13. Chatterton, S; Punja, ZK. (2012) Colonization of geranium foliage by Clonostachys rosea f. catenulata, a biological control agent of botrytis grey mould.Botany-Botanique 90: 1-10 Colonization of geranium foliage by Clonostachys rosea f. catenulata, a biological control agent of botrytis grey mould
biological control; geranium; leaf colonization; Gliocladium catenulatum
The ecological requirements for the colonization of geranium leaves by the biocontrol agent Clonostachys rosea f. catenulata strain J1446 were investigated. Although this biocontrol agent is a soil-inhabiting fungus, treatment of geranium foliage with the agent can reduce grey mould caused by Botrytis cinerea in the greenhouse. To characterize the extent of foliar colonization, a GUS-transformed isolate of C. rosea f. catenulata was applied to foliage of two geranium cultivars, Pelargonium x hortorum and Pelargonium x domesticum. Population levels of C. rosea f. catenulata were found to be highest on senescent leaves and stems, followed by fully expanded leaves, and lowest on newly emerged leaves of both cultivars. Optimum temperature for leaf and petiole colonization was 20-25 degrees C for both cultivars. The biocontrol agent required at least 12 h of continuous leaf wetness to achieve maximum population densities on the leaves and stems of both cultivars. On whole plants, colonization was significantly higher on wounded leaves, stems, and senescing leaves compared with that on nonwounded leaves, stems, and mature leaves, respectively. GUS staining indicated that the fungus preferentially colonized the wound sites of leaves and the cut portions of stems. Results indicate that this biocontrol agent can successfully colonize the foliage of geraniums, thus demonstrating the endophytic ability of C. rosea f. catenulata in both root and foliar tissues. DOI
12. Elmhirst, JF; Haselhan, C; Punja, ZK. (2011) Evaluation of biological control agents for control of botrytis blight of geranium and powdery mildew of rose.Canadian Journal of Plant Pathology-Revue Canadienne de Phytopathologie 33: 499-505 Evaluation of biological control agents for control of botrytis blight of geranium and powdery mildew of rose
biological control; botrytis; geranium; ornamental disease management; powdery mildew; rose
Four commercially formulated biological control products, containing Gliocladium catenulatum (Prestop (R) WP), Trichoderma harzianum (PlantShield (R)) and Bacillus subtilis [Serenade (R) MAX (TM) (wettable powder) and Rhapsody (R) ASO (TM) (liquid)] were evaluated for control of rose powdery mildew (Podosphaera pannosa) on outdoor, container-grown roses and botrytis blight (Botrytis cinerea) on greenhouse-grown zonal geraniums in 2006 and 2007. The products were applied every 7-14 days and disease incidence and severity were compared to the fungicides captan for botrytis blight control and myclobutanil for powdery mildew control. Gliocladium catenulatum provided the best control of botrytis blight of geranium in both years, and disease incidence was significantly lower compared with plants treated with captan. Both G. catenulatum and B. subtilis (Serenade MAX (TM) applied every 14 days or Rhapsody ASO (TM) every 7 days) provided significant control of rose powdery mildew, which was comparable to that provided by myclobutanil. These preventative disease-suppressive biological control products may have a useful role in commercial nursery crop production. DOI
11. Jayaraman, J; Norrie, J; Punja, ZK. (2011) Commercial extract from the brown seaweed Ascophyllum nodosum reduces fungal diseases in greenhouse cucumber.Journal of Applied Phycology 23: 353-361 Commercial extract from the brown seaweed Ascophyllum nodosum reduces fungal diseases in greenhouse cucumber
Ascophyllum; Cucumber; Fungal diseases; Resistance; Mechanism
This study examined the effects of Stimplex (TM), a marine plant extract formulation from Ascophyllum nodosum, on some common cucumber fungal pathogens. Greenhouse cucumber plants were sprayed and/or root drenched using Stimplex (TM) at 0.5% or 1% concentration twice at 10-day intervals. Treatments also included application of fungicide (chlorothalonil, 2 g L(-1)) alternating with Stimplex (TM) application. Treated plants were inoculated with four cucumber fungal pathogens including Alternaria cucumerinum, Didymella applanata, Fusarium oxysporum, and Botrytis cinerea. Stimplex (TM) application resulted in a significant reduction in disease incidence of all the pathogens tested. The disease control effect was greater for Alternaria and Fusarium infection, followed by Didymella and Botrytis. Combined spray and root