Xinzhi Ni

Hydrolase and Oxido-Reductase Activities in Diuraphis noxia and Rhopalosiphum padi (Hemiptera: Aphididae)

Abstract Four hydrolases and five oxido-reductases were examined using native stacking polyacrylamide gel electrophoresis. Homogenate of Russian wheat aphid, Diuraphis noxia (Mordvilko), bird cherry-oat aphid, Rhopalosiphum padi (L.), ‘Arapahoe’ (aphid-susceptible) and ‘Halt’ (aphid-resistant) wheat, Triticum aestivum L., and powdery mildew–infected Erysiphe graminis DC. ex Merat f. sp. tritici Em. Marchal, Arapahoe wheat leaves were assayed for enzyme activities. Pectinesterase, polygalacturonase (or pectinase), cellulase, and amylase activities were examined in the hydrolase group. Catalase, peroxidase, catechol oxidase, superoxide dismutase, and ascorbate oxidase activities were examined in the group of oxido-reductases. The two aphid species had the same hydrolases but different oxido-reductases. Although pectinesterase and cellulase enzymes were present in D. noxia and R. padi, the banding patterns were different. Polygalacturonase and δ-amylase were not detected from either aphid species. In the oxido-reductase group, catalase was detected from D. noxia, wheras peroxidase was detected from R. padi. Superoxide dismutase and ascorbate oxidase activities also were detected from both aphids. Enzyme assays using aphid head tissue that included salivary glands but excluded aphid foregut supported the enzyme assays using whole aphids. Peroxidase activity was detected from the salivary tissue of R. padi, but not D. noxia, and catalase activity was detected from D. noxia salivary tissue, but not R. padi. We suggest that the salivary enzyme difference between the 2 aphid species (i.e., catalase and peroxidase) is important in the type of damage symptom formation on susceptible wheat plants.

Identification and quantification of hydroxamic acids in maize seedling root tissue and impact on western corn rootworm (Coleoptera: Chrysomelidae) larval development.

Abstract Hydroxamic acid content was analyzed in the root tissue of four maize, Zea mays L., lines using high-performance liquid chromatography (HPLC) and related to western corn rootworm, Diabrotica virgifera virgifera LeConte, larval development and survivorship. Maize lines evaluated included Mp710 (PI 596627), MpSWCB-4 (PI 550498), Sc213 (PI 548792), and Dk580 (DeKalb commercial hybrid). Maize plants from each line were grown in test tubes containing a transparent agarose gel medium in a growth chamber. After 8 d of growth, root tissue of each line was harvested and hydroxamic acid content analyzed using HPLC. Three hydroxamic acids, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), 6-methoxybenzoxazolinone (MBOA), and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), were identified in the maize roots tested. DIMBOA concentration was quantified and ranged from 246.37 ± 70.53 μg to 91.84 ± 49.82 μg DIMBOA per gram of root tissue. No significant difference was found among lines in D. v. virgifera larval development and survivorship.

Comparison of Diuraphis noxia resistance in wheat isolines and plant introduction lines

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is one of the most important aphid pests of wheat, Triticum aestivum L., worldwide. Among the various pest management options, plant resistance is an economical management tactic to control D. noxia in cereal crops such as wheat. Researchers have identified D. noxia resistant germplasm and it has been incorporated into wheat. This study compared D. noxia resistance between the ’Betta‘ wheat isolines Betta‐Dn1, Betta‐Dn2, and Betta‐Dn5 and their corresponding donor gene plant introduction (PI) lines PI 137739 (Dn1), PI 262660 (Dn2), and PI 294994 (Dn5). Although the Betta isolines and PI lines showed D. noxia resistance when compared with Betta wheat, the degree of resistance in the isolines to D. noxia was different from their corresponding PI donors. Aphid number, aphid fecundity, and biomass per aphid were not different between Betta‐Dn1 and PI 137739 or Betta‐Dn2 and PI 262660; however, the same parameters were significantly lower on PI 294994 compared with Betta‐Dn5. This indicated that aphid resistance in PI 137739 and PI 262660 was probably governed by a single dominant gene, while the resistance in PI 294994 was controlled by more than one gene. Additionally, plant biomass reduction was aphid density dependent, which suggested that use of appropriate aphid infestation level is important when using plant biomass reduction as an indicator of resistance. Plant resistance categorization showed that there was no detectable difference in antixenosis among the seven lines evaluated. However, the higher aphid fecundity observed on PI 262660 compared with PI 137739 and PI 294994, in addition to no significant differences among the three PIs in plant biomass reduction, suggested PI 262660 was a tolerant line, while PI 137739 and PI 294994 were antibiotic lines. Plant tolerance could not be elucidated among the three Betta isolines using aphid fecundity and plant biomass reduction as indicators.

