Showing papers on "Leaf spot published in 1973"

The Yellowing Virus Diseases of Beet

Abstract: Publisher Summary The yellowing virus diseases, characterized by stunting of infected plants, accompanied by rolling, yellowing, reddening, and brittleness of affected leaves, are emerging as the most important artificial group of plant virus diseases. The viruses inducing these diseases fall into three currently recognized virus groups; persistent aphid-transmitted viruses with isometric particles, 25-30 nm; semipersistent aphid-transmitted viruses with flexuous, filamentous particles; and viruses transmitted by whiteflies. Because of the general high frequency of the yellowing diseases in affected crops and their severe effect on the physiology of diseased plants, disease interactions play an important role in the losses induced by these diseases. A number of reports state that leaves of beet plants infected with yellowing viruses are very susceptible to infection with Alternaria spp. and other fungi. An interaction between BMYV and Alternaria leaf spot on leaves of mature sugar beet plants has been reported by Russell. Alternaria leaf spot is of no commercial importance in beet crops that have little BMYV infection. In BMW-infected crops, however, Alternaria can cause severe losses of yield. Observations by Bennett indicate that yellows niay render spinach plants much more susceptible than healthy plants to certain types of vascular parasites and root rot organisms. Zink and Duffus reported that losses in California were severe as a result of a severe interaction between BWYV and lettuce mosaic virus on certain lettuce cultivars.

Wind-Blown Soil in the Epidemiology of Bacterial Leaf Spot of Alfalfa and Common Blight of Bean

Abstract: Potted, healthy alfalfa and bean plants were placed in a laboratory wind tunnel and exposed to naturally infested dry field soil blown at regulated air speeds. The plants were then kept on a greenhouse bench for 10-14 days, and the resulting incidence of bacterial leaf spot of alfalfa and common blight of bean was determined. Disease incidence increased as wind speed and exposure time increased and was greater in the row nearest the wind source. Lesions were mostly contined to the lower 10-cm of plant shoots where the blowing particles were most concentrated. Lesions on stems were confined to their windward side. Bacterial leaf spot incidence increased from 6% after 3-min exposure to soil blown 9.4 m/sec to 26% after 5-min exposure at 13.9 m/sec. Blight incidence in 2-week-old bean plants from exposure to soil blown 13.9 a/sec for 3 and 5 min was 25 and 55%, respectively. Phytopathology 63: 1417-1419 Additional key words: wind, Xanthomonas alfalfae, Xanthomonas phaseoli. Researchers (1, 6, 8) have suggested that wind-blown soil and debris not only disseminate bacterial plant pathogens but wound host tissue and permit bacterial penetration. Vakili (7) reported wind-blown, naturally infested soil t o be important in the epidemiology of bacterial spot of tomatoes in the field. Plant injury caused by wind-blown sand or soil is well documented. Wind speeds of 17.9 mlsec (40 mph) without abrasive flux slightly damaged green bean plants but adding 6 g/cm widthlmin of sand into the wind-stream greatly increased injury and reduced yields up to 53% (5). The average yield reduction of alfalfa exposed to sand blown at 7 wind velocities between 8.9 m/sec (20 mph) and 13.9 m/sec (31 mph) for 12 min was 55% (4). In Kansas, summer prevailing winds are from the south, and most stem lesions of common blight of beans and bacterial leaf spot of alfalfa occur on their south side, frequently during hot, dry periods. This suggests that wind-blown soil could be an inoculating agent. The effects on the incidence of bacterial leaf spot of alfalfa and common blight of bean from exposing healthy plants to naturally infested soil or artificially infested sand blown at different speeds and durations in a wind tunnel are reported in this

Control of peanut leaf rust alone or in combination with Cercospora leaf spot

Abstract: In field trials in 1971, it was shown that rust caused by Puccinia arachidis can be a potentially serious leaf disease of groundnuts in the near absence of Cercospora arachidicola and C. personata. Losses from P. arachidis were significantly reduced by weekly applications of chlorothalonil at 1.7-1.8 l/ha, Dithane M45 (Zn + maneb) at 1.7 kg/ha, and Fungi Sperse Magi-Cal (30.5% S, 5.7% Zn, 23% organic Ca) at 9.4 l/ha to plants treated with 560 g benomyl/ha for control of Cercospora leaf spot. These fungicides and Manzate 200 (Zn + maneb) and combinations of benomyl + Manzate 200, benomyl + Manzate 200 + oil, Dithane M45 + Du-Ter (triphenyltin hydroxide) and Benlate M (commercial mix of benomyl and Manzate 200) also significantly reduced losses on plants affected with both diseases.

