Mycosphaerella Pinodes Research Articles

Effect of pea canopy architecture on microclimate and consequences on ascochyta blight infection under field conditions

In order to investigate the impact of pea canopy architecture and development on microclimate and infection by Mycosphaerella pinodes, two field experiments were conducted in 2009 and 2010 at Le Rheu (France) to obtain canopies contrasted in height, closure dynamic, leaf area index (LAI) and leaf area density (LAD). Three pea cultivars (Athos, Antares, Gregor) were sown at two (80 and 40 seeds/m2 in 2009) and three densities (80, 40 and 30 seeds/m2 in 2010) and microclimatic sensors were located inside the canopy (at the bottom and in the middle) and outside. Two main sources of wetness were identified: rainfall and dew. During rainfall periods, average daily leaf wetness duration (LWD) was about 15 h, and 3 to 10 h longer inside than outside the canopies. LWD was positively correlated with LAI until canopy closure during these periods. During dry periods when dew was the only source of leaf wetness, average daily LWD was short, decreasing as the canopy developed. Shorter LWDs were observed at the base than at the mid-level of the canopies and longer LWDs were observed outside the canopy and inside the less dense canopies irrespective of the cultivar. LWD was negatively correlated with canopy height and LAI during these periods. Slow wind speeds were recorded inside the canopies (less than 0.5 km/h) and no significant canopy effect was observed on air temperature. An infection model was developed and showed that only rainfall periods which induced long LWDs inside the canopy, were favourable to M. pinodes infection under our climatic conditions and suggested a more favourable microclimate inside dense canopies.

Using crop canopy modification to manage plant diseases

Modifying crop canopies can suppress plant diseases in some crops. For example, in carrot, lateral trimming of the canopy by 30–40 % after canopy closure reduced sclerotinia rot (Sclerotinia sclerotiorum) to zero under moderate disease pressure without the use of fungicides. Trimming reduced relative humidity within the carrot canopy and increased air and soil temperature, inhibiting the formation of apothecia of S. sclerotiorum. Trimming also severed infected petioles, which reduced the opportunity for infection to progress to the carrot crown. Trimming combined with application of foliar fungicide was even more effective. Trimming reduced carrot leaf blights (Alternaria dauci, Cercospora carotae) in 1 of 3 years, when disease pressure was low. However, there was no advantage of combining trimming and fungicide sprays for leaf blight control. Canopy modification also reduces disease in legume crops. Soybean cultivars with reduced height and lodging, and early maturity, had up to a 74 % reduction in apothecia of S. sclerotiorum within the crop, and up to an 88 % reduction in disease incidence at harvest. In field pea, artificially supporting plants to reduce lodging, in combination with fungicide application, reduced the severity of mycosphaerella blight (Mycosphaerella pinodes) on pods by 67 % and increased seed yield by 54 %. In chickpea, paired-row planting that opened the canopy increased seed yield by 12 %, likely by increasing fungicide deposition. Modifications of the crop canopy can reduce disease, the need for fungicide sprays, and sometimes improve fungicide efficacy, but the results are often pathosystem-specific.

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>.

Suppression of Defense Response Related to Plant Cell Wall

In plant–parasite interactions, “effectors” are thought to play an important role in suppressing the innate immune response, but the vast majority of effector functions and host target molecules remain unclear, except for several combinations 1 . A pea pathogenic fungus, Mycosphaerella pinodes, secretes compounds that block defense responses of the host plants only and also induce local susceptibility (“accessibility”), even to avirulent pathogens. These compounds have been called “suppressors” or “suppressors of defense.” The M. pinodes-suppressors, which are low-molecular weight mucin-type glycopeptides, were named supprescins and their presence markedly blocked elicior-induced resistance, such as the generation of superoxide, formation of infection-inhibitors, production of phytoalexin and so on, in host plants. For three decades from 1977, it was found that supprescins disturb the fundamental functions of the host cells, particularly apyrase and redox enzymes in the host cell wall in a speciesspecific manner. In this review, the role of supprescins with the plant cell wall in determining specificity was introduced.

