Influence of drought stress after anthesis on growth and yield of wheat cultivars from Ethiopia

Abstract

English: The situation in Ethiopia, where post anthesis water stress caused by early cessation of rainfall is a serious constraint to crop production, supplied the rationale to study the performances of two Ethiopian bread wheat cultivars under induced post-anthesis water deficit stress. The study also involved the investigation of the possible role of ComCat in circumventing the effects of the stress condition as well as its effects on pre- and post-anthesis growth and development of the cultivars, including its effects on the protein and starch contents in seed. The two Ethiopian bread wheat cultivars (HAR-2508 and ET-13) were grown under glass house conditions and subject to post anthesis water deficit stress while the effects of treatment with ComCat, a biocatalyst from plant origin, were followed during the vegetative growth phase as well as at harvest. Observations made through the different growth stages indicated that the two cultivars were growing at more or less similar rates during the early growth stages after which significant differences between cultivars were observed during later growth stages with ET-13 being superior to HAR-2508 in terms of most of the vegetative as well as yield parameters under both non-water stress and stress conditions, including the most important yield parameter, i.e. grain yield per unit area. The cultivars also showed significant differences in their grain protein and starch contents. The cultivar ET-13 was superior to HAR-2508 in seed starch content expressed as g g-1FW while the latter was superior in terms of starch content expressed on a mg seed" basis. On the other hand, seeds of HAR-2508 were superior to those of ET-13 in total protein content (expressed on both a mg g-1and mg seed-1 basis) as well as in water soluble protein content (mg seed"), Moreover, the water stress condition induced at growth stage 60 caused significant reductions in vegetative growth and yield components in both cultivars, with the reductions being more pronounced in the cultivar ET-13. On the other hand, the ComCat treatments at different growth stages tended to enhance root development and tended to circumvent the negative effects the water stress treatment had on the vegetative growth of the plants. However, ComCat had no significant enhancing effect on the grain yield per unit area, which was in contrast to what was observed in field trials on both wheat and maize as well as to claims made by the manufacturers of the compound (Agraforum, Germany). Lack of a significant effect of ComCat on grain yield under glass house conditions was presumed to be related to the restriction imposed on the growth of roots of the plants by the small sized pots in which the plants grew. The biocatalyst, when applied at early growth stages and particularly at growth stage 13, however, significantly increased the total protein content in seeds of water stressed plants. Finally, based on the observations made in this study and because of its shorter life cycle, the cultivar HAR-2508 seems to be a better choice to ET-13 in wheat growing areas of Ethiopia where terminal water stress, particularly through early cessation of rainfall, is prevalent. However, full recommendation of this cultivar to such areas require the investigation of its performance under other prevalent limiting factors such as diseases, weeds and bread making qualities. With regard to the biocatalyst, ComCat, although it showed no significant effect in improving grain yield per unit area under glass house conditions, based on the claims of the manufacturers and also on the findings during field trials (results not shown) as well as its significant effect in enhancing root development and increasing protein content of seeds as observed in this study, it appears essential to test it further in field trials under Ethiopian conditions.

Afrikaans: Die situasie in Ethiopiê, waar droogtestremming na blomvorming algemeen is as gevolg van die lae reênval gedurende hierdie periode, is 'n ernstige probleem wat gewasproduksie benadeel. Laasgenoemde het dan ook die rasionaal verskaf vir hierdie studie en meer spesifiek die vergelyking van twee Ethiopiese broodkoring cultivars wat na blomvorming aan gesimileerde droogtestremming blootgestel was. Die studie het ook 'n ondersoek na die moontlike rol van ComCat, om die effek van droogtestremming teen te werk, ingesluit asook die invloed daarvan op die groei en ontwikkeling van die twee cultivars gedurende die voor- en nablom groeifases en die effek op die proteïen en styselinhoude van sade. Die twee Ethiopiese broodkoring cultivars (HAR-2508 en ET-13) is onder glashuis toestande gekweek en tydons die nablom fase aan droogtestremming blootgestel terwyl die effek van behandeling met ComCat, 'n natuurlike biokatalis wat uit plantmateriaal vervaardig is, tydens die vegetatiewe groeifase en met oes gemoniteer is. Die twee cultivars het veral gedurende die vroeê groeifases teen min of meer dieselfde tempo's gegroei waarna betekenisvolle verskille gedurende die latere groeifases waargeneem is. In terme van meeste van die vegetatiewe en oesopbrengs parameters, insluitende oesopbrengs per oppervlak eenheid, het ET-13 beter as HAR- 2508 presteer onder beide kontrole- en droogtestremmingstoestande. Betekenisvolle verskille tussen die twee cultivars ten opsigte van die proteïen en styselinhoude van saad is ook waargeneem. 'n Hoër styselinhoud, uitgedruk as g g-1vars massa, is in sade van die cultivar ET-13 gemeet maar die styselinhoud was weer hoër in sade van HAR-2508 toe die inhoud as mg saad" uitgedruk was. Andersyds is 'n hoêr totale proteïeninhoud (uitgedruk as beide g g-1 vars massa en mg saad-1) asook 'n hoêr wateroplosbare proteïeninhoud (mg saad-1) in sade van HAR-2508 gemeet. Die droogtestremmingsbehandeling op groeistadium 60 het betekenisvolle reduksies in terme van beide vegetatiewe groei en oesopbrengsparameters in albei rultivars teweeggebring maar die reduksies was meer geaksentueer in HAR-2508. Die ComCat behandelings by verskillende groeistadia het wortelontwikkeling geïnduseer en ook die neiging getoon om die negatiewe invloede van die droogtestremmingsbehandeling op vegetatiewe groei in 'n mate teë te werk. Maar, ComCat het nie die finale oesopbrengs per oppervlak eenheid verhoog nie en dit was in kontras met die bevindinge op beide koring en mielies onder veldtoestande asook die aanspraak in hierdie verband deur die vervaardigers van die produk (Agraforum, Duitsland). Die onvermoë van ComCat om onder glashuistoestande tot oesopbrengsverhoging aanleiding te gee word toegeskryf aan die beperkinge wat op die plante deur die relatief klein potte geplaas is. ComCat behandeling, en veral die vroeë behandeling op groeistadium 13, het egter aanleiding gegee tot 'n betekenisvolle verhoging van die totale proteïeninhoud in sade van plante wat aan droogtestremming blootgestel was. Ten slotte, gebaseer op die waarnemings tydens hierdie studie asook vanweë die korter lewensiklus, blyk dit dat die cultivar HAR-2508 aanbeveel behoort te word vir verbouing in die streke van Ethiopieë waar droogtestremming teen die einde van die groeisiklus van koring aan die orde van die dag is. Maar, vir laasgenoemde aanbeveling om op volledigheid aanspraak te maak behoort ander aspekte soos prestasie onder die invloed van ander beperkende faktore naamlik siektes en onkruid, asook bakkwaliteit in aanmerking geneem word. Alhoewel ComCat behandeling nie noemenswaardige oesopbrengsverhoging onder glashuistoestande teweegebring het nie, behoort die gebruik van hierdie natuurlike biokatalis verder onder Ethiopiese veldtoestande ondersoek te word. Laasgenoemde aanbeveling spruit ook voort uit die aanspraak wat in hierdie verband deur die vervaardigers van die produk gemaak is en is ook gebaseer op die bevindinge wat bekom is tydens veldproewe (resultate nie, getoon).