North American Fruit Explorers mailing list at ibiblio

["Gene Spears" <Spears@LMC.edu>]

        I'm on the state board of the Carolinas Chapter of The American 
Chestnut Foundation (TACF), so thought I'd summarize what that organization 
(and there are a couple of others, too) is trying to accomplish.
        TACF is focusing primarily on traditional palnt breeding techniques 
to develop a mostly (>97%) American Chestnut with resitance to the blight, 
and hopefully to Phytophora, too, which apparently had already eliminated a 
large number of chestnuts before the blight came along later. The main 
sources of genetic material are two lines of native American that show fairly 
good resistance, combined with a number of Chinese parents.  Most of the 
breeding work is done at a large facility in Meadowview VA (SW VA), where 
there are acres of chestnut trees growing like corn stalks.  
        Nuts from hand crosses are planted & fertilized, and grow remarkably 
quickly.  Some nuts go to flowering trees within six years.  Because of this 
fast turn around time, much of the new planting is third generation 
backcrosses, and are now about 95% American.  Each generation is deliberately 
infected with virulent strains of the blight, and only those that show good 
resistance are used for the next generation.  Even trees with good resistance 
develop cankers, but they seem to be able to contain the infection & the tree 
survives.
        In addition to the work at Meadowview, state chapters, like the 
Carolinas Chapter, scour the woods for native trees that show some 
resistance.  There are hand pollinated with pollen from the resistant trees 
growing at Meadowview, and the nuts are collected and planted in local, 
volunteer-operated nurseries (we've got one on some of our college's 
property).  This increases the genetic diversity of the trees in the breeding 
program, and adds local gene complexes that may be better adapted to 
particular environments.
        The goal of the breeding program is to develop a resistant tree that 
has the growth characteristics of the American Chestnut, that can be 
reintroduced to the eastern forests.  Chinese, Japanese and European 
Chestnuts all have a fairly short, spreading growth habit.  The American, on 
the other hand, was a canopy dominant tree, growing to impressive heights.  
        Will our resistant trees exhibit these American growth 
characteristics?  Can a resistant tree with cankers grow fast enough to 
out-compete other species?  Will even low-levels of blight stunt American 
Chestnuts?  Maybe another technique, involving hypovirulence, or genetic 
engineering will work better.  Maybe some combination of all the techniques 
will work.  Maybe none of them will be enough to restore the American to the 
eastern forest.  We're still facing a lot of uncertainty, and the Foundation 
is well-aware of these uncertainties.  Still, we think the effort is 
worthwhile.  
        From a NAFEX perspective, there are some interesting issues that TACF 
isn't really addressing (but I'm curious about them).  The American nut is 
apparently much sweeter than either the Chinese or japanese - it also 
contains a higher fat concentration and lower starch concentrations that the 
other species.  (One article suggested that the flavor and composition of the 
nut is influenced by the species of both the male and female parent - since 
endosperm - nut meat - contains chromosomes from both parents, this seems 
reasonable.) Unfortunately, the American nut is a lot smaller than other 
species' nuts.  For a backyard orchardist, the ideal Chestnut tree would 
probably grow fast, have the growth form of a Japanese or Chinese (low and 
sprawling), be resistant to blight and phytophora, have nuts as large as a 
Japanese tree, but with the sweet, rich flavor of the American.  Nobody's 
breeding with these goals in mind, though.

gene
spears@lmc.edu