Genetic diversity of rubber trees can at last be known and preserved

Brazilian researchers, in collaboration with French colleagues, analyzed more than 1,000 specimens of Hevea brasiliensis available in South American public germplasm banks.

By Elton Alisson  |  Agência FAPESP – The genetic diversity of Hevea brasiliensis, a native of the Amazon forest and the world’s only plant cultivated for the commercial production of natural rubber, can at last be known and preserved.

The genetic diversity of the rubber tree has been described by a group of Brazilian researchers affiliated with several different universities and research institutions in collaboration with colleagues at France’s Agricultural Research Center for International Cooperation & Development (CIRAD).

The researchers analyzed over 1,000 exemplars of Hevea spp plants available in South American public germplasm banks (genetic heritage). They also assembled a core collection of germplasm from almost 100 rubber trees representing all the genetic diversity identified in the study.

The study, which resulted from a project supported by FAPESP, was published in the journal PLoS One.

“This core collection of almost 100 genotypes can be used as a basis for rubber tree breeding programs not just in Brazil but also in any other part of the world where there’s an interest in cultivating it and will protect the plant’s germplasm,” said Anete Pereira de Souza, principal investigator for the project, in an interview with Agência FAPESP. Souza is a professor at the University of Campinas’s Biology Institute (IB-UNICAMP) in São Paulo State, Brazil, and a researcher at the same university’s Center for Molecular Biology & Genetic Engineering (CBMEG).

The researchers analyzed 1,117 accessions, genotyping them with microsatellite molecular markers, also called simple sequence repeats (short segments of DNA that indicate the most recent evolutionary variations in an individual organism). These exemplars had been conserved in Brazil and French Guiana by collecting expeditions conducted during the past 35 years in the area of Madre de Dios, Peru, and the Brazilian states Acre, Rondônia, Mato Grosso, Pará and Amazonas.

Approximately 500 of the accessions analyzed were collected during an expedition conducted in 1995 by the Brazilian Agricultural Research Corporation (EMBRAPA) and the Rubber Research Institute of Malaysia (RRIM) in Pará and Amazonas. EMBRAPA stored the seeds in an experimental area of cerrado in Planaltina, 40 km from Brasília. Until now, this material has never been described, multiplied or used in breeding programs.

The other samples analyzed came from surveys performed in the Brazilian states Acre, Mato Grosso and Rondônia in 1974 and 1981 by France’s Rubber Research Institute (IRCA), EMBRAPA, and the International Rubber Research & Development Board, leading to collections held in different locations.

Genetic analysis of the accessions showed that rubber tree populations can belong to two distinct groups based on genetic distance: a group from Mato Grosso and another group from Acre, Rondônia, Amazonas and Pará in Brazil, and Madre de Dios in Peru.

The study showed, for example, that cultivated rubber trees from Asia, where plantations were not successfully developed until the 1920s, are similar to those from Mato Grosso.

One reason for this, according to the researchers, is that the first rubber trees grown in Southeast Asia originated from more than 70,000 seeds smuggled out of an area near the Tapajós River, Pará, Brazil, by British adventurer and imperialist Henry Wickham (1846-1928) in 1876. The Tapajós River rises in Mato Grosso.

Wickham, who became famous as the “biopirate who destroyed Brazil’s rubber monopoly”, took the seeds to Kew Gardens in London, where a couple of thousand eventually germinated. The few seedlings obtained after germination were sent to Malaysia, currently the world’s leading producer of natural rubber, and were the origin of all the rubber plantations in Southeast Asia, according to the article in PLoS One.

“Malaysia still uses germplasm originally taken from Brazil in the nineteenth century,” Souza said.

Using microsatellite molecular markers, the researchers also identified 408 alleles (variants of the same gene) among the 1,117 samples analyzed: 319 alleles were shared by all groups, while 89 were exclusive to specific groups. Based on this finding, they compiled a core collection of 99 seeds, representing all the genetic diversity from the plants they analyzed.

“This ‘compact’ collection of 99 trees contains all the alleles present in the more than 1,000 rubber trees studied and can more easily be conserved,” Souza said.

