Lower Root Rot Research Articles

The Effect of Propagation Substrate on Pythium Root Rot Severity and the Efficacy of Biopesticides

Modern greenhouse crop production utilizes soilless substrates that range from inorganic substrates (Oasis foam and rockwool) to blends of organic substrates (sphagnum peat moss, coconut fiber, bark mulch, wood chips, and wood products). Additionally, greenhouse growers utilize beneficial microorganisms in the form of commercial biopesticides to reduce disease. Few research studies have examined the effect of propagation substrate on the efficacy of commercial biopesticides under greenhouse production conditions. The objective of this study was to evaluate the effect of propagation substrates on commercially available microbial biopesticides (Rootshield WP, Cease, and Regalia) applied during propagation and at transplant for management of Pythium root rot. In this study, cucumber and calibrachoa were used as model crops. Over both cropping systems, plants propagated in Oasis foam had lower root rot compared with plants propagated in coconut coir. Across all biopesticide treatments, cucumber plants propagated in Oasis foam had 52% less root rot compared with plants propagated in coconut coir. In both infested and noninfested calibrachoa plants, plants propagated in Oasis foam had 45 to 67% less disease, and plants propagated in peat had 25 to 40% less disease compared with plants propagated in coconut coir. There was no effect of biopesticide on Pythium root rot severity, except for a reduction seen in calibrachoa plants propagated in coconut coir and treated with Rootshield WP. This research suggests that propagation substrate is important for root disease management.

Response of Cover Crops to Phytopythium vexans, Phytophthora nicotianae, and Rhizoctonia solani, Major Soilborne Pathogens of Woody Ornamentals

Management of plant diseases is a subject of concern for researchers as well as growers. Different management practices are being developed and used to combat the rising number of plant pathogens, which threaten nursery crop production. Use of cover crops for sustainable management of soilborne diseases is being explored as an alternative strategy to the chemicals. However, the potential threat of these cover crops acting as a secondary host of these devastating soilborne pathogens has not been described. We studied the response of the major cover crops being used by woody ornamental growers in the Southeastern United States to Phytopythium vexans, Phytophthora nicotianae, and Rhizoctonia solani in greenhouse conditions to identify the effective cover crops that can be used in a nursery field production system. Data related to post-emergence damping-off and plant growth parameters (plant height increase and fresh weight) were recorded. Similarly, cover crop roots were assessed for root rot disease severity using a scale of 0–100% roots affected. Among the tested cover crops, the grass cover crops triticale (×Triticosecale Wittm. ex A. Camus.), annual ryegrass (Lolium multiflorum L.), Japanese millet (Echinochloa esculenta (A. Braun) H. Scholz), and the legumes Austrian winter pea (Pisum sativum var. arvense (L.) Poir) and cowpea ‘Iron and Clay’ (Vigna unguiculata (L.) Walp.), showed lower root rot disease severity and post-emergence damping-off in the soil inoculated with P. nicotianae, R. solani, or P. vexans compared to the other crops. Since these cover crops can act as non-host crops and benefit the main crop in one way or another, they can be used in the production system. Further research is recommended to evaluate their performance in a natural field setting.

Heritable Variation in Pea for Resistance Against a Root Rot Complex and Its Characterization by Amplicon Sequencing.

Soil-borne pathogens cause severe root rot of pea (Pisum sativum L.) and are a major constraint to pea cultivation worldwide. Resistance against individual pathogen species is often ineffective in the field where multiple pathogens form a pea root rot complex (PRRC) and conjointly infect pea plants. On the other hand, various beneficial plant-microbe interactions are known that offer opportunities to strengthen plant health. To account for the whole rhizosphere microbiome in the assessment of root rot resistance in pea, an infested soil-based resistance screening assay was established. The infested soil originated from a field that showed severe pea root rot in the past. Initially, amplicon sequencing was employed to characterize the fungal microbiome of diseased pea roots grown in the infested soil. The amplicon sequencing evidenced a diverse fungal community in the roots including pea pathogens Fusarium oxysporum, F. solani, Didymella sp., and Rhizoctonia solani and antagonists such as Clonostachys rosea and several mycorrhizal species. The screening system allowed for a reproducible assessment of disease parameters among 261 pea cultivars, breeding lines, and landraces grown for 21 days under controlled conditions. A sterile soil control treatment was used to calculate relative shoot and root biomass in order to compare growth performance of pea lines with highly different growth morphologies. Broad sense heritability was calculated from linear mixed model estimated variance components for all traits. Emergence on the infested soil showed high (H2 = 0.89), root rot index (H2 = 0.43), and relative shoot dry weight (H2 = 0.51) medium heritability. The resistance screening allowed for a reproducible distinction between PRRC susceptible and resistant pea lines. The combined assessment of root rot index and relative shoot dry weight allowed to identify resistant (low root rot index) and tolerant pea lines (low relative shoot dry weight at moderate to high root rot index). We conclude that relative shoot dry weight is a valuable trait to select disease tolerant pea lines. Subsequently, the resistance ranking was verified in an on-farm experiment with a subset of pea lines. We found a significant correlation (rs = 0.73, p = 0.03) between the controlled conditions and the resistance ranking in a field with high PRRC infestation. The screening system allows to predict PRRC resistance for a given field site and offers a tool for selection at the seedling stage in breeding nurseries. Using the complexity of the infested field soil, the screening system provides opportunities to study plant resistance in the light of diverse plant-microbe interactions occurring in the rhizosphere.

