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Sweet cherry (Prunus avium) is a commercially important species in China, experiencing a rapid increase in production. In June 2022, a severe infection, affecting more than 8% of sweet cherry trees, was observed on the Tetian cultivar in a 2–3‐year‐old orchard in Dalian City, northern China. Initially, spindle‐shaped brown disease spots formed on the surfaces of the branches. These spots continued to spread and merge, and the middle portion of the cankers sunk inward and gradually dried. Small black particles were found on the surface of the stems. The disease spread was more prevalent during the rainy season, leading to the withering of numerous branches and the death of the whole plant. Seven isolates, named lncy1‐1, lncy4‐1, lncy5‐1, lncy6‐1, lncy7‐1, lncy8‐1 and lncy9‐1, were obtained from 24 disease samples. Phylogenetic analysis based on three loci (rDNA ITS, TEF1 and TUB2) coupled with morphological identification confirmed that these seven isolates belong to Diaporthe eres. A representative isolate, lncy1‐1, was inoculated onto sweet cherry branches in a controlled environment, and showed that the isolate lncy1‐1 was pathogenic. The fungus isolated from diseased tissues was identified as D. eres based on morphological and molecular criteria. To the best of our knowledge, this is the first report of stem canker in sweet cherry caused by D. eres in China, which will promote disease management and expand the known host range of D. eres. [ABSTRACT FROM AUTHOR]

Neoscytalidium dimidiatum is an asexual, opportunistic and necrotrophic pathogen that causes the devastating stem canker disease of dragon fruit species (Selenicereus spp.). Despite this, information about its intraspecific diversity remains lacking. Examination of the morphological variations of 40 N. dimidiatum isolates hosted by S. megalanthus, S. monacanthus and S. undatus from eight allopatric regions in the Philippines detected three distinct morphotypes. Sequencing of three partial gene markers (ITS, ACT and TUB2) of representative isolates revealed low intraspecific genetic diversity of the pathogen from the three hosts. Phylogenetic analysis of internal transcribed spacer (ITS) sequences of the isolates in this study and worldwide collections of the phytopathogen in the GenBank database infers similar founding populations and the possible specificity of the dragon fruit‐infecting N. dimidiatum. Pathogenicity and aggressiveness assay of the isolates on detached stems of dragon fruit did not detect host specificity to S. monacanthus and S. undatus. However, some isolates (i.g., MBDF0802A, MBDF0808B, MBDF0339A and MBDF0007A) significantly had shorter latent period to the stems of S. undatus than S. monacanthus. A higher aggressiveness component of lesion size development on S. undatus stems by isolates from S. monacanthus was recorded suggesting a possible directional selection of highly aggressive N. dimidiatum in this host. This is the first population study on the phenotypic traits and the genetic structure of N. dimidiatum. Valuable inputs for further study of the pathogen are provided, which may help inform the design of management options for stem canker disease of dragon fruit. [ABSTRACT FROM AUTHOR]

Idesia polycarpa is a woody oil plant with great development and application prospects. However, stem canker disease of I. polycarpa was frequently observed in Henan and Hubei provinces of China in 2020–2022. The seriousness of the disease caused a large number of trees deaths, which affected seedling production and fruit yield, restricting the development of the I. polycarpa industry. We performed isolation, purification and pathogenicity analysis of canker samples. Pathogenicity tests reproduced typical canker disease symptoms on detached branches of I. polycarpa. Based on morphological observations, conidial morphology and phylogenetic analysis of isolates with high similarity to the rDNA internal transcribed spacer (ITS), EF‐1α and TUB2 sequences screened in GenBank by BLAST, the pathogen of canker disease on I. polycarpa was identified as Botryosphaeria dothidea. This is the first report of B. dothidea as the pathogen of stem canker of I. polycarpa. [ABSTRACT FROM AUTHOR]

