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GENETIC SIMILARITY OF Macrophomina pseudophaseolina ISOLATES ASSOCIATED WITH WEEDS IN THE BRAZILIAN SEMIARID REGION

SIMILARIDADE GENÉTICA DE ISOLADOS DE Macrophomina pseudophaseolina ASSOCIADOS A PLANTAS DANINHAS NO SEMI-ÁRIDO BRASILEIRO

ABSTRACT

Macrophomina pseudophaseolina has recently been reported in association with weeds in melon producing areas in Northeastern Brazil. Species from this genus are the causal agents of root rot and vine decline (RRVD) in melon, reducing its productivity. It is needed to know the genetic variability of the pathogen to develop effective control methods. Thus, this work aimed to assess the genetic diversity among M. pseudophaseolina isolates collected from the weeds Trianthema portulacastrum L. and Boerhavia diffusa L. using ISSR and RAPD markers. For this, 41 M. pseudophaseolina isolates were submitted to amplification with five ISSR and ten RAPD primers. Genetic similarity was analyzed using the Jaccard’s coefficient and cluster analysis was performed by the UPGMA method. Combining data from both markers, the 41 isolates were separated into eight groups. Most groups were not arranged according to geographical origin and host of the pathogen. The genetic similarity among isolates ranged from 0.15 to 0.87. On the other hand, the highest genetic dissimilarity (85%) was observed between the isolate MpBr11, collected from T. portulacastrum in Icapuí (CE), and MpBr65, collected from B. diffusa in Assú (RN). Results obtained herein can assist breeding programs for the selection of resistance sources and the development of effective control methods against RRVD in melon.

Keywords:
Genetic variability; RAPD; ISSR; Melon

RESUMO

Macrophomina pseudophaseolina foi recentemente relatada em áreas produtoras de melão em associação com plantas daninhas na região Nordeste. Espécies do gênero são agentes da podridão radicular e declínio das ramas (PRDR) do meloeiro, doença que reduz sua produtividade. O conhecimento da diversidade genética do patógeno é importante no desenvolvimento de métodos de controle eficientes. Nesse contexto, o objetivo desse trabalho foi analisar a variabilidade genética de isolados de M. pseudophaseolina coletados das plantas daninhas Trianthema portulacastrum L. e Boerhavia diffusa L. por meio dos marcadores moleculares ISSR e RAPD. Para isto, 41 isolados de M. pseudophaseolina foram submetidos à amplificação com cinco iniciadores ISSR e dez RAPD. A similaridade genética foi analisada através do coeficiente de Jaccard e o agrupamento obtido com o método UPGMA. Com a combinação dos dados dos marcadores os 41 isolados foram agrupados em 8 grupos principais. Não foi observado, para grande maioria dos grupos gerados, a relação do agrupamento de acordo com hospedeiro ou local de coleta. A similaridade genética entre os isolados variou de 0,15 a 0,87. A maior dissimilaridade genética (85%) foi observada entre o isolado MpBr11, coletado de T. portulacastrum no município de Icapuí/CE, do isolado MpBr65, coletado de B. diffusa em Assú/RN. Estas informações podem ser úteis para auxiliar programas de melhoramento genético na seleção de fontes de resistência e/ou em testes de métodos de controle contra PRDR do melão.

Palavras-chave:
Variabilidade genética; RAPD; ISSR; Melão

INTRODUCTION

Melon (Cucumis melo L.) is the second most produced cucurbit in the world (27.35 million tons) and Brazil ranks 11th among producing countries (FAO, 2020). Most of the national production is destined for export, generating an income of US$ 160 million (ABRAFRUTAS, 2019; ANUÁRIO, 2019).

