Response of three root rot fungi to strawberry phenolics and the relation of phenolics to disease resistance

Pythium irregulare, Rhizoctonia solani, and Alternaria alternata, usually associated with strawberry root rot diseases, were sensitive in vitro to several phenolics present in strawberry roots, fruits, and leaves, P. irregulare was the most sensitive. Eighteen strawberry cultivars were divided into two types, based on qualitative phenolic content. Five contained an unidentified xanthone and generally less kaempferol-7-glucoside than the remaining thirteen. Although these differences were not correlated with resistance to three strawberry diseases, quantitative difference of certain phenolics may be important in seasonal resistance to root rot pathogens.Cooperative Investigations, Agricultural Research Service, United States Department of Agriculture and Plant and Soil Science Department, School of Agriculture, Southern Illinois University, Carbondale, Illinois.Research Plant Pathologist, formerly located at Carbon dale, Illinois.     

Isolation and characterization of mutants of <Emphasis Type="Italic">Pseudomonas maltophila</Emphasis> PM-4 altered in chitinolytic activity and antagonistic activity against root rot pathogens of clusterbean (<Emphasis Type="Italic">Cyamopsis tetragonoloba</Emphasis>)

Pseudomonas maltophila PM-4, an antagonist of pathogenic fungi including Rhizoctonia bataticola, R. solani, Fusarium oxysporum and Sclerotinia sclerotiorum associated with root rot of clusterbean (Cyamopsis tetragonoloba) was mutagenized with Tn5. Hyperchitinase producing mutants showing large zone of colloidal chitin dissolution were identified on medium containing calcoflor dye as an indicator. A mutant P-48 producing 137% higher chitinase activity than the parent strain PM-4 was identified. Seed bacterization of clusterbean (Cyamopsis tetragonoloba) with P-48 controlled the root rot upto 40.8% in the presence of conglomerate of all the four fungal pathogens Rhizoctonia bataticola, R. solani, F. oxysporum and Sclerotinia sclerotiorum.     

Root rot of onion caused byPythium irregulare andPythium coloratum

Pythium irregulare andPythium coloratum were isolated consistently from roots of onion plants exhibiting root rot and associated foliar symptoms in fields located in Organe County, NY.P. coloratum predominated following extremely wet weather in 1984 and 1986, whileP. irregulare was prevalent following moderately wet weather in 1985. Both species produced root rot symptoms similar to field symptoms when 12 week old onion plants (cv Downing Yellow Globe) were inoculated and incubated in a growth chamber at 14°C for 10 days. This is the first report ofP. irregulare andP. coloratum as causes of root rot of onion.     

Inter-relationship between shoot weight,severity of root rot and survival rate of subterranean clover inoculated with certain pathogenic fungi

Summary Plant survival rate, root disease index and fresh shoot weight of subterranean clover seedlings inoculated with fungal pathogens (Fusarium avenaceum, F. oxysporum, Phoma medicaginis, Pythium irregulare andRhizoctonia solani, both singly and in combinations) were generally inter-correlated over a wide range of temperature (10, 15, 20 and 25°C) and moisture conditions (45, 65% water holding capacity and flooding). There was a negative correlation between root disease index and shoot weight for all treatments exceptF. avenaceum + P. irregulare. Root disease index and seedling survival rate were negatively correlated except forF. oxygsporum, Phoma medicaginis, P. irregulare andF. oxysporum + F. avenaceum. However, a good positive correlation was found between the survival rate and shoot weight for all treatments with the exception ofPhoma medicaginis.     

Establishment and effectiveness of inoculated arbuscular mycorrhizal fungi in agricultural soils

Arbuscular mycorrhizal fungi (AMF) are promoted as biofertilizers for sustainable agriculture. So far, most researchers have investigated the effects of AMF on plant growth under highly controlled conditions with sterilized soil, soil substrates or soils with low available P or low inoculum potential. However, it is still poorly documented whether inoculated AMF can successfully establish in field soils with native AMF communities and enhance plant growth. We inoculated grassland microcosms planted with a grass–clover mixture (Lolium multiflorum and Trifolium pratense) with the arbuscular mycorrhizal fungus Rhizoglomus irregulare. The microcosms were filled with eight different unsterilized field soils that varied greatly in soil type and chemical characteristics and indigenous AMF communities. We tested whether inoculation with AMF enhanced plant biomass and R. irregulare abundance using a species specific qPCR. Inoculation increased the abundance of R. irregulare in all soils, irrespective of soil P availability, the initial abundance of R. irregulare or the abundance of native AM fungal communities. AMF inoculation had no effect on the grass but significantly enhanced clover yield in five out of eight field soils. The results demonstrate that AMF inoculation can be successful, even when soil P availability is high and native AMF communities are abundant.     