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.

Effect of Tillage and Cultivar on Plant Population, Sudden Death Syndrome, and Yield of Soybean in Iowa

Conservation tillage has become a common practice of soybean farming in the Midwestern United States owing to the benefits of soil and moisture conservation. Field trials were established in a field with a history of sudden death syndrome (SDS; caused by Fusarium virguliforme) in Iowa in 2011 and evaluated for five consecutive years to determine the impact of tillage on SDS and yield. The experiment was laid out in a split-split-plot design with four replicates. The main plot factor was tillage (no-till both crops, no-till corn and chisel plow soybean, and disc corn and chisel plow soybean), and each main plot was divided into subplots of corn or soybeans (in a 2-year rotation). Each subplot was again divided into two subsubplots, in which two soybean cultivars, moderately susceptible (MS) and moderately resistant (MR) to SDS, were planted each year. Root rot and SDS disease index (FDX) differed among years, because some years were more favorable for the disease than the others. However, tillage did not affect any parameters, including yield, in any year (P > 0.05). Cultivar effect was significant for each parameter occasionally. When significant, the MR cultivar had lower root rot and FDX and greater yield than the MS cultivar. These data suggest planting resistant cultivars can be an effective management tactic, but tillage does not help for SDS management.

Effect of times and levels of inoculum of <italic>Trichoderma</italic> for controlling root rot and collar rot of lentil

The experiments were carried out during 2010 to 2011 to find out the time of application and level of inoculum of <italic>T.</italic> <italic>harzianum</italic> for controlling root rot (<italic>F. solani)</italic> and collar rot (<italic>S. rolfsii</italic>) of lentil (<italic>Lens culinaris</italic> Medik). <italic>F. solani</italic> and <italic>S. rolfsii</italic> and their antagonist, <italic>Trichoderma</italic> were collected from different pulses growing areas of Bangladesh. The experiments were carried out following CRD with five replications. Fourteen isolates of <italic>Trichoderma</italic> were tested against <italic>F. solani</italic> and <italic>S.</italic> <italic>rolfsii</italic> under Dual Culture Technique. The inhibition was ranged from 60.42 to 99.27% at 10 DAI against <italic>F. solani</italic> and from 64.07-99.41% at 6 DAI against <italic>S. rolfsii.</italic> The highest inhibition 99.27% against <italic>F. solani</italic> was found in isolate, Th-2 and 99.41% was found in isolate TG-2 against <italic>S. rolfsii</italic>. In the pot, the treatment of soil with the Th-2 isolate of <italic>T.</italic> <italic>harzianum</italic> at 2g/kg shown the highest germination (96.67%) and plant stand (81.67%) and the lowest root rot (15.52%), where the isolate of TG-2 of <italic>T. harzianum</italic> at 20g/kg of soil was observed better for controlling <italic>S. rolfsii</italic>. <italic>T. harzianum</italic> (Th-2) increased germination (17.86%), plant stand (171.43%), vigour index (33.27%) and yield (260.74%) over control against root rot. <italic>T. harzianum</italic> (TG-2) also increased germination (248%), plant stand (600%), vigour index (865.91%) and yield (1209.81%) of lentil over control against collar rot. The soil treatment with <italic>Trichoderma</italic> at 9, 6 and 3 days before sowing and also at the time of sowing showed significantly better effect in increasing germination, plant stand and reducing root rot and collar rot compared to control. The highest germination, seed yield and lower root rot was obtained by treating soil with <italic>Trichoderma</italic> before 9 days of sowing against both the pathogens.

Temperature, Moisture, and Seed Treatment Effects on Rhizoctonia solani Root Rot of Soybean.