In many cultivated crops, sources of resistance to diseases are sparse and rely on introgression from wild relatives. Agricultural crops often are allopolyploids resulting from interspecific crosses between related species, which are sources of diversity for resistance genes. This is the case for Brassica napus (oilseed rape, canola), an interspecific hybrid between Brassica rapa (turnip) and Brassica oleracea (cabbage). B. napus has a narrow genetic basis and few effective resistance genes against stem canker (blackleg) disease, caused by the fungus Leptosphaeria maculans, are currently available. B. rapa diversity has proven to be a valuable source of resistance (Rlm, LepR) genes, while B. oleracea genotypes were mostly considered susceptible. Here we identified a new resistance source in B. oleracea genotypes from America, potentially effective against French L. maculans isolates under both controlled and field conditions. Genetic analysis of fungal avirulence and subsequent cloning and validation identified a new avirulence gene termed AvrLm14 and suggested a typical gene‐for‐gene interaction between AvrLm14 and the postulated Rlm14 gene. AvrLm14 shares all the usual characteristics of L. maculans avirulence genes: it is hosted in a genomic region enriched in transposable elements and heterochromatin marks H3K9me3, its expression is repressed during vegetative growth but shows a strong overexpression 5–9 days following cotyledon infection, and it encodes a small secreted protein enriched in cysteine residues with few matches in databases. Similar to the previously cloned AvrLm10‐A, AvrLm14 contributes to reduce lesion size on susceptible cotyledons, pointing to a complex interplay between effectors promoting or reducing lesion development. [ABSTRACT FROM AUTHOR]

The study of oomycetes associated with crops is highly important due to the economic losses they might cause. In cacao, the genus Phytophthora has been extensively studied, but little is known about other genera and species of oomycetes associated with this plant. This study aimed to determine the oomycetes' diversity present in Colombian cacao crops. A total of 146 isolates were obtained from diseased plants and soil in 11 departments. Analysis of internal transcribed spacer (ITS) and cytochrome oxidase subunit I (coxI) sequences was performed along with the assessment of morphological characteristics. Nine species were identified, distributed in four genera: Phytophthora (P. palmivora, 54%; P. nicotianae, 1%), Phytopythium (Phy. chamaehyphon, 15%; Phy. cucurbitacearum, 9%; Phy. vexans, 7%; Phy. helicoides, 1%), Globisporangium (G. splendens, 3%), and Pythium (Py. delicense, 1%; Py. inflatum,1%). Additionally, an unidentified and possibly new species of Phytophthora (5%) and three unidentified species of Phytopythium (3%) were found. This is the first report of Globisporangium, Phytopythium, and Pythium in cacao crops of Colombia and the first report of the species Phy. chamaehyphon in the country. Interestingly, some isolates of Phytopythium spp. were isolated from necrotic leaves and vascular section of stems, which may suggest a role in cacao diseases traditionally associated with Phytophthora. Also, it is proposed that the new species of Phytophthora may be contributing significantly to black pod disease in Colombian cacao crops, and we highlight that the study of P. palmivora is urgent because of its distribution all over the country. [ABSTRACT FROM AUTHOR]

Oilseed rape residues are a crucial determinant of stem canker epidemiology as they support the sexual reproduction of the fungal pathogen Leptosphaeria maculans. The aim of this study was to characterize the impact of a resistance gene against L. maculans infection on residue microbial communities and to identify microorganisms interacting with this pathogen during residue degradation. We used near‐isogenic lines to obtain healthy and infected host plants. The microbiome associated with the two types of plant residues was characterized by metabarcoding. A combination of linear discriminant analysis and ecological network analysis was used to compare the microbial communities and to identify microorganisms interacting with L. maculans. Fungal community structure differed between the two lines at harvest, but not subsequently, suggesting that the presence/absence of the resistance gene influences the microbiome at the base of the stem whilst the plant is alive, but that this does not necessarily lead to differential colonization of the residues by fungi. Direct interactions with other members of the community involved many fungal and bacterial amplicon sequence variants (ASVs). L. maculans appeared to play a minor role in networks, whereas one ASV affiliated to Plenodomus biglobosus (synonym Leptosphaeria biglobosa) from the Leptosphaeria species complex may be considered a keystone taxon in the networks at harvest. This approach could be used to identify and promote microorganisms with beneficial effects against residue‐borne pathogens and, more broadly, to decipher the complex interactions between multispecies pathosystems and other microbial components in crop residues. [ABSTRACT FROM AUTHOR]

