Journal of Plant Diseases and Protection

Ahmed, H.; Chang, K.; Hwang, S.; Strelkov, S.; Bing, D.; Turnbull, G.

doi: 10.1007/BF03356218pmid: N/A

Sixty-three isolates of Didymella rabiei collected from southern Alberta were analyzed for pathogenic variability using six differential chickpea genotypes. Although all isolates were pathogenic on all of the differentials, they varied in virulence. The reaction of host genotypes was classified as resistant or susceptible based on the severity of disease symptoms, and isolates were grouped into 25 pathotypes, suggesting a very high level of diversity in the population of D. rabiei. The predominant pathotypes were XV and XVI, each comprising 14% of the total number of isolates tested. Pathotypes VII and XXV each represented 8% of the isolates tested, while patho-types III, IV and XIX each represented 6%. The rest of the pathotypes each represented 2–3% of the total isolates. Cluster analysis generated two main groups, at an average distance of 1.0 between the clusters. Fourteen subgroups were identified among the isolates at an average distance between isolates and within subgroups of 0.5. No associations were found between geographical origins, pathotypes, cluster groupings, parts of the plants or the host varieties from which the isolates were obtained.

Omar, M.; Abd-Elsalam, K.; Aly, A.; El-Samawaty, A.; Verreet, J.

doi: 10.1007/BF03356219pmid: N/A

Pathogenicity of 21 isolates of Macrophomina phaseolina was tested on three cotton cultivars under greenhouse conditions. Analysis of variance (ANOVA) showed that the main effects of both isolates (P= 0.000) and cultivars (P= 0.000) were very highly significant sources of variation in postemergence dampingoff and survival. Isolate x cultivar interaction was also a significant source of variation in postemergence damping-off (P= 0.03) and survival (P= 0.04). Statistically significant isolate, cultivar, and isolate x cultivar interaction suggest that physiologic specialization exists within M. phaseolina isolates pathogenic on cotton. It also implies that the resistance of the tested cultivars is a mixture of both vertical and horizontal resistance and there are significant differences among cultivars in both types of resistance. Cluster analysis of the isolates, based on their virulence patterns on different cultivars, differentiated the isolates reasonably well and grouped them into three pathotypes. The isolates were distinguished phenotypically by using a defined medium containing 120 mM potassium chlorate. Chlorate-resistant isolates (33.3%) grew densely on chlorate medium, while the remaining isolates (66.7%) were chlorate sensitive and showed either a restricted (23.8%) or feathery (42.9%) growth. No associations were observed between grouping the isolates based on their virulence patterns and their chlorate phenotypes. Random amplified polymorphic DNA (RAPD) analysis was used to evaluate the genetic diversity of the isolates. In this analysis, polymerase chain reaction was performed by using four random decamer primers. All the primers detected polymorphisms in all the tested isolates. Cluster analysis by the unweighted pairgroup method of arithmetic mean (UPGMA) placed the isolates in three distinct groups. Grouping the isolates based on cluster analysis of their virulence patterns did not match that based on cluster analysis of their RAPD profiles while, grouping the isolates based on cluster analysis of their RAPD profile exhibited clear correlation with their chlorate phenotypes.

Sieling, K.; Ubben, K.; Christen, O.

doi: 10.1007/BF03356220pmid: N/A

The soilborne fungus Gaeumannomyces graminis var. tritici (Ggt) causing take-all in wheat, barley and rye is regarded as the most important disease on wheat in short rotations with a high proportion of cereals. In 1996/97–1998/99, winter wheat was grown in a field trial with two preceding crops (oilseed rape (OSR) vs. winter wheat), two sowing dates (end of September vs. end of October), eight mineral nitrogen (N) fertilizer treatments (0–200 kg N ha−1) and fluquinconazole seed treatment (no vs. yes), which was carried out at the Hohenschulen Experimental Station near Kiel in NW Germany. Tiller numbers m−2, biomass m−2, grain yield, and yield components at harvest of wheat (cv. Toronto) were investigated. During the growing season, the incidence of take-all caused by Ggt was rated on a scale of 1–9.

