Root Rot Severity Research Articles

First Report of Root Rot Caused by Plectosphaerella cucumerina on Cabbage in China

Severe root rot was observed in fields of cabbages (Brassica oleracea L.) in 2015 in China. Cardinal symptoms of this disease included root rot and wilting leaves. A fungus was isolated from diseased tissues consistently. Based on the morphological features and molecular analysis of the ITS-5.8S rDNA and D1/D2 domain of the 28S rRNA gene, it was identified as Plectosphaerella cucumerina. This is the first report of P. cucumerina causing cabbage root rot in China and the world.

Epidemiology of Fusarium agave wilt in Agave tequilana Weber var. azul

Fusarium oxysporum is reported as the principal causal agent limiting production of Agave tequilana Weber var. azul, but frequent isolation of F. solani, and symptoms typical of F. solani as a pathogen like severe reddish coloured root rot and loss of soil anchorage are frequently associated with diseased agaves. Inoculations of agave plantlets with F. solani induced typical agave root rot symptoms in greenhouse trials. The incidence of both pathogens was determined molecularly with specific primers in the ITS2 sequence. Dispersion patterns of agave wilt, determined in plantations of different age, indicated a tendency to produce aggregated patterns over time as the disease spread from the initial symptomatic plant to adjacent plants. Although both fungi were isolated from agave diseased plants, and in spite of the higher percentage of detection and root rot symptoms, it is concluded that F. solani may have a greater impact in agave wilt.

Environmental factors determine severity of Rhizoctonia damping-off and root rot in subterranean clover

This study defines the importance of environmental conditions occurring across southern Australian subterranean clover (Trifolium subterraneum) forages on the severity of Rhizoctonia (Rhizoctonia solani) damping-off and root rot and on consequent plant productivity. Environmental factors tested included temperature regimes 14/9; 18/13 and 22/17 °C day/night, high vs. low soil moisture; sand vs. loam soil; high vs. low nutrition, and clover cultivars Riverina, Seaton Park and Woogenellup. Environmental factors significantly affected the severity of damping-off, root disease and root and shoot productivity. Damping-off was at or close to 100% at the two cooler of the three temperature regimes. At the warmest of the three temperature regimes (22/17 °C), significant numbers of subterranean clover plants germinated and survived, and germination, dry root and shoot weights all increased conversely with decreased tap and lateral root disease under higher moisture, better nutrition and under ‘heavier’ soil conditions. Findings demonstrate how variations in environmental factors like temperature in particular, but also soil type, nutrition, moisture, individually and interacting, have profound effects on the expression and severity of Rhizoctonia damping-off and root disease and the consequent productivity of subterranean clover forages. Findings explain the severe devastation to subterranean clover pastures observed in the presence of this pathogen when cool seasonal conditions occur across the critical autumn feed-gap period; especially under relatively drier soil conditions and in nutritionally impoverished sandy soils where there is little competition from other soil microbes.

Growth of Grapevine Rootlings in Soil from a Field Nursery Naturally Infested with Meloidogyne incognita and Rhizoctonia solani

Grapevine rootlings (V. vinifera cv. Colombard and V. champini cv. Ramsey) were grown in pots containing soil from a field nursery naturally infested with Meloidogyne incognita and Rhizoctonia solani. Vine growth in untreated soil with or without dilution using clean sand was compared with growth in soil subjected to a range of treatments including: disinfestation either by aerated steaming or by fumigation with methyl bromide, amendment with 1 % (w/w) corn-meal, or treatment with fungicides and/or fenamiphos. Vines grown in infested soil suffered root rot caused by R. soiani and galling caused by M. i11cog11ita. Both disinfestation treatments effectively prevented root rotting and galling, and increased the growth of Colombard but not Ramsey. Fenamiphos increased the growth of the nematode-susceptible Colombard but not Ramsey at a low initial population density of three juveniles per 200 g of soil. Nematode reproduction on Ramsey in the shadehouse and in the field nursery on other rootstocks regarded as being highly resistant to root-knot nematode was higher than previously reported with other South Australian Meloidogyne spp. populations. Soil dilution increased Colombard growth and amendment with corn-meal reduced nematode reproduction on both cultivars. Rhizoctonia solani caused root rot in both cultivars but quintozene and tolclofos-methyl increased root growth only of Ramsey. These fungicides and pencycuron reduced the severity of root rot; tolclofos-methyl was particularly effective in reducing the frequency of isolation of R. solani from roots. Potassium phosphite did not reduce root rot or increase root growth. Quintozene, tolclofos-methyl and pencycuron also inhibited nematode reproduction but these effects were not consistently observed in both cultivars. Most isolates of R. solani from grapevine roots belonged to anastomosis group 4. Field observations suggested that galled roots were more prone to infection by R. solani than ungalled roots.

