Guidelines for the improvement of Jatropha for the production of biofuels

Jatropha curcas L. is a perennial, monoecious species belonging to the Euphorbiaceae family, the same as castor beans, cassava and rubber trees. The plant grows spontaneously in several regions of Brazil, although it cannot be said that the species is native to the country.

It is a fast-growing, deciduous shrub that can reach more than 5 m in height. The fruits are of the ovoid capsule type, 1,5 to 3,0 cm in diameter, trilocular, containing, as a rule, 3 seeds, one seed per locule. The seeds are 1,5 to 2,0 cm long and 1 to 1,3 cm wide and represent between 53 and 79% of the fruit's weight, with an oil content varying between 33 and 38%. The species has the potential to produce over 1.200 kg of oil per hectare.

Despite the lack of basic technical information, the culture has been disseminated and implemented in several regions of Brazil. Commercial Jatropha plantations in Brazil are still in the initial phase of implementation, with an age of less than or equal to 3 years, and the potential for denser production in periods longer than this is not known. The Jatropha materials being implemented are genetically unknown and uneven and do not have minimum guarantees regarding the environmental adaptability and productivity of each genotype.

Currently, Embrapa is working on the implementation of a genetic improvement program for Jatropha aimed at selecting commercial cultivars with high grain and oil productivity, without toxicity (absence of phorbol esters), resistant to biotic and abiotic stresses and adapted to main producing regions in Brazil.

The program's activities include actions that involve the enrichment and characterization of genetic resources, the use of breeding methods aimed at obtaining superior genotypes and, finally, the evaluation of improved materials in different regions with a view to indicating materials and systems for planting. The Program also develops actions to provide technical-scientific support for the botanical and molecular characterization of Jatropha, aiming to subsidize the registration of cultivars and shorten paths to obtaining genetically improved materials.

The first step in starting breeding programs for a species undergoing domestication is to obtain as many genetic materials as possible in order to initially have a broad genetic base for the selection and development of cultivars. In this sense, Embrapa Agroenergia together with Embrapa Cerrados created a germplasm bank with around 200 accessions from different regions of the country, which is currently in the characterization phase.

Genetic diversity studies are very useful in the species improvement process. It is important to highlight that just knowing genetic diversity is not enough for the success of breeding programs, and it is essential to determine the existing variability in relation to the characters of interest. For this, it is necessary to have reliable phenotypic information evaluated on existing genotypes. Complementary to phenotyping, genotyping helps in studies of genetic diversity, as it allows the distinction of accessions early and without influence from the environment.

The molecular characterization of Embrapa's jatropha germplasm bank revealed that the materials collected in different locations in Brazil have a narrow genetic base, probably caused by common ancestry when introduced in past centuries. Therefore, aiming for long-term genetic gains in the species improvement program, it is essential to introduce materials from other countries, mainly from the center of origin and/or diversity of the species.

The breeding program must seek to obtain cultivars with characteristics that meet the demands of producers (management and economic gain) and the market (biodiesel quality specifications). For Jatropha, the program must seek cultivars that have higher grain productivity and high oil content, absence of toxicity, flowering synchronization, rusticity and tolerance to drought, diseases and insect pests, among other characteristics. However, it is important to emphasize that obtaining genetic gains to meet any of these objectives is dependent on the existence of genetic variability for the trait that is desired to improve in the population.

As can be seen, almost all agronomic traits that are desired to be improved in Jatropha are quantitative, therefore, influenced by the environment and, as a result, tend to have low heritability. Characters like these must be improved gradually, over several generations.

During the stages of the breeding program, genetic materials with high average and wide genetic variability must be selected, to provide continuous gains with selection over several generations. The breeding methods adopted must seek to gradually and continuously increase the frequencies of favorable alleles and, simultaneously, maintain genetic variability at adequate levels to allow new selective cycles to be carried out.

Marker Assisted Selection (SAM) is a powerful tool that can assist the breeding program. It is important, especially when working with perennial species, as any help to increase selection efficiency is significant due to the large time required to carry out a selection cycle. In this context, SAM can contribute to the early selection of superior genotypes. In several studies, the efficiency of this tool in the selection for characters controlled by a few genes and the inefficiency of SAM in the selection for quantitative characters have been verified. Therefore, it is a tool that can assist during the improvement of the species, mainly in the introduction of specific characters in genetic materials that are in an advanced process of improvement.

The use of cloning, a technique that perpetuates superior individuals in the population, makes it possible to capitalize on all the genotypic variance present in the population. When using cloning, it is important that the population improvement program is maintained in parallel, so that it is increasingly possible to obtain new, superior hybrid combinations.

The evaluation of improved genotypes in different regions is essential for recommending cultivars for planting under specific or broad conditions. In this sense, as a step in the breeding program, studies of genotype x environment interactions and stability and adaptability of improved genotypes become essential.

In conclusion, as Jatropha is a non-domesticated perennial species, it is estimated that it will take 5 to 7 years to obtain improved cultivars and scientifically based information on crop production systems that support commercial cultivation in different regions. .

Bruno Galvêas Laviola

Researcher, Embrapa Agroenergia

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