Cassava Root Rot Research Articles

Culture medium and inoculation methodology for the study of soft root rot caused by Phytopythium sp.

ABSTRACT: Cassava (Manihot esculenta Crantz) is an important crop in Brazil and Pará is the major producer of roots. High temperature and humidity of tropical regions favor the development of various diseases, among them the cassava root rot. The objective of this study was to evaluate the effect of luminosity and culture medium on the mycelial growth and sporulation of Phytopythium sp. associated with different methods of inoculation on cassava roots. In vitro tests for pathogen growth were established in a 2 x 6 factorial design (luminosity x culture medium) with five replicates and the means were compared by t test (P≤0.05). The culture medium containing sweet cassava root produced greater mycelial development and higher pathogen sporulation and it was the most suitable medium for pathogen culture. The culture under absence of light generated better mycelial growth than culture under 12 hour of light. Regarding the type of inoculation, the response was better when deeper injuries were induced.

Methodologies for selecting cassava with resistance to dry and black root rot under controlled conditions

ABSTRACT Cassava root rot diseases such as dry and black root rot are listed among the major threats, since its affect the main product (tuberous roots), causing a progressive decline in yield and affecting subsequent crop cycles, being the use of resistant varieties the most reliable control measure on field level. The objective of this study was to identify inoculation methods for the early evaluation of genotypes, considering the level of resistance to dry (DRR) and black (BRR) root rot diseases. Different methodologies and plant tissues were evaluated, based on the immersion of cassava tissues (roots and stem cuttings), soil infestation, and inoculation of detached tissues (leaves, tuberous roots and stem cuttings). The following parameters were evaluated for inoculations based on tissue immersion: disease index (ω); aerial part weight (g); fresh weight of the roots (g); and volume (cm3). For the inoculations on detached tissues, the percentage of lesioned area was determined. Immersion methods for roots and lesioned stems did not show typical symptoms of DRR and BRR during the two-month evaluation period. The soil infestation method did not differ from the stem immersion method as to the reduction of aerial part weight and the disease index, whereas both can be recommended for resistance selection trials. There was a positive correlation between the BRR and DRR data for the stem inoculation (r = 0.94, p = 0.001) and for DRR in the peel and root pulp (r = 0.73, p = 0.05). Therefore, the resistance within each tissue is apparently independent and should be compared with the behavior of the genotypes in the field.

Identification of fungi causing cassava root and stem rot disease isolated in Thailand

Identification of fungi causing cassava root and stem rot disease isolated in Thailand

First Report of Phytopythium sp. Causing Storage Root Rot and Foliage Blight of Cassava in Brazil

First Report of <i>Phytopythium</i> sp. Causing Storage Root Rot and Foliage Blight of Cassava in Brazil

Genome-wide association study for resistance to cassava root rot

SUMMARYCassava root rot (CRR) disease associated with a complex of soil pathogens has caused great yield losses in the crop. The objective of the current work was to obtain insights about the genetic architecture of CRR resistance caused byFusarium(dry root rot – DRR),Phytophthora(soft root rot – SRR) and Botryosphaeriaceae (black root rot – BRR) species, using genome-wide association studies (GWAS). Phenotyping data of 263 accessions (artificial inoculation) and 14 094 single-nucleotide polymorphisms (SNP) (missing data &lt;0·10 and minor allele frequency &gt;0·05) were used. The severity of CRR in peel and pulp was variable among accessions, but the pathogens that caused DRR were more aggressive. Broad-sense heritability ($h_g^2 $) was of medium magnitude for all groups of resistances for pathogens, with variation from 0·16 ± 0·019 (Fspp Pulp) to 0·31 ± 0·028 (Fspp Peel). The kinship matrix was used to correct for stratification as well as for clustering the accessions. Overall, this analysis showed that there was no relationship between agronomic traits and resistance to CRR and the four clusters obtained from kinship matrix. The GWAS identified 38 significant SNPs, of which eight and 22 are related to the severity of DRR in the pulp and peel, respectively. The other eight SNPs were associated with SRR-peel (1), SRR-pulp (1), BRR-peel (3) and BRR-pulp (3). Half of the SNPs associated with CRR resistance have functional annotations related to defence and response to pathogen attack as well as general cellular processes. The current study revealed that resistance to CRR is controlled by multiple loci with small effects, and significant SNPs can be used to identify putative genes that control these traits.

