Rubbery taproot disease of sugar beet in Serbia associated with 'Candidatus phytoplasma solani'

Rubbery taproot disease (RTD) of sugar beet was observed in Serbia for the first time in the 1960s. The disease was already described in neighboring Bulgaria and Romania at the time but it was associated with abiotic factors. In this study on RTD of sugar beet in its main growing area of Serbia, we provide evidence of the association between 'Candidatus Phytoplasma solani' (stolbur phytoplasma) infection and the occurrence of typical RTD symptomatology. 'Ca. P. solani' was identified by PCR and the sequence analyses of 16S ribosomal RNA, tuf, secY, and stamp genes. In contrast, the causative agent of the syndrome “basses richesses” of sugar beet-namely, 'Ca. Arsenophonus phytopathogenicus'-was not detected. Sequence analysis of the stolbur strain's tuf gene confirmed a previously reported and a new, distinct tuf stolbur genotype (named 'tuf d') that is prevalent in sugar beet. The sequence signatures of the tuf gene as well as the one of stamp both correlate with the epidemiological cycle and reservoir plant host. This study provides knowledge that, for the first time, enables the differentiation of stolbur strains associated with RTD of sugar beet from closely related strains, thereby providing necessary information for further epidemiological work seeking to identify insect vectors and reservoir plant hosts. The results of this study indicate that there are differences in hybrid susceptibility. Clarifying the etiology of RTD as a long-known and economically important disease is certainly the first step toward disease management in Serbia and neighboring countries.This is the peer reviewed version of the following article: Ćurčić Ž., Stepanović J., Zübert C., Taški-Ajduković K., Kosovac A., Rekanović E., Kube M., Duduk B. Rubbery taproot disease of sugar beet in Serbia associated with 'Candidatus phytoplasma solani'. Plant Disease 2021, 105 (2), 255 – 263. [https://doi.org/10.1094/PDIS-07-20-1602-RE]

Identification and quantification of surface wax compounds covering aerial organs of selected plant species

The cuticle is an external barrier of aerial plant organs that prevents desiccation. It is composed of hydrophobic waxes, i.e. complex mixtures of very-long-chain aliphatics, alicyclics and aromatics, lying on top of (epicuticular) and in between (intracuticular) a polyester matrix known as cutin. Wax compositions vary greatly between plant species, organs and tissues, both qualitatively and quantitatively. This thesis describes the identification and quantification of cuticular waxes of three plant species, including structure elucidation of novel compounds, chain length profiling, and wax compound distributions between intracuticular and epicuticular compartments for the first two species. Leaves of Aloe arborescens were found covered with 15 μg/cm² wax on the adaxial side and 36 μg/cm² on the abaxial side, with 3:2 and 1:1 ratios between epicuticular and intracuticular wax layers on each side, respectively. Along with ubiquitous wax compounds, three homologous series were identified as novel 3-hydroxy fatty acids (predominantly C₂₈), their methyl esters (predominantly C₂₈), and 2-alkanols (predominantly C₃₁), and their biosynthetic pathways were hypothesized based on structural similarities and homolog distributions. The adaxial side of young and old Phyllostachys aurea leaves was found covered with 1.7 to 1.9 μg/cm² each of epi- and intracuticular waxes. In addition to typical aliphatics and alicyclics, novel primary amides were identified, with their chain length profile peaking at C₃₀, and found exclusively in the epicuticular waxes, hence near the true plant surface. Flag leaves and peduncles of Triticum aestivum cv. Bethlehem were found covered with 16 and 49 μg/cm² wax, respectively, dominated by 1-alkanols in the case of the former and β-diketones and hydroxy-β-diketones for the latter. Along with previously reported wax classes, numerous new classes were identified as homologous series: 2-alkanol esters, benzyl esters, phenethyl esters, p-hydroxyphenethyl esters, secondary alcohols, primary/secondary diols and their esters, hydroxy- and oxo-2-alkanol esters, 4-alkylbutan-4-olides, internally methyl-branched alkanes, and 2,4-ketols. Other new compounds were found as single homologs: C₃₃ 2,4-diketone, C₃₁ mid-chain β-ketols, C₃₀ mid-chain α-ketols and α-diketone, as well as C₃₁ mid-chain ketones. Biosynthetic pathways are proposed in the thesis for the new compounds, based on common structural features and matching chain length patterns between related compound classes.Science, Faculty ofChemistry, Department ofGraduat

Identification of In-Chain-Functionalized Compounds and Methyl-Branched Alkanes in Cuticular Waxes of <i>Triticum aestivum</i> cv. Bethlehem

