Root Rot Severity Research Articles

The effect of chemical and biological treatment on root and crown rot disease caused by Phytophthora cryptogea Pethybr. & Lafferty in Gerbera

AbstractPhytophthora root and crown rot (Phytophthora cryptogea) on gerbera is difficult to manage because most gerbera cultivars are susceptible to P. cryptogea. This study was conducted in order to determine the in vivo (pot experiment) efficacy of some fungicides and biofungicides. In pot experiments, fungicides were applied 7 days after inoculation with P. cryptogea, while biofungicide was applied 7 days before inoculation. In this study, soil drenches of five fungicides were tested. “Ametoctradin+dimethomorph (100 ml/day),” “mandipropamid+difenoconazole (60 ml/day),” “propamocarb+fosetyl‐Al (200 ml/day),” “mancozeb+metalaxyl‐M (250 g/day)” and “azoxystrobin+difenoconazole (100 ml/day)” active substances were used. Similarly, one biofungicide Bacillus amyloliquefaciens syn. MBI 600 (50 g/100 L) was applied by soil drenching. Efficacy of treatments was assessed according to the percentage of the root system which was visibly rotten at the end of the experiment. Root and crown rot severity was rated on a scale of 0 = 0% root system necrotic, 1 = 1%‐25% necrotic, 2 = 26%‐50% necrotic, 3 = 51%‐75% necrotic and 4 = 76%‐100% necrotic from 12 to 21 days. In this experiment, “azoxystrobin 200 g/L + difenoconazole 125 g/L” exhibited the highest efficacy against P. cryptogea with a ratio of 43.75%. The other fungicides and biofungicides ametoctradin 300 g/L + dimethomorph 225 g/L, mandipropamid 250 g/L + difenoconazole 250 g/L, propamocarb 530 g/L + fosety‐Al 310 g/L, mancozeb 64%+metalaxyl‐M 4% and Bacillus amyloliquefaciens syn. MBI 600 11% were ineffective. Importance should be given to management strategies of P. cryptogea of and more experiments should be carried out for a better understanding of the use of registered fungicides and biofungicides.

Aggressiveness and Fumonisins Production of Fusarium Subglutinans and Fusarium Temperatum on Korean Maize Cultivars

Fusarium root rot and stalk rot are becoming a threat to maize production worldwide. However, there is still limited information about the aggressiveness of Fusarium subglutinans Edwards and Fusarium temperatum and their relationship with fumonisin production. In this study, for the first time, the reaction of seven Korean maize cultivars to F. subglutinans and F. temperatum was investigated. The results showed that among the maize cultivars, Hik-chal and Miheung-chal had the highest Fusarium-induced root rot and stalk rot severity, while De Hack-chal had the lowest disease severity regardless of the Fusarium species. Furthermore, the disease resistant cv. De Hack-chal accumulated low levels of fumonisins (FUM) in the infected stalk, while cv. Hik-chal and Miheung-chal had the highest level of FUM. It is worth to note that, plants infected with F. temperatum had a higher FUM concentration compared to cultivars infected with F. subglutinans. The present study shows a significant correlation between stalk rot ratings and FUM levels and it also presents new information about the potential risk of FUM contamination of maize stalk with F. subglutinans and F. temperatum in South Korea. In addition, enzyme activities like polyphenol oxidase (PPO), peroxidase (POD), and the amount of total phenol content (TPC) were studied in selected susceptible cultivar Miheung-chal and resistant cultivar De Hack-chal. The activity of PPO, POD and concentration of TPC were generally higher in the roots of the resistant cultivar than the susceptible cultivar. Moreover, following inoculation of either F. subglutinans or F. temperatum, there was a significant increase in PPO and POD activity in the roots of both cultivars. Hence, the information provided in this study could be helpful to better understand the mechanisms of resistance response to infection of Fusarium root rot pathogens.

Interactions Between Root Rotting Phytophthora, Abies Christmas Trees, and Environment.

