Source Parameters for Stick-Slip and for Earthquakes

Source parameters of stick-slip friction events measured in the laboratory show particle and rupture propagation velocities which are similar to those observed for earthquakes and inferred from seismic source theory. This dynamic similarity strongly supports the idea that stick-slip is the mechanism for shallow earthquakes.

The effect of surgical denervation on dentin formation in the incisor of the rat

Unilateral removal of the inferior dental nerve and superior cervical ganglion in rats produced no alteration in the quantitative deposition of dentin in developing incisors as shown by double tetracycline labeling. This finding, however, may be peculiar to rats because of the apparently singular innervation of these teeth.

A data processing system for hospital bacteriology

A system for the automatic capture and retrieval of information contained in routine bacteriology reports is described. The system depends on the preparation of reports on an electric typewriter producing punched paper tape as a byproduct. Periodically the information contained on the tape is analysed by computer. The potential value of the system for the analysis of the results of antibiotic sensitivity testing and for the study of the epidemiology of hospital infections is briefly discussed.

Haemolytic disease of the newborn caused by anti-Lan antibody

The first recorded example of anti-Lan associated with haemolytic disease of the newborn is reported. This emphasizes the importance of screening for atypical antibodies early in pregnancy, even though prophylactic use of anti-D immunoglobulin will eventually reduce the incidence of haemolytic disease due to anti-D antibody.

SPECIFICITY IN THE EFFECT OF HIGH TEMPERATURE ON THE ADULT PLANT REACTION OF WHEAT VARIETIES TO RACES OF STEM RUST

The reactions of adult plants of 10 wheat varieties to stem rust (Puccinia graminis f. sp. tritici Erikss. & Henn.) races 11, 12, 15A, 15B-1, 15B-2, 15B-3, 17A, 29, 29A, and 139 were determined at temperatures of about 60° F. and 80° F. The varieties K338 AC 2.E.2 and K117A were resistant to all races at both temperatures. Redman was resistant to all races at both temperatures except for the races 15B-1, -2, -3, which attacked it at both temperatures. This variety was somewhat more susceptible to race 12 at the low than at the high temperature. The other varieties were more susceptible at the high temperature to one or more races to which they were resistant at the low temperature. McMurachy was more susceptible at the high than at the low temperature to races 15B-1, 15B-2, and 17A; Selkirk to races 15B-1 and 15B-2; Red Egyptian to races 15B-1 and 17A; Triticum timopheevi to races 15B-1, 15B-2, and 15B-3; Frontana × Thatcher II-47-37 to race 15B-1; Kentana to races 12 and 15B-2; and K58 to races 12, 15A, 17A, and 29. Since the resistance of these varieties broke down to different races, the effect of high temperature on the rust reaction of adult plants is specific for certain combinations of host variety and rust race.

SELFING STUDIES WITH PHYSIOLOGIC RACES OF WHEAT STEM RUST, PUCCINIA GRAMINIS VAR TRITICI

Forty-two cultures of wheat stem rust (Puccinia graminis var. tritici Erikss. and Henn.), comprising 34 physiologic races, were subjected to selfing studies each of which involved the inoculation of barberry plants with the sporidia of a race, and the determination of the races in the uredial cultures derived from the aeciospores. In all of the cultures studied, the pathogenic properties expressed on the differential hosts appeared to be inherited according to the same principles. On the varieties Marquis and Kota (Triticum vulgare), pathogenicity of the races in the progeny tended to resemble that of the parent race. On Reliance (T. vulgare), avirulence was a dominant character, virulence a recessive one. On the durum wheats Arnautka, Mindum, and Spelmar, virulence was a dominant and avirulence a recessive character. On Einkorn (T. monococcum) and on Vernal (T. dicoccum), avirulence was dominant to virulence. In the progenies of some races, pathogenic variation occurred though it did not transgress the circumscribed limits of the parent race; the population therefore consisted chiefly of substrains (biotypes) of the same race.