The Role of Salicylic Acid and Pseudomonas fluorescens in Systemic Resistance Against Rhizoctonia solani kühn in Guar (Cyamopsis tetragonoloba (l.) Taub.)

Rhizoctonia solani was found to be associated with root rot symptoms of guar plants collected from different fields in New Valley governorate, Egypt. All the obtained isolates were able to attack guar plants (cv. Local) causing damping-off and root rot diseases. R. solani isolates No. 8 (RG8) was the more virulent ones in the pathogenicity tests. Salicylic acid (SA) and Pseudomonas fluorescens (PF) individually or in combination were examined for their potential in suppression damping-off and root rot and growth promotion of guar plants in vitro and in vivo. Both SA and P. fluorescens either individually or in combination inhibited the growth of the tested pathogenic fungi.SA combined with P. fluorescens recorded the highest inhibited growth followed by P. fluorescens alone. Under greenhouse and field conditions, all treatments significantly reduced damping-off and root rot severity. The combination of SA and P. fluorescens was more effective than using them individually. Under field conditions, all these treatments significantly increased growth parameters (plant height and No. of branches plant-1) and yield components (No. of pods plant-1, weight of 100 seeds and total yield fed.-1 and Guaran content (gm plant-1) in both locations (El-Kharga and Mallawy Agric. Res. Stations) during growing season 2014.The combination of SA and P. fluorescens were recorded the highest growth parameters and yield components. Generally, the combination of SA and P. fluorescens recorded the best results for controlling damping-off and root rot diseases in greenhouse and field with addition improved plant growth and increased yield components in the field. In physiological studies, activity of defense-related enzymes, including peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), pathogenesis related (PR) protein (chitinase and β 1,3 gluconase), were increased in inoculated and non-inoculated plants treated with the SA and P. fluorescens either individually or in combination, during the experimental period. The combination of SA and P. fluorescens recorded the highest increase in activity of all enzymes. In general, the activity of these enzymes begins to accumulate after two days of treatment and reached maximum levels at 6 to 10 days, then the activities of these enzymes were decreased progressively. On the other hand, total phenols and lignin increased in guar plants inoculated with R. solani and treated with SA and P. fluorescens individually or in combination. The highest accumulation of phenols was recorded 8th days from application, while lignin recorded the highest level at 10th days from application. In the end, these results suggested that SA and P. fluorescens either individually or in combination may play an important role in controlling the guar damping-off and root rot diseases, though they have induction of systemic resistance in guar plants.

Antagonistic activity of Trichoderma spp. against Scytalidium lignicola CMM 1098 and antioxidant enzymatic activity in cassava

Trichoderma spp. are used as antagonists against different pathogens. Despite many possibilities of using Trichoderma as an antagonist, there are gaps in the knowledge of the interaction between Trichoderma, cassava and Scytalidium lignicola. This fungus causes cassava black root rot and is an inhabitant of the soil, so it is difficult to control. Antagonists may contribute to the possible induction of resistance of plants because, when exposed to such pathosystems, plants respond by producing antioxidative enzymes. The test for potential inhibition of growth of S. lignicola CMM 1098 in vitro was performed in potato-dextrose-agar with two Trichoderma strains T. harzianum URM3086 and T. aureoviride URM 5158. We evaluated the effect of the two selected Trichoderma to reduce the severity of cassava black root rot and shoots. Subsequently, the production of enzymes (ascorbate peroxidase, catalase, peroxidase and polyphenol oxidase) was evaluated in cassava plants. All two Trichoderma strains show an inhibition of the growth of S. lignicola CMM 1098. The most efficient was T. harzianum URM 3086, with 80.78% of mycelial growth inhibition. T. aureoviride URM 5158 was considered the best chitinase producer. All treatments were effective in reducing severity, especially treatments using Trichoderma. Cassava plants treated with T. aureoviride URM 5158 had the highest enzyme activity, especially peroxidase and ascorbate peroxidase. Trichoderma harzianum URM3086 and Trichoderma aureoviride URM 5158 were effective in reducing the severity of cassava black root rot caused by S. lignicola CMM 1098.

