Genetic variability among Commelina weed species from the states of Paraná and São Paulo, Brazil

Variabilidade genética entre espécies de plantas daninhas do gênero Commelina provenientes dos estados do Paraná e São Paulo, Brasil

ARTIGOS

Rocha, D.C.^I; Rodella, R.A.^II; Marino, C.L.^III; Martins, D.^IV

^IDep. de Biologia Geral da Universidade Estadual de Ponta Grossa, Ponta Grossa-PR, <[e-mail]>

^IIDep. de Botânica do Instituto de Biociências de Botucatu - UNESP/Botucatu-SP

^IIIDep. de Genética do Instituto de Biociências de Botucatu - UNESP, Botucatu-SP

^IVDep. de Produção Vegetal da Faculdade de Ciências Agronômicas - UNESP, Botucatu-SP

ABSTRACT

This work aims to carry out a comparative analysis using RAPD molecular markers in four Commelina weed species from the state of Paraná and C. benghalensis populations from the states of Paraná and São Paulo, Brazil. The genomic plant DNA sample was extracted from the leaves, separated, randomly fragmented and amplified by PCR. Random amplified polymorphic DNA fragments (RAPD markers) were analyzed by using POPGENE statistical program. Eighty-five primer sequences were tested but only three were suitable as molecular markers producing 37 DNA polymorphic fragments for comparisons among four Commelina species and 22 polymorphic fragments for comparisons among C. benghalensis populations. The results showed that there were inter-specific and intra-specific genetic variabilities among Commelina plant genera. Genetic diversity analysis between species indicated four mono-specific clusters and it was suggested to keep C. villosa as one species. Regarding the intra-specific genetic variability of C. benghalensis alone, three groups were verified, although there were 13 populations from two geographical areas. However, these clusters do not correspond to the distinct characteristics verified.

Keywords: biotype, Commelinaceae, molecular markers, weeds.

RESUMO

O presente trabalho procurou analisar a variabilidade genética, utilizando-se de marcadores RAPD, comparando quatro espécies de Commelina procedentes do Estado do Paraná e entre populações de C. benghalensis procedentes dos Estados do Paraná e São Paulo. Foi amostrado o DNA genômico extraído das folhas, o qual foi separado, fragmentado aleatoriamente e amplificado por PCR. Os fragmentos polimórficos de DNA (marcadores RAPD) foram analisados pelo programa estatístico POPGENE. Oitenta e cinco primers foram testados, mas somente três sequências foram consideradas marcadores moleculares, produzindo 37 bandas de DNA polimórfico para comparação entre as quatro espécies de Commelina e outras 22 para comparação entre as populações de C. benghalensis. Os resultados mostraram que há variabilidade genética inter e intraespecífica nas plantas do gênero Commelina. A análise da diversidade genética entre as espécies indicou quatro agrupamentos monoespecíficos, e isso sugere manter C. villosa como uma espécie. Considerando a variabilidade genética intraespecífica somente de C. benghalensis, apesar das 13 populações provenientes de dois Estados geográficos, três grupos foram identificados. Entretanto, esses agrupamentos não correspondem às características morfológicas distintas observadas.

Palavras-chave: biótipo, Commelinaceae, marcadores moleculares, planta daninha.

INTRODUCTION

The importance of some members of the Commelinaceae family was emphasized by Holm et al. (1977) since Commelina weed plants occur in more than 100 countries in soybean, bean, corn and other cultivated plant crops. Weed species of such family grow in crops and compete for light and nutrients with cultivated plants and might be an alternative host for viruses, fungi and nematodes (Wilson, 1981). The success and spread of Commelina weed species in many crops may be attributed to their high environmental adaptation, mainly because their vegetative and seed reproduction systems are highly efficient (Maheshwari & Maheshwari, 1955; Wilson, 1981).

Investigation on the genetic variability of cultivar plants has been conducted for species, variety,cultivar and biotype characterization. Although few studies have been carried out on the genetic diversity of weed plants, some of the more important taxa have been evaluated, such as Cyperus esculentus (Horak & Holt, 1986), Cyperus rotundus (Silva et al., 2000), and Commelina benghalensis (Ahanched & Gasquez, 1992).

In Brazil, four Commelina species occur as weed plants, with C. benghalensis being considered the most important one because it is the best known, infesting different crops (Silva et al, 2009a, b). However, three other species, C. diffusa, C. erecta and C. villosa, are also important because of their tolerance to glyphosate (Santos, 2002; Rocha et al., 2007).