drenching with Stimplex (TM) was more effective than either spray or root drenching alone. The alternation of one fungicide application, alternated with Stimplex (TM) application, was highly effective and found to be the best treatment in reducing the disease ratings. Plants treated with Stimplex T showed enhanced activities of various defense-related enzymes including chitinase, beta-1,3-glucanase, peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, and lipoxygenase. Altered transcript levels of various defense genes, including chitinase, lipoxygenase, glucanase, peroxidase, and phenylalanine ammonia lyase were observed in treated plants. Cucumber plants treated with Stimplex (TM) also accumulated higher level of phenolics compared to water controls. These results suggest that seaweed extracts enhance disease resistance in cucumber probably through induction of defense genes or enzymes. DOI
10.Punja, ZK. (2011) American Ginseng: Research Developments, Opportunities, and Challenges.Journal of Ginseng Research 35: 368-374 American Ginseng: Research Developments, Opportunities, and Challenges
Panax quinquefolius; Genetic variation; Disease; Transgenic research
American ginseng (Panax quinquefolius L.) is grown in some regions of the USA and Canada and marketed for its health promoting attributes. While cultivation of this plant species has taken place in North America for over 100 years, there are many challenges that need to be addressed. In this article, the current production method used by growers is described and the challenges and opportunities for research on this valuable plant are discussed. These include studies on pharmacological activity, genetic diversity within the species, genetic improvement of currently grown plants, molecular characterization of gene expression, and management of diseases affecting plant productivity. The current research developments in these areas are reviewed and areas requiring further work are summarized. Additional research should shed light on the nature of the bioactive compounds and their clinical effects, and the molecular basis of active ingredient biosynthesis, and provide more uniform genetic material as well as improved plant growth, and potentially reduce losses due to pathogens. DOI
9. Wally, O; Punja, ZK. (2010) Enhanced disease resistance in transgenic carrot (Daucus carota L.) plants over-expressing a rice cationic peroxidase.Planta 232: 1229-1239 Enhanced disease resistance in transgenic carrot (Daucus carota L.) plants over-expressing a rice cationic peroxidase
Peroxidase; Lignin; Hydrogen peroxide; Pathogen resistance; Oxidative burst
Plant class III peroxidases are involved in numerous responses related to pathogen resistance including controlling hydrogen peroxide (H2O2) levels and lignin formation. Peroxidases catalyze the oxidation of organic compounds using H2O2 as an oxidant. We examined the mechanisms of disease resistance in a transgenic carrot line (P23) which constitutively over-expresses the rice cationic peroxidase OsPrx114 (previously known as PO-C1) and which exhibits enhanced resistance to necrotrophic foliar pathogens. OsPrx114 over-expression led to a slight enhancement of constitutive transcript levels of pathogenesis-related (PR) genes. These transcript levels were dramatically increased in line P23 compared to controls [GUS construct under the control of 35S promoter (35S::GUS)] when tissues were treated with cell wall fragments of the fungal pathogen Sclerotinia sclerotiorum (SS-walls), and to a lesser extent with 2,6-dichloroisonicotinic acid. There was no basal increase in basal H2O2 levels in tissues of the line P23. However, during an oxidative burst response elicited by SS-walls, H2O2 accumulation was reduced in line P23 despite, typical media alkalinization associated with oxidative burst responses was observed, suggesting that OsPrx114 was involved in rapid H2O2 consumption during the oxidative burst response. Tap roots of line P23 had increased lignin formation in the outer periderm tissues, which was further increased during challenge inoculation with Alternaria radicina. Plant susceptibility to a biotrophic pathogen, Erysiphe heraclei, was not affected. Disease resistance to necrotrophic pathogens in carrot as a result of OsPrx114 over-expression is manifested through increased PR transcript accumulation, rapid removal of H2O2 during oxidative burst response and enhanced lignin formation. DOI
8. Wally, O; Jayaraj, J; Punja, ZK. (2009) Broad-spectrum disease resistance to necrotrophic and biotrophic pathogens in transgenic carrots (Daucus carota L.) expressing an Arabidopsis NPR1 gene.Planta 231: 131-141 Broad-spectrum disease resistance to necrotrophic and biotrophic pathogens in transgenic carrots (Daucus carota L.) expressing an Arabidopsis NPR1 gene
