Reduced Root Rot Research Articles

Growth Enhancement of shrunken-2 (sh2) Sweet Corn by Trichoderma harzianum 1295-22: Effect of Environmental Stress

Sweet corn (Zea mays L.) varieties carrying the sh2 gene are in high demand, but such varieties have poor stress tolerance, especially during plant establishment. Trichoderma harzianum Rifai strain 1295-22 is a biocontrol fungus developed to provide season-long colonization of crop roots. It has the potential to reduce root rot and increase root growth. In the absence of detectable disease, colonization by Trichoderma increased root and shoot growth by an average of 66%. The enhancement was not uniform among the plants. Low- and intermediate-vigor plants were larger in the presence of Trichoderma, but high-vigor plants were not further enhanced by the fungus. Seeds that were subjected to oxidative stress with 0.05% NaOCI had much-reduced vigor; subsequent treatment with Trichoderma fully restored vigor. This result indicates that the damage caused by hypochlorite is specifically repaired by Trichoderma. Treatment of imbibed but unemerged seeds with cold (5/10 °C night/day) for varying periods reduced subsequent growth. Plants with Trichoderma-colonized roots were 70% larger at all durations of cold treatment. The absence of interation indicates the growth reduction due to cold and the growth enhancement due to Trichoderma are by different mechanisms. Allelopathic reduction in root growth by rye was mimicked by applying benzoxazolinone to the soil. Trichoderma-colonized roots grew faster, but the characteristic shortening of the radicle still occurred. There was no interaction between Trichoderma and allelopathy, indicating that these two treatments affect growth by independent mechanisms. The different ways that growth was enhanced by Trichoderma lead us to propose that this fungus acts, in part, by reversing injurious oxidation of lipids and membrane proteins. Root growth is markedly enhanced by colonization with Trichoderma harzianum. This enhancement can restore some stress-induced growth reduction and may directly reverse oxidative injury.

Effects of row spacing, seeding rate and seed-placed phosphorus on root diseases of spring wheat and barley under zero tillage

Changes in tillage and other agronomic practices have shown benefits of increased grain yield for many crops, but these changes may alter the micro-environment resulting in changes to populations of disease-causing agents and other micro-organisms. This study examined the effects of row spacing (10, 20, 30 cm), seeding rate (54, 108, 161 kg ha−1 for barley; 67, 134, 202 kg ha−1 for spring wheat) and seed-placed phosphorus (0, 8, 16 kg ha−1) on root diseases in spring wheat and barley using a zero-tillage production system in four environments. Root rot severity was assessed by visual ratings and the causal agents were identified. Analyses of variance indicated significant differences in root rot severity and the incidence of some causal agents for the main treatment effects (i.e. row spacing, seeding rate, seed-placed phosphorus) and no significant interactions between locations, years, and cultural practices. Contrasts of treatment means showed that higher rates of seeding decreased root rot severity and the incidence of Fusarium in wheat but these effects were small (less than 6%). The higher rates of monoammonium phosphate fertilizer reduced root rot severity in barley by 7% and the incidence of Gaeumannomyces graminis var. tritici in wheat by greater than 40%. Wider row spacings showed a small reduction of 6% in root rot severity in wheat but mostly had no effect on root diseases. Wheat yields were negatively associated with root rot severity in three of four environments. Fertility, root rot severity, and seeding rate had the greatest impact on wheat yield. Root diseases did not affect barley yields. Therefore, the use of wider row spacings and higher seeding rates with zero tillage practices will not lead to adverse effects on root diseases in wheat and barley. Phosphorus fertilizer should be used to reduce losses resulting from take-all disease in wheat. Key words: Zero tillage, cultural practices, common root rot, take-all, cereals

EFFECT OF PEELING OF TULIP BULBS ON PYTHIUM TRANSMISSION FROM FIELD INTO GREENHOUSE

A cultural practice which is becoming more common in Dutch tulip-bulb production is peeling of the bulbs by machine. If this method is not used properly old roots can be left on the base of the bulb. An experiment was conducted to investigate if this might be hazardous with respect to development of root rot, caused by Pythium spp., during tulip-flower forcing in the greenhouse. Severe root rot developed in case old roots from bulbs collected from the field were not removed properly. No clear difference was observed between root rot severity of bulbs harvested from patches with above-ground Pythium symptoms and bulbs from a part of the field without above-ground symptoms. Removal of the old roots reduced root rot severity. Treatment of the poorly peeled bulbs with formaldehyde could not prevent root rot completely. Combination of proper peeling of the bulbs and formaldehyde dip gave a crop with a healthy root system.

