Root Rot of Miniature Roses Caused by Pythium helicoides

Miniature roses growing in an ebb-and-flow watering system developed dieback during the summer growing season of 1996 in Gifu Prefecture. The main diagnostic symptoms were chlorosis of leaf followed by blight, and a brown, water-soaked root rot followed by dieback. Pythium isolates were recovered from the rotted root. The isolates form proliferous ellipsoidal papillate sporangia, spherical smooth oogonia, elongate antheridia, and aplerotic oospores. The optimum temperature for hyphal growth was 35°C with a growth rate of 34 mm/24 hr. Optimum temperature of zoospore formation (25-30°C) was lower than that of mycelial growth, and zoospores were produced even at 10°C. The isolates were identified as P. helicoides on the basis of these characteristics. In pathogenicity tests disease severity was highest at the highest tested temperature (35°C) at which the disease naturally occurred in summer. Four days after inoculation, the leaves turned yellow and the roots had a water-soaked rot, followed by leaf blight and root dieback after 7 days. The disease transmission test showed that diseased plants were found throughout the bench after 10 days. Received 4 July 2001/ Accepted in revised form 10 October 2001     

Effects of Soil Fumigation and Flooding on Suppression of Pythium Root Rot in Ornamental Bulb Culture

The effects of flooding and soil fumigation with cis-dichloropropene or methylisothiocyanate (MIT) on disease suppression against Pythium spp. were tested in pot and field experiments in sandy soil. Disease suppression was reduced by both flooding and fumigation treatments, resulting in severe infection in Iris and Crocus and reduction of bulb yields. It is demonstrated that the disease suppression has a biological nature, and that disease severity is more related to effects of the soil treatments on the soil microflora than to the initial inoculum density of Pythium. After flooding, disease suppression was restored within the experimental period of two years, whereas after fumigation, disease suppression was only partially restored. The effect of repeated fumigation in two consecutive years on the disease suppression was less severe than the effect of a single fumigation treatment prior to cultivation of a susceptible crop.     

Effect of Ultraviolet Disinfection of Hydroponic Solutions on Pythium Root Rot and Non-target Bacteria

Dispersal of root pathogens is a major concern in closed hydroponic cultures. To limit dispersal, ultraviolet (UV) disinfection technology has been used to remove pathogens but its effect on non-target bacterial populations is largely unknown. In this study, the circulating solution was disinfected with various UV doses (i.e., 19, 38, 59, 88mJcm^–2) before recirculation. At the beginning of the experiment, the hydroponic solution was inoculated with Pythium aphanidermatum at 6.7±1.5CFUmL^–1. Four months later the population density of P. aphanidermatum reached 1030CFUmL^–1 in the control and 1028, 970, 610, and 521CFUmL^–1 in the solutions treated by the above UV doses. In all UV-treated solutions, significant (P<0.05) reduction of both Pythium and bacterial populations was noted. For the former, its reduction did not result in decrease of Pythium root rot nor increase of tomato fruit yield. For the latter, its reduction showed a concomitant decrease of the populations in the rhizosphere. The bacterial populations in the rhizosphere were 6.77×10⁹CFUmg^–1 fresh roots at the beginning of the experiment and were 7.89×10⁸, 9.93×10⁷, 7.33×10⁷, and 3.51×10⁷CFUmg^–1 fresh roots at the end of the experiment in the control, UV38, UV59, and UV88 treatments, respectively. The bacterial density also decreased with time in the control (UV0) although at a low rate. The results suggest that the attempt to control Pythium root rot by UV irradiation of recirculating solutions to remove P. aphanidermatum also affects the non-target bacterial populations in the rhizosphere. The interaction between the target pathogen and non-target bacterial flora in UV-treated hydroponics needs further investigation.     

Pathogenicity, Electrophoretic Characterisation and In planta Detection of the Cocoyam Root Rot Disease Pathogen, Pythium myriotylum

