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Hello, thank you for attending my presentation.
Today I will be answering the question: is finger millet a promising opportunity crop – otherwise termed an under-utilised, or minor crop.
So firstly, let me introduce you to finger millet.
Finger millet is small grain crop of the Poaceae family; to which most of the accessions in the core collection are found in the semi-arid regions of Eastern and Southern Africa, as well as the tropics of South-East Asia. And if we zoom into Western Kenya, we begin to see why it’s so important to study finger millet. Here, cultivation trends show that 95% of farming respondents grow finger millet. It is a staple food in the area, and therefore worth evaluating as an opportunity crop.
According to the VACS, there are 3 characteristics of a promising opportunity crop. These are that they:
- Provide health benefits
- Are resilient to modern changing conditions
- And that they are highly productive
In order to evaluate if finger millet is indeed a promising opportunity crop, I will investigate to what extent it satisfies each of these characteristics, in turn.
For each characteristic I will cover a series of questions, illustrated in this flow chart…
The first will be: does finger millet have the potential to achieve this characteristic?
Next: is this potential actually realised?
If yes, is there a large-scale impact achieved by this realised potential?
And if no, why has the potential not yet been realised; and can we improve finger millet, such that it can?
So, let’s get started with the evaluation.
Let’s start with health benefits.
Does finger millet have the potential to benefit health?
Well, fractionation of polyphenols extracted by high performance liquid chromatography shows that finger millet has a diversity of bioactive phenolic compounds. The most prevalent of these is proto-catechuric acid, which is associated with iron chelation, and therefore prevention of the Fenton reaction, and the production of reactive oxygen species. As such, phenolic compound presence certainly indicates a potential for health benefits.
Next: is this potential actually realised?
Well, Kumari et al. investigated the effects of phenols in finger millet ambali; a traditional thin porridge. They measured the ferric ion reducing antioxidant power (or FRAP), which is a measure of the plasma antioxidant capacity, across time. To improve this experiment, rather than measuring FRAP from a baseline after fasting, I would compare FRAP trajectories between poridges from different crops, to truly evaluate the realised potential of finger millet’s health benefits. However we can see that, post-porridge consumption, FRAP was raised significantly at all time points measured, indicating a realised potential to benefit health in finger millet.
Finally, does the realised potential of finger millet’s health benefits have a large scale impact?
To investigate this, I will use a recent example from Li et al. Here, they conducted a restricted cubic spline analysis to investigate the relationship between participants’ dietary total antioxidant content (or DTAC), and the odds ratio of developing type 2 diabetes mellitus. The following graph illustrates that higher dietary total antioxidant content is associated with lower odds of developing type 2 diabetes mellitus; in a non-linear fashion. However, their 95% confidence intervals are broad at the highest DTACs, suggesting sparse data in this range. Hence, a more even sample, or greater sample size, would have bolstered the conclusions of this experiment.
Ultimately, the indication that higher dietary antioxidant content,
which we know is provided by the high diversity of functional phenols in finger millet, illustrates that it can have a large-scale impact in decreasing the odds of developing type 2 diabetes mellitus; which affects approximately 24 million African citizens.
Let’s now consider the resilience of finger millet to changing conditions.
Here, I will consider whether finger millet has potential resilience to the changes of soil salinity that are arising from anthropogenic climate change.
We have known for more than 20 years that proline osmoprotection is implicated in plant salinity tolerance. Bhatt et al. have observed that under leaf tissue homogenisation, chromophore extraction and absorbance measurement, proline increases tenfold in finger millet under salinity stress. Hence, the potential for resilience is certainly there.
Now, is this potential for salinity tolerance realised?
Well, the answer is yes, but only in a genotype-specific manner.
On the left here we have genotype CO 12, which, due to its leaf scorching and necrotic symptoms, was deemed salinity sensitive. However, the Trichy genotype, shown here on the right, realised its potential for salinity tolerance – it lacked these deficits .
So, can this realised potential for resilience have a large-scale effect?
Well, the study conducted a transcriptomic analysis to eludicate the differentially expressed genes (or DEGS), between sensitive and tolerant finger millet genotypes. They found a vast array of DEGs: including 283 that were upregulated in the tolerant genotype; one of which underpinning proline biosynthesis. However, this experiment is limited in terms of a large scale impact, as transcriptomic analyses often ultimately pose more questions than they do answers. What we need to yet achieve a large-scale impact is functional annotation of all of the genes that work in congruence to provide salinity tolerance. According to the literature this is ongoing, and my opinion, shows that finger millet shows future promise as a resilient opportunity crop.
Finally, then; let’s consider whether finger millet is a promising opportunity crop, with regards to its productivity?
Firstly – is there potential for finger millet to demonstrate high productivity?
Well, Oduori finds that, when binning yield categories of 310 finger milet accessions into 8 segments (although methodologically these bins are arbitrary), the resulting frequency distribution chart is normal, demonstrating extreme outliers with much higher yields, as high as 8000kg per hectare. Hence, I argue that finger millet does have potential for high productivity.
So, is this productivity potential realised?
Well, 2 years ago Berie et al conducted the first field-based assessment of yield gains in improved finger millet varieties that have been released over 25 years in Ethiopia. Under this study they found that there was an approximately linear relationship between year of release and yield, showing an estimated annual yield gain of 30.88 kilograms per hectare per year. Despite there being no indication of a yield plateau for the varieties tested, which would insinuate the possibility of further increase in finger millet yield, the maximum yield reached only 2563.3 kg ha–1 in 2019, firmly within the 2-3000 kg/ha, average bin of Oduori’s yield potential chart. From this, we can infer that, despite subtle progress, the significant potential of finger millet for productivity is currently not being realised.
Maximising yield is therefore a crucial step in making finger millet the most promising opportunity crop it can be.
To achieve this maximisation, we must first understand why this significant potential for high productivity has not yet been realised.
Two principal mechanisms limit the realisation of the significant potential of finger millet for high productivity; these are limitations in both morphology, and genomics.
With regards to morphology,
finger millet is relatively recalcitrant. Since it is a self-pollinator, finger millet requires artificial hybridisation in breeding programmes. However, due to its infloresence morphology, manual emasculation of finger millet florets is practically very difficult. This necessitates the use of the contact method, which holds a success rate of just 2% to 3% (it is also resource and labour intensive); or genetic male sterility, which must be induced for every season/generation, and is hazardous to laboratory workers.