The Eucalyptus stem canker pathogens Teratosphaeria gauchensis and T. zuluensis (Capnodiales, Teratosphaeriaceae) are found in many tropical regions of the world where their hosts are cultivated for plantation forestry. Population genetic analyses have suggested that some populations undergo recombination, even though their sexual states have never been observed. Against this background, the aim of this study was to characterize the mating type (MAT) locus of these species and thus to better understand the basis of their diversity. Known Mycosphaerellaceae MAT genes were used to identify and investigate the MAT locus in the T. gauchensis and T. zuluensis genomes. Both species were found to be heterothallic and primers were designed to amplify the opposite MAT idiomorphs as well as conserved regions within the MAT1‐1‐1 and MAT1‐2‐1 genes. Each Teratosphaeria MAT idiomorph was defined by either the MAT1‐1‐1 or the MAT1‐2‐1 gene, and an idiomorph‐specific hypothetical protein (MAT1‐1‐10 and MAT1‐2‐12). Populations of T. zuluensis from Asia and southern Africa were dominated by a single mating type, whereas the proportions of the different idiomorphs for T. gauchensis in South America and southern Africa were similar. There was no physical evidence of sexual reproduction for either species and it is argued that although recombination may be possible, it is unlikely to form an important part of their life cycles in diseased Eucalyptus plantations. Instead, continuous human‐mediated multiple introductions of these species have probably resulted in the current genetic structure of their populations, which holds risk for future disease outbreaks and interspecific hybridization. [ABSTRACT FROM AUTHOR]

Summary: Background : Teratosphaeria gauchensis and T. zuluensis are closely related fungi that cause Teratosphaeria (previously Coniothyrium) stem canker disease on Eucalyptus species propagated in plantations for commercial purposes. This disease is present in many countries in which Eucalyptus trees are planted, and continues to spread with the international trade of infected plant germplasm. Taxonomy: Fungi, Ascomycota, Pezizomycotina, Dothideomycetes, Dothideomycetidae, Capnodiales, Teratosphaeriaceae, Teratosphaeria. Identification: The causal agents form dark masses of pycnidia that are visible on the surface of distinct stem cankers that typically form on young green stem tissues. Accurate diagnosis of the causal agents requires DNA sequence data. Host range: Nine species of Eucalyptus are known to be affected. Of these, E. grandis and its hybrids, which include some of the most important planting stock globally, appear to be particularly vulnerable. Disease symptoms: Small necrotic lesions develop on young green stem tissue. These lesions coalesce to form large cankers that exude gum. Epicormic shoots develop below the girdling canker and, in severe cases, trees die. Useful websites: Mycobank, https://www.mycobank.org; Publications of the Forestry and Agricultural Biotechnology Institute (FABI), https://www.fabinet.up.ac.za/index.php/journals. [ABSTRACT FROM AUTHOR]

Blackleg disease, caused by Leptosphaeria maculans, is a serious threat to canola production in western Canada. While specific major resistance (R) genes can be effective, they can also be eroded rapidly by a shift in pathogen race composition. Quantitative resistance (QR) has the potential to provide more durable, if less complete, protection. However, the effectiveness of QR may vary widely in the field. It has long been suspected that elevated temperatures may limit the expression of QR. To test this hypothesis, the infection development of blackleg was assessed on three common Canadian canola cultivars (74‐44 BL, PV 530 G and 45H29) showing QR, with and without a heat treatment of 7 h daily exposure to 32 °C for 1 week during rosette to early flowering under controlled environment conditions. The impact of elevated temperature on the susceptibility to blackleg was compared with that of a moderate temperature with a 22 °C daytime high. A susceptible cultivar, Westar, was used as a control. When data from both temperatures were pooled, all three QR cultivars showed lower blackleg severity relative to Westar. Elevated temperatures increased blackleg severity in Westar only (in terms of the stem‐lesion length from the inoculation of the first true‐leaf petiole in trials involving Westar and 74‐44 BL) and in pooled data for disease severity index in trials involving Westar, PV 530 G and 45H29. These findings suggest that the QR traits in 74‐44 BL, PV 530 G and 45H29 are useful for blackleg management in western Canada, especially under warmer growing conditions when plants are at the rosette to early flowering stages. [ABSTRACT FROM AUTHOR]