Defining host-pathogen interactions between species of root-rotting Phytophthora and Abies in Christmas tree production areas is important for tailoring management activities on a regional scale and for developing molecular tools for identifying resistant host species. Classifying Abies species as resistant or susceptible is complicated by regional variation in abundance and aggressiveness of Phytophthora species and the influence of environment on symptom expression and host vigor. Because previous studies performed to assess host response to Phytophthora root rot (PRR) have focused on one or a few species of either the host or pathogen, a multifactorial experiment was conducted to assess the responses of seven species of Abies challenged with three isolates each of four Phytophthora species under contrasting temperature conditions. Evaluation of mortality, root rot severity, and remaining root biomass after 16 weeks of exposure to the pathogen confirmed prior inferences regarding inherent variation in the resistance responses of various species of Abies and demonstrated evidence of variation in aggressiveness among species of Phytophthora as well as different isolates of the same Phytophthora species. The ambient temperatures at which studies were conducted had a conspicuous effect on host mortality, root rot severity, and radial growth of Phytophthora. Understanding how host responses differ under variable pathogen attack and ambient environment will improve efforts to control PRR using host species substitutions on infested ground.

EFFECTS OF SEED DRESSER APPLICATION TO OBTAIN HEALTHY SEEDS AND CROPS OF WINTER CEREALS UNDER CONDITIONS OF BELARUS

Long-term data (2010–2018) of investigation of the role of fungicides in protection of winter cereals crops against diseases in the Republic of Belarus are given. The efficacy of fungicides including systemic and contact compounds against the snow mold, the most harmful disease in the Republic, was estimated during the periods of outbreaks, low and moderate severity of the disease. Root rot severity was observed at moderate level. Phytopathological analysis of winter wheat and triticale seeds showed high prevalence of genera Fusarium and Alternaria. Biological efficacy of fungicides against seed contamination varied from 78.8 to 100 % against Fusarium and from 73.3 to 99.9 % against Alternaria depending on the fungicide and crop. It was shown that fungicides containing fludioxonil or prochloraz were more effective against seeds contamination and snow mold severity. The maximum biological efficacy of fungicides reached 60.2 % and 66.9 % for protection of winter wheat and winter triticale, respectively. Fungicide seed treatment in periods of snow mold outbreaks allowed to save up to 38.1 c/ha of winter wheat grain and up to 29.5 c/ha of winter triticale.

Eight Species of Fusarium Cause Root Rot of Corn (Zea mays) in South Dakota

Fusarium root rot of corn (Zea mays L.) is yield-limiting in the United States, but there is no information available on the disease in South Dakota. In 2015, corn seedlings with discolored roots were arbitrarily sampled from 50 South Dakota fields, and 198 isolates were recovered. Eight species (F. acuminatum, F. boothii, F. equiseti-incarnatum complex, F. graminearum, F. oxysporum, F. proliferatum, F. solani, and F. subglutinans) were identified by morphology and translation elongation factor 1-α gene sequencing. F. graminearum (26.8%) was the most common fungus, and F. boothii (0.5%) was the least recovered. Fourteen isolates, representing the eight species, were evaluated for their pathogenicity on 2-week-old seedlings of inbred ‘B73’ using the inoculum layer method in the greenhouse. Fourteen days postinoculation, root rot severity was evaluated on a 1-to-5 rating scale and expressed as relative treatment effects (RTEs). F. proliferatum isolate P2 caused significantly greater RTE (based on 95% confidence intervals) on seedlings than the other isolates and the noninoculated control, except F. graminearum isolate FG23. This study indicates that the eight species of Fusarium are aggressive root rot pathogens of corn in South Dakota, and this information will help evaluate strategies for producers to manage these pathogens in their fields.

