Morphological and Genotypic Characterization of Fungi Associated with the Ascochyta Blight Complex in Western Regions of Algeria

The study is conducted in two growing areas of garden pea (Pisum sativum L.) in northwestern Algeria. Damages caused by Ascochyta sp complex are important in particular for the variety of Kelvedon Wonder. Observations carried out on the infected plants for several years, indicate the presence of superimposed necrosis of different sizes on all aerial organs. However, these observations do not differentiate symptoms by species. The results of morphological and molecular characterization with sequencing in internal transcribed spacer (ITS) regions and inoculation tests on 32 isolates in the laboratory of symbiosis and plant pathology from Toulouse (France), show a reconciliation of the sequencing by polymerase chain reaction (PCR) products and size necrosis for all Ascochyta pinodes and pinodella. Alone, Ascochyta pisi is distinguished by a smaller size necrosis. On the molecular level, all isolates whose ITS regions were amplified by PCR, expresses similar size products (550 bp). This molecular weight is found on a large set of pathogenic fungi. The three species of Ascochyta sp complex do not exhibit polymorphism for Pisum sativum species and have an identical molecular weight. The pathogenicity tests performed showed differences in aggressiveness on the host plant. Ascochyta pinodes is the most aggressive than the other two species. As a result, it causes more damage to the crop.

Sensitivity of Ascochyta Species Infecting Pea, Lentil, and Chickpea to Boscalid, Fluxapyroxad, and Prothioconazole

Management of Ascochyta blight in pea, lentil, and chickpea relies on repeated fungicide applications, which has led to development of fungicide resistance and disease control failures in some systems. In vitro assays were conducted to determine baseline fungicide sensitivity in Mycosphaerella pinodes (Ascochyta pinodes), A. lentis, and A. rabiei populations to the demethylation-inhibiting fungicide prothioconazole and the succinate dehydrogenase-inhibiting fungicides boscalid and fluxapyroxad by determining the effective concentration at which 50% of germination or fungal growth was inhibited (EC50). Mean boscalid EC50 values from conidial germination assays were 0.669, 0.639, and 0.171 μg/ml and from mycelial growth assays were 0.258, 0.791, and 0.443 μg/ml for M. pinodes, A. lentis, and A. rabiei, respectively. Mean fluxapyroxad EC50 values were 0.050, 0.763, and 0.057 μg/ml for M. pinodes, A. lentis, and A. rabiei, respectively. Mean baseline EC50 values for prothioconazole with mycelial growth were 0.541, 0.604, and 0.283 μg/ml for M. pinodes, A. lentis, and A. rabiei, respectively. A single discriminatory fungicide concentration of 1 μg/ml was selected for all species. Established sensitivity profiles and discriminatory concentrations will be used to monitor sensitivity shifts in populations of Ascochyta spp. and to make effective disease management recommendations.

Studies susceptibility of peas and field peas cultivars to Ascochyta pinodes (Jones)

The aim of the work was to find plants resistant to <i>Ascochyta pinodes</i> causing leaf and pod spot-pot of peas and field peas. Fourty five cultivars of peas and field peas and 6 breeding materials were tested in the field in the period 1975-1979 on artificially inoculated field plots. Cultivars: Bartel, Birte, Bodil, Borek, Jubilat, Karo, Meteor, Rondo and Żółty Pomorski were to found be less susceptible. In laboratory and greenhouse conditions pea and field pea cultivars were examined for susceptibility. to pathotypes 3 and 5 of <i>Ascochyta pinodes</i>. The results obtained proved that cultivars: Bartel, Birte, Bodil, Borek, Jubilat, Karo, Meteor, Rondo and Żółty Pomorski to be less susceptible to two pathotypes of <i>Ascochyta pinodes</i>.

Occurrence of pathotypes of Ascochyta pinodes (Jones) in the Olsztyn district

The causal agent of leaf and pods spot-pot of peas and field peas in the Olsztyn district was the fungus <i>Ascochyta pinodes</i> (Jones). Investigated isolates of <i>A. pinoides</i> different by macroscopic and microscopic features. From diseased leaves and pods of peas and field peas saprophytic fungi were also obtained. Among them <i>Alternaria alternata, Cladosporium cladosporioides, Epicoccum purpurascens, Stemphylium botryosum, Sordaria fimicola</i> and mycelia sterilia were dominant. In the study on the identification and distribution of pathotypes of <i>A. pinodes</i> (Jones) six pathotypes were identified among which pathotypes 3 dominated. The identified pathotypes differed by macroscopic and microscopic features.

Field assessment of partial resistance to mycosphaerella blight in Pisum subspecies accessions

Conner, R. L., Gossen, B. D., Hwang, S. F., Chang, K. F., McRae, K. B. and Penner, W. C. 2012. Field assessment of partial resistance to mycosphaerella blight in Pisum subspecies accessions. Can. J. Plant Sci. 92: 289–296. Mycosphaerella blight, caused by Mycosphaerella pinodes (Berk. & Bloxam) Vestergr., the teleomorph of Ascochyta pinodes Jones, is an important foliar disease of field pea in the major production areas of the world. Partial resistance to mycosphaerella blight has been reported in some field pea cultivars, but, at best, they are only moderately susceptible. A 3-yr field study was conducted to evaluate the mycosphaerella blight reactions of 28 accessions from a number of subspecies of Pisum sativum L. and one accession of P. fulvum Sibth. A few of the accessions carried mutations for the genes af, tl, and st that affect the morphology of the leaflets, stipules and tendrils. Reactions to mycosphaerella blight were characterized based on the mean of the severity ratings taken on the two final assessment dates before the crop matured and also on the change in mycosphaerella blight severity between these two dates. In many of the accessions, severity ratings were similar to that of the moderately susceptible check cultivar, CDC Peko, while a few had high severity ratings similar to those of the susceptible check cultivars. The accession PI 512079, which has small stipules, branched petioles with many leaflets but no tendrils, had the lowest ratings for mycosphaerella blight severity. Four other accessions exhibited the smallest change in mycosphaerella blight severity at the end of the growing season. Differences in leaf morphology likely influenced the change in disease severity, since all the semi-leafless and leafless accessions had smaller changes in mycosphaerella blight severity than the susceptible check cultivars. In a detached leaf assay with two isolates of Mycosphaerella pinodes (Berk. & Bloxam) Vestergr., the smallest lesions formed on PI 512079, but otherwise the results failed to show a relationship with the observed severity values in the field trials.