CULTURAL VARIABILITY IN SEPTORIA AVENAE FRANK

Cultures from field collections of Septoria avenae Frank produce "wild type" colonies of rather uniform appearance—a creamy-white mycelium, a brown substrate, and few, if any, pycnidia. Subculturing on potato sucrose agar usually leads to the production of a great variety of variants that fall into two broad classes: mycelial and pycnidial, the latter usually producing scant mycelium, many pycnidia, and a blue-green substrate pigment. In some cultures, staling, i.e., cessation of growth, occurs commonly but is generally followed, after an interval of time, by renewed growth. Cultures of the pycnidia! type show a marked tendency to produce mycelial type variants and, conversely, cultures of the mycelial type will give rise to pycnidial type variants. In certain cultures, strains have arisen that predominantly produce small pycnidia containing spermatium-like microspores, but which are still capable of producing macro-spores. Cultures from microspores show several distinct types including dark-pigmented cultures, albino cultures with dark pycnidia, albino cultures with colorless pycnidia, and cultures of purely mycelial type. Attempts to demonstrate that the microspores perform a function in the production of the perfect stage of the organism were unsuccessful.

THE SOURCE OF RESISTANCE AND THE INHERITANCE OF REACTION TO 12 PHYSIOLOGIC RACES OF STEM RUST, PUCCINIA GRAMINIS AVENAE (ERIKSS. AND HENN.)

Resistance to 12 races of oat stem rust was unexpectedly obtained from three crosses, Hajira–Jostrain, Hajira–Richland, and Hajira–Banner, between the years 1932 and 1940. Recent investigations have shown that the Hajira parent was the source of this resistance, as 10% of plants selected from this variety were found to be highly resistant. Inheritance studies have shown that, in some crosses involving this source of resistance, two main genes are involved and in others only a single main gene. A probable explanation is that the highly resistant plants in Hajira may have differed genetically. The studies also reveal that the Hajira type of resistance to race 8, either in the seedling or adult stage, is indicative of resistance to the 12 races that occur in Canada and the United States.

INTERVARIETAL CROSSES IN PUCCINIA GRAMINIS

Crosses made in all possible combinations between varieties Tritici, Secalis, Avenae, Agrostidis, and Poae of Puccinia graminis Pers. have shown the existence of considerable intersterility in crosses between some of the varieties. Fertility was relatively high in crosses between vars. Tritici and Secalis, Avenae and Agrostidis, Avenae and Poae, and Agrostidis and Poae. Fertility was much lower in crosses between vars. Tritici and Avenae, Secalis and Avenae, and Secalis and Poae. In crosses between certain pairs of varieties the degree of fertility varied according to the direction of the cross. Tritici × Agrostidis, Tritici × Avenae, Tritici × Poae, Secalis × Agrostidis, and Secalis × Poae crosses succeeded much better than the reciprocal crosses. Sporidia from the F1 teliospores of Tritici × Secalis hybrids infected barberry with the production of normal pycnia and aecia. Sporidia of Tritici × Avenae and Secalis × Avenae hybrids produced, on barberry, infections with few pycnia and these excreted little nectar; no aecia were formed but urediospores and teliospores were occasionally produced in old infections. Generally, an F1 hybrid rust possessed a wider host range than did either of the parent varieties; but the pathogenicity of the hybrid on a given host was less than that of the parent variety that attacked that host. In hybrids of varieties that differed markedly in urediospore size the urediospores of the F1 hybrid rusts were intermediate in size between those of the parents. The pathogenic characteristics of the F2 (uredial) generation were studied only in Tritici × Secalis hybrids. Variation in pathogenicity was rather restricted. The races isolated were moderately pathogenic to barley and weakly pathogenic to wheat and rye.

