Beating Fungal Diseases Naturally
Imagine a farmer who has spent months nurturing precious yam plants, only to watch them succumb to relentless black spots spreading across leaves or mysterious rot destroying stored tubers. This heartbreaking scenario plays out repeatedly across tropical farms, where two fungal villains—anthracnose and tuber rot—wreak havoc on one of the world's most important staple crops.
Yams represent food security and cultural significance across West Africa, the Caribbean, Asia, and Latin America. Nigeria alone produces nearly 75% of the world's yams.
When Colletotrichum gloeosporioides attacks a yam plant, the effects are visibly devastating. The fungus begins as small brown spots on leaves that rapidly expand, merging into extensive blackened areas.
Critical Timing: Anthracnose typically strikes during the critical growth phase when plants should be channeling energy into tuber bulking 1 .
Infected plants struggle merely to survive, resulting in significantly reduced tuber size and quantity.
Botryodiplodia theobromae specializes in attacking tubers during storage, often entering through wounds incurred during harvesting.
Stealthy Nature: Farmers may believe they've successfully navigated the growing season only to discover their stored harvest progressively deteriorating 1 .
The economic impact extends beyond immediate household food supplies to affect commercial yam production and market viability 1 4 .
Calcium facilitates the formation of calcium pectate, providing structural stability to plant cell walls 1 .
Calcium-treated yam plants produce higher levels of protective compounds like flavonoids, lignin, and tannins 1 .
The nitrate component contributes to chlorophyll production and overall plant vigor 1 .
Antimicrobial properties
Strengthens cell walls
Inhibits fungal enzymes
Natural defense compounds
Comprehensive study focusing on the Dioscorea alata variety 'Alakisa'—known for its early susceptibility to fungal diseases 1 .
Conducted on a plot that had been monocropped with yams for two consecutive years, representing realistic farming conditions 1 .
3×3 factorial design with three replications, examining three different soil application rates of calcium nitrate (0, 1, and 2 kg ha⁻¹ of calcium) combined with three foliar spray concentrations (0, 100, and 500 mg L⁻¹) 1 .
Soil amendment at three months after planting (MAP), when plants are establishing their growth trajectory, and foliar spray at five MAP, coinciding with the period of heightened vulnerability to anthracnose 1 .
The combination of soil amendment and foliar spraying demonstrated significant reductions in anthracnose severity.
Most treatment combinations resulted in resistance-level scores (1) or moderate susceptibility (2), a substantial improvement over the high susceptibility typically seen without intervention 1 .
Interestingly, the most effective combinations weren't necessarily the highest dosage rates, suggesting that balance and timing are crucial rather than simply applying more 1 .
Tubers from calcium nitrate-treated plants showed remarkably low infection rates (1.03%) and virtually no weight loss (0%) when inoculated with B. theobromae 1 .
This represents one of the most successful reductions in tuber rot reported from calcium fertilization research, highlighting the potential for significantly extending yam storage life 1 .
| Soil Amendment (kg ha⁻¹) | Foliar Spray (mg L⁻¹) | Anthracnose Severity Score | Resistance Category |
|---|---|---|---|
| 2 | 0 | 1 | Resistant |
| 0 | 100 | 1 | Resistant |
| 1 | 100 | 2 | Moderately susceptible |
| 1 | 500 | 2 | Moderately susceptible |
| 2 | 500 | 3.67 | Susceptible |
| 0 | 0 | 3-5 | Moderately to very susceptible |
Beyond disease protection, the calcium nitrate treatments delivered impressive yield outcomes. The average yield reached 18.24 tons per hectare, well within the potential range of 16-25 tons per hectare achieved with conventional NPK fertilizers under continuous yam monocropping systems 1 .
This demonstrates that the disease protection benefits don't come at the expense of productivity.
tons/ha
For farmers working with early susceptible varieties like Alakisa, the research suggests:
The potential for reduced fungicide use represents a significant advantage for both farmer economics and environmental health 1 .
When farmers can successfully implement calcium nitrate strategies, the benefits extend beyond individual farms:
| Material/Reagent | Function/Purpose | Application Details |
|---|---|---|
| Calcium nitrate fertilizer | Soil amendment and foliar spray | Provides calcium and nitrogen nutrition; enhances plant defense mechanisms |
| Polysorbate 20/Tween 20 | Surfactant | Helps foliar solutions adhere to leaf surfaces (used at 0.01%) |
| Fungicides (e.g., Benomyl) | Seed treatment protection | Prevents fungal infections in seed setts before planting |
| Soil auger | Soil sample collection | Obtains representative soil samples from experimental plots |
| Ethanol (80%) | Surface sterilization | Sterilizes tools and tuber surfaces for inoculation studies |
| Cork borers | Inoculation tools | Creates standardized wound sites for pathogen tests |
The battle against yam diseases represents more than just an agricultural challenge—it's a struggle for food security, economic stability, and cultural preservation. The compelling evidence for calcium nitrate fertilizer offers hope for a natural, accessible, and effective weapon in this fight. By understanding and harnessing the innate defense systems of plants themselves, we open new possibilities for sustainable agriculture that works with nature's wisdom rather than against it.