FAMES AND MICROBIAL ACTIVITIES INVOLVED IN THE SUPPRESSION OF CASSAVA ROOT ROT BY ORGANIC MATTER

ABSTRACT The incorporation of organic matter has been used to manage of diseases caused by soilborne pathogen, but there is a gap in the use of coffee residues on disease supressiveness. The objective of this study was to evaluate the effect of organic matter sources against cassava root rot caused by F. solani CFF109. Fertilization with coffee residue (CR), cattle manure (CM), earthworm excrements (EE) and goat manure (GM) resulted in suppression of cassava root rot. The treatments of CR and CM presented higher reduction in the cassava disease severity. There were changes in the soil microbial community structure by organic matter incorporation, mainly in total fungi and Gram-negative bacteria populations. The total organic carbon and magnesium are negatively associated with disease severity. The microbial quotient, alkaline and acid phosphatase activities were positively and the biomarker a-15:0 was negatively associated with disease severity. This study indicated that agro-industrial residues can be recycled for providing organic matter and nutrients with effect for management of plant diseases by suppressing soilborne pathogens. This is the first evidence that the industrial residue of coffee can be use in the management of cassava root rot, caused by F. solani.

Selection of cassava accessions with multiple resistance to pathogens associated with root rot disease

Cassava root rot disease (CRRD) severely affects productivity in several countries. The objective of this study was to estimate genetic parameters and to identify multiple resistance sources against pathogens associated with CRRD. The symptoms caused by Fusarium spp., Phytophthora spp., and Botryosphaeriaceae species in peel and pulp from the roots were evaluated in 277 accessions using a whole tuberous root inoculation method. The resistance data were obtained by REML/BLUP (restricted maximum likelihood/best linear unbiased predictor). The classic selection index (CI), multiplicative (MI), and sum of ranks (SRI) were used to identify the accessions with multiple resistance. For all pathogens, the environmental variance ( $$\sigma_{e}^{2}$$ ) was the most important component. Individual heritability $$\left( {h_{g}^{2} } \right)$$ was of low magnitude for resistance to most pathogens (0.16 ± 0.02—peel and 0.31 ± 0.03—pulp for Fusarium spp.; 0.26 ± 0.03—peel and 0.30 ± 0.03—pulp for Phytophthora spp.; and 0.28 ± 0.03—peel and 0.27 ± 0.03—pulp for Botryosphaereacea species). The distribution of CRRD symptoms indicated the presence of quantitative inheritance. The direct selection of the 15 more resistant accessions based on the genotypic predicted values result in high reductions of disease (>50%). However, there was a low matching rate of the most resistant accessions for each pathogen and the different parts of the tuberous roots (peel and pulp). The CI and MI were the most promising compared to the SRI to ensure high and balanced resistance for each pathogen. Understanding the genetic basis of resistance to CRRD and the identification of sources with multiple resistance may be useful in various management strategies to control the disease.

Survey of fungi associated with cassava root rot from different producing regions in Brazil

Although root rot is one of the major diseases affecting Brazilian cassava (Manihot esculenta Crantz.), little is known about the diversity of root rot pathogens. In this study, diseased plants exhibiting root rot symptoms were collected from cassava-producing regions in five Brazilian states: Bahia, Sergipe, Paraiba, Maranhao, Tocantins, and Parana. Seventy isolates were obtained and assigned to species complexes based on rDNA's ITS (internal transcribed spacer of the ribosomal DNA) region (ITS1, ITS2 and 5.8S). A total of seven species complexes was found belonging to the genus Fusarium (56/74), followed by Lasiodiplodia (8/74), Neoscytalidium (6/74), and Diaporthe/Phomopsis complex (2/74), Phytophthora, and Corallomycetella (1/74 each). These species were distributed differently according to sample locations and states, but overall, the F. solani species complex (FSSC) was the most prevalent. A number of phylogenetic lineages had not been previously reported as being associated with cassava-root rot disease, such as: F. graminearum (FGSC), F. incarnatum-equiseti (FIESC) and F. chlamydosporum (FCSC) complexes, and a phylogenetic lineage most closely related to P. phaseolorum. Results suggest the need to improve knowledge of the species associated with cassava, including multilocus phylogeny for a more specific characterization, and differences in the resistance background associated with these species, as a strategy to incorporate resistance to multiple pathogens in cassava breeding programs.