The Northeast region accounts for 95% of the national production, mainly from the states of Ceará (CE) and Rio Grande do Norte (RN) (IBGE, 2020). Melon is adapted to the edaphoclimatic conditions of the region, such as high temperatures and radiation (MAIA; LIMA; LIMA, 2013MAIA, L. K. R.; LIMA, R. E. M.; LIMA, J. S. IMPORTÂNCIA DO MELOEIRO E ASPECTOS RELACIONADOS À RESISTÊNCIA A Rhizoctonia solani. ENCICLOPÉDIA BIOSFERA, 9: 1609-1622, 2013.), and the high technological level employed in the cultivation allowed its production to be intensified.

Continuous cropping and expansion of planted areas without effective disease management increased the incidence and severity of numerous pathologies in producing fields in the Northeast region (SALES JÚNIOR et al., 2019SALES JÚNIOR, R et al. Weeds as potential hosts for fungal root pathogens of watermelon. Revista Caatinga, 32: 1-6, 2019.). Root rot and vine declining (RRVD), caused by soilborne fungi species, limits melon production in the region (PORTO et al., 2019PORTO, M. A. F. et al. Interaction of Fusarium solani, Macrophomina phaseolina and Rhizoctonia solani as root rot pathogens of Cucumis melo. Summa Phytopathologica, 45: 355-360, 2019.; SALES JÚNIOR et al., 2012). Species from the genus Macrophomina are commonly reported as the causal agents of RRVD in producing areas in the Northeastern Brazil (NEGREIROS et al., 2019NEGREIROS, A. M. P. et al. Identification and pathogenicity of Macrophomina species collected from weeds in melon fields in Northeastern Brazil. Journal of Phytopathology, 167: 326-337, 2019.).

Macrophomina pseudophaseolina Crous, Sarr & Ndiaye, belonging to the phylum Ascomycota, family Botryosphaeriaceae, was reported by Sarr et al. (2014) as a new species from the genus Macrophomina that shares distribution characteristics and host range with Macrophomina phaseolina.

Moreover, species from the genus Macrophomina have been found in association with weed species in off-season cultivation of cucurbits in Northeastern Brazil (SALES JÚNIOR et al., 2012SALES JÚNIOR, R. et al. Ervas daninhas como hospedeiras alternativas de patógenos causadores do colapso do meloeiro. Revista Ciencia Agronômica, 43: 195-198, 2012.; 2019). Negreiros et al. (2019NEGREIROS, A. M. P. et al. Identification and pathogenicity of Macrophomina species collected from weeds in melon fields in Northeastern Brazil. Journal of Phytopathology, 167: 326-337, 2019.) reported M. pseudophaseolina associated with weed species such as Trianthema portulacastrum and Boerhavia diffusa in melon producing fields in states of CE and RN.

Associating with weeds and producing resistance structures, the pathogen can remain in producing areas for long periods (KAUR et al., 2012KAUR, S. et al. Emerging phytopathogen Macrophomina phaseolina: biology, economic importance and current diagnostic trends. Critical Reviews in Microbiology, 38: 136-151, 2012.). It is aggravated by the lack of tolerant cultivars and effective chemical control (GARCÍA et al., 2019GARCÍA, M. E. M. et al. Reaction of lima bean genotypes to Macrophomina phaseolina. Summa Phytopathologica, 45: 11-17, 2019.), which hampers the disease management by producers.

In this context, using resistant cultivars is the first strategy for integrated and sustainable disease management (ALMEIDA et al., 2014ALMEIDA, A. M. R. et al. Macrophomina phaseolina em soja. Londrina: Embrapa Soja, 2014. 55 p.). For the development of resistant cultivars, in addition to knowing the genetic diversity of the plant, it is needed to consider the pathogen’s degree of variability. High intraspecific diversity of the pathogen can influence the degree of resistance developed by plants (ZIVANOV et al., 2019ŽIVANOV, S. T. et al. Analysis of genetic diversity among Macrophomina phaseolina (Tassi) Goid. isolates from Euro-Asian countries. Journal of Plant Diseases and Protection, v. 126, 565-573, 2019.).

