Apple fungal resistance without genetic engineering

EXCERPT: While the JKI breeders were successful without genetic engineering, the genetic engineers are not making any progress. As early as 2011, researchers at the Dutch University of Wageningen began field trials with apples of the Gala variety, into which they had incorporated the Rvi6 gene. According to the genetic engineering-friendly platform transgen.de, the trials ran until 2021. It doesn't say why they were stopped after that and the plants were never marketed, but it seems obvious: Conventionally bred scab-resistant varieties had long since been cultivated and the fungus was already able to overcome the Rvi6 gene. This is why there are currently no genetically modified (GM) scab-resistant apples on the market.
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Apple farming: Fungal resistance without genetic engineering

Informationsdienst Gentechnik, 9 April 2023
https://www.keine-gentechnik.de/nachricht/34813?cHash=c68d8ee4140af0baa523269d58b1a786
(Google translated from the German)

The federally owned Julius Kühn Institute (JKI) has bred a fungus-resistant apple that has now been approved as a variety. The new variety Pia41 resists scab fungi that have already broken through the resistance of other varieties. The breeding success was achieved without genetic modification, through conventional crossing.

The researchers from the JKI Institute for Fruit Breeding Research in Dresden-Pillnitz used the apple varieties Honeycrisp and Nicoter. Nicoter is a Belgian breed of the common varieties Gala and Braeburn, which is also marketed as an exclusive club variety under the name Kanzi. The Honeycrisp, which is little known to us, was bred at the University of Minnesota and is now one of the top 3 varieties in the USA. She has two scab resistance genes in her genome called Rvi19 and Rvi20. At least one of these, Rvi19, passed Honeycrisp to Pia41.

The advantage from the perspective of apple growers: The resistance of well-known European apple varieties such as Santana, Topaz and Natyra to apple scab caused by the ascomycete fungus Venturia inaequalis is based on the resistance gene Rvi6 of the wild apple Malus floribunda. Many scab fungi are now able to break through this resistance, so that the effect is increasingly decreasing. Such breakthroughs are not yet known in Europe with Rvi19 and Rvi20. The JKI researchers infected Pia41 plants in the greenhouse with scab isolates that can break resistance mediated by the Rvi6 gene. The plants showed no scab infestation and remained scab-free even during the five-year testing phase. They didn't show any particular vulnerabilities in any other way, writes Herbert Knuppen from the company New Fruit Varieties and Consulting.

In addition to scab resistance, the breeders also paid attention to appearance, taste and other important marketing properties such as shelf life. An apple that doesn't taste good or goes bad quickly is of no interest to customers in the store or, as a result, to fruit producers. “A green-yellow skin, juicy, crunchy pulp and a sweet taste with an intense aroma, these are the outstanding properties of Pia41,” wrote the JKI. The fruits store very well and last in cooled and gas-tight storage until spring without any loss of quality. “This increases the chance that resistant varieties like Pia41 can establish themselves on the market,” explained Henryk Flachowsky, who heads the specialist institute for breeding research.

While the JKI breeders were successful without genetic engineering, the genetic engineers are not making any progress. As early as 2011, researchers at the Dutch University of Wageningen began field trials with apples of the Gala variety, into which they had incorporated the Rvi6 gene. According to the genetic engineering-friendly platform transgen.de, the trials ran until 2021. It doesn't say why they were stopped after that and the plants were never marketed, but it seems obvious: Conventionally bred scab-resistant varieties had long since been cultivated and the fungus was already able to overcome the Rvi6 gene. This is why there are currently no genetically modified (GM) scab-resistant apples on the market.

For the apple expert (pomologist) and organic breeder Hans-Joachim Bannier, crossing (with and without genetic engineering) individual resistance genes is fundamentally the wrong approach. Such a variety could bring cultivation advantages for a certain period of time. “But the strategy of monogenic resistance always involves the risk of resistance breakthroughs,” explains Bannier. In addition, crossing individual genes would not make modern apple varieties, which are generally very susceptible to disease, more resistant to diseases. They still need a lot of pesticides. With the apfel:gut eV breeding initiative, Bannier is pursuing a different approach to breeding robust apple varieties: “We look at the vitality of apple varieties in unsprayed fruit stocks and always use at least one polygenically disease-resistant variety as parent varieties. So we don't look at individual genes, but simply at the vitality of the entire plant out in the field and not just in the laboratory." 

Sources/more information

Julius Kühn Institute: Green, sweet and crunchy – new apple variety Pia41 approved (August 31, 2023)

New types of fruit and advice, Herbert Knuppen: Pia41 (accessed on August 31, 2023)

Transgen.de: Apfel (accessed on August 31, 2023)

Hans-Joachim Bannier: The false promise (Ecology & Agriculture April 2023)

Information service: Will the next genetically modified apple come from South Tyrol? (10/15/2021)

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