Effect of storage on seed viability and vigour in different Ethiopian wheat and maize cultivars

Abstract

English: Seed viability and vigour loss during storage, is one of the several factors limiting crop yield in Ethiopia. Ambient storage conditions (high temperature and relative humidity) as well as high moisture content during storage are considered to be the most important factors causing inferior quality of seeds (Anonymous, 1995). This supplied the rationale to study the effect of ambient temperature (more or less similar to that applying in Ethiopian conditions) and low temperature (4°C) on seed viability and vigour as well as biochemical and physiological aspects related to seed viability and vigour of Ethiopian bread and durum wheat as well as maize cultivar seeds. Additionally, the effects of storage in open and closed containers at different temperatures were also investigated. Seeds from three bread and durum wheat as well as two maize cultivars were stored at low (4°C) or ambient temperatures (18-30°C) in open or closed containers for a period of six months. Seed viability and vigour as well as biochemical and physiological aspects related to seed viability and vigour were measured before (fresh seeds) and after different storage treatments. Seed viability (germination percentage) and vigour (germination index and dry shoot mass) of seeds from both bread and durum wheat cultivars stored in open containers at ambient temperature were not significantly influenced while the other storage treatments affected the viability and vigour to various degrees. A more or less similar tendency was observed for seeds of the two maize cultivars, when only the raw data was considered. The mentioned storage condition also maintained most of the seed metabolite levels measured in this study. The lower relative humidity of the ambient storage environment contributed to maintain the moisture level of seeds at a much lower level compared to those aged at low temperature. This situation contributed to seeds aged in open containers at ambient temperature in retaining their viability and vigour during the six month storage period, indicating the need to dry seeds to a lower moisture content level before storage and/or the need for dehumidifying the storage environment, especially under Ethiopian storage conditions. Like the other two vigour tests, the measurement of electrical conductivity and the respiration rate clearly showed cultivar variations. However, they did not seem to clearly distinguish between the vigour of seeds stored under different conditions. Future work should focus towards developing a range of correlating seed vigour test methods under local conditions. In addition, the results of laboratory seed vigour tests should be correlated with field emergence in order to assess the quality of seeds with respect to its field performance potential. Biochemical tests performed in this study did not seem to correlate with the viability and vigour of seeds aged under different conditions. However, the relatively higher metabolite content of some cultivars, such as HAR-1685 (bread wheat) and E-26 (durum wheat) appeared to have contributed to their higher viability and vigour. Future research might focus on elucidating the biochemical and physiological processes underlying seed deterioration and consider developing new and cheaper screening methods for seed viability and vigour. It should also be considered to correlate future findings regarding physiological changes in stored seeds with mechanisms of seed deterioration in order to understand the mechanism of seed deterioration better in terms of biochemical process and metabolite content changes.Afrikaans: Die verlies van saad kiemkragtigheid ("viability") en vitaliteit ("vigour") tydens berging, is een van die faktore wat oesopbrengste van landbougewasse in Etiopië beperk. Saadberging by heersende omgewingstemperatuur (hoë temperatuur en relatiewe humiditeit) asook die hoë voginhoud van saad word beskou as die belangrikste faktore wat aanleiding gee tot swak saadkwaliteit (Anoniem, 1995). Laasgenoemde het die rasionaal verskaf om die effek van bergingstoestande (kamertemperatuur, wat min of meer ooreenstem met heersende toestande in Etiopië, asook berging by lae temperatuur, 4°C) op saad kiemkragtigheid en vitaliteit in brood en durum koring, asook mielie cultivars, te ondersoek. Daarby is die invloed van berging in oop en geslote houers by verskillende temperature op saad kiemkragtigheid en vitaliteit ook ondersoek. Aandag is ook gegee aan die invloed van berging op biochemiese en fisiologiese aspekte wat met saad kiemkragtigheid en vitaliteit verband hou. Saad van drie Etiopiese brood- en durum koring, asook twee mielie cultivars, is by lae temperatuur (4°C) of kamertemparatuur (18-300C) in oop en geslote houers geberg vir ses maande. Saad kiemkragtigheid en vitaliteit, asook biochemiese en fisiologiese aspekte wat hiermee verband hou/is deur middel van verskillende tegnieke voor (vars saad) en na berging bepaal. Saad kiemkragtigheid (persentasie kieming) en vitaliteit (kiemingsindeks en droë biomassa van jong saailinge) van beide brood en durum koringsaad is nie noemenswaardig deur berging in oop houers by kamertemperatuur beïnvloed nie maar wel deur die ander bergingsomgewings. 'n Min of meer soortgelyke tendens is by sade van die twee mielie cultivars waargeneem. Metabolietvlakke het by beide koring en mielies tog tydens die bergingstydperk variasies getoon. Die laer relatiewe humiditeit van die kamertemperatuur bergingsomgewing het daartoe bygedra dat die voginhoud van sade ook op 'n laer vlak gehou is in vergelyking met die bergingsomgewing by lae temperatuur. Hierdie situasie het waarskynlik daartoe bygedra dat berging in oop houers by kamertemperatuur die saad kiemkragtigheid en vitaliteit nie nadelig beïnvloed het nie. Laasgenoemde dui daarop dat vooraf droging van sade, om die voginhoud op 'n laer vlak te kry voor berging begin, of die verlaging van die relatiewe humiditeit van die beegingsomgewing, moontlikhede is om saadkwaliteit minstens tydens die stoorperiode in Etiopië te behou. Die tegnieke om saad vitaliteit te meet, en veral elektriese konduktiwiteit en respirasietempo metings, het duidelike cultivar verskille uitgewys maar het nie werklik duidelik tussen die vitaliteit van saad wat op verskillende maniere geberg is onderskei nie. Toekomstige navorsing behoort daarop te fokus om 'n reeks korrelerende tegnieke te ontwikkel wat wel hierdie onderskeiding kan maak. Verder behoort die uitkoms van hierdie tegnieke met saad prestasie onder veldtoestande gekorreleer te word ten einde die werklike potensiaal van saad te evalueer. Biochemiese toetse wat in hierdie studie uitgevoer is het egter ook nie te alle tye positief met die kiemkragtigheid van saad, wat op verskillende maniere geberg is, gekorreleer nie. Die relatief hoër metaboliet inhoud in sade van sekere cultivars, soos HAR-1685 (brood koring) en E-26 (durum koring), het egter positief met kiemkragtigheid gekorreleer. Toekomstige navorsing behoort daarop te fokus om biochemiese en fisiologiese prosesse onderliggend aan saad kiemkragtigheid en vitaliteit te ondersoek ten einde nuwe, en hopelik vinnige en goedkoop, metodes te ontwikkel. Dit behoort ook oorweeg te word om in die toekoms besondere aandag te gee aan onderliggende fisiologiese prosesse wat met saad agteruitgang tydens storing verband hou, ten einde die meganisme hiervan beter te verstaan. Daar is aanduidings dat koolhidraat metabolietvlakke asook proteïeninhoud as parameters kan dien om saadagteruitgang te meet.