Fungicidal control of damping-off and seedling root rot in Brassica species caused by Rhizoctonia solani in the growth chamber*

Eight fungicides (benodanil, carboxin, cyproconazole, fenpropimorph, fur-mecyclox, iprodione, pencycuron and tolclofos-methyl) were evaluated, under growth chamber conditions, as seed treatments against pre-emergence damping-off and post-emergence seedling root rot in six Brassica species. Five cultivars of B. rapa, four cultivars of B. juncea, four cultivars of B. napus and one cultivar/ strain from each of B. carinata, B. nigra and B. oleracea were grown in soilless mix infested with an isolate of Rhizoctonia solani AG-2-1. B. nigra and B. juncea were considerably less susceptible to R. solani than the four other species. Cyproconazole at 0.05-0.1 g a.i./kg seed and the other fungicides at 2–4 g a.i./ kg seed provided almost complete control of pre-emergence damping-off in most Brassica species and their cultivars. Their efficacy varied against the post-emergence seedling root rot. Furmecyclox, iprodione, tolclofos-methyl and pencycuron consistently gave good control of seedling root rot in all Brassica species and their cultivars. Benodanil and fenpropimorph provided moderate control, and carboxin and cyproconazole gave poor control against root rot. Efficacy of carboxin, cyproconazole, benodanil and fenopropimorph against seedling root rot varied significantly (P ≤ 0.05) among cultivars within a Brassica species.     

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

Several 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.     

Influence of the endomycorrhizal fungus Glomus mosseae on the development of peanut pod rot disease in Egypt

Glomus mosseae and the two pod rot pathogens Fusarium solani and Rhizoctonia solani and subsequent effects on growth and yield of peanut (Arachis hypogaea L.) plants were investigated in a greenhouse over a 5-month period. At plant maturity, inoculation with F. solani and/or R. solani significantly reduced shoot and root dry weights, pegs and pod number and seed weight of peanut plants. In contrast, the growth response and biomass of peanut plants inoculated with G. mosseae was significantly higher than that of non-mycorrhizal plants, both in the presence and absence of the pathogens. Plants inoculated with G. mosseae had a lower incidence of root rot, decayed pods, and death than non-mycorrhizal ones. The pathogens either alone or in combination reduced root colonization by the mycorrhizal fungus. Propagule numbers of each pathogen isolated from pod shell, seed, carpophore, lower stem and root were significantly lower in mycorrhizal plants than in the non-mycorrhizal plants. Thus, G. mosseae protected peanut plants from infection by pod rot fungal pathogens. Accepted: 10 February 2000     

Cross-pathogenicity of Rhizoctonia solani strains on pasture legumes in pasture-crop rotations