The effects of temperature and soil moisture on infection and disease development by Rhizoctonia solani on soybean were studied individually. In addition, the anastomosis group of R. solani isolates recovered from soybean from 35 fields in 15 counties was determined. All of the 44 isolates recovered in this study were AG-2-2 IIIB. Five isolates of R. solani were able to infect and colonize soybean roots and hypocotyls at 20, 24, 28, and 32°C in growth chamber studies. The temperatures evaluated in this study were not limiting to the isolates tested. In greenhouse studies, nine R. solani isolates and a noninoculated control were evaluated at 25, 50, 75, and 100% soil moisture holding capacity (MHC). Root weights were greater and percent stand averages higher at 50 and 75% than at 25 or 100% MHC; however, as percentage of control, the main effect on percent moisture for percent stand, plant height, or root weight was not significant. There were significant differences among the isolates for the percent stand, root rot rating, and root fresh weight of soybean in each study. In both temperature and moisture studies, the R. solani isolates could be separated as predominantly causing (i) seed rot, as detected by greatly reduced plant stand; (ii) root rot generally having no effect on plant stand but a high root rot rating and low root weight; or (iii) hypocotyl lesions, having no effect on plant stand, a low root rot score, and a high number of red lesions on the hypocotyl. In the greenhouse seed treatment evaluations of five fungicides, there was no fungicide by isolate interaction using these pathogenic types of R. solani. None of the seed treatments evaluated in this study provided 100% control of the four isolates tested. Due to the wide range of environmental factors that permit R. solani infection and disease on soybeans, other control measures that last all season, such as host resistance, should be emphasized.

Field Evaluation of Two Bacterial Antagonists, Pseudomonas putida (PDBCAB 19) and P. fluorescens (PDBCAB 2) against Wilt and Root-Rot of Chickpea

Talc based formulations of two antagonistic bacteria viz., Pseudomonas putida (PDBCAB 19) and P. fluorescens (PDBCAB 2) were evaluated against natural incidences of wilt and wet root-rot of chickpea. Observations on rhizoclonia root-rot incidence indicated that the disease was prevalent up to 60 days of plant growth whereas fusarial wilt was observed from 60 days. At 30th day. highest root-rot incidence (10.8%) was observed in pathogen control plots and minimum was in fungicide treated plots (3.1 %). P. fluorescens (PDBCAB 2) treated plots also exhibited low root-rot (4.4%). However, at day 60 lowest root-rot incidence (5%) was recorded in P. fluorescens (PDBCAB 2) treated plots and highest root-rot incidence (13.9%) was observed in pathogen control. Low root-rot incidence (5.8%) was also noticed in P. putida (PDBCAB 19) treated plots. Fusarium wilt was lowest (3.3%) in P. putida (PDBCAB 19) treated and highest (13.3 %) in control plots at day 90. Combination of both P. fluorescens (PDBCAB 2) and P. putida (PDBCAB 19) exhibited suppression of root-rot and wilt incidences by 5.8 and 7.5 per cent, respectively. Highest plant stand and seed yield was observed in P. fluorescens (PDBCAB 2) treated plots. There were no significant differences in the shoot and root lengths among bioagent treatments, however, vigour index was highest in plots treated with a combination of P . fluorescens (PDBCAB 2) and P. putida (PDBCAB 19).

Development of formulations of biological agents for management of root rot of lettuce and cucumber.

The effect of various carrier formulations of Bacillus subtilis and Pseudomonas putida were tested on germination, growth, and yield of lettuce and cucumber crops in the presence of Pythium aphanidermatum and Fusarium oxysporum f.sp. cucurbitacearum, respectively. Survival of B. subtilis and P. putida in various carriers under refrigeration (about 0 degree C) and at room temperature (about 22 degrees C) was also studied. In all carrier formulations, B. subtilis strain BACT-0 survived up to 45 days. After 45 days of storage at room temperature (about 22 degrees C), populations B. subtilis strain BACT-0 were significantly higher in vermiculite, kaolin, and bacterial broth carriers compared with other carriers. Populations of P. putida were significantly higher in vermiculite, peat moss, wheat bran, and bacterial broth than in other carriers when stored either under refrigeration (about 0 degree C) or at room temperature (about 22 degrees C) for 15 or 45 days. Germination of lettuce seed was not affected in vermiculite, talc, kaolin, and peat moss carriers, but germination was significantly reduced in alginate and bacterial broth carriers of B. subtilis compared to the non-treated control. Germination of cucumber seed was not affected by any of the carriers. Significantly higher fresh lettuce and root weights were observed in vermiculite and kaolin carriers of B. subtilis compared with P. aphanidermatum-inoculated control plants. Lettuce treated with vermiculite, and kaolin carriers of B. subtilis, or non-inoculated control lettuce plants had significantly lower root rot ratings than talc, peat moss, bacterial broth, and P. aphanidermatum-inoculated control plants. Growth and yield of cucumber plants were significantly higher in vermiculite-based carrier of P. putida than the other carriers and Fusarium oxysporum f.sp. cucurbitacearum-inoculated plants.

