Root Rot Complex Research Articles

Management of disease complex of balsam caused by Meloidogyne javanica and Macrophomina phaseolina by using biofertilisers and pesticides

An investigation was conducted to study the effect of biofertilisers (Glomus fasciculatum, Azospirillum brasilense, Azotobacter chroococcum and Micro Phos) and pesticides (carbofuran and bavistin) on the management of root-rot and root-knot disease complex of balsam. The individual application of biofertilisers (G. fasciculatum, A. brasilense and A. chroococcum) significantly improved the plant growth parameters viz., length, dry weight and number of flowers compared to untreated-uninoculated plants. The simultaneous inoculation of plant with Meloidogyne javanica and Macrophomina phaseolina in the pots treated with either of the biofertilisers (G. fasciculatum, A. brasilense and A. chroococcum) and pesticides (carbofuran/bavistin) significantly improved the plant growth parameters and reduced the reproduction factor, number of galls and intensity of root-rot compared to untreated-inoculated plants. On the other hand, the plants treated with Micro Phos neither significantly improved the plant growth parameters nor reduced the reproduction factor, number of galls and intensity of root-rot. Among the biofertilisers and pesticides, carbofuran was found to be the most effective in the management of disease complex of balsam followed by bavistin, G. fasciculatum, A. brasilense and A. chroococcum.

Response of soybean cultivars to root rot caused by Fusarium species

Fusarium root rot complex is a major soybean disease in Canada and the United States. Since 2006, four Fusarium species, F. oxysporum Schlechtendahl emend. Snyder & Hansen, F. graminearum Schwabe, F. avenaceum (Corda: Fr.) Sacc., and F. tricinctum (Corda) Sacc., have frequently been isolated from soybean roots in eastern Ontario, Canada. The objective of the current study was to screen 57 soybean cultivars that are commercially available in Canada for resistance to these four Fusarium root rot pathogens under greenhouse conditions. Based on root rot severity and reductions in seedling emergence, plant height and root dry weight, F. avenaceum was the most pathogenic species, followed by F. graminearum. The pathogenicity of F. oxysporum on soybean cultivars was not significantly different from that of F. tricinctum, but was significantly lower than that of F. graminearum. In replicated experiments, six, nine, eleven and seven cultivars were consistently rated as the most resistant to F. avenaceum, F. graminearum, F. oxysporum and F. tricinctum, respectively. Cultivar Maple Amber was resistant to all four Fusarium species based on root rot severity, while cultivar Altona was resistant to F. avenaceum, F. oxysporum and F. tricinctum. Four cultivars, 9004, AC Harmony, Lanark and Maple Arrow, each showed resistance to two different Fusarium species.Key words: Soybean, Glycine max, Fusarium root rot, Fusarium oxysporum, F. graminearum, F. avenaceum, F. tricinctum

Interaction of Rhizoctonia solani and Rhizopus stolonifer Causing Root Rot of Sugar Beet.

In recent years, growers in Michigan and other sugar beet (Beta vulgaris) production areas of the United States have reported increasing incidence of root rot with little or no crown or foliar symptoms in sugar beet with Rhizoctonia crown and root rot. In addition, Rhizoctonia-resistant beets have been reported with higher levels of disease than expected. In examining beets with Rhizoctonia root rot in Michigan, over 50% of sampled roots had a second potential root rot pathogen, Rhizopus stolonifer. Growing conditions generally were not conducive to disease production by this pathogen alone, so we investigated the potential for interaction between these two pathogens. In greenhouse tests, four of five sugar beet varieties had more severe root rot symptoms when inoculated with both pathogens than when inoculated with either pathogen alone. This synergism occurred under conditions that were not conducive to disease production by R. stolonifer. Host resistance to Rhizoctonia crown and root rot reduced diseases severity, but was insufficient to control the disease when both pathogens were present. This raises concerns about correct disease diagnosis and management practices and indicates that a root rot complex may be important on sugar beet in Michigan.

