Leaf-residing <Emphasis Type="Italic">Methylobacterium</Emphasis> species fix nitrogen and promote biomass and seed production in <Emphasis Type="Italic">Jatropha curcas</Emphasis>

Background

Jatropha curcas L. (Jatropha) is a potential biodiesel crop that can be cultivated on marginal land because of its strong tolerance to drought and low soil nutrient content. However, seed yield remains low. To enhance the commercial viability and green index of Jatropha biofuel, a systemic and coordinated approach must be adopted to improve seed oil and biomass productivity. Here, we present our investigations on the Jatropha-associated nitrogen-fixing bacteria with an aim to understand and exploit the unique biology of this plant from the perspective of plant–microbe interactions.

Results

An analysis of 1017 endophytic bacterial isolates derived from different parts of Jatropha revealed that diazotrophs were abundant and diversely distributed into five classes belonging to α, β, γ-Proteobacteria, Actinobacteria and Firmicutes. Methylobacterium species accounted for 69.1 % of endophytic bacterial isolates in leaves and surprisingly, 30.2 % which were able to fix nitrogen that inhabit in leaves. Among the Methylobacterium isolates, strain L2-4 was characterized in detail. Phylogenetically, strain L2-4 is closely related to M. radiotolerans and showed strong molybdenum-iron dependent acetylene reduction (AR) activity in vitro and in planta. Foliar spray of L2-4 led to successful colonization on both leaf surface and in internal tissues of systemic leaves and significantly improved plant height, leaf number, chlorophyll content and stem volume. Importantly, seed production was improved by 222.2 and 96.3 % in plants potted in sterilized and non-sterilized soil, respectively. Seed yield increase was associated with an increase in female–male flower ratio.

Conclusion

The ability of Methylobacterium to fix nitrogen and colonize leaf tissues serves as an important trait for Jatropha. This bacteria–plant interaction may significantly contribute to Jatropha’s tolerance to low soil nutrient content. Strain L2-4 opens a new possibility to improve plant’s nitrogen supply from the leaves and may be exploited to significantly improve the productivity and Green Index of Jatropha biofuel.

     

Insufficient Evidence of <Emphasis Type="Italic">Jatropha curcas</Emphasis> L. Invasiveness: Experimental Observations in Burkina Faso,West Africa

Biofuel plants such as Jatropha curcas L. have potential to support the livelihoods of rural communities and contribute to sustainable rural development in Africa, if risks and uncertainties are minimized. Yet, recent papers have warned of the risk of biological invasions in such tropical regions as a consequence of the introduction of exotic biofuel crops. We investigated the seed dispersal risk and invasiveness potential of both J. curcas monoculture plantations and live fences into adjacent cultivated and uncultivated land use systems in Sissili province, Burkina Faso. Invasiveness potential was assessed through (i) detecting evidence of natural regeneration in perimeters around J. curcas plantations and live fences, (ii) assessing seed dispersal mechanisms, and (iii) assessing seedling establishment potential through in situ direct seed sowing. Spontaneous regeneration around the plantation perimeters of the three sites was very low. Individual seedling density around J. curcas live fences was less than 0.01 m^?2 in all sites. Seventy percent of the seedlings were found close to the live fence and most of them derived from the same year (96 %), which indicates low seed-bank longevity and seedling survival. J. curcas can be dispersed by small mammals and arthropods, particularly rodents and ants. In some sites, such as in Onliassan, high secondary seed dispersal by animals (up to 98 %) was recorded. There were highly significant differences in germination rates between seeds at the soil surface (11 %) and those buried artificially at 1–2-cm depth (64 %). In conclusion, we failed to find convincing evidence of the spreading of J. curcas or any significant impact on the surrounding environment.     

