Showing papers on "Leaf spot published in 1988"

Angular leaf spot.

Abstract: Common bean angular leaf spot (ALS), caused by Phaeoisariopsis griseola (Sacc.) FeiT., is widely distributed in tropical and subtropical regions worldwide, being responsible for great economic losses, especially in Latin America and the great lakes region in Africa In recent years, this disease became one of the most important bean productions constraints in Brazil. In this country, seed yield loss can be as high as 80% depending on the susceptibility of the cultivars and the time of the disease symptoms appearance In addition to yield losses, the quality, market value and suitability of seed for transport and use across bean-producing regions and national borders may be severely affected. In Brazil, a major part of bean production is by medium/small or subsistence farmers who do not apply fungicides to their crops due to its high cost. Although ALS can be controlled by fungicides, the development of resistance cuhivars would constitute a more environmentally and friendly alternative of the disease control that could be used in integrated crop protection strategies to reduce pesticide inputs. This paper reports results of the evaluation for bean angular leaf spot resistance to Mesoamerican races of P. griseola aiming the development and deployment of durable resistance do this disease. Plant material for the screening consisted of part of the CIAT's P. vulgaris core collection, including 357 accessions, representing the available range of crop types and ecogeographical location within the species. Out of the 357 P. vulgaris accessions evaluated, 281 belonged to the Middle American and 76 to the Andean gene pool. The pathotypes 63-15, 63-39, 63-23 and 31-31 of P. griseola were obtained from naturally infected common bean cultivars collected in different places in Brazil. Seeds of each cultivar were sown in aluminum pots containing 2,0 kg of soil at the rate of five seeds per pot. Conidia suspensions, for all inoculations, were obtained by culturing the fungus in bean-leaf-dextrose-agar medium. Inoculum was adjusted to 2 x 10^ conidia mL"^ Bean plants were inoculated 14-16 days after planting by spraying the conidial suspension onto the upper and lower leaves surfaces The inoculated plants were incubated in a moist chamber (> 95% RH) for 36-40 h. After this period of time, plants were transferred to greenhouse benches for another 14-18 days and evaluated for disease symptoms by determining the percentage of leaf area affected by the disease. Plants up to 5% of leaf area affected by the disease were considered as resistant. As expected a great variability of reactions to Mesoamerican races of P. griseola was found between accessions of the core collection, ranging from complete resistance to full susceptibility. Fourteen (Table 1) of the 357 accessions were resistant to the four pathotypes, 44 to three, 35 to two and 70 to only one pathotype. Pathotype 31-31 were the most pathogenic followed by pathotypes 63-51, 63-39 and 63-23.

Diseases of major pulse crops in Pakistan—a review

Abstract: The major pulse crops of Pakistan are chickpea, lentil, mungbean, and urdbean. Diseases are a constant threat and often a limiting factor in the cultivation of pulse crops. Chickpea is attacked mainly by blight, wilt and root rot complex. The main diseases of mungbean and urdbean are yellow mosaic virus (YMV), leaf crinkle virus (LCV), cercospora leaf spot, bacterial blight and charcoal rot. Lentil is attacked by rust, wilt and blight. Details are given of the symptoms, distribution and control of the diseases of economic importance.

Race-specific resistance to light leaf spot in Brassica oleracea

Abstract: Hybrid cultivars of Brassica oleracea , together with the inbred lines used commercially to produce them, were inoculated, as seedlings in the glasshouse, with conidia of Pyrenopeziza brassicae . Symptoms of light leaf spot, similar to those observed after field infection, were produced. A differential interaction between several host genotypes and pathogen isolates was shown, indicating the presence of specific resistance and corresponding virulence in the host and pathogen respectively. Resistance to P. brassicae appeared, in most cases, to be expressed as a dominant character.

Inheritance of Cercospora Leaf Spot Resistance in Mung Bean, Vigna radiata (L.) Wilczek

Abstract: Inheritance of Cercospora leaf spot resistance in mungbean was studied in 20 crosses involving crosses of resistant × susceptible, resistant × resistant, susceptible × susceptible lines. 3:1 ratio was observed in all 14 F2s involving resistant × susceptible parents. The inheritance of Cercospora leaf spot resistance is thus controlled by a single recessive gene. Our results are contradictory to observations of Thaklk et al. (1977 a, b) who found monogenic dominant inheritance of Cercospora leaf spot resistance in mungbean.

Identification of the pathogens responsible for bacteriosis of tea plant occurred in 1983.

Abstract: A bacterial disease of tea plant was observed in Shizuoka Prefecture in July, 1983. The symptoms were characterized by leaf spots with irregular shape and apparent necrosis of the spongy parenchyma tissue. Two distinct pseudomonads were isolated from these lesions. On the basis of bacteriological and pathological tests, they were identified as Pseudomonas syringae pv. theae and P. avenae, respectively. P. syringae pv. theae was isolated with high frequency, and produced the typical shoot blight symptoms or the characteristic leaf spot symptoms depending upon the temperature and humidity in inoculation tests and the variety of tea plants. P. avenae was isolated with lower frequency, and produced leaf spot symptoms different from those observed in the field in color and shape. From these results, the present disease was determined as one of the symptoms of bacterial shoot blight caused by P. syringae pv. theae. The role of P. avenae in this hacteriosis remained to be clarified.