Jamar, L.; Lefrancq, B.; Lateur, M.

doi: 10.1007/BF03356221pmid: N/A

The effectiveness of potassium bicarbonate against Venturi a inaequalis, the cause of apple scab, was studied. In vitro experiments with sodium, ammonium and potassium bicarbonate, as well as potassium phosphate used at 1% (w/v), reduced colony growth of V. inaequalis by 99, 98, 90 and 64%, respectively. Under controlled conditions in greenhouse experiments, a single spray of 0.5 or 1% (w/v) aqueous solution of sodium or potassium bicarbonate applied on young apple seedlings, 24 h before or 24 h after scab artificial inoculation, significantly controlled the disease. Greater effectiveness of potassium bicarbonate was recorded when the period of time before or after the inoculation was reduced. A significant increase of the fungicide activity of potassium bicarbonate was observed when salt was mixed with mineral oils. However, combining potassium bicarbonate with vegetable linseed oil and grapefruit seed extract did not increase its efficacy whereas these two vegetable products used alone reduced significantly scab infections. Formulated potassium bicarbonate, under the trade name Armicarb® 100 and containing surfactant compounds, was more effective than bicarbonate alone. A phytotoxicity effect of potassium bicarbonate was observed with a 0.75% dose. The potential and limitations of potassium bicarbonate used to control apple scab in the field are discussed.

Yang, X.; Ma, X.; Yang, L.; Yu, D.; Ni, H.

doi: 10.1007/BF03356222pmid: N/A

This paper developed an in vivo bioassay method of determining bioactivity of compounds against Magnaporthe grisea (Hebert) Barr. with barley (Hordeum vulgare L.) plants, instead of rice (Oryza sativa L.) plants. To confirm whether this method could be used to screen active compounds against this fungus or not, experiments were conducted using the five fungicides tricyclazole, kasugamycin, thiophanatemethyl, iprobenfos and salicylic acid with different action modes. The results showed there were close correlation in disease severity and no significant difference in EC50 values between rice and barley, and the coefficients of variations of EC50 values were similar between rice and barley for the four tested fungicides in both detachedleaf-segment and pot-seedling tests. The advantage in bioactivity determination with barley was timesaving. Plant materials could be used at the 1-leaf stage for barley while at the 5-leaf stage for rice. So it shortened about 14 days for the preparation of plant materials for tests.

Boss, D.; Schläpfer, E.; Fuchs, J.; Défago, G.; Maurhofer, M.

doi: 10.1007/BF03356223pmid: N/A

Field bindweed (Convolvulus arvensis) and hedge bindweed (Calystegia sepium) are noxious perennial weeds which can only partially be controlled by chemical or mechanical methods. Therefore biological control as an alternative is of increasing public and commercial interest. In this study we show that a mycoherbicide based on the fungus Stagonospora convolvuli LA39 efficiently controls bindweed infestations in three noncrop field trials conducted at different locations in two different years. It was the aim of this study to optimize the application strategy of the mycoherbicide regarding number and date of applications, as well as the application rate. It could be shown that conidia of LA39 should be applied two to five times from the beginning of May to the beginning of July, depending on the size and density of bindweed infestation. For an efficient bindweed control the mycoherbicide has to be applied at 40–160 ml m−2 and 5 × 106 conidia ml−1. Since pathogenic fungi often lose their aggressiveness upon continuous in vitro subcultivation, the influence of subcultivation on the virulence of LA39 was monitored over 30 vegetative generations. LA39 lost aggressiveness against both bindweed species between the third and the ninth vegetative generation. However, virulence of the fungus was fully restored after a single host plant contact. Thus continuous subcultivation should be avoided when using LA39 as a biocontrol agent.