The Effect of Plant Height on Tan Spot on Durum Wheat in Southern Saskatchewan.
Tan spot [caused by Pyrenophora tritici-repentis (Died.) Drechs.] is the most important leaf disease of durum wheat (Triticum turgidum L. var. durum). Most of the durum cultivars in western Canada are of conventional height but development of shorter cultivars is desirable. Changes in microenvironment resulting from a height reduction might cause greater leaf spot development. The effect of plant height on tan spot of durum wheat was determined in five pairs of genotypes near-isogenic for plant height and five randomly selected populations, each with a semidwarf and a conventional height parent. These were grown in five environments in Saskatchewan (1996-1998 at Swift Current, 1997-1998 at Indian Head), and evaluated for tan spot reaction in a growth chamber. There was no difference in tan spot reaction under controlled conditions between short and tall genotype(s) in each pair or population, although there were differences within each height category. Under field conditions, short genotypes had either equal or greater disease than tall genotypes. Contrasts between all short and tall genotypes also showed that the tall had less disease in 1998 at Indian Head (9.8 for tall, 10.2 for short) and in all years at Swift Current (9.5 and 9.9 in 1996, 8.1 and 8.7 in 1997, 8.5 and 8.9 in 1998, for tall and short, respectively). However, there was genetic variability within populations, with some short having equal or less disease than tall genotypes. Some of these short genotypes also had a low tan spot lesion type under controlled conditions. We conclude that plant height could affect tan spot development in durum wheat under conditions prevalent in southern Saskatchewan, and that this is probably mediated by canopy density.
Factors affecting the vertical progression of Septoria leaf blotch in short-statured wheats.
BAHAT, A., I. GELERNTER, M. B. BROWN, and Z. EYAL. 1980. Factors affecting the vertical progression of Septoria leaf blotch in short-statured wheats. Phytopathology 70:179-184. The meteorological factors affecting the development and vertical similar to the rate on the equally receptive semi-dwarf cultivars despite the progress of Septoria leaf blotch of wheat were assessed for equally difference in plant architecture and maturity. Functions were developed to susceptible dwarf (70-80 cm) and semi-dwarf (100-120 cm) spring wheat analyze the net contribution of climatological factors on the progress of the cultivar pairs of different maturity in both an arid and a rainy region in disease within the temperature range of 10-25 C. The vertical progress of Israel. In the dwarf cultivars, pycnidia of Septoria tritici were found the disease was correlated with the number of rainy and dewy days and immediately after leaf emergence; in the semi-dwarf cultivars there was a temperature indices 7-21 days prior to disease observation and disease 10to 20-day lag between the emergence of the four upper leaves and severity was correlated mainly with the number of dewy days and pycnidia formation on those leaves. The time lag increased for plants of temperature indices 7-21 days prior. There were lower correlations in the both dwarf and semi-dwarf cultivars in the rain-sparse region. The vertical arid region which was characterized by less rainfall, prolonged rainless progress of the pathogen from lower to higher leaves was affected by the periods, and hot spells toward the end of the growing season than in the distances between consecutive leaves--the "ladder effect". The rate of rainy coastal plains. vertical progress on the dwarf wheats under the severe epidemics was Additional key words: Septoria tritici, Triticum aestivum, epidemiology. Septoria leaf blotch of wheat, which is caused by Septoria tritici consecutive days with a minimum temperature of 7 C or less Rob. ex Desm., is a major wheat disease in many parts of the world, inhibited infection. Many investigators suggested 20-24 C as the particularly on the Mediterranean seacoast, in South America, in optimum range for disease development, but disease development the highlands of East Africa, and in Australia (11,13,17,18). Severe usually proceeds well over the range of 16-27 C (17,18). Certain Septoria leaf blotch epidemics which caused significant economic phases in pathogen development probably are temperature crop losses in the recently introduced semi-dwarf wheats dependent; however, specific information on the relationship (4,11,13,18) occurred in North Africa during the unusually wet and between disease development and temperature during the wheatcool 1968-1969 growing season. Although Septoria leaf blotch was growing season are lacking (15,16) reported in Israel on indigenous emmer (Triticum dicoccoides The objective of this study was to determine the relationship Koern.), on some'land varieties' of bread (T. aestivum L.), and on between environmental factors and the vertical progress of durum wheats (T. durum Desf.), only occasionally were Septoria leaf blotch on susceptible short-statured spring wheat appreciable yield losses sustained by the 'classical' commercial cultivars