Infection process of <Emphasis Type="Italic">Pseudocercospora musae</Emphasis> on banana leaf

Yellow Sigatoka that is caused by Pseudocercospora musae is an important banana disease. The aim of this study was to elucidate the infection process of P. musae in banana leaves by scanning electron microscopy. Leaf samples were inoculated on the abaxial surface with P. musae and then analysed at 12, 24, 36, 48, 72, 96, 120, 144, and 168 h post inoculation (hpi) and at 36 and 50 days post inoculation (dpi). The conidia were found to be germinated between 24 and 36 hpi and penetrated through the stomata between 96 and 120 hpi, or more generally from 144 hpi. P. musae colonized the spongy parenchyma at 36 dpi and the palisade parenchyma at 50 dpi. Sporulation occurred at 50 dpi on the adaxial surface of leaves through the emergence of conidia on conidiophores through the stomata. Considering the importance of yellow Sigatoka in banana production, our results provide a better understanding of the life cycle of the fungus for treatment processes.     

Defective Long-distance Transport of <Emphasis Type="Italic">Cucumber mosaic virus </Emphasis>in Radish Is Efficiently Complemented by <Emphasis Type="Italic">Turnip mosaic virus</Emphasis>

A strain of Cucumber mosaic virus (CMV-D8) systemically infects Japanese radish (Raphanus sativus), but the Y strain of CMV (CMV-Y) only infects the inoculated leaves. Both of these strains cause severe systemic mosaic on the plants after dual infection with Turnip mosaic virus (TuMV). Synergistic interactions on long-distance transport of CMV-Y and CMV-D8 with TuMV were analyzed using an immunobinding assay. Direct tissue blots probed with either anti-CMV-Y or anti-TuMV antiserum clearly showed that CMV-Y efficiently spread and accumulated in the tissues of noninoculated upper leaves and roots when co-inoculated with TuMV, and that long-distance movement of CMV-D8 was enhanced by the presence of TuMV. Received 16 September 1999/ Accepted in revised form 5 February 2000     

<Emphasis Type="Italic">Trichoderma harzianum</Emphasis> elicits defence response genes in roots of potato plantlets challenged by <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

Biological control of Rhizoctonia solani with Trichoderma harzianum has been demonstrated in several studies. However, none have reported the dynamics of expression of defence response genes. Here we investigated the expression of these genes in potato roots challenged by R. solani in the presence/absence of T. harzianum Rifai MUCL 29707. Analysis of gene expression revealed an induction of PR1 at 168 h post-inoculation (hpi) and PAL at 96 hpi in the plants inoculated with T. harzianum Rifai MUCL 29707, an induction of PR1, PR2 and PAL at 48 hpi in the plants inoculated with R. solani and an induction of Lox at 24 hpi and PR1, PR2, PAL and GST1 at 72 hpi in the plants inoculated with both organisms. These results suggest that in the presence of T. harzianum Rifai MUCL 29707, the expression of Lox and GST1 genes are primed in potato plantlets infected with R. solani at an early stage of infection. Mycothèque de l’Université catholique de Louvain of S. Cranenbrouck's affiliation is part of the Belgian Coordinated Collections of Micro-organisms (BCCM).     

Cucumber mosaic virus Establishes Systemic Infection at Increased Temperature Following Viral Entrance Into the Phloem Pathway of Tetragonia expansa

ABSTRACT A potential regulatory site for Cucumber mosaic virus (CMV, pepo strain) movement necessary to establish systemic infection was identified through immunological and hybridization studies on Tetragonia expansa, which was systemically infected by CMV at 36 degrees C but not at 24 degrees C. In inoculated leaves, cell-to-cell movement of CMV was enhanced at 36 degrees C compared with that observed at 24 degrees C. CMV was distributed in the phloem cells of minor veins as well as epidermal and mesophyll cells at both 36 and 24 degrees C. CMV was detected in the petioles of inoculated leaves, stems, and petioles of uninoculated upper leaves at 36 degrees C, whereas CMV was detected only in the petioles of inoculated leaves and in stems at 24 degrees C. CMV moved into the phloem and was transported to the stem within 24 h postinoculation (hpi) at 36 degrees C. However, it did not accumulate in the petioles of the upper leaves until 36 hpi. In petioles of inoculated leaves at 24 degrees C, CMV was detected in the external phloem but not in the internal phloem. From these results, we conclude that systemic infection is established after viral entrance into the phloem pathway in T. expansa at 36 degrees C.     