Cocoyam (Xanthosoma sagittifolium), an important staple food crop for many people in the tropics and subtropics, suffers great losses from a root rot disease which is most probably caused by Pythium myriotylum, although it has been claimed that a complex of three root pathogens is needed to cause the disease. In this study, we compared two Pythium isolates from diseased cocoyam roots, CRPm and Bokwai, with other putative P. myriotylum isolates from culture collections and from Cameroonian soil, with respect to host range and isozyme patterns. Pathogenicity was tested on tomato, bean, cowpea, tobacco and cocoyam. CRPm and Bokwai were only pathogenic to tobacco and cocoyam. On cocoyam, these isolates caused typical symptoms within 48h on 100% of the inoculated plantlets. Only two other isolates of P. myriotylum from culture collections were moderately to weakly pathogenic to cocoyam. Isolates of P. myriotylum were very variable in their pathogenicity to bean, cowpea, tomato and tobacco. Isozyme patterns of - and -esterases were used to differentiate CRPm and Bokwai from all other isolates. Unlike the other P. myriotylum strains, cocoyam isolates were unable to grow at 37°C. Malate dehydrogenase isozyme bands originating from CRPm were consistently detected in CRPm-infected cocoyam roots grown in vitro and in vivo. These findings indicate that CRPm can penetrate cocoyam roots and cause disease in the absence of other root pathogens. This study also indicates that P. myriotylum from cocoyam developed a certain degree of host specialisation.     

Local and Systemic Effects of NaCl on Root Composition, Rhizobacteria, and Fusarium Crown and Root Rot of Asparagus

ABSTRACT The role of NaCl in suppression of Fusarium crown and root rot of asparagus was investigated in split root culture so the direct effects of NaCl on the root and rhizosphere could be separated from effects that were translocated to the nontreated root side. One side of the root system was exposed to 100 ml of 0, 0.5, or 1.0% NaCl, while the other side received deionized water. Both sides of the root system were inoculated with conidial suspensions of the pathogens Fusarium oxysporum and F. proliferatum. When plants were harvested and assayed, root lesions and CFUs of F. oxysporum or F. proliferatum per centimeter of root from both exposed and nonexposed roots decreased as the NaCl rate increased to 1.0%, but the reduction relative to the control was significantly greater on roots that were directly exposed to NaCl (51% reduction in root lesions) than on adjacent nonexposed roots (31% reduction in root lesions). On both sides of the root systems, disease suppression with NaCl was associated with increases in the rhizosphere densities of fluorescent pseudomonads and Mn-reducing bacteria in the rhizosphere soil. In addition, as the NaCl rate increased, root tissues had marked reductions in malic acid and amino acids while concentrations of Cl and Mn increased in equal proportions on both sides of the root system. Chloride ions were absorbed in greater amounts than Na ions, and were more mobile in the plant than Na. Plants treated with 1% NaCl (171 meq of Cl(-) per liter) had soil leachates 1 week later of 47 meq of Cl(-) per liter from pots exposed to NaCl, but in the adjacent nonexposed pots, the amount of Cl in the leachates slowly increased over the course of the study to 20 meq/liter, presumably through the root exudation. These findings suggest that suppression of Fusarium crown and root rot of asparagus with NaCl may be due to multiple mechanisms. Maximum suppression occurs when NaCl is directly applied to roots, but suppression still occurs on distal non-treated roots resulting from systemic mechanisms. The latter mechanism may be associated with a root-mediated alteration in the rhizobacteria.     

大蒜根系分泌物对烟草镰刀菌根腐病的控制作用

为探讨大蒜根系分泌物对烟草尖孢镰刀菌的抑菌活性,采用琼脂法培养大蒜,利用气相色谱—质谱技术（GC-MS）测定其主要成分,研究大蒜根系分泌物对烟草尖孢镰刀菌根腐病的影响。对菌丝生长速率和孢子萌发的测定表明,当大蒜根系分泌物粗提物浓度为1 g/mL时,其菌丝生长抑制率为30.56%,孢子萌发抑制率高达100.00%。大蒜根系分泌物主要成份2,6—二异丙基苯酚和邻苯二甲酸二丁酯分别对其菌丝生长和孢子萌发具有较强的抑菌作用。邻苯二甲酸二丁酯的防控效果较好,其浓度为5 mmol/L,接菌21 d后其病情指数为55.00,防控效果达32.38%。大蒜根系分泌物及主要成分对尖孢镰刀菌所引起的烟草根腐病有显著的抑制作用,这为研制含大蒜成分的植物保护剂和间作套种大蒜防控烟草尖孢镰刀菌根腐病提供科学参考。     

Effect of the Indigenous Microflora on the Development of Root and Crown Rot Caused by Pythium aphanidermatum in Cucumber Grown on Rockwool

