Dynamic adsorption of α-pinene and linalool on silica nanoparticles for enhanced antifeedant activity against agricultural pests

The terpene compounds, α-pinene and linalool were formulated with silica nanoparticles (SNPs) by a simple immersion method and the antifeedant activity of these formulations was evaluated against two major agricultural pests, the tobacco cutworm (Spodoptera litura F.) and the castor semilooper (Achaea janata L.) in laboratory bioassays. The interaction between terpenes and SNPs, shelf-life, suspension stability as well as the bioactivity of the nanoformulations were also studied. Both these terpenes in their pure form are known to deter feeding in several lepidopterous insects. However, formulating these pure terpene compounds with nano silica enhanced their biological activity up to 25 times to S. litura. Fourier transform infrared spectroscopy analysis of these nano botanical formulations indicated the presence of hydrogen bonding between terpenes and the surface of SNPs. Transmission electron microscopy images confirmed the higher aggregation property of the SNPs. Suspension studies validated the improved shelf-life of the nano-biocomposites, while X-ray diffraction (XRD) revealed the amorphous nature of formulations and no crystalline impurities. Adsorption of α-pinene and linalool onto SNPs resulted in an effective formulation that enhanced the antifeedant potential of the individual terpenes against insects while producing longer shelf-life for the terpenes.     

Identification of molecular markers associated with sugar-related traits in a <Emphasis Type="Italic">Saccharum</Emphasis> interspecific cross

The cultivated sugarcane (Saccharum spp. hybrids, 2n = 100–130) is one crop for which interspecific hybridization involving wild germplasm has provided a major breakthrough in its improvement. Few clones were used in the initial hybridization event leading to a narrow genetic base for continued cultivar development. Molecular breeding would facilitate the identification and introgression of novel alleles/genes from the wild germplasm into cultivated sugarcane. We report the identification of molecular markers associated with sugar-related traits using an F₁ population derived from a cross between S. officinarum ‘Louisiana Striped’ × S. spontaneum ‘SES 147B’, the two major progenitor species of cultivated sugarcane. Genetic linkage maps of the S. officinarum and S. spontaneum parents were produced using the AFLP, SRAP and TRAP molecular marker techniques. The mapping population was evaluated for sugar-related traits namely, Brix (B) and pol (P) at the early (E) and late (L) plant growing season in the plant cane (04) and first ratoon (05) crops (04EB, 04LB, 04LP, 05EB and 05EP). For S. officinarum, combined across all the traits, a total of 30 putative QTLs was observed with LOD scores ranging from 2.51 to 7.48. The phenotypic variation (adj. R²) explained by all QTLs per trait ranged from 22.1% (04LP) to 48.4% (04EB). For S. spontaneum, a total of 11 putative QTLs was observed with LOD scores ranging from 2.62 to 4.70 and adj. R² ranging from 9.3% (04LP) to 43.0% (04LB). Nine digenic interactions (iQTL) were observed in S. officinarum whereas only three were observed in S. spontaneum. About half of the QTLs contributed by both progenitor species were associated with effects on the trait that was contrary to expectations based on the phenotype of the parent contributing the allele. Quantitative trait loci and their associated effects were consistent across crop-years and growing seasons with very few QTLs being unique to the early season. When the data were reanalyzed using the non-parametric discriminant analysis (DA) approach, significant marker-trait associations were detected for markers that were either identical to or in the vicinity of markers previously identified using the traditional QTL approach. Discriminant analysis also pointed to previously unidentified markers some of which remained unlinked on the map. These preliminary results suggest that DA could be used as a complementary approach to traditional QTL analysis in a crop like sugarcane for which saturated linkage maps are unavailable or difficult to obtain.     