Some investigations were carried out on the genetic variability of Commelinaceae using enzymatic markers. Ahanched & Gasquez (1992) observed two genetic patterns in C. benghalensis populations from Northern to Southern Benin, Africa and Godt & Hamrick (1993) analyzed enzymatic variability among 13 Tradescantia hirsuticaulis populations in three US states.

The present work aimed to conduct a comparative analysis using RAPD molecular markers of four Commelina weed species naturally occurring from the state of Paraná and matching C. benghalensis populations from the states of Paraná and São Paulo, Brazil.

MATERIAL AND METHODS

The genomic DNA from leaves of C. erecta, C. diffusa, C. villosa and C. benghalensis populations from Paraná was compared. C. benghalensis populations from Paraná and São Paulo, Brazil were also compared (Table 1). The plants were collected from agricultural fields and grown in pots to evaluate their development under greenhouse conditions at the Department of Botany, Biosciences Institute of Botucatu, Universidade Estadual Paulista (UNESP), SP, Brazil.

RAPD analysis protocol was performed as reported by Ferreira & Grattapaglia (1996). Genomic DNA was extracted from matured leaf fragments for maceration in liquid nitrogen. Eighty-five primer DNA sequences (Operon Technologies) were tested, 1 to 20 sequences of primers W, N and P; 2 to 17 sequences of primer J; and 1 to 9 of primer X. Each reaction (final volume 13 μL) had a buffer (10 mM Tris HCl pH 8.0), dNTPs (1.0 mM), primer sequences selected (10 ng μL^-1 ), Taq polimerase (Pharmacia) and around 10 ng of genomic DNA (quantified previously by gel electrophoresis of agarose 0.8%). PCR amplification was conducted in a thermocycler (MJ Research model PTC 100) in 40 cycles. Each cycle was programmed to 1 min at 92 °C, 1 min to 35 °C and 2 min to 72 °C; while the least cycle was increased 5 min to 72 °C.

DNA quantification and DNA amplification were detected after DNA samples were mixed with ethidium bromide and run in agarose gel electrophoresis technique. DNA polymorphism was identified as a band in the autoradiography reported in the photography made with the "Eagle Eyes" program. The band auto radiographs scored as either present (1) or absent (0).

Three sequence primers (W02, W13 and J13) produced 37 DNA polymorphic fragments, for comparisons among four Commelina species, and 22 polymorphic fragments, for comparison among C. benghalensis populations. Using 1 and 0 as numeric values, two matrices were calculated. Inter-specific and intra-specific clusters were analyzed using the POPGENE program. Two dendrograms were constructed as a result of these analyses.

RESULTS AND DISCUSSION

Only three (2.55%) of the 85 sequence primers used to test amplified Commelina genomic DNA indicated low polymorphism rate. However, this is a preliminary DNA analysis in Commelina weeds, indicating genetic diversity between species, as four mono-specific clusters were constructed using statistical analysis. This may be an important contribution to taxonomic evaluations, corroborating with morphological studies on Commelina species identification (Rocha et al., 2007).

Amplified DNA fragments after PCR reaction using sequence primer J13 are shown in Figure 1. There are different band patterns among four Commelina species (1 to 12) from Paraná. However, there are similarities among C. benghalensis species, although there are 13 populations from the states of Paraná and São Paulo (10 to 48).

The first dendrogram shown in Figure 2A is the result of the statistical analysis using 37 molecular markers produced by PCR with three sequences primers to four Commelina species from Paraná. There has been a controversy about the taxonomic position of C. villosa as to whether this taxon is another species or a variety of C. erecta (Barreto, 1997).The statistical analysis of the present RAPD markers shows that the genetic standard of C. villosa is more similar to that of C. diffusa and C. benghalensis than to that of C. erecta (Figure 2A). These results will help further the taxonomic studies of Commelina and reinforce the concept that C. villosa is a species.

The second dendrogram (Figure 2B) was constructed to compare the intra-specific genetic variability of C. benghalensis alone, using the same statistical analysis of the other 22 molecular markers of the 13 populations from the states of Paraná and São Paulo, with the three main groups (GI, GII, GIII) being observed and within each group, with other similarity groups being detected. However, morphological characteristics that justified these three genetic clusters were not detected.

