Expert Talk: Microbial Preparations for Onion Storage in Maharashtra

Black mold destroys thousands of tons of onions each season in warm, humid regions like Maharashtra. Chemical solutions are becoming less acceptable — but microbial protection is emerging as a safe and effective alternative. Here’s how biocontrol works in real storage systems.

Microbial Protection for Onions in Maharashtra: Why It Matters and How It Works

Warm, humid weather at harvest makes Maharashtra one of the world’s most challenging environments for onion storage. These conditions are ideal for Aspergillus niger, the black mold responsible for rapid rot, weight loss, and high post-harvest losses.

With chemical fungicides becoming less desirable or restricted, growers are turning toward microbial biocontrol - a natural, residue-free solution that protects onions when paired with proper curing and ventilation.

Why Onions in Maharashtra Need Microbial Protection

The combination of:

• high temperature,

• high humidity,

• dense harvest season,

• traditional open curing,

• and warm-storage systems (27–31 °C)

creates perfect conditions for A. niger to colonize bulbs.

Black mold attacks the outer scales, penetrates through the neck, and spreads quickly in storage rooms lacking airflow uniformity. Losses can exceed 15–25% without intervention.

Microbial treatments act as natural competitors — blocking mold spores before they enter.

Which Microorganisms Work Best Against Black Mold?

These strains show the strongest scientific and field-backed results:

1. Bacillus subtilis & related Bacillus species

• Produce natural antibiotics

• Form protective biofilms

• Colonize surfaces very quickly

• Widely used in post-harvest agriculture

2. Trichoderma spp. (T. harzianum, T-22, T. viride)

• Extremely competitive fungi

• Activate plant defense mechanisms

• Effective on a wide range of pathogens

3. Aureobasidium pullulans

• Yeast-like fungus

• Highly effective on fruit and vegetable surfaces

• Strong antagonist to storage molds

4. Antagonistic yeasts (Metschnikowia, Candida)

• Rapid colonizers

• Block infection sites on the onion skin

• Excellent for high-humidity environments

5. Clonostachys rosea

• Proven globally in post-harvest management

• Works well in warm-storage systems

These microorganisms do not act like chemicals — they build a protective biological layer that outcompetes pathogens.

How Microbial Treatments Are Applied

Timing is everything. Microbial protection works only after full curing and drying.

Standard application protocol:

1. Spray or dip onions in a microbial suspension of 10⁷–10⁸ CFU/ml.

2. Add a 1% jaggery solution as a natural sticker — helps microbes adhere.

3. Dry treated onions in shade for 1–2 hours.

4. Load into warm-storage chambers at:

   • +27 °C

   • 60–65% RH

   • strong, uniform airflow

If onions are wet, un-cured, or stacked without ventilation, no microbial product will compensate.

What Does a Pilot Project Look Like?

A typical field trial includes:

1. Selecting 2–3 candidates (e.g., Bacillus, Trichoderma, a yeast).

2. Running lab tests against local A. niger isolates.

3. Small-scale trials with 1,000–2,000 bulbs.

4. Comparing treated vs. untreated onions for 30–60 days.

5. Measuring:

   • visible mold,

   • weight loss,

   • rot progression,

   • sprouting behavior.

This approach identifies the best strain for local climate and bulb type.

Expected Results

With correct curing and stable warm-storage conditions:

• visible reduction of black mold can appear in 2–4 weeks,

• weight loss slows,

• neck rot decreases,

• shelf life improves,

• and losses often drop from 15–25% → 5–12%.

However:

Microbes are not a magic bullet.
If onions enter storage wet, immature, or poorly ventilated — nothing will work.

Want to Improve Onion Storage in Warm Climates?

Agrovent designs warm-storage systems and climate-controlled chambers for India, the Middle East, Africa, and South America.

We help clients integrate:

• curing solutions,

• optimized airflow design,

• CO₂ and temperature monitoring,

• microbial protection workflows,

• and warm-storage engineering (27–31 °C).

📞 Call: +971 50 437 7119
📧 Email: info@agrovent.com