Studying genetic variability using PCR (Polymerase Chain Reaction)-based molecular markers is an efficient and practical method to assess the genetic diversity among phytopathogenic fungi species (PAPLOMATAS, 2004PAPLOMATAS, E. J. Molecular diagnostics for soilborne fungal pathogens. Phytopathologia Mediterranea, 43: 213-220, 2004.). Random Amplified Polymorphic DNA (RAPD) and Inter Simple Sequence Repeat (ISSR) are dominant markers that do not require prior knowledge of the genome to detect genetic variability among organisms. In addition, they are low-cost and time-saving methods for obtaining results (SOUZA, 2015SOUZA, D. C. L. Técnicas moleculares para caracterização e conservação de plantas medicinais e aromáticas: uma revisão. Revista Brasileira de Plantas Medicinais, 17: 495-503, 2015.; SINGH; SINGH; PANDEY, 2013SINGH, Y.; SINGH, J.; PANDEY, A. K. Molecular markers in diagnosis and management of fungal pathogens: a review. International Journal of Advanced Biotechnology and Research. 4: 180-188, 2013.).

To generate knowledge for assisting in the development of control methods against RRVD, this study aimed to assess the genetic variability among M. pseudophaseolina isolates associated with weed species using RAPD and ISSR markers and evaluate the effectiveness of each primer for detecting the genetic diversity of this species. '

MATERIAL AND METHODS

Description of fungal material

The 41 M. pseudophaseolina isolates used in this study belong to the mycological collection of the Phytopathology Laboratory II, Department of Agronomic and Forest Sciences, Federal Rural University of the Semiarid Region (UFERSA). Description of hosts and collection sites of the isolates are shown in Table 3.

Table 1
Name, identifier code in the Culture Collection of Phytopathogenic Fungi Prof. Maria Menezes (CMM) and GenBank, hosts, and collection sites of the M. pseudophaseolina isolates used in this study.
Table 2
Identification, sequence, and annealing temperature (AT) of the molecular markers used in this study.
Table 3
Resolving power of the ISSR and RAPD markers used in this study. Number of amplified fragments (NAF), number of polymorphic fragments (NPF), percentage of polymorphism (%P), polymorphism information content (PIC), effective multiplex ratio (EMR) and marker index (MI).

Fungal cultivation and DNA extraction

The isolates were cultivated in PDA (potato dextrose agar) medium for ±5 days at 28 °C in darkness to promote enough mycelium growth for DNA isolation. DNA was extracted using the method of Smith et al. (2001SMITH, S. N. et al. Soil-borne populations of Fusarium oxysporum f. sp. vasinfectum, a cotton wilt fungus in California fields. Mycologia, 93: 737-743, 2001.) with modifications. The mycelium frozen in liquid nitrogen was ground to a fine powder inside 2.0 ml microtubes. Then, SDS extraction buffer (2% and 3% SDS, 100 mM Tris-HCl pH 8.0, 500 mM NaCl, 50 mM EDTA, 0.6% 0-mercaptoethanol, and q.s. ultrapure water) was mixed with the mycelial powder, and the tubes were incubated in a water bath at 60 °C for 40 min. Afterward, the mixture phases were separated with chloroform:isoamyl alcohol (24:1). The supernatant layer was transferred to a new tube, added to isopropanol and kept at -20 °C for ±12 h. Then, the tubes were washed with 70% and 90% alcohol, sequentially, and the pellet was resuspended in RNase solution (10 pg ml-1) (Ludwig Biotec, Brazil). Subsequently, the DNA was quantified on 1% agarose gel stained with ethidium bromide (0.5 pg ml-1) by electrophoresis at 110 V for 30 min.

ISSR analysis

The genomic DNA of the 41 M. pseudophaseolina isolates was amplified via PCR using the ISSR primers listed in Table 2. Reactions were carried out in 12 pl volumes containing 1x MgCl2 buffer, 0.16 mM of dNTP, 1 U Taq DNA polymerase (Cellco), 0.33 pM of each primer, BSA (bovine serum albumin) (0.25 mg ml-1), and 30 ng of DNA. Amplification was performed in an automatic thermocycler (Amplitherm) programmed to operate an initial denaturation at 94 °C for 4 min, followed by 40 cycles of denaturation at 94 °C for 40 s, annealing at the specific temperature of each primer (Table 2) for 40 s, and extension at 72 °C for 2 min, followed by an extension at 72 °C for 7 min.

