摘要:

A culture filtrate ofStreptomycessp. containing antibiotic P-9 was partially purified and then tested in a greenhouse experiment for its effect on stem rust. Increased control of stem rust development (Puccinia graminisPers. f. sp.triticiErikss. and Henn. race 15B1(Can.)) was obtained with increased dosage on 7-day-old seedlings of Marquis wheat. At the maximum dosage, which wetted the primary leaf with a 5000 μg/ml (0.5% w/v) aqueous solution, rust development in the first four leaves was reduced considerably when the leaves were inoculated up to 15 days after treatment. The results indicated a downward translocation in the primary leaf and an upward movement in the younger leaves, thus protecting the plant until the new growth diluted the antibiotic substance(s) to a concentration below the inhibitory level of the rust.

ISSN:0008-4026    

DOI:10.1139/b66-159

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

Pyrenophora semeniperda(Brittlebank & Adam) n. comb. (≡Pleosphaeria semeniperdaBrittlebank&Adam) (=Pyrenophora horridaH. Sydow) is the ascogenous state of a fungus with three described conidial states. The pycnidial state was not named, butPodosporiella verticillataO'Gara andBipolaris cyclops(Drechs.) Sprague had been proposed for, respectively, the synnematous and mononematous conditions of the species. The formation of synnemata was found to depend on culture substrate. Consequently, one name,Drechslera verticillata(O'Gara) n. comb., is proposed for the hyphomycetous state. The fungus is redescribed and illustrated from type and other specimens representing records from Australia, Canada, the Republic of South Africa, and the United States of America.

ISSN:0008-4026    

DOI:10.1139/b66-160

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

Shoot elongation and associated phenological and morphological variables were measured and analyzed for an 8-year-old provenance experiment planted in central Wisconsin. Geographic origin of seed significantly affected elongation and all associated characteristics except initiation date of elongation. Lammas growth had a significant effect on the initiation date and termination date of shoot elongation. Rate and duration of elongation contributed about equally to the extent of elongation. Bud length influenced elongation through rate. The pattern of weekly shoot elongation corresponded more closely to weekly mean temperature than to weekly mean precipitation.

ISSN:0008-4026    

DOI:10.1139/b66-161

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

This investigation deals with the injury caused to four varieties of alfalfa (Medicago sativaL.), under freezing–thawing conditions comparable with those of Australian tableland regions.Evidence is presented to show that the intactness of cell membranes influences the magnitude of the low-frequency resistance attained in frozen tissues.Measurements of the maximum resistance attained during freezing, the proportionate drop in resistance after freezing, and the minimum resistance attained after freezing, are considered in relation to two subsequently determined criteria of injury. The results are interpreted as showing that injury occurs in tissue during freezing, in the frozen state, and during thawing.Brief comments follow concerning causes of injury at the various stages, factors responsible for hardiness, and the procedure necessary for selecting the most hardy genotype.

ISSN:0008-4026    

DOI:10.1139/b66-162

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

Single-drop applications of nickel salts, cobalt salts, or kinetin induced similar patterns in the delay of the rapid senescence of detached wheat leaf tissue (Triticum aestivum compactum'Little Club'). Tissues near treatment sites remained green as more distant parts of the leaves became chlorotic. Yeast extract, coconut milk, and benzimidazole also preserved the green pigment but the activity of the last two was sometimes displaced away from treatment sites. Total nitrogen content increased markedly in the portions of detached leaves treated with nickel sulfate or kinetin, indicating that nitrogenous substances moved from senescing tissues into the green tissues at treatment sites. The green tissues increased in dry weight and stained heavily with I–KI.The slowly senescing tissues of attached leaves were kept green by high concentrations of either kinetin or benzimidazole in treatment drops but not by nickel sulfate. However, moderate concentrations of nickel sulfate or kinetin increased the dry weight and retarded the slow natural loss of nitrogen content of attached leaf tissue, indicating that both substances induced a temporary senescence delay.

ISSN:0008-4026    

DOI:10.1139/b66-163

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

The ultrastructure of the mycelium of bothPhytophthora infestansandP. parasiticais consistent with that reported for other Oomycetes. A distinct plasmalemma, porate nuclei, tubular endoplasmic reticulum, mitochondria with tubular cristae, Golgi dictyosomes, and lipid bodies are present within the protoplast. The haustoria produced byP. infestansin the leaves of susceptible potato varieties consist of an expanded haustorial head surrounded by a fungus wall which is continuous with the wall of the intercellular mycelium. The haustorium lacks the long narrow stalk or neck often associated with this organ, and there is considerable cytoplasmic continuity between the haustorium and the intercellular mycelium. AllP. infestanshaustoria observed were anucleate and generally contained only a few mitochondria and sparse endoplasmic reticulum. The haustorium is enclosed in an encapsulation surrounded by a membrane which is continuous with the host plasmalemma. There is no evidence, around any portion of the haustorium, of a sheath originating from the cell wall of the host. A survey of the current literature on the ultrastructure of the Eumycotinia shows that the parasitic fungi exhibit no unique cytoplasmic features when compared with non-parasitic fungi, and the ultrastructure of the haustoria-producing facultative saprophyte is similar to that of the obligate parasites.