Cross Pathogenicity Studies Show South Dakota Isolates of Fusarium acuminatum, F. equiseti, F. graminearum, F. oxysporum, F. proliferatum, F. solani, and F. subglutinans from Either Soybean or Corn are Pathogenic to Both Crops

In South Dakota, despite that integrated pest management options are available, Fusarium root rot is an emerging disease on soybean (Glycine max L.) and corn (Zea mays L.). Surveys were conducted across South Dakota on soybean and corn fields in 2014 and 2015, respectively, to assess the prevalence of species of Fusarium causing root rot. Fusarium acuminatum, F. equiseti, F. graminearum, F. oxysporum, F. proliferatum, F. solani, and F. subglutinans were identified common to soybean and corn. A total of 21 isolates, representing these seven species, were evaluated for their pathogenicity on soybean (‘Williams 82’) and corn (‘B73’) using the inoculum layer inoculation method in the greenhouse. At 14 days postinoculation, the seedlings were evaluated for root rot severity (1-to-5 rating scale), and relative treatment effects (RTEs) were estimated. A significant effect of the treatments was observed on RTE for soybean (P = 1.1 × 10−7) and corn (P = 3.0 × 10−14). Two F. proliferatum isolates and one F. graminearum isolate from corn caused significantly greater RTE than the other treatments (including the noninoculated control) on soybean and corn. Results indicate that soybean and corn can serve as inoculum sources of the seven species of Fusarium that are pathogenic to both crops.

Impact of Glomus macrocarpon inoculation and phosphorus amendments on root rot of mungbean caused by Macrophomina phaseolina (Tassi) Goid

The purpose of present study was to develop a management strategy based on a time effective inoculation of arbuscular mycorrhizal fungi (AMF) to mitigate the yield losses of Mungbean (Vigna radiata (L.) wilczek) due to Macrophomina phaseolina (Tassi) Goid. The interactions between AMF (Glomus macrocarpon, Myc) and Mp were studied in experiments conducted in sterilized soil at pot house during spring 2017 and 2018 seasons, respectively. In particular, investigations were done to observe the effect of mycorrhiza on disease intensity of dry root rot, the effect of Mp on mycorrhisation (root colonization and AMF spore density/100 g soil) and the interactive effects of Myc and Mp on phosphorus (P) content and dry root rot severity index of Vigna radiata. Pre-inoculating plants with AMF (Myc + Mp) considerably reduced Mp population density, as compared to (MP/Myc). Early inoculation of AMF (Myc + Mp) increased mycorrhisation, P content of plants and reduced disease intensity up to 70 and 85.0%, respectively. The results suggested that soil pretreated with AMF acted as bioprotectant against the dry root rot in mungbean.

Importance and causal agents of root rot on field pea and lentil on the Canadian prairies, 2014–2017

Surveys of pulse crops across the Canadian prairies were undertaken between 2014 and 2017 to assess the distribution and severity of root rot of field pea and lentil, to identify the most important causal agents, and to compare the efficiency of culturing techniques with multiplex PCR. Root rot was present in every pea and lentil field surveyed in all three provinces. When assessed based on province and soil zone, moderate to severe symptoms (severity > 3 on a 1–7 scale) occurred in 25–99% of pea fields, but only 8–34% of lentil fields. Root rot severity on both crops was higher in growing seasons with high precipitation and was lower in drier years, but only lentil showed any difference associated with soil zone, with lower severity in the brown soil zone. This study demonstrated that Aphanomyces euteiches occurs across the Prairie region, where it caused moderate to severe injury on many field pea crops. Fusarium avenaceum was the most common pathogen identified in both culturing and PCR analyses, but other Fusarium spp., together with Pythium spp. and Rhizoctonia solani, were also components of the complex. Use of PCR for pathogen identification routinely resulted in identification of many pathogens from an infected root, whereas culturing and isolation resulted in only one or two pathogens per root. PCR was extremely important for assessing the impact of A. euteiches, which was almost never identified using culturing approaches. This observation explains why A. euteiches was not initially recognized as an important pathogen of pulses in the region.

Soil-Plant Indices Help Explain Legume Response to Crop Rotation in a Semiarid Environment.