Leptosphaeria maculans is the fungus responsible for the stem canker disease of oilseed rape ( Brassica napus). AvrLm3 and AvrLm4-7, two avirulence effector genes of L. maculans, are involved in an unusual relationship: AvrLm4-7 suppresses the Rlm3-mediated resistance. Here, we assessed AvrLm3 polymorphism in a collection of 235 L. maculans isolates. No field isolates exhibited deletion or inactivating mutations in AvrLm3, as observed for other L. maculans avirulence genes. Eleven isoforms of the AvrLm3 protein were found. In isolates virulent towards both Rlm3 and Rlm7 (a3a7), the loss of the Rlm3-mediated resistance response was due to two distinct mechanisms. First, when AvrLm4-7 was inactivated (deletion or inactivating mutations), amino acid substitutions in AvrLm3 generated virulent isoforms of the protein. Second, when only point mutations were observed in AvrLm4-7, a3a7 isolates still contained an avirulent allele of AvrLm3. Directed mutagenesis confirmed that some point mutations in AvrLm4-7 were sufficient for the fungus to escape Rlm7-mediated resistance while maintaining the suppression of the AvrLm3 phenotype. Signatures of positive selection were also identified in AvrLm3. The complex evolutionary mechanisms enabling L. maculans to escape Rlm3-mediated resistance while preserving AvrLm3 integrity, along with observed reduced aggressiveness of isolates silenced for AvrLm3, serves to emphasize the importance of this effector in pathogenicity towards B. napus. While the common response to resistance gene pressure is local selection of isolates depleted in the cognate avirulence gene, this example contributes to complexify the gene-for-gene concept of plant-pathogen evolution with a 'camouflaged' model allowing retention of nondispensable avirulence effectors. [ABSTRACT FROM AUTHOR]

This study used a versatile temperature-control device to assess the effect of temperature (12-40°C) and duration (2-12 weeks) of flooding on the survival of Leptosphaeria spp. in canola ( Brassica napus) stubble. Canola basal stems with blackleg symptoms were submerged in water in small glass jars containing 20 cm3 soil on a thermogradient plate capable of simultaneously maintaining up to 96 independent temperature regimes. Flooded stems were sampled at 2-week intervals, surface-sterilized, and incubated on V8-juice agar for 10 days to recover the pathogen. Flooding for 2 weeks substantially reduced pathogen recovery relative to non-flooded controls and the pathogen was not recovered after 6 weeks of flooding, irrespective of temperature. The pathogen was eliminated slightly more rapidly at flooding temperatures >20°C than at 12-16°C. There was no difference between Leptosphaeria maculans and L. biglobosa in their ability to survive flooding. Stem tissues degraded most rapidly during the first 2 weeks of flooding, corresponding to a quick decline in pathogen survival during the same period. These results indicate that a paddy rice crop following winter rapeseed may minimize the impact of blackleg by eradicating the inoculum of Leptosphaeria spp. in stubble. [ABSTRACT FROM AUTHOR]

During the year 2008 to 2009, a new disease of stem canker was noticed in most red-fleshed dragon fruit ( Hylocereus polyrhizus) plantations in Malaysia. The symptoms observed were small circular sunken orange spot, black pycnidia and rotted stem. This study was conducted to determine the occurrence of the stem canker on H. polyrhizus in Malaysia, subsequently to isolate, identify and characterize the fungal pathogen based on morphology and molecular characteristics and pathogenicity test. From the surveyed 20 plantations in Malaysia, stem canker was detected in all the plantations. A total of 40 isolates of Scytalidium-like fungus were isolated and identified as Neoscytalidium dimidiatum based on morphological characteristics and ITS region sequences, which showed 99% similarity to N. dimidiatum ( FJ648577). From the phylogenetic analysis using maximum-likelihood tree, isolates of N. dimidiatum from stem canker of H. polyrhizus were grouped together and did not show any sequence variation. From pathogenicity test, all 40 isolates of N. dimidiatum were pathogenic causing stem canker on H. polyrhizus. To our knowledge, this is the first report of stem canker of H. polyrhizus caused by N. dimidiatum in Malaysia. [ABSTRACT FROM AUTHOR]

