Int. J. LifeSc. Bt & Pharm. Res. 2013 C P Malik And Jyoti .
Int. J. LifeSc.LifeSc.BtBt&&Pharm.Pharm.Res.Res.20132013C P Malik and Jyoti, 2013ISSN 2250-3137 www.ijlbpr.comVol. 2, No. 3, July 2013 2013 IJLBPR. All Rights ReservedReview ArticleSEED DETERIORATION: A REVIEWJyoti1 and C P Malik1**Corresponding Author: C P Malik, cpm malik@yahoo.comSeed deterioration is an undesirable and detrimental attribute of agriculture. This process is aseparate event from seed development and germination. Losses in seed quality occur duringfield weathering, harvesting and storage. Deterioration caused by field weathering is directlyrelated to seed exposure to adverse conditions. Seeds are highly susceptible to damage andmechanical injury during post-harvest handling. Several environmental factors contribute to seeddeterioration and these conditions make very difficult to maintain viability during storage. Seedquality is depends upon initial seed quality, temperature, moisture content and mycoflora. Rapiddeterioration occurs due to these environmental conditions make very difficult to maintain itsviability during storage. However, the seed quality and viability during storage depend upon theinitial quality of seed and the manner in which it is stored. Seed deterioration is associated withvarious cellular, metabolic and chemical alterations including lipid peroxidation, membranedisruption, DNA damage, impairment of RNA and protein synthesis and cause several detrimentaleffects on seed.Keywords: Deterioration, Field weathering, Lipid peroxidation, Membrane disruptionINTRODUCTIONdegenerative and inexorable process (Kapoor etal., 2011). As seed deterioration increases, seedperformance is progressively decreases. Thephysiology of seed deterioration is a distinguishconsequence from seed development andgermination.Seed deterioration is loss of seed quality, viabilityand vigor due to effect of adverse environmentalfactors (Kapoor et al., 2010). Deteriorativechanges enhance when seed exposure toexternal challenges increases and decrease theability of the seed to survive. It is an undesirableattribute of agriculture. Annual losses due todeterioration can be as much as 25% of theharvested crop. It is one of the basic reasons forlow productivity (Shelar et al., 2008). The processhas been described as cumulative, irreversible,1Losses in seed quality occur during fieldweathering, harvesting and storage. Severalfactors contribute to the susceptibility for seeddeterioration. The basic causes are temperature,relative humidity, seed moisture content and byinvasion of and damage to tissues bySchool of Life Sciences, Jaipur National University, Jaipur, Rajasthan, India.This article can be downloaded from http://www.ijlbpr.com/currentissue.php374
Int. J. LifeSc. Bt & Pharm. Res. 2013C P Malik and Jyoti, 2013attainment is a genotypic character which isinfluenced by several environmental factors(Mahesha et al., 2001a).microorganisms, insects. The rate of deteriorationfluctuates critically from one species to anotherand also among varieties of the same species(Jatoi et al., 2001). Deterioration is evident as areduction in percentage germination, produceweak seedlings, loss of vigor, become less viableand ultimately seed death (Maity et al., 2000;Tilebeni and Golpayegani, 2011). The percentageemergence of deteriorated seeds is less thanhealthy seeds. Hence, deteriorated seedproduces uneven stands, spotty fields, and fewerplants per hectare than healthy seed (Biabani etal., 2011). Plants that have originated fromdeteriorate seed can also reduce growth rate(Kapoor et al., 2010).Deterioration of seed in the field before harvest(field weathering) begins when the seed reachesphysiological maturity and it extends till the seedsare harvested. The moisture content ofphysiological maturated seed is approximately 5055%. Because of the high moisture content, theseed cannot be harvested commercially andmust remain in storage on the plant through adesiccation period till moisture levels areadequately low to permit mechanical harvestwithout causing undue damage to the seed. Thisdesiccation period vary from a few days to severalweeks before the seed attains a harvestablemoisture level, about 14%. During this postmaturation, pre-harvest period weather conditionshave a great influence on the quality of theharvested seed. Field conditions are rarelyfavorable for such storage. Seed quality isinfluenced by numerous factors that occur in thefield before harvesting and during harvesting,drying, processing and storage. The losses areworsened if seeds are stored at hightemperatures and high relative humidityconditions (Mosavi Nik et al., 2011).WHAT IS DETERIORATION?Seed deterioration can be defined as “deteriorativealterations occurring with time that increase theseed’s exposure to external challenges anddecrease the ability of the seed to survive”. Seeddeterioration causes loss of seed quality with time.It is a natural process which involves cytological,physiological, biochemical and physical changesin seeds. These changes reduce viability andultimately cause