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.

Sources of resistance to cassava root rot caused by Fusarium spp.: a genotypic approach

The development of cassava cultivars resistant to root rot (PRM) is a viable strategy for disease control. The objectives of this study were to identify stable sources of PRM resistance and to estimate genetic parameters. Inoculation with Fusarium spp. (Fspp) species was performed in 697 accessions and five environments that were then assessed for symptom severity in the peel (cortex and periderm) and root pulp. The environment and genotypes was considered to have random effects via analysis of mixed models. The resistance stability, resistance adaptability, and resistance stability + adaptability for Fspp were assessed using the harmonic means of genotypic value (Si), relative performance of genotypic values (Ai), and harmonic mean of the relative performance of genotypic value (Zi), respectively. About 10 % of the accessions were considered resistant to Fspp. Discrepancies in the accession classification for PRM resistance in the root peel and pulp indicate the existence of different defense mechanisms in these parts of the root. The individual heritability and mean genotypic heritability through environments were of low magnitude, resulting in medium accuracy selective magnitude. Despite the existence of strong genotype × environment interaction (G × E), accessions with high adaptability and stability were identified. The 22 accessions resistant to PRM in the peel and pulp enabled significant and balanced disease reduction on Zi estimates (−48.18 and −46.42 %, respectively). The lack of complete resistance and continuous distribution of PRM suggest quantitative inheritance of resistance. The Zi method is a useful approach in the capitalization of G × E interaction for disease resistance.

First report of Phytophthora melonis causing cassava wilt and root rot in Bahia State, Brazil

Cassava (Manihot esculenta Crantz.) is a major source of carbohydrates for millions of people in several regions, particularly in developing countries. An important component of the low productive performance of cassava in different Brazilian regions is the occurrence of disease, such as cassava root rot (CRRD). The CRRD complex is one of the most destructive diseases worldwide and can lead to total crop failure. During 2013-2015, a survey was conducted to determine the species involved in the cassava root rot complex in Brazil, and a total of 110 isolates were obtained from different regions, which belonged to different pathogen species. In February 2014, a typical isolate of Phytophthora sp. (CBPPR3001) was obtained from plants in one of the maintenance areas of the Brazilian Cassava Germplasm (located at “Embrapa Mandioca e Fruticultura”, Cruz das Almas, Bahia State, Brazil). Root rot symptoms consisting of soft irregular brown patches occurred on tuberous roots, with tissue collapse, bad smell, and affected plants exhibiting wilt and partial defoliation (Figure 1A). For the isolation procedure, diseased root tissue was cut into 0.5-cm pieces, washed in distilled water, soaked in a solution of 0.5% sodium hypochlorite for 3 min, placed on Petri dishes with Corn-Meal Agar (HiMedia Laboratories), added of ampicillin and rifampicin, and incubated at 25±2°C for 7 days. Sporangia were ovoid to pyriform, 27.5 to 54.7 × 20.5 to 41.6 μm, average 38.3 × 30.4 μm (n=50), with one or occasionally two papillae. Chlamydospores were spherical, 20.2 to 30.0 μm in diameter, average 25.1 μm. Pathogenicity was confirmed in detached roots and leaves inoculated by depositing 5 mm plug of V8-medium with structures of the pathogen on the wounded tissue, and ten replicates per treatment. Both were incubated in a moist chamber at 25 °C and symptoms appeared after 3 to 5 days. No symptoms were observed on negative controls inoculated with V8-medium plug. The DNA was extracted by CTAB protocol and the ITS rDNA sequence was generated with the primer pair ITS1/ITS4 (Figure 1B). The sequence (GenBank Accession No. KT211567) was used in BLAST search in GenBank and >99% similar to P. melonis. Phylogenetic studies were conducted based on neighbor-joining analysis and Bayesian inference for the ITS rDNA region (ITS1, 5.8S and ITS2) matched with the ex-type strain CBS 582.69 (HQ643283), with 99% similarity (E-value = 0.0) and 100% similarity (E-value = 0.0) with the isolate P12 (AY739021). P. melonis associated with cassava root rot was first described in 2004 in plants from Manaus (AM), Northern Region of Brazil, but this is the first report of this pathogen causing CRRD in Bahia State, where until now, only P. dreschsleri and P. palmivora had been found causing this disease. The presence of different Phytophthora species must be investigated since management strategies, such as resistant variety, can be different regarding the pathogen species.