The role of phenolic compounds in disease resistance in geranium

The present study was conducted in the hill station of G B Pant University of Agriculture and Technology, Ranichauri, Uttarakhand, which is known for its diversity in medicinal and aromatic plants. The plant geranium, also known as rose or lemon geranium is highly valued for its essential oil which is used in the cosmetic and preferring industries. The plant suffers due to stem and root rot both during summer and winter seasons. In the present study, geranium plants showed maximum stem rot incidence (60.55%) and plant mortality (17.20%) during the winter season, whereas in summer the crops showed maximum root rot and wilt complex incidence (38.33%) with plant mortality up to (12.22%). The average stem rot mortality was comparatively low (16–20%) in summer but increased to 18–26% in winter crop. Several phenolic acids such as as tannic, gallic, caffeic, ferulic and benzoic were detected by using high performance liquid chromatography (HPLC) in variable amounts in these plants. The disease intensity varied from 97.77 to 92.46% from season to season. The significance of the phenolic compounds is discussed in relation to disease prevalence.

First report ofNeocosmospora vasinfectaassociated with the root rot complex of peanuts in Vietnam

The occurrence of Neocosmospora vasinfecta is reported for the first time from Vietnam where it was found in association with peanut roots affected by root rot. It was isolated from diseased roots from peanut crops in Nghe An Province in March 2007 but perithecia were not observed on the diseased roots. However, characteristic perithecia were produced abundantly in pure cultures on potato dextrose agar and carnation leaf-piece agar. Subsequently, perithecia were observed on diseased peanut roots in Thua Thien Hue Province. Representative cultures from Nghe An were confirmed as Neocosmospora vasinfecta by the Centraalbureau voor Schimmelcultures (CBS).

Fungal community diversity and soil health in intensive potato cropping systems of the east Po valley, northern Italy

AbstractAn ecological approach was used to investigate the relationship between diversity of soil fungal communities and soil‐borne pathogen inoculum in a potato growing area of northern Italy affected by yield decline. The study was performed in 14 sites with the same tillage management practices: 10 named ‘potato sites’, that for many years had been intensely cultivated with potatoes, and 4 named ‘rotation sites’, subject to a 4‐year rotation without potatoes or any recurrent crop for many years. Fungal communities were recorded using conventional (soil fungi by plate count and endophytic fungi as infection frequency on pot‐grown potato plant roots in soil samples) and molecular approaches [Basidiomycetes and Ascomycetes with specific and denaturing gradient gel electrophoresis (DGGE) analysis]. Diversity of fungal communities in potato sites was significantly lower than that in rotation sites. In addition, fungal communities in rotation sites showed lower Berger–Parker dominance than those in the potato sites, suggesting that rotation sites had a higher diversity as well as a better fungal community balance than potato sites. The ANalysis Of SIMilarity test of soil fungi and root endophytic fungi revealed that the two cropping systems differed significantly for species composition. Root endophytic fungal communities showed a greater ability to colonise potato roots in soil samples from potato sites than those from rotation sites. Moreover, the majority of endophytic root fungal community species in potato sites belonged to the potato root rot complex and storage disease (Colletotrichum coccodes,Fusarium solaniandFusarium oxysporum), while those in rotation sites were mainly ubiquitous or saprobic fungi. Soil rDNA analyses showed that Ascomycetes were much more frequent than Basidiomycetes in all the soils examined. DGGE analysis, with the Ascomycete‐specific primer (ITS1F/ITS4A), did not reveal distinctions between the communities found at the potato and rotation sites, although the same analysis showed differences between the communities of Basidiomycetes (specific primer ITS1F/ITS4B). These findings showed that recurrent potato cropping affected diversity and composition of soil fungal communities and induced a shift in specialisation of the endophytic fungi towards potato.