ABSTRACT The capacity of the microflora in rockwool to suppress Pythium aphanidermatum, the causative agent of root and crown rot in cucumber, was assessed. Disease development of cucumber (Cucumis sativus) grown on rockwool was evaluated in an "ebb-and-flood" system with a recirculating nutrient solution after inoculation with P. aphanidermatum. In five independent experiments from 1995 to 1998, 11 batches of used rockwool were tested. All batches without P. aphanidermatum problems in the preceding cucumber crop had significantly lower numbers of diseased plants in nonautoclaved than in autoclaved used rockwool; the disease incidence was reduced by 52 to 100%. Suppressiveness also was present in rockwool previously used to grow other vegetable crops. Rockwool originating from a cucumber crop that was severely attacked by Pythium resulted in a high disease incidence. Previously unused (new) rockwool had higher or similar percentages of diseased plants than did nonsterilized used rockwool. Disease suppression in used rockwool could also be measured in a smaller test system. In both systems, autoclaved rockwool became suppressive to Pythium after recolonization with the indigenous microflora. Population sizes of total culturable aerobic bacteria as well as of fluorescent pseudomonads did not correlate with disease suppressiveness, as numbers of bacteria and pseudomonads were similar or lower in nonautoclaved (suppressive) than in autoclaved (nonsuppressive) rockwool. Differences in the structure of the bacterial populations could be visualized by using eubacterial polymerase chain reaction (PCR) followed by denaturing gradient gel electrophoresis (DGGE). Interestingly, the nonautoclaved and the recolonized used rockwool, which were both suppressive, showed different dominating bacterial groups as compared with the autoclaved rockwool. PCR-DGGE patterns obtained at different sampling times showed that the composition of the bacterial populations changed during plant growth. Fungal populations were present in the treatments that yielded suppressive rockwool, i.e., the nonautoclaved and the recolonized rockwool, but they were absent or present in low numbers in the autoclaved rockwool, which permitted a high disease incidence. Suppressiveness of rockwool to Pythium root and crown rot is a hitherto undescribed phenomenon, and knowledge of the mechanism and microorganisms involved will stimulate the development of microbially balanced soilless growing systems.     

Net Carbon Gain and Growth of Bell Peppers, Capsicum annuum 'Cubico', Following Root Infection by Pythium aphanidermatum

ABSTRACT The first characterization of alterations in whole-plant photosynthetic rate and carbon assimilation of bell peppers associated with infection by Pythium aphanidermatum is described. Relationships of root disease caused by P. aphanidermatum to whole-plant net carbon exchange rate (NCER), total carbon accumulation, dark respiration rates, water loss, and destructive growth parameters were quantified in vegetative, hydroponically grown pepper plants (Capsicum annuum 'Cubico'). Inoculated plants displayed lower whole-plant NCER. This translated into a loss of 28% in cumulative C gain during 7 days after inoculation and occurred before visible shoot symptoms developed. Leaf area and dry weight of shoots and roots were significantly decreased and the shoot/root ratio was higher in inoculated plants than in noninoculated plants. We propose that reduced NCER in inoculated plants was mainly due to restricted development of leaf area, because no differences in NCER and evapotranspiration were observed between control and inoculated plants when expressed based on leaf area and root dry mass, respectively. These findings indicate that Pythium infection did not affect the photosynthetic apparatus directly and that the reductions in photosynthesis and growth were not caused by inefficient water transport by diseased roots. These results enlarge on the understanding of physiological responses of host plants to early stages of root disease.     

Fusarium Redolens f.sp asparagi, Causal Agent of Asparagus Root Rot, Crown Rot and Spear Rot

Two Fusarium species, F. oxysporum f.sp. asparagi and F. proliferatum, are known to be involved in the root and crown rot complex of asparagus. We have investigated reports on the involvement of F. redolens, a third species, which until recently was considered conspecific with F. oxysporum because of morphological similarities. RFLP analysis of the rDNA internal transcribed spacer region and AFLP fingerprinting identified eight strains from asparagus unambiguously as F. redolens. Four of these were tested and found to be pathogenic to asparagus either in this study (two strains) or in a previous one in which they were classified as F. oxysporum (three strains). Disease symptoms and disease development were the same as with F. oxysporum f.sp. asparagi and F. proliferatum. Present data and literature reports identify F. redolens as a host-specific pathogen involved in root, crown and spear rot of asparagus. The pathogen is formally classified as F. redolens Wollenw. f.sp. asparagi Baayen.     

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.     

棉花烂种烂根病原因浅析及防治对策

沙湾县地处北疆天山中部的依连哈比尔尕山北麓与准葛尔盆地南缘之间,棉花种植面积２．８３万ｈｍ２,占全县作物种植面积的４２．５％,成为农村经济重要组成部分,而棉花烂种烂根是历年来影响棉花生产的重要病害,因此,防治棉花烂种烂根已成为夺取棉花持续高产的重要措施。１　流行实况棉花烂种烂根在沙湾县自１９８１年以来的１８ａ中,重发生有３ａ,发病率６０％～８４％,发病面积占棉花种植面积的５０．４％～７４．１％,重种、补种和改种面积占１６．１％～３１．５％;中度发生有７ａ,发病率２０％～５５％,发病面积占棉花种植…     

Apricot Root Rot, Armillariella mellea (Vahl.) Karst.

