Mutation breeding increases drought resilience in wheat
Another phase of an extended project by ACCI students to breed climate-smart wheat with bigger root mass is nearing completion.
For her PhD research, Boluwatife OlaOlorun, who came to the University of KwaZulu-Natal from Nigeria in July 2017, has focused on inducing genetic variation in wheat, using mutation breeding to harness the traits of drought tolerance and carbon sequestration.
Her work adds to that done by ACCI graduates Dr Learnmore Mwadzingeni, Dr Isack Mathew and Kwame Shamuyarira (MSc), all three of whom have researched different aspects of the overall project. OlaOlorun’s work is being supervised by ACCI deputy-director Professor Hussein Shimelis and ACCI director Professor Mark Laing.
The long-term goal is to develop wheat cultivars that have bigger root systems and are better able to withstand drought and sequestrate atmospheric carbon in the soil, thereby helping to mitigate the effect of climate change.
In plant breeding the preoccupation with increasing yield has meant that the size of root mass has decreased in many varieties. Now, that trend is being reversed to increase crop resilience to climate change through yield gains, drought tolerance and carbon sequestration.
Mwadzingeni kicked off the project in 2014 by conducting a genetic analysis of 100 or so wheat genotypes for grain yield and yield influencing traits, obtained mainly from CIMMYT’s drought and heat tolerance nurseries. Mathew laid the groundwork for breeding for carbon sequestration by evaluating these genotypes and identifying the ten best. These are currently being used by Shamuyarira, who has crossed them to produce 90 progeny that he is developing further for his PhD research.
OlaOlorun came to plant breeding by accident when her desire to study veterinary medicine was thwarted by lack of access. She started studying plant breeding, intending to change, but got interested and carried on. “I felt there was a niche as plant breeding was a silent field in agriculture. Not many people were going into it and very few women.”
Her PhD focus has been on working with chemical mutagenesis using Ethyl methanesulfonate (EMS) to create genetic variability in wheat genotypes. The aim of her research is to develop early generation wheat mutants for drought tolerance and improved biomass allocation— i.e. produce bigger roots and better root-to-shoot allocation.
“Chemical mutagenesis is a fast way to create genetic variability when compared to hybridisation. It’s done in the lab, where a chemical causes a change in DNA sequence after seed mutagenesis treatment,” she explains.
This is done using protocols including varying temperatures, times and doses of EMS so as to identify optimal conditions.
OlaOlorun started her preliminary research by choosing three of the genotypes selected by Mwadzingeni that had potential for drought tolerance.
“The focus was on optimising EMS treatment conditions (temperature, dose concentration and time of exposure) in three different wheat genotypes with a particular treatment condition for each genotype,” she says. This produced 81 different combinations that she planted to see what worked best.
“After the chemical application I could see promising seedlings at an early stage. Seedlings from treatment conditions which gave 50% germination and vigour were considered ideal. Once promising seedlings had been selected I went back to the lab and exposed a large number of seeds to those conditions.”
An optimal treatment for each of the three genotypes was determined and 2500 seeds were produced for each treatment. These seeds were then planted and exposed to different conditions in the field and the greenhouse.
OlaOlorun was targeted to get to the fourth generation so she had to plan to produce two generations per year. The first generation was planted in March 2018 and harvested after six months. The fourth generation was harvested recently.
“With the first generation, the plants looked the same with no abnormalities. In the second generation I began to see variations in both quantitative and qualitative traits and segregation patterns, however some plants looked promising. Based on their physical appearance, I selected seeds from 180 healthy and normal-looking plants, as well as those with high yield-related traits,” she says.
The third and fourth generation seeds were planted in controlled and field conditions and fourth generation plants are being analysed to determine high root and shoot biomass after being subjected to drought and non-drought conditions.
“The end goal of my research is to recommended a certain number of individual mutants that have been improved for drought tolerance and biomass allocation,” says OlaOlorun.