Augmentation of Soil with Sporangia of Actinoplanes spp. for Biological Control of Pythium Damping-off

A method was developed for applying strains of Actinoplanes spp. that are hyper-parasites of oospores of Pythium ultimum to soil for reducing Pythium damping-off of plants. The method is based on the augmentation of soil with sporangia of a strain of Actinoplanes spp. borne on clay granules. In vitro sporulation of strains K30, W57, W257 and 25844 was: (1) greater for most strains on dilute Czapek-Dox agar than on four other agar media; (2) inhibited by continuous exposure to fluorescent light of intensity 4-150 μEm−2s−1, but not by exposure to 1 μEm−2s−1 or darkness; (3) greater at 20-307deg;C than at 10°C;and (4) greater at pH 6-7 than at pH 5 or 8. On solid carriers treated with dilute Czapek-Dox broth (pH 7) and incubated in the dark at 30°C for 3 weeks, strains sporulated poorly or not at all on vermiculite, perlite and rice hulls, but sporulated abundantly (107-109 colony-forming units (CFU) g−1 of granules) on montmorillonite clay granules. When strains 25844, W57 and W257 were applied as granules (4 107 - 4 × 108 CFU g−1) at 5% (w/w) to field plots infested with 750-1000 oospores of P. ultimum g−1 of soil, only strain 25844 consistently increased emergence and reduced root rot of table beets 8- 1 at 24-28 days after planting compared with controls. Strain 25844 (108 CFU g−1 of granules) at 1% (w/w) also increased the emergence of bush beans at 28 days after planting in P. ultimum-infested plots, but lower rates were ineffective. The inoculum viability of strain 25844 on clay granules declined 100-fold during 2 months of storage at 5-35°C, but thereafter remained stable for another 4 months. Strain 25844 on 6-month-old granules retained a high degree of hyper-parasitic activity toward oospores of P. ultimum. Augmentation of field soil with sporangia of Actinoplanes spp. is a valid approach to the biological control of pythium damping-off.

The Effect of the Fungicides Metalaxyl and Fosetyl-Al on Root Rot (Phytophthora cactorum) of American Ginseng (Panax quinquefolium) in the Greenhouse

Ginseng seedlings were inoculated with Phytopthora cactorum by dipping their roots for 5 min in a suspension of 105 zoospores/ml. Inoculated plants were repotted and grown under shade in the greenhouse. In various experiments, fungicides were applied 1 week before inoculation, at the time of inoculation, 2 days after inoculation, or a combination of the first two of these. Treatments included fosetyl-Al applied as a foliar spray until run-off at a concentration of 2.5, 5.0, or 10 g a.i./liter of water or as a soil drench containing 0.25, 0.5, or 1.0 g a.i./100 ml water per plant and metalaxyl applied as a soil drench containing 5 or 10 mg a.i./100 ml of water per plant. The treatments with fosetyl-Al as a spray did not reduce root rot ratings, but fosetyl-Al applied as a drench significantly reduced root rot ratings at all three concentrations when applied at inoculation. The best control was achieved using metalaxyl at either 5 or 10 mg a.i./plant applied either at inoculation or both 1 week before inoculation and at inoculation.

Tillage effect on root rot severity, growth and yield of beans

The effect of soil tillage on plant growth, yield and root rot severity of beans was investigated in field plots with and without root rot infestation in 1992 and 1993. There was a significant reduction in root rot severity, and an increase in plant dry weight and yield in the root-rot-infested soils with deep tillage in both years. Deep tillage also significantly increased plant dry weight and yield in the non-root-rot soils in a dry year. The resistant cultivar (A300) had significantly less root rot damage than the susceptible cultivar (Harowood) in both root rot and non-root rot infested soils. Significant differences in plant dry weight and yield in relation to cultivars were not detected. Therefore, deep tillage can reduce soil compaction and increase yield of beans and reduce root rot severity. Key words:Phaseolus vulgaris L., deep tillage, fusarium root rot, rhizoctonia root rot, yield

Soil receptivity toFusarium solani f. sp.pisi and biological control of root rot of pea

