Cassava root rot disease is caused by a complex of soil-borne pathogens and has high economic impacts because it directly affects the tuberous roots, which are the main commercial product. This study ...aimed to evaluate cassava genotypes for resistance to root rot disease in a field with a previous history of high disease incidence. It also aimed to identify possible genomic regions associated with field resistance based on genome-wide association studies. A total of 148 genotypes from Embrapa Mandioca and Fruticultura were evaluated over two years, including improved materials and curated germplasms. Analysis of phenotypic data was conducted, as well as a genomic association analysis, based on the general linear model, mixed linear model, and fixed and random model circulating probability unification. The observed high disease index (ω) was directly correlated with genotype survival, affecting plant height, shoot yield, and fresh root yield. The genotypes were grouped into five clusters, which were classified according to level of root rot resistance (i.e., extremely susceptible, susceptible, moderately susceptible, moderately resistant, and resistant). The 10 genotypes with the best performance in the field were selected as potential progenitors for the development of segregating progenies. Estimates of genomic kinship between these genotypes ranged from -0.183 to 0.671. The genotypes BGM-1171 and BGM-1190 showed the lowest degree of kinship with the other selected sources of resistance. The genotypes BGM-0209, BGM-0398, and BGM-0659 showed negative kinship values with most elite varieties, while BGM-0659 presented negative kinship with all landraces. A genome-wide association analysis detected five significant single nucleotide polymorphisms related to defense mechanisms against biotic and abiotic stresses, with putative association with fresh root yield in soil infested with root rot pathogens. These findings can be utilized to develop molecular selection for root rot resistance in cassava.
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.
One of the main limiting factors in banana production is the fungus
Fusarium oxysporum
f. sp.
cubense
(
Foc
), the causal agent of Fusarium wilt. The objective of this work was to evaluate 23 diploid ...and eight tetraploid banana hybrids developed by Embrapa, for resistance to Fusarium wilt race 1 in an artificially infested area. Scores of external and internal symptoms were transformed into a severity index. Additionally, the genotypes were agronomically characterized using selection indices to identify superior genotypes. Based on a combined analysis of the selection indices, three improved diploids were selected for their resistance to
Foc
race 1 and characteristics of agronomic interest, such as short height, more than 100 fruits per bunch and early cycle FAO (2018). Two tetraploids hybrids were selected, includes one Prata type and another of the Pacovan type.
Cassava (Manihot esculenta Crantz) is an important food security crop in many parts of the developing world. The crop's high yield potential and multitude of uses-both for nutrition and ...processing-render cassava a promising driver for the development of rural value chains. It is traditionally propagated from stem cuttings of up to 30 cm in length, giving a multiplication rate as low as 1:10. Propagating cassava traditionally is very inefficient, which leads to challenges in the production and distribution of quality planting material and improved cultivars, greatly limiting the impact of investments in crop breeding. The work described in the present study aimed to develop a seed treatment approach to facilitate the use of shorter seed pieces, increasing the multiplication rate of cassava and thus making the crop's seed systems more efficient. After several tests, formulation was identified, consisting of thiamethoxam 21 g ha-1, mefenoxam 1.0 g ha-1, fludioxonil 1.3 g ha-1, thiabendazole 7.5 g ha-1 and Latex 2% as a binder. Plant growing from seed pieces treated with this formulation displayed increased crop establishment and early crop vigor, leading to an improved productivity throughout a full growing cycle. This allowed to reduce the cassava seed piece size to 8 cm with no negative effects on germination and crop establishment, leading to yields comparable to those from untreated 16 cm pieces. This, in turn, will allow to increase the multiplication ratio of cassava by a factor of up to 3. Notably, this was possible under regular field conditions and independently of any specialised treatment facilities. Compared with existing seed production protocols, the increased multiplication rates allowed for efficiency gains of between 1 to 1.9 years compared to conventional five-year cycles. We believe that the technology described here holds considerable promise for developing more reliable and remunerative delivery channels for quality cassava planting material and improved genetics.
Cassava frog skin disease (CFSD) causes significant yield losses in cassava (
Manihot esculenta
Crantz). One issue with control is late diagnosis. The objective of this work was to test near-infrared ...spectrometry (NIRS) and compare calibration and classification models for early detection of CFSD. NIRS analysis was performed on 238 cassava accessions (120 healthy and 118 with CFSD). Six classification models were used: a support vector machine with a linear kernel (SVM), a Bayesian generalized linear model (BGLM), a parallel random forest (PRANDF), an extreme learning machine (ELM), a high dimensional discriminant analysis (HDDA), and a partial least squares (PLS) model. Their predictive abilities were evaluated based on their accuracy and agreement (based on Cohen’s Kappa coefficient). The models demonstrated high efficiency at distinguishing diseased and healthy accessions, with an overall accuracy >80%. The Cohen’s Kappa coefficient values (0.83–0.98) for four of the models (the SVM, BGLM, PRANDF and PLS) indicated that there was almost perfect agreement between their classification results. The SVM and BGLM models exhibited high accuracy (99.07 and 98.92%, respectively) and reproducibility (both 0.98) in classifying the accessions according to their CFSD status. NIRS is a viable alternative for the detection of CFSD with the advantages of early and accurate detection, high speed and low cost compared to traditional diagnostic methods.