Crop productivity is typically affected by various soil–plant factors systematically as they influence plant photosynthesis, soil fertility, and root systems. However, little is known about how the productivity of legumes is related to crop rotation systems. The objectives of this study were to determine the effect of rotation systems on legume productivity and the relationships among legume productivity and soil–plant factors. Three annual legumes – chickpea (Cicer arietinum L.), pea (Pisum sativum L.), and lentil (Lens culinaris Medikus), were included in various diversified rotation systems and compared with legume monoculture in the 8-year rotation study. Soil N and water conditions, and canopy and root systems were evaluated at the end of 8-year rotation in the semiarid Canadian prairies. Results showed that diversified rotation systems improved leaf greenness by 4%, shoot biomass by 25%, nodule biomass by 44%, and seed yield by 95% for chickpea and pea, but such effects were not found for lentil. Pea monocultures increased root rot severity by threefold compared with diversified rotations, and chickpea monoculture increased shoot rot severity by 23%, root rot severity by 96% and nodule damage by 219%. However, all the legume monocultures improved soil N accumulation by an average 38% compared to diversified systems. Pea and chickpea displayed considerable sensitivity to plant biotic stresses, whereas lentil productivity had a larger dependence on initial soil N content. The 8-year study concludes that the rotational effect on legume productivity varies with legume species, the frequency of a legume appearing in the rotation, and the integration of relevant soil and plant indices.

Effect of Time after Incorporation of Lablab Green Manure on Root Rot Pathogens and Establishment of Common Bean ( Phaseolus vulgaris L.)

Green manure incorporation is important for restoration of soil quality, particularly buildup of organic matter and supply of nutrients to plants. However, undecomposed plant residues reduce crop establishment and plant stand. Therefore, there is need to determine suitable time for green manure incorporation before planting. The effect of time after incorporation of lablab green manure on soilborne pathogens and bean crop establishment was evaluated by incorporating 12t/ha of lablab green manure at planting and at 7, 14, and 28 days before planting. Soil samples were collected before and after incorporation of green manure at planting, and at two, four and six weeks after planting. Data was collected on crop emergence, plant stand, yield, incidence and severity of root rot, and population of root rot pathogens. Incorporation of lablab residues 28 days before planting resulted in 21% improvement in germination, with corresponding reduction in root rot incidence and severity of 8% and 36%, respectively, compared to plots incorporated with green manure at planting. Plots incorporated with lablab green manure earlier before planting had reduced population of root rot pathogens, while those incorporation at planting excited the population of root rot pathogens and also had up to 71% reduction in grain yield compared to plots where lablab residue was incorporated 28 days before planting. The results of the study showed that a period of 28 days between Lablab green manure incorporation and planting is necessary to allow for proper decomposition, resulting in a reduction in root rot incidence and an increase in grain yield.

Virulence of Phytophthora asparagi, susceptibility of asparagus cultigens to spear and root rot, and the efficacy of seed treatments

In 2016, Michigan led the United States in production (11.7 million kg) and hectares (3,723.1 ha) of asparagus spears grown for fresh market and processing, a crop worth $20.2 million to Michigan growers. Phytophthora asparagi, causal agent of spear and root rot of asparagus, contributes to crop decline in Michigan. Management strategies are limited, and identifying resistant cultigens and seed treatments could provide valuable strategies. Nine isolates of P. asparagi were tested for virulence using spears of five cultivars and seedlings of three cultivars. On spears, differences in isolate virulence and host susceptibility were observed with ‘Jersey Knight’ being the least susceptible and ‘Jersey Supreme’ the most susceptible. No significant differences were detected among cultivars or isolates in the seedling root rot experiment. Two virulent isolates were selected to inoculate seedlings of 18 cultigens. Isolate SP317 was significantly more virulent than SP316, and ‘Jersey Giant’ and ‘UG009’ were the least susceptible cultigens. The interaction between isolate virulence and cultigen susceptibility significantly affected root rot severity. ‘Pacific 2000’ and ‘Jersey Giant’ were the least susceptible cultigens for isolates SP316 and SP317, respectively. Seven seed treatments, including experimental fungicides and biocontrol agents, were screened for efficacy against two isolates of P. asparagi on ‘Millennium’ in vitro. Seeds treated with mefenoxam and Bacillus subtilis had the highest germination overall and on plates inoculated with SP326. When seeds were inoculated with SP316, mefenoxam, oxathiapiprolin, and B. subtilis treatments germinated at the highest percentages. Antagonism of mycelial growth was observed in the B. subtilis treatment, which resulted in significantly decreased disease incidence compared to all other treatments. These results are consistent with previous research suggesting that virulence of isolates of Phytophthora spp. is a combination of host and pathogen genetics and that some asparagus cultigens are less susceptible than others to P. asparagi.