This paper deals with honey root rot of apricots, caused by the fungus Armillariella mellea (Vahl.) Karst. =Armillaria mellea (Vahl.) Quelet. Symptoms of the disease are described, both on the root system and on the aerial parts, where the action of the fungus mostly provokes a sudden wilting or apoplexy. The infection process is elaborated and the importance of the subterranean rhizomorph in the infection cycle is emphasized. Conditions favourable and unfavourable to the disease are briefly discussed and it is shown that presence of woody remains in the soil is the most important factor in the spread of the disease. Some isolation and inoculation methods are described. Discussion of the methods of control places emphasis mainly on preventive measures, such as use of tolerant rootstocks, destruction of potential nutrient sources and soil disinfection by fumigation.     

Effects of Irrigation and Verticillium dahliae on Cauliflower Root and Shoot Growth Dynamics

ABSTRACT Cauliflower root and plant growth and Verticillium wilt development were evaluated under different moisture regimes in the presence or absence of V. dahliae. Treatments included two main plots (V. dahliae-infested and fumigated), two subplots (furrow and subsurface drip irrigation), and three sub-subplots (deficit, moderate, and excessive regimes) that were arranged in a split-split-plot design in the field. Soil cores with roots were periodically sampled at 5 and 25 cm distance from plants. Total roots in each soil core were extracted with a hydropneumatic root elutriator, and root length from each sample was determined with a digital image analysis system. Incidence and severity of Verticillium wilt, plant height, number of leaves, and dry weights of leaves and roots were determined on 10 plants sampled at 7- to 10-day intervals 1 month after cauliflower transplanting and continued until harvest. To evaluate the effects of Verticillium wilt-induced stress on cauliflower plants, stomatal resistance was measured in upper healthy and lower (or diseased) leaves. Root length density at 5 and 25 cm from plant was significantly (P < 0.05) higher in subsurface drip than in furrow irrigation. Root length density was significantly higher in excessive irrigation regime than in the other regimes. Concomitantly, there was higher wilt incidence and severity in excessive and moderate regimes than deficit regime regardless of the irrigation method. Plant height was affected by irrigation methods and deficit regime. Neither the method of irrigation nor the quantity of water affected the other variables. Stomatal resistance in lower diseased leaves was significantly higher in infested than in fumigated plots but it was not in the upper healthy leaves. In this study, cauliflower yield was not affected by V. dahliae and irrigation method, but the deficit irrigation regime resulted in reduced yield even though it suppressed wilt in cauliflower. Thus, higher moisture levels resulted in higher root length density in V. dahliae-infested plots that in turn lead to greater incidence of Verticillium wilt and severity. The pathogen also affected physiological processes such as hydraulic conductance of cauliflower leaves, but not shoot growth or yield under these experimental conditions.     

Effects of Potato-cyst Nematodes (Globodera pallida) and Soil pH on Root Growth, Nutrient Uptake and Crop Growth of Potato

Potato-cyst nematodes (Globodera pallida) cause severe yield losses in potato. Plants infected with potato-cyst nematodes generally have reduced concentrations of nitrogen, phosphorus and potassium in the foliage. This study investigated whether reduced growth of nematode-infected potato is caused by nutrient limitation.Experiments in the field and in containers showed that phosphorus concentration correlated best with total crop biomass at early stages of growth. The role of phosphorus in nematode damage was further investigated in the field and in the Wageningen Rhizolab. The experimental field was infested with potato-cyst nematodes and two levels of nematode density were established by fumigation with a nematicide. Prior applications of calcium carbonate resulted in pHKCl levels of 4.8 and 6.1. Two levels of phosphorus fertiliser were applied: either 0 or 225kgPha–1. In the Wageningen Rhizolab, soil of both pH levels from the field was used after treatment with 1MRad gamma irradiation to kill the nematodes. Subsequently, half of the soil was inoculated with cysts to give a nematode density of 30 viable juveniles per gram of soil.In the field, nine weeks after planting, the total crop biomass ranged from 107gm–2 for the treatment with nematodes at pHKCl 6.1 without phosphorus fertiliser to 289gm–2 for the fumigated treatment at pHKCl 4.8 with phosphorus fertiliser. The differences in total biomass for the various treatments were explained by differences in foliar phosphorus concentration. Nematodes induced or aggravated P deficiency and reduced total biomass. This was not the only damage mechanism as at high, non-limiting levels of foliar phosphorus concentration, nematodes still reduced total biomass.In the Wageningen Rhizolab, directly after planting, the number of roots visible against minirhizotrons was reduced by nematodes. However, the increase of root number in the nematode treatment continued longer than in the control, until root number was higher than that of the control. The compensary root growth of the nematode treatment was restricted to the top 30cm and nematodes reduced rooting depth.High soil pH reduced growth, mainly by reducing the availability of phosphate. Both nematodes and high soil pH reduced nutrient uptake per unit root length. Our results lead us to suggest an interaction between nematodes and soil pH, with nematode damage being higher at pHKCl 6.1 than at pHKCl 4.8.     