Infection process of <Emphasis Type="Italic">Gilbertella persicaria</Emphasis> in papaya (<Emphasis Type="Italic">Carica papaya</Emphasis> L.) fruits

Gilbertella persicaria is a pathogenic fungus recently reported as a causative agent of soft rot in papaya fruits. Here the interactions between G. persicaria and papaya fruits was analyzed under laboratory conditions using histological techniques and optical microscopy to elucidate the process of pathogenesis. Healthy and disinfested fruits of papaya cv. Maradol were also inoculated with a suspension of sporangiospores of G. persicaria. Tissue sections were cut, which were subjected to differential staining with safranin-fast green for different times. Sporangiospores presumably adhered to the cuticle of the fruit by 3 h post inoculation (hpi) and germinated by 6 hpi; invasive intracellular hyphae were growing in host cells by 9 hpi. By 15 hpi, fruit epidermis was macerated, presumably by enzymatic activity reported for mucoral fungal species and appeared as a wet-looking lesion on the cuticle. Fruit mesocarp was colonized by 30 hpi, and asexual reproduction structures had formed by 48 hpi. This process of infection and disease development of G. persicaria in papaya fruits corresponds to that used by pathogens with a necrotrophic lifestyle.     

Epidemiology of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">syringae</Emphasis> on tomato

Leaf spot of tomato, incited by Pseudomonas syringae pv. syringae, has been reported recently in Italy on grafted and non-grafted tomato plants (scion Cuore di Bue, rootstock Solanum lycopersicum x Solanum hirsutum cv. Beaufort). In some greenhouses, more than 80% of plants were affected, with a marked reduction in yield. This work was undertaken in order to understand the effect of the number of hours of incubation at high relative humidity (r.h.) and temperature as well as the effect of the presence of wounds at infection time on the development of leaf spot. A difference in sensitivity to leaf spot was observed in the various cultivars tested, in terms of severity of P. syringae pv. syringae, with “Cuore di Bue” being the most susceptible of these cultivars. The development of leaf spot is mostly favored by the presence of wounds, at temperatures between 15 and 20°C. The severity of the disease is lower at 10 and 25°C and very low at 30°C. Under the most favorable temperature conditions, the presence of wounds is sufficient to allow the development of the pathogen immediately upon incubation at high r.h. The effect of wounds and the relatively low requirement of hours of incubation at high r.h. suggest the need for careful management and handling of plants when temperatures range between 15 and 25°C, and particularly within 15 and 20°C. All operations carried out, particularly at transplant and immediately after, should avoid the creation of wounds.     

Vascular blackening of wasabi rhizomes caused by <Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> subsp. <Emphasis Type="Italic">carotovorum</Emphasis>

Wasabi (Wasabia japonica) is grown for its highly-valued rhizome which is used as a condiment in Japanese food. Symptoms of vascular blackening in the rhizome were first observed in 2005 in plants grown in British Columbia, Canada. Microscopic observations and microbial isolation from infected tissues revealed that most of the xylem tracheid cells were blackened and bacteria were consistently associated with symptomatic plants. The bacterium most frequently recovered was identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) using BioLog™ and sequencing of a specific ~510 bp IGS region. Pathogen-free plants obtained using meristem-tip micropropagation were inoculated with a wasabi isolate of Pcc. Vascular blackening symptoms developed in the rhizome after 8 weeks when the rhizome was first wounded by stabbing or cutting, or if the roots were pre-inoculated with Pythium species isolated from rhizome epidermal tissues, followed by inoculation with Pcc at 1 × 10⁸ cells ml⁻¹. Xylem tracheid cells were blackened and Pcc was reisolated from all diseased tissues. The highest frequency of rhizome vascular blackening occurred at 22°C and 27°C and these tissues occasionally succumbed to soft rot at higher temperatures, but not when inoculated tissues were incubated at 10°C. The rooting medium used by growers for vegetative propagation of wasabi was shown to contain Pcc but the pathogen was not recovered from the irrigation water. Entry of Pcc through wounds on wasabi rhizomes and the host tissue response result in symptoms of vascular blackening.     

