Pomegranate breeding and germplasm

Just stumbled up on a review of pomegranate genetic resources:

Pomegranate Plant Material: Genetic Resources and Breeding, a Review (CIHEAM)

I'm feeling a little grouchy tonight because a nursery lost my tree order (including pomegranates) and now the ones I want aren't available from where I wanted them until next year.

Trees of Endangeredstan

Central Asia is possibly the region of the world least on most people's radar (despite its proximity to that perennial focus, the Middle East), but it is a center of diversity for many, many fruit crops, and as such has genetic resources which could prove critical for future breeders of such things as apples, almonds, walnuts, peaches, pomegranates and many other crops. It also has environmental degradation, unstable governments, and widespread poverty, which threaten those resources, many of which have never made it out of the region thanks to nearly a century of Soviet rule and isolation.

Flora & Fauna International has compiled a "Red List" of endangered fruit and nut species in the area. Critically endangered species include pears, hawthorns, currants, and barberries. Some of these things are down to a single tiny population.

Red List of Trees of Central Asian

An interesting read about a bunch of species I at least hadn't heard much (or anything) about.

Fruit Genetics Friday #8: Picking a Scab Resistance Gene

I know the title is a pretty bad pun, and not even that accurate. Sorry. Anyway, here's the bit about scab resistance I hacked out of the draft on the WineCrisp apple:

The Vf gene comes out of a selection Malus floribunda. The original introgression of the Vf gene (or genes, but more on that later) was done by Purdue back in the 1940's, and has been used heavily in breeding, including as a fairly early target of marker assisted selection (a detailed history of scab resistance breeding is available from Purdue. I'll hit the highlights here.)

There are at least seven distinct loci governing resistance to apple scab, each named according to the original source (the "V" is for Venturia inaequalis, the name of the pathogen):

Vf - Malus floribunda
Vm - Malus micromalus
Va - 'Antonovka'
Vb - Malus baccata Hansen's #2
Vbj - Malus baccata ssp. jackii
Vr - Malus pumila R12740-7A
Vr2 - Malus pumila GMAL 2743

There are distinct races of the scab pathogen, though, and they react differently to the different resistances. Race 5 overcomes Vm, for example, while Race 2 overcomes the resistance in some M. baccata. In 40 years of breeding, no resistance breaking isolate of Vf was identified, but towards the end of the twentieth century reports began to surface in Europe of strains which could overcome Vf.

As I hinted before, it's probably more appropriate to refer to the Vf locus, rather than the Vf gene, because the Mendelian Vf gene is in reality a collection of genes. (Although I use it as much as anyone else (probably more), the word "gene" is actually kind of a problematic one anyway--it's really better to use "locus", to refer to a specific point in the genome, or "allele" to refer to a specific sequence at that locus.) Sequencing showed the so-called Vf gene to be a cluster of four genes, Vfa1, Vfa2, Vfa3, and Vfa4. Clusters of resistance genes aren't uncommon and have been shown in lots of species--it may be the extra copies strengthen the resistance by increasing expression, or allow a broader resistance by having multiple versions. It's also possible that resistance alleles are more likely to evolve from duplicated genes, because the plant can better survive mutations in a gene it already has backup copies of. In this case, Vfa3 has sustain some pretty serious mutation, and no longer produces a full length transcript. Although the similarity among the remaining four led researchers to suggest that all activate the same defensive systems, Vfa1 and Vfa2 (along with the partial transcript of Vfa3) are primarily expressed in immature leaves, while Vfa4 is expressed in mature leaves. Of these, Transgenic apples transformed with each of these apples showed that susceptible varieties expressing Vfa1 and Vfa2 became resistant, suggesting these two genes are capable of conveying resistance.

The Vf locus was really one of the first fruit genes to really be thoroughly investigated and described, from its introgression from a wild species, description as a Mendelian trait, and detailed dissection on the molecular level. Although other source of scab resistance are gaining in importance, and molecular tools such as linked markers developed to improve their usefulness to breeding programs, the Vf locus remains possibly the most studied disease resistance locus in any fruit crop. (I'm just speaking off the top of my head...Anybody think of any other contenders?)

Australian New Crops Newsletter

Just came across a collection of on-line issues of the Australian New Crops Newsletter, from 1994-2002. Lots of different crops are discussed as well as the practicalities of developing new crops, both as industries and as species.

Here are a few selected articles...I just glanced through and picked out a handful I thought might be relevant to my readers (most are quite brief):

Nashi Fruit (Pyrus pyrifolia)
The Trials of New Crop R&D: Getting the Germplasm
Longan (Euphoria longan)
Kakadu Plum (Terminalia ferdinandiaana)
Edible Indigenous Nuts of Papua New Guinea
Beach Plum (Prunus maritima)
Australian Native Citrus