In Australia, in the past, pasture legumes were rotated mainly with cereals, but increasingly these rotations now involve pasture legumes with a wider range of crops, including legumes. This increasing frequency of the leguminous host in the rotation system may be associated with increased root rots in legumes in the current pasture-crop rotations. The primary aim of this study was to see whether the pathogenicity on pasture legumes of strains of Rhizoctonia solani sourced from lupins and cereals (common crops in rotation with pastures) is associated with increased incidence of root rots in pasture legumes in the disease conducive sandy soils of the Mediterranean regions of southern Australia. The second aim was to determine sources of resistance among newly introduced pasture legumes to R. solani strains originating from rotational crops as this would reduce the impact of disease in the pasture phase. Fifteen pasture legume genotypes were assessed for their resistance/susceptibility to five different zymogram groups (ZG) of the root rot pathogen R. solani under glasshouse conditions. Of the R. solani groups tested, ZG1–5 and ZG1–4 (both known to be pathogenic on cereals and legumes) overall, caused the most severe root disease across the genotypes tested, significantly more than ZG6 (known to be pathogenic on legumes), in turn significantly >ZG4 (known to be pathogenic on legumes) which in turn was >ZG11 (known to be pathogenic on legumes including tropical species). Overall, Ornithopus sativus Brot. cvs Cadiz and Margurita, Trifolium michelianum Savi. cvs Paradana and Frontier and T. purpureum Loisel. cv. Electro showed a significant level of resistance to root rot caused by R. solani ZG11 (root disease scores ≤1.2 on a 1–3 scale where 3 = maximum disease severity) while O. sativus cvs Cadiz and Erica showed a significant level of resistance to root rot caused by R. solani ZG4 (scores ≤1.2). O. compressus L. cvs Charano and Frontier, O. sativus cv. Erica, and T. purpureum cv. Electro showed some useful resistance to root rot caused by R. solani ZG6 (scores ≤1.8). This is the first time that cvs Cadiz, Electro, Frontier, Margurita and Paradana have been recognised for their levels of resistance to root rot caused by R. solani ZG11; and similarly for cvs Cadiz and Erica against ZG4; and for cvs Charano, Erica, and Electro against ZG6. These genotypes with resistance may also serve as useful sources of resistance in pasture legume breeding programs and also could potentially be exploited directly into areas where other rotation crops are affected by these R. solani strains. None of the tested genotypes showed useful resistance to R. solani ZG1–4 (scores ≥2.0) or ZG1–5 (scores ≥2.5). This study demonstrates the relative potential of the various R. solani ZG strains, and particularly ZG1–4, ZG1–5, ZG4 and ZG6 to attack legume pastures and pose a significant threat to non-pasture crop species susceptible to these strains grown in rotation with these pasture legumes. Significantly, the cross-pathogenicity of these strains could result in the continuous build-up of inoculum of these strains that may seriously affect the productivity eventually of legumes in all rotations. In particular, when choosing pasture legumes as rotation crops, caution needs to be exercised so that the cultivars deployed are those with the best resistance to the R. solani ZGs most likely to be prevalent at the location.     

Influence of Seed‐borne Cochliobolus sativus (Anamorph Bipolaris sorokiniana) on Crown Rot and Root Rot of Barley and Wheat

The effect of seed‐borne pathogens of wheat and barley on crown and root rot diseases of seven barley cultivars (Jimah‐6, Jimah‐51, Jimah‐54, Jimah‐58, Omani, Beecher and Duraqi) and three wheat cultivars (Cooley, Maissani and Shawarir) was investigated. Bipolaris sorokiniana and Alternaria alternata were detected in seeds of at least eight cultivars, but Fusarium species in seeds of only two barley cultivars (Jimah‐54 and Jimah‐58). Crown rot and root rot symptoms developed on barley and wheat cultivars following germination of infected seeds in sterilized growing media. Bipolaris sorokiniana was the only pathogen consistently isolated from crowns and roots of the emerging seedlings. In addition, crown rot and root rot diseases of non‐inoculated barley cultivars correlated significantly with B. sorokiniana inoculum in seeds (P = 0.0019), but not with Fusarium or Alternaria (P > 0.05). These results indicate the role of seed‐borne inoculum of B. sorokiniana in development of crown rot and root rot diseases. Pathogenicity tests of B. sorokiniana isolates confirmed its role in inducing crown rot and root rot, with two wheat cultivars being more resistant to crown and root rots than most barley cultivars (P < 0.05). Barley cultivars also exhibited significant differences in resistance to crown rot (P < 0.05). In addition, black point disease symptoms were observed on seeds of three barley cultivars and were found to significantly affect seed germination and growth of some of these cultivars. This study confirms the role of seed‐borne inoculum of B. sorokiniana in crown and root rots of wheat and barley and is the first report in Oman of the association of B. sorokiniana with black point disease of barley.     

Biocontrol of fungal root rot diseases of crop plants by the use of rhizobia and bradyrhizobia

Twenty-oneRhizobium andBradyrhizobium strains were testedin vitro against the mycelial growth of three pathogenic fungi on solid and liquid media. All tested rhizobia and bradyrhizobia significantly suppressed the growth of the three soil-borne root-infecting fungi (Fusarium solani, Macrophominia phasolina andRhizoctonia solani) either in the absence or presence of iron. This indicates that the siderophore played a minor role in the biocontrol potential ofRhizobium andBradyrhizobium against pathogenic fungi. Pot experiments revealed that the numbers of propagules causing disease after 4 weeks of planting varied with species and host plant. The three most activeRhizobium andBradyrhizobium strains (R. leguminosarum bv.phaseoli TAL 182,B. japonicum TAL 377 andBradyrhizobium sp. (lupin) WPBS 3211 D) tested under greenhouse conditions for their ability to protect one leguminous (soybean) and two non-leguminous (sunflower and okra) seedlings from root rot caused byFusarium solani, Macrophominia phaseolina andRhizoctonia solani provided significant suppression of disease severity compared with nonbacterized control in both leguminous and non-leguminous seedlings.Bradyrhizobium sp. (lupin) WPBS 3211 D provided the lowest degree of resistance against all the tested pathogens with all host plants. *** DIRECT SUPPORT *** A00EN058 00013     

