Roses, Wild and Moreso

I've been very busy lately with the new full-time job and the ongoing efforts in my yard and garden areas. Unfortunately, this means my blog has drifted back to things I think about but don't spend much time on.

I did get to spend a recent weekend camping and hiking with the love of my life and some friends. I took lots of photos that will likely be scattered through several less-intensive biology posts than I started the blog with. I expect to do longer-form postings and have several that are in the works, but they may become less common until I get some of the house/yard duties done with.

So, what is that lovely flower you've been looking at in the photos at left? It is a wild rose I found growing in Devil's Lake State Park, just south of Baraboo, WI. It produces small white flowers in large numbers. Those small flowers are followed later by equally small rose hips (at right). The species grows wild over much of the USA, but it is only here because we brought it from its native range in eastern Asia. The large numbers of flowers produced in each cluster give it its name, Rosa multiflora.

The tiny rose-hips are spread by many small birds and the stupendous number of the fruit that a mature plant can produce helps to ensure that it grows densely (and spreads) whenever it is given the chance.

I'm somewhat interested in what a cross between R. multiflora and some smaller rose (like the presumed native rose at right, also from Devil's Lake) might look like, as well as the mix of traits that would crop up in the F2 generation.

I have plenty of interesting rose seeds already that I need to grow, so I probably don't need to start collecting breeding projects for them just yet.


References:

• Devil's Lake State Park: dnr.wi.gov/topic/parks/name/devilslake/
  
• Rosa multiflora: en.wikipedia.org/wiki/Rosa_multiflora
• Chromosomes and breeding in Rosa: bulbnrose.x10.mx/Roses/Hurst/Hurst_1928.html
• Wisconsin shrubs: www.uwgb.edu/biodiversity/herbarium/shrubs/shrub_list_by_common.htm

The Case of the Marvelous Meiosis

1. Meiosis in male (A) and female (B).

The typical story of meiosis is described in detail in many a biology textbook. It all starts with a diploid somatic cell. The chromosomes duplicate and homologs align along the cell's mid-line. The aligned chromosome doublets crossover and then the doublets are divided into two new cells (Meiosis I). The chromosome doublets align along the mid-lines and the new cells divide again (Meiosis II) to produce the final gametes. This model well matches the process of spermatogenesis (Fig 1A), which was used as a model to study and understand the process. Oogenesis follows basically the same process, except that each division is asymmetric. The result is one large gamete (Fig 1B) and two or three non-viable cell fragments with the extra chromosomes.

2. Meiosis in male (A) and female (B) Caninae group roses.

Roses in the group Caninae (Dog Roses) do a peculiar version of the process. The basic example is tetraploid, but produces haploid male (Fig 2A) and triploid female (Fig 2B) gametes. During meiosis I, two homologs for each chromosome align to form a bivalent and the rest remain as monovalents. The monovalents are lost during spermatogenesis, but retained during oogenesis. This system is referred to as "permanent odd polyploidy".  It even works with extra uneven chromosome copies. The extras form monovalents and are discarded or retained just like the red and blue chromosomes in Figure 2. This system allows fertility to be maintained even with odd chromosome counts that would normally make a plant sterile.

I came across this peculiar variant of meiosis while researching what complications might develop in a cross between Rosa pomifera (4n, group Caninae) and R. rugosa (2n). Both parent species have relatively large fruit. My initial plan was to hybridize the two species, generating at least one F1 plant, then allow them to self and screen many F2 progeny plants for increased fruit size.

That the two roses are not very closely related and both species have numerous smaller-fruited relatives suggests their large fruit was evolved separately. This is useful for a breeding project as it means that different mutations accumulated as each plant developed large fruit. Those separate mutations can possibly be recombined via hybridization to generate a progeny plant with even larger fruit.

I expect the project of domesticating roses as [more of] a fruit will take decades. It should be an amusing hobby and I expect to have enough time left to see some nice results.

References:

1. Meiosis: en.wikipedia.org/wiki/Meiosis
2. Rose groups: en.wikipedia.org/wiki/List_of_Rosa_species
3. Dog rose meiosis:
1. www.nature.com/hdy/journal/v101/n4/abs/hdy200863a.html
2. www.ncbi.nlm.nih.gov/pubmed/24685720