CHEMICAL ALTERNATIVES TO METHYL BROMIDE FOR STRAWBERRY IN THE AREA OF HUELVA (SPAIN): 2002-2007 RESULTS

The Spanish Methyl Bromide (MB) Alternatives Project (INIA) has carried out experiments over ten-years in Huelva for strawberry production. More than 20 soil fumigant treatments have been evaluated on cv. 'Camarosa'. The last series has been carried out in two locations of Eastern coastal Huelva (Moguer and Palos de la Fra.) from 2002-2003 until now. Treatments: MB + chloropicrin, 1,3-dichloropropene + chloropicrin (1,3D:CP), chloropicrin (CP) alone, metam sodium (MS), dimethyl disulphide (DMDS), ethanedinitrile (EDN), propylene oxide (PO), sodium tetrathiocarbamate (ENZ), methyl iodide + chloropicrin (MI), essential oils (EO), were shank-applied, or drip-irrigated such as sodium azide (SEP), furfural (FUR) under mulched (VIF film) pre-formed beds, or incorporated into the soil: dazomet (DAZ) and calcium cyanamide (CC). Treatments were applied in September and cultivation cycle was between October and the end of May every year. Black root rot complex and nematodes Meloidogyne hapla and Pratylenchus penetrans appear as the main phytosanitary problems related to soil. Our results supported feasible alternatives to MB with 1,3D:CP, CP alone or DMDS plus CP (DMDS:CP). In coastal Huelva, significant amounts of alternative fumigants have been applied to the strawberry crop since 2005, mainly 1,3D:CP, CP alone, DAZ:1,3D and MS. This activity has allowed 100% MB replacement rates in 2007. However some concerns remain due to the implementing of the Directive 91/414/EEC.

Marker‐Facilitated Selection for a Major QTL Associated with Root Rot Resistance in Snap Bean (Phaseolus vulgarisL.)

The use of molecular markers associated with quantitative trait loci (QTL) can improve the efficiency of breeding programs. In previous research, randomly amplified polymorphic DNA marker alleles AD9.950+derived from the root rot resistant snap bean (Phaseolus vulgarisL.) cultivar Puebla 152 and S18.1500−derived from the susceptible cultivar Eagle were linked in repulsion phase and mapped to the same locus. The alleles were associated with a major QTL that explained 25 and 49% of the variation for the root rot complex for plant vigor and plant biomass, respectively. The objective of the current study was to estimate the average effect of allelic substitution in BC1F3families that were indirectly selected for root rot resistance or susceptibility based on the AD9.950 and S18.1500 marker phenotypes. Four BC1F3inbred backcross populations were developed by crossing two susceptible snap bean cultivars (Hercules and Nicelo) with two root rot resistant donor inbred lines. When evaluated in a field with high levels of root rot inocula, families carrying the AD9.950+/S18.1500−marker alleles had a mean plant vigor of 3.95 ± 0.96 and mean plant biomass of 25.09 ± 0.89 g plant−1compared with 7.01 ± 0.96 and 7.05 ± 0.90, respectively, in families that lacked these alleles. Realized gains in plant biomass and plant vigor validate the effectiveness of substituting the AD9.950+and the S18.1500−marker alleles to introgress root rot resistance into susceptible genetic backgrounds.

Root and Crown Rot Fungi Associated with Spring, Facultative, and Winter Wheat in Turkey

The objective of this study was to determine the distribution frequency of the fungi associated with wheat (Triticum aestivum) crowns and roots in cereal producing areas of Turkey through a targeted survey of 518 commercial fields over a 2-year period. More than 26% of the fields had one or more of the fungal species commonly reported as part of the dryland root rot complex, Fusarium culmorum (14%) > Bipolaris sorokiniana (10%) > F. pseudograminearum (2%). The fungi considered to be part of the high rainfall root rot complex were found at very low frequencies: 2% for Gaeumannomyces graminis and 3% for Pythium spp. Species of Rhizoctonia were found in 22% of the fields. Several Fusarium species considered to be less or nonpathogenic to cereals were also found in high frequencies at 11% (F. oxysporum, F. chlamydosporum), 10% (F. sporotrichioides), and 8% (F. avenaceum and F. solani). The mostly random distribution of cereal root-rotting species across the survey area suggests the fungi are not distributed in any distinct agroecological relationship. As a result, the relative economic importance of a given species on wheat will be determined by a number of factors, such as their fungal pathogenicity, host susceptibility/tolerance, and the seasonal conditions. Results from this study suggest that there are a wide range of fungal species associated with root and crown tissues of wheat.