Cool-season grain legume improvement in Australia—Use of genetic resources

The cool-season grain legume industry in Australia, comprising field pea (Pisum sativum L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), lentil (Lens culinaris ssp. culinaris Medik.), and narrow-leaf lupin (Lupinus angustifolius L.), has emerged in the last 40 years to occupy a significant place in cropping systems. The development of all major grain legume crops—including field pea, which has been grown for over 100 years—has been possible through large amounts of genetic resources acquired and utilised in breeding. Initially, several varieties were released directly from these imports, but the past 25 years of grain legume breeding has recombined traits for adaptation and yield for various growing regions. Many fungal disease threats have been addressed through resistant germplasm, with varying successes. Some threats, e.g. black spot in field pea caused by Mycosphaerella pinodes (Berk. and Blox.) Vestergr., require continued exploration of germplasm and new technology. The arrival of ascochyta blight in chickpea in Australia threatened to destroy the chickpea industry of southern Australia, but thanks to resistant germplasm, it is now on its way to recovery. Many abiotic stresses including drought, heat, salinity, and soil nutritional toxicities continue to challenge the expansion of the grain legume area, but recent research shows that genetic variation in the germplasm may offer new solutions. Just as the availability of genetic resources has been key to successfully addressing many challenges in the past two decades, so it will assist in the future, including adapting to climate change. The acquisition of grain legume germplasm from overseas is a direct result of several Australians who fostered collaborations leading to new collection missions enriching the germplasm base for posterity.

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.

Plant cell walls as suppliers of potassium and sodium ions for induced resistance in pea (Pisum sativum L.) and cowpea (Vigna unguiculata L.)

When an elicitor is applied to plants to induce resistance, one of the first detectable events is the efflux of ions from the treated tissue. Here we are the first to demonstrate that an elicitor from Mycosphaerella pinodes evokes leakage of Na+ and K+ ions from isolated cell walls of pea and cowpea in vitro, as observed for epicotyl tissues. Pharmacological experiments showed that this elicitor-stimulated leakage was sensitive to vanadate and N-(3-methylphenyl)biphenyl-4-sulfonamide (NGXT-191), that inhibit a cell wall-associated ATPase (apyrase). Vanadate or NGXT-191 suppressed elicitor-induced superoxide generation and expression of defense genes in vivo. On the basis of these results, we assume that the leakage of these ions, probably associated with an ATP-dependent process(es) in the cell wall, is likely associated with induced defenses of pea and cowpea.

Identification of Mycosphaerella Blight Resistance in Wild Pisum Species for Use in Pea Breeding

ABSTRACTMycosphaerella blight caused by Mycosphaerella pinodes (Berk. and Blox.) Vestergren is the most important disease of pea (Pisum sativum L.) in the world. It reduces seed yield and quality and limits the areas where field pea can effectively be grown. Extensive studies have failed to identify high levels of resistance. However, some accessions of Pisum fulvum Sm., a wild relative of field pea, may be a source of new resistance genes. The objective of this study was to identify mycosphaerella blight‐resistant wild pea accessions for use in introgression breeding in Canada. Twenty‐six P. fulvum accessions and 18 accessions of wild subspecies of P. sativum {subsp. elatius (Steven ex M. Bieb.) Asch. & Graebn., subsp. transcaucasicum Govorov, subsp. asiaticum Govorov, subsp. sativum var. arvense (L.) Poir., and Pisum abyssinicum A. Braun [syn. P. sativum subsp. abyssinicum (A. Braun) Govorov]} were evaluated along with the check cultivars CDC Striker (moderate resistance) and Alfetta (poor resistance). Among the 44 wild accessions tested under greenhouse condition, 12 accessions had significantly lower disease scores than CDC Striker (P < 0.0001). The 18 most promising accessions along with checks including ‘Radley’ (moderate resistance), CDC Striker, and Alfetta were evaluated for disease resistance under field conditions. None of these accessions had significantly lower disease scores than Radley and CDC Striker. Pisum fulvum accessions PI595937, P651, W615017, and PI560061 and P. sativum subsp. elatius accession PI344538 were considered the most promising for resistance breeding.

Characterization of mechanisms of resistance against Didymella pinodes in Pisum spp.

Ascochyta blight caused by Didymella pinodes is a serious disease of pea (Pisum sativum ssp. sativum) to which little resistance has been identified so far. Only incomplete resistance is available in pea germplasm although higher levels of resistance have been reported in related Pisum species. In this study we characterized histochemically the underlying resistance mechanisms in these wild species and in the pea cv. Radley, the pea cultivar with the highest level of resistance to D. pinodes. Resistance was characterized by a reduced success of colony establishment and lesion size. Histologically this was associated with higher frequency of epidermal cell death and protein cross-linking in infected epidermal cells but not with H2O2 accumulation and peroxidase activity.

