Genetic variation & tolerance indices interactions among wheat accessions under drought

by Victor Olugbenga Olumekun, Abiola Toyin Ajayi and Oluwasegun Victor Ibidapo

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In recent times, wheat has gained more acceptance and utilisation over the traditional staples such as tubers and  other cereals in Africa as a  consequence of increased demand for dietary enhancement  due to urbanisation and increased population in regions  where staple was predominantly known to come from  maize. The pressure on wheat has now  risen to the level in which local production is grossly  overwhelmed by demand, hence the reliance on  importation to cater for the deficit in local supply. Developing nations in general have therefore  progressively become significant net importers of wheat,  accounting for 43% of their food imports. Africa’s wheat  importation is anticipated to increase by 23.1 million  metric tonnes by 2050 with both the largest rate of  population growth and wheat consumption per person.

Wheat provides 20 and 21% of the protein and nourishment  calories respectively in human diet to over three billion  individuals residing in ninety countries of the world . Global wheat production is estimated to be about  761.5 million tonnes and roughly 21% of the food consumed  worldwide depend on wheat as raw material. It serves as a major  raw material in cakes, animal feeds, pasta, bread, spaghetti,  biscuits, semovita and macaroni. The stalks after harvest are  used in mulching, construction and bedding for animals. In Nigeria, wheat cultivation has been going  on for millennia, and there are reports that its cultivation started before 200 BC, although the present  cultivated varieties are comparatively latest introductions  .  

In spite of the heavy consumption pattern, national wheat  production in Nigeria has been limited because of restrictions  arising from climatic demands, agronomic procedures and the  preference for vegetable cultivation in the majority of the  wheat producing regions. Introduction of better agronomic procedures, appropriate land preparation,  and other cultural practices revolving around sowing,  nourishment, watering regime, crop protection, crop yield  and post yield technology have been the main focus of  workers.


Despite the importance of wheat in Nigeria, its  productivity can be stunted by drought which according to  Ajayi et al. in 2018, drought is a state of persistent  insufficiency in soil moisture preventing effective crop  growth and development, hence significantly reducing  yield. Advancement of climatological techniques make it  possible to predict an upcoming drought, nevertheless, its overwhelming effect on the  economy persists.  Adaptation and survival of plants under drought condition  requires that plants possess inherent ability to deploy diverse mechanisms which can be morphological,  physiological and molecular.

Rapid decrease in wheat productivity is a  consequence of impeded growth caused by drought. The main cropping season of wheat in Nigeria falls between November and March (the dry  season) hence there is a heavy dependence on irrigation  which could be expensive to deploy. The drier Northern  region is favourable to wheat cultivation being a temperate  crop, but unfortunately this region is  characterised by poor rainfall distribution during the  cropping season.

Information on genetic variation and heritability of  yield characteristics in wheat under drought stress is  limited in Nigeria. Adequate genetic information about  crop yield characters of wheat will make a positive  contribution to its productivity. Grain yield determination  under drought stress is hard because its manifestation is a  consequence of interactions between many other  contributing characters.

Therefore, the  choice of genotypes based on yield traits might be more  efficient than the direct selection for yield. Its selection under drought stress is also laborious and time consuming requiring many decades of  work and evaluation in multiple  environments because of its propensity to influence the  genotype by environment interaction. Correlation offers information on the linkage between  morphological characters and economic characters that  allow indirect selection.

The Principal Component  Analysis (PCA) is an additional multivariate process  effective for the analysis of relative contribution of  individual features under prevailing conditions. This  technique identifies a tiny set of variables which represent  a big percentage of the complete variance in the original  variable. Correlation and PCA have  been used successfully to select drought tolerant genotypes  of many crop species.  

Many criteria have been used in crop species for  selection under drought stress. Notable among these are  markers assisted selection (MAS), expression profiling of drought responsive genes, biochemical and molecular traits, physiological traits,  morphological traits, root phenotype and architecture, and stress tolerance index (STI) of  yield traits. STI was  highly appropriate for selecting high yielding tolerant wheat  and cowpea genotypes under stress and well-watered  conditions. In Nigeria,  however, there is restricted data on the use of STI for  assessment of drought tolerance in wheat genotypes, and no  report exists that utilises STI of quantitative traits in selection  of wheat genotypes for drought tolerance. 


The study, aimed to evaluate the amount of genetic variation for drought  tolerance among genotypes; heritability of suitable  characteristics for choice, and association among stress  tolerance indices of yield traits which should be useful tools in  establishing a breeding programme for drought tolerance in  wheat, has been carried out by the authors. The result gotten and the information provided in the study would be useful  for effective selection of wheat genotypes for drought-prone  environments in future breeding programs

References
Victor Olugbenga Olumekun, Abiola Toyin Ajayi and Oluwasegun Victor Ibidapo. Genetic variation and tolerance indices interactions among wheat  (Triticum aestivum L.) accessions under drought stress. Journal of Pure and Applied Agriculture (2020) 5(3): 91-101 ISSN (Print) 2617-8672, ISSN (Online) 2617-8680 

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