The race structure and genotypic diversity of four Leptosphaeria maculans populations isolated from Brassica oleracea (broccoli, cauliflower, cabbage, etc.) in central Mexico (Aguascalientes, Guanajuato and Zacatecas states) were analysed. Race structure was characterized by an unusually low diversity at three locations out of four. Fourteen minisatellite markers revealed a high proportion of repeated multilocus genotypes in these populations, combined with a significant linkage disequilibrium and strong clonal fraction (65-87%). The occurrence of the mating-type idiomorphs always significantly departed from the 1:1 proportion expected in the case of random mating. Each population thus consists of a few (four to nine) multilocus genotypes which are specific to each location. These data strongly support the hypothesis of exclusive, or a high rate of, clonal multiplication. Comparison of cropping practices between B. oleracea and B. napus indicate that the shift in reproductive behaviour of the fungus is chiefly man-mediated. [ABSTRACT FROM AUTHOR]

Fourteen polymorphic microsatellite DNA markers derived from the draft genome sequence of Rhizoctonia solani anastomosis group 3 (AG-3), strain Rhs 1AP, were designed and characterized from the potato-infecting soil fungus R. solani AG-3. All loci were polymorphic in two field populations collected from Solanum tuberosum and S. phureja in the Colombian Andes. The total number of alleles per locus ranged from two to seven, while gene diversity (expected heterozygosity) varied from 0.11 to 0.81. Considering the variable levels of genetic diversity observed, these markers should be useful for population genetic analyses of this important dikaryotic fungal pathogen on a global scale. [ABSTRACT FROM AUTHOR]

Glasshouse and field experiments showed that the pathogenicity and disease type on potato varied between different anastomosis groups (AGs) of Rhizoctonia solani. For example, severe stem and stolon disease developed in plants inoculated with a single isolate of AG3PT and AG5. Severe root disease was observed with single isolates of AG8 and to a lesser extent AG3PT, but rarely with single isolates of the other AGs tested. In both field and glasshouse experiments the AG2-1 isolate (X81) produced only small lesions (<5 mm). However, this was not representative of two other AG2-1 isolates. When AG2-1 isolates of the three different rDNA IGS1 types were tested in a glasshouse trial, one caused more severe stem and stolon infection than AG3PT. In the field experiment, the yield of tubers, by weight, was significantly less ( P < 0·05) in all inoculated plants than for uninoculated (control) plants. Yield losses were greatest and tuber numbers smallest in plots inoculated with an AG8 isolate, suggesting that root infection is important in determining quantitative yield loss. The incidence of black scurf was greatest in the progeny tubers in plots inoculated with AG3PT (83·9%), whereas only very small amounts of black scurf developed on tubers from plants infected with AG2-1 (510 bp) or AG5 isolates. This is supported by laboratory tests, where isolates of AG3PT produced significantly more sclerotia on potato dextrose agar than isolates of AGs 2-1, 4, 5 and 8. [ABSTRACT FROM AUTHOR]

• Random insertional mutagenesis was used to investigate pathogenicity determinants in Leptosphaeria maculans. One tagged nonpathogenic mutant, termed m20, was analysed in detail here. • The mutant phenotype was investigated by microscopic analyses of infected plant tissues and in vitro growth assays. Complementation and silencing experiments were used to identify the altered gene. Its function was determined by bioinformatics analyses, cell biology experiments and functional studies. • The mutant was blocked at the invasive growth phase after an unaffected initial penetration stage, and displayed a reduced growth rate and an aberrant hyphal morphology in vitro. The T-DNA insertion occurred in the intergenic region between two head-to-tail genes, leading to a complex deregulation of their expression. The unique gene accounting for the mutant phenotype was suggested to be the orthologue of the poorly conserved Saccharomyces cerevisiae gpi15, which encodes for one component of the glycosylphosphatidylinositol (GPI) anchor biosynthesis pathway. Consistent with this predicted function, a functional translational fusion with the green fluorescent protein (GFP) was targeted to the endoplasmic reticulum. Moreover, the mutant exhibited an altered cell wall and addition of glucosamine relieved growth defects. • It is concluded that the GPI anchor biosynthetic pathway is required for morphogenesis, cell wall integrity and pathogenicity in Leptosphaeria maculans. [ABSTRACT FROM AUTHOR]