Changes in leaf epicuticular wax,gas exchange and biochemistry metabolism between <Emphasis Type="Italic">Jatropha mollissima</Emphasis> and <Emphasis Type="Italic">Jatropha curcas</Emphasis> under semi-arid conditions

Jatropha curcas and Jatropha mollissima plants were evaluated under conditions of high (HSM) and low (LSM) soil moisture in a semi-arid environment, as changes in the content and concentration of epicuticular wax and the leaf metabolism which could have a relationship with drought tolerance. Besides epicuticular wax, gas exchange, antioxidant system and biochemical parameters of the photosynthetic metabolism were measured. The epicuticular wax content increased only in J. mollissima leaves 95 % under LSM, when compared with HSM conditions. Therefore, J. curcas invested less in the production of long-chain n-alkanes than did J. mollissima under LSM conditions. J. mollissima plants showed the highest CO₂ assimilation rate during the HSM period compared to J. curcas. Both species showed high stability in some leaf biochemistry products, highlighting the highest sugar content, free amino acids, total soluble protein, and photosynthetic pigments in the leaves of J. mollissima plants under both of the soil moisture conditions. Moreover, the stability and performance of the different parameters, such as morphologic variables, seem to allow J. mollissima plants to tolerate semi-arid conditions.     

Positive feedback with mycorrhizal fungi alleviates negative effects of intercropping the energy crop <Emphasis Type="Italic">Jatropha curcas</Emphasis> with <Emphasis Type="Italic">Crotalaria retusa</Emphasis>

Little is known about the arbuscular mycorrhizal status of the ligneous plant Jatropha curcas, an energy crop that raises high expectations worldwide. We hypothesized that its early mycorrhization and growth could be improved by co-culturing it with Crotalaria retusa, a mycotrophic legume species. Soil samples collected from a 15-year-old J. curcas hedgerow were transferred to the greenhouse, along with soil sampled from the contiguous fallow field. Three pot-culture modalities were studied for 3 months: jatropha alone, jatropha sowed after the clipping of 2-month-old C. retusa, and jatropha sowed next to 2-month-old C. retusa. J. curcas biomass was significantly lower when it was co-cultured with C. retusa in both soil types as compared to when it was grown individually, while its biomass following the cut of C. retusa was not impacted. J. curcas shoot P content was significantly improved only when both plant species grew in the hedgerow soil, and so was mycorrhization intensity. Additionally, the composition of the J. curcas root mycorrhizal community was closer to that of C. retusa when using this hedgerow soil. Overall, J. curcas development was not improved by its association with C. retusa, but the soil cropping history appeared essential to their mycorrhizal interactions. These were favored by a soil mycorrhizal community shaped by multiple years of J. curcas monoculture. Improved knowledge about these preferential association patterns with J. curcas is needed to improve its co-culture with compatible mycotrophic legumes.     

Genetic variability,character association and divergence studies in <Emphasis Type="Italic">Jatropha curcas</Emphasis> for improvement in oil yield

Key message

Variability in traits of 15, diverse 6-year-old candidate plus trees of Jatropha curcas was determined to identify the best gain heritable traits correlating with oil yield for Jatropha improvement.

Abstract

Study was carried out on 15 6-year-old candidate plus trees of Jatropha curcas adapted on semi-arid wasteland with an objective to assess variation in morphological, physiological and oil quality characters. Heritable and non-heritable components of the total variability of the characters were determined by genotypic (GCV) and phenotypic (PCV) co-efficient of variation, heritability and genetic advance (GA) and the best gain traits for Jatropha improvement through selection and breeding were assessed. Further, association among the traits were assessed and germplasm were separated into different clusters. Significant variation was found among the different genotypes for all the characters. The photosynthetic and transpiration rate correlated with oil content, seed and oil yield. The chlorophyll pigments correlated positively with the photosynthetic rate and oil content. The seed oil content varied considerably from 27.68 % (JCN01) to 37.49 % (JCN14) and had high heritability, but it had low PCV and GCV and moderate GA. The oil yield plant^?1 had high genetic variability and varied significantly from 0.07 (JCN15) to 0.47 kg plant^?1 (JCN09/IC 565733). Though the different fatty acids differed significantly with different germplasm and also had high heritability, they had low PCV, GCV and GA. Seed weight, fruit weight, seed weight fruit^?1 and seed yield plant^?1 strongly correlated with oil yield and had moderate to high GCV, PCV, coupled with high heritability and GA. Germplasm were separated into four distinct clusters with a maximum inter distance found between cluster II and IV, and minimum between cluster I and III. The study helped to identify the superior germplasm among diverse genotypes of J. curcas that can serve as parents with desirable characters like high oil yield, low stomatal conductance and high water use efficiency for further breeding purposes.

