New Phytologist 154(2): 275 (May 2002)
Coevolution of roots and mycorrhizas of land plants
Mark C. Brundrett
http://bulbnrose.x10.mx/Heredity/Mycorr ... e2002.html
The author traces the association of plants and fungi back to the early lichens, and then through long evolution of green plants. He makes the case that the fungi evolved first, getting better at their adopted role of roots for rootless plants. Green plants are rich in sugar, of course, and the fungi happily (I assume) traded minerals and sometimes water for the sweet energy source.
Later, the plants evolved some more to strengthen the mutually beneficial association. The development of roots was not merely coincidental.
Some plants have given up this association. They have grown numerous long root hairs to compensate. Crucifers, for example, make a sulphur compound that is toxic to fungi. Even so, the association of green plants with mycorrhizal fungi should be understood as the default condition. Exceptions have their own reasons.
Medve: Mycorrhizal Status of the Cruciferae (1983)
http://bulbnrose.x10.mx/Heredity/Mycorr ... s1983.html
While I'm on the subject, a while back (2006), I happened across a statement on the beneficial interactions of tomatoes and mycorrhizal fungi.
"One of Mr. Chapman's customers, a Master Gardener, reported the yield of his tomatoes doubled with fungi, while ripening time was as much as a week earlier. He also said the tomatoes tasted much better. "
This little comment hit me with a sense of deja vu. I had read of the same group of benefits in a very different contest ... vegetative hybrids.
I won't go into the subject of vegetative hybrids just now, except to mention that the people who were most rabidly opposed to even the concept had, in most cases, never heard of epigenetics, RNAi, gene regulation/silencing and many other interesting things. Furthermore, they had not bothered to study the reports published in agricultural journals going back to the early 19th century.
"Vegetative hybrids obtained by grafting tomato on nightshade (Solanum [nigrum]) and Lycium barbarum are now undergoing fundamental varietal trials. It may already be said that, as far as early-maturation is concerned, these vegetative hybrids are not inferior, or are even superior, to the earliest maturing tomato varieties. As regards yield (as may be judged by the number of fruits), these hybrids are considerably superior to the early-maturing varieties. The vegetative hybrids are distinguished by one valuable quality—they show no tendency whatever to shed buds or ovaries, whereas shedding of buds and ovaries in one degree or another is characteristic of all known varieties of tomato." (M. A. Olshansky, 1948)
"...long before the war, at the Academy's experimental base at Gorki-Leninskiye, graftings of tomatoes were made on solanum. As a result of the grafting the fruits not only of the hybrids but also of their seed progeny acquired a rather pleasant piquant flavour. The seed progeny obtained from these vegetative hybrids were so abundant that their fruits were sent to the local cooperative store for sale. People from surrounding villages, who apparently got to like the piquant flavour of the hybrid fruits, used to come to the store and simply say: 'Weigh me a kilogram of vegetative hybrids.' These were plain common folk, who appreciated the tomatoes for their taste, and not for their name." (I. I. Prezent, 1948)
The connecting link may be found in Richmond: Inoculation of grafted beans (1926).
http://bulbnrose.x10.mx/Heredity/Bacter ... s1926.html
It had already been established that the Lima bean, Phaseolus lunatus, cannot be inoculated by the bacteria found in the nodules of the Navy bean (P. vulgaris), and vice versa. He made a series of experiments and made a striking discovery.
1) When a lima bean top is growing upon a navy bean root, in quartz sand, a pure culture of lima bean bacteria will not cause the formation of nodules upon the roots of the grafted plant, but the roots are stimulated, the plant grows to maturity, and appears to be able to obtain atmospheric nitrogen.
2) When such a graft is inoculated with a navy bean culture, nodules are formed and the plant grows to maturity. The navy bean organisms in the roots apparently are able to furnish nitrogenous compounds to the lima bean tops, in exchange for carbohydrates synthesized by a top not normal to the nodule organism used.
3) Similar results are obtained with the reciprocal grafts and inoculations.
4) A lima bean top grafted upon an inoculated navy bean root grew to maturity and developed seeds.
5) When seeds are produced by a grafted plant, either lima or navy, they are so modified that plants grown from such seeds no longer have the power of selective adaptation for the specific nodule organism common to it, but are inoculated by either the lima or navy bean organism.
Perhaps seeds from a tomato grafted to a locally adapted cousin, such as the Black Nightshade or Goji Berry, can hook-up with the local mycorrhizal fungi.
BTW, Hoffman (1927) gives more details on Richmond's work, including on the method of grafting.
This method might prove useful in grafting seedlings of species that are not strictly compatible. For instance, there are no wild roses in my low desert vicinity, but there are some Rubus and Prunus. If I wanted to adapt a rose seedling to local fungi, this might be the best bet.METHOD OF MAKING GRAFTS
Beans are very tender and can be grafted only while they are growing on their own roots. For this reason the approach method of grafting was found to be the most effective. The plants to be grafted were grown close together in a gallon pot. After the seedlings had straightened out, or prior to the time that the first whorl of leaves had formed, each seedling was wounded or abrased up and down the length of the stem. The two surfaces were pressed together and tied securely. To hasten union between the tissues, numerous wounds were made by piercing both stems all the way through with a needle. The callus growth which resulted made a very effective coalescence of the component tissues. After the union was established the roots corresponding to the scion were severed, thus leaving a rootstock of one variety, top-grafted with a scion of another.