SYSTEMIC ACQUIRED-RESISTANCE; FOLIAR FUNGAL PATHOGENS; DISPLAY ENHANCED RESISTANCE; SALICYLIC-ACID; DEFENSE RESPONSES; SCLEROTINIA-SCLEROTIORUM; SIGNALING PATHWAY; BOTRYTIS-CINEREA; NPR1-LIKE GENES; RICE
The development of transgenic plants highly resistant to a range of pathogens using traditional signal gene expression strategies has been largely ineffective. Modification of systemic acquired resistance (SAR) through the overexpression of a controlling gene such as NPR1 (non-expressor of PR genes) offers an attractive alternative for augmenting the plants innate defense system. The Arabidopsis (At) NPR1 gene was successfully introduced into 'Nantes Coreless' carrot under control of a CaMV 35S promoter and two independent transgenic lines (NPR1-I and NPR1-XI) were identified by Southern and Northern blot hybridization. Both lines were phenotypically normal compared with non-transformed carrots. Northern analysis did not indicate constitutive or spontaneous induction in carrot cultures of SAR-related genes (DcPR-1, 2, 4, 5 or DcPAL). The duration and intensity of expression of DcPR-1, 2 and 5 genes were greatly increased compared with controls when the lines were treated with purified cell wall fragments of Sclerotinia sclerotiorum as well as with 2,6-dichloroisonicotinic acid. The two lines were challenged with the necrotrophic pathogens Botrytis cinerea, Alternaria radicina and S. sclerotiorum on the foliage and A. radicina on the taproots. Both lines exhibited 35-50% reduction in disease symptoms on the foliage and roots when compared with non-transgenic controls. Leaves challenged with the biotrophic pathogen Erysiphe heraclei or the bacterial pathogen Xanthomonas hortorum exhibited 90 and 80% reduction in disease development on the transgenic lines, respectively. The overexpression of the SAR controlling master switch in carrot tissues offers the ability to control a wide range of different pathogens, for which there is currently little genetic resistance available. DOI
7. Jayaraj, J; Devlin, R; Punja, Z. (2008) Metabolic engineering of novel ketocarotenoid production in carrot plants.Transgenic Research 17: 489-501 Metabolic engineering of novel ketocarotenoid production in carrot plants
beta-carotene ketolase; carotenoid pathway engineering; ketocarotenoids; astaxanthin; root pigmentation; biopharming
Carotenoids constitute a vast group of pigments that are ubiquitous throughout nature. Carrot (Daucus carota L.) roots provide an important source of dietary beta-carotene (provitamin A), alpha-carotene and lutein. Ketocarotenoids, such as canthaxanthin and astaxanthin, are produced by some algae and cyanobacteria but are rare in plants. Ketocarotenoids are strong antioxidants that are chemically synthesized and used as dietary supplements and pigments in the aquaculture and neutraceutical industries. We engineered the ketocarotenoid biosynthetic pathway in carrot tissues by introducing a beta-carotene ketolase gene isolated from the alga Haematococcus pluvialis. Gene constructs were made with three promoters (double CaMV 35S, Arabidopsis-ubiquitin, and RolD from Agrobacterium rhizogenes). The pea Rubisco small sub-unit transit peptide was used to target the enzyme to plastids in leaf and root tissues. The phosphinothricin acetyl transferase (bar) gene was used as a selectable marker. Following Agrobacterium-mediated transformation, 150 plants were regenerated and grown in a glasshouse. All three promoters provided strong root expression, while the double CaMV 35S and Ubiquitin promoters also had strong leaf expression. The recombinant ketolase protein was successfully targeted to the chloroplasts and chromoplasts. Endogenous expression of carrot beta-carotene hydroxylases was up-regulated in transgenic leaves and roots, and up to 70% of total carotenoids was converted to novel ketocarotenoids, with accumulation up to 2,400 mu g/g root dry weight. Astaxanthin, adonirubin, and canthaxanthin were most prevalent, followed by echinenone, adonixanthin and beta-cryptoxanthin. Our results show that carrots are suitable for biopharming ketocarotenoid production for applications to the functional food, neutraceutical and aquaculture industries. DOI
6. Verma, N; MacDonald, L; Punja, ZK. (2007) Environmental and host requirements for field infection of blueberry fruits by Colletotrichum acutatum in British Columbia.Plant Pathology 56: 107-113 Environmental and host requirements for field infection of blueberry fruits by Colletotrichum acutatum in British Columbia