Effects of cultivar and fungicides on stem-base pathogens, determined by quantitative PCR, and on diseases and yield of wheat

The polymerase chain reaction (PCR) was used to identify and quantify all fungal pathogens of wheat (Triticum aestivum) stem bases in nine field experiments at three locations in England. The main aim was to apply quantitative PCR to provide robust data on the efficacy of new fungicides against the individual components of the stem‐base disease complex. Cyprodinil most effectively controlled eyespot by decreasing both pathogens, Tapesia yallundae and T. acuformis (the most widespread species), and sometimes contributed to increased yields. Prochloraz controlled eyespot less consistently, its effectiveness dependent mainly on the presence of T. yallundae or on rainfall events soon after application. Azoxystrobin contributed to yield increases most consistently. Although it decreased sharp eyespot and its pathogen, Rhizoctonia cerealis, these effects were insufficient to account for much of the yield increases. The effects of fungicides on eyespot were sometimes greatest on the most susceptible cultivars. Amounts of Tapesia DNA were usually consistent with cultivar susceptibility ratings. The only pathogens of brown foot rot present in significant amounts were Microdochium nivale vars nivale and majus. They appeared not to affect yield or to respond greatly to fungicides. The susceptibility of cultivars to these pathogens was sometimes similar to their susceptibility to eyespot, suggesting that they may respond to the same host resistance genes or may in some cases be secondary colonisers of eyespot‐infected plants.     

Integrated control of root rot and wilt disease of faba bean by soil amendment with suppressive compost in combination with seed coating with an antagonistic yeast

For this study, 21 isolates of fungi belonging to Rhizoctonia and Fusarium genera were isolated from the diseased faba bean plants, obtained from the different localities in Assiut governorate, showing root rot and wilt symptoms. The isolates proved to be pathogenic on Masr 1 faba bean cultivar under greenhouse conditions. F. oxysporum isolates caused wilt disease; however, the isolates of R. solani and other Fusarium species caused root rot. The virulence of isolates on the tested faba bean cultivar was different. The highly pathogenic isolates of these fungi were employed in this study. The effect of soil amendment with Planta Rich and Rich Composts (CMs) alone or in combination with seed coating by the antagonistic yeast Pichia guilliermondi before sowing on the severity of Rhizoctonia and Fusarium root rot and Fusarium wilt of faba bean was tested under greenhouse and field conditions. The tested isolates of yeast proved to be highly antagonistic to the pathogen in vitro. The test rates of CMs were equivalent to 2, 7, 10 and 14 ton/feddan in the greenhouse and 7 and 10 t/feddan in the field conditions. Uncomposted soil was used as a control. The results showed that the tested CMs have a suppressive effect on the severity of root rot and wilt diseases of faba bean under greenhouse and field conditions. The application of CMs (Planta Rich and Rich) alone at the rates equivalent to 2, 7, 10 and 14 t/feddan in greenhouse and 7 and 10 t/feddan in the field conditions to the soil infested with the tested pathogens reduced percentage of the tested diseases compared with uncomposted soil. Combined CMs treatments with yeast seed treatment increased the suppressive effect of CMs on the disease severity.     

Bulb and Root Rot in Lily (Lilium longiflorum) and Onion (Allium cepa) in Israel

In the past 10 years, there has been a substantial increase in reports, from growers and extension personnel, on bulb and root rots in lily (Lilium longiflorum) in Israel. Rot in these plants, when grown as cut flowers, caused serious economic damage expressed in reduction in yield and quality. In lily, the fungal pathogens involved in the rot were characterized as binucleate Rhizoctonia AG‐A, Rhizoctonia solani, Pythium oligandrum, Fusarium proliferatum (white and purple isolates) and F. oxysporum, using morphological and molecular criteria. These fungi were the prevalent pathogens in diseased plants collected from commercial greenhouses. Pathogenicity trials were conducted on lily bulbs and onion seedlings under controlled conditions in a greenhouse to complete Koch's postulates. Disease symptoms on lily were most severe in treatments inoculated with binucleate Rhizoctonia AG‐A, P. oligandrum and F. proliferatum. Plant height was lower in the above treatments compared with the control plants. The least aggressive fungus was R. solani. In artificial inoculations of onion, seedling survival was significantly affected by all fungi. The most pathogenic fungus was F. proliferatum w and the least were isolates of F. oxysporum (II and III). All fungi were successfully re‐isolated from the inoculated plants.     