<div><p>In this work, cuticular waxes from flag leaf blades and peduncles of <i>Triticum aestivum</i> cv. Bethlehem were investigated in search for novel wax compounds. Seven wax compound classes were detected that had previously not been reported, and their structures were elucidated using gas chromatography-mass spectrometry of various derivatives. Six of the classes were identified as series of homologs differing by two methylene units, while the seventh was a homologous series with homologs with single methylene unit differences. In the waxes of flag leaf blades, secondary alcohols (predominantly C₂₇ and C₃₃), primary/secondary diols (predominantly C₂₈) and esters of primary/secondary diols (predominantly C₅₀, combining C₂₈ diol with C₂₂ acid) were found, all sharing similar secondary hydroxyl group positions at and around C-12 or ω-12. 7- and 8-hydroxy-2-alkanol esters (predominantly C₃₅), 7- and 8-oxo-2-alkanol esters (predominantly C₃₅), and 4-alkylbutan-4-olides (predominantly C₂₈) were found both in flag leaf and peduncle wax mixtures. Finally, a series of even- and odd-numbered alkane homologs was identified in both leaf and peduncle waxes, with an internal methyl branch preferentially on C-11 and C-13 of homologs with even total carbon number and on C-12 of odd-numbered homologs. Biosynthetic pathways are suggested for all compounds, based on common structural features and matching chain length profiles with other wheat wax compound classes.</p></div

Structure elucidation of internally branched alkanes in wheat leaf and peduncle wax.

<p>(A) Mass spectrum of co-eluting isomers of C₃₂ internally branched alkane and major fragmentations of the main isomer. (B) EICs showing intensities of the alkyl fragment <i>m/z</i> 85 and of regiomer-characteristic α-fragments <i>m/z</i> 140, 168, 196 and 224. a.u.: arbitrary units. (C) Mass spectrum of co-eluting isomers of C₃₃ internally branched alkane and major fragmentations of the main isomer. (B) EICs showing intensities of the alkyl fragment <i>m/z</i> 85 and of regiomer-characteristic α-fragments <i>m/z</i> 154, 182, 210 and 238.</p

Total coverages of new compound classes in wheat leaf and peduncle waxes.

<p>Coverages (μg/cm²) of compound classes identified in the total wax mixtures covering the (A) flag leaf blade and (B) peduncle of <i>T</i>. <i>aestivum</i> cv. Bethlehem. Bars represent mean ± standard deviation (<i>n</i> = 5).</p

Structure elucidation of hydroxy-2-alkanol esters in wheat leaf and peduncle wax.

<p>(A) Mass spectrum of co-eluting TMS derivatives of C₃₅ hydroxy-2-alkanol ester isomers. (B) Major fragmentations of all isomers in (A). (C) EICs showing cumulative intensity of <i>m/z</i> 73 and 75, as well as intensities of: metamer-shared α-fragments <i>m/z</i> 185 and 199, regiomer-characteristic α-fragments <i>m/z</i> 173, 187, 201 and 215, and TMS-transfer acid fragments <i>m/z</i> 385 and 413. a.u.: arbitrary units. (D) Mass spectrum of co-eluting Ac derivatives of C₃₅ hydroxy-2-alkanol ester isomers. (E) Major fragmentations of all isomers in (D). (F) Mass spectrum and major fragmentations of TMS derivatives of co-eluting C₁₅ diol isomers obtained via LiAlH₄ reduction of the C₃₅ hydroxy-2-alkanol ester isomer mixture (corresponding information for C₁₃ diol isomers not shown).</p

Structure elucidation of secondary alcohols in wheat leaf wax.

<p>(A) Mass spectrum of co-eluting TMS derivatives of C₃₃ <i>sec</i> alcohol isomers and major fragmentations of main isomer. (B) EICs showing cumulative intensity of <i>m/z</i> 73 and 75, as well as intensities of short α-fragments of main isomer and the four next most abundant isomers. a.u.: arbitrary units. (C) Mass spectrum of co-eluting Ac derivatives of C₃₃ <i>sec</i> alcohol isomers and major fragmentations of main isomer.</p

Structure elucidation of 4-alkylbutan-4-olides in wheat leaf and peduncle wax.

<p>(A) Mass spectrum and major fragmentations of C₂₈ 4-alkylbutan-4-olide. (B) Mass spectrum and major fragmentations of its product of transesterification with CH₃OH/BF₃. (C) Mass spectrum and major fragmentations of TMS derivative of LiAlH₄ reduction product from C₂₈ 4-alkylbutan-4-olide.</p

Structure elucidation of oxo-2-alkanol esters in wheat leaf and peduncle wax.

<p>(A) Mass spectrum of co-eluting isomers of C₃₅ oxo-2-alkanol ester. (B) Major fragmentations of all isomers from (A). (C) EICs showing intensity of <i>m/z</i> 57, as well as intensities of: metamer-characteristic alkyl fragments <i>m/z</i> 197 and 225, regiomer-characteristic α-fragments <i>m/z</i> 99, 113, 127 and 141, and M_acid+1 fragments 3 <i>m/z</i> 13 and 341. a.u.: arbitrary units. (D) Mass spectrum of co-eluting isomers of methoxime derivatives of C₃₅ oxo-2-alkanol ester. (E) Major fragmentations of all isomers from (D).</p