First report of alstroemeria wilt caused by Fusarium oxysporum in India

Hybrids of Alstroemeria spp. (Alstroemeriaceae), commonly called Peruvian Lily, are an exotic, rhizomatous and perennial cut flower crop widely cultivated under protection in India. Nine hybrids (cvs Alladin, Amor, Capri, Cinderella, Pluto, Rosita, Serena, Tiara and No. 14) were procured from three locations in India by the Institute of Himalayan Bioresource Technology (IHBT) in 2000–2001. During cultivation, plants of all cultivars exhibited leaf chlorosis and slight vein clearing on outer leaflets, followed by leaf yellowing and abscission, discolouration of stem vascular tissue and death. Fusarium oxysporum was consistently isolated when sections of discoloured stem vascular tissue were surface sterilised (2% sodium hypochlorite) and incubated on potato dextrose agar or carnation leaf agar. Single-spore isolates were identified based on morphological characters (Nelson et al., 1983). Conidiophores were unbranched or branched short monophialides. Microconidia were abundant, generally single celled, oval to kidney shaped and produced only in false heads 5–12 × 3–3·5 μ m. Macroconidia were abundant, slightly sickle-shaped and thin-walled, with an attenuated apical cell and a foot-shaped basal cell 35·0–60·0×3·0–5·0 μ m. Chlamydospores were single or in pairs and profusely distributed. Thepresence of chlamydospores and microconidia borne in false heads on short monophialides distinguished the fungus from closely related Fusarium species. The culture has been deposited in the Microbial Type Culture Collection (MTCC 7677) of the Institute of Microbial Technology, Chandigarh, India. The identity of the culture was also established by PCR amplification and sequencing of the internal transcribed spacer (ITS) region (White et al ., 1990) (GenBank Acc. No. AM 261761). Pathogenicity tests were done twice in a screen house on 8-week-old plants of cv. No. 14. Wounded roots were submerged for 10 min in a conidial suspension (1 ×10 6 conidia per mL in sterile tap water), while control plants were dipped in sterile tap water. Seedlings were transplanted into pots and maintained in a polytunnel. Symptoms observed on inoculated plants were similar to those in commercial glasshouses, including leaf wilt (3 weeks after inoculation), chlorosis, necrosis and plant death. The pathogen was re-isolated from the stems of affected inoculated plants to confirm Koch’s postulates. The control plants did not exhibit symptoms. Root rot complex of alstroemeria caused by F. oxysporum in association with Pythium irregulare and Rhizoctonia solani was earlier reported in Canada (Chang & Mirza, 1993) and Germany (Chang et al ., 1994). This is the first report of Fusarium oxysporum causing alstroemeria wilt in India.

Effects of Glomus fasciculatum and Rhizobium sp. on the growth and root-rot disease complex of chickpea

Effects of Glomus fasciculatum and Rhizobium was observed on the growth, chlorophyll, nitrogen, phosphorus and potassium contents and on the root-rot disease complex of chickpea caused by Meloidogyne incognita and Macrophomina phaseolina. Application of G. fasciculatum and Rhizobium alone and in combination to plants with pathogens increased plant growth, pod number, chlorophyll, nitrogen, phosphorus and potassium contents and also reduced galling, multiplication of nematodes and root-rot index. Inoculation of Rhizobium caused greater reduction in galling and nematode multiplication than caused by G. fasciculatum. Inoculation of both the symbionts together were more beneficial for plant growth and reducing root-rot index than either of them. Pathogens had adverse effects on root colonization by G. fasciculatum. However, root colonization and root nodulation was increased when both symbionts were inoculated together both in the presence and absence of pathogens.