Exploration on Soil Actinomycetes Against Phytophthora sp. Causing Root Rot of Cassava and Plant Growth Promoting Activities

Exploration on Soil Actinomycetes Against Phytophthora sp. Causing Root Rot of Cassava and Plant Growth Promoting Activities

English

Root rot diseases constitute a major constraint to cassava production in Cameroon. However, not much is known about the identity of pathogens associated with them. It is in this light that this study was realized with the aim of characterizing the various root rot diseases and identifying their associated fungal causal agents in Cameroon. Sixty four cassava stems with root rot symptoms were sampled in the Littoral, Southwest and West Regions of Cameroon. Results revealed that cassava root rot (CRR) is either wet (soft) or dry depending on the region of study. Isolation was done on PDA medium enriched with Chloramphenicol. After purifying thrice on the PDA medium, 20 isolates were collected. Identification with the help of the Barnett and Hunter key revealed the existence of seven fungi including Colletotrichum sp., Fusarium sp., Pestalotia sp., Geotrichum sp., Sphaerostilberepens, Trichoderma viride and Botryodiplodia theobromae. Key words: Cassava root rot, pathogen, sustainable agriculture, disease control.

New occurrences of Botryosphaeriaceae causing black root rot of cassava in Brazil

Despite the occurrence of several diseases of cassava, the cassava black root rot (CBR) represents one of the main limiting factor for crop rentability in the world. However, the etiology of CBR is complex and it needs to be revised based on current molecular analysis. On this work, molecular and morphological studies allowed for the identification of three species of Botryosphaeriaceae causing black root rot disease of cassava in the states of Maranhao and Paraiba, Brazil, namely: Lasiodiplodia euphorbicola, Lasiodiplodia pseudotheobromae and Neoscytalidium hyalinum. This is the first report of these three fungal species as causal agents of CBR in the world.

English

Sandy soils of 19 arable fields were analyzed for disease suppressiveness against root rot disease of cassava, caused by Fusarium solani CFF109. Analysis of chemical, physical, biochemical, microbial population and activity, and soil characteristics were assessed. Soils with different management histories and covers most commonly found in the region were collected to build a greenhouse experiment, to evaluate the natural suppressiveness of soils against cassava root rot. The severity was submitted with all data across correlation and multivariate analyses to find correlation between disease suppressiveness and abiotic or biotic soils attributes. Differences in disease suppressiveness were found between the treatments for cassava root rot. Significant disease suppression was found in 37% of the soils. The sandy soil covered with consortium of Zea mays + Vigna unguiculata was the most efficient in suppressiveness against disease caused by F. solani. The data indicated significant correlation between soil characteristics and suppressiveness cassava root rot. The soil supressiveness against cassava root rot was favored by increase by total bacteria, fluorescent group bacteria populations and activity of acid and alkaline phosphatase and β-glucosidase. Key words: Disease suppression, soil characteristics, enzyme activity, soil communities, abiotic factor, biotic factor.

Effect of biocontrol agents and biofertilizers on root rot, yield, harvest index and nutrient uptake of cassava (Manihot esculanta Crantz)

Cassava is an important subsidiary food and industrial raw material in the tropics. Root rot disease, caused by Phytophthora palmivora, poses a serious threat to cassava cultivation in Tamil Nadu, India. Field experiments (2008–09) were conducted to study the effect of biocontrol agents (Trichoderma spp. and Pseudomonas fluorescens) and biofertilizers (Azospirillum, vesicular–arbuscular mycorrhizal fungi and phosphorus-solubilizing bacteria) on root rot, yield, harvest index and nutrient uptake of cassava at two NPK rates. The design of the experiment was a split plot with two NPK rates, recommended and 50% recommended rate, as the main plot treatments and five biocontrol agents and biofertilizers as subplot treatments. The results clearly indicated that use of a bioinoculants consortium significantly reduced root rot infection/disease incidence over uninoculated controls. Azospirillum significantly improved the yield of cassava at 50% of the recommended rate of NPK. NPK rates had no significant impact on harvest index of cassava and Trichoderma and vesicular–arbuscular mycorrhizal fungi resulted in a higher harvest index even at 50% of the recommended NPK rate. Nitrogen, phosphorus and potassium uptake was significantly improved when treated with biofertilizers and/or a consortium.