Pathogenicity of <Emphasis Type="Italic">Mycochaetophora gentianae</Emphasis>, causal fungus of gentian brown leaf spot,as affected by host species,inoculum density,temperature, leaf wetness duration,and leaf position

When the influence of host species, inoculum density, temperature, leaf wetness duration, and leaf position on the incidence of gentian brown leaf spot caused by Mycochaetophora gentianae, was examined, the fungus severely infected all seven Gentiana triflora cultivars, but failed to infect two cultivars of G. scabra and an interspecific hybrid cultivar. Inoculum density correlated closely with disease incidence, and a minimum of 10² conidia/mL was enough to cause infection. In an analysis of variance, temperature and leaf wetness duration had a significant effect upon disease incidence, which increased with higher temperature (15–25°C) and longer duration of leaf wetness (36–72 h). No disease developed at temperatures lower than 10°C or when leaf wetness lasted <24 h. At 48-h leaf wetness, disease incidence was 0, 28, 77, and 85% at 10, 15, 20, and 25°C, respectively. Middle and lower leaves on the plant were more susceptible than upper leaves. In microscopic observations of inoculated leaves, >50% of conidia germinated at temperatures >15°C after 24-h leaf wetness. More appressoria formed at higher temperatures (15–25°C) with extended duration of leaf wetness (24–72 h). At 48-h leaf wetness, appressorium formation was 0, 8, 26, and 73% at 10, 15, 20, and 25°C, respectively. These results suggest that temperature and leaf wetness duration were important factors for infection of gentian leaves.     

Induced resistance against Fusarium diseases of <Emphasis Type="Italic">Cymbidium</Emphasis> species by weakly virulent strain HPF-1 (<Emphasis Type="Italic">Fusarium</Emphasis> sp.)

The mechanism by which Fusarium diseases of cymbidium plants are suppressed by a weakly virulent strain HPF-1 of Fusarium sp. was studied. Strain HPF-1 produced microscopic, necrotic local lesions on cymbidium leaves, causing minor damage to palisade tissues at the infection sites. This weakly virulent strain remained near the site of infection and did not develop further. It systemically and nonselectively suppressed some diseases of cymbidium such as yellow spot of leaves caused by Fusarium proliferatum and F. fractiflexum, bulb and root rot caused by F. oxysporum, and dry rot of bulbs and roots caused by F. solani. Because endogenous salicylic acid levels increased in cymbidium leaves inoculated with strain HPF-1, the mechanism of disease suppression is thought to be systemic acquired resistance.     

Immunolocalization of <Emphasis Type="Italic">Pepper mild mottle virus</Emphasis> in developing seeds and seedlings of <Emphasis Type="Italic">Capsicum annuum</Emphasis>

The location of Pepper mild mottle virus (PMMoV) within seeds as they developed on inoculated seedlings of pepper (Capsicum annuum) was followed over time by detecting the viral coat protein using immunofluorescence microscopy. Seedlings were inoculated with PMMoV when the flower buds on the first and second branching nodes were in bloom. Fluorescence indicating the presence of PMMoV was first observed around immature seeds and placentas in the ovaries on the fourth branching node at 20 days post-anthesis (20 DPA), which corresponded to 39 days post-inoculation (39 DPI). The area with fluorescence gradually expanded from the placenta into the integument and the parenchyma, and finally reached the tip of the immature seeds by 34 DPA (53 DPI). The embryo or endosperm beyond the endothelium never fluoresced during the experiment [i.e., ending at 81 DPA (102 DPI)]. For visualizing viral routes of invasion from seeds into new seedlings, PMMoV-infected C. annuum seeds that were heterozygous for the L ³ tobamovirus-resistance gene were sown in soil at 30°C. After ~2 weeks, the cotyledon developed virally induced necrosis. These findings shed light on the infection cycle of PMMoV through vertical transmission in C. annuum.     

<Emphasis Type="BoldItalic">Didymella glomerata</Emphasis><Emphasis Type="Bold">causing leaf blight on pistachio</Emphasis>

During 2015 and 2016, we detected blighted leaves of pistachio (Pistacia vera) trees in different orchards in Arizona (USA). A Phoma-like species was isolated from pycnidia that appeared embedded in the leaf tissue. The pathogen was identified by means of morphological characteristics and DNA analysis (by sequencing of the ITS, BT, and EF regions) as Didymella glomerata. The optimum temperature for mycelial growth of the pathogen was around 25 °C. Inoculation tests were conducted on healthy and wounded pistachio leaves, fruits, and shoots of the cv. Kerman (female) and the cv. Peters (male). Overall, the pathogen was highly virulent on leaves of both pistachio cultivars and did not need injuries for infection. Conversely, the pathogen did not cause any macroscopic symptoms on the inoculated fruits and shoots but showed a certain endophytic behavior in the shoots. Also, data on the ability of different fungicides to inhibit the in vitro mycelial growth of the pathogen are presented.     

