With watering restrictions becoming more common, drought tolerance is something important to breed for in warm areas. I am looking for drought tolerant roses which are also fertile. Any suggestions are welcome.
The Canadian âParklandâ prairie roses were based on:
âThe key to the development of the âParklandâ group by Dr. Marshall was Rosa arkansana, a native prairie tetraploid rose. This plant tolerates the hot dry summers and extreme cold found on the Prairies and is recurrent, with blooms produced on both older and new growth.â
I think this is an excellent topic to mention, considering that climate warming will increase the need of drought resistant plants in the future.
Rather than looking for drought resistant cultivars (there likely are few or none modern rose cultivars that are), the easiest approach is to develop a breeding program producing selections that are short and compact. Less foliage means less transpiration of the leaves and thus reduces the need for water to keep the shrub alive.
Itâs likely one will have to go back to the species or species hybrids to develop drought resistant roses. There are several strategies to take.
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Developing roses having a deep root system. Rosa arkansana, for example. Whether Parkland cultivars, even the first hybrid âAssiniboineâ with one-half Rosa arkansana in the parentage is extra dought tolerant, has not been scientifically determined. They likely arenât because of the dominance of Floribunda or Hybrid Tea characteristics.
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Developing roses with slender leaflets. Rosa foliolosa, for example. Again, whether Rosa foliolosa hybrids like âBasyeâs Purpleâ with slender leaflets are more drought resistant than other Rugosa hybrids has not been determined. But in theory they should be.
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Developing roses with small leaflets. Rosa spinosissima, for example. However, unless the size of the shrub is substantially reduced from the usual size (quite tall) of this species, this strategy will likely be of no advantage.
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Developing roses with grey-green foliage. Plants with grey foliage are usually tolerant of hot and dry conditions. Likely not a major advantage to increase drought resistance except if the leaflets are also small. Fortunately, rose species like Rosa beggeriana and Rosa fedtschenkoana with grey-green foliage have relatively small leaflets. These two species are likely drought resistant.
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Developing roses with less leaflets. Rosa setigera is the only species with three leaflets but they are relatively large (7.5 cm. + long). Since this is a tall rangy shrub, its hybrids would have to be substantially reduced in size and the leaflets also reduced in size to have a positive effect. Likely one of the least effective strategies.
When hybridizing roses, more attention (is any?) should be paid to root characteristics. After all, itâs a major and important part of the plant. Generally, the focus should be on developing root systems that are very fibrous and therefore efficient in taking up water and nutrients to the rest of the plant. It canât be ignored that a root systemâs characteristics are a factor whether a rose can survive and grow well in particular climate and soil conditions.
All of the Oregon species roses are drought tolerant. Although Woodsii, Pisocarpa and Gymnocarpa prefer shaded forest edges. Rosa acicularis and Rosa califorica can easily be found in the middle of untended fields as large masses. Rosa californica readily mixes with modern roses. Rosa acicularis has random ploidy as far as I know.
" Developing roses with grey-green foliage. Plants with grey foliage are usually tolerant of hot and dry conditions. Likely not a major advantage to increase drought resistance except if the leaflets are also small."
Rosa primula has a grey tint to the dark green, tiny leaflets!
I went round and round with this in terms of my own breeding gols and finally decided that the most widely adapted roses for drought tolerance and garden use are likely those old garden roses which have survived and flourished over time in places like TX.
Many roses dry regions of the world basically go dormant until rains return. This doesnât mean they are at all attractive while dormant.
I donât think it gets much better than old Chinas or roses like Harrisonâs Yellow in terms of toughness and esthetics.
One could argue that species cannot be improved upon in those areas where they are endemic.
They have evolved for the climate and conditions present.
âOne could argue that species cannot be improved upon in the areas where they are endemic. They have evolved for the climate and conditions present.â
Robert, itâs true plant species in an ecosytem are fully adapted because that is where they evolved. But thatâs not to say they canât be âimproved uponâ biologically or aesthetically. Take Rosa arkansana, for example. Biologically, it has a deep root system but is not too fibrous. If it was crossed with another cold hardy species with fibrous roots and selections made from the progeny with a deep root sytem, plus having fibrous roots that made the plant more drought resistant, no one would argue that is not an improvement.
Secondly, native rose species can be improved aesthetically by selecting genotypes with superior foliar and flower characteristics and then crossed to obtain progeny more attractive than its parents. This is what Robert Erskine did to obtain Rosa acicularis â Kinistinoâ, which has almost red flowers. It also has large, deep green leaflets enhancing the shrubâs attractiveness.
Having said the above, itâs not probably what you meant. But I think itâs good to point these things out.
If you meant that other species cannot survive and grow better in an ecosytem having native species, they may not be an improvement but they can do as well. Certainly, in Zone 5 or better climates, species like Rosa canina, Rosa eglanteria and Rosa multifolora having escaped into the wild can flourish as well as native species.
Hi Paul, no thatâs not exactly what I meant but you make some good points.
Charles said,
âdrought tolerance is something important to breed for in warm areasâ
Thereâs drought tolerance and thereâs drought tolerance and thereâs warm and thereâs warm. I suppose that depends on where you garden? I consider TX fairly warm and dry.
I garden in one of the hottest driest growing regions on earth near Palm Springs CA. There are no native species adapted to my area.
I have to use those best adapted to lower water use and minimal chill hours and prefer those that repeat.