Rhizoctonia solani, the causal agent of stem canker and black scurf on potato, survives as sclerotia on tubers, in soil and in plant residues. The objective of the present study was to evaluate the importance of inoculum source on disease development. Disease-free minitubers and seed tubers contaminated with low levels ofR. solaniwere planted in fumigated or artificially inoculated growth mixture in greenhouse experiments. Black scurf incidence and severity were significantly higher when the inoculum was present in both seed tubers and soil, compared with either of them separately. The severity of disease symptoms on the subterranean parts of the plant also were significantly higher in plots where both seed tubers and soil were contaminated, compared with plots where the inoculum source was either the seed tubers or the soil. Thus, both major sources of inoculum, seed tubers and soil, are important in disease development. However, when both sources are present, black scurf incidence and severity are increased, leading to economical damage to tuber yield and quality. Additional results from field trials support these findings. Disease incidence and severity on daughter tubers were correlated with levels of contamination in seed tubers and soil. When seed tubers and soil were heavily infested, the levels of black scurf incidence and severity on daughter tubers were very high; when seed tuber and soil infestation were very low, black scurf incidence and severity on progeny were also lower. Disease levels were reduced by in-furrow fungicide treatment, but were less effective when the initial levels of the fungus on the seed tubers and in the soil were high. [ABSTRACT FROM AUTHOR]

Abstract Leptosphaeria maculans isolates have been assigned to one of two groups, A or B, on the basis of differences in their characteristics. Group A can further be divided into pathogenicity groups (PG) 2, 3 and 4 and group B into PG1. To determine if isolates belonging to the aggressive canker forming group A are present in Sweden, physiological and genetic characterisation of 120 isolates collected in the year 2000 were performed. Thirty-seven isolates were classified as belonging to pathogenicity group PG3 and 63 isolates as PG4, based on a cotyledon assay. Twenty isolates did not cause any symptoms at all, and were classified as PG1. When comparing two geographical regions, Skåne and Östergötland, equal numbers of PG3 and PG4 isolates were found. By analysing the isolates by PCR, the collection was further classified into 100 group A isolates and 20 group B isolates. A corresponding classification of the isolates was observed when the ability to produce pigments in Czapek Dox broth was examined. The results showed a clear predominance of group A. This was also the case for the isolate collection from 2001. In a detailed survey of disease development in a L. maculans infected winter oilseed rape field in southern Sweden (Skåne), basal stem canker was not observed until early June Although the disease index value increased from 8.4 in June to 18.0 in July, few severely damaged plants were observed before harvest in mid-July, despite infection with group A isolates. [ABSTRACT FROM AUTHOR]

In controlled-environment experiments, ascospores of both A-group and B-group Leptosphaeria maculans were able to infect leaves of oilseed rape and produce phoma leaf spot lesions at temperatures from 5 to 20°C and wetness durations from 8 to 72 h after inoculation. Lesions formed on leaves inoculated with B-group ascospores had few pycnidia and were darker, smaller and less noticable than the larger, pale grey lesions with many pycnidia produced by A-group ascospores. Lesions formed by A-group or B-group L. maculans on naturally infected winter oilseed rape experimental crops were similar to lesions produced by the two groups on inoculated plants. The greatest numbers of lesions were produced with a leaf wetness duration of 48 h and at temperatures of 15–20°C for both A-group and B-group ascospores. As leaf wetness duration and temperature decreased below the optimal values, the number of lesions decreased. The incubation period, estimated as the time from inoculation to the appearance of the first lesions (t1), or the time to the appearance of 50% of the lesions (t50), of B-group was often shorter than that of A-group L. maculans. As temperature decreased below 20°C, the length of the incubation period of both A-group and B-group L. maculans increased. [ABSTRACT FROM AUTHOR]

