Mahela/Freshworld Kiwi Disease investigation By Dry Tech Aerogels (DTA)

Mahela/Freshworld Kiwi Disease investigation By Dry Tech Aerogels (DTA)

23 April 2024

Investigation Team:

Maritza

Thys Katzke

Willie Coetzee

Wilma Dorfling

1. Mandate:

Pig-up a crate half full of Kiwi fruit from Mahela Kiwi farm at Magoebas Kloof and investigate the symptom of a small dark indent that  appear on the kiwi skin. This indent grow larger during harvesting and packaging and become a full blown disease. Recommend a solution for the problem.

Figure 1

The middle sections was treated with Atom8, Leave Wash when still green that shown very little infection, Top section (control) was more ripe and bottom section (Control) even more ripe showing more symptoms.

2. Identification of disease:

The fruit was still green and hard at collection and after an evaluation it seems to be healthy and only a few indents could be found. At DTA premises we placed the fruit in an ambient temperature room at approx. 26ᵒC where they lie for six days until becoming soft and showing many more indents and infections, especially the untreated ones. The room is 100% free from external fungus and could be only get contaminated by the very same fruit. Some of the fruit were treated with Atom8, Leaf Wash and place in the middle sections of the carton.

After investigation I found that the symptom refer to a common disease, Botrytis Soft Rot is a pre-harvest disease that exponentially grow at the postharvest handling and storage. The disease occurring in kiwifruit that can cause substantial losses and is difficult to detect when initially contaminated at a very early stage. In this study, infection of the disease on kiwifruits was measured.

Botrytis Fruit Rot identified to infected the sample fruit, also known as Gray Mold decay, is a soft fruit rot that can result in significant crop losses during storage. Symptoms of decay and signs of the pathogen develop as shrivelled fruit that may have Gray Fungal growth mostly at the stem end and occasionally around the sepals or over the entire surface of the fruit. Diseased internal fruit tissues appear water-soaked and dark green. In advanced stages of the disease black, irregular-shaped sclerotic of the fungus up to about 0.2 inch (5 mm) in diameter may form on the infected, indented fruit.

Figure 2

Botrytis Fruit Rot, also known as Gray Mold decay, is a soft fruit rot that can result in significant crop losses during storage

Figure 3

Diseased internal fruit tissues appear water-soaked and dark green

3. Test results after 7 days under ambient temperatures 26-28ᵒ

Presenting the results of a test conducted to assess the effectiveness of a treatment against Botrytis Soft Rot contamination in fruit. Here’s a breakdown of the information provided:

1. Total Fruit supplied were tested: There were 42 fruits tested in total.

2. Untreated Fruit Contamination: Out of the total 42 fruits, 30 showed symptoms of Botrytis Soft Rot contamination. This indicates a contamination rate of 100% in the untreated group.

3. Treated Section with Leaf Wash (Middle): Within the tested fruits, there was a section (the middle portion) that received treatment.

4. Treated Section Results: Out of the 12 fruits in the treated section, only 4 showed symptoms of contamination after 6 days. This indicates a contamination rate of 33% in the treated group. (Middle group)
5. Observations: Despite the treatment, there was still a significant level of contamination in the treated group. Additionally, it’s noted that the treatment did not prevent internal contamination of the fruit. This suggests that while the treatment may have had some effect in reducing contamination, it was not entirely effective, especially in preventing internal growth of the fungus. This means that contamination took place at a fairly young stage.

In conclusion, while the treatment showed some improvement compared to untreated fruit, further refinement or alternative methods may be necessary to achieve a satisfactory level of control over Botrytis Soft Rot contamination in fruits, particularly addressing internal contamination.

1. Comments on the Disease

Symptoms cannot be seen on immature fruit. Infections already begin but can’t be seen in the pre-harvest green stage, however, it can get infected at bloom and continue during fruit maturation and ripening in storage. Early infections generally do not cause immediate decay, but the pathogen can resume growth as the fruit ripens, usually in cold storage, causing postharvest rot. Infections commonly develop from the stem end where the stem is snapped off during harvest or from surface wounds that occur during harvest and handling. Infections may also start on the fruit sepals and invade the fruit stem.

The pathogen Botrytis cinerea can tolerate low storage temperatures from -1° to 1°C and grow over a wide range of temperatures commonly used to store and market kiwifruit. The pathogen can overwinter in the vineyard on fruit decaying on the ground and vines, on infected plant tissues including weeds, and leaves blown into the vineyard from neighbouring orchards (e.g., citrus, almond, and stone fruit). Fruits that have been partially consumed by rodents and birds and were left behind in the vineyard are even more likely to harbour the pathogen.