Infection of Lolium and Festuca spp. by Drechslera siccans and D. catenaria

Abstract: Drechslera siccans was the commonest of the species of this leaf spot pathogen found on single spaced plants of Lolium perenne at Aberystwyth. D. catenaria and D. dictyoides were also frequently isolated. A wide range of genotypes within the host species L. perenne, L. multiflorum, Festuca arundinacea and F. pratensis, and structural hybrids between F. arundinacea and L. multiflorum, were all equally susceptible to conidial infection by D. siccans in the glasshouse and showed similar development of leaf spot symptoms, even though Festuca spp. are not normally attacked in the field. However, when exposed to infection out of doors there was significant variation in resistance, both between species and often also between genotypes within the same species. As in so many other instances of fungal infection, tetraploidy appeared to confer a higher level of resistance. The degree of resistance of a F. arundinacea × L. multiflorum amphiploid and two succeeding backcross generations to L. multiflorum approximated to that of the more susceptible L. multiflorum parent. By contrast to D. siccans, when plants were inoculated with D. catenaria in the glasshouse, both intervarietal and intravarietal variation in leaf spot development was evident. Resistance to D. siccans appears to depend partly on a limitation of conidial production, and to D. catenaria on restriction of hyphal growth following infection, which may explain the relative discrepancies between field and glasshouse results. The implications for resistance breeding are discussed.

Distribution and morphology of Alternaria tenuis associated with leaf spots in the Sudan

Abstract: Altemaria leaf spot symptoms have been observed on eight different host species in the dry arid regions of northern Sudan. A. tenuis Nees was the only Altemaria species isolated from diseased plants. In the more humid regions southwards A. solani Sorauer and other Alternaria species are known to be responsible for the disease. Hence infection by A. tenuis seems to be favoured by more arid climatic conditions. Isolates from the eight host species varied markedly in colonial morphology. Significant differences between the isolates were shown by measurements of spore body length, total spore length, spore body width and growth rate. It is concluded that these isolates represent distinct strains of A. tenuis .

Leaf spot and leaf drop of the apple cultivar Golden Delicious : a physiological disorder.

Abstract: The results are given of several experiments on the effects of temperature, daylength and light intensity on the incidence of leaf spot and leaf drop on young pot-grown Golden Delicious apple trees on M9 The number of spotted leaves was much the highest at 21 deg C and declined successively at the following temperatures: 17 deg > 25 deg > 9 deg > 13 deg Plants grown in sunlight had the fewest spotted leaves at most temperatures, and those grown under fluorescent light with 16- or 8-h photoperiods the most Differential effects of high or low light intensities were slight The oldest leaves on long shoots were usually the first to be affected Foliar sprays of K, Ca, Mg, Mn or sugars did not affect the disorder, neither did soil moisture variation (Abstract retrieved from CAB Abstracts by CABI’s permission)

Effect of Cercospora Leaf Spot of Peanuts on Forage Yield and Quality and on Seed Yield1

Abstract: Epidemics of Cercospora leaf spot reduce the forage and seed yield of peanuts (Arachis hypogaea L.). The purpose of this study was to determine the effect of different levels of control of Cercospora leaf spot disease on defoliation, forage yield, quality, mineral composition, and seed yield of peanuts. Adapted peanut cultivars were grown according to recommended management practices in the Coastal Plain Region of Georgia during 1971 and 1972. Three foliar fungicides (benomyl 50W, chlorothalonil 75W, and copper-sulfur dust) were compared with an unsprayed control. Fungicides were applied on a 14- day schedule, with five applications in 1971 and six applications in 1972. Benomyl and chlorothalonil gave significantly better control of Cercospora leaf spot than copper-sulfur dust as evidenced by reduced defoliation. Copper-sulfur dust was superior to the unsprayed control. As a consequence of disease control (very little defoliation), forage yields, in vitro digestibility, protein content, and seed yields were higher, and forage fiber content was lower. Higher calcium levels in forage were associated with good disease control in both years; Mg, Mn, Fe, Al, and Mo were higher in only 1 year. These differences between years could have been due to the use of different peanut cultivars. Several elements (P, B, Zn, Sr, Ba and Na) were not changed as a result of leaf spot control in either year. During both years, potassium decreased with control of leaf spot. Higher levels of Cu were observed in the forage treated with copper-sulfur dust in both years. Thus, control of Cercospora leaf spot in peanuts was accompanied by an increase in yield and quality of forage and yield of seed, and levels of control achieved were highly correlated with yield and quality.