Effects of microbial inoculations on soil chemical, biochemical and microbial biomass carbon of cassava (Manihot esculenta Crantz) growing Vertisols

Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P2O5:K2O (NPK) rate (50:25:50 kg ha−1) significantly increased soil available nitrogen (142.81 kg ha−1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha−1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g−1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g−1 soil h−1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g−1 soil) and β-glucosidase activity (48.82 μg PNP g−1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g−1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.

English

In Nigeria cassava root rot causes serious yield losses in cassava tuber production every year. However, the influence of root rot incidence on cassava genotype at harvest on consumers’ acceptability of the gari produced from it has not been studied. A sensory evaluation was conducted on gari processed from the tuberous root yield of rot susceptible TME-1 and improved TMS 30572, harvested at 12 months after planting at Sabongidda-Ora (humid forest eco-zone) of Nigeria during the 2003 and 2004 cropping seasons. A 5-point hedonic scale ranging from like extremely, through neither like nor dislike, to dislike extremely was designed to measure the degree of liking for the gari processed from both genotypes. 28 panelists were asked to indicate their degree of preference for the colour, odour and taste of each gari sample by choosing the appropriate category in the hedonic scale. The results were compared with the tuberous root rot incidence and severity of genotypes in the field. All experiments were repeated and the data collected were statistically analysed using the general linear model statistical procedures with the SAS system for windows. Comparisons among treatment means was done with the least significant square, with the Duncan multiple range test (P = 0.05). Variety TME-1 with the highest root rot incidence and severity of 53 and 21% respectively was less preferred for gari colour, texture and odour compared to TMS 30572 which had 15 and 6% rot incidence and severity respectively. In the second year trial where TME-1 still possessed the highest rot incidence and severity, panellists still showed more preference for the colour, taste and odour in TMS 30572 gari than TME-1 gari. All the differences observed and reported above between TMS 30572 and TME-1 were significantly different at probability 0.05%. The results of this experiment clearly show that high root rot incidence of a cassava genotype in the field can reduce consumer’s acceptability of the gari produced from it.

ROOT ROT RESISTANCE IN NEW CASSAVA VARIETIES INTRODUCED TO FARMERS IN NIGERIA

SUMMARYIn 2004 and 2005 through field trials in over 2500 locations in several agroecological zones, 40 new cassava varieties were introduced in Nigeria. The trials were managed by scientists, extension workers and farmers. The aim in introducing these new varieties was to pre-emptively manage cassava mosaic disease, to avert an imminent threat from the Ugandan strain of the pathogen and prevent damage to the Nigerian cassava economy. From these trials, 10 new varieties were selected and officially released for high root yield, high dry matter content and acceptability for food, industry and livestock. Cassava root rot is a major source of yield loss in Nigeria, especially where farmers practice late harvest because they wait for a good price from the market before harvest and sales. This paper investigated how the 40 varieties together with three old improved varieties currently in farmers' fields during the formal trials responded to root rot disease. No absolutely resistant variety was found, indicating that early harvest (9–11 months after planting) is still the best way to reduce losses from root rot. Root rot is also significantly (p ≤ 0.05) influenced by genotype and environment interaction. Most root rot was recorded in the humid forest and the least was in the Sudan savanna agroecological zone. Using a rank-sum method, the 43 varieties were separated into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible classes.

English

The effective in vitro screening tests of Trichoderma viride for antagonism against post harvest pathogens of cassava roots (Manihot esculenta Crantz) rot together with its competitive and mycoparasitic abilities informs its selection as the most promising candidate for the biocontrol of post harvest cassava root rot pathogens. While the percentage germination of the spores were observed to increase with increasing dilution of the culture filtrate (100, 50, 25, and 10% ) at a concentration of 20,000 spores/ml, the percentage rot recorded amongst the untreated cassava roots ranged from 4% (Rhizopus oryzae) to 44% (Aspergillus flavus). Treatment with the antagonist and the subsequent storage resulted in a remarkable reduction in the frequency of occurrence of the normal root surface mycoflora and the pathogens over a 3 weeks storage period. Botryodiplodia theobromae and R. oryzae were isolated only in the first week of storage and at a frequency of 3 and 2% rot, respectively, after treatment whereas A. flavus and Fusarium solani persisted throughout the whole storage period with 2 and 3% rot on the third week, respectively. The observed results suggest that T. viride is root surface competent and highly antagonistic.