Potential antagonists ofFusarium solani f. sp.pisi (Fsp) were selected from soil samples with varying degrees of receptivity to this pathogen. They were tested against Fsp isolate 48 (Fs48), in increasingly complex systems. Most species testedin vitro were able to antagonize Fs48. No relation could be establishedin vitro between the receptivity of the soil from which an isolate originated and its antagonism to Fs48. In soils naturally infested with pea root rot pathogens, which were stored humid at 4°C for a period longer than a year, various isolates ofFusarium, Gliocladium andPenicillium spp. were able to reduce root rot. After sterilization of these soils, onlyGliocladium roseum isolates, added at 105 conidia g−1 dry soil, significantly reduced disease severity and prevented root weight losses caused by Fs48 at 104 conidia g−1 dry soil. In soils in which the biota were activated by growing peas before the assays, doses of 106 and 107 ofG. roseum were required to reduce root rot. In these soils, the antagonistic effects of fluorescent pseudomonad strains from soil of low receptivity to Fsp were variable. Some strains of fluorescent pseudomonads, from soil moderately receptive to Fsp and from highly infested soils, were also able to reduce root rot. Disease suppression by pseudomonad strains was more evident in the absence than in the presence ofAphanomyces euteiches in the root rot pathogen complex. The role of receptiveness of the soil with regard to potential antagonists is discussed.

Variation in pyrone production, lytic enzymes and control of rhizoctonia root rot of wheat among single-spore isolates of Trichoderma koningii

Fifty-four single-spore isolates were obtained from two wheat field strains of Trichoderma koningii. These isolates inhibited the growth of Rhizoctonia solani to varying levels when tested on potato dextrose agar. 6-Pentyl-α-pyrone was isolated only from the extracts obtained from those isolates which showed strong inhibition of the pathogen on agar. Six isolates, three pyrone producers and three non-producers, were tested for protection of wheat against rhizoctonia root rot under controlled conditions. Only the pyrone producers significantly reduced root rot when applied to the soil and incubated for 14 d with the pathogen before planting. Those not producing pyrone did not reduce the disease when applied to the soil either with or without an incubation period in soil. There was no relationship between the disease protection ability of the isolates and their mycoparasitic ability or their production of chitinase, glucanase, cellulase or xylanase. This indicates that the pyrone antibiotic may have an important role in the reduction of rhizoctonia root rot of wheat by the effective strains and that the ability to produce the antibiotic may vary among asexually produced progenies.

Red Clover Seed Production: II. Plant Water Status on Yield and Yield Components

Limited information on crop water stress response is available for red clover (Trifolium pratense L.) seed production. The purpose of this study was to quantify the effects of plant water status on red clover flower production, seed yield, and seed yield components. Five supplemental irrigation treatments were applied in 1990 and 1991 to first and second year red clover grown on a Woodburn silt loam (fine‐silty, mixed, mesic Aquultic Argixeroll) near Corvallis, OR. A nonirrigated control was also maintained. Increased plant water stress reduced the duration of season‐long bud and flower production, stem length, potential seed yield, and seed yield. Application of water soon after haying increased total above‐ground phytomass but increased seed yield less than watering at peak flowering. Root deterioration from a root and crown rot disease complex reduced second‐year seed yield. Root rot index increased with increased levels of plant water stress, indicating that supplemental water applications reduced root rot severity. The reduction in seed yield resulting from increased plant water stress was primarily caused by a decrease in floral fertility, and less conclusively, by reductions in flower number per unit area. One irrigation filling the active soil profile during peak flowering provided adequate water to maintain seed production and achieve high water‐use efficiency. Contrary to popular belief, it was shown that red clover was not adversely affected by high levels of available soil water in a well drained soil. Also, yield losses to root disease in the second year of seed production can be greatly reduced by supplemental irrigation compared to non‐irrigated clover.

Evaluation of Rhizosphere Bacteria for Biological Control of Pythium Root Rot of Greenhouse Cucumbers in Hydroponic Culture

Five bacterial isolates were evaluated for their ability to reduce root rot caused by Pythium aphanidermatum (Pa) on cucumber (Cucumis sativus L. cv. Corona) grown under simulated commercial conditions in a rock wool hydroponic system. Two isolates of Pseudomonas corrugata (Pc13 and Pc35) and three of Pseudomonas fluorescens (Pf15, Pf16, and Pf27) were evaluated in both spring and early fall 1991 crops. Isolates Pc13, Pc35, and Pf15 were also evaluated in a 1992 spring crop. In all crops, 5-wk-old plants were set onto rock wool slabs and treated with water or 200 ml of a bacterial suspension (10 6 cells per milliliter)

Influence ofPseudomonas fluorescenson Hyphal Growth and Biocontrol Activity ofTrichoderma harzianumin the Spermosphere and Rhizosphere of Pea