Reactions of six cultivars of rice (Oryza sativa L.) to three fungal diseases

Abstract

Fungal diseases are the most important threat for rice production in the world. Rice fields were visited and sampled from diseased bushes to identify fungal diseases in Kohgiluyeh and Boyer-Ahmad province, in the south-west of Iran. Fungi were isolated from diseased tissues by Agar-plate method, and purified by single-spore or hyphal-tip methods. They were identified by studying morphological characteristics. The virulence of isolated fungi was evaluated on six dominant rice cultivars, Champa of temperate region, Champa of subtropical region, Gerdeh, Shamim, Fajr and Tarom, under greenhouse conditions. The experiment was set up in a factorial experiment in completely randomized design with four replicates. The incidence of three fungal diseases: brown spot caused by Curvularia australiensis and Bipolaris cookei, foot rot caused by Fusarium globosum and Fusarium sambucinum, and black root rot caused by Exserohilum pedicellatum, was proven in this study. Although, all of the tested cultivars significantly showed different reaction to these fungi, but the cultivars Champa of subtropical region and Tarom were resistant to foot rot as well as the black root rot and the cultivar Gerdeh was resistant to brown spot disease.     

Pathogenicity of Rhizoctonia solani and Phytophthora nicotianae to Brassicaceae cover crops

Soil-borne diseases can reduce nursery crop performance and increase costs to nursery producers. In particular, soil-borne diseases caused by Phytophthora nicotianae and Rhizoctonia solani are the most economically important problems of Southeastern United States nursery producers. Methyl bromide was widely used as a standard treatment for management of soil-borne diseases until the implementation of the Montreal protocol. Since then, many chemical and non-chemical soil-borne disease management methods have been tested, but are not yet providing effective and consistent results like methyl bromide. Cover crops that belonged to the Brassicaceae family can be incorporated into the soil to control soil-borne diseases and this process is widely known as biofumigation. But, the use of Brassicaceae cover crops has not been widely explored as a method of controlling soil-borne diseases in woody ornamental nursery production. The objective of this study was to evaluate Brassicaceae cover crops for susceptibility to most destructive soil-borne pathogens of nursery production, P. nicotianae and R. solani, to identify effective cover crops that can be used in the biofumigation process in woody ornamental nursery production. Brassica species intended to be used in the fresh market or biofimigation were screened for their susceptibility to R. solani and P. nicotiane in an environmentally controlled greenhouse. At the end of experiments, plant growth data (plant height, width and fresh weight), total damping-off were recorded, and cover crop root systems were assessed for disease severity using a scale of 0–100% roots affected. Among the tested 15 cover crops in the Brassicaceae family, oilseed radish (Raphanus sativus L.), yellow mustard “White Gold” (Sinapis alba L.), turnip “Purple Top Forage” (Brassica rapa L.), arugula “Astro” (Eruca vesicaria (L.) Cav. ssp. sativa (Mill.) Thell.), mighty mustard^® “Pacific Gold” (B. juncea (L.) Czern.), brown mustard “Kodiak” (B. juncea (L.) Czern.), rape “Dwarf Essex” (B. napus L.) and mustard green “Amara” (B. carinata A. Braun) showed numerically lower root rot disease severity and total damping-off in topsoil which had pre-existing populations of R. solani or P. nicotinanae compared to other cover crops. Since these above mentioned Brassicaceae crops shows the ability to withstand the higher disease pressure from R. solani and P. nicotinanae under the greenhouse conditions they can be used in the further experiments to evaluate their ability in biofumigation. Further research is necessary to evaluate the performance of these cover crops under the field conditions.     