Genetic heritage at risk

According to Souza, there have been several unsuccessful attempts to create and conserve rubber tree germplasm banks in Brazil in the last 40 years.

Half the seeds collected by IRRDB and EMBRAPA in their 1981 expedition remained in Brazil and were planted in the Amazon region. The other half went to Ivory Coast in Africa and Malaysia, where the material is still conserved.

The seeds planted in the Amazon, however, were decimated by South American leaf blight caused by Microcyclus ulei, a fungus that infects young leaves, stems and fruits of H. brasiliensis, resulting in defoliation and eventual tree death.

Leaf blight had already exterminated a plantation of rubber trees in Fordlandia. This was the largest plantation maintained by a company in the Amazon. Henry Ford (1863-1947) began building Fordlandia on the banks of the Tapajós in Pará in 1927 with the intention of producing latex for automotive tires.

“Unfortunately, the lessons of Fordlandia were ignored, and the Hevea germplasm collected by the 1981 expedition and planted in the Amazon was totally lost,” Souza said. “The other half of the germplasm collected at that time is in Malaysia.”

The material collected by the 1995 EMBRAPA-RRIM expedition was split between Brazil and Malaysia. The Brazilian half was planted by EMBRAPA Cerrado, as already noted. In 2004, however, the area was invaded by landless worker movement activists.

“We were alarmed because if the germplasm bank had been destroyed, Brazil would have been left without any H. brasiliensis germplasm at all,” Souza said. “The areas in which the most precious rubber trees are found – areas in Rondônia, Mato Grosso and Acre – were being destroyed by the advance of deforestation.”

In a project supported by FAPESP and also conducted in collaboration with French colleagues, the Brazilian researchers started to analyze the rubber tree germplasm remaining at EMBRAPA Cerrado.

“The researchers at EMBRAPA Cerrado did everything they could and managed to save most of the germplasm,” Souza said.

In 2014, when the researchers were finishing their study, the government of the Federal District announced a plan to build some 4,000 apartments for low-income families on EMBRAPA’s 2,100-hectare experimental farm. “Luckily, a copy of this material had been kept by French Guiana,” Souza said.

CIRAD also ran a rubber tree breeding program for more than 20 years on a farm in Mato Gross belonging to Michelin, the French tire maker. In 2011, however, the farm was sold to a soybean growing company. “CIRAD had the sense to negotiate with the soybean company, ensuring that the area where the germplasm is conserved will be left intact for ten years,” Souza said.

CIRAD recently offered to donate the trees from this area to the Campinas Agronomy Institute (IAC) on the condition that it starts an international rubber tree breeding program at the Rubber Tree & Agroforestry Systems Research Center (CAPSA), recently established by the IAC at Votuporanga, São Paulo State.

“With this research center and the international breeding program, we’ll be in a position to ask Malaysia for a copy of the germplasm collected in 1981,” Souza said. “It’s invaluable because the seeds were collected in forest areas where there’s no longer any forest left.”

In addition to CBMEG and CIRAD, researchers from Southwest Bahia State University (UESB), the São Paulo State Agribusiness Technology Agency (APTA), EMBRAPA Cerrados and the Ilha Solteira campus of São Paulo State University (UNESP) also participated in the study.

One of these researchers, Paulo de Souza Gonçalves, affiliated with EMBRAPA and the IAC, has been studying H. brasiliensis for 45 years and participated in the 1981 expedition to collect seeds in the Amazon alongside French colleagues and IRRDB.

“His extreme dedication to the collection and breeding of H. brasiliense, and his determination to conserve its genetic heritage, inspired us and motivated us to perform this study,” Souza said.

The article “Genetic diversity strategy for the management and use of rubber genetic resources: more than 1,000 wild and cultivated accessions in a 100-genotype core collection” (doi: 10.1371/journal.pone.0134607) by Souza et al. can be read in the journal PLoS One at http://journals.plos.org/plosone/article/authors?id=10.1371/journal.pone.0134607.