The amplified products were separated on 2.5% agarose gel stained with ethidium bromide (0.5 pg ml-1) by electrophoresis at 110 V for ± 2 h in 1x TBE buffer (0.89 M Tris-base, 0.02 M boric acid, 0.89 M EDTA). A 1 kbp DNA ladder (BioLabs, New England) was used as a molecular weight standard.

RAPD analysis

RAPD analysis was performed using ten arbitrary primers (Table 2). Amplification reactions were carried out in 12 pl volume under the same conditions as described for the ISSR markers, except for primer concentration, which was 0.82 pM, and without bovine serum albumin.

Amplifications were performed under the following conditions: initial denaturation at 95 °C for 5 min, followed by 40 cycles of denaturation at 92 °C for 1 min, annealing at 40 °C for 1 min, and extension at 72 °C for 2 min, followed by an extension at 72 °C for 5 min. The amplified products were separated on 1.5% agarose gel stained with ethidium bromide (0.5 pg ml-1) by electrophoresis at 100V for ± 2 h in 1x TBE buffer. A 1 kbp DNA ladder (BioLabs, New England) was used as a molecular weight standard.

Statistical analysis

The fragments generated by both markers were converted into a binary matrix, attributing number 1 to the presence and 0 to the absence of bands. Then, a genetic similarity matrix was calculated using the Jaccard’s coefficient and cluster analysis was performed using the UPGMA (Unweighted Pair Group Method with Arithmetic

Average) hierarchical method in NTSYSpc software. The cut-off line position on the dendrogram was calculated as the mean of genetic similarity (JAMSHIDI; JAMSHIDI, 2011JAMSHIDI, S; JAMSHIDI, S. NTSYSpc 2.02 e implementation in molecular biodata analysis (clustering, screening, and individual selection). In: 4th International Conference on Environmental and Computer Science. Proceedings... Singapore. 2011. p. 165-169.). Also, polymorphism information content (PIC), effective multiplex ratio (EMR), and marker index (MI) were calculated according to Chesnokov and Artemyeva (2015CHESNOKOV, Y. V.; ARTEMYEVA, A. M. Evaluation of the measure of polymorphism information of genetic diversity. Agricultural Biology, 50: 571-578, 2015.). Principal Coordinates Analysis (PCoA) was performed in NTSYSPc using the Eigen mode and the graph was generated in Mod3D mode.

RESULTS AND DISCUSSION

In this study, the genetic diversity among 41 Macrophomina pseudophaseolina isolates from two weed species collected in melon producing areas of Ceará and Rio Grande do Norte states were evaluated using ISSR and RAPD markers. Five ISSR markers with reproducible and polymorphic bands were used to detect the genetic diversity among the 41 isolates. The selected ISSR markers generated 108 loci, of which 79 (73.1%) were polymorphic (Table 3). The genetic similarity coefficient ranged from 0.13 to 0.91. By the UPGMA method, the dendrogram arranged isolates into 11 groups, at 58% similarity (Figure 1).

Figure 1
Dendrogram obtained by the UPGMA method using the Jaccard coefficient derived from the ISSR analysis of 41 M. pseudophaseolina isolates.

In turn, the RAPD analysis with ten markers produced well-defined and polymorphic fragments for genetic diversity analysis among M. pseudophaseolina isolates. In total, 148 loci were amplified, of which 98 (66.2%) were polymorphic (Table 3). The genetic similarity coefficient ranged from 0.07 to 0.84. The dendrogram by the UPGMA method using Jaccard's coefficient arranged the 41 isolates into nine groups at 55.5% similarity (Figure 2).