Characterization of isolates of binucleate Rhizoctonia spp. associated with strawberry black root rot complex using fatty acid methyl ester (FAME) profiles

Black root rot is an important disease of strawberry caused by a complex of fungi that includes species of Rhizoctonia. In this study, a modified MIDI method (Microbial Identification System) was investigated for its utility to differentiate isolates of the three different anastomosis groups (AGs) of binucleate Rhizoctonia spp., associated with strawberry black root rot complex representing AG-A, AG-G, and AG-I. A total of 11 fatty acids were detected, and the FAME profiles for isolates of the three different AGs of Rhizoctonia spp. varied quantitatively and qualitatively. Moreover, the modified MIDI method will be a useful discriminatory tool for fungal identification and classification of the AGs of binucleate Rhizoctonia spp. associated with strawberry black root rot complex.

Biological control of root-rot disease complex of chickpea by AM fungi

Six species AM fungi, namely Glomus fasciculatum, G. constrictum, G. intraradices sp., Gigaspora margarita, Acaulospora sp. and Sclerocystis sp., were used for the biological control of root-rot disease complex of chickpea caused by Meloidogyne incognita and Macrophomina phaseolina. Application of these AM fungi increase plant growth, pod number, chlorophyll, nitrogen, phosphorus and potassium contents in diseased plants and also reduced nematode multiplication and root-rot index. G. fasciculatum caused greater increase in plant growth, pod number, chlorophyll, nitrogen, phosphorus and potassium contents of pathogen inoculated plants followed by G. intaradices, G. constrictum, Sclerocystis, G. margarita and Acaulospora sp. Percent root colonization caused by G. fasciculatum was high followed by G. intaradices, G. constrictum, Sclerocystis sp., G. margarita and Acaulospora sp. Glomus fasciculatum also caused higher reduction in root-rot index, galling and nematodes multiplication while Acaulospora sp. produced the least.

Annual Meeting, Québec, Quebec, 2006, The Canadian Phytopathological Society / Réunion annuelle, Québec, Québec, 2006, La Société canadienne de phytopathologie

Annual Meeting, Québec, Quebec, 2006, The Canadian Phytopathological Society / Réunion annuelle, Québec, Québec, 2006, La Société canadienne de phytopathologie

Gnomonia fragariae, a Cause of Strawberry Root Rot and Petiole Blight

Gnomonia fragariae has been occasionally listed among the fungi associated with diseased strawberry plants. However its pathogenicity has not been established. During the investigation on strawberry decline in Latvia and Sweden, a fungus was repeatedly recovered from discoloured root and crown tissues of severely stunted plants. Attempts to induce sporulation of the isolates grown on several agar media resulted in the formation of mature ascomata only on potato carrot agar and oatmeal agar. On morphological grounds and comparisons with reference herbarium specimens these isolates were identified as Gnomonia fragariae. The pathogenicity of the fungus was evaluated initially in the detached leaf assay and subsequently in three bioassays on strawberry plants. All the bioassays showed that G. fragariae was pathogenic on strawberry and capable of causing severe root rot and petiole blight. The symptoms that developed in the greenhouse experiments closely resembled those observed in the fields. The fungus did not cause rapid plant death but growth and development of inoculated strawberry plants was severely affected. To our knowledge this is the first time when pathogenicity of G. fragariae as a root rot pathogen has been clearly established. Our study shows that G. fragariae is one of the serious pathogens involved in the root rot complex of strawberry in Latvia and Sweden.