The rapid and accurate detection of this pathogen will lead to better disease monitoring and control efforts. A loop-mediated isothermal amplification (LAMP) method was then developed to rapidly and specifically identify B. dothidea. These results offer value to further research into kiwifruit ripe rot, such as disease prediction, pathogen rapid detection, and effective disease control. With kiwis rapid detection is not easy as the fungus can penetrates at a very young stage of the fruit development.

2. Facts

Based on the additional information provided, here are some implications for the treatment of Botrytis cinerea contamination:

1. Early Detection and Treatment: Since Botrytis cinerea invades at a very early stage and cannot be treated once it has penetrated the skin, it’s crucial to detect and treat the fruit before this stage. This might involve implementing preventive measures or treatments during the growth and development stages of the fruit especially with a systemic killing product.

2. Preventive Treatments: Given that the manifestation of the disease occurs post-harvest and during ripening, it’s essential to implement preventive treatments or measures before this stage. This could involve applying treatments during growth or transportation to prevent the onset of symptoms. A systemic product would be ideal and can be treated at very an early stage.

3. Internal Penetration: Understanding that the disease can already be present internally before any external symptoms manifest indicates the need for treatments that can penetrate and target the pathogen inside the fruit. Merely treating the surface or using contact treatments may not be sufficient to address internal contamination.

4. Treatment Timing: Since it’s already too late for treatment once ripening starts, treatments should be applied well before this stage, ideally during early stage of fruit forming to prevent the development of the disease during post-harvest.

In light of this knowledge, treatment strategies should focus on early detection, preventive measures, and treatments capable of penetrating the fruit to target the pathogen internally before symptoms appear. This may involve a combination of approaches such as fungicides, cultural practices, and environmental management to effectively control Botrytis cinerea contamination in fruits.

3. Recommended Management (Solution)

4. Recommendation

Atom8 Leaf Wash with Chitosan is an absolute organic product and can be used on plants as early as possible, in the case of growing kiwis it will prove to be very effective due to its double action killing method of pathogens systemic and contact. Spraying according to a program to control the soft rot disease. As can be seen from fig 4, 70% of the product were treated with Leaf Wash has not contracted the disease but about 30% had it internally before treatment.

Figure 4

Four from 12 outside treated fruit contracted the fungus at a very young stage and

was not protected or treated internally. Also apparent was that the affected area stayed dormant and didn’t developed any further.

Based on the provided information about the DTA product Atom8 Leaf Wash, which contains chitosan (CTS) along with stabilised HOCL and zinc phosphate, it appears to offer a systemic solution for controlling Botrytis cinerea (Soft Rot) in kiwi fruit. Here’s a breakdown of how this product and its components can address the challenges posed by Soft Rot:

1. Systemic Solution: Atom8 Leaf Wash, containing chitosan, is described as a systemic product. This implies that it can be absorbed and distributed throughout the kiwi plant, providing protection against Botrytis cinerea at various growth stages, including early stages when the pathogen may lie latent within the fruit.

2. Chitosan (CTS): Chitosan is a natural compound known for its systemic antibacterial and antifungal properties. It forms a film on the fruit surface, acting as a physical barrier against pathogens like Botrytis cinerea. Additionally, chitosan can trigger plant defence responses, further enhancing the plant’s resistance to diseases.

3. Stabilised HOCL: Stabilised Hypochlorous acid (HOCL) is included for its antimicrobial properties and immediate killing response. It can contribute to the overall efficacy of the product in controlling pathogens, including Botrytis cinerea, by providing additional antimicrobial activity.

4. Zinc Phosphate: Zinc phosphate serves to enhance the blocking of UV radiation, which can help preserve the quality of kiwi fruit during hot days and storage. Additionally, it may contribute to the overall effectiveness of the product in preventing Soft Rot by creating an environment less conducive to pathogen growth.

5. Chitosan Composite Film (CCF): The use of a chitosan composite film sprayed before pathogen infection suggests a preventative approach to controlling Soft Rot. By applying the composite film before the fruit is infected, it forms a protective barrier that inhibits pathogen ingress and development.

Overall, the combination of chitosan, stabilised HOCL, and zinc phosphate in Atom8 Leaf Wash offers a multi-faceted approach to controlling Soft Rot in kiwi fruit. Its systemic nature, along with its preventative application, makes it a promising solution for effectively managing this challenging postharvest disease while also being economically efficient and environmentally friendly.