Damping-off caused by Pythium sylvaticum on soybeans subjected to periods of cold stress is reduced by seed treatments

Soybean damping-off caused by Pythium spp. is frequently associated with the occurrence of cold weather fronts soon after spring planting. In this study, we evaluated the efficacy of a commercial seed treatment with metalaxyl and ethaboxam on emergence during various simulated cold stress conditions. A growth chamber experiment utilized a five-way factorial design with two cold stress temperatures (4ºC and 10ºC), two cold stress timings (initiated 24 and 96 h after planting), three durations of cold stress (24, 48 and 96 h), and two levels of seed treatment (INTEGO SUITETM and untreated). Cups planted with soybean seeds IA 2094 were inoculated with P. sylvaticum or not inoculated. Cups were incubated at 18ºC and evaluated 21 days after planting. Seedling emergence was reduced when the pathogen was present compared with the non-inoculated controls. In untreated seed, cold stress duration reduced seedling emergence, but no differences in emergence were detected in response to either initiation of cold stress or cold stress temperature. The seed treatment improved seedling emergence, reduced root rot severity and increased shoot weight. There was no significant effect of seed treatment on root weight. Data from this study confirm that cold stress soon after planting can increase the risk of reduced crop stands in Iowa and suggest that seed treatment with metalaxyl and ethaboxam protects seedlings when cold conditions are expected soon after planting.

Evaluation of host resistance and fungicide application as tools for the management of root rot of field pea caused by Aphanomyces euteiches

Aphanomyces root rot (ARR) of field pea (Pisum sativum), caused by Aphanomyces euteiches, can cause severe root damage, wilting, and large yield losses under wet soil conditions. To identify ways to manage this disease, the effect of A. euteiches inoculum density on field pea was studied under greenhouse and field conditions in 2015 and 2016. Increases in inoculum density reduced seedling emergence, root nodulation, and plant vigor, and resulted in increased root rot severity in both field and greenhouse tests. Seed treatments with the fungicides Apron Advance (thiabendazole + fludioxonil + metalaxyl) + Vibrance (difenoconazole + metalaxyl-M + sedaxane), INTEGO Solo (ethaboxam), BAS 516F (boscalid + pyraclostrobin), BAS 720F (metalaxyl + pyraclostrobin + fluxapyroxad), and BAS 516F + BAS 720F (3:1) were evaluated for their efficacy against ARR. All seed treatments except Apron Advance + Vibrance reduced root rot severity under controlled conditions. BAS 516F, BAS 720F and INTEGO Solo improved plant vigor and all treatments reduced seedling blight to varying degrees under greenhouse conditions, but not in the field. A collection of 22 pea genotypes was evaluated for resistance to root rot in field plot experiments. Line 00–2067 showed the least severe root rot symptoms, whereas ‘Spring D’ showed the lowest reduction in yield. The results suggest that there may be an opportunity to combine partial host resistance and fungicidal seed treatments to adequately manage ARR of field pea.

Effect of Pseudomonas Bacteria on Peroxidase Activity in Wheat Plants when Infected with Bipolaris sorokiniana

We investigated the effect of treating soft wheat seeds (Triticum aestivum L.) with two Pseudomonas bacteria strains, isolated from earthworm coprolites, showing a significant antifungal and growth-promoting action in preliminary screening on the activity of guaiacol-dependant peroxidase under phytopathogenic load in the presence of Bipolaris sorokiniana (Sacc.) Shoemaker as a mechanism for inducing plant resistance to the pathogen. We established a statistically significant decrease (P < 0.05) in root rot disease incidence and severity during bacterization, which is indicative both of antifungal activity of the used bacterial isolates and of their successful colonizing the rhizosphere of wheat plants. We noted a response of free and weakly bound peroxidase of wheat plants to infection with B. sorokiniana: the enzyme activity increased during pathogenesis. Bacterization also increased peroxidase activity in plant leaves and roots, the greatest differences from non-bacterized plants being observed in wheat roots in the presence of the pathogen. We detected a direct link between peroxidase activity in wheat roots and leaf tissues in the absence of the pathogen and the feedback between peroxidase activity and plant infestation by the root rot pathogen. In the presence of the phytopathogen, there is a lack of correlation between peroxidase activity in wheat roots and leaves, and there is a shift of activity towards its increase in roots, which plays an important role in the development of systemic resistance against the root rot pathogen that penetrates into plants through the roots and root collar.

