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Jatropha curcas is an oil-bearing semievergreen shrub or small tree with potential as a source of sustainable biofuel, yet information regarding vegetative and fruit biomass in relation to plant architecture is lacking. Research conducted in Indonesia used the tree based functional branch analysis (FBA) model as a non-destructive method to estimate above and belowground biomass, and plant architecture. The FBA utility for shrubs was unknown and required modification. This research used destructive measurements to validate modifications to the FBA model that included subcategorisation of the tapering coefficient for twig, branch, and wood diameter classes, and addition of a fruit load parameter in the distal link. The modified FBA model confirmed jatropha to be a shrub rather than a tree, producing variable estimates for aboveground biomass. This variation was due to morphological plasticity in the length-diameter relationship of the branches that diverged from fractal branching architecture. Fruit biomass variation between replicates was not well estimated and total proximal root diameter was a poor predictor of total root biomass, due to the proximal roots having enlarged water storage structures that do not follow fractal branching assumptions. Jatropha fruit was shown to predominate on twigs with a diameter between 0.9 and 1.4 cm. Understanding the correlation between fruit development and plant architecture will be necessary for fine-tuning the FBA model for future commercial breeding and selection. The high degree of morphological plasticity displayed by jatropha requires consideration when determining plant biomass.

at 11 a.m. in the Aula. AbstractJatropha curcas L. is a biofuel crop that has not lived up to expectations due to a combination of hype and disappointment and biophysical factors. This PhD thesis is based on the plant production component of the JARAK programme which aimed to bridge the gap between truth and fiction. This study reviewed the jatropha hype and disappointment and further investigated the hypothesis that jatropha growth and yield are limited by biophysical factors of plant characteristics, cropping systems, and management. My review of the hype and disappointment shows that despite the high expectations fuelled by market pull and technology push, and numerous actors, the commercial potential for jatropha is limited by policy and governance, economics, social, technology, logistical, and environmental. A study of the biophysical components confirms that no current varieties suited to different cropping systems and locations are available. Jatropha aboveground biomass is partitioned predominantly into a structure of stem, branches, and twigs. The below to aboveground biomass ratio was 0.5 and fruit which was found only on productive twigs accounted for the smallest portion of biomass measured. Seed yields were disappointingly small (109 kg ha -1 ) and were largest in monoculture, followed by intercropping and hedgerows in that order, although yields were influenced by age and management of pruning and fertiliser. Seed yield across the three cropping systems can be predicted using plant height and the number of productive twig/branch, although the number of inflorescence clusters per productive twig may be important. Intercropping between jatropha and maize (Zea mays L.) resulted in competition for resources both belowground and aboveground that reduced maize yields. Shoot pruning was effective in managing aboveground competition, while root pruning and root barriers effectively managed competition belowground. Leaf prunings provided a limited, but positive fertility effect on maize yield comparable to 21 kg N ha -1. Jatropha -maize intercropping has potential for long-term productivity provided management practices such as fertiliser, pruning, and planting density can be developed to minimise competition and enhance complementarity. Based on my review of the jatropha hype and disappointment and my biophysical research results, the planting of jatropha by smallholders, or as a plantation crop cannot be recommended. Once the issues I highlight have been resolved and market confidence restored, jatropha may finally become a commercial source of biodiesel able to provide improved socio-economic and environmental benefits.