anthracnose; disease prediction; epidemiology; ripe-rot; Vaccinium corymbosum; weather conditions
Higher recovery of Colletotrichum acutatum, the causal agent of anthracnose (ripe-rot), from blueberry tissues during the growing seasons of 2002 and 2003 was found at bloom and ripe berry than at other stages of plant development. The effects of leaf-wetness duration and ambient temperature on fruit infection frequency were determined during the growing seasons of 2001-03. Potted 2-year-old blueberry plants were exposed for 1-week periods to prevailing environmental conditions and natural inoculum in a commercial field, and grown to harvest, when fruit infection was assessed. Three peaks of infection were observed: early during bloom, mid-season during the mature green berry stage, and later in the season when berries had ripened. Weather data collected simultaneously indicated that a minimum of 10 h of leaf wetness at 11 degrees C was sufficient for fruit infection. These conditions preceded each peak of infection. To determine whether peaks of infection in the field were also caused by changes in host susceptibility or available inoculum, groups of potted blueberry plants were artificially inoculated at weekly intervals during the growing season of 2004, exposed to prevailing environmental conditions, and fruit infection assessed at harvest. Flowers and developing fruits were found to be susceptible throughout the season, indicating that specific peaks of infection were associated with environmental conditions and availability of inoculum. DOI
5. Park, Y; Chen, XB; Punja, ZK. (2006) Molecular and biological characterization of a mitovirus in Chalara elegans (Thielaviopsis basicola).Phytopathology 96: 468-479 Molecular and biological characterization of a mitovirus in Chalara elegans (Thielaviopsis basicola)
black root rot; fungal virus; mycovirus
A 2.8-kb double-stranded RNA (dsRNA) element in strain BK18 of Chalara elegans originally isolated from cotton soil in California was characterized by obtaining a full-length cDNA sequence (2,896 nucleotides in length) from a series of overlapping clones. Sequence analysis revealed the presence of one large open reading frame (ORF I) using the initochondrial genetic code, with 20 to 34% amino acid identity to the ORF I of other previously reported fungal mitochondrial RNA viruses. The ORF I encoded a putative protein of 705 amino acids and contained the conserved motif characteristic of RNA-dependent RNA polymerases. Purification of mitochondria from strain BK 18 confirmed the co-localization of this dsRNA. and northern blot hybridization with a strand-specific probe revealed the (+) single-stranded nature. This Chalara elegans mitovirus (CeMV) is designated as a new member of the genus Mitovirus of the family Narnaviridae. Using dsRNA-specific primers. the ORF I region (positions 427 to 2544) was obtained from an additional 2.8-kb dsRNA element in strain HA2 originating from carrot roots in the Netherlands. Both ORFs had 98% homology at the nucleotide and amino acid levels. CeMV was also found to be present in five additional strains of C. elegans from different geographic locations worldwide, and a 97 to 100% nucleotide sequence identity was observed within a 300-bp region of ORF I in these strains. To determine the biological effects of CeMV on C. elegans, attempts to cure strain BK 18 of the dsRNA were made. Sequential transfers of mycelium at 35 to 37 degrees C yielded a colony which lacked the 2.8-kb dsRNA when visualized on agarose gels and also in northern blot hybridization analysis. However. reverse transcription-polymerase chain reaction with specific primer sets revealed a band., indicating that dsRNA replication had been significantly repressed (latent). The wild type and latently infected strains were compared for colony morphology, growth rate, melanin production, various enzymatic assays (polyphenoloxidase, laccase. tyrosinase, and esterase), and virulence on carrot roots. Colony morphology on V8 agar was comparable between the two strains. while growth rate, melanin production, and virulence were enhanced in the latently infected strain. There were no detectable differences in enzymatic activity. Transmission electron microscopy of hyphae of the wild type and latently infected strains revealed differences in the number and size of the mitochondria, which were enhanced in the latently infected strain. Our results show that CeMV is a new member of the genus Mitovirus with some disruptive effects on its fungal host and is present in C. elegans strains from different locations worldwide.
