Hairy leaves

[aletheia]

Does anybody know why some solanum species have hair on the foliage.
Since I have my new camera I can make good macro pictures of plant parts. Later on, viewing them on the computer I saw some interesting details on my solanum verrucosum seedlings. In the www I found some Explanations that it should be responsible for insect defense but I am not convinced at all.
Here are some potatoe experts. Does anybody know why some potatoes have this hair and why do some S. verrucosum seedlings have hair and some doesn't?

Here my picture of S. verrucosum

[DarJones]

It can be both a positive and a negative. The hairy plants repel insects, but they are more susceptible to fungal diseases. This is based on growing Smoky Mountain Red tomato.

[Tom Wagner]

Does anybody know why some potatoes have this hair and why do some S. verrucosum seedlings have hair and some don't?

I am going to try to answer the verrucosum question and ignore the Smokey Mountain Red Tomato response for the time being.

I have been growing verrucosum TPS off and on for the last 50 years, but not a whole lot to show for it. I know that the species collected (about 42) are from two locations in Mexico have been reviewed by Dr. Bamberg a number of times and it seems that some introgression of other species may have contributed some variation. I think that hairiness is one of those things that we just don't understand well. From a few observations the hairs don't protect from Flea Beetles so well, so what is the advantage?

I like Solanum tarijense but since five years ago renamed berthaultii......it is one of my most featured hairy potato species bred into my breeding lines.  I sold TPS of a number of those but not a lot of feedback.  I have lots of TPS of those yet and should relist them.

There is some technical language on the internet...
Leaf characters described by the Russian National Potato Collection.

Length of average adaxial leaf pubescence (mm)
Density of adaxial leaf pubescence (number of hairs/cm2
Length of average abaxial leaf pubescence (mm)
Density of abaxial leaf pubescence (number of hairs/cm2
Leaf surface: dull, shiny, very shiny

Hairiness can be on the upper side of the leaf or the lower side.


The most basic terms used in plant collections are glabrous—lacking hairs— and pubescent—having hairs. I have both tomatoes and potatoes with these traits....and for what reason I will have to wait to explain.

It might be useful to read what is available on the subject:

Hairs on plants are extremely variable in their presence across species, location on plant organs, density (even within a species), and therefore functionality. However, several basic functions or advantages of having surface hairs can be listed. It is likely that in many cases, hairs interfere with the feeding of at least some small herbivores and, depending upon stiffness and irritability to the "palate", large herbivores as well. Hairs on plants growing in areas subject to frost keep the frost away from the living surface cells. In windy locations, hairs break-up the flow of air across the plant surface, reducing evaporation. Dense coatings of hairs reflect solar radiation, protecting the more delicate tissues underneath in hot, dry, open habitats. And in locations where much of the available moisture comes from cloud drip, hairs appear to enhance this process.

Many of the verrucosum lines are from 7,000 ft elevation with good rainfall in the summer months but fairly dry the rest of the year.  It rarely exceeds 88 F for a high and no lower than 44 for an average low.  Kinda the opposite from Washington where the rain is in the fall winter spring and not in the summer.  Not sure how to make an adaptive relevance here.

I like this blurb about grape leaves.....

The Photoprotective Role of Epidermal Anthocyanins and Surface Pubescence in Young Leaves of Grapevine (Vitis vinifera)
• Background and Aims

Depending on cultivar, surfaces of young leaves of Vitis vinifera may be glabrous-green (‘Soultanina’) or transiently have anthocyanins (‘Siriki’) or pubescence (‘Athiri’). A test is made of the hypothesis that anthocyanins and pubescence act as light screens affording a photoprotective advantage to the corresponding leaves, and an assessment is made of the magnitude of their effect.

My Wooly Blues may have some value somewhere in the world.....some woolliness and blue in the stem and a bit in the leaves. Might be a good test.
This plant is a new one for me .....an F-2 that combines the recessives for woolliness and blue. It is in a greenhouse near Duvall.



I like reading about hairy plants from the desert......
Summary

The effects of leaf hairs on photosynthesis, transpiration, and leaf energy balance were measured on the desert shrub Encelia farinosa in order to determine the adaptive significance of the hairs. The pubescence reduces leaf absorptance resulting in a reduced heat load, and as a consequence lower leaf temperatures and lower transpiration rates. In its native habitat where air temperatures often exceed 40° C, the optimum temperature for photosynthesis in E. farinosa occurs at 25° C, and at leaf temperatures above 35° C net photosynthesis declines precipitously. An advantage of leaf pubescence is that it allows a leaf temperature much lower than air temperature. As a result, leaf temperatures are near the temperature optimum for photosynthesis and high, potentially lethal leaf temperatures are avoided. However, there is a disadvantage associated with leaf pubescence. By reflecting quanta that might otherwise be used in photosynthesis, the presence of leaf hairs reduces the rate of photosynthesis. A tradeoff model was used to assess the overall advantage of possessing leaf hairs. In terms of the carbon gaining capacity of the leaf, the model predicted that for different environmental conditions different levels of leaf pubescence were optimal. In other words, under aird conditions and/or high air temperatures, leaves of E. farinosa would have a higher rate of photosynthesis by being pubescent than by not being pubescent. The predictions from this model agreed closely with observed patterns of leaf pubescence in the field.
But pubesence is also defined as "A covering of soft down or short hairs, as on certain plants and insects."
It is a protective adaptation of some plants originating in regions with a long dry season.
A leaf contains thousands of tiny pores called stomata through which it transpires. These openings are also vulnerable portals for moisture loss. Plants develop various strategies for reducing this loss, and one of them is pubescence.
A pubescent leaf will feel furry to the touch. This texture is produced by microscopic hairs called trichomes that help it stand up to brutally dry conditions

More on trichomes and hairs....

If you've ever experienced the hot winds of the desert, you know how quickly it can draw moisture out of your own skin.
Moisture loss increases with wind speed. It does exactly the same to plants. The trichome hairs help to baffle the air at the leaf surface so it slows down. Even a minor slowing can have a significant effect on reducing moisture loss through stomata.
Pubescence also helps to shade the leaf surface. Each tiny hair casts a microscopic shadow to protect the leaf's outer layer from direct solar exposure

Mayflowers....

....selection of more and more pubescent individuals of Mayflowers and elimination of glabrous ones in the areas close to prairies. The advantages of pubescence on leaves has been increasing in the dryer prairies  over the more common glabrous plants on the Atlantic

Potatoes with berthaultii in the background...both 'Prince Hairy' and 'King Harry' potato varieties are fairly well known to be some control on some insects. I have TPS of those and crosses plus the original berthaultii accession used by Bob Plaisted many years ago in the formation of those Kings. It has more to do with the exudate from the trichomes controlling he insects.

Reminds me to look at the leaves of my Harry Kaighin series of potato clones which has King Harry as a grandparent. I need to look at the trichomes on those.

[aletheia]

Thanks Tom, and snickeringbear


It was interesting to see that they seem to have some kind of "glands hair" which contain a lot of chemical components (found that during my research in the net) and indeed on my picture you can see hair filled with some kind of a clear liquid.
I didn't know that till now.

I have to destroy some hair the next days and make some pictures of that to see what happens then.