Linkage mapping and genome analysis in a Saccharum interspecific cross using AFLP, SRAP and TRAP markers

Framework genetic linkage maps of two progenitor species of cultivated sugarcane, Saccharum officinarum ‘La Striped’ (2n = 80) and S. spontaneum ‘SES 147B’ (2n = 64) were constructed using amplified fragment length polymorphism (AFLP), sequence related amplified polymorphism (SRAP), and target region amplification polymorphism (TRAP) markers. The mapping population was comprised of 100 F₁ progeny derived from the interspecific cross. A total of 344 polymorphic markers were generated from the female (S. officinarum) parent, out of which 247 (72%) were single-dose (segregating in a 1:1 ratio) and 33 (9%) were double-dose (segregating in a 3.3:1 ratio) markers. Sixty-four (19%) markers deviated from Mendelian segregation ratios. In the S. spontaneum genome, out of a total of 306 markers, 221 (72%) were single-dose, 43 (14%) were double-dose, and 42 markers (14%) deviated from Mendelian segregation ratios. Linkage maps with Kosambi map distances were constructed using a LOD score ≥5.0 and a recombination threshold of 0.45. In Saccharum officinarum, 146 markers were linked to form 49 linkage groups (LG) spanning 1732 cM whereas, in S. spontaneum, 121 markers were linked to form 45 LG spanning 1491 cM. The estimated genome size of S. officinarum ‘La Striped’ was 2448 cM whereas that of S. spontaneum ‘SES 147B’ was 3232 cM. Based on the two maps, genome coverage was 69% in S. officinarum and 46% in S. spontaneum. The S. officinarum parent ‘La Striped’ behaved like an auto-allopolyploid whereas S. spontaneum ‘SES 147B’ behaved like a true autopolyploid. Although a large disparity exists between the two genomes, the existence of simple duplex markers, which are heterozygous in both parents and segregate 3:1 in the progeny, indicates that pairing and recombination can occur between the two genomes. The study also revealed that, compared with AFLP, the SRAP and TRAP markers appear less effective at generating a large number of genome-wide markers for linkage mapping in sugarcane. However, SRAP and TRAP markers can be useful for QTL mapping because of their ability to target gene-rich regions of the genome, which is a focus of our future research.     

Regeneration through somatic embryogenesis from petal-derived calli of Rosa hybrida L. cv arizona (hybrid tea)

Summary Somatic embryogenesis in callus cultures of petal explants of rose cv arizona is reported here. The calli from petals initiated on dicamba containing medium were friable and gave rise to embryos after several subcultures while those obtained from other explants did not show embryogenesis. Abscisic acid and phloroglucinol were necessary during maturation and plant development, respectively. The individual embryos grew into true-to-type plants.     

Competitiveness of native Bradyrhizobium japonicum strains in two different soil types

Interstrain competitiveness is a key factor affecting the performance of rhizobium inoculant. In the present study five native strains of Bradyrhizobium japonicum, namely SSF 4, SSF 5, SSF 6, SSF 7 and SSF 8, were assessed for their competitiveness in nodulating soybean using serological methods. The strains were inoculated individually or with the type strain USDA 110 at a 1:1 ratio. Nodule occupancy determined by immunofluorescence and dot immunoblot assay revealed that under in vitro conditions SSF 8 is more competitive than USDA 110 whereas the others were less competitive. The competitive ability of these strains was also estimated in pot culture in the field. In red soil both SSF 8 and USDA 110 were equally competitive whereas in black soil SSF 8 competed better than USDA 110 and produced more nodules. In a black soil field trial using a randomized block design, USDA 110 or SSF 8, when inoculated alone, occupied the majority of the nodules and enhanced nodule dry weight and shoot biomass. SSF 8 was more competitive when the strains were co-inoculated. Received: 1 November 1996     

Direct evidence for the function of FUM13 in 3-ketoreduction of mycotoxin fumonisins in Fusarium verticillioides

Fumonisins are mycotoxins produced by Fusarium verticillioides, a widespread pathogen of corn. Although the gene cluster for the biosynthesis of fumonisins has been cloned, the majority of the genes have not been biochemically characterized. Here, we report the biochemical characterization of FUM13, a gene that encodes a short-chain dehydrogenase/reductase required for fumonisin biosynthesis. FUM13 has been expressed in E. coli, and the produced protein, Fum13p, has been purified. When the protein was incubated with 3-keto fumonisin B(3) (FB(3)) in the presence of NADPH, FB(3) was produced. The data provide direct evidence for the role of FUM13 in the 3-ketoreduction of fumonisins. In a functional complementation experiment, FUM13 gene was introduced into tsc10 mutants of the yeast Saccharomyces cerevisiae, which carry a mutation in the 3-ketosphinganine reductase gene in the sphingolipid pathway. The tsc10 mutants were not able to grow on the selection medium, but the same mutants transformed with FUM13 were able to grow. The results further confirm the function of FUM13 in 3-ketoreduction in vivo.     