Additional experiences to elucidate the microbial component of soil suppressiveness towards strawberry black root rot complex

SummarySeveral studies were carried out to investigate the soil microbial components involved in suppressing strawberry black rot root which occurs throughout the Italian strawberry growing region. Quantitative and qualitative evaluation of fungi involved in black root rot were combined with several soil microbial parameters involved in soil suppressiveness towards black root rot agents. The first survey, carried out in an intensively cultivated area of northern Italy, identified Rhizoctonia spp. as the main root pathogen together with several typical weak pathogens belonging to the well‐known black rot root complex of strawberry crop: Cylindrocarpondestructans, Fusarium oxysporum, F. solani, Pestalotia longiseta and others. The root colonisation frequency of strawberry plants increased strongly from autumn to spring at harvesting stage. Rhizoctonia spp. were the only pathogens which followed the rising trend of root colonisation with relative frequency; all the weak pathogens of strawberry black root rot complex did not vary their frequency. Only non‐pathogenic fungi decreased from autumn to spring when at least 60% of colonising fungi were represented by Rhizoctonia. These data suggested that the late vegetative stage was the best time to record the soil inoculum of root rot agents in strawberry using root infection frequency as a parameter of soil health. A further study was performed in two fields, chosen for their common soil texture and pH, but with significant differences in previous soil management: one (ALSIA) had been subjected to strawberry monoculture without organic input for several years; the other (CIF) has been managed according to a 4‐year crop rotation and high organic input. In this study Pythium artificially inoculated was adopted as an indicator for the behaviour of saprophytically living pathogens in bulk soil. Pythium showed a sharp, different response after inoculation in bulk soil from the two soil systems evaluated. Pythium was suppressed only in the CIF field where the highest levels of total fungi and fluorescent bacteria and highest variability were observed. The suppressiveness conditions towards Pythium, observed in the CIF and absent in the ALSIA field, corresponded with the root infection frequency recorded at the late vegetative stage on strawberry plants grown in the two fields: strawberry plants from the CIF field showed lower root colonisation frequency and higher variability than that recorded on those coming from the ALSIA field.

Effects of soil compaction, temperature, and moisture on the development of the Fusarium root rot complex of pea in southwestern Ontario

The pea root rot complex (Fusarium spp.) is known to be affected by compaction, temperature, and moisture of the soils. This paper reports the effects of these factors on root rot severity and pea (Pisum sativum) growth tested in a controlled environment, using a Fusarium-infested soil collected from a field with a severe root rot history. For each factor, several increments were used. The results showed that in a controlled environment, an increase in soil bulk density due to compaction significantly increased root rot incidence and disease severity, and drastically reduced the fresh weight of pea plants. Stepwise increases in soil temperature from 10 to 30°C resulted in increases in estimated root rot severity and foliar symptom expression. Pea plants grown in soil moisture at 75% of field capacity had significantly lower Fusarium root rot incidence and severity than those grown in soil at 100%, 50% or 25% of field capacity. Pea plants subjected to temporary flooding exhibited an increased root rot incidence and severity as the duration of flooding increased from 1 to 5 d.

Efficacy of Clonostachys rosea strain ACM941 and fungicide seed treatments for controlling the root rot complex of field pea

The efficacy of seed treatments with bioagent ACM941 (a strain of Clonostachys rosea), its formulated products GB116 and ACM941-Pro, and common fungicides for the control of pea root rot complex were examined in six field trials in western Canada from 1996 to 2000. The effects on seedling emergence, root rot severity, and yield varied among years. In trials 1 and 2 (1996–1997), none of the treatments significantly reduced root rot severity or increased yield. ACM941 + Thiram 75WP was the most effective treatment, increasing emergence by 17.4% and was significantly better than that of the untreated controls. In trials 3 and 4 (1997–1998), Apron FL alone and ACM941 + Apron FL were significantly better than the untreated control, increasing emergence by 6.2 and 7.7%, and yield by 10.8 and 11.5%, respectively. In trials 5 and 6 (1999–2000), AC M 941 and GB116 were equally the most effective treatments, increasing emergence by 11.5 and 12.2%, and yield by 8.2 and 6.3%, respectively. These effects were significantly greater than that of the untreated control, but not significantly different from those of Apron FL or Vitaflo-280. ACM941-Pro was developed and tested in 2000 only, and it increased emergence by 17.1% and reduced root rot severity by 29.6%. Key words: Bioagent, Clonostachys rosea, field pea, Pisum sativum, pea root rot complex (PRRC), seed treatment, fungicide