death of the seed.TYPES OF DETERIORATIONField WeatheringDeterioration is evident as a decrease inpercentage germination, while those seeds thatgerminate produce weak seedlings. Losses inseed quality occur during field weathering,harvesting and storage (Farhadi et al., 2012).Harvesting time of several crops depends on itsmaturity time and on physiological maturity.Harvesting stage influences the quality of seed,germination, vigor, viability and also storability(Khatun et al., 2009). Physiological maturityThe deterioration of seed quality, vigor and viability,due to high relative humidity and high temperatureduring the post-maturation and pre-harvest periodis referred to as field weathering (Bhatia et al.,2010). Weathering occurs in the period betweenthe attainment of physiological maturity tillharvesting in the field. Deterioration caused byweathering is directly related to seed exposureto adverse conditions, so that the physiologicalThis article can be downloaded from http://www.ijlbpr.com/currentissue.php375
Int. J. LifeSc. Bt & Pharm. Res. 2013C P Malik and Jyoti, 2013parts; broken seed coats permit early entry andeasy access for microflora, make the seedvulnerable to fungal attack and reduce storagepotential (Shelar, 2008). In its severest form,physical seed damage is exhibited by splitting ofthe cotyledon, shattered and broken seeds. Largeseeded varieties are more sensitive to mechanicaldamage than small seeds.quality is depending on the environmentalconditions preceding harvesting (Pádua et al.,2009).Exposure to hot and humid conditions, rainfall,photoperiod after ripening are pre-harvest factors,cause seed quality loss following physiologicalmaturity. Among all these factors, influence ofmoisture on seeds during ripening appears toexert the major influence on predisposition toweathering. Adverse environmental conditionsduring seed filling and maturation result in forcedseed maturation, which is associated with lowyields, leading to a significant decrease in qualityand an extensive reduction in the crop productivity(França-Neto et al., 2005; Pádua et al., 2009).StorageStorability of seeds is mainly a geneticallyregulated character and is influenced by qualityof the seed at the time of storage, pre-storagehistory of seed (environmental factors during preand post-harvest stages), moisture content ofseed or ambient relative humidity, temperatureof storage environment, duration of storage andbiotic agents (Shelar et al., 2008; Baleševiæ-Tubicet al., 2005; Khatun et al., 2009; Biabani et al.,2011). Damage of seed during storage isinevitable (Balesevic-Tubic et al., 2005).After physiological maturity if the seeds areretained on mother plant seeds will deteriorate,physiological changes in seed may lead toformation of rigid seeds or off color seeds in pulsecrops (Khatun et al., 2009). Harvest delaysbeyond optimum maturity extend field exposureand intensify seed deterioration. Weathering notonly lowers seed germination, but also increasessusceptibility to mechanical damage and diseaseinfection. Timely harvesting avoids prolongedexposure to moisture, and is the best means ofavoiding weathering.These environmental conditions are verydifficult to maintain during storage. The seedstorage environment highly influences the periodof seed survival. After planting of deteriorateseeds, seedling emergence may be poor andtransmission of pathogens to the new crop mayoccur. Lower temperature and humidity result indelayed seed deteriorative process and therebyleads to prolonged viability period (Mohammadiet al., 2011).Harvest and Post-harvest DeteriorationSeed quality is highly affected by harvesting andhandling methods. Harvest and post-harvestdeterioration comprises threshing, processingmachinery, seed collection, handling, transportingand drying. Mechanical damage is one of themajor causes of seed deterioration duringstorage. Very dry seeds are prone to mechanicaldamage and injuries. Such damage may resultin physical damage or fracturing of essential seedMECHANISMS OF SEEDDETERIORATIONOnce seed deterioration has happened, thiscatabolic process cannot be reversed It is asequence of events beginning with a chain ofbiochemical events, predominantly membraneThis article can be downloaded from http://www.ijlbpr.com/currentissue.php376
Int. J. LifeSc. Bt & Pharm. Res. 2013C P Malik and Jyoti, 2013damage and impairment of biosyntheticreactions, and then the resulting losses of variousseed performance attributes, starting withreduced germination rate, reduced fieldemergence, increased numbers of abnormalseedlings and finally seed death. Viability lossresults in irreversible chemical and structuralchanges to cellular constituents (Walters et al.,2010).viability. During seed deterioration, membranedegradation increase electrolyte leakage. Declinein seed germination, field emergence andseedling vigor is associated with high level ofelectrolytes leakage.Alterations of membrane systems, such as thetonoplast, plasmalemma and endoplasmicreticulum, result in diminishing of normal cellfunction and energy production. MembraneStructural