4. Rahman, M; Punja, ZK. (2006) Influence of iron on cylindrocarpon root rot development on ginseng.Phytopathology 96: 1179-1187 Influence of iron on cylindrocarpon root rot development on ginseng
Cylindrocarpon root rot, caused by Cylindrocarpon destructans, is an important disease on ginseng (Panax quinquefolius) in Canada. We studied the effects of iron (Fe) on disease severity and pathogen growth. When Hoagland's solution was amended with Fe at 56 and 112 mu g/ml compared with 0 mu g/ml, disease initiation and final severity on hydroponically maintained ginseng roots was significantly (P < 0.0001) enhanced. Under field conditions. wounding of roots with a fine needle followed by application of 0.05% FeNaEDTA to the rhizosphere of treated plants significantly enhanced Cylindrocarpon root rot in 2003 and 2004 compared with unwounded roots with Fe or wounded roots without Fe. Foliar applications of Fe (as FeNaEDTA) to ginseng plants three times during the 2002 and 2003 growing seasons significantly increased Fe levels in root tissues. These roots developed larger lesions following inoculation with C. destructons in vitro. When radioactive Fe (Fe-59) was applied to the foliage of ginseng plants, it was detected in the secondary phloem and in cortical and epidermal tissues within I week. Artificially wounded areas on the roots accumulated more Fe-59 than healthy areas. Diseased tissue also had threefold higher levels of phenolic compounds and Fe compared with adjoining healthy tissues. High-performance liquid chromatography analysis revealed enhanced levels of protocatechuic acid, chlorogenic acid, caffeic acid, ferulic acid, cinnamic acid, phloridizin, and quercetin. Phenolic compounds produced in diseased and wounded tissues sequestered Fe in vitro. The effects of Fe on mycelial growth, conidial germ tube length, and secondary branching of germ tubes of C destructans were examined in vitro. When grown on Chrome-azurol S medium, Fe also was sequestered by C. destructans through siderophore production, which was visualized as a clearing pigmented zone at the margin of colonies. Mycelial dry weight was significantly increased in glucose/yeast broth containing Fe at 56 or 112 mu g/ml. Conidial germ tube length and secondary branching of hyphae also were enhanced after 8 and 16 h by Fe. Colony growth of C. destructans was not enhanced by Fe, but significantly greater spore production was observed with Fe at 56 and 112 mu g/ml compared with no Fe in the medium. Although these levels of Fe had no effect on fungal pectinase enzyme activity, polyphenoloxidase (PPO) activity was significantly (P < 0.0001) enhanced. We conclude that Fe enhances Cylindrocarpon root rot through enhanced pathogen growth, sporulation, and PPO enzyme activity. Fe sequestered by phenolic cornpounds produced in wounded tissues can enhance Fe levels at the site of infection. The pathogen also has the ability to sequester Fe at these sites.
3. Verma, N; MacDonald, L; Punja, ZK. (2006) Inoculum prevalence, host infection and biological control of Colletotrichum acutatum: causal agent of blueberry anthracnose in British Columbia.Plant Pathol 55: 442-450 Inoculum prevalence, host infection and biological control of Colletotrichum acutatum: causal agent of blueberry anthracnose in British Columbia
biological control; diagnostics; epidemiology; Gliocladium catenulatum; Trichoderma harzianum; Vaccinium corymbosum
To identify the causal organism of anthracnose (ripe-rot), which reduces yield and postharvest quality of blueberries grown in British Columbia, Canada, 80 isolates were recovered from diseased fruits collected from commercial blueberry fields during 2002-04 and identified as Colletotrichum acutatum using colony morphology, growth rate and species-specific PCR primers. In vitro incubation of replicated sets of inoculated detached berries at various temperatures produced infection at temperatures of 7-30 degrees C, with an optimum at 20 degrees C. Colletotrichum acutatum could not survive on the soil surface as mummified berries but the pathogen was detected mostly within flower buds and less so in blueberry twigs and fruit trusses. Infection of developing flower buds in May-June of the preceding growing season gave the highest inoculum recovery in the following year. Two commercial fungal biocontrol agents, Prestop (Gliocladium catenulatum) and PlantShield (Trichoderma harzianum), each reduced anthracnose development in 2003 and 2004 by up to 45% when sprayed three times onto plants between flowering and fruit ripening.