Soybean Sudden Death Syndrome Caused by Fusarium virguliforme is Impaired by Prolonged Flooding and Anaerobic Conditions.

High soil moisture usually favors soybean sudden death syndrome (SDS), caused by Fusarium virguliforme (Fv), but the effects of the duration of the flooding period and accompanying anaerobic conditions on the soybean-Fv interaction are not clear. Greenhouse studies were conducted using susceptible and resistant cultivars exposed to the following treatments: 3, 5, or 7 days of continuous flooding, repeated short-term flooding of 8 h/week for 3 weeks, and a no-flood check treatment. At 7, 14, and 21 days after flooding (DAF), seedlings in the no-flood, 3-day, and repeated short-term treatments showed the highest root rot and foliar symptom severity, whereas seedlings in the 7-day treatment showed the lowest severity. Fv inoculum density in soil was lowest in the 7-day flooding treatment. In a hydroponic system, the steady transcript levels of soybean defense genes and Fv candidate virulence genes were measured in response to different oxygen levels using qPCR. Fv-infected roots exposed to 12 h of anaerobic conditions showed down-regulation of the defense-related soybean genes Laccase, PR3, PR10, PAL, and CHS, and the Fv virulence genes pectate lyase (PL), and Fv homolog of the pisatin demethylase (PDA). Our study suggests that short-term flooding tends to increase SDS, while prolonged flooding negatively impacts SDS due to reduction of Fv density in soil. Moreover, anaerobic conditions down-regulate both soybean defense genes and Fv candidate virulence genes.

Effect of seed treatment with novel strains of Trichoderma spp. on establishment and yield of spring wheat

Fusarium head blight (FHB) is the most important disease of wheat in Canada. FHB reduces grain yield and quality and results in seed contamination with Fusarium spp. that is associated with reduced seed vigor and poor stand establishment in wheat. The effect of seed treatments with six strains representing three species Trichoderma, selected based on their superior antagonistic ability on mycelium growth of F. graminearum in dual culture assays, on wheat seed lots contaminated with Fusarium spp. (28–43%) was examined in field trials in 2008, 2009, and 2011. None of the six strains of Trichoderma spp. showed a significant seed treatment effect for all parameters measured each year, but over the three years, all six strains significantly reduced root rot severity and increased yield, three stains (Trich12, TrichC70 and TrichPine) increased emergence and four strains (Trich06, TrichC39, TrichC70, and TrichMM7) increased plant dry weight, compared with the untreated control. TrichC70 was the only strain that showed a significant improvement to all four parameters, increasing emergence by 10.9%, dry weight by 51.7%, and yield by 11.0% and reducing root rot severity by 51.7%. These effects were less but not significantly different from that of the registered fungicide Vitaflo-280 (carbathiin + thiram) used as the positive control in the field trials. The results indicate that Trichoderma stain TrichC70 may be used as an alternative to fungicide seed treatments to alleviate the detrimental effect of the seed-borne phase of FHB in wheat.

Severity of phytophthora root rot and pre‐emergence damping‐off in subterranean clover influenced by moisture, temperature, nutrition, soil type, cultivar and their interactions

Studies were carried out in controlled environment rooms reflecting field situations. In the presence of the devastating soilborne pathogen Phytophthora clandestina, subterranean clover (Trifolium subterraneum) seedling emergence was significantly affected by moisture, soil type, temperature and cultivar. The level of rotting of tap and lateral roots was significantly affected by nutrition, soil type, temperature and cultivar. There were significant interactions involving temperature, moisture, soil type and cultivar; cultivar resistance, high moisture, high or medium temperature, high nutrition and sand soil all contributed towards less pre‐emergence damping‐off and tap and lateral root disease and to greater clover productivity. Host resistance of subterranean clover cultivars was critical for reducing disease severity and increasing productivity, even when favourable environmental conditions for severe disease occurred. In the presence of P. clandestina, the most resistant cultivar, Seaton Park, performed best under a high temperature, high nutrition and high moisture combination, but showed lower productivity under conditions of low nutrition or lower temperature, even when moisture level was high. In contrast, less resistant cultivars Riverina and Meteora had less disease and greater productivity under low moisture conditions. Findings reflect field observations that pre‐emergence damping‐off and root disease from P. clandestina in subterranean clover is particularly severe under colder conditions and in nutritionally impoverished sandy soils, and demonstrate how variations in soil type, nutrition, moisture, temperature and cultivar have profound effects on the expression and severity of phytophthora pre‐emergence damping‐off and root disease and the productivity of subterranean clover forages.