changes associated with oxidationare reduced membrane fluidity, altered folding ofDNA, lost elasticity of proteins and increasedbrittleness of the cellular matrix. Moleculesoxidation leads to either smaller molecules withreactive carbonyl or nitrogen groups that easilydiffuse through cells, or adducts betweencarbohydrates, proteins and nucleic acids thatcause intermolecular cross-linking and furtherdegrade into advanced glycation end-products(Walters et al., 2010).deterioration and loss of permeability occur at anearly stage during the seed deterioration.Enzymes AlterationsEnzyme alterations, such as reduced activity oflipase, ribonuclease, acid phosphatase, protease,diastase, catalase, peroxidase, and amylase,DNase and dehydrogenase enzymes. ROS andhydrogen peroxides are produced from severalmetabolic reactions and could be destroyed bythe activity of scavenger enzymes like catalaseBiochemical Manifestation of SeedDeteriorationand peroxides. Peroxides activity decreasessubstantially with ageing. Due to this seedsSeed deterioration is associated with variouscellular, metabolic and chemical alterationsincluding chromosome aberrations and damageto the DNA, impairment of RNA and proteinsynthesis, changes in the enzymes and foodreserves and loss of membrane integrity (Kibinzaet al., 2006). Some of the major physiological andbiochemical events of deterioration are presentedbelow.become more sensitive to the effects of oxygenand free radicals in membrane unsaturated fattyacids and produce lipid peroxidation productssuch as monaldehyde and lipid conjugants.Changes in Cell Chemical ConstituentsIn deteriorate seeds significant decrease inprotein, oil content and total sugars and increasein free fatty acids and reducing sugars has beenMembrane Degradationstudied. Verma et al. (2003) showed thatIt is extensively consented that loss in cellularmembrane integrity is one of the primary causesfor loss of viability. Under harsh storage conditionsloss in membrane permeability leads to increasedleaching of seed constituents and hence loss incarbohydrates increased with decrease in proteincontent in deteriorated seeds. Some studiesindicated that oligosaccharide which has beenassociated in stabilizing membranes decreasedduring storage.This article can be downloaded from http://www.ijlbpr.com/currentissue.php377
Int. J. LifeSc. Bt & Pharm. Res. 2013C P Malik and Jyoti, 2013Reduced Metabolic Activity Enzyme degradation and inactivation(amylase, dehydrogenase, oxidases,phospholipase, glutamic acid decarboxylase),High relative humidity hastens deterioration andresults in reduction of nucleic acids withincreased storage period. Metabolic activities ofseeds were low in non-viable seeds than in viableseeds. Long term storage decreases the abilityto form nucleic acids and nucleotides. Formation and activation of hydrolyticenzymes, Starvation of meristematic cells, Increases in seed leachates and free fatty acidcontent,Free Radical DamageDeterioration is partially associated to theaccumulation of free-radicals produced by themetabolic process. Seed storage subjects lipidsto slow consistent attack by oxygen, forminghydrogen peroxides, other oxygenated fatty acidsand free radicals. The free radicals are unstableand may react and damage nearby molecules.Oxygenated fatty acids in the absence ofenzymes activity in the dry seed wouldaccumulate and damage cellular componentsand leads to deterioration of seeds. Lipidperoxidation and free radicals formation are themajor causes for the deterioration of oil seeds instorage. Reduced respiration, and Accumulation of toxic compounds.Moreover the main cause of seed damage,lipid peroxidation causes initial biochemicalchanges in seed that can be observed duringstorage. Autooxidation of lipids and increase inthe content of free fatty acids throughout storageperiod are the main reasons for rapid deteriorationof seed of oil plants (Balesevic-Tubic et al., 2005).In sunflower seeds, loss of viability isassociated with an accumulation ofmalondialdehyde (MDA), suggesting that seeddeterioration is accompanying with lipidperoxidation related to a decline in the efficiencyof the antioxidant defense system (Kibinza et al.,2006).Chromosome AberrationsOne of the changes linked with seed ageing isaberration of chromosomes, sometimespertained to as mutagenic effects. Some of thechromosome alterations in seeds comprisefragmentation, bridges, fusion, ring formation ofchromosomes and variations in nuclear size.Membrane disruption is one of the primaryreasons attributed to seed deterioration. As aresult, seed cells are not capable to hold theirnormal physical condition and function. Causesof membrane disruption are enhancing in freefatty acid level and free radicals productivity bylipid peroxidation (Ghassemi-Golezani et al.,2010). Lipid peroxidation can result in not onlydestruction of the lipid itself, but also damage tocell membranes and other cellular components.Free fatty acid can damage lipid bilayerSome other causes of deterioration are: Degradation of functional structures, Biochemical changes resulting in lower levelsof ATP, Decline in sugar content, Inability of ribosomes to dissociate,This article can be downloaded from http://www.ijlbpr.com/currentissue.php378
