):62-69.
13. Milosevic M, Vujakovic M, Karagic D. Vigour tests as indicators of seed viability. Genetika. 2010;42(1):103-118.
14. Mokashi YS. Effect of seed coat color on seed quality, nutrition and seed longevity in cowpea [Vigna unguiculata (L.) Walp.]. Bengaluru: University of Agricultural Sciences; 2017.
15. Panse VG, Sukhatme PV. Statistical methods for agricultural workers. New Delhi: Indian Council of Agricultural Research; 1985. p. 158-161.
16. Roberts EH. Storage environment and the control of viability. In: Roberts EH, editor. Viability of seeds. Dordrecht: Springer; 1972. p. 14-58.
17. Saxena OP, Maheshwari DC. Biochemical aspects of viability in soybean. Acta Botanica Indica. 1980;8(2):229234.
18. Tiryaki G, Cil A, Tiryaki I. Revealing seed coat colour variation and their possible association with seed yield parameters in common vetch (Vicia sativa L.). International Journal of Agronomy. 2016;2016.
19. Yousif AM. Increased stored soybean dietary fibre concentration is positively correlated to testa darkening measured chromaticity. Journal of Cereal Science. 2014;60(1):25-30.
20. Zhang J, Cui Y, Zhang L, Wang Y, Li J, Yan G, et al. Seed coat color determines seed germination, seedling growth and seed composition of canola (Brassica napus). International Journal of Agriculture and Biology. 2013;15(3).