Susceptibility of cover crop plants to Fusarium virguliforme , causal agent of soybean sudden death syndrome, and Heterodera glycines , the soybean cyst nematode

Greenhouse studies were conducted to evaluate the susceptibility of cover crop species to infection by Fusarium virguliforme (Fv), a soilborne fungus that causes sudden death syndrome (SDS) of soybean (Glycine max [L.] Merr.), and the soybean cyst nematode (SCN; Heterodera glycines), both important soybean pathogens. In the SDS experiments, cover crops were planted in Fv-infested soil, and plants were assessed for fresh biomass, root rot severity, foliar symptoms, and amount of Fv DNA in roots. Inoculated alfalfa (Medicago sativa L.), crimson clover (Trifolium incarnatum L.), red clover (Trifolium pratense L.), and pea (Pisum sativum L.) had more root necrosis than the noninoculated controls, and Fv DNA quantities in roots did not differ from those found in soybean roots. Inoculated alfalfa, corn (Zea mays L.), crimson clover, oat (Avena sativa L.), red clover, sorghum (Sorghum bicolor L.), and turnip (Brassica rapa L.) plants had lower biomass compared to noninoculated controls, although corn, oat, and turnip had no root necrosis. Biomass reduction and root necrosis were not observed in inoculated hairy vetch (Vicia villosa Roth), false flax (Camelina sativa [L.] Crantz), millet (Pennisetum glaucum [L.] R.Br.), mustard (Brassica juncea L.), rye (Secale cereale L.), ryegrass (Lolium multiflorum Lam.), triticale (Triticale hexaploide Lart.), and wheat (Triticum aestivum L.), and Fv DNA quantity in the roots of these species was lower than in soybean. These results suggest that the legume species tested are hosts of Fv whereas grasses and Brassicas spp. are nonhosts or poor hosts. In the SCN experiment, select leguminous and nonleguminous cover crop plants were grown in soil naturally infested with SCN, and the number of females formed per root after 30 days was determined. There were very few (zero to five) SCN females on the roots of multiple varieties of leguminous cover crop species studied. No females were recovered from the roots of any of the nonleguminous species studied, except for a single female on four plants from three different species. None of the cover crop plants studied were susceptible hosts for SCN. With the increasing interest in using cover crops as a soil conservation practice in corn–soybean production systems, it is important to understand how this practice would impact major soybean diseases. Knowing the impact that cover crops may have on SDS and SCN is important to help farmers make better decisions when planting cover crops in areas with history of these diseases.

Influence of drainage on soybean seedling health

Subsurface tile drainage is a commonly used agricultural practice in Iowa croplands. Little is known about the effect of drainage on soybean (Glycine max) disease. Field and greenhouse studies were conducted to study the effect of drainage on seedling health. A field experiment was conducted at the Iowa State University research farm near Crawfordsville, Iowa, in 2012 and 2013. Four treatments were compared: conventional drainage (CvD, subsurface drains installed 1.2 m [3.9 ft] deep with 18 m [59 ft] spacing), shallow drainage (SD, 0.76 m [2.5 ft] deep with 12.2 m [40 ft] spacing), controlled drainage (CtD, 1.2 m [3.9 ft] deep and 18 m [59 ft] spacing with a water table control structure located at the outlet), and no drainage (ND, no artificial drainage). A greenhouse experiment was conducted three times to compare two soil sources (ND and CvD soil from the field experiment), two soybean cultivars (Ripley and Williams 82), and three watering intensities (low, moderate, and saturated). Plants were sampled at the second trifoliate stage to assess root rot severity, root dry weight, root size, and Fusarium spp. incidence in roots. In the field, root rot severity was significantly (p

Evaluation of Cowpea Genotypes for Resistance to <i>Fusarium redolens</i> in Uganda