Figure 2
Dendrogram obtained by the UPGMA method using the Jaccard coefficient derived from the RAPD analysis of 41 M. pseudophaseolina isolates.

Moreover, the dendrogram generated by the UPGMA method using both ISSR and RAPD markers separated the 41 M. pseudophaseolina isolates into eight groups at 56.2% similarity level (Figure 3). The genetic similarity coefficient ranged from 0.15 to 0.87.

Figure 3
Dendrogram obtained by the UPGMA method using the Jaccard coefficient derived from combination of ISSR and RAPD analysis of 41 M. pseudophaseolina isolates.

Of the 41 isolates, 22 were clustered in Group 2, with 60% similarity on average. Of these 22, seven isolates were obtained from T. portulacastrum (four from Assú-RN and three from Mossoró-RN) and 15 from B. diffusa (eight from Mossoró-RN and seven from Assú-RN). The second largest group (Group 5) contained four isolates obtained from T. portulacastrum (three from Mossoró-RN and one from Assú-RN) and three from B. diffusa (all from Assú). Group 6 combined five isolates from Assú-RN, and Group 3 comprised two isolates from Mossoró-RN and one from Assú-RN, all obtained from B. diffusa. Groups 1, 4, 7, and 8 contained one isolate each, MpBr11 (from T. portulacastrum, Icapuí-CE), MpBr71, MpBr25 (from T. portulacastrum, Assú-RN) and MpBr65 (from B. diffusa, Assú-RN), respectively. Principal Coordinates Analysis (Figure 4) confirmed clustering in the dendrogram, showing that isolates MpBr11 and MpBr65 are the most genetically distant.

Figure 4
Genetic relationships among 41 M. pseudophaseolina isolates according to the Principal Coordinates Analysis of data from ISSR and RAPD markers.

The high dissimilarity found among the M. pseudophaseolina isolates may be related to species specialization to the cultivation conditions of each region (IQBAL; MUKHTAR, 2014IQBAL, U.; MUKHTAR, T. Morphological and pathogenic variability among Macrophomina phaseolina isolates associated with mungbean (Vigna radiata L.) Wilczek from Pakistan. The Scientific World Journal, 2014: 1-9, 2014.). It was evident by the high genetic diversity between the isolate MpBr11 collected from Icapuí-CE and isolates collected from other sites (Mossoró-RN and Assú-RN), despite being obtained from the same weed species (T. portulacastrum) (Figure 3).

This ability allows the pathogen to have greater adaptation and survival, which hampers disease management through generalist strategies (GARCÍA et al., 2019GARCÍA, M. E. M. et al. Reaction of lima bean genotypes to Macrophomina phaseolina. Summa Phytopathologica, 45: 11-17, 2019.; COSER et al., 2017COSER, S. M. et al. Genetic architecture of charcoal rot (Macrophomina phaseolina) resistance in soybean revealed using a diverse panel. Frontiers in Plant Science, 8: 1-12, 2017.). Also, the high genetic diversity among M. pseudophaseolina isolates makes it difficult to develop resistant melon varieties to all isolates (ALMEIDA et al., 2014ALMEIDA, A. M. R. et al. Macrophomina phaseolina em soja. Londrina: Embrapa Soja, 2014. 55 p.).

Furthermore, the high genetic diversity among M. pseudophaseolina isolates we observed may explain its pathogenic variability in plants (BABU et al., 2010BABU, B. K. et al. Genetic diversity of Macrophomina phaseolina isolates from certain agro -climatic regions of India by using RAPD markers. Indian Journal of Microbiology, 50: 199-204, 2010.), as well as its ability to adapt to different agroecological conditions. Csondes et al. (2012CSONDES, I. et al. Genetic diversity and effect of temperature and pH on the growth of Macrophomina phaseolina isolates from sunflower fields in Hungary. Molecular biology reports, 39: 3259-3269, 2012.) found that the genetic variability of M. phaseolina isolates collected from different regions was correlated with the pathogen’s ability to grow and develop under different temperature and pH conditions, characteristics that allow it to adapt to different environments and hosts (IQBAL; MUKHTAR, 2014IQBAL, U.; MUKHTAR, T. Morphological and pathogenic variability among Macrophomina phaseolina isolates associated with mungbean (Vigna radiata L.) Wilczek from Pakistan. The Scientific World Journal, 2014: 1-9, 2014.).