     

Growth and photosynthetic responses in Jatropha curcas L. seedlings of different provenances to watering regimes

Seedlings from four provenances of Jatropha curcas were subjected to 80, 50, and 30% of soil field capacity in potted experiments in order to study their responses to water availability. Our results showed that with the decline of soil water availability, plant growth, biomass accumulation, net photosynthetic rate, stomatal conductance (g_s), and transpiration rate (E) decreased, whereas leaf carbon isotope composition (δ¹³C), leaf pigment contents, and stomatal limitation value increased, while maximal quantum yield of PSII photochemistry was not affected. Our findings proved that stomatal limitation to photosynthesis dominated in J. curcas under low water availability. The increase of δ¹³C should be attributed to the decrease in g_s and E under the lowest water supply. J. curcas could adapt to low water availability by adjusting its plant size, stomata closure, reduction of E, increasing δ¹³C, and leaf pigment contents. Moreover, effects of provenance and the interaction with the watering regime were detected in growth and many physiological parameters. The provenance from xeric habitats showed stronger plasticity in the plant size than that from other provenances under drought. The variations may be used as criteria for variety/provenance selection and improvement of J. curcas performance.     

Effects of chilling stress on the accumulation of soluble sugars and their key enzymes in <Emphasis Type="Italic">Jatropha curcas</Emphasis> seedlings

As osmolytes and signaling molecules, soluble sugars participate in the response and adaptation of plants to environmental stresses. In the present study, we measured the effect of chilling (12 °C) stress on the contents of eight soluble sugars in the leaves, cotyledons, stems, and roots of Jatropha curcas seedlings, as well as on the activities of eight rate-limiting enzymes that are critical to the metabolism of those soluble sugars. Chilling stress promoted both starch hydrolysis and soluble sugar accumulation. The soluble sugar contents of the leaves and cotyledons were affected more than that of the stems and roots. Meanwhile, the activities of the corresponding metabolic enzymes (e.g., β-amylase, uridine diphosphate glucose phosphorylase, and sucrose phosphate synthase) also increased in some organs. The gradual increase of soluble neutral alkaline invertase activity in the four studied organs suggested that sucrose catabolic production, such as glucose and fructose, was especially important in determining resistance to chilling stress and hexose signal transduction pathway. In addition, the substantial accumulation of raffinose family oligosaccharides and increase in corresponding metabolic enzyme activity suggested that galactinol and raffinose play an important role in determining the chilling resistance of J. curcas. Together, these findings establish a foundation for determining the relationship between the chilling resistance and soluble sugar accumulation of J. curcas and for investigating the mechanisms underlying sugar signaling transduction and stress responses.     

Detection of symbionts and virus in the whitefly <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Hemiptera: Aleyrodidae), vector of the <Emphasis Type="Italic">Mungbean yellow mosaic India virus</Emphasis> in Central India

Legume crops in Central India, the main soybean production area of the country, may suffer from yellow mosaic disease caused by the Mungbean yellow mosaic India virus (MYMIV). MYMIV is transmitted by the sweet potato whitefly, Bemisia tabaci (Gennadius), which is a species complex composed of various genetic groups. This vector species harbors different endosymbionts among regional strains and among individuals. To elucidate fundamental aspects of this virus vector in the state of Madhya Pradesh, the infection status of the symbionts and the virus in whiteflies was studied. A polymerase chain reaction (PCR) survey of the whiteflies collected in Madhya Pradesh found four secondary endosymbionts, Arsenophonus, Hemipteriphilus, Wolbachia, and Cardinium, in addition to the primary endosymbiont Portiera. Arsenophonus and Hemipteriphilus were highly infected but the infection rates of Wolbachia and Cardinium were low. MYMIV was detected in whitefly populations collected from various host plants in Madhya Pradesh. The whitefly populations belonged to the Asia I and II genetic groups; several different Asia II populations were also distributed. Specific relations were not observed among symbiont infection status, virus infection, and the whitefly genetic groups in the populations of Madhya Pradesh, though Cardinium was highly detected in the Asia II-1 group. New primers, which can be used for PCR template validation and for discriminating two phylogenetically close endosymbionts, were designed.