Influence of cereal leaf epicuticular wax on Diuraphis noxia probing behavior and nymphoposition

The effect of cereal leaf surface wax on Diuraphis noxia (Mordvilko), the Russian wheat aphid, probing behavior and nymphoposition was evaluated. Ultrastructure of leaf epicuticular wax from wheat (Triticum aestivum L.) c.v. ‘Arapahoe’ and ‘Halt’ was different from barley (Hordeum vulgare L.) c.v. ‘Morex’, and oat (Avena sativa L.) c.v. ‘Border’. Both wheat cultivars had similar rod‐shaped epicuticular wax, while barley and oat plants had flakes. The chemical composition comparison of gas chromatograms also indicated that the extract of the two wheat cultivars had similar pattern of peaks, while the barley and oat leaves had similar peaks. Cereal variety significantly affected aphid probing behavior (P < 0.05), but wax removal using ethyl ether swab did not (P > 0.05). Aphids initiated significantly more probes on Border oat leaves than on Morex barley irrespective of wax removal, although total probing duration per aphid was not significantly different among the four cereals examined. Accumulative salivation duration per aphid on oat leaves with wax was significantly longer than other cereal leaves with wax, while accumulative ingestion duration per aphid on Arapahoe wheat and Morex barley was significantly longer than on oat. Nymphoposition of D. noxia on cereal leaves maintained on the benzimidazole‐agar medium showed that aphids produced a greater number of nymphs on Morex barley and less on Border oat leaves, although wax removal did not affect aphid nymphoposition. Removal of leaf epicuticular waxes from the 4 cereal genotypes using ethyl ether swab indicated that the influence of wax on plant resistance to D. noxia probing and reproduction was limited. Morex barley was the most favorable, while Border oat was the least favorable cereal host of D. noxia.

Comparison of DIMBOA concentrations among wheat isolines and corresponding plant introduction lines

The concentration of a hydroxamic acid, also known as DIMBOA (2,4‐dihydroxy‐7‐methoxy‐1, 4‐benzoxazin‐3‐one), in 6‐d old wheat seedlings was examined using reverse‐phase high performance liquid chromatography (HPLC). Wheat plant introduction (PI) lines PI 137739 (Dn1 gene), PI 262660 (Dn2 gene), and PI 294994 (Dn5 gene), the corresponding near‐isogenic lines‘Betta’‐Dn1, Betta‐Dn2 and Betta‐Dn5, and susceptible Betta wheat were used in the study. The Dn2 gene conferring Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae), tolerance was not related to DIMBOA concentration in wheat. Of the lines with Dn1 and Dn5 genes that confer antibiosis to D. noxia, only lines with the Dn5 gene showed increased DIMBOA accumulation. However, the Dn5 and the DIMBOA biosynthesis genes are not located in the same chromosome group. Possible relationship between the Dn5 gene and DIMBOA accumulation was discussed. This study indicates that DIMBOA concentration does not completely explain D. noxia resistance in the wheat lines examined and a comprehensive examination of other allelochemicals (e.g., phenolics) is necessary.