> the lecturer made clear, that plants infested with endophytes
> never show any phenological symptoms.... might only be valid
> for the small grasses he worked with...
You mean "phenological" or "phenotypical." The Festuca sp. may not look
different, but they sure are more toxic to animals when infected with the
typical endophytes.
> there never was any REAL strong infestation of fusarium ON the
> plants. that was amazing, as we know of several larger regions,
> where corn is grown very intensively. the real problem is not
> corn after corn, but small grains after corn. 6 or 7 years of
> corn and then a wheat on this field will result in a DESASTER.
> in several years though we had problems with the corn cob
> mixtures from these plots. it wasn't analysed, but my
> predecessor highly suspected it to be F. oxysporum.
In moist northern climates corn ears and stalks are often rotted by Fusarium
graminearum (Gibberella zea). This fungus also causes scab in small grains.
The Fusarium moniliforme complex (moniliforme, subglutinans, proliferatum)
is more subtle. If you split a normal, healthy corn plant when knee-high
you will see a faint darkening in the center of the stem at the base of the
plant. This is more pronounced in sweet corn. Whenever I have tried, I
have been able to isolate F. moniliforme from aseptic cubes of this tissue.
What is more, I have isolated ergosterol (a uniquely fungal lipid) from this
part of the stem.
> how do you understand "good" varieties ? infection resistant ? or
> might most of the "good" properties even be the major result of
> resistance ?
I am thinking that in selection for yield and late-season stalk strength,
inadvertent selection for a favorable association has occurred. Modern
breeders do inoculate with these things, but in my hands, F. moniliforme
seems strangely non-virulent when inoculated.
> our experience clearly show, that the grade of fusarium
> infection is a (highly significant) function of the length of the
> stalk. the shorter the stalk, the faster the infection and the
> more intense.
It may be that southern (US) dent germplasm develops a more favorable
association with F. moniliforme than do the northern flints, from which
short, early corn varieties are largely derived. In my garden, ultra-early
sweet corns (northern flint background) seem to have more stalk Fusarium
than later sweet corns (also flinty, but probably with more S. dent
introgression).
My model is that F. moniliforme and it's ilk, infect the seedling as the
radicle wounds and penetrates the coleorhiza. The fungus grows up the
mesocotyl and forms a latent infection in the crown, and only becomes
"pathological" under certain kinds of stress. After flowering, the fungus
begins to ramify in the stalk. In favorable associations, nothing bad
happens to the corn plant, but F. moniliforme gets to eat it all at
senesecence. Ears become infected largely via silk infection and the fungus
is transmitted in the pedicel remnant at the base of the kernel.
> in our
> experience the infection level of the cob depended much more on
> environmental factors (mostly humidity resp. the lack of soil
> water) and even more on the tillage system (no-till with mulch-
> seeding had the worst effect on infection in small grains, which
> followed after corn) than on seed infection rates.
Again, are you sure we are talking about the same species of Fusarium?
> would you confirm our observations, that breeders are more and more
> breeding for industrial usage properties and less and less for
> agronomical advantages ? and even more: at the expense of
> agronomical properties ?
Pioneer has always been, and still is very, very focused on agronomic
traits. The big things have been yield and standability. Special grain
traits get more press intentionally, but yield and stalk are still our bread
and butter. The grain traits I hear the most about include:
- improved milling properties (better product recovery)
- reduced mycotoxin (better food-grade corn)
- high oil (high energy corn)
- exotic starches and polymers for special uses
- low phytate (reduced P in manure)
- high sucrose soybeans (not so fartatious in soymilk and tofu and in feed)
Some of these will be challenging in the seed quality area, since dinking
around with the grain is also messing with the seed. (seed quality is my
thing).
Dale
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