differing in maturity and plant height. bread wheat cultivars (3,4,6). The widespread and rapid replacement of the local wheats by the high-yielding cultivars, MATERIALS AND METHODS combined with favorable environmental conditions and changes in The trials were conducted during the 1975-1976 growing season agronomic practices, contributed to the recent occurrence of severe the tris Er e onducted in g searid leafat the Lakhish Experiment Station (situated in the semiarid leafbloch piphtotcs 4,1113,8).s uthern coastal plains [average rainfall of 300--400 mm] and There is little specific information on the relation of weather to the epidemics of Septoria leaf blotch. Saari and Wilcoxson (13) duplicated At the Bet-Dagan Experiment Station (situated in the reported that epidemics caused in wheat by S. tritici occurred in rainy centra:l coastal plain [average rainfall of 500-600 mm]). Five high-yielding, short-strawed, autumn-sown spring wheat cultivars countries in the Mediterranean basin in areas receiving 700 mm or more of rainfall annually, and that with decreased rainfall, the were sown,: susceptible early-maturing cultivars, the dwarf 'Barkai' disease becomes progressively less of a problem. Severe Septoria (V238-8822-1 I / Miriam 2; V238-8822-1 = Yt/ / Nrn10/ B2Ileaf blotch epidemics causing substantial losses in yield occur in the IC/3/FA), the semi-dwarf cultivars 'Miriam' (Ch53/2/Nrn semiarid southern plains of Israel with average annual rainfall of 10/B26/3/Yq 54/4/2 Merav), and 'Hazera 337' (Inia "s" [Son 300 mm or less (3,6). All stages of the infection cycle, from 64-Tzpp/Yq 54]); and two susceptible wheats with intermediate pycnidiospore liberation, dispersal, penetration, lesion maturity date, the dwarf, 'Bet-Dagan 131' (Yt//NrnlO/B21development, and pycnidial formation, are dependent on moisture, 1 C/ 3 / FA), and the semi-dwarf'Lakhish', a sib selection of the same both as rainfall and dew (7,8,15,17,19). Shaner and Finney (16) cross. All cultivars originated at the Volcani Center except Hazera reported that severe epidemics of Septoria leaf blotch occurred at 337, which originated at the Hazera Seed Co., Israel. Lafayette, Indiana in seasons with 40 or more rainy days from 1 Wheat plots (5m X 9m) were sown in four replications, each plot April to 14 June. Renfro and Young (12) observed that two separated from adjacent plots by 2-i-wide buffer strips to reduce interplot interference. The mean number of seedlings per square meter was about 250 for each of the wheat cultivars tested. Septoria leaf blotch epidemics were established by spreading wheat straw 0031-949X/80/03017906/$03.00/0 infested with viable pycnidia of S. tritici that contained viable ©1980 The American Phytopathological Society pycnidiospores, just after seedling emergence. Finely chopped Vol. 70, No. 3,1980 179 infested straw was spread over the wheat canopy twice during the Twenty randomly selected plants in each wheat plot were marked rainy days, approximately 10 days following the first straw for future observations on plant and disease development. The application. disease development throughout the season was assayed at 7-day Standard meteorological stations were placed at the center of the intervals from the detection of Septoria leaf blotch symptoms on wheat plots at the two locations. Each station contained a standard the main culms of each marked plant. The following parameters rain gauge, a minimum-maximum thermometer, a thermowere determined: hygrograph (Model 594, The Bendix Corporation, Baltimore, MD) fitted with a dew duration recorder (Machine Shop, Iowa (a) Disease severity: the percent of green area of each leaf covered State University, Ames). The dew duration apparatus operated on by pycnidia of S. tritici (5). the principle of recording changes in the length of a lamb gut (b) The maximum height (centimeters) above ground level at membrane (Gold-beater's skin method) fitted between two levers which pycnidia of S. triticicould be found on green plant tissue. connected to a microswitch and an electromagnet. The membrane, which expanded when wet and contracted when dry, was located at The phenology for each plant was recorded throughout the season plant height level in the wheat plot. in parallel with disease development observations according to the
KANT'S SECOND THOUGHTS ON RACE
During the 1780s, as Kant was developing his universalistic moral theory, he published texts in which he defended the superiority of whites over non-whites. Whether commentators see this as evidence of inconsistent universalism or of consistent inegalitarianism, they generally assume that Kant's position on race remained stable during the 1780s and 1790s. Against this standard view, I argue on the basis of his texts that Kant radically changed his mind. I examine his 1780s race theory and his hierarchical conception of the races, and subsequently address the question of the significance of these views, especially in the light of Kant's own ethical theory. I then show that during the 1790s Kant restricts the role of the concept of race, and drops his hierarchical account of the races in favour of a more genuinely egalitarian and cosmopolitan view.