Soil suppressiveness to Rhizoctonia solani and microbial diversity

Rhizoctonia solani anastomosis group 2-2IIIB causes damping-off, black root rot and crown rot in sugar beet (Beta vulgaris). Based on experiences of growers and field experiments, soils can become suppressive to R. solani. The fungus may be present in the soil, but the plant does not show symptoms. Understanding the mechanisms causing soil suppressiveness to R. solani is essential for the development of environmentally friendly control strategies of rhizoctonia root rot in sugar beet. A bioassay that discriminates soils in their level of disease suppressiveness was developed. Results of bioassays were in accordance with field observations. Preliminary results indicate an active role of microbial communities. Our research is focused on the disentanglement of biological mechanisms causing soil suppressiveness to R. solani in sugar beet. Therefore, we are handling a multidisciplinary approach through experimental fields, bioassays, several in vitro techniques and molecular techniques (PCR-DGGE).     

Effects of Fungal Root Pathogens on the Population Dynamics of Biocontrol Strains of Fluorescent Pseudomonads in the Wheat Rhizosphere

The influences of Gaeumannomyces graminis var. tritici (which causes take-all of wheat), Rhizoctonia solani AG-8 (which causes rhizoctonia root rot of wheat), Pythium irregulare, P. aristosporum, and P. ultimum var. sporangiiferum (which cause pythium root rot of wheat) on the population dynamics of Pseudomonas fluorescens 2-79 and Q72a-80 (bicontrol strains active against take-all and pythium root rot of wheat, respectively) in the wheat rhizosphere were examined. Root infection by either G. graminis var. tritici or R. solani resulted in populations of both bacterial strains that were equal to or significantly larger than their respective populations maintained on roots in the absence of these pathogens. In contrast, the population of strain 2-79 was significantly smaller on roots in the presence of any of the three Pythium species than on noninfected roots and was often below the limits of detection (50 CFU/cm of root) on Pythium-infected roots after 40 days of plant growth. In the presence of either P. aristosporum or P. ultimum var. sporangiiferum, the decline in the population of Q72a-80 was similar to that observed on noninfected roots; however, the population of this strain declined more rapidly on roots infected by P. irregulare than on noninfected roots. Application of metalaxyl (which is selectively inhibitory to Pythium spp.) to soil naturally infestated with Pythium spp. resulted in significantly larger rhizosphere populations of the introduced bacteria over time than on plants grown in the same soil without metalaxyl. It is apparent that root infections by fungal pathogens may either enhance or depress the population of fluorescent pseudomonads introduced for their control, with different strains of pseudomonads reacting differentially to different genera and species of the root pathogens.     

Biocontrol of Rhizoctonia crown and root rot of sugar beet by binucleate Rhizoctonia spp. and Laetisaria arvalis

Two isolates of Laetisaria arvalis and 10 of binucleate Rhizoctonia spp. (BNR) from the Ohio sugar beet production area, were tested in the greenhouse and field for biocontrol of Rhizoctonia crown and root rot of sugar beet, caused by Rhizoctonia solani anastomosis group 2, type 2. L. arvalis was ineffective in standard greenhouse tests, and the single isolate used in the field was generally ineffective. Seven of 10 BNR isolates effectively controlled crown and root rot in greenhouse tests. Delayed application of biocontrol agents to plants 5 – 10 wk old was generally more effective than applications made at planting. A BNR isolate significantly reduced % plant loss and disease ratings and increased yield in a 1985 field test as compared with the control infested with R. solani alone. Two BNR isolates were effective in a 1986 field test and increased yields c. 22% in comparison to a L. arvalis treatment, which did not differ from the R. solani-infested control. The Ohio binucleate Rhizoctonia isolates appear to have considerable potential as applied biocontrol agents and may play a role in the natural ecology of R. solani in the sugar beet production area of Ohio.     

First Detection of Root Rot and Foliar Blight on Pittosporum (Pittosporum tenuifolium) Caused by Pythium irregulare in Italy

During 2013, a new root rot and leaf blight was detected on potted Pittosporum tenuifolium cv. ‘Silver Queen’ plants in a nursery located in the Catania province (eastern Sicily, Italy). On the basis of morphological and cultural features as well as internal transcribed spacer sequence data, the causal agent was identified as Pythium irregulare. Koch's postulates were fulfilled by pathogenicity tests carried out on potted P. tenuifolium cv. ‘Silver Queen’ plants. To our knowledge, this is the first detection of P. irregulare root rot and foliar blight disease on P. tenuifolium in Europe, and it is the first detection using molecular methods for this oomycete pathogen in Italy.