Saulo Alves Santos de Oliveira

Identification of passion fruit genotypes resistant to Fusarium oxysporum f. sp. passiflorae

This study aimed to characterize the resistance of 31 passion fruit (Passiflora sp.) genotypes to Fusarium oxysporum f. sp. passiflorae (FOP). About 20 seedlings of each genotype were inoculated by immersing the roots in a suspension of 106 macroconidia mL-1 for five minutes and then transplanting them into pots containing a mixture of soil and sterile substrate. They were evaluated daily for 120 days for the occurrence of wilt symptoms and death. These data were used to calculate the area under the disease progress curve, for survival analysis and grouping. The mortality rate ranged from 0 to 100% and the AUDPC ranged from 0 for genotypes without symptoms of the disease to 6,650.63 for the hybrid HFOP-01. Genotypes were classified into four subgroups: resistant, moderately resistant, susceptible and highly susceptible. The resistance was genotype dependent, but no significant variation was found between the purple and the yellow P. edulis.

Molecular fingerprinting of Fusarium oxysporum f. sp. passiflorae isolates using AFLP markers

Fusarium oxysporum f. sp. passiflorae W.L. Gordon (FOP) is one of the most important fungal pathogens of passion fruits. Understanding molecular variation of isolates from different areas is of utmost importance. Molecular fingerprinting on 14 isolates of FOP were conducted using AFLP molecular markers (Amplified Fragment Length Polymorphism), and their genetic variability were estimated. Twenty-five AFLP primer combinations were selected for amplification of FOP isolates and one for Fusarium oxysporum f. sp. cubense W.C. Snyder & H.N. Hansen (FOC), resulting in 99% polymorphic fragments, with an average of 40 fragments per primer combination. Specific fingerprints could be generated for most of the isolates evaluated; we observed a high power of discrimination of the AFLP primer combinations, with the presence/absence of up to 26 specific fragments per isolate. Thus, specific fingerprinting was obtained for 10 of the 15 isolates analyzed. The values of the polymorphic information content, the index and the resolving power of the markers showed wide variation and reflected the high informative contents of the primers used in the characterization of the FOP isolates. The FOP isolates were divided into four groups, irrespective of their geographic origins, with the allocation of 5, 7, 1 and 1 FOP isolates into Groups II, III, IV and V, respectively. A wide genetic diversity was observed in FOP isolates, which should be taken into consideration when implementing strategies for the improvement of passion fruit in the search for cultivars with multiple resistance to different isolates.

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.

Resistance to Fusarium dry root rot disease in cassava accessions

The objective of this work was to identify sources of resistance to dry root rot induced by Fusarium sp. in cassava accessions. A macroconidial suspension (20 µL) of 11 Fusarium sp. isolates was inoculated in cassava roots, from 353 acessions plus seven commercial varieties. Ten days after inoculation, the total area colonized by the pathogen on the root pulp was evaluated by digital image analysis. Cluster analysis revealed the presence of five groups regarding resistance. The root lesion areas ranged from 18.28 to 1,096.07 mm2 for the accessions BGM 1518 and BGM 556, respectively. The genotypes BGM 1042, BGM 1552, BGM 1586, BGM 1598, and BGM 1692 present the best agronomical traits.

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 rDNAs 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.

First report of Colletotrichum theobromicola and C. siamense causing anthracnose on cultivated and wild cassava species in Brazil

Cassava is an important staple food crop in Brazil. Surveys were conducted during three seasons (2014 to 2016) to collect symptomatic stem and leaf samples of cultivated cassava in the Reconcavo Region of Bahia, northeastern Brazil. Additionally, samples from 10 germplasm accessions of wild cassava species were also collected. Symptomatic tissues were disinfested with 70% ethanol (30 s), 0.5% sodium hypochlorite and then washed with sterilized distilled water three times, plated on PDA and incubated at 24 °C for 7 days, (12h photoperiod). A total of 94 isolates of Colletotrichum sp. were obtained from cultivated cassava and 15 from wild species. The genetic diversity of the isolates was accessed by rep-PCR (Mahuku and Riascos, 2004), with the formation of three groups: ‘group 1’ with 101 isolates closely related with C. gloeosporioides and C. fructicola and groups ‘2 and 3’ with no correspondence with previous reported species, with five and three isolates, respectively. Four isolates (PPAM 08, PPAM 15, A...

SOURCES OF RESISTANCE TO Fusarium oxysporum f. sp.cubense IN BANANA GERMPLASM

Fusarium wilt (syn= Panama disease), caused by Fusarium oxysporum f. sp. cubense (FOC), is one of the most destructive diseases of banana, being genetic resistance the main management strategy for this disease. Since the pathogen is constantly evolving to supplant the genetic resistance, new sources of resistance must be investigated by genetic improvement programs aiming to developing new varieties. The objective of the present study was to identify sources of resistance from the different accessions maintained in the banana active germplasm bank (BAGB) at Embrapa Mandioca e Fruticultura. Forty-one BAGB accessions were evaluated, including 17 diploids, 21 triploids, and two tetraploids. The area under the disease progress curve, disease index, and incubation period were also evaluated. In relation to FOC resistance, there is genetic variability available among the BAGB accessions. The genotype M53 is notable for the complete resistance it expressed, and the accessions Birmanie, PA Songkla, Pirua, Imperial, Poyo, Ambei, Walebo, and Kongo FRF 1286 expressed quantitative resistance.

Diversidade genética de Xylella fastidiosa em regiões produtoras de citros na Bahia

O objetivo deste trabalho foi avaliar, por meio de marcadores SSR, a diversidade genetica de Xylella fastidiosa no Estado da Bahia. Foram estudadas duas das principais regioes produtoras de citros no Estado, o Litoral Norte e o Reconcavo Sul. Para fins comparativos, utilizaram-se dez amostras provenientes do Estado de Sao Paulo. Foram empregados os seguintes iniciadores: ASSR20, OSSR9, OSSR17, CSSR4, CSSR12 e CSSR20, dos quais os quatro ultimos permitiram identificar 22 loci polimorficos. As populacoes de X. fastidiosa presentes em citros no Estado da Bahia apresentam elevada diversidade genetica, com base nos marcadores SSR, com pools genicos distintos e agrupamento geografico. No Litoral Norte, as populacoes do isolado apresentam maior diversidade genetica do que as da regiao do Reconcavo Sul da Bahia.

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

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.

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.