The Medicago truncatula–Mycosphaerella pinodes interaction: a new pathosystem for dissecting fungal-suppressor-mediated disease susceptibility in plants

A model pathosystem involving Mycosphaerella pinodes, causal agent of Mycosphaerella blight on pea and barrel medic(k) Medicago truncatula has been developed. Nineteen M. truncatula ecotypes were evaluated for disease susceptibility to M. pinodes strain OMP-1, using detached leaves inoculated with a pycnospore suspension. Inoculation of ecotype R108-1 with the pycnospores allowed direct penetration into the host’s epidermal cells, eventually causing leaf spots. Since pycnidia formed abundantly in infected tissues by 3 days post inoculation, M. pinodes is considered to have completed its infection cycle as on a natural host plant. Expression of phenylalanine ammonia-lyase (PAL)-, chalcone synthase (CHS)- and isoflavone reductase (IFR) mRNAs as well as subsequent accumulation of a major phytoalexin, medicarpin, was induced in ecotype R108-1 with an elicitor preparation from M. pinodes, whereas this phytoalexin response was markedly attenuated by supprescins from the same fungus. A transcriptional study of a salicylic acid (SA)-regulated gene encoding pathogenesis-related protein 10-1 (PR10-1) indicated that the suppressor likely interferes with the signal transduction process leading to inducible defenses in M. truncatula. Indeed, the suppressor rendered the host tissues (ecotype R108-1) susceptible to unrelated nonpathogenic fungi, probably through targeting ATPase activity of the host cells. Accordingly, the resistant and susceptible response of pea can be recapitulated in M. truncatula. This model pathosystem thus will allow us to verify the molecular basis underlying the fungal suppressor-mediated plant susceptibility.

A single, plastic population of Mycosphaerella pinodes causes ascochyta blight on winter and spring peas (Pisum sativum) in France.

Plant diseases are caused by pathogen populations continuously subjected to evolutionary forces (genetic flow, selection, and recombination). Ascochyta blight, caused by Mycosphaerella pinodes, is one of the most damaging necrotrophic pathogens of field peas worldwide. In France, both winter and spring peas are cultivated. Although these crops overlap by about 4 months (March to June), primary Ascochyta blight infections are not synchronous on the two crops. This suggests that the disease could be due to two different M. pinodes populations, specialized on either winter or spring pea. To test this hypothesis, 144 pathogen isolates were collected in the field during the winter and spring growing seasons in Rennes (western France), and all the isolates were genotyped using amplified fragment length polymorphism (AFLP) markers. Furthermore, the pathogenicities of 33 isolates randomly chosen within the collection were tested on four pea genotypes (2 winter and 2 spring types) grown under three climatic regimes, simulating winter, late winter, and spring conditions. M. pinodes isolates from winter and spring peas were genetically polymorphic but not differentiated according to the type of cultivars. Isolates from winter pea were more pathogenic than isolates from spring pea on hosts raised under winter conditions, while isolates from spring pea were more pathogenic than those from winter pea on plants raised under spring conditions. These results show that disease developed on winter and spring peas was initiated by a single population of M. pinodes whose pathogenicity is a plastic trait modulated by the physiological status of the host plant.

Identification and Genetic Diversity Analysis of Ascochyta Species Associated with Blight Complex of Pea in a Northwestern Hill State of India

Forty isolates of Ascochyta spp. infecting pea collected from different commercial pea growing areas of Himachal Pradesh were characterized into three species—Ascochyta pinodes, A. pisi and A. pinodella—based on symptoms, morphological and cultural traits. The identity of the isolates was confirmed by studying the rDNA sequence patterns. Based on various cultural and morphological trait combinations, 36 isolates were identified as A. pinodes, one isolate as A. pisi and one isolate as A. pinodella. Whereas two isolates, As3 and As14, could not be placed in any of the species as equal number of characters matched with A. pisi and A. pinodes. However, sequencing of ITS region of these isolates resolved the ambiguity and placed them in A. pinodes. This necessitates ITS sequencing as one of the criteria to establish the taxonomic status of Ascochyta species infecting pea. RAPD, RAMS, and Rep-PCR analysis with 10, 4 and universal ERIC, and BOX-AIR primers categorized different isolates according to their geographical locations. This study established the predominance of A. pinodes in Himachal Pradesh where edible pea is one of the remunerative off-season vegetable crops. This also constitutes first report of genetic variability of Ascochyta species infecting pea in India.