Effect of three species of bacteria on damping‐off, root rot development, and ectomycorrhizal colonization of lodgepole pine and white spruce seedlings

SummaryInteractions between three species of bacteria (Burkholderia cepacia, Pseudomonas chlororaphis and Pseudomonas fluorescens), an ectomycorrhizal fungus (Paxillus involutus), and three root pathogenic fungi (Fusarium moniliforme, Fusarium oxysporum and Rhizoctonia solani) were studied. Burkholderia cepacia significantly reduced the in vitro mycelial growth of P. involutus, whereas, B. cepacia, Ps. chlororaphis, Ps. fluorescens and P. involutus reduced the mycelial growth of F. moniliforme, F. oxysporum and R. solani. Culture filtrates of B. cepacia, Ps. chlororaphis, Ps. fluorescens and P. involutus reduced conidial germination and increased the formation of chlamydospores of F. moniliforme and F. oxysporum. Burkholderia cepacia also reduced the formation of ectomycorrhizal short roots by P. involutus on lodgepole pine (Pinus contorta) and white spruce (Picea glauca) seedlings 2 months after inoculation. However, no significance difference in mycorrhizal short roots was observed after 4 months. The fungicide Anchor (a mixture of carboxine and thiram) significantly reduced root rot severity and increased the survival of lodgepole pine seedlings grown in a growth mix infested with F. moniliforme, F. oxysporum and R. solani. Control of the diseases of white spruce caused by these pathogens was not as successful. Treatment of seeds with either B. cepacia or P. involutus alone significantly increased the survival of seedlings grown in a mix that was inoculated with F. moniliforme and reduced the root rot severity caused by F. moniliforme and F. oxysporum, but not R. solani. Higher seedling survival and lower root rot severity were observed when conifer seeds were concomitantly inoculated with one of the bacterial species, P. involutus and Anchor.

Inhibition of Aphanomyces euteiches f. sp. pisi by Volatiles Produced by Hydrolysis of Brassica napus Seed Meal.

Seed meal from Brassica napus (rapeseed) produced volatile fungitoxic compounds potentially of value in the control of Aphanomyces root rot of pea. Hyphal growth, germination of encysted zoospores, and oospore survival and inoculum potential, were determined in the presence of volatiles produced from B. napus seed meal. Volatile compounds from B. napus meal completely suppressed mycelial growth and germination of encysted zoospores on agar. In growth chamber bioassays, pea (Pisum sativum) seed inoculated with zoospore suspensions and incubated 24 h in the presence of volatiles from rapeseed meal had 50% lower root rot disease severity than in the absence of meal. Volatile compounds passing through soil also significantly decreased survival and inoculum potential of oospores. Gas chromatographic analysis of rapeseed tissues and the volatile compounds evolved from tissues showed that substrate glucosinolates were hydrolyzed enzymatically to produce mainly isothiocyanates. Non-autoclaved rapeseed meal produced significantly higher levels of volatile compounds than did autoclaved meal. Also, volatile compounds produced from autoclaved meal were dominated by nitriles, whereas isothiocyanates were more common volatile products from non-autoclaved meal. Our results indicate that B. napus allelochemicals responsible for toxic effects toward A. euteiches f. sp. pisi are enzymatic hydrolysis products of glucosinolates.

Selection for Fusarium root rot resistance in red clover

SUMMARYIntercrossing red clover plants, selected for reaction to Fusarium root rot (F. avenaceum), produced progenies with lower root rot scores than the parental cultivar Hermes II. Eleven percent of the progenies had less than 2 mm root rot after two cycles of selection, compared to less than 1% in the parental cultivar. Root rot severity in two old local strains of red clover, as well as in two populations of wild red clover, was lower than in cv. Hermes II. This could indicate that a natural selection for root rot resistance can occur in red clover.

Effect of Pea Seed Genotype on Preemergence Damping‐Off and Resistance to Fusarium and Pythium Root Rot1

Pea (Pisum sativum L.) lines, isogenic for the major A gene in various combinations with the genes F, Pl, M, I, and R were developed and tested for emergence and root rot resistance in soils infested with Fusarium and Pythium. Lines homozygous for A had significantly better emergence than a counterparts, presumably due to the fungistatic effects of phenols associated with anthocyanin pigmentation. Significantly lower root rot scores were noted in one test for the A isolines as compared to their a counterparts. The M gene appeared to give better emergence in the presence of either A or a Genes F, M, I, and R in the presence of A and a had a cumulative effect in reducing scores for pre‐emergence damping‐off and root disease.