Determining the biosynthetic sequence in the early steps of the fumonisin pathway by use of three gene-disruption mutants of Fusarium verticillioides

Fumonisins are polyketide-derived mycotoxins produced by Fusarium verticillioides, a fungal pathogen of corn plants. Although a gene cluster for the biosynthesis of fumonisins has been cloned, the biosynthetic pathway is still not clear. We have used three gene-disrupted mutants, designated DeltaFUM1, DeltaFUM6, and DeltaFUM8, to study the early steps of the pathway. Fumonisins were not produced in single-strain cultures of the DeltaFUM1, DeltaFUM6, and DeltaFUM8 mutants. However, fumonisins were produced by DeltaFUM1 or DeltaFUM8 mutants when they were cocultured with the DeltaFUM6 mutant. No fumonisins were produced when the DeltaFUM1 and DeltaFUM8 mutants were cocultured. These results suggest that the DeltaFUM6 mutant produces a fumonisin intermediate that can be further metabolized by fumonisin biosynthetic enzymes in the DeltaFUM1 and DeltaFUM8 mutants. To isolate the potential intermediates produced by DeltaFUM6, we followed a time course of cocultures of the DeltaFUM1 and DeltaFUM6 and the DeltaFUM8 and DeltaFUM6 mutants. Liquid chromatographic-mass spectrometric data suggested that metabolites having the general carbon skeleton of fumonisins with 1-4 hydroxyl groups were accumulated over a 7-day period. These results indicate that fumonisin biosynthesis starts with Fum1p-catalyzed carbon-chain assembly followed by the Fum8p-catalyzed alanine condensation. The resulting product then can be further oxidized by Fum6p and other enzymes.     

Induction of systemic resistance to Xanthomonas oryzae pv. oryzae by salicylic acid in Oryza sativa (L.)

Journal of Plant Diseases and Protection - The effect of salicylic acid (SA) is hypothesized to be a natural signal that triggers the systemic induction of phenolics, pathogenesis-related proteins...     

Isolation and acclimation of a microbial consortium for improved aerobic degradation of alpha-hexachlorocyclohexane

A microbial consortium that can utilize alpha-hexachlorocyclohexane (alpha-HCH) as a sole source of carbon and energy was isolated from soil and sewage through a novel technique involving an initial enrichment in a glass column reactor followed by a shake flask enrichment. This consortium took 14 days to completely mineralize 5 and 10 microg mL(-)(1) alpha-HCH in mineral salts medium in shake flasks. The degradative ability of this consortium improved very markedly on acclimation by successive and repeated passages through media containing increasing concentrations of alpha-HCH. The acclimated consortium could degrade 100 microg mL(-)(1) of alpha-HCH within 72 h at a degradation rate of 58 microg mL(-)(1) day(-)(1) with concomitant release of stoichiometric amounts of chloride. Accumulation of any intermediary metabolites was not detected in the culture broth as tested by TLC and GC, implying complete mineralization of the substrate. The acclimated consortium contained eight bacterial strains and a fungus. The individual strains and the different permutations and combinations of them, however, were able to utilize only 10 microg mL(-)(1) of alpha-HCH. Mesophilic temperatures (20-30 degrees C) and near-neutral pH (6.0-8.0) were most favorable for alpha-HCH degradation. Among the auxiliary carbon sources tested, ethanol, benzoate, and glucose (at higher concentrations) retarded the degradation of alpha-HCH, whereas the addition of cellulose, sawdust, and low concentrations of glucose (<200 microg mL(-)(1)) and acetone enhanced the rate of degradation.