A Vf gene a day keeps the fungus away

applespottyEver gotten apples from the farmer’s market or grocery store only to have them go bad in the back of your fridge? I know I have. Just a few weeks ago, I got about 20 apples from the CSA. Unfortunately, I can only eat so many per day and they started to go bad before I got to eat them. Some of them got really nasty (as you can see to the right) within just a few days despite being in the fridge.

Eating locally is great, but since apples only ripen once per year, and they spoil relatively fast, that means we only have fresh apples for a short time each year. That’s too bad, since apples are a wonderful crunchy snack loved by kids and adults that provide health benefits from their fiber and antioxidants.

Shipping the apples from another place (like New Zealand) extends the time that apples are available, but shipping in refrigerated containers is expensive and results in greenhouse gas emissions, and we all know that those apples from far away just don’t taste as good as local ones.

Scab Resistant Selection RS103-130. Image from "Organic Production of a New Australian-bred Scab Resistant Apple in Queensland, Australia" by Middleton, et. al

Scab Resistant Selection RS103-130. Image from "Organic Production of a New Australian-bred Scab Resistant Apple in Queensland, Australia" by Middleton, et. al

There might be a way to have local apples available for a much longer time, as well as to have apples shipped in that use less energy and less pesticides!

After more than 20 years of work, researchers in Australia have developed apples that are resistant to black spot aka apple scab, a fungus that destroys fruit and leaves. The scab resistant line, called RS103-130, also stays fresh and crunchy much longer than typical apple lines. They achieved this through some initial crosses with a crabapple species followed by years of selective breeding. The crabapple provided RS103-130 with the Vf gene complex, which has been previously used to produce transgenic scab-resistant apples, which I’ll describe in more detail shortly. You can find the Australian patent for RS103-130 at FreePatentsOnline.

In 2005 and 2006, comparison experiments showed RS103-130 to have many benefits over Galaxy, a typical non-resistant cultivar (see chart below). According to Middleton, et. al, RS103-130 has off white flesh and medium texture, is crisp, sweet, low-acid, and juicy, with a mild flavor.

Chart from "Organic Production of a New Australian-bred Scab Resistant Apple in Queensland, Australia" by Middleton, et. al.

Chart from "Organic Production of a New Australian-bred Scab Resistant Apple in Queensland, Australia" by Middleton, et. al.

Because of all of these benefits and the reduced pesticides needed, organic apple growers in Australia are very interested in RS103-130. I wasn’t able to find any information on whether RS103-130 has been commercialized yet, or on how long it might be before I can try them. Apparently something happened with RS103-130 lately, because stories appeared in The Independent and in the New York Daily News last week. Neither of the stories say what prompted the coverage, nor does Treehugger, which picked up on the 1st two. If you know what’s new with these apples, please comment!

My first question upon reading these articles was: why has it taken twenty years?! Selective breeding can be painstaking, especially when you’re talking trees. There is a faster way…

The HcrVf2 gene from a wild apple confers scab resistance to a transgenic cultivated variety showed that the Vf gene can be inserted with biotechnology into apple varieties (in this case, the gene was inserted by Agrobacterium tumefaciens into the Gala apple cultivar). In the introduction of this paper from 2003, Belfanti et. al point out that:

the transfer of these genes by classical breeding to cultivated apples is difficult because of the long juvenile phase, self-incompatibility, and the impossibility of exactly reproducing the heterozygous state of cultivated varieties. Starting from the wild species Malus floribunda 821 carrying the Vf gene, breeders have developed several scab-resistant apple cvs. (2), but not one has met with commercial success. Indeed, when compared with such commercially popular cvs. as Golden Delicious and Gala, the main horticultural and fruit-quality traits of these scab-resistant cvs. are notably different and undoubtedly less acceptable.

Using biotechnology, the researchers were able to confer scab resistance in one generation. In this paper, the authors don’t mention any increase in lifespan for the fresh apples – I’ll look on Web of Science for more info tomorrow. I do appreciate that the authors are hopeful for the future of apple biotech.

The cloning of an apple scab resistance gene represents the basis for further investigation of the resistance mechanism. It also represents a step toward a gene therapy (restoring resistance where lost) of the scab-susceptible cvs. that currently dominate the apple industry. This strategy will allow the transfer of resistance from a wild apple species to any commercial apple genotype while maintaining the horticultural and fruit-quality traits growers and consumers prize most. It may also be possible to achieve greater resistance durability by the simultaneous transfer of several resistance genes from wild apple species. Going one step further, it may be possible to use apple promoters and novel techniques that, by eliminating selective marker genes (38, 39), generate transgenic varieties without any foreign genes and, hence, may make genetically modified plants more acceptable to growers and consumers alike.

I’m particularly interested that Balfanti et. al mentioned cisgenics, although they didn’t use the term. There is potential to insert genes like Vf into many varieties of apples, meaning that cultivars developed for specific microclimates may be quickly made resistant to scab (and potentially given a longer shelf life) without any loss of their other traits. This is a good example of how biotechnology and breeding can have the same results – get a gene into a cultivar – although one takes much longer than the other.

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Anastasia is a Board Member of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favorite produce is artichokes! Learn more about Anastasia at about.me. Disclaimer: Anastasia's words are her own and views expressed do not necessarily represent the views of her employer(s). She is not paid to blog or conduct any social media activities. Any mention of a specific company or product does not indicate endorsement of that company or product.


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