H2O2 production by copper amine oxidase, a component of the ecto-apyrase (ATPase)-containing protein complex(es) in the pea cell wall, is regulated by an elicitor and a suppressor from Mycosphaerella pinodes

Blue native PAGE analysis for cell wall proteins from pea epicotyls demonstrated that cell wall-associated ecto-apyrase (ATPase) formed a large protein complex(es) ranging from 450 to 900 kDa; one of the components of the complex was copper amine oxidase (CuAO), which catalyzes the oxidation of amines with the subsequent generation of ammonia and hydrogen peroxide. CuAO activity was coordinately regulated in vitro with ATP-hydrolyzing activity by an elicitor and a suppressor from Mycosphaerella pinodes. Moreover, treatment of cell wall proteins with the suppressor caused the appearance of the apyrase monomer. On the basis of these results, M. pinodes may target the apyrase-containing protein complex(es) of the host to attenuate cell wall-based, extracellular defense(s) including the production of hydrogen peroxide.

Pinolide, a new nonenolide produced by Didymella pinodes , the causal agent of ascochyta blight on Pisum sativum.

An aggressive isolate of Didymella pinodes isolated from pea ( Pisum sativum ) produced four different metabolites in vitro. The metabolites isolated from the culture filtrates were characterized by spectroscopic and optical methods. A new nonenolide, named pinolide, was isolated and characterized as (2S*,7R*,8S*,5E,9R*)-2,7,8-trihydroxy-9-propyl-5-nonen-9-olide. Pinolidoxin, the main toxin produced by D. pinodes, was also isolated together with two other closely related nonenolides, identified as herbarumin II and 2-epi-herbarumin II. Herbarumin II and 2-epi-herbarumin II have been previously isolated from the fungi Phoma herbarum and Paraphaeosphaeria recurvifoliae , respectively, but described here to be isolated for the first time from D. pinodes. When tested on leaves of the host plant and other legumes and weeds, pinolidoxin was phytotoxic in all of the plant species, whereas the other three nonenolides did not produce any symptoms. The importance of the stereochemistry of the hydroxy group at C-7 on phytotoxicity also is discussed.

GENETIC VARIABILITY AND POPULATION STRUCTURE OF MYCOSPHAERELLA PINODES IN WESTERN ALGERIA USING AFLP FINGERPRINTING

The genetic diversity and population structure of Mycosphaerella pinodes (Dydimella pinodes) in Algeria were investigated by AFLP markers. A total of 75 isolates from different collection sites corresponding to four geographic regions were analyzed. Data from AFLP loci were used to estimate gene diversity, genetic distances, and to make indirect measures of gene flow between population groups. Extensive diversity was detected in the M. pinodes population regardless of the population group. The percentage of polymorphic loci varied from 41% in the semi-arid superior region to 50% in the sub-humid region. Nei’s gene diversity across loci was 0.471 and the Shannon’s index across loci was 0.663. A high level of differentiation (Gst = 0.308) and a low gene flow (Nm = 1.118) among population groups were found. Based on the analysis of molecular variance, 58% of the genetic variation of M. pinodes was within populations, 31% of the variation was between geographical regions and 11% among populations within a region. Cluster analyses using individual isolates failed to group them according to population. This is the first report on genetic diversity and population structure of M. pinodes on pea in Algeria.

Field assessment of partial resistance to mycosphaerella blight inPisumsubspecies 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.

Plant age and timing of epidemic initiation affect mycosphaerella blight in field pea

Mycosphaerella blight (Mycosphaerella pinodes) occurs throughout western Canada and can severely reduce seed yield and quality of field pea (Pisum sativum). Field experiments were conducted to assess the impact of seeding date and timing of epidemic initiation on the severity of mycosphaerella blight on field pea. Early seeding or early initiation of the epidemic (early July) resulted in the highest severity and area under disease progress curve of mycosphaerella blight at the end of the growing season. Plants seeded later in the growing season showed less severe symptoms of mycosphaerella blight compared to those seeded earlier, and the blight severity was declined by delaying 1–2 weeks of disease initiation. However, late seeding reduces yield potential offsetting the benefit of disease reduction. A greenhouse study on the effect of both plant and tissue age on susceptibility to mycosphaerella blight revealed that both whole plants and leaf tissues became more susceptible as they aged. We conclude that delay of epidemic initiation in late June to early July through the use of foliar fungicides is effective in reducing mycosphaerella blight severity on the Canadian prairies.