In other molecular studies, high genetic diversity among species from the genus Macrophomina was found considering different hosts and geographical origins. By PCR-RFLP, Purkayastha et al. (2006PURKAYASTHA, S. et al. Characterization of Macrophomina phaseolina, the charcoal rot pathogen of cluster bean, using conventional techniques and PCR-based molecular markers. Plant Pathology, 55: 106-116, 2006.) found highly aggressive isolates for beans grouped separately from less aggressive ones. Zivanov et al. (2019ŽIVANOV, S. T. et al. Analysis of genetic diversity among Macrophomina phaseolina (Tassi) Goid. isolates from Euro-Asian countries. Journal of Plant Diseases and Protection, v. 126, 565-573, 2019.), using RAPD markers, observed high variability among M. phaseolina isolates collected from different hosts in different countries in Asia and Europe.

Results showed that the RAPD and ISSR markers were effective in detecting genetic diversity among the 41 M. pseudophaseolina isolates. The dendrogram obtained with a combination of data showed a significant correlation (r = 0.86) between the genetic similarity matrix and cluster analysis. Furthermore, the EMR obtained with ISSR analysis (11.67) was greater than that obtained with RAPD (6.71) (Table 3), showing the more resolving power of the ISSR marker as compared to RAPD to assess the genetic variability among M. pseudophaseolina isolates.

The ISSR and RAPD markers, isolated or associated, could not differentiate the M. pseudophaseolina isolates according to their geographical origin and host plant, as observed by Babu et al. (2010BABU, B. K. et al. Genetic diversity of Macrophomina phaseolina isolates from certain agro -climatic regions of India by using RAPD markers. Indian Journal of Microbiology, 50: 199-204, 2010.) when evaluating the genetic diversity among 50 M. phaseolina isolates using RAPD markers. Despite the low correlation between host and geographical origin where the M. pseudophaseolina isolates were sampled, a pattern was observed in clusters of isolates from the same origin or host.

The ISSR markers grouped three isolates from T. portulacastrum (MpBr25, MpBr27, and MpBr28) and two from B. diffusa (MpBr53 and MpBr58) collected in Assú. Also, the same markers grouped eight isolates in Group 2, all from B. diffusa, indicating that a clustering pattern can be obtained by molecular markers. Sánchez et al. (2017SÁNCHEZ, S. et al. Genetic and biological characterization of Macrophomina phaseolina (Tassi) Goid. causing crown and root rot of strawberry. Chilean Journal of Agricultural Research, 77: 325-331, 2017.) and Tarakanta, sharma and Singh (2005TARAKANTA, J. A. N. A.; SHARMA, T. R.; SINGH, N. K. SSR-based detection of genetic variability in the charcoal root rot pathogen Macrophomina phaseolina. Mycological Research, 109: 81-86, 2005.) using SSR markers reported that M. phaseolina isolates strongly tended to group according to their geographical origin. In contrast, using RAPD markers, clusters of M. pseudophaseolina isolates were not associated with the host or geographical origin where the pathogen was sampled (ZIVANOV et al., 2019ŽIVANOV, S. T. et al. Analysis of genetic diversity among Macrophomina phaseolina (Tassi) Goid. isolates from Euro-Asian countries. Journal of Plant Diseases and Protection, v. 126, 565-573, 2019.).