Fusarium redolens, a virulent fungus which causes damping off, leaf yellowing, wilting and root rots has recently been devastating cowpea fields in Uganda. This study aimed at identifying cowpea genotypes that are resistant to Fusarium redolens. Therefore, ninety cowpea genotypes were evaluated two times against a highly virulent Fusarium redolens (isolate from Zombo in Paidha district) in the screen house in 2016. Genotype effect was highly significant (P 0.001) for root rot severity. Based on the Index of Susceptibility (IS), three genotypes (Asontem, Dan1 LA and IT89KD-88) remained resistant (IS 3.5) over the two screening periods, 72 moderately resistant (3.5 ≤ IS 6.5) and 11 susceptible (IS ≥ 6.5). Resistance was found to be enhanced by presence of lateral roots above or at the ground level. Further results suggested a difference in genetic control of resistance to root rots and seed rots caused by Fusarium redolens. All the released varieties tested (SECOW 1 T, SECOW 2 W, SECOW 3 B, SECOW 4 W and SECOW 5 T) had moderate resistance to Fusarium redolens. Correlation analysis revealed root rot severity was strongly correlated to disease incidence (+0.64, P 0.001), to proportion of plants with lateral roots (-0.56, P 0.001), to amount of leaf chlorophyll (-0.53, P 0.001) and to proportion of plants that died prematurely due to Fusarium redolens infection (+0.45, P 0.001). No significant correlation was detected between root rot severity and proportion of plants that germinated. The established resistance could be exploited for improvement of farmer preferred cowpea varieties towards Fusarium redolens resistance in Uganda.

Soilborne root disease pathogen complexes drive widespread decline of subterranean clover pastures across diverse climatic zones

Subterranean clover (Trifolium subterraneum L.) is an important pasture legume in many regions of Australia, and elsewhere. A survey was undertaken in 2014 to define the levels of soilborne disease and associated pathogens in annual subterranean clover pastures across southern Australia. Most of the 202 samples processed had very severe levels of taproot rot disease (disease index 60–80%) and extremely severe lateral root rot disease (disease index 80–100%). A complex of soilborne root pathogens including Aphanomyces trifolii, Phytophthora clandestina, and one or more of Pythium, Rhizoctonia and Fusarium spp. was found responsible for severe pre- and post-emergence damping-off and root disease. This is the first study to highlight the high incidence of A. trifolii across southern Australian pastures and the first to highlight the existence of natural synergistic associations in the field between Rhizoctonia and Pythium spp., Pythium and Fusarium spp., Pythium spp. and A. trifolii, and P. clandestina and A. trifolii. Nodulation was generally poor, mainly only in the 20–40% nodulation index range. There was no relationship between rainfall zone and tap or lateral root disease level, with root disease equally severe in lower (330 mm) and higher (1000 mm) rainfall zones. This dispels the previous belief that severe root disease in subterranean clover is an issue only in higher rainfall zones. Although overall the relationship between tap and lateral root disease was relatively weak, these two root-disease components were strongly positively expressed within each pathogen’s presence grouping, providing explanation for variability in this relationship across different field situations where soilborne root disease is a major problem. Most producers underestimated the levels and effect of root disease in their pastures. This study established that tap and lateral root diseases are widespread and severe, having devastating impact on the feed gap during autumn–early winter across southern Australia. Severe root disease was independent of the highly variable complex of soilborne pathogens associated with diseased roots, geographic location and rainfall zone. It is evident that soilborne root diseases are the primary factor responsible for widespread decline in subterranean clover productivity of pastures across southern Australia. Implications for disease management and options for extension are discussed.

Olive Cultivar Reaction and Biochemical Changes Due to Infection by Root Rot Pathogens

Root rot disease was studied in several olive nurseries and orchards in Ismailia, Behera, Giza and Fayoum governorate. Observed disease symptoms were leaves internal rolling, partial wilt, yellowing or browning of leaves, drying of branches and leaves, twig dieback and severe root rot. Fusarium konzum was the most pathogenic fungus, followed by F. solani. All evaluated olive cultivars were susceptible to the tested fungi however, cultivar Picual was the most susceptible while Koratina was the least one. The infection of Picual, Maraki, Kroneiki and Koratina with F. konzum increased the total sugars and decreased total sugar contents and non-reducing sugars in Toffahi. Also, the infection of olive transplants of cultivar Kroneiki with F. konzum or F. solani increased the total phenols however, decreased the total phenols in cvs. Toffahi, Maraki and Koratina. Oleuropin, Pyrogallol and E-vanillic increased in infected olive transplants of cv. Picual by F. konzum or F. solani. The highest amounts of flavonoids in both of healthy and infected tissues of cvs. Koratina and Picual were Luteo.6-arbinose8-glucose and Apig. 6-glucose8-rhamnose. The oxidative enzymes peroxidase, poly-phenoloxidase and catalase recorded an increment in infected tissues of the tested olive cultivars compared to the control and catalase was the highest activity however, poly-phenoloxidase was the least one.

