Genetic variation in Jatropha curcas, a prospective biodiesel plant, is limited, and interspecific hybridization needed for its genetic improvement. Progeny from interspecific crosses between J. curcas and Jatropha integerrima can be used to improve agronomic characters and to increase oil content and yield. However, these hybrids have not been characterized cytologically. The present study was aimed at the analysis of chromosome behavior during meiosis and chromosome composition of S1 plants derived from an interspecific F1 hybrid using genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH). Bivalents that formed as a result of interspecific pairing were frequently observed, suggesting the presence of homoeologous chromosomes from the two species. Almost half of microspores were derived from the reduction division; GISH analysis indicated random transmission of the parent chromosomes to microspores. Male fertility measured as pollen staining with acetocarmine was 48.4%. In contrast, GISH analysis of S1 plants revealed preferential transmission of J. curcas chromosomes. We also found segment exchange between chromosomes of the two species (interspecific translocation) by GISH and FISH analyses. Introgression of J. integerrima chromosome segments into the J. curcas genome would help to improve Jatropha cultivars for mass production.

An interspecific hybrid Jatropha curcas (Jc) × Jatropha integerrima (Ji) was developed between jatropha (Jc) from Mexico and Ji from Thailand. Jc is a large canopy plant with soft wood, while Ji is a tall plant with semi-hard wood. The F1 hybrid and their parents were grown under field conditions at a spacing of 1 m × 1.5 m. One-year-old plants were harvested and determined for biomass yield, calorific value and chemical composition of wood, as well as for heterosis (hybrid vigour) of these characters. The F1 plants gave an average fresh wood weight of 18.07 kg/plant, a moisture content of 46.56%, a dry wood weight of 9.56 kg/plant and a wood density of 0.62 g/cm3. The F1 hybrid had less ash (2.60%) than Jc (6.93%), but a higher heat value of wood (18.73 MJ/kg) than Jc (17.77 MJ/kg). Heterosis over mid-parent was very high and positive in dry wood weight, fresh wood weight and number of secondary branches at 542, 310 and 450%, respectively, while negative heterosis was found in moisture content ( − 24.86%). The desirable traits found in the F1 hybrid can be fixed by cutting propagation of the selected plants.

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Jatropha (Jatropha curcas) is one of the most popular tree crops for seed production as a source of oil for biodiesel. However, currently grown cultivars are too large in canopy size and thus have very low harvest index. Alteration of canopy height and size can lead to identification of a desirable plant architecture for jatropha. A study was conducted to determine genetic control of dwarfiness and erect growth habit in jatropha populations derived from an interspecific cross between J. curcas with tall-erect (TL-ER) plant type and J. integerrima with dwarf-spreading (DW-SP) plant type. Crosses were made between both species to develop F1, F2, BC1F1, and BC1F2 generations. The F2 plants segregated at a 1:2:1 ratio for tall (TL), intermediate (ID), and dwarf (DW) plant types as well as for spreading (SP), upright (UP), and erect (ER) canopy angles. Both characters segregated independently producing nine phenotypes including TL-ER, TL-UP, TL-SP, ID-ER, ID-UP, ID-SP, DW-ER, DW-UP, and DW-SP at a 1:2:1:2:4:2:1:2:1 ratio. The BC1F1 (J. curcas × F1) plant segregated into TL-ER, TL-UP, ID-ER, and ID-UP at a 1:1:1:1 expected ratio. Six BC1F2 lines were also evaluated to confirm the results by selfing two trees each of BC1F1 showing TL-ER, TL-UP, and ID-ER growth habits. The progenies of TL-ER trees were all TL-ER; the progenies of TL-UP trees segregated into TL-ER, TL-UP, and TL-SP at an expected 1:2:1 ratio, whereas the progenies of ID-ER trees segregated into TL-ER, ID-ER, and DW-ER at an expected 1:2:1 ratio. The results indicated that dwarfiness and erect growth habit were each controlled by independent genes with incomplete dominant action. The knowledge and progenies obtained from this study can be used in breeding jatropha for desirable canopy size and shape.