materials that would be subject to beta oxida- 
tion in the fashion that the selective, hormonal 
herbicide 2,4-D is derived from the inactive 
butyric acid homolog. The 2,4-dichlorophen- 
oxybutyric acid (or butanol derivatives) canbe 
converted into 2,4-D only by those plants that 
have beta oxidases, so these, in substance, 
commit suicide after taking the material into 
their cells, It is known that some valuable 
crop plants, such as alfalfa, do not have B-oxi- 
dases and still others, such as wheat, are 
deficient in a-oxidases, so much materials 
with a nitrile group in place of the carboxyl 
group would not be phytotoxic but would be 
injurious to any fungus with a- andf-oxidases. 
Because of the intense lipid chemistry in plant 
pathogenic fungi, it would be logical to expect 
them to have f-oxidases, 
There must be a multitude of such materials 
that could be developed if only sufficient thought 
is applied in this direction. These unstable 
molecules would be the ideal sort to designfrom 
all viewpoints. No poisonous residue would be 
in the environment, hazard to crops without 
the oxidizing enzymes would be minimal, and 
the toxicant would not occur on food products, 
so residue tolerances could be eased a bit. 
Development of Systemic Toxicants 
Evidence is appreciable that some of the 
fungitoxicants can be taken in and move as 
systemic toxicants inside plant tissues. How- 
ever, most of the protective fungicides have 
been designed to have the wrong physical at- 
tributes to survive in the cytoplasm. Since 
they are chosen for low solubility in water and 
for high chemical reactivity, they are prone 
to remain fixed in one spot and to react so 
readily they are detoxified very promptly. How- 
ever, if relatively simple toxophore groups 
were attached to known mobile metabolites 
containing a generous supply of polar groups, 
such as one would find in an amino acid, the 
mobility might be enhanced substantially. 
Most persons automatically think of chemo- 
therapeutants as being taken up by the roots 
and transported through the tracheal tubes, 
where they could destroy the wilt fungi and 
bacteria, or to the leaves, where they could 
prevent foliage and fruit infection. However, 
the opposite route offers even more promising 
47 
possibilities if someone could develop a mate- 
rial that would penetrate the leaves through 
cuticle, stomata, or hydrathodes and pass into 
the phloem and be exuded by the roots. Such 
materials could change the rhizosphere either 
by serving as toxicants or by modifying the 
competition between micro-organisms in this 
vital area, where the soil-inhabiting pathogen 
must first establish itself. It is known that 
certain cell metabolites may take this route 
and affect soil micro-organisms within 2 or 
3 hours after a molecule of “C is taken in by 
the leaf. It should be possible to design or- 
ganic phosphates that would be ideal for 
destroying nematodes by this route, The prob- 
lem is to make the molecules sufficiently 
stable to endure the rigors of the route without 
accumulating as harmful persistent residues 
in the plant tissue. 
If toxicants cannot be developed for such 
purposes, it is potentially possible to change 
the secretion of normal metabolites in the soil. 
For example, antibiosis in the soil could be 
stimulated against Texas root rot (Ozonium 
omnivorum) by stimulating carbohydrate se- 
cretion from the roots during midseason so 
antagonistic bacteria would create a protective 
zone around the root hairs just as is done 
around seedlings early in the season before 
growth and food storage rob the roots of food 
reserves. More information is needed on the 
forces operating in the rhizosphere of all 
plants subject to root invasion. It is known, 
for example, that pea varieties resistant to 
the near wilt Fusarium secrete materials toxic 
to the fungus, whereas secretions from sus- 
ceptible varieties stimulate its growth, but 
the materials responsible for this biological 
control over the pathogen have not been iso- 
lated. They might provide valuable leads to the 
synthesis of systemics that would not create 
harmful residues. 
Stimulation of Natural Antibiosis 
Stimulation of natural antibiosis in the soil 
has scarcely been exploited. In addition to 
changing the rhizosphere, as discussed above, 
it is possible to alter the soil environment so 
it encourages harmless saprophytes at the 
expense of pathogenic fungi and bacteria. Many 
of these are poor soil competitors and would 