Comparison of cultural growth and in planta quantification of Didymella pinodes, Phoma koolunga and Phoma medicaginis var. pinodella, causal agents of ascochyta blight on field pea (Pisum sativum)

The causal agents of ascochyta blight on field pea in South Australia, Didymella pinodes, Phoma medicaginis var. pinodella and Phoma koolunga, are isolated from a single plant within a crop, suggesting competition for space and nutrients. Interactions among these pathogens were investigated. Diameters of colonies of D. pinodes and of P. medicaginis var. pinodella were significantly reduced on PDA amended with filtrate from broth cultures of P. koolunga as were diameters of colonies of D. pinodes on PDA amended with filtrate from P. medicaginis var. pinodella or D. pinodes. This effect was negated when cultures were transferred to unamended PDA, indicating filtrates were fungistatic instead of fungicidal. The diameter of P. koolunga colonies was not influenced by filtrate from any of the three species. When pathogens were co-inoculated in pairs onto leaves on field pea plants, the quantity of DNA of D. pinodes and of P. medicaginis var. pinodella was significantly reduced if co-inoculated with P. koolunga. The quantity of DNA of P. koolunga was not influenced by co-inoculation. When co-inoculated onto excised leaf disks on sterile water the mean lesion diameter due to D. pinodes and to P. medicaginis var. pinodella was significantly reduced if co-inoculated with P. koolunga isolate DAR78535. Lesions caused by D. pinodes were significantly reduced when inoculum was self-paired. Conversely the diameter of lesions caused by P. koolunga DAR78535 increased when self-paired or when co-inoculated with P. medicaginis var. pinodella. Unlike leaf disks on sterile water, co-inoculation had no influence on lesion size or quantity of pathogen DNA in leaf disks on water agar. Antagonism, including self-antagonism, was detected among these species, leading to reduction in lesion size and quantity of pathogen DNA. The slower growing species, P. koolunga, was not self-antagonistic, and in a few instances the effect of co-inoculation was additive or synergistic.

First Report of Black Spot Caused by Boeremia exigua var. exigua on Field Pea in Australia.

Black spot is a major disease of field pea (Pisum sativum L.) production across southern Australia. Known causal agents in Australia include one or more of Mycosphaerella pinodes (Berk. & Bloxam) Vestergr., Phoma medicaginis var. pinodella (L.K. Jones), Ascochyta pisi Lib., or P. koolunga (Davidson, Hartley, Priest, Krysinska-Kaczmarek, Herdina, McKay & Scott) (2), but other pathogens may also be associated with black spot symptoms. Black spot generally occurs on most plants and in most pea fields in Western Australia (W.A.), and during earlier winter/spring surveys of blackspot pathogens, some isolates were tentatively allocated to P. medicaginis var. pinodella despite different cultural characteristics on potato dextrose agar (PDA). Recently, single-spore isolations of a single culture each from an infested pea crop at Medina, Moora, and Mt. Barker in W.A. were made onto PDA. A PCR-based assay with TW81 and AB28 primers was used to amplify from the ITS-5.8S rDNA region. Purified DNA products were sequenced for the three isolates and then BLASTn was used to compare sequences with those in GenBank. Our sequences (GenBank Accession Nos. JN37743, JN377439, and JN377438) had 100% nucleotide identity with P. exigua Desm. var. exigua accessions (GI13385450, GI169894028, and GI189163921), an earlier synonym of what is now known as Boeremia exigua var. exigua ([Desm.] Aveskamp, Gruyter & Verkley) (1). Davidson et al. (2) used the same primers to identify P. koolunga, but none of our isolates were P. koolunga. A suspension of 107 conidia ml-1 of each representative isolate was inoculated onto foliage of 15-day-old field pea cv. Dundale plants and maintained at >90% relative humidity for 72 h postinoculation. Control plants inoculated with just water remained symptomless. Brown lesions were evident by 8 to 10 days postinoculation and mostly 1 to 3 mm in diameter. B. exigua var. exigua was readily reisolated from infected leaves. Isolates have been lodged in the W.A. Culture Collection Herbarium maintained at the Department of Agriculture and Food W.A. (Accession Nos. WAC13500, WAC13502, and WAC13501 from Medina, Moora, and Mt. Barker, respectively). Outside Australia, its synonym P. exigua var. exigua is a known pathogen of field pea (4), other legumes including common bean (Phaseolus vulgaris L.) (4) and soybean (Glycine max [L.] Merr.) (3), and is known to produce phytotoxic cytochalasins. In eastern Australia, P. exigua var. exigua has been reported on common bean (1930s and 1950s), phasey bean (Macroptilium lathyroides [L.] Urb.) and siratro (M. atropurpureum (DC.) Urb.) (1950s and 1960s), mung bean (Vigna radiata [L.] Wilczek.) (1960s), ramie (Boehmeria nivea [L.] Gaudich.) (1939), potato (Solanum tuberosum L.) (1980s), and pyrethrum (Tanacetum cinerariifolium [Trevir.] Schultz Bip.) (2004 and 2007) (Australian Plant Pest Database). To our knowledge, this the first report of B. exigua var. exigua on field pea in Australia, and because of its potential to be a significant pathogen on field pea, warrants further evaluation.