Evaluation of Resistance to Phytophthora sojae in Soybean Mini Core Collections Using an Improved Assay System.

Stem and root rot disease caused by Phytophthora sojae is devastating to soybean crops worldwide. Developing host resistance to P. sojae, considered the most effective and stable means to control this disease, is partly hampered by limited germplasm resources. In this study, we first modified conventional methods for a P. sojae resistance assay to a simpler and more cost-effective version, in which the P. sojae inoculum was mixed into the soil and the resistance was evaluated by survival rate (%) of soybean seedlings. This rating had significant correlations (P < 0.01) with the reduction in root fresh weight and the visual root rot severity. Applying this method to evaluate P. sojae resistance in soybean mini core collections comprising either 79 accessions originating from Japan (JMC) or 80 accessions collected around the world (WMC) revealed a wide variation in resistance among the individual varieties. In total, 38 accessions from the JMC and 41 from the WMC exhibited resistance or moderate resistance to P. sojae isolate N1 (with virulence to Rps1b, 3c, 4, 5, and 6), with ≥50% survival. Of these, 26 from the JMC and 29 from the WMC showed at least moderate resistance to P. sojae isolate HR1 (vir Rps1a-c, 1k, 2, 3a-c, 4-6, and 8). Additionally, 24 WCS accessions, in contrast to only 6 from the JMC, exhibited 100% survival after being challenged with both the N1 and HR1 isolates, suggesting a biogeographical difference between the two collections. We further verified two JMC varieties, Daizu and Amagi zairai 90D, for their resistance to an additional four P. sojae isolates (60 to 100% survival), which may provide new and valuable genetic sources for P. sojae resistance breeding in soybean.

Biochar effect on severity of soybean root disease caused by Fusarium virguliforme

Background and aims Biochar is known to decrease soil bulk density, increase nutrient and water retention, and to suppress certain soil-borne pathogens. The aims of our glasshouse and field experiments were to; 1) determine whether biochar amendments impact the severity of soybean root rot caused by Fusarium virguliforme; 2) to determine if biochar reduces severity of root rot by changes in physicochemical properties of soil; 3) whether biochar induces systemic resistance to root rot in soybean plants.

Trichoderma aureoviride URM 5158 and Trichoderma hamatum URM 6656 are Biocontrol Agents that act against Cassava Root rot through different Mechanisms

AbstractTrichoderma has been used to manage a large number of pathogens, but there is a gap in the mechanisms used by these biocontrol agents regarding the physiological response of cassava plants (Manihot esculenta) when it is subjected to cassava root rot. The aims of this study were to investigate the antagonist activity of ten Trichoderma isolates against Fusarium solani on potato dextrose Agar (PDA), to quantify the chitinase production, to select and test in vivo the best isolate from each experiment and to assess the physiological response of cassava to the production of oxidative enzyme complex production (ascorbate peroxidase, catalase, peroxidase and polyphenol oxidase). All Trichoderma isolates have shown competitive capability against F. solani, and Trichoderma hamatum URM 6656 showed the highest inhibition of pathogen growth (88.91%). All isolates have shown chitinase activity, but Trichoderma aureoviride URM 5158 produced the highest amount of chitinase. T. hamatum URM 6656 and T. aureoviride URM 5158 were selected to be applied in vivo. The two Trichoderma strains reduced 64 and 60% of the disease severity in the shoot and 82 and 84% in the root. Cassava plants infected with Trichoderma have shown the highest peroxidase and ascorbate peroxidase production. Our results have indicated that T. aureoviride URM 5158 is an effective biocontrol agent against cassava root rot caused by F. solani, because it presented competitive antagonist capability in vitro, the highest chitinase production, and reduced the cassava root rot severity. The application of T. aureoviride has led to the maximum enzyme activity of reactive oxygen species group in cassava plants.