2. Park, YJ; James, D; Punja, ZK. (2005) Co-infection by two distinct totivirus-like double-stranded RNA elements in Chalara eleganse (Thielaviopsis basicola).Virus Research 109: 71-85 Co-infection by two distinct totivirus-like double-stranded RNA elements in Chalara eleganse (Thielaviopsis basicola)
Chalara elegans; dsRNA sequence; Totiviridae; fungal viruses
A full-length cDNA clone was developed from a 5.3 kb double-stranded (ds) RNA element present in strain CKP of the plant pathogenic fungus Chalara elegans. The complete nucleotide sequence was 5310bp in length and sequence analysis revealed that it contained three large putative open reading frames (ORFs). ORFI was initiated at nucleotide position 329 and encoded a putative coat protein, which shared some homology (35-45% amino acid identity) to other dsRNAs in the family Totiviridae. Both ORF2 and ORF3 were initiated at nucleotide positions 2619 and 4071, respectively, and encoded a putative RNA-dependent RNA polymerase (RdRp). Sequence comparison using deduced amino acid sequences of both ORF2 and ORF3 revealed that all RdRp conserved motifs shared highest homology (41% identity) to that of SsRNA1 of Totiviridae. This dsRNA in C. elegans was designated Chalara elegans RNA Virus 1 (CeRV1). During the development of the full-length cDNA clone of CeRV1, several partial cDNA clones from an additional dsRNA fragment in strain CKP were obtained, which when aligned with each other, produced one linear fragment which was 2336 bp long. Northern blot and sequence analysis of this second clone showed it differed in sequence composition from CeRV1. This dsRNA in C. elegans was designated Chalara elegans RNA Virus 2 (CeRV2). Sequence analysis of CeRV2 showed it contained all conserved motifs and shared some homology (45% amino acid identity) to RdRp regions of Totiviridae. The nucleotide and amino acid sequences of the conserved motifs of the RdRp regions between CeRV1 and CeRV2 showed an identity of 56% and 50%, respectively. These findings suggest that co-infection of two distinct totivirus-like dsRNAs (CeRV1 and CeRV2) in C. elegans, a first report in this fungus. Transmission electron microscopy of strain CKP of C. elegans revealed the presence of putative virus-like particles in the cytoplasm, which were similar both in shape and size to viruses in the Totiviridae. (C) 2004 Elsevier B.V. All rights reserved.
1. Rahman, M; Punja, ZK. (2005) Factors influencing development of root rot on ginseng caused by Cylindrocarpon destructans.Phytopathology 95: 1381-1390 Factors influencing development of root rot on ginseng caused by Cylindrocarpon destructans
disappearing root rot; epidemiology; Panax quinquefolius; pathogenicity
The fungus Cylindrocarpon destructans (Zins) Scholten is the cause of root rot (disappearing root rot) in many ginseng production areas in Canada. A total of 80 isolates of C. destructans were recovered from diseased roots in a survey of ginseng gardens in British Columbia from 2002-2004. Among these isolates, 49% were classified as highly virulent (causing lesions on unwounded mature roots) and 51% were weakly virulent (causing lesions only on previously wounded roots). Pectinase and polyphenoloxidase enzymes were produced in vitro by C. destructans isolates when they were grown on pectin and phenol as a substrate, respectively. However, highly virulent isolates produced significantly (P < 0.001) higher enzyme levels compared with weakly virulent isolates. Histopathological studies of ginseng roots inoculated with a highly virulent isolate revealed direct hyphal penetration through the epidermis, followed by intracellular hyphal growth in the cortex. Subsequent cell disintegration and accumulation of phenolic compounds was observed. Radial growth of highly and weakly virulent isolates on potato dextrose agar was highest at 18 and 21 degrees C, respectively and there was no growth at 35 degrees C. Mycelial mass production as significantly (P <= 0.01) lower at pH 7.0 compared with pH 5.0. To study the effects of pH (5.0 and 7.0) and wounding on disease development, ginseng roots were grown hydroponically in Hoagland's solution. Lesions were significantly larger (P < 0.001) at pH 5.0 compared with pH 7.0 and wounding enhanced disease by a highly virulent isolate at both pHs. In artificially infested soil, 2-year-old ginseng roots were most susceptible to Cylindrocarpon root rot among all root ages tested (I to 4 years) when evaluated using a combined scale of disease incidence and severity. Root rot severity was significantly (P < 0.002) enhanced by increasing the inoculum density from 3.45 x 10(2) CFU/g of soil to 1.86 x 10(3) CFU/g of soil. Disease severity was higher at 20 degrees C compared with 15 and 25 degrees C and at -0.02 MPa soil moisture compared with -0.005 and -0.001 MPa. A significant interaction between soil moisture and temperature was observed for root rot severity.