A FORM OF LEPTOSPHAERIA AVENARIA ON WHEAT IN CANADA

In the late summer of 1942, a Septoria sp. with spores longer than those of Septoria nodorum Berk., and conforming rather closely to those of S. Avenae Frank, was found commonly in the Prairie Provinces of Canada on leaves of wheat and, in one instance, on leaves of barley. It was found again on wheat and more rarely on barley in both Eastern and Western Canada each year from 1943 to 1946. Occasionally, perithecia, attributable to the genus Leptosphaeria, were found on leaves that previously had borne numerous pycnidia of this organism. That the perithecia represented the perfect stage of this Septoria sp. was shown by the development of similar perithecia in many cultures established from pycnidiospores, and by the formation of pycnidia in certain cultures grown from ascospores of perithecia collected on wheat. The perithecia, asci, and ascospores conform closely though not identically with the description of Leptosphaeria avenaria Weber.The organism under discussion differs from S. nodorum not only in the size of its pycnidiospores but also in its inability to cause glume blotch, its longer incubation period, and lack of ability to attack the seedlings of certain wheat varieties susceptible to S. nodorum. It differs from S. Avenae in symptoms, host range, length of incubation period, and cultural characteristics. It differs from both these species by a lower parasitic vigour and a marked tendency to develop on fading leaves and sheaths. Owing to its morphological similarity to L. avenaria it is here described as a forma specialis of that species.

PHYSIOLOGIC RACES OF PUCCINIA GRAMINIS TRITICI IN CANADA, 1919 TO 1944

During the period 1919 to 1944, 65 physiologic races were identified from a total of 4543 isolates derived from uredial collections of Puccinia graminis Pers. var. Tritici Erikss. & Henn. Forty-nine races were obtained in the Prairie Provinces from a study of 3475 isolates; 40 in Eastern Canada from 1013 isolates, and 12 in British Columbia from 55 isolates. During this period, the predominant races have shown notable fluctuations in their prevalence. Races 36, 17, and 21 were the most common races until shortly after 1930 and were largely responsible for the severe rust losses suffered by Marquis and other common wheats during the decade preceding that year. Races 34 and 49 were collected frequently from 1927 to about 1935. All of these races diminished greatly in their prevalence between 1930 and 1936, whereas race 56, which was first collected in Canada in 1931, has become the predominant race since 1934. It was this race that played a major part in the stem rust epiphytotic of 1935. Another recent change in the racial population was a recrudescence in 1940 of race17, which for several previous years had been of minor importance. In 1941 this race challenged the pre-eminent position of race 56 but receded again in succeeding years to minor significance.The distribution of races is somewhat similar but not identical in different parts of Canada. Races 36 and 21 have been relatively more common in the Prairie Provinces than in Eastern Canada, while the contrary is true of race 38. Only about a dozen of the 65 races collected in Canada have thus far assumed much economic importance, a few others may be considered of minor significance, but at least two-thirds of the races have been found only occasionally and have, for reasons not fully understood, failed to gain even a limited distribution.A comparison of the number of physiologic races collected in Eastern Canada and the Prairie Provinces, respectively, has indicated a somewhat greater variety of physiologic races in the former region, a condition that may perhaps be explained by the presence of the common barberry in many localities in Eastern Canada.

THE EFFECT OF DDT ON THE STEM RUST REACTION OF KHAPLI WHEAT

Seedling leaves of Khapli wheat—a variety highly resistant to physiologic races of wheat stem rust prevalent in North America—became susceptible to stem rust a few days after they had been sprayed with DDT (1 oz. in 5 gal. water). The response to DDT was highly specific, as only one other of the resistant wheats tested (Arnautka) showed any indication of susceptibility consequent on spraying. Specificity of response was also indicated by the development of marked chlorosis on leaves of some varieties, whereas other varieties remained unaffected.

