ences are utilizing the techniques for biopsy stud- 

 ies while a patient is still on the operating table. 

 Other research led to the discovery of a new class 

 of organisms named spiroplasmas. It has been 

 proven that spiroplasmas are the causal agents of 

 several plant diseases including the corn stunt 

 disease. Spiroplasmas can now be cultured and 

 provide a means by which new vectors and un- 

 known plant hosts can be identified. From basic 

 RNA studies of the cucumber mosaic virus 

 (CMV), a fifth RNA was recently discovered. 

 When RNA 5 is present, CMV causes severe 

 tomato necrosis. This discovery explains the 

 cause of the disastrous loss of tomato production 

 in France in 1972. 



Davis, R. E.. J. F. Worley, R. F. Whitcomb. T. Ishijima and 

 R. L. Steere. 1972. Corn stunt disease. Science. 176:521-523. 



Davis. R. E. and J. F. Worley. 1973. Spiroplasma: motile, helical 

 microorganism associated with corn stunt diseases. Phytopathol- 

 ogy. 63:403-408. 



Diener. T. O. 1971. Potato spindle ■'Virus" IV. A replicating 

 low molecular weight RNA. Virology. 45:41 1-428. 



Kaper, J. M., M. E. Tousignant and H. Lot. 1976. Plant virus: 

 defective or satellite RNA.' Biochemical and Biophysical Re- 

 search Communications. 72:1237-1243. 



Alleviation of Root Diseases by Antibiosis 



Many soil saprophytes have been found to 

 produce antibiotic substances that suppress or de- 

 stroy plant pathogens, and some saprophytes ac- 

 tually parasitize or debilitate harmful organisms. 

 The best possibility of alleviating plant diseases 

 caused by soil inhabiting fungi, bacteria, and 

 nematodes is to manage soils to increase the anti- 

 biotic potential by commensal organisms. A rich 

 field soil regularly contains up to 2 million orga- 

 nisms per gram, each competing for space and 

 nutrients and producing metabolic products that 

 influence the welfare of neighboring organisms. 

 The pattern for using this knowledge is being 

 well-established by research now in progress. 

 Additional research is needed on the biochemistry 

 of antagonisms and on isolating, identifying, and 

 learning how to use the inhibitory substances. 



Baker, K. F., et al. 1965. Ecology of soil-borne plant patho- 

 gens. University of California Press. 



Baker, K. F. and R. J. Cook. 1974. Biological control of plant 

 pathogens. W. H. Freeman and Co., ,San Francisco, CA. 433 

 pp. 



Bruehl. G. W. ed. 1975. Biology and contriil of soil-borne 

 plant pathogens. The American Phytopath. Soc. 



Plant Breeding for Improved Productivity and 

 Resistance to Pests 



Research on photorespiration has shown that 

 plants differ drastically in their efficiency in con- 



1 2 AGRICULTURE 



verting carbon dioxide into carbohydrates and 

 other storage products. Plants that undergo photo- 

 synthesis through 4-carbon chains vs. 3-carbon 

 chains have been found twice as eflfective in uti- 

 lizing carbon dioxide. Moreover, photorespiration 

 inhibitors or somatic hybridization with plants of 

 low photorespiration can enhance water utiliza- 

 tion. In addition, recent research has indicated the 

 potential for improved nutritional quality to ani- 

 mals. A single mutant gene in forage sorghum has 

 been discovered to increase the rate of digestion 

 of forage sorghum by ruminant animals. [Discov- 

 ery of opaque-2 and fiour-2 genes in maize has 

 increased the amino acid balance for nonruminant 

 animals. Gel electrophoresis methodology has 

 permitted fingerprinting and classification of pro- 

 teins for rapid screening by plant breeders. 



Much early research on breeding for pest resist- 

 ance gave ephemeral results due to the pest's abil- 

 ity to produce new races. Recent research resort- 

 ing to multigenic or broad forms of resistance 

 geometrically reduces the chances of the pest to 

 readjust according to the number of genes in- 

 volved. Using this approach, resistance to late 

 blight fungus in potatoes and black stem rust in 

 wheat has been stabilized. It has also been discov- 

 ered that certain cultivars produce fungicidal, bac- 

 teriostatic, or insecticidal substances when invad- 

 ed by plant pests. Absence of precursors or inade- 

 quate enzyme systems for generation of these 

 substances leaves the plant susceptible and vul- 

 nerable to attack. 



Cummins, D. G., J. W. Dobson. Jr. 1972. Digestibility of 

 bloom and bloomless sorghum leaves as determined by a mod- 

 ified in Wfro technique. Agron. J. 64:682-683. 



Jackson, W. A. and R. J. Volk. 1970. Annual Review Plant 

 Physiology. 21:385-432. 



Mertz, E.T., L.S. Bates, and O. E. Nelson. 1964. Mutant gene 

 that changes protein composition and increases lysine content 

 of maize endosperm. Science. 145:279-280. 



Savory, C. D. 1976. Peanut (Arachis hypogals L.) seed protein 

 characterization and genotype sample classification using poly- 

 acrylamide gel electrophoresis. Biochemical and Biophysical 

 Research Communication 68:886-894. 



Zelitch, I. 1971. Photo Respiration Review. Academic Press. 



Mathematical Modeling of Plant Growth and 

 Pest Development 



Mathematical modeling techniques are simulat- 

 ing plant growth as affected by known input fac- 

 tors such as soil and environment temperatures, 

 radiation, soil moisture, relative humidity of the 

 air, nutrient availability, cultural practices, photo- 

 synthetic activity, etc. Various stages of plant 

 development may be predicted with anticipated 

 events. Pest population development can also be 