Int. J. LifeSc. Bt & Pharm. Res. 2013C P Malik and Jyoti, 2013particularly of mitochondria leading to reduceenergy production and free radicals have potentialto damage membrane, DNA, enzymes, proteinand ultimately cellular repair mechanism(Ghassemi-Golezani et al., 2010).Genotypic FactorsFactor Affecting DeteriorationInitial Seed QualityThe rate of seed deterioration is highly influencedconditions during seed producing stage, pests,High initial viability of seeds maintains their qualityin storage longer than those with less initialviability. Vigorous and undeteriorated seeds canstore longer than deteriorated seeds. Seeds thathave been broken, cracked, or bruised due tohandling deteriorate more rapidly in storage thanundamaged seeds. Cracks in seeds serve asentrance to pathogens causing consequentdeterioration. Seeds that have been developedunder environmental stress conditions (such asdrought, nutrient deficiency and hightemperatures) become more susceptible to rapiddeterioration.diseases, seed oil content, storage longevity,Effect of Temperaturemechanical damages of seed in processing,High temperature hastened the rate of thesefluctuations in moisture (including drought),weathering, nutrient deficiencies, packaging,biochemical processes triggering more rapiddeterioration that resulted in rapid losses in seedpesticides, improper handling, drying andhaving high moisture content (Shelar et al., 2008).biochemical injury of seed tissue can affect vigorSeeds sensitivity to high temperatures is stronglyof seeds (Krishnan et al., 2003; Marshal andLevis, 2004; Astegar et al., 2011; Simic et al.,dependent on their water content, loss of viabilitybeing quicker with increasing moisture content2007).(Kibinza et al., 2006). Temperature is importantSome types of seeds are inherently long lived;others are short lived, while others have anintermediate life span owing to their differenceson genetic makeup.by environmental (temperature, relative humidityand seed moisture content) and biological factors(such as fungi that create their own biologicalniche) (Ghassemi-Golezani et al., 2010). Seedlongevity is determined by seed moisture,temperature and seed attributes that areinfluenced by genetic and environmentalinteractions during seed maturation, harvestingand storage (Walters et al., 2010).Several other factors such as environmentalbecause it influences the amount of moisture andKind/variety of the Seedalso enhances the rate of deteriorative reactionsoccurring in seeds as temperature increases.The seed storability is considerably determinedby the kind or variety of seeds. Some seeds arenaturally short-lived, e.g., onion, soybeans,peanuts, etc., whereas some seeds like, tallfescue and annual rye grass, appear very similarbut differ in storability. Genetic make-up ofvarieties also influences storability.Effect of Moisture ContentDeteriorative reactions occur more readily inseeds at higher moisture content andsubsequently, this condition constitute hazard tothe longevity of seed survival (Vashisth andNagarajan, 2009).This article can be downloaded from http://www.ijlbpr.com/currentissue.php379
Int. J. LifeSc. Bt & Pharm. Res. 2013C P Malik and Jyoti, 2013known as equilibrium moisture content. The lowerthe moisture content, the longer seeds can bestored provided that the moisture level can becontrolled all through the storage period.Seeds stored at high moisture contentdemonstrate increased respiration, heating, andfungal invasion resulting in reduced seed vigorand viability. After physiological maturity the rateof seed quality loss depends on the degree ofunfavorable environmental conditions surroundingthe seed. Environmental moisture, predominantlyintermittent or prolonged rainfall, during the postmaturation and pre-harvest period, is quitedetrimental to seed quality and cause rapiddeterioration. When exposed to humid conditions(heavy rain), dried seeds can absorb enoughmoisture to reach 27% and subsequently expandin volume. At this moisture level, seed respirationis hastened. Cotyledonary reserves will beconsumed, not only by the seed itself, but alsoby fungi allied with the seed. It has been reportedthat seed moisture content of about 6-8% isoptimum for maximum longevity of most cropspecies. Below 4-6% seed moisture content lipidautoxidation becomes a damaging factor andseeds become more susceptible to mechanicaldamage.Effect of Organisms Associated with SeedsOrganisms associated with seeds in storage arebacteria, fungi, mites, insects and rodents. Theactivity of these entire organisms can lead
Int. J. LifeSc. Bt & Pharm. Res. 2013 C P Malik and Jyoti, 2013 SEED DETERIORATION: A REVIEW Jyoti1 and C P Malik1* Review Article Seed deterioration is an undesirable and detrimental attribute of agriculture. This process is a separate event from seed development and germination. Losses in s
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