Genetic basis of resistance to zonate leaf spot disease in forage sorghum.

Abstract: Generation mean analysis was carried out for ten crosses between two resistant and two susceptible parents to find the genetic basic of resistance to zonate leaf spot disease in forage sorghum. In all crosses except one, at least one type of non-allelic interaction was present. Both additive and dominance gene effects were significant for most crosses. Duplicate type epistasis was present for the inheritance of this disease. Resistance to this disease revealed overdominance. Appropriate breeding plans were suggested to exploit the disease resistance.

Interactions between an acute ozone dose, eastern cottonwood, and Marssonina leaf spot: implications for pathogen community dynamics

Abstract: The effect of an acute ozone dose applied to eastern cottonwood (Populus deltoides Bartr.) on subsequent lesion production of the leaf spot fungus Marssonina brunnea (Ell. et Ev.) P. Magn. was investigated. Two cottonwood clones were exposed to 393 μg∙m−3 (0.20 ppm) ozone for 5 h and then inoculated with conidia of M. brunnea in leaf-disk and whole-plant assays on leaves of different ages (according to the leaf plastochron index (LPI)). There was no significant difference in lesion production on ozone-treated or control foliage, and significantly more lesions were produced on LPI 5 leaves compared with LPI 3, 7, and 9 leaves, irrespective of clone or treatment. These results show that infection of plants by facultative parasites will not necessarily increase when plants are exposed to air pollutants. In another study, urediospore production by an obligate parasite, the cottonwood leaf rust fungus (Melampsora medusae Thum.), was shown to decrease on cottonwood plants treated with an acute ozone dose in com...

Life cycle of a new species of Blumeriella (Ascomycotina: Dermateaceae), a leaf-spot pathogen of spirea

Abstract: Cylindrosporium filipendulae Thuem. was isolated from diseased Spiraea ×vanhouttei Zabel in Tennessee. On the basis of acervulus formation and conidial morphology, C. filipendulae is transferred to the genus Phloeosporella. Apothecia observed on overwintered S. ×vanhouttei leaves were determined by cultural methods to be the teleomorph of the Phloeosporella species. Conidia produced in culture by ascospore isolates infected spirea leaves and induced symptoms identical with those caused by the Phloeosporella species. Morphology and development of the teleomorph were compared with those of Blumeriella jaapii (Rehm) v. Arx (= Coccomyces hiemalis Hig.) and found to be quite similar. The new teleomorph is described as a species of Blumeriella.

Cryptosporiopsis citri sp. nov.; cause of a citrus leaf spot in the Pacific Islands.

Abstract: A fungus causing a leaf-spotting disease and leaf drop of Citrus spp. in the Pacific Islands is described as Cryptosporiopsis citri sp. nov. Previously, this fungus was recorded as Guigndrdia citricarpa Kiely. C. citri differs from G. citricarpa in morphology, cultural characteristics, and disease symptoms.

Effects of stubble-borne fungal inoculum on incidence of leaf diseases and yields of barley in Western Australia

Abstract: Effect of stubble residues on leaf diseases and yield of barley (Hordeum vulgare L. cv. Dampier) were studied by adding small quantities of infested stubble to test plots grown on land where a non-barley crop or pasture had been grown in the previous year. Experiments conducted at 5 locations in 198 1 and 1982 showed that stubble residues increased leaf disease. The severity of leaf disease varied with location and year. High levels of scald (Rhynchosporium secalis) were recorded at all locations, but substantial levels of net blotch (Drechslera teres) occurred only at northern locations. Halo spot (Selenophoma donacis) and a leaf spot caused by Drechslera verticillata were either absent or occurred in minor proportions. The incidence of powdery mildew (Erysiphe graminis f.sp. hordei) at Mt Barker in 1982 was not related to the presence of stubble residues. Grain yield losses of 9 and 28% occurred in the stubble amended plots in 1981 and 1982, respectively. Reductions in number of heads and number of seeds per plot appeared to be the major components of yield loss.

Evaluation of Asparagus officinalis L. germplasm for resistance to Stemphylium leaf spot

Abstract: Asparagus officinalis L accessions were screened for resistance to Stemphylium leaf spot under controlled environmental conditions The plants were inoculated with a conidial suspension of two isolates of Stemphylium sp from asparagus Disease severity assessments, based on percentage stem area necrosis (% SAN), were made 13—17 days after inoculation Estimates of mean % SAN ranged from 31 to 74% None of the accessions showed outstanding levels of resistance, but significant differences were observed in disease susceptibility between accessions The accessions also differed for within-accession variability Selection for increased levels of resistance is likely to be most effective in accessions with high within-accession variance values

Improving field screening of groundnut genotypes for resistance to foliar fungal diseases

Abstract: In order to avoid problems encountered in field trials for resistance to rust (Puccinia arachidis and late leaf spot (Phaeoisariopsis personata) [Mycosphaerella berkeleyi]) caused by damage from one disease when the other is being evaluated, each genotype was tested for reaction to each disease in separate trials. The use of Bavistin [carbendazim] to prevent the establishment of leaf spot in the rust resistance trial and Calixin [tridemorph] in the leaf spot trial to prevent establishment of rust enabled these trials to be effective.