PHYSIOLOGIC SPECIALIZATION OF OAT STEM RUST IN CANADA

An account is given of the results of studies on the physiologic specialization of Puccinia graminis Avenae Erikss. and Henn. in Canada since the inception of the work. Twelve physiologic races were identified from 2586 isolates studied during the period 1921 to 1943. The annual surveys of the prevalence of physiologic races during this period show that each year races 1, 2, and 5 have comprised the bulk of the oat stem rust in all parts of Canada. The predominance of these races has been greatest in the three Prairie Provinces, where barberry is virtually non-existent. In regions where barberry is present, other races of greater range of pathogenicity have been found more frequently than in these three provinces. The occurrence of such races, however, was sporadic until 1943, in which year races 8, 10, and 11 attained a wide distribution, apparently traceable to wind-borne urediospores from the south. There is evidence that the strains of these races present in 1943 remain in the uredial stage for much longer periods than do strains of the same races collected in previous years—a fact that may have favoured their spread in this year.The role of barberry in the origination of generally virulent physiologic races is discussed. The possibility that such races may also originate by mutation is suggested by spontaneous pathogenic changes that occurred, in the greenhouse, in a culture of race 3 that gave rise to several cultures of race 7.The effect of environment on the identification of physiologic races is demonstrated by the seasonal influences on the reaction of the variety Sevnothree to races 1 and 11. On this variety the characteristic type 1 is frequently replaced, in summer, by type x.Experiments on the influence of temperature on the reaction of adult oat plants to stem rust showed that a constant temperature of about 80° F. does not appreciably affect the reaction of White Tartar and Richland, or of other varieties with the same type of resistance, but is capable of breaking down the resistance of certain varieties derived from the crosses Hajira × Joanette, Hajira × Banner, and Victoria × (Hajira × Banner).

MELANISM IN WHEAT INDUCED BY HIGH TEMPERATURE AND HUMIDITY

Results of experiments performed in the greenhouse have shown that, under conditions of a high temperature especially when combined with a high humidity, melanistic areas may develop on the glumes, lemmas, peduncles, and internodes of Apex and Renown wheat in the absence of any infection by pathogenic organisms.

THE INHERITANCE OF A MUTANT CHARACTER IN PUCCINIA GRAMINIS TRITICI

A study was made of the inheritance of an abnormal characteristic of Puccinia graminis Tritici Erikss. and Henn. race 21, namely, the production on barberry of white haploid pustules that developed few or no pycnia and rarely produced aecia but occasionally gave rise to uredia and telia. In this race, approximately 50% of the pustules were white, the remainder normal. By selfing studies and by crosses with another physiologic race, it was demonstrated that diploidisation of the mycelia of normal pustules by pycniospores from white pustules initiated physiologic races that produced white and normal pustules, on the barberry, in approximately equal numbers, whereas normal × normal matings produced normal rust and white × white matings were sterile. Uredia that occasionally arose in white pustules as a result of diploidisation by either pycniospores or mycelia of normal pustules gave rise to physiologic races producing white and normal pustules in about equal numbers. The capacity to develop white pustules is not confined to any one sex and is not limited to any particular physiologic race. It is assumed that a mutation affecting one of the conjugate nuclei took place in the original culture of race 21 and that, during meiotic divisions in the germinating teliospore, the mutant factor is segregated so that half of the sporidia give rise to white and half to normal pustules.

THE EFFECT OF HIGH TEMPERATURE ON THE STEM RUST RESISTANCE OF WHEAT VARIETIES

Eighteen stem rust resistant wheat varieties were tested, in the greenhouse, for their reaction to three physiologic races of Puccinia graminis Tritici Erikss. and Henn. at three different temperatures: a constant low temperature of about 60° F., a constant high temperature of about 80° F., and an intermediate temperature which fluctuated daily from 50° to 55° F. at night to 70° to 85° F. at midday.At the low and at the intermediate temperature some of the varieties proved immune while others proved highly or moderately resistant. At the high temperature five varieties (Bokveld, Iumillo, Gaza, Red Egyptian, and N.A. 95 Egypt) were immune or highly resistant; six varieties (Marquillo × Waratah, Hope, Hochzucht, Minor, Bobin Gaza Robin, and Federation × Acme) were moderately resistant; and seven varieties (Kenya, Syria, McMurachy, Sweden, Rhodesian, Talberg, and Eureka) were moderately or completely susceptible.

