Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Ecological and physical factors affecting growth, productivity and herbivory load in the physic nut (Jatropha curcas L.)

Auteur : Lama, Ang Dawa

Université de soutenance : University of Turku

Grade : Doctoral dissertation (article-based) 2017

Résumé
Jatropha curcas (L.) is a multipurpose oil bearing shrub assumed to be able to survive in a wide range of ecological conditions across the tropical regions of the world. The thesis is composed of two parts, the first one based on experimental research, and the second one on literature reviews. In the experimental part, I assessed the effects of simulated herbivory and drought stress on defence, physiology and compensatory growth of J. curcas seedlings (I and II). In the latter part I reviewed arthropod herbivores, seed yield and genetic variability of J. curcas across the globe (III and IV). Experimental results showed that the highest concentration of flavonoids was found in the leaves of J. curcas seedlings exposed to 50 % herbivory stress and grown in 200 mm y-1 rainfall, whereas the lowest growth and biomass was produced by J. curcas seedlings exposed to 25 % herbivory stress and grown in 200 mm y-1 rainfall (I and II). J. curcas seedlings exhibited an undercompensatory growth response to herbivory stress in all the drought stress levels (II). Our literature review showed that arthropod herbivore load associated with J. curcas was relatively low (78 species) across the globe. Flower and fruit feeders were more common than foliage feeders (III). The highest average genetic diversity was observed, as expected, within the native range of J. curcas (IV) with record levels observed in populations sampled in the State of Chiapas of Mexico. The annual seed yield varied greatly across the globe from 26 to 11,150 kg ha-1 ; the global mean annual seed yield was 2,220 kg ha-1. Age had a linear whereas rainfall and plant density had a significant quadratic effect on seed yield. Differences in seed yields of J. curcas across the globe might be due to differences in site-specific agro-climatic, soil fertility and genetic factors as well as agronomic practices applied to achieve a high seed yield (IV). Further genetic improvements will be required to produce cultivars which can provide consistently high seed and oil yields. My results contribute to promote commercial production of J. curcas by providing more information on the ecological requirements of the species.

Présentation Version intégrale ( 7 Mb)