Modifications were made in the PCR conditions aiming to overcome the problem of non-amplification of the Xanthomonas phaseoli pv. manihotis (Xpm) fragment, using the primer pair XV / XK described in ...the literature. The objective of this study was to propose changes in the primers already described (XV / XK_MOD) and validate the use of these new primers in identifying Xpm. The validation procedure was carried out with the primer pair XV and XK_MOD, using different strains of Xpm, other plant pathogenic and endophytic bacteria genera and one isolate of X. phaseoli pv. passiflorae. As a control, additional reactions were conducted in multiplex with the universal primers for the 16S rRNA gene of the bacteria together with XV / XK and XV / XK_MOD. Using the forward primer (XV) described in the literature together with the modified reverse primer (XK_MOD), it was possible to achieve amplification from DNA extracted from in vitro cultures and from infected tissue, but no amplification was noticed for the primer pair described in the literature, confirming the effectiveness of the proposed modification.
BRS Rendeira and BRS Progresso are cassava (Manihot esculenta Crantz) cultivars with tolerance to post-harvest deterioration and high mean yields of fresh root (31.1 and 27.9 t ha-1) and starch (8.9 ...and 8.1 t ha-1) in annual production cycles. Both new varieties are recommended for the flour and starch industry.
A survey to investigate the occurrence of cassava anthracnose disease (CAD) and distribution of
Colletotrichum
spp. in cassava plantations in different eco-zones of the Reconcavo Region in Bahia, ...Brazil, investigated during the rainy season of 2014. A total of 50 cassava fields distributed among 18 municipalities were visited and intensity of anthracnose evaluated. The highest disease incidence (DI) (83.3%) was in samples collected in São Félix, and the lowest (34.4%), in Varzedo. Municipalities that presented the highest values for DI were located within the ‘
Af
’ Köppen–Geiger eco-zone, also presenting the highest values for the estimated McKinney disease index. Based on previous studies of multilocus phylogeny, seven different species of
Colletotrichum
were identified (
Colletotrichum fructicola
,
Colletotrichum tropicale
,
Colletotrichum gloeosporioides
s.s,
Colletotrichum theobromicola
,
Colletotrichum siamense
,
Colletotrichum brevisporum
and
Colletotrichum plurivorum
) and a new approach based on ERIC-PCR was used aiming to group the 82 isolates according to these findings. The highest percentage of genetic variance (> 78%) was among isolates within fields. Based on the survey and genetic analysis,
C. fructicola
is probably the main causal agent of cassava anthracnose in the Recôncavo Region, since this species was present with highest incidence in all eco-zones, 47.61, 42.86 and 57.14% for
Af
(tropical rainforest climate),
As
(tropical dry savanna climate) and
Aw
(tropical wet savanna climate), respectively. This study is the first report of
C. fructicola
lineages as the most likely pathogen causing anthracnose disease of cassava in Brazil, and these findings may be used to guide the selection of resistant varieties.
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, Paraíba, Maranhão, Tocantins, and Paraná. 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.
•Diploids Jaran, Birmanie, Pipit, and Malaccensis are options to use in crosses with elite cultivars.•Simple Sequence Repeat markers (SSR) detected genetic variability among the Genotypes.•SSR ...markers contribute to improve strategies to develop banana genotypes resistant to Fusarium oxyxporum f. sp. cubense (Foc) race 1.•Correlation between the disease index in the field and greenhouse data was 0.85 (p ≤ 0.001).
The objectives of this work were to identify banana genotypes resistant to Fusarium wilt race 1 and to estimate the genetic diversity among these genotypes using SSR markers, with the goal of selecting progenitors for future crosses aiming resistance. The experiment was conducted in an artificially infested field with the pathogen and under greenhouse conditions with inoculated plantlets. For the environmental control tests, the genotypes were inoculated with 10 g of inoculum (106 UFC mL−1) distributed in four holes around the plantlets. Disease indices (DI) were calculated for the field and greenhouse experiments, and the area under the disease progress curve (AUDPC) was calculated for the greenhouse experiment. Genotypes resistant to Fusarium wilt race 1 were identified, including four diploids that can be used in crosses with elite susceptible cultivars. The correlation between the DI in the field and greenhouse data was 0.85 (p ≤ 0.001), which allows us to infer about the efficiency of the early selection method. To our knowledge, this is the first work that compares field and greenhouse methodologies to select Musa spp. genotypes resistant to this pathogen. The SSR markers detected genetic variability among the genotypes, which will contribute to improvement strategies to develop Foc resistant cultivars.
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