The greatest similarity (87%) was observed between isolates MpBr27 and MpBr28, both obtained from T. portulacastrum collected in Assú. Also, high similarity (79% and 75%, respectively) was observed between isolates MpBr40 (T. portulacastrum, Mossoró-RN) and MpBr51 (T. portulacastrum, Assú-RN), and between MpBr40 and MpBr30 (both from T. portulacastrum, Mossoró -RN). The high similarity between isolates from different geographical origins suggests they share a common ancestor (ALMEIDA et al., 2003ALMEIDA, A. M. R. et al. Genotypic diversity among Brazilian isolates of Macrophomina phaseolina revealed by RAPD. Fitopatologia Brasileira, 28: 279-285, 2003.), or they were propagated by contaminated soil and seeds among cultivation areas (AGHAKHANI; DUBEY, 2009AGHAKHANI, M.; DUBEY, S. C. Determination of genetic diversity among Indian isolates of Rhizoctonia bataticola causing dry root rot of chickpea. Antonie van Leeuwenhoek, 96: 607-619, 2009.).

On the other hand, high genetic distances were found between MpBr11 (T. portulacastrum, Icapuí-CE) and MpBr65 (B. diffusa, Assú-RN) as compared to the other isolates, by the combination of the ISSR and RAPD markers (Figure 3). Such high intraspecific variability in the species complex of the genus Macrophomina can be explained by the high mutation rate during the parasexual reproduction of the species (PURKAYASTHA et al., 2006PURKAYASTHA, S. et al. Characterization of Macrophomina phaseolina, the charcoal rot pathogen of cluster bean, using conventional techniques and PCR-based molecular markers. Plant Pathology, 55: 106-116, 2006.) and high amount of transposable elements and repetitive DNA in the genome (ISLAM et al., 2012ISLAM, M. S. et al. Tools to kill: genome of one of the most destructive plant pathogenic fungi Macrophomina phaseolina. BMC Genomics, 13: 116, 2012.).

Search for sources of disease resistance in melon accessions must consider the genetic heterogeneity of the pathogen species, which allows using a uniform population in resistance tests (MUNDT, 2014MUNDT, C. C. Durable resistance: a key to sustainable management of pathogens and pests. Infection, Genetics and Evolution, 27: 446-455, 2014.). Sources of genetic variability directly influence the pathogen adaptation to host resistance genes (CASELA, 2005CASELA, C. R. Variabilidade genética de patógenos e resistência de cultivares. In: Embrapa Milho e Sorgo-Artigo em anais de congresso (ALICE). In: SEMINÁRIO NACIONAL DE MILHO SAFRINHA, 8., 2005, Assis. Anais... Campinas: Instituto Agronômico, 2005. p. 189-194, 2005.). Therefore, integrated control methods should be used to avoid selection pressure in the pathogen population.

High genetic variability among M. pseudophaseolina isolates, as we observed in the present study, hinders breeding for disease resistance. It directly affects the effective strategy for disease management, since using resistant cultivars is the most efficient and economically viable control method against root rot and vine decline in melon (ALMEIDA et al., 2014ALMEIDA, A. M. R. et al. Macrophomina phaseolina em soja. Londrina: Embrapa Soja, 2014. 55 p.). In this study, the isolates MpBr11 and MpB65 stood out for being more genetically distant from the others.

Therefore, for melon cultivars highly susceptible to isolates MpBr11 and MpBr65, developing resistant cultivars is crucial for sustainable management of the disease. Moreover, ISSR and RAPD markers were effective in detecting genetic variability among isolates, assisting in decision making in sustainable management systems. Thus, we suggest that pathogenicity tests be carried out to identify isolates or groups of isolates that cause high productivity losses for the crop.

CONCLUSION

Genetic variability among 41 M. pseudophaseolina isolates could be detected using ISSR and RAPD markers, and high intraspecific variability was detected among isolates from the same host and origin or not. Both markers were satisfactory in detecting genetic diversity among the isolates, but ISSR markers showed greater resolving power. Results obtained herein can assist in developing effective control methods against root rot and vine decline in melon.

ACKNOWLEDGMENTS

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

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Publication Dates

  • Publication in this collection
    23 Nov 2020
  • Date of issue
    Oct-Dec 2020

History

  • Received
    20 Apr 2020
  • Accepted
    15 July 2020
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