First Report of Phoma herbarum on Field Pea (Pisum sativum) in Australia.

Black spot disease on field pea (Pisum sativum) in Australia is generally caused by one or more of the four fungi: Mycosphaerella pinodes (anamorph Ascochyta pinodes), Phoma medicaginis var. pinodella (synonym Phoma pinodella), Ascochyta pisi, and Phoma koolunga (1,2,4). However, in 2010 from a field pea blackspot disease screening nursery at Medina, Western Australia, approximately 25% of isolates were a Phoma sp. that was morphologically different to Phoma spp. previously reported on field pea in Western Australia, while the remaining 75% of isolates were either M. pinodes or P. medicaginis var. pinodella. Single-spore isolations of 23 isolates of this Phoma sp. were made onto potato dextrose agar. A PCR-based assay with the TW81 and AB28 primers was used to amplify from the 3' end of 16S rDNA, across ITS1, 5.8S rDNA, and ITS2 to the 5' end of the 28S rDNA. The DNA products were sequenced and BLAST analyses were used to compare sequences with those in GenBank. In each case, the sequence had ≥99% nucleotide identity with the corresponding sequence in GenBank for P. herbarum. Isolates also showed morphological similarities to P. herbarum as described in other reports (e.g., 3). The relevant information for a representative isolate has been lodged in GenBank (Accession No. JN247437). The same primers were used by Davidson et al. (2) to identify P. koolunga, but none of our 23 isolates were P. koolunga. A conidial suspension of 107 conidia ml-1 from a single-spore culture was spray inoculated onto foliage of 10-day-old Pisum sativum cv. Dundale plants maintained under >90% relative humidity conditions for 72 h postinoculation. Symptoms evident by 11 days postinoculation consisted of pale brown lesions that were mostly 1.5 to 2 mm long and 1 to 1.5 mm wide. Approximately 50% of lesions showed a distinct chlorotic halo extending 1 to 2 mm outside the boundary of the lesion. P. herbarum was readily reisolated from infected foliage. A culture of this representative isolate has been lodged in the Western Australian Culture Collection Herbarium maintained at the Department of Agriculture and Food Western Australia (Accession No. WAC13499). Outside of Australia, P. herbarum, while generally considered a soilborne opportunistic pathogen, has been reported on a wide range of species, including field pea (3). Molecular analysis of historical isolates collected from field pea in Western Australia, mostly in the late 1980s, did not show any incidence of P. herbarum, despite this fungus being reported on alfalfa (Medicago sativa) and soybean (Glycine max) in Western Australia in 1985 (Australian Plant Pest Database). In Western Australia, this fungus has also been recorded on a Protea sp. in 1991 and on Arabian pea (Bituminaria bituminosa) in 2010 (Australian Plant Pest Database). To our knowledge, this is the first report of P. herbarum as a pathogen on field pea in Australia. These previous reports of P. herbarum on other hosts in Western Australia and the wide host range of P. herbarum together suggest the potential for this fungus to be a pathogen on a wider range of genera/species than field pea.