ISSN:0008-4026    

DOI:10.1139/b66-164

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

Toxosporiopsis capitatan. gen., n. sp., collected on bark ofCeiba pentandra(L.) Gaertn., the Kapok tree, in Sierra Leone, is described and illustrated. The fungus is tentatively assigned to the Melanconiales and characterized by versicolored, 3-septate, dark-banded blastospores, each with an apical mucilaginous appendage, and filiform paraphyses which have a mucilaginous sheath. Cylindrical, aseptate, unbranched conidiophores produce a single apical conidium which terminates growth of the conidiophore. It is compared and contrasted withSantiellaand related genera.

ISSN:0008-4026    

DOI:10.1139/b66-165

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

In the cambium of mature trees a general conformity was found in the orientation of the partition in the pseudotransverse division of fusiform initials through out sectors of varying size. The proportion of divisions deviating from the preferred orientation varied with the tree, the locality, and the species, but was usually less than 10%. As radial accretion followed, periodic reversals occurred in the orientation of anticlinal divisions, the spacing between reversals, in terms of xylem increment, being related to the frequency of anticlinal division. The mean interval shortened as the rate of division rose according to the equationxy = k. While this overall relationship obtained, there was generally some inequality in the relative duration of leftward and rightward orientations of division. In species with grain in the outer wood slanted to the right, a rightward tilt of division persisted for longer periods than a leftward tilt. Conversely, in species with grain slanted to the left, thickness of xylem showing leftward orientation of multiplicative divisions exceeded that with rightward orientation. Changes associated with growth from sapling to adult were studied inPicea, in which genus grain is usually to the left in the inner wood and to the right in the outer wood. Here multiplicative divisions were usually inclined to the left in the growth of the first few years, whereas in the later growth orientation to the right endured for longer periods than to the left. Both orientation of pseudo-transverse division and direction of cell elongation after division seem to be under a general polar control. This apparently is an important element in the induction of spiral grain. Above-average net gain of fusiform initials in the turmoil of cell addition and loss, which accompanies circumferential expansion, may be a contributory factor. Serving to restrain the development of an excessive spirality are periodic reversals in direction of tilt in anticlinal division, and a high ratio of loss of cambial cells relative to the frequency of anticlinal division.

ISSN:0008-4026    

DOI:10.1139/b66-166

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

Based on present knowledge of the origin, amounts, chemical form, and distribution of nitrogen (N) in wood, hypotheses are proposed to explain radial gradients in N content that exist across the xylem cylinder of tree stems: (1) N in the cytoplasm of developing wood cells is diluted by apposition of cell wall substances; (2) after maturation of wood fiber cells, N in their cytoplasm is removed by elution into the transpiration stream; (3) death of xylem parenchyma cells during aging of sapwood and formation of heartwood is accompanied by removal of much of the N in their cytoplasm. Hypotheses 2 and 3 above suggest strongly that trees possess an internal recycling mechanism for conservation and reuse of the N in the cytoplasm of xylary cells.Although the supply of N in wood is meager, wood-destroying fungi readily metabolize the carbon-rich constituents of wood and produce large fruiting structures that release vast numbers of spores in nature. To account for these capacities, we postulate that these fungi employ one or more of the following three mechanisms: (1) preferential allocation of N obtainable from wood to substances and pathways highly efficient in the use of wood constituents; (2) reuse of N obtainable from wood by a dynamic and continuous process of autolysis and reuse without significant loss of N; (3) utilization of N sources outside the wood itself, for example, by fixation of atmospheric N.

ISSN:0008-4026    

DOI:10.1139/b66-167

出版商:NRC Research Press    

年代:1966

数据来源: NRC

摘要:

Radial gradients in nitrogen content across stems of three hardwoods and two softwoods followed similar patterns. Sapwood and inner bark contained a higher proportion of the total nitrogen in cross sections than heartwood and outer bark, respectively. Nitrogen content of individual annual increments decreased progressively from the cambium to the transition zone between sapwood and heartwood, or, in species without heartwood, to the increments nearest the pith. In some cases, an abrupt decrease in nitrogen content was observed across the sapwood–heartwood boundary. The diminution of nitrogen content across the sapwood was associated with death of parenchyma cells. As the cells die, nitrogen in their cytoplasm apparently is retrieved for possible reuse elsewhere in the tree. Pith contained more nitrogen by weight than heartwood and in some cases more than sapwood. Nitrogen content was correlated directly with parenchyma volume for sapwood but not for heartwood of 16 species of angiosperms.Nitrogen extractable from sapwood with neutral solvents consisted in part of free amino acids but only traces of these acids were detected in heartwood. Hydrolysates of sapwood and heartwood prepared with 6 NHCl contained many typical protein amino acids.

ISSN:0008-4026    

DOI:10.1139/b66-168

出版商:NRC Research Press    

年代:1966

数据来源: NRC