Trichoderma harzianum isolate ThzID1 was grown in liquid culture, was formulated with alginate and polyethylene glycol 8000, and was milled into fine granules (average diameter 500 μm). Granules contained chlamydospores, conidia, and hyphal fragments. Viability of the encapsulated fungus remained high for at least 6 mo when stored at 5 C (i.e., >90% of the granules produced hyphal growth when incubated on agar); viability was reduced significantly when granules were stored at 22 C. Application of the granular formulation of T. harzianum to pea seeds reduced root rot by Aphanomyces euteiches f. sp. pisi in growth-chamber experiments and also increased plant top weights compared to noncoated seeds []

Evaluation of in-furrow fungicide treatments to control rhizoctonia root rot of wheat

The efficacy of eight fungicides, placed in-furrow at sowing, to reduce rhizoctonia root rot and increase yields of wheat was examined in glasshouse and field experiments. Under glasshouse conditions three of the fungicides, coated on clay granules at a rate equivalent to 400 g a.i. ha −1, reduced root rot of wheat grown in soil inoculated with Rhizoctonia solani. None of the chemicals stimulated growth of wheat in the absence of disease, but three retarded growth. Experiments at six sites with different soil types and rhizoctonia risk in north-west Victoria, Australia, showed that the fungicide-coated granules were generally ineffective at reducing both incidence and severity of rhizoctonia root rot of wheat. However, tebuconazole was effective at two sites and at one of these flutriafol, RH-7592, cyproconazole and diniconazole also reduced disease severity. Yields were increased by 51% with tebuconazole at one site, by 40% with diniconazole at another and by between 23 and 30% with RH-7592, diniconazole, flutriafol and flutolanil, at a third site.

Control of Phytophthora root rot in processing tomatoes by metalaxyl and fosetyl-Al

The efficacies of metalaxyl and fosetyl-A1 were evaluated for the control of root rot in tomatoes (Lycopersicon esculentum Mill.) caused by Phytophthora nicotianae var. nicotianae in a greenhouse and in the field. In greenhouse experiments, disease severity was significantly (P<0.05) reduced with metalaxyl applied at rates of 1.5-25 g a.i./L as a soil drench and with fosetyl-A1 applied as a foliar spray at 3.2 g a.i./L. In the field, disease severity was reduced by applications of metalaxyl at rates up to 3 kg a.i./ha banded below the fertiliser at sowing and with additional applications to the bed shoulders at regular intervals for a period of 10 weeks after sowing. Metalaxyl treatments applied at sowing significantly reduced root rot severity for the first 12 weeks of crop development but failed to provide season-long protection. Yield of tomatoes at harvest was not significantly increased by the fungicide treatments, The use of metalaxyl granules in the field to control P. nicotianae root rot is not recommended.

Phosphorous acid treatments control Phytophthora diseases in Australia1

Treatments with a partially neutralized formulation of phosphorous acid containing potassium phosphite were assessed for control of Phytophthora diseases in subtropical and temperate crops in Australia. In Queensland, trunk injections of phosphite (10% solution) controlled severe root rot (Phytophthora cinnamomi) of avocado trees and resulted in the recovery of trees. Single pre‐harvest sprays (2.5 kg ha‐1) of phosphite controlled root and heart rot (P. cinnamomi) of pineapples. Foliar sprays of phosphite (64 g per tree) controlled root rot (P. nicotianae var. parasitica) and trunk canker (P. citrophthora) of mandarin trees. In Victoria, a foliar spray of phosphite (300 g ha‐1) reduced root rot (P. clandestina) of subterranean clover and increased dry matter by 1.96 to 5.11 t ha‐1. Trunk injections of phosphite (10% solution) controlled trunk rot (P. cactorum) of peach trees and foliar sprays (10 kg ha‐1) reduced severity of root rot (P. nicotianae var. nicotianae) of tomatoes.

Evaluation of Crucifer Green Manures for Controlling Aphanomyces Root Rot of Peas

In a 2-yr field study, crucifers were planted the first year as full season crops or as fall cover crops following peas.(.)A fall crop of white mustard (Sinapis alba L.) following peas appeared most promising and was chosen for further study. In subsequent field studies, a fall crop of white mustard significantly reduced root rot severity ratings of pea plants grown the following year(.)

Evaluation of Phosphonic (Phosphorous) Acid for the Control of Phytophthora Root Rot in Processing Tomatoes.

Phosphonic acid was evaluated as a control for Phytophthora root rot in processing tomatoes in greenhouse and field experiments. The chemical was effective in reducing the incidence and severity of root rot in greenhouse tomato seedlings at a rate of 10 g a.i./L and protected seedlings for at least 8 weeks. In the field, the application of phosphonic acid increased yields of tomatoes and significantly reduced root rot severity.