One can select superior clones or breed with species or species hybrids native to cooler wetter regions but were we get minimal rainfall thatâs not an option.
Our best flowering season here is Winter.
Iâm using my own Basyeâs Legacy hybrids which incorporate Arkansana, Virginiana and acicularis as a side project.
I do get Winter flowering using some of these hybrids. (See latest photo on page link) I doubt they are anymore drought tolerant than most garden varieties in an area like mine. They would certainly be drought tolerant in an area like yours.
Hopefully I will merge some of my hybrids to be both heat and cold tolerant and have Winter flowering characteristics.
Itâs hard to have it all.
Fertility may be somewhat debatable and Iâm not experienced enough with them to make more specific recommendations, but watching some of the roses survive very hot and dry summers in Washington, DC, Iâd carefully consider teas and Rosa bracteata. The latter appears genuinely unfazed by just about everything nature throws at it; teas are fairly adept at going into pseudo-dormancy between waterings. Of course, those are roses for areas with moderate winter temperatures and might take special care to maintain in a more northerly breeding program.
I know you think itâs hot and dry in Summer in Washington DC but trust me, you have no idea of the concept. You have humidity which makes it seem very warm but itâs not dry.
Come to my neck of the woods in July or August and we can compare notes.
The saving grace is that we usually experience very low humidity and sublime Winters.
We are too hot and dry for most Teas to be happy except in Winter.
Those species best adapted to climates like mine WITH irrigation include bracteata, clinophylla and laevigata.
Chinas are generally tougher and accept drier conditions than Teas in my experience.
I wonder if the hulthemias would offer drought tolerant possibilities?
Jim Sproul
From what I understand Hulthemia go dormant during periods of water stress. We see this in desert plants that shed their leaves in Summer to preserve moisture.
Itâs been theorized that one of the reasons we have black spot derived from yellow species is that those species were primarily adapted to regions wherein their leaves would normally be shed relatively early in the season compared to Chinas and the like.
They were not evolved to grow year round. Their genes contribute to the development of blackspot as a function of extended senescence in modern hybrids.
Hulthemia in itâs natural range is more or less a weedy, annual or ephemeral type of pasture or meadow perennial?
The area to which it is native supports grasses.
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To quote a friend and colleague - selection works. Of course here is the catch, first you need genetic variation for the trait of interest - drought tolerance, but you also have to be willing and able to select for that trait. For me, it is relatively easy to select for disease resistance, I am in an environment that yearly experiences disease. Drought tolerance on the other hand is more difficult to select for. There are atleast 2 reasons for this I suspect, first we need to learn how to create a âmanaged stress environmentâ for drought. What this entails is having uniform, moderate, constant water stress. This is very difficult to achieve. I think the other problem is that for this particular trait, we really have to wait until we have an established plant before screening can start. And I am not quite sure how rootstock would impact this trait either. Anyway, those are my somewhat random thoughts this morning.
Liz
I totally agree Liz.
Then we have to decide if we are going to accept a rose that doesnât bloom year around and perhaps even support leaves under drought conditions as part of the equation?
I decided Iâm not going to live long enough to make much of an impact in terms of the generations of seedlings needed to do such work.
Itâs easier to start with what works best and go from there.
I canât test for most diseases in my climate so I have to assume everything is questionable, and make an effort to get seedlings tested for cold tolerance and disease resistance elsewhere.
Robert, you are exactly right. I think that many of the characteristics that have been enhanced by breeders over the decades in roses go against general âfitnessâ of the plant.
A great example of this is bloom period and hardiness. One of the things that I have noticed with the Explorer and Parkland roses in zone 5 is that as a group they tend move into dormancy well before all the other roses, in other words they stop producing flowers and new growth, and start dropping leaves. I really believe that this is at least a part of why they are winter hardy.
My feeling is that some the smaller floribundas and shrubs might be more efficient when it comes to water use. They would still as own roots have a reasonable root system, and have less surface area (stomates) for water loss. But until we let go of some of our standards for what makes a good rose, true drought tolerance is probably not achievable.
I have not really followed the Earth Kind program all that much, but perhaps they are looking at water use in their evaluation program.
Liz
the earthkind roses are drought tolerant in abilene, texas. zone 7.
The only problem I have with my only china (Rosa chinensis sanguinea) is that the leaves crisp. But that is probably minor to the deserts of California =P The only other rose I had close to a China was Leonie Lamesch and it seemed to be fine without water. China/Tea/Noisettes grow horribly here (they hate the cold, wet winter soilsâŚmust be grown high and dry!) so take that for what itâs worth.
When I think of something truly bred for survival without human intervention I think of roses like âHarrisonâs Yellowâ which is very nearly a species in itâs own right.
Ironically we probably lose more plants to over irrigation than any other cause here in the low desert. Humanâs have a tendency to over compensate.
Liz, your observations regarding varieties that drop leaves early echo mine here. I think it would be relatively easy to select out those seedlings that go deciduous early.
My bet would be that these will also tend to be the most disease resistant and most cold tolerant.
Iâll bet they are also those that leaf out latest in the season to avoid late frosts.
Conversely, more evergreen cultivars seem better adapted to Southern climates.
I think these are cues we could use in seedling selection.
Robert, what would you think of Rosa chinensis x Rosa primula? Dumb idea?
I think thatâs a terriffic idea Jadae, especially if you used something like Safrano or Trier as seed parent.