Temperature and plant age drive downy mildew disease epidemics on oilseed <Emphasis Type="Italic">Brassica napus</Emphasis> and <Emphasis Type="Italic">B. juncea</Emphasis>

Studies were undertaken on the effects of temperature (14/10 °C and 22/17 °C day/night) and plant age (15, 23, 31 and 40 day-old-plants) on the severity of downy mildew (Hyaloperonospora parasitica) on oilseed Brassica cultivars (temperature: Brassica juncea Montara, B. napus Atomic, ATR-Hyden, Hyola 432, Hyola 450 TT, Thunder TT; plant age: B. juncea Dune, B. napus Surpass 402 and Hyola 450 TT). For temperature studies, there were significant (P?<?0.001) effects of temperature, cultivar, and cultivar x temperature interaction. On cotyledons of susceptible cultivars (B. napus Hyola 450 TT and Thunder TT), plants were symptomatic at 22/17 °C by 48 h post inoculation (hpi) and with abundant sporulation evident by 72 hpi, and with all cotyledons of B. napus Thunder TT collapsed by 7 days post inoculation (dpi). However, at 14/10 °C, there were no symptoms on the same cultivars until 5 dpi, and sporulation only observed at 7 dpi. Percent disease index values (DI%) at 22/17 °C of B. juncea Montara and B. napus ATR-Hyden, Hyola 432, Atomic, Hyola 450 TT and Thunder TT were 4.5, 49.0, 51.4, 65.8, 86.3 and 96.0, respectively, with all except B. juncea Montara having significantly lower (P?<?0.001) disease at 14/10 °C with DI% values of 2.8, 30.4, 27.9, 31.1, 44.4 and 76.4, respectively. For plant age studies, there were significant (P?<?0.001) effects of plant age, cultivar, and cultivar x plant age interaction. DI% was significantly higher at 15 compared to 40 day-old-plants (dop) across all cultivars. B. juncea Dune showed greatest resistance, particularly on 40 dop, with DI% values of 25.8, 24.6, 22.9 and 7.5, for 15, 23, 31 and 40 dop, respectively. B. napus Surpass 402 showed high susceptibility on cotyledons of 15 dop but moderate resistance on leaves of other ages, with DI% values of 59.0, 31.2, 27.1 and 26.2 for 15, 23, 31 and 40 dop, respectively. B. napus Hyola 450 TT showed very high susceptibility at the cotyledon stage on 15 dop, but some resistance on 23 dop and more so on 31 and 40 dop, with DI% values of 84.0, 41.2, 35.4 and 32.9 for 15, 23, 31 and 40 dop, respectively. Together, these findings explain for the first time why development of downy mildew epidemics on susceptible cultivars occurs early in the growing season when warmer seasonal temperatures in autumn coincide with presence of seedlings; in contrast to later in the growing season on less susceptible older plants coinciding with cooler and less favourable winter temperatures. Increasing maximum and minimum temperatures associated with climate change have likely fostered the increased severity of downy mildew over the past 15 years.     

First report of blueberry red ringspot disease caused by <Emphasis Type="Italic">Blueberry</Emphasis><Emphasis Type="Italic">red</Emphasis><Emphasis Type="Italic">ringspot</Emphasis><Emphasis Type="Italic">virus</Emphasis> in Japan

Virus-like symptoms—red ringspots on stems and leaves, circular blotches or pale spots on fruit—were found on commercial highbush blueberry (Vaccinium corymbosum) cultivars Blueray, Weymouth, Duke and Sierra in Japan. In PCR testing, single DNA fragments were amplified from total nucleic acid samples of the diseased blueberry bushes using primers specific to Blueberry red ringspot virus (BRRV). Sequencing analysis of the amplified products revealed 95.7–97.7% nucleotide sequence identity with the BRRV genome. This paper is the first report of blueberry red ringspot disease caused by BRRV in Japan. The nucleotide sequence data reported in this paper are available in the GenBank/EMBL/DDBJ database as accessions AB469884 to AB469893 for BRRV isolates from Japan.     

<Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> isolated from Amazon lily (<Emphasis Type="Italic">Eucharis grandiflora</Emphasis>)

Cucumber mosaic virus (CMV) was isolated from a mosaic diseased plant of Eucharis grandiflora. The virus caused mosaic symptoms on leaves and slight distortion of flower petals in E. grandiflora by either mechanical or aphid inoculation. The virus was identified as a strain of CMV subgroup I from its biological and serological characteristics.     

New potyvirus isolated from <Emphasis Type="Italic">Cryptotaenia japonica</Emphasis>

 A potyvirus, for which the name Japanese hornwort mosaic virus (JHMV) is proposed, was isolated from Japanese hornwort plants (Cryptotaenia japonica) with mosaic disease symptoms. The virus was used to inoculate mechanically 34 plants belonging to 33 species of 10 families. Of these species seven from two families were infected. Faint chlorotic spots appeared on the inoculated leaves of Chenopodium quinoa and C. amaranticolor, but no systemic infection occurred in these plants. JHMV systemically infected only Umbelliferae plants; they did not infect 26 other species in eight families. JHMV was transmitted in a nonpersistent manner by aphids (Myzus persicae). The virus was a flexuous rod-shaped particle about 750 nm in length. Sequencing the nucleotides in the 3′ terminal region of JHMV revealed that the coat protein contains 280 amino acids with a molecular mass of 32.2 kDa. The nucleotide sequence of the coat protein of JHMV had the highest similarity with that of Zantedeschia mosaic virus (83.3%) compared to those of other potyviruses (57.0%–64.9%). An antiserum against JHMV reacted strongly with JHMV and weakly with Potato virus Y. These results indicate that JHMV is a new potyvirus. Received: September 9, 2002 / Accepted: November 7, 2002 RID="*" ID="*" The nucleotide sequence determined in this work appears in the DDBJ/EMBL/GenBank nucleotide sequence databases with the accession number AB081518     

<Emphasis Type="Italic">Colletotrichum acutatum</Emphasis> occurs asymptomatically on sweet cherry leaves

Leaves of sweet cherry, exposed to either paraquat or freezing to quickly senesce the leaf tissue, were incubated in about 100% RH at 25°C for 6 d. Sporulating colonies of Colletotrichum acutatum, the cause of anthracnose, developed on up to 100% of the paraquat-treated and frozen leaves, and on none of the untreated controls. Number of leaves and leaf area containing C. acutatum on naturally infected leaves increased over time from May to September. Mean incidence of C. acutatum on leaf blades on fruit spurs and vegetative shoots from eight orchard/year samplings were 41 and 33%, respectively. Secondary conidiation (formation of short hyphae and new conidia) from conidia applied to detached leaves took place 6 h after inoculation, but only up to 3% of the conidia formed new conidia. It may be concluded that asymptomatic sweet cherry leaves frequently host C. acutatum and may be a potential inoculum source for cherry fruit.     

Using metabolic profiling to assess plant-pathogen interactions: an example using rice (<Emphasis Type="Italic">Oryza sativa)</Emphasis> and the blast pathogen <Emphasis Type="Italic">Magnaporthe grisea</Emphasis>

A metabolomics based approach has been used to study the infection of the Hwacheong rice cultivar (Oryza sativa L. cv. Hwacheong) with compatible (KJ201) and incompatible (KJ401) strains of the rice blast fungal pathogen Magnaporthe grisea. The metabolic response of the rice plants to each strain was assessed 0, 6, 12, 24, 36, and 48 h post inoculation. Nuclear Magnetic Resonance (NMR) spectroscopy and Gas and Liquid Chromatography Tandem Mass spectrometry (GC/LC-MS/MS) were used to study both aqueous and organic phase metabolites, collectively resulting in the identification of 93 compounds. Clear metabolic profiles were observed at each time point but there were no significant differences in the metabolic response elicited by each pathogen strain until 24 h post inoculation. The largest change was found to be in alanine, which was ~30% (±9%) higher in the leaves from the compatible, compared to the resistant, plants. Together with several other metabolites (malate, glutamine, proline, cinnamate and an unknown sugar) alanine exhibited a good correlation between time of fungal penetration into the leaf and the divergence of metabolite profiles in each interaction. The results indicate both that a wide range of metabolites can be identified in rice leaves and that metabolomics has potential for the study of biochemical changes in plant-pathogen interactions.     