Perpetuation of Species of Cercospora and Ramularia Parasitic on Oilseed Crops

Abstract: Mode of perpetuation of 4 pathogens viz. Cercospora carthami Sundararaman and Ramakrishnan, Ramularia carthami Zaprometov, Cercospora linicola Pavgi and Rathaiah and Cercospora sesamicola Mohanty inciting leaf spot diseases of safflower, flax and sesame has been investigated. C. carthami and C. linicola perpetuate through a) the vegetative saprobic mycelium and b) viable stromata embedded in the crop debris. R. carthami and C. sesamicola perpetuate only through the viable sclerotia in the crop debris.

Identification of Fusarium leaf spot(Fusarium nivale) newly reported in Korea

Abstract: From the new rice variety Tong-il, disease symptoms similar to Fusarium leaf spot reported in Japan was observed in Korea. Causal organism was isolated and identified as Fusarium nivale causing Fusarium leaf spot through the study of conidia shape, ascus formation on diseased spot, and ascospore. These results also showed good agreement with that of other investigators. Under the field condition, marked occurrence of this disease has observed by heavy nitrogen application. The optimum temperature for the growth of this fungus was .

Bacterial leaf spot of cowpea in Queensland

Abstract: A bacterial leaf spot of cowpea (Vigna sinensis) was observed for the first time in Queensland in a seed increase plot on the Darling Downs in 1971. The disease at that time was particularly severe in one line, C.P.I. 200201. In 1973 the disease recurred on cowpeas planted in the same area. In 1925 Gardner and Kendrick (3) recorded a bacterial disease of cowpeas and named the causal organism Bacterium vignae Gardner and Kendrick, 1923. This bacterium was later found to be synonomous with Pseudomonas syringae Van Hall, 1902 (1). Noble et al (9) recorded B. vignae on cowpeas in New South Wales in 1934 but this is the first report from Queensland of a bacterial leaf spot disease of this host. Individual leaf spots varied from small circular spots to larger oval or lobed lesions 5 to 8 mm in diameter. Spots on mature leaves had a light tan central area surrounded by a dark red marginal zone. Adjacent leaf spots coalesced causing considerable damage to the leaf lamina (figure 1). Pod symptoms were not observed in the field.

Control of mercury-resistant Pyrenophora avenae on seed oats with methyl arsenic sulphide

Abstract: British and New Zealand seed oats infected with Pyrenophora avenae Ito & Kuribayashi were treated with a number of different non-mercury compounds and one organic mercury compound in an attempt to evaluate their effectiveness in controlling leaf spot and seedling blight caused by this fungus. Best control was obtained with seed dressings containing methyl arsenic sulphide (‘Rhizoctol’ and ‘Rhizoctol Combi’). A thiram seed soak, ‘Dithane M-45’, RH 893, and ‘Vitavax 75’ reduced recovery of P. avenae but did not give complete control. ‘Voronit Extra’ and ‘Orthocide 75’ gave about 75 percent control, HPMTS gave about 50 percent, and ‘Ceredon’ and ‘Cerenox’ gave little control.

Occurrence of Angular Leaf Spot Disease of Tobacco in Japan

Abstract: An unfamiliar disease of tobacco plants, the symptom of which is brownish or blackish angular spot on the leaves, occurred in Yamaguchi prefecture in 1970. The author obtained five bacterial isolates from the diseased leaves, and tested their characteristics in comparison with Pseudomonas tabaci.Not any differences were observed between the pathogenic isolates and P. tabaci in bacteriological and serological characteristics.Angular leaf spot symptoms produced by these pathogenic isolates were found to be apparently distinguishable from those produced by P. tabaci.From these results, the pathogenic isolates were tentatively identified as P. angulata causing angular leaf spot disease of tobacco.