Detection of interactions between the pea root rot pathogens Aphanomyces euteiches and Fusarium spp. using a multiplex qPCR assay

Pea root rot complex (PRRC) describes a group of closely associated soilborne pathogens that cause root rot disease in field pea. Aphanomyces euteiches and several Fusarium spp. are the most prevalent and damaging microorganisms within this complex, although the impact of interspecific interactions on disease progression remains largely unexplored. Furthermore, a fast and reliable method of detecting and quantifying these pathogens is not currently available. The objectives of this experiment were to: (i) investigate the effect of microbial interactions on root rot severity in pea under greenhouse conditions; and (ii) characterize changes in colonization rates when multiple pathogens are present using qPCR. Seeds were exposed to three species of Fusarium and were planted into A. euteiches‐infested soil in varying combinations. For each experimental treatment, an index of disease severity was used to visually rate disease symptoms. Additionally, two triplex quantitative PCR (qPCR) assays were designed to detect and quantify changes in pathogen population dynamics on the roots. Both assays demonstrated a high degree of sensitivity and efficiency. Results from two independent greenhouse trials indicated an increase in disease severity in the presence of multiple pathogen species compared to single inoculations. Specifically, roots infected with A. euteiches were more susceptible to fusarium root rot than those exposed only to Fusarium spp. These observations were confirmed by qPCR results, which revealed significant changes in colonization rates when multiple species were present. These findings suggest an increased risk of yield loss in regions where A. euteiches and Fusarium spp. co‐occur.

Biocontrol and plant-growth-promoting capacities of actinobacterial strains from the Algerian Sahara and characterisation of Streptosporangium becharense SG1 as a promising biocontrol agent

ABSTRACTSixteen actinobacterial strains isolated from various ecological niches in the Algerian Sahara were screened for their biocontrol potential in root rot disease caused by Fusarium culmorum and their promotion of durum wheat growth. All actinobacteria were studied for in vitro antagonistic activity and plant-growth-promotion traits, for the production of cyanhydric acid, siderophores, chitinases and indole-3-acetic acid, and for the solubilisation of inorganic phosphate. Strongly antagonistic actinobacteria were selected for the biocontrol of F. culmorum in vivo and for the growth promotion of durum wheat plants in autoclaved and non-autoclaved soils. The Streptosporangium becharense strain SG1 exhibited remarkable positive results in all trials. Compared to untreated wheat seeds, the root rot severity index was decreased significantly (P < 0.05) by all seed bacterization treatments. However, the highest protective effect was obtained by the strain SG1, which reduced the disease severity index from 77.8% to 16%, whereas it was only reduced to 24.2% by chemical seed treatment with Dividend®. Moreover, strain SG1 led to significant increases in the shoot length, root length and dry weight of plants, thus opening up interesting perspectives for possible exploration in crop enhancement.

Cropping System Diversification Reduces Severity and Incidence of Soybean Sudden Death Syndrome Caused by Fusarium virguliforme.

Current management of sudden death syndrome (SDS) of soybean, caused by Fusarium virguliforme, focuses on planting resistant varieties and improving soil drainage; however, these measures are not completely effective. A 6-year study evaluated the effects of cropping system diversification on SDS and soybean yield. SDS, root health, yield, and F. virguliforme density in soil were assessed in a naturally infested field trial comparing a 2-year cropping system consisting of a corn-soybean rotation and synthetic fertilizer applications with 3- and 4-year cropping systems consisting of corn-soybean-oat + red clover and corn-soybean-oat +alfalfa-alfalfa rotations, respectively, with both manure and low synthetic fertilizer rates. In 5 of 6 years, SDS incidence and severity were lower and yield higher in the 3- and 4-year systems than in the 2-year system. SDS severity and incidence were up to 17-fold lower in the diversified systems than in the 2-year system. Incidence and severity of SDS explained 45 to 87% of the variation in yield. Plants in the 2-year system generally showed more severe root rot and lower plant weights than plants in the diversified systems. F. virguliforme density in soil was up to fivefold greater in the 2-year system compared with the 4-year system. The processes responsible for the suppression of SDS and yield protection in the diversified cropping systems still need to be determined.