Considering only the morphology of C. benghalensis, three samples from Paraná (Cascavel, Ponta Grossa and Campo Mourão) and two samples from São Paulo (Presidente Prudente and Araçatuba) were collected displaying leaves without pilosity. Leaf pilosity is cited as an important morphological feature of C. benghalensis species (Rocha et al., 2007). Other morphological characteristics were also observed between these plants indicating two phenotypical standards, although a corresponding genomic variability was not observed. Morton (1967) verified these two morphological leaf structures of C. benghalensis in the wet African mountains and classified them as two subspecies: C. benghalensis subsp. benghalensis, without leaf pilosity and C. benghalensis subsp. hirsute, with intense leaf pilosity. Lorenzi (2000) presents illustrations, though not citing the two subspecies classification, noting that leaf structure is the only difference between them.

The geographic distribution only of the C. benghalensis populations studied is shown in Figure 3. While low genetic similarity seems to exist among the four Paraná populations, all the São Paulo populations were congregated in one group. There were no samples of C. benghalensis from southern Parana (latitude below 25°) as this species was not found there. Some genotypic standards were observed among the four Paraná populations. Group I was formed with Ponta Grossa and Campo Mourão of C. benghalensis populations which are more similar. Londrina (Paraná) populations presented more similarities with other São Paulo populations, constituting Group II. C. benghalensis populations from Cascavel were isolated to form Group III as their genetic patterns are more different than that of other populations from Paraná. Again, this segregation does not match the morphological characteristics. C. benghalensis has autogamic reproduction (Maheshwari & Maheshwari, 1955; Wilson, 1981) and this could be the cause of the low gene flow among the populations from Paraná.

However, climatic conditions also might explain this group arrangement, despite the distance between local populations and geographical boundaries. There is more similarity between the climatic conditions of northern Paraná and those of São Paulo than with other Paraná regions (IBGE, 1977). Northern Paraná's climate, relief and natural vegetation are more similar to those in the state of São Paulo and C. benghalensis populations from Londrina probably present more similarity with C. benghalensis populations from São Paulo because they are adapted to these environmental conditions.

There is also a difference in agricultural methods applied by farmers in the Paraná regions. No-tillage cropping system has been used in central and southern Paraná regions since the 1970s, aiming to decrease weed infestation and reduce the need of herbicide control (Pauletti & Seganfredo, 1999; Gomes & Christoffoleti, 2008). However, this technique is not commonly applied in the northern Paraná regions and in the state of São Paulo. Ahanched & Gasquez (1992) verified similar results, citing a significant genetic variability among C. benghalensis populations from Southern and Northern Benin-Western Africa. These authors conducted enzymatic polymorphism analyses and concluded that the genetic variability observed was due to the agricultural techniques applied. In another study using enzymatic polymorphism analysis with Commelinaceae species, Godt & Hamrick (1993) verified genetic similarities among Tradescantia hirsuticaulis populations from Alabama, Georgia and South Carolina. These results are similar to the data presented in this work, as cluster formation surpassed geographic boundaries and a low gene flow occurred in great distances. Considering that the reproduction system of Commelinaceae species presents asexual strategies (Maheshwari & Maheshwari, 1955; Wilson, 1981; Gamerro, 1986), their genomics is likely being preserved.

On the other hand, genetic similarity among accesses of Avena sterilis were studied by Heun et al. (1994) who conducted a comparative analysis using RAPD molecular and enzymatic markers, and concluded that RAPD markers were highly efficient in separating the 24 biotypes tested. McCloskey & Holt (1990) also reported genetic differences between two biotypes of Senecio vulgaris (one resistant and the other susceptible to the herbicide triazine) using molecular analysis with RAPD technique. Preliminary genetic variability analysis among species and clones of Populus plants were observed by Sanchez et al. (1998), using only one sequence primer. The present study is similar, although using a few primer sequences.

RAPD molecular markers did not reveal specific gene information in this work, but further research and more complex studies must be conducted to identify more efficient molecular markers that can be used to separate different genetic clusters within weed species as it has been already done with cultivated plants by Chen et al. (1998) and Pejic et al. (1998).

ACKNOWLEDGEMENTS

We thank the students of the Department of Genetic, Biosciences Institute of Botucatu, Universidade Estadual Paulista (UNESP), Botucatu, SP, Brazil, especially Alessandro Paris, for sharing their technical knowledge. The first author was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and also by the University of Ponta Grossa, Paraná, Brazil.

LITERATURE CITED

Recebido para publicação em 27.5.2008 e na forma revisada em 15.5.2009.

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Genetic variability among Commelina weed species from the states of Paraná and São Paulo, Brazil

Variabilidade genética entre espécies de plantas daninhas do gênero Commelina provenientes dos estados do Paraná e São Paulo, Brasil

Publication Dates

• Publication in this collection
  16 Oct 2009
• Date of issue
  2009

History

• Accepted
  15 May 2009
• Received
  27 May 2008