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202306 Fresh Quarterly Issue 21 06 Smit
Issue 21June 2023

PHYLA focuses on phytosanitary research

A new Hortgro-funded facility protects and expands South African pome- and stone-fruit market access. By Anna Mouton.

Gaining and maintaining market access for South African deciduous fruit often comes down to phytosanitary risk management. We must demonstrate that we can export our products without simultaneously exporting unwanted pests. And we have to achieve this without compromising fruit quality or consumer health.

In practice, this requires continuous research to develop and validate postharvest treatments that will kill pests without leaving residues or damaging fruit. Previously, Hortgro outsourced much of this work, but since 27 January 2023, it can be carried out at PHYLA, a bespoke phytosanitary laboratory for the pome- and stone-fruit industries.

Fresh Quarterly toured PHYLA under the expert guidance of PHYLA manager and researcher Dr Renate Smit and phytosanitary entomology and market-access specialist Dr Shelley Johnson.

Inside the insectarium

A facility dedicated to killing insects needs a steady supply of insects to kill, so a row of climate-controlled rooms at PHYLA is allocated to breeding infamous phytosanitary pests like codling moths and false codling moths. In one of these, insectarium employee Ricardo Daniels collects pupae of false codling moths from a tray of vermiculite. He transfers them to a black tote box where they will emerge as adults.

The adult moths do not feed — they have other priorities. The insectarium staff rear the moth larvae on a special diet developed by entomologist Dr Daleen Stenekamp and technical assistant Terence Asia.

In addition to moths, the insectarium houses other pests, notably colonies of banded fruit weevils. The weevils live in a stack of transparent containers. Weevil larvae eat carrots.

“It’s one of their recorded host plants,” says Johnson. “We tried making a rearing diet with carrots and all sorts of other ingredients.” But the weevils did best on plain carrots, so now this is what they get, sometimes supplemented with carrot tops.

Besides the proper diet, pest colonies demand carefully calibrated temperature, humidity, light, and shelter.

“The idea is to rear the numbers we need for our trials,” says Smit. “We know that we’re using the best quality insects, as close to the natural state possible, because natural collection is not viable.”

High-tech treatment trials

Postharvest phytosanitary treatments generally involve fumigation or manipulating the temperature and the atmosphere. In the past, fruit were fumigated with methyl bromide, but this is no longer acceptable to most markets, so developing alternatives is a research priority.

The PHYLA team is investigating four treatment types: cold sterilisation, ozone, ultra-low oxygen either as a stand-alone or in combination with nitric oxide, and ethyl formate.

“The nice thing about this facility is that we can upscale,” says Smit. She shows off a modified two-litre container with three valves and a sampling port. “This is a small version of the ultra-low oxygen system for me to do preliminary studies.”

If a treatment works on the smallest scale, the next step is a cubic-metre box, followed by a cold room, of which PHYLA has four. Each cold room can hold four pallets of fruit under controlled atmosphere. The temperature and atmosphere are continually monitored, and Smit can check cold-room conditions on her phone.

“This facility is quite high-tech,” she says. “I can dial in and see exactly what’s happening. If anything changes, I get alerts. If I get an alarm about temperature or oxygen, I can dial in and often just reset the system from a distance.”

One cold room is modified for fumigation trials. Some fumigants, like ethyl formate, are considered explosive, so fumigation rooms must comply with stringent safety measures, including spark-proof fans and lights installed by a master electrician. However, the fumigation room runs at very low oxygen levels, so there is no real risk of PHYLA blowing up.

Johnson and Smit have already shown that ethyl-formate fumigation is effective against pests like grain chinch bugs. But rather than fumigating cold rooms or containers, they are exploring the incorporation of ethyl formate in sheets, similar to the sulphur-dioxide sheets used for table grapes.

“If you fumigate bins of fruit, the fruit still has to be packed, so you have a risk of reinfestation,” says Johnson. “If the sheets go in when the fruit is packed into cartons, their risk of reinfestation is mitigated — similar to cold treatment — because the treatment is applied to already packed fruit.”

Proof by probit

Once a treatment has been developed, researchers must prove it works before importing countries accept it. This proof is generated by probit analysis, a statistical method for estimating a treatment response. More specifically, in the case of phytosanitary pests, the probit analysis demonstrates the efficacy of a treatment.

“There are international standards and guidelines that prescribe the sample numbers that should be used in the different phases of the analysis,” explains Johnson. “For example, if you do cold treatment, you need to start by determining the most cold-tolerant life stage of the insect because then you’d carry on with that one.”

For the final probit analysis, the PHYLA team individually inoculates fruit with the correct pest life stage. “For moths, you can put more than one larva in a fruit,” says Johnson, “but since they eat each other, we rather only have one per fruit.”

The numbers needed to meet the standards are staggering: 10 000 fruit per treatment, repeated three times, plus more fruit for the untreated control. Fruit-fly trials are even more onerous because the fruit are inoculated with eggs, which are counted out for each fruit.

Once treated, the fruit are stored to simulate transport and then cut open to assess mortalities.

Probit analysis is usually only required for new treatment protocols, but importing countries can demand additional data in support of existing protocols. And PHYLA also tries to keep ahead of the curve by anticipating future market demands and testing potential treatments before they become mandatory.

“If a market asks us how we are going to handle a particular pest or a new challenge, we want to be proactive and have the data to present to them,” says Johnson.

“The vision of PHYLA is to find and develop treatments that kill insects while keeping fruit quality intact,” summarises Smit. By doing this, PHYLA is an indispensable link in the chain from orchard to consumer.

What are people saying about this research?

“The PHYLA facility is a direct investment by the industry in both the physical and human capacity needed to address any phytosanitary risks that might jeopardise our export markets. It should also assure our trading partners that we have the ability to address and mitigate these risks.”

Stephen Rabe. Horticultural consultant and chair of the Hortgro Science Advisory Council.

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