Worldwide, there are several research projects that are introducing genes derived from animals into experimental apples, which are justified by the supposed need to transform current commercial varieties into fire blight resistant forms of the same variety, i.e. a 'Gala' apple tree that is identical to other 'Gala' apple trees, producing indistinguishable fruit from other 'Gala' apple trees, but has an introduced gene that allows the tree to defend itself from Erwinia amylovora, the bacterium that causes fire blight disease in apple, pear and other rosaceous hosts. Cornell University introduced a gene into a Royal Gala scion cultivar that encodes a protein produced as a resistance response to bacterial infection in Hyalophora cecropia, the Giant Silk Moth. In Germany, apple cultivars 'Elstar' and 'Royal Gala' were transformed with the gene encoding human lactoferrin with the intention to retard the bacteria's growth and allow the plant to establish a second line of defence (Schneider et al. 2006). I am a little surprised about the latter, for I was under the impression that a general disdain existed in Europe for transgenic, or "genetically engineered" crops. In addition, they state that biocontrol agents are not giving the same protection as streptomycin (a bactericide, which, though effective, can lead to resistant strains of the bacteria -- it is recommended for use immediately after a hail storm, but not as a calendar-scheduled spray); and that conventional breeding is unlikely to give any resistant cultivar in the near future with the necessary characters of existing cultivars. These statements are shown to be false just by reading the other articles published in the same journal (Acta Horticulturae 704, published by ISHS 2006). Several yeast strains are shown to inhibit the bacteria, copper oxychloride emended with essential oil from savory or thyme could reduce blossom blight infections (Hassanzadeh 2006), and various epiphytic bacteria, such as that found in the natural product "Serenade", have shown some effectiveness. Several breeding programs around the world are working with disease-resistant hybrids, derived from conventional breeding, such as at Budapest, Angers, and various universities in North America. Cornell University has released a half-dozen rootstocks with good-to-excellent fire blight resistance (and other desirable traits,) that derived from conventional breeding. The University of Minnesota's relatively small breeding program has released several apple cultivars with high resistance to fireblight, such as 'Honeycrisp'. Apple is one of the most genetically diverse crop plants we grow. There are hundreds, if not thousands, of distinct varieties in collections around the world, and many thousands more related Malus species in the wild and collections as well. The genes for disease resistance and necessary characters for agricultural cultivation are all present in the apples of the world; they do not require input from animal genes. Growers should take into account that planting resistant varieties is one of the most effective means of prevention of fire blight. Consumers should value diversity and disdain grocery shelves with perfect displays of red, yellow, and green. "Why do we need so many kinds of apples? Because there are so many folks. A person has a right to gratify his legitimate tastes. If he wants twenty or forty kinds of apples for his personal use, running from Early Harvest to Roxbury Russet, he should be accorded the privilege. Some place should be provided where he may obtain trees or scions. There is merit in variety itself. It provides more points of contact with life, and leads away from uniformity and monotony." - Liberty Hyde Bailey, The Apple Tree 1922 A partial resistance involving a complex polygenic mechanism is the nature of fire blight resistance. Introduction of this type of resistance through genetic engineering would be rather difficult (Lespinasse and Paulin, 1990). In the long term, breeding fire blight resistant varieties and rootstocks offers a realistic solution for non-chemical control. H. Percy, HortResearch, Ruakura Well, there are some thoughts and facts. Anyone more interested in reading about the genetic diversity of apples might find Apples, by Frank Browning, very enjoyable. Scientific types should look up the Acta Hort journals that deal with fire blight.
Interesting post! I'd have no problems with locating genes for resistance to fireblight in closely related species (other species of Maloideae) and introducing those to fireblight-susceptible apples, but using genes from bacteria, animals, etc, doesn't strike me as a good idea; first the gene might not be very effective against fireblight, second, one can't predict what else might arise.
I agree, Michael, that would be the sensible approach. This is a very new technology, around 20 years old, but routinely a gene from a vastly unrelated organism is inserted into another (and the transgenic result released for farmers to grow and the public to consume, although the 'Gala' apples I mention have not been released). Apparently gene transfer is a natural process; in fact, there is evidence that chloroplasts in plants were evolved from (originally were) a separate organism. Nonetheless, a wise approach would be to cross genes among close relatives. One argument for genetic engineering is that generation time in breeding a new variety is drastically reduced, but there is no way in the lifespan of mankind that a moth and an apple tree could be interbred! Introducing a gene from quince, for example, to an apple or pear, is more acceptable. As I mention before, within the Malus genus there are genes for disease resistance, annual cropping, drought tolerance, etc. that can be utililized in a modern breeding program. Concerning resistance to fire blight, here is an Alabama Extension sheet that lists several members of the rose family of plants either as susceptible or resistant, and also reactions of apple & pear cultivars, including ornamentals: http://www.aces.edu/pubs/docs/A/ANR-0542/ANR-0542.pdf Fruit breeders should refer to Genetic Resources of Temperate Fruit and Nut Crops 1, published by ISHS 1990. This discusses sources (e.g. various Malus species & cultivars) of desirable traits and the relevant scientific studies.
Ron B, thanks for the link. That discussion is getting pretty long; I just got through half of it. Someone had a link to an interesting article I thought would be relevant, "Selective Breeding Gets Modern": http://www.wired.com/news/technology/0,71433-0.html My original post to start this thread has a quote from someone at HortResearch in New Zealand, which this article mentions. From their website: "We use conventional breeding techniques to create new cultivars, but we also are using our genomics resources to develop new and more efficient methods of [apple & pear] breeding, such as the application of marker assisted selection (MAS)." The page about their apple breeding program is here.
I tried to look up the subfamily Maloideae on a USDA website I sometimes reference (http://plants.usda.gov/), but it doesn't appear to accommodate the classification. Here is a site I found listing the genera within Maloideae: http://www.botany.utoronto.ca/courses/BOT307/D_Families/307D1RosMaloidgenera.html
'Sansa' is a newer apple variety with some disease resistance; it derived from a cooperative effort between New Zealand and Japanese apple breeders (in the traditional manner: growing seedlings and evaluating them). This is a daughter of (seed came from) 'Gala'. An excellent small book, The Best Apples to Buy and Grow, was recently published by Brooklyn Botanic Garden. I recommend this book, and it is available from Amazon.com and elsewhere.