The resistance carried by chromosome 4 of the Brassica B genome confers on the Brassica napus–B. nigra addition line ‘LA4+’ a high level of resistance to Leptosphaeria maculans isolates at the cotyledon stage under controlled conditions and at all growth stages under field conditions. This resistance has never been used commercially in B. napus varieties. To determine the potential durability of this new resistance, it is necessary to investigate whether it exerts selective pressure on fungus populations. A study of the pathogenicity of 57 single ascospore isolates of L. maculans on this line at the cotyledon stage was carried out to examine possible race specificity of the resistance. Two isolates were clearly virulent and three had intermediate aggressiveness on the ‘LA4+’ line. Two B-group isolates and 53 A-group isolates, including isolates from darkening tissue of resistant plants of the ‘LA4+’ line and cv. Junius (B. nigra), were virulent on the susceptible isogenic ‘LA–’ line. These results demonstrate that: (i) the resistance of the ‘LA4+’ oilseed rape line, conferred on B. napus by B. nigra chromosome 4, is race specific at the cotyledon stage; and (ii) the resistant material can act as a reservoir of virulent isolates for susceptible oilseed rape lines. [ABSTRACT FROM AUTHOR]

Six male sterile sunflower lines were crossed with seven restorers in a factorial mating design. The 13 inbred lines and their 42 F1 hybrids were planted in a randomized block design with three replicates. Each replicate consisted of two rows, 5 m long (30–35 plants per replicate). Resistance to natural Phomopsis infection, presented as the percentage of plants with no encircling necrosis lesions of the fungus on the main stem, was determined at physiological maturity. Analysis of variance showed that female and male general combining abilities (GCA) and specific combining abilities (SCA) of F1 hybrids were significant. The ratio of additive variance to total variance was 0.662, a high value which indicates prevailing additive effects. The additive variance due to females was more important than that of males, probably because of the existence of maternal effects or more effective genes for resistance in the female lines used in this experiment. The estimates of GCA were significant and positive for LC1004A, KO549A, 50KD8 and LC1064C inbred lines. These lines should be considered in developing hybrids with improved resistance to Phomopsis in sunflower breeding programmes. [ABSTRACT FROM AUTHOR]

Stem canker or blackleg of brassicas, caused by Leptosphaeria maculans, is one of the most damaging diseases of winter oilseed rape in the UK. Airborne ascospores, released in autumn and winter, initiate leaf infections which may lead to colonization of the petiole and, later in the season, formation of stem lesions and cankers. Although isolates of the pathogen differ in ability to cause damaging stem cankers, this is not readily apparent from leaf spotting or stem lesion symptoms. However, several cultural, biochemical and genetic characteristics appear to be associated with the ability to form damaging stem cankers and isolates can be assigned to one of two groups, termed A and B, on the basis of differences in these characteristics. To investigate the relationship between leaf spotting symptoms and subsequent stem canker formation, and to improve understanding of the epidemiology of this pathogen, it is desirable to differentiate between the stem canker forming A group and the less damaging B group of L. maculans. Characterization of isolate type is also important in seed testing and crop breeding programs, particularly in countries such as Canada and Poland where the A type is not ubiquitous. This article reviews methods, including plant assays, assessments of growth characteristics in vitro, isozyme analyses, secondary metabolite profiling, serology, and nucleic acid analyses, that can be used to differentiate the A and B groups. [ABSTRACT FROM AUTHOR]

Rhizoctonia solani, the causal agent of stem canker of beans, does not commonly infect beans more than two weeks old. Treatment of the cuticular layer by abrasion or chloroform rinsing results in decreased cuticular autofluorescence and the ability of stains to penetrate the hypocotyl surface. Infection cushions preferentially formed near these treated areas on both young and old plants. The morphology of infection cushions on older plants is simpler than those found on young, susceptible plants, but they are fully competent to form lesions. [ABSTRACT FROM AUTHOR]

The article reports that Glomerella miyabeana was the causal agent of two new diseases that have been observed attacking willows in New Zealand. One and two year-old willows growing in the Aokautere Research Nursery infected with Glomerella miyabeana exhibited stem lesions and leaf spots. Willows in the willow collection kept at the Aokautere Research Nursery were examined closely throughout the growing season for stern lesions, leaf spotting and defoliation. study showed that black stem cankers and leaf spotting and defoliation of willows in New Zealand were caused by the same fungus, Glomerella miyabeana.