花椒根腐病拮抗真菌的分离鉴定及其生防潜力探究

为获得花椒根腐病菌腐皮镰孢菌Fusarium solani的优良拮抗菌株,本研究以健康花椒侧根为拮抗菌来源,采用组织分离法获得花椒根部内生真菌,通过平板对峙法筛选出1株对病原菌具备明显拮抗作用的真菌HB21-1,平板抑制率为61.00%,其无菌发酵滤液抑制率为41.24%,可致腐皮镰孢菌菌丝出现皱缩膨胀、孢子畸形现象,经形态学和分子生物学鉴定为草酸青霉Penicilium oxalicum。盆栽试验结果表明HB21-1对花椒根腐病的防效为56.59%,经HB21-1处理的花椒根部POD、SOD酶活性和土壤蔗糖酶、酸性磷酸酶活性随时间均呈升高趋势,且始终高于空白对照。本研究表明草酸青霉HB21-1对花椒根腐病病原菌具有显著拮抗作用,能降低发病率,在生物防治方面有潜在应用价值。     

8种除草剂对红麻幼芽和幼根生长的影响

进行了8种除草剂对红麻幼芽和幼根生长影响的室内生物测定.结果表明,氯氟吡氧乙酸对红麻幼芽和幼根的抑制作用十分强烈,抑制率分别为80.63％、54.66％.苯达松、异丙隆和甲咪唑烟酸对红麻幼根和幼芽的抑制率均小于18％.     

The Use of a GUS Transformant of Trichoderma Harzianum, Strain T3a, to Study Metabolic Activity in the Spermosphere and Rhizosphere Related to Biocontrol of Pythium Damping-off And Root Rot

The activity of Trichoderma harzianum in the spermosphere and rhizosphere of different plant species was studied by use of a beta-glucuronidase (GUS) transformant (strain T3a). Hereby, direct observation of micro-habitats supporting metabolic activity of T. harzianum is reported. Germination of conidia and mycelial growth were not supported by exudates from healthy roots of various ages. Instead, growth and activity of T. harzianum depended on access to dead organic substrates such as seed coats, decaying roots, and wounds, including those caused by infecting pathogens. A correlation between the GUS activity of T. harzianum and the biomass of Pythium ultimum in infected roots was established. On the basis of our observations, we suggest that the biocontrol ability of T. harzianum involves competition with the pathogen for substrates including the seed coat, and wounded or infected root tissue.     

Aggressiveness and production of cell-wall degrading enzymes by Pythium violae, Pythium sulcatum and Pythium ultimum, responsible for cavity spot on carrots

This study investigated the relationships between pathogenesis, types of symptoms and in vitro production of cell-wall degrading enzymes by P. violae, P. sulcatum and P. ultimum. The three pathogens, considered as the three Pythium species principally responsible for cavity spot on carrot roots, secreted only low levels of fatty acid esterases activity, suggesting they have limited ability to degrade suberin in the walls of the outer cell layers of carrot tissues. Among the enzymes that degrade cell-wall polysaccharides, only pectate lyases and cellulases were produced by P. violae, and these were produced late and in small amounts: the symptoms caused by P. violae were limited and typical of cavity spot. Conversely, P. ultimum caused maceration of tissues, and secreted polygalacturonases and -1,4-glucanases earlier and in larger amounts than P. violae. P. ultimum also produced a large diversity of proteins and cellulase isoenzymes. Although secreting all the monitored enzymes in higher quantity than the two previous species, P. sulcatum was responsible for only typical limited symptoms of cavity spot, with a brown colouring. The role of plant reactions induced in response to early pectinolytic enzyme production by P. sulcatum may account for this apparent inconsistency.Died on April 11, 1997