THE INFLUENCE OF LIGHT AND CERTAIN OTHER ENVIRONMENTAL FACTORS ON THE MATURE-PLANT RESISTANCE OF HOPE WHEAT TO STEM RUST

Experiments have been conducted to determine the degree to which the mature-plant reaction of Hope wheat to race 21 of P. graminis Tritici Erikss. and Henn. is affected by variation in light intensity, length of daily light period, temperature, soil moisture, and supply of mineral nutrients. All these factors gave evidence of influencing rust reaction. A 60% reduction in light intensity during the whole growing period of the plants tended to influence their rust reaction in the direction of increased susceptibility and caused a modification in the morphology of the plants in that they were softer, less rigid, and higher in moisture content than plants grown in full daylight. The shift towards susceptibility was, however, not very marked, and in only one experiment did the reaction of the plants approach complete susceptibility. Reduction in length of daily light period also influenced the rust reaction of the plants towards susceptibility. Plants receiving six hours of light daily were less resistant than plants receiving ten hours of light and these, in turn, were slightly less resistant than plants receiving full daylight for the period of the experiment (February to June). Experiments on the effect of temperature on the reaction of Hope wheat have shown that constant high temperature (75° to 80° F.) is capable of causing a partial or even complete breakdown of mature-plant resistance. Some evidence was secured that abundance of soil moisture and of mineral nutrients diminished rust resistance.

STRIPE RUST, PUCCINIA GLUMARUM, IN CANADA

A study was made of the distribution of Puccinia glumarum (Schm.) Erikss. and Henn. in Canada, its specialization, host range, and reaction to environmental conditions. Unlike Puccinia graminis Pers., this rust has a limited distribution, being confined to British Columbia, Alberta, and the western half of Saskatchewan. The natural hosts include a number of native grasses, particularly Hordeum jubatum L. and certain species of Agropyron, Elymus, and Bromus. Wheat and barley also become infected although to a rather limited extent: Stripe rust collected on the above-mentioned hosts has been studied in the greenhouse and has in all cases shown ability to attack wheat varieties. In all instances where identification of physiologic forms was carried out the rust strains were classified as either form 8 or form 13 of wheat stripe rust, the latter form being the more common. The fact that the present authors have collected known physiologic forms of wheat stripe rust on species of Hordeum, Elymus and Agropyron, and have shown that forms 4, 6, 8 and 13 can attack seedling plants of Hordeum, Agropyron, and Elymus species throw a doubt on the existence of the Hordei, Elymi, and Agropyri varieties created by Eriksson.Greenhouse studies showed that P glumarum is extremely sensitive to environmental conditions, particularly temperature. The optimum for uredospore germination is 10° to 12 °C., and for rust development 13° to 16 °C. Varieties susceptible at from 10° to 16 °C. developed resistance at higher temperatures, becoming extremely resistant at 25 °C. On account of the sensitiveness of this rust to high temperatures it seems improbable that it will ever become thoroughly established in Manitoba and Saskatchewan, as in these two provinces the summer temperature is probably too high to permit its development.

STUDIES ON THE NATURE OF DISEASE RESISTANCE IN CEREALS: II. THE RELATIONSHIP BETWEEN SUGAR CONTENT AND REACTION TO STEM RUST OF MATURE AND IMMATURE TISSUES OF THE WHEAT PLANT

In Part I of these studies it has been shown that the rapidly growing tissues of the wheat plant are more susceptible to stem rust than the older tissues. An attempt was made to discover if a physiological or chemical basis could be found for the difference in reaction of the young and older tissues.Analyses were made to determine the sugar content of young (susceptible) and older (resistant) tissues of four wheat varieties resistant in the adult stage and of the corresponding plant parts of three wheat varieties which in the adult stage showed little or no resistance to rust. The young tissues comprised the young leaves still enfolded by the uppermost sheaths and the young stems below the uppermost node; the older tissues were represented by the fully developed upper leaves and their adherent sheaths. The analyses showed a considerably higher content of sugars in the young than in the older tissues of the seven varieties tested. The difference was particularly great in the content of reducing sugars but rather slight in the disaccharide content (expressed as invert sugar). However, as all the varieties, irrespective of resistance or susceptibility to rust in the adult stage, showed much the same difference in the sugar content of their young and older tissues, it does not seem likely that there is any direct relation between sugar content and reaction to rust.