Effect of conservation agriculture associated crop rotation systems on root and crown rot severity and respective soil-borne pathogens of maize (Zea mays L.) in the Highveld area of South Africa

Although crop rotation reduces the incidence of soil-borne diseases, reduced tillage practices create the risk of increased disease incidence. Monoculture maize (MM) under both conventional tillage (CT) and conservation agriculture (CA) crop systems were evaluated against two-and three-year rotation CA systems of maize with cowpea and sunflower, respectively. Pearl millet was the third crop in the three-year rotation systems. Plant mass, root and crown rot severity and frequencies of 15 soil-borne fungi on maize roots and crowns were investigated at three sampling dates, i.e. 21, 70 and 100 days after planting (DAP), together with yield. The trial was initiated during 2008/09 on a sandy loam soil in the Highveld climatic area of South Africa and the current study focused on the 2011/12, 2012/13 and 2013/14 seasons. Lower yields and plant mass at 100 DAP were obtained for the MM-CT treatment compared with MM-CA and rotated maize during the drought-stricken 2012/13 season. Yields obtained for this season correlated with crown rot severity at 100 DAP. Stenocarpella maydis and Macrophomina phaseolina correlated negatively with crown rot and plant mass at 100 DAP as well as yield (2012/13). Both fungi were most prominent in the MM-CT system.

Effect of Leaf Mold Mulch, Biochar, and Earthworms on Mycorrhizal Colonization and Yield of Asparagus Affected by Fusarium Crown and Root Rot.

Asparagus can suffer from a crown and root rot caused by Fusarium oxysporum f. sp. asparagi and F. proliferatum. The disease is exacerbated when allelopathic toxins from old, rotting asparagus crowns are present in the soil. To minimize the damage from the replant problem, three strategies were examined: (i) biochar, (ii) application of earthworms (Lumbricus terrestris), and (iii) leaf mold to serve as a compost mulch and food source for earthworms. In a greenhouse, asparagus transplants were grown in soil amended with pathogen-infested asparagus residues or in nonamended soil, then both types of soil were augmented with biochar, earthworms, the combination of biochar and earthworms, or no treatment. Biochar increased arbuscular mycorrhizae (AM) colonization by 170% and reduced the incidence of root lesions by 57%; however, plant weight was not affected by any of the soil treatments and there were no significant interactions among the main effects. In the absence of infested asparagus residues, biochar reduced plant growth by 32%. Field plots that had severe crown and root rot, along with two other fields that had never been planted to asparagus, were planted with asparagus crowns and treated with leaf mold mulch, earthworms plus leaf mold mulch, biochar, or biochar plus earthworms plus leaf mold mulch. Untreated plots served as the control treatment. One year later, asparagus roots sampled from plots in the two new fields had a threefold increase in AM colonization when treated with biochar compared with control plots. Biochar did not increase yield over the duration of the 2012 to 2014 harvests when compared with that of the control plots. No soil treatment affected root colonization by AM in the field where Fusarium crown and root rot was severe. Compared with the untreated control plots, the leaf mold mulch treatment applied alone increased the marketable yields in each year of harvest. Combining leaf mold with earthworms provided no added benefit. Soil amendment with leaf mulch alone may hold promise for improving asparagus production in newly planted asparagus fields.

Reduced incidence of tomato yellow leaf curl virus and leafminer in a tomato cultivar in northern Thailand

Tomato yellow leaf curl virus (TYLCV), a whitefly-vectored begomovirus, is a major limiting factor for tomato production worldwide, including Thailand. Field evaluation of commercial tomato cvs. for resistance to the virus endemic in northern Thailand has not been reported. Experiments conducted in northern Thailand in 2011–2013 compared the field performance of three tomato cvs. from the US with a commonly grown Thai cultivar. There were few significant differences observed among the cvs. in marketable yield, and the severity of root-knot and root rot. However there were significant differences noted in TYLCV incidence; virus incidence ranged from 38 to 100% and 8–41% in experiments one and two, respectively. In both experiments ‘Husky Cherry Red’ from the US had the lowest TYLCV incidence, leafminer damage (Liriomyza sp.), and progression of foliar necrosis primarily caused by thrips feeding and possibly exacerbated by air pollution. TYLCV infection was confirmed by a simplified method of nuclear inclusion visualization with light microscopy in experiment one, and by virus inclusion detection and PCR in experiment two.