Biological Control of Pathogens Causing Root Rot Complex in Field Pea Using Clonostachys rosea Strain ACM941

ABSTRACT Pea root rot complex (PRRC), caused by Alternaria alternata, Aphanomyces euteiches, Fusarium oxysporum f. sp. pisi, F. solani f. sp. pisi, Mycosphaerella pinodes, Pythium spp., Rhizoctonia solani, and Sclerotinia sclerotiorum, is a major yield-limiting factor for field pea production in Canada. A strain of Clonostachys rosea (syn. Gliocladium roseum), ACM941 (ATCC 74447), was identified as a mycoparasite against these pathogens. When grown near the pathogen, ACM941 often was stimulated to produce lateral branches that grew directly toward the pathogen mycelium, typically entwining around the pathogen mycelium. When applied to the seed, ACM941 propagated in the rhizosphere and colonized the seed coat, hypocotyl, and roots as the plant developed and grew. ACM941 significantly reduced the recovery of all fungal pathogens from infected seed, increased in vitro seed germination by 44% and seedling emergence by 22%, and reduced root rot severity by 76%. The effects were similar to those of thiram fungicide, which increased germination and emergence by 33 and 29%, respectively, and reduced root rot severity by 65%. When soil was inoculated with selected PRRC pathogens in a controlled environment, seed treatment with ACM941 significantly increased emergence by 26, 38, 28, 13, and 21% for F. oxysporum f. sp. pisi, F. solani f. sp. pisi, M. pinodes, R. solani, and S. sclerotiorum, respectively. Under field conditions from 1995 to 1997, ACM941 increased emergence by 17, 23, 22, 13, and 18% and yield by 15, 6, 28, 6, and 19% for the five respective pathogens. The seed treatment effects of ACM941 on these PRRC pathogens were greater or statistically equivalent to those achieved with thiram. Results of this study suggest that ACM941 is an effective bioagent in controlling PRRC and is an alternative to existing chemical products.

Management of soilborne diseases of beetroot in Australia: a review

Soilborne fungal diseases threaten the viability of the Australian processing beetroot industry. Globally, Pythium spp., Aphanomyces cochlioides and Rhizoctonia solani are the predominant soilborne fungal pathogens responsible for a root rot complex in beet crops. In Australia, the disease problems have been exacerbated in recent years because crops are now grown virtually year round, and under environmental conditions favourable to infection. This has lead to increased inoculum levels in soils sown to beetroot. Moreover, nowhere in the world does there seem to be a single strategy that is completely efficacious in controlling these pathogens, so an effective management strategy will almost certainly involve a combination of tactics. The most likely combination seems to involve fungicide seed treatments, rotations of gramineous or biofumigant crops and the use of disease-resistant varieties of beet. The first of these, fungicidal seed dressings, are a cost-effective means of reducing pathogen inoculum and protecting young beets from infection. Hymexazol may be particularly useful in the Australian system, since it is active against both Pythium and Aphanomyces. To combat Rhizoctonia, it should be applied in combination with either pencycuron or toclophos methyl. Second, rotations of gramineous crops, such as maize or oats, or biofumigant brassica crops, such as white mustard, brussel sprouts or cabbage should also reduce the build-up of inoculum and offers a tactic to relieve the problem in the longer term. Third, alternative beetroot cultivars with resistance to Rhizoctonia have now been developed in USA breeding programs and should be considered by the Australian industry. Resistant varieties are potentially very useful since they offer a long-term approach to disease management that can be easily incorporated into existing production systems. Fourth, the alteration of sowing dates to avoid periods of high disease risk (e.g. confining sowing to the cooler, drier months) needs to be seriously considered by the Australian industry if it is committed to disease management. There is also evidence to suggest that seed priming may warrant consideration as a tool to use in combination with fungicide dressings to reduce disease in young plants. Biological seed treatments and soil fumigation appear to be tactics of limited value to the Australian beet industry.