Suppression of <Emphasis Type="Italic">Papaya ringspot virus</Emphasis> infection in <Emphasis Type="Italic">Carica papaya</Emphasis> with CAP-34, a systemic antiviral resistance inducing protein from <Emphasis Type="Italic">Clerodendrum aculeatum</Emphasis>

CAP-34, a protein from Clerodendrum aculeatum inducing systemic antiviral resistance was evaluated for control of Papaya ringspot virus (PRSV) infection in Carica papaya. In control plants (treated with CAP-34 extraction buffer) systemic mosaic became visible around 20 days that intensified up to 30 days in 56% plants. During this period, CAP-34-treated papaya did not show any symptoms. Between 30 and 60 days, 95% control plants exhibited symptoms ranging from mosaic to filiformy. In the treated set during the same period, symptoms appeared in only 10% plants, but were restricted to mild mosaic. Presence of PRSV was determined in induced-resistant papaya at the respective observation times by bioassay, plate ELISA, immunoblot and RT-PCR. Back-inoculation with sap from inoculated resistant plants onto Chenopodium quinoa did not show presence of virus. The difference between control and treated sets was also evident in plate-ELISA and immunoblot using antiserum raised against PRSV. PRSV RNA was not detectable in treated plants that did not show symptoms by RT-PCR. Control plants at the same time showed a high intensity band similar to the positive control. We therefore suggest that the absence/delayed appearance of symptoms in treated plants could be due to suppressed virus replication.     

Specific inhibition of spore germination of <Emphasis Type="Italic">Alternaria brassicicola</Emphasis> by fistupyrone from <Emphasis Type="Italic">Streptomyces</Emphasis> sp. TP-A0569

Fistupyrone (FP), a metabolite from Streptomyces sp. TP-A0569, inhibited the in vivo infection of Chinese cabbage seedlings by Alternaria brassicicola. To detect the possible action sites of FP, the effect of FP on the infection behavior of A. brassicicola and A. alternata was investigated. When spores of A. brassicicola were suspended in FP solution and inoculated on host leaves, FP at 0.1ppm significantly inhibited spore germination, appressorial formation, and infection hypha formation of A. brassicicola. Host-specific AB-toxin production and lesion formation by A. brassicicola spores were also reduced significantly by treatment with FP 1ppm. The effect of FP seemed to be irreversible because significant washing of FP-treated spores with distilled water (DW) did not change the inhibitory effects. In contrast, A. alternata isolates such as Japanese pear pathotype, apple pathotype, and saprophyte behaved almost equally in both FP- and DW-treated spores. Mycelial dry weight in potato dextrose broth and mycelial diameters on potato dextrose agar, gelatin glucose agar, and Czapek solution agar of both A. brassicicola and A. alternata were not different with or without addition of FP. These results indicate that FP at low concentrations has a fungicidal effect on spores of A. brassicicola but not on spores of A. alternata; FP also does not affect the vegetative phase of these fungi.     

Epidemiology of root rot caused by <Emphasis Type="Italic">Leptosphaeria maculans</Emphasis> in <Emphasis Type="Italic">Brassica napus</Emphasis> crops

The infection of above-ground tissues of Brassica napus by Leptosphaeria maculans is well understood. However, root infection (root rot) under field conditions, the development of root rot over time and its relationship to other disease symptoms caused by L. maculans has not been described. A survey of B. napus crops was conducted in Australia to investigate the incidence and severity of root rot. Additionally, the pathway of root infection was examined in field experiments. Root rot was present in 95% of the 127 crops surveyed. The severity and incidence of root rot was significantly correlated with that of crown canker; however, the strength of this relationship was dependent on the season. Root rot symptoms appeared before flowering and increased in severity during flowering and at maturity, a pattern similar to crown canker suggesting that the infection of the root is an extension of the crown canker phase of the L. maculans lifecycle. All isolates of L. maculans tested in glasshouse experiments caused root rot and crown canker in B. napus and Brassica juncea. In the field, the main pathway of root infection is via invasion of cotyledons or leaves by airborne ascospores, rather than from inoculum in the soil. Root rot was present in crops in fields that had never been sown to B. napus previously, in plants grown in fumigated fields, and in glasshouse-grown plants inoculated in the hypocotyl with L. maculans.