Use of three screening techniques for the evaluation of fungicides to control rhizoctonia root rot of wheat

SummaryTwenty fungicides were screened for their abilities to reduce the saprophytic growth of Rhizoctonia solani on agar and in soil, and to control root rot of wheat (Triticum aestivum) in pots of soil. Thirteen showed some activity against the in vitro growth of R. solani, the most promising being Sandoz 619F and flutolanil, although none of these reduced saprophytic growth of the fungus in soil. Only benomyl and thiabendazole, which were ineffective on agar and against disease in pots, reduced saprophytic growth in soil. None of the fungicides reduced the number of plants infected in the pot experiments and only six (flutriafol, diniconazole, Schering 539865, propiconazole, Bayer HWG1608 and flutolanil) of the thirteen active on agar (+ triadimefon which was not) reduced root rot severity. The results of this study indicate the differing reactions towards R. solani of chemicals in the three screening tests and confirm the potential for chemical control of rhizoctonia root rot of wheat.

Use of soil solarization to control root rots in gerberas (Gerbera jamesonii)

An investigation was conducted during the summer months of 1986–1987 and 1987–1988 in Western Australia to evaluate the effect of soil solarization on the control of root rot of gerbera an also on the microbial and nutrient status of the soil. Infested soil cores were sampled from a site where root-rot was a severe problem and were removed to a non-infested site where they were subjected to soil solarization or fumigation. Soil solarization resulted in reduced root rot (root disease index 28.6%) in comparison to the untreated control (52.0%) 8 months after planting. Plants in the fumigated plots had 15.8% less disease than those in solarized plots. Solarization increased the total numbers of bacteria and actinomycetes, and the proportion of bacteria and fungi antogonistic to Fusarium oxysporum, F. solani and Rhizoctonia solani. The proportion of actinomycetes antagonistic to these fungi, however, did not differ between solarized and control soil treatments. There was a significant reduction in disease in plants grown in infested fumigated soil to which a 10% concentration of solarized soil had been added, suggesting the development of microbial suppression in solarized soil. Phytophthora cryptogea was eradicated to 30 cm by solarization as well as by fumigation. Solarization eliminated R. solani but not F. oxysporum to a soil depth of 10 cm. Solarization increased the levels of NO n3 − -N and NH4+-N in soil, but did not affect the concentrations of PO43−, K+, Fe2+, organic C and pH. Yield (as number of flowers per plant) was increased by soil solarization and by fumigation.

Fungi associated with root and hypocotyl diseases of seedling lupins in Western Australia

Pleiochaeta setosa, Pythium irregulare, Fusarium spp. and Rhizoctonia spp. were frequently isolated from root lesions on lupin seedlings growing at 18 locations in the temperate south-west of Western Australia. P. setosa was isolated from all 13 sites where lupins had previously been grown (average isolation frequency 90%) but from none of the 5 sites with no lupin history. P. setosa was pathogenic in pot experiments using colonized millet or conidia as inoculum. Certain isolates of P. irregulare and Rhizoctonia spp. were pathogenic, but all Fusarium isolates appeared very weak or non-pathogenic. In a fungicide drench field experiment Rovral� reduced the isolation of P, setosa from roots by 97% and reduced root rot by 42%, providing complementary evidence for the importance of P. setosa as a root pathogen in Western Australia.Rhizoctonia solani was isolated from characteristic reddish-brown hypocotyl lesions and reproduced these symptoms in pathogenicity tests.

EFFECTS OF SEED SPACING ON COMMON ROOT ROT OF SOME BARLEY CULTIVARS

The effect of varying interplant competition on common root rot and yield was examined in barley over a 4-yr period. One experiment studied the effects of thinning. Other tests with a constant level of interplant competition examined the effects of interplanted root-rot-resistant barley or oat cultivars on the root rot reaction and yield of susceptible barley cultivars. Increasing interplant spacing by thinning reduced root rot significantly in Gateway and Bonanza barley in 1 out of 4 years, but yield was increased significantly only in Gateway in 2 out of 4 years. Yield reduction due to root rot was significantly less in 1 out of 2 years when the distance between Gateway plants was increased due to the interplanting of oats. The lack of a consistent reduction in root rot or yield loss by reducing plant competition or interplanting with moderately resistant barley or oats precludes use of lower seeding rates or mixed crops as an economic method of reducing root rot.Key words: Interplant competition, common root rot, barley