Showing papers in "Botanical Review in 1953"

The cytogenetics of Triticale

Abstract: The hybrids between common wheat (Triticum aestivum L. emend. Fiori et Paoletti (= T. vulgare)) and common rye (Secale cereale L.) have been of both practical and theoretical interest. The agronomist has long been attempting to combine in one strain the quality and uniformity of wheat and the hardiness, vigor and disease-resistance of rye. The cytogeneticist has studied these two species in combination to ascertain the basic cytological phenomena of hybrids between species which are indisputably in different genera. The term Triticale, a compound of Triticum and Secale, was first used to designate the allopolyploid between T. aestivura and S. cereale. Since other allopolyploids between these genera are possible, the term must include all possible allopolyploids, and it will be used in this wider sense in this discussion. Since the behavior and properties of aUopolyploids are related to the cytology of the undoubled hybrids, meiosis in the simple hybrids must also be considered in detail.

The telome theory

Abstract: Morphologists have long been concerned with the fundamental nature of the vascular plant body-with the relationships between root, stem and leaf, and with the origin of reproductive structures. Attempts at analysis on the basis of either formal or phyletic morphology have given rise to a number of theories dealing with the organization of the plant body. Those related to the flowering plants are summarized by Arber (1930) and need not concern us here, since they are of historical interest only. A theory which encompasses a consideration of all vascular plants, and which is based primarily upon studies of the lower Tracheophyta, recent and fossil, has had greater vitality-so much so, indeed, that it has permeated the thinking of many morphologists and paleobotanists to a degree not realized by those who have not followed the literature in these fields. This is the telome theory, perhaps better termed the " telome concept". Among other aspects the telome concept has assisted in a clarification of our ideas on the relationships between root, stem and leaf, and emphasizes that the plant body is an axis, with a descending portion, the root, and an aerial portion, the shoot, whose appendages are merely modified parts of the stem. Before considering the telome theory itself, it is desirable to point out that, like many another concept, it did not arise de novo, but was foreshadowed by the work of earlier investigators. Reference will repeatedly be made to a fundamental principle advocated by all of these workers which is an essential part of the telome theory itself. This is the principle of overtopping, shown diagrammatically in its simplest form in Fig. 1. This principle involves the belief that the oldest method of branching was dichotomous (a dichopodium). If, at each fork, one of the two branches becomes stronger than the other, a sympodium will result, with an apparent main axis composed of one of the two forks. Continued development of the main axis results in a monopodium which gives off

Production of vitamin B12 by microorganisms and its occurrence in plant tissues

Abstract: During the four years which have passed since the microbiological fermentation of vitamin B12 complex was first accomplished, major developments have occurred, and the production of vitamin B12 and its various complexes has become a major fermentation industry with substantial markets in human and animal nutrition. Factors which have contributed to the highly successful developmental work on the production of this vitamin include the isolation of cultures, the selection of media, a study of the optimum conditions of temperature, aeration and agitation necessary for largescale fermentation, and the establishment of suitable recovery processes for the fermentation broths. The natural occurrence of this vitamin appears to be attributable to microorganisms and algae instead of higher plants or animals.

Physiological studies on the actinomycetes

Abstract: Studies on the physiology of the actinomycetes have not been too extensive to date. The literature indicates that members of this group of microorganisms are able to oxidize carbohydrates and lipids to carbon dioxide, but the intermediates in this chain of reactions are unknown. Most of the actinomycetes are quite proteolytic and attack proteins and polypeptides, and are also able to utilize nitrates and ammonia as sources of nitrogen. Nearly all synthesize vitamin B12 when grown on media containing cobalt salts, and many are able to synthesize rather complex organic molecules which have antibiotic properties. The mechanism of synthesis of these substances is not understood, and their role in the organism’s metabolism has not been investigated.

Physiologic specialization and genetics of the smut fungi. II

Abstract: Much has been added to the store of information on physiologic specialization and genetics of the smut fungi in the 12-year period since Christensen and Rodenhiser (14) reviewed the literature on this subject. These authors referred to the complicating implications of physiologic specialization and genetics in the fungi in relation to plant disease control. Experiences of the last decade should have erased any doubt of the practical significance of this problem. During this time devastating epiphytotics of black stern rust occurred which were traceable to races of the rust fungus that originated by hybridization on the common barberry, its alternate host. Also during this period the Victoria blight and smut races specialized to Victoria oats came into prominence, forcing abandonment of commercial production of varieties with Victoria germ plasm. New races of wheat bunt appeared on varieties that had been resistant, and the distribution of known races was extended into new regions. These examples indicate the dynamic nature of plant disease agents and serve to reemphasize the practical problems of plant disease control resulting from pathogenic specialization in the fungi. Consequently, an extension of Christensen and Rodenhiser's (14) review of specialization and genetics in the smut fungi seems appropriate at this time.

Rootrots of cereals. II

Abstract: The literature on rootrots of cereals that has appeared since the first review reveals a continued interest in these maladies. There have been no major changes in research trends. There have been, however, notable elaborations of work previously initiated, in many cases with ingeniously devised techniques. Advances have been made in studies on the relationship between root disease organisms and soil and other micro-organisms. Much information has been added to our knowledge of the take-all rootrot by intensive research in Germany, England and Australia. In North America it appears that common rootrot may now be classed as a major research challenge. Browning rootrot of wheat, once of great economic importance in Canada, has declined with the introduction of better farming practices and the application of control methods developed after years of research. Helminthosporium blight has appeared as a serious stem, crown and rootrot of oats. There are several types of cereal rootrots considered of minor importance at present, but these must be kept under surveillance. Notable progress has been made in fundamental studies on the perplexing variability of the pathogensHelminthosporium sativum andFusarium spp.