Cultivation of Jatropha shows the importance of conservation

Jatropha curcas could be an oil crop with major biofuel potential, but the breeding germplasm has little variation. Botanists have found that there is genetic potential in previously overlooked non-toxic jatropha, but it needs conservation.

Jatropha curcas is a plant that has already been “ailed as a ‘wonder plant‘. The seeds yield around 25% – 40% oil, that can be used for biodiesel, but there are also problems. “The Asian and African cultivars currently being used do not achieve the initially anticipated high seed yields…,” say Vandepitte and colleagues in the Annals of Botany. “This is partly explained by the narrow genetic base of this exotic germplasm that clearly passed through a genetic bottleneck… Therefore, additional indigenous genetic variation could be exploited to breed more productive cultivars.”

An additional problem is that much jatropha is toxic, due to phorbol esters (PE) that can cause vomiting and diarrhoea. They can also cause tumours. There is, however, some hope for finding suitable genetic stock. “In some rural communities of southern Mexico, jatropha plants occur whose seeds are consumed by indigenous people, have a high nutritional value and do not or contain or contain low PE levels…,” said the authors in their paper. “This edible ‘genotype’ is considered to have been domesticated and proliferated through vegetative propagation by ancient indigenous people, probably the Mayans. Recent ethnobotanical research by Valdés-Rodríquez et al. (2013), however, suggests that non-toxic jatropha originates from the northern part of Veracruz state and surrounding areas (north of the historical Mayan territory), from where it was spread across Veracruz, adjacent southern Mexican states and the Yucatan Peninsula by the expanding influence of Totonac culture (from 1600 BC onwards).”

If the assumed source of jatropha was wrong, then could there be more genetic variation waiting to be found in Mexico? To find out, Vandepitte and colleagues went on a two-year quest in Mexico, starting in Veracruz and heading south, to find out more about the variability of jatropha.

“Trees were typically retrieved in natural areas, along rural paths and in the orchards of native Mexicans or their descendants, where they were cultivated together with other native or naturalized plants,” said the authors. “Toxic plants were also frequently used as a live fence. Non-toxic trees were particularly abundant in the state of Veracruz, where older informants (85–90 years old) stated that their great-great-grandparents used jatropha seeds as food, reportedly at least over the last 300 years.”

Map of all Mexican Jatropha curcas provenances genotyped, labelled according to toxicity type. Source: Vandepitte et al. 2019.

The team found both unexpectedly high SNP (genetic) diversity in edible jatropha in Veracruz. There were also a lot more edible jatropha plants there. While the results were unexpected, they also help corroborate other studies say the authors. “These findings are in line with available ethno-botanical data and plant distribution patterns. In northern Veracruz, non-toxic trees are far more prevalent than in other regions, as recently demonstrated by PE analysis. In this area, jatropha seeds are also (still) used to prepare traditional meals by local Native Mexicans of Totonac and Huastecan descent, whereas outside northern Veracruz non-toxic jatropha is typically cultivated by immigrants with a Totonac background.”

The genetic variation in this non-toxic jatropha could bring in traits enabling jatropha to become a more efficient and more sustainable source of biofuel. But this does depend on that wild variation been accessible, say Vandepitte and colleagues. “As the persistence of non-toxic jatropha is currently at risk due to replacement by foreign toxic cultivars, and the increasing abandonment of indigenous cuisine by Native Mexicans…, conservation actions are urgently needed to prevent the loss of potentially valuable non-toxic genotypes. Efforts should concentrate on the high diversity present in northern Veracruz, from where extant non-toxic jatropha was probably dispersed to other regions within and outside Mexico.”

“More generally, this work underpins the value of conservation genomic research on the indigenous (wild) germplasm of economically important plant species (cf. crop wild relatives or CWRs). It was estimated that about 30 % of of the increase in crop yields in the late 20th century could be attributed to the use of CWRs in plant breeding programmes. Furthermore, considering climate change and the mounting human population, the importance of conserving the wild gene pool of crop species will only increase.”