Characterization and Chemical Control of Neopestalotiopsis rosae the Causal Agent of Strawberry Root and Crown Rot in Egypt

Strawberry (Fragaria x ananassa Duch.) is a widely grown vegetable crop in Egypt. During a routine survey,wilt and root rot symptoms were observed on strawberry plants cv. Festival. Samples were collected and isolation was done on potato dextrose agar (PDA) medium. The frequently isolated fungi were Pestalotiopsis spp. along with other associated fungi. Koch’s postulates were fulfilled against two strawberry cultivars Fortuna and Festival under greenhouse conditions. Pestalotiopsis fungal isolates were identified by amplification and sequencing of ITS, TEF-1α and β-tubulin gene regions. The BLASTn search of GenBank database revealed that all obtained sequences exhibited similarity of 99–100% to Neopestalotiopsis rosae. Four fungicides were evaluated against N. rosae through in vitro and in vivo trials. In vitro trials revealed that fungicides Thiram and Hymexazole inhibited the mycelial growth of N. rosae at concentrations 1000 and 1250 ppm, respectively. In vivo trials showed that Thiram reduced significantly disease severity of crown and root rot on both cultivars.

Diversity of Trichoderma species in chili rhizosphere that promote vigor and antagonism against virulent Phytophthora capsici

Abstract The oomycete Phytophthora capsici causes chili pepper (Capsicum annuum L.) blight that is extremely hard to control. In this work, the diversity of Trichoderma species from chili farms and their antagonistic activity against virulent strains of P. capsici were studied. The maximum likelihood phylogenetic analysis based on translation elongation factor 1α (TEF1α) locus revealed divergent evolution in the population structure of Trichoderma species exhibiting antagonistic activities against P. capsici. In vitro confrontation analysis revealed that Trichoderma harzianum, T. viride and T. reesei displayed over 85.5% inhibition of mycelial growth of P. capsici. Furthermore, soil application of Trichoderma species under greenhouse conditions effectively suppressed root–rot severity by 11.24–26.50% (P

Isolation and pathogenicity of Phytophthora species and Phytopythium vexans recovered from avocado orchards in the Canary Islands, including Phytophthora niederhauserii as a new pathogen of avocado

Root rot, caused by Phytophthora cinnamomi , is the most important disease of avocado, but few studies have determined whether other Phytophthora or oomycete species are involved in crop decline. Avocado orchards in the Canary Islands were surveyed for the presence of Phytophthora and Phytophthora -like oomycetes. Isolates obtained were identified morphologically and by sequence analysis of their internal transcribed spacer (ITS) regions, and their pathogenicity was tested by root and stem inoculation of avocado seedlings. Phytophthora species were isolated in 41 of 99 orchards sampled, and 10% of orchards were infected with more than one species. The species most frequently isolated was P. cinnamomi , which was detected in 26 orchards. In addition, P. multivora (ten orchards), P. niederhauserii (four orchards), P. nicotianae (four orchards), P. palmivora (one orchard) and Phytopythium vexans (20 orchards) were isolated. Phytophthora nicotianae and P. palmivora have been previously reported as pathogens of avocado, but P. niederhauserii, P. multivora and Pp. vexans are reported for the first time to be associated with this host. Phytophthora niederhauserii was the most virulent of these species. It was isolated from declining trees, and root rot severity was comparable to that caused by P. cinnamomi in two independent pathogenicity tests. In addition, P. niederhauserii caused cankers after stem inoculation. The pathogenicity results for P. multivora and Pp. vexans varied depending on isolates and pathogenicity tests. This study increases the knowledge of oomycetes associated with avocado, highlighting the potential threat posed by P. niederhauserii to this important fruit crop.