Robert P. Doss

Response ofNp mutant of pea (Pisum sativum L.) to pea weevil (Bruchus pisorum L.) oviposition and extracts

TheNp mutant of pea (Pisum sativum L.) is characterized by two physiological responses: growth of callus under pea weevil (Bruchus pisorum L., Coleoptera: Bruchidae) oviposition on pods, and formation of neoplastic callus on pods of indoor-grown plants. Although these two responses are conditioned byNp, they are anatomically and physiologically distinguishable, based on sites of origin, distribution pattern, and sensitivity to plant hormones. Further characterization of the response to extracts of pea weevil showed that response of excised pods, measured by callus formation, was log-linear, and treatment with as little as 10−4 weevil equivalents produced a detectable response. Mated and unmated females contained similar amounts of callus-inducing compound(s), and immature females contained significantly less of the compound(s). Female vetch bruchids (Bruchus brachialis F., Coleoptera: Bruchidae), a related species, contained callus-inducing compound(s), but usually less than pea weevils on a per weevil basis. Males of both species contained less than 10% of the activity of the mature females. Extracts of female black vine weevils, a nonbruchid species, did not stimulate callus formation. Based on partitioning and TLC analysis, the biologically active constitutent(s) was stable and nonpolar. Thus, theNp allele probably conditions sensitivity to a nonpolar component of pea weevil oviposition as a mechanism of resistance to the weevil.

Bruchins—Mitogenic 3-(Hydroxypropanoyl) Esters of Long Chain Diols from Weevils of the Bruchidae

Abstract Mono- and bis 3-(hydroxypropanoyl) esters of long chain, unsaturated diols have been isolated and identified from two genera of the family Bruchidae, and have been shown to be responsible for the mitogenic activity observed on pea pods resulting from oviposition by the pea weevil, Bruchus pisorum . The mitogenic compounds have been characterized and synthesized.

A PCR-Based Technique for Detection of Neotyphodium Endophytes in Diverse Accessions of Tall Fescue

A previously described polymerase chain reaction (PCR)-based method used for detection of Neotyphodium coenophialum in tall fescue detected Neotyphodium endophytes in some, but not all, infected plants from a geographically diverse sample. In the study reported here, a different set of primers, based on intervening sequences of the tubulin 2 gene, were prepared and used for PCR. PCR with these primers yielded the expected 444 base pair amplification product with DNA from 104 of the 106 infected accessions tested. In addition, one accession originally scored as endophyte-free on the basis of a tissue culture test was correctly rated as endophyte-infected using the PCR procedure. Results suggest that primers based on intervening sequences of the tubulin 2 gene can be used for PCR-based detection of Neotyphodium endophytes in tall fescue accessions of diverse origin.

Bruchins, Plant Mitogens from Weevils: Structural Requirements for Activity

Bruchins are 3-hydroxypropanoate esters of long-chain α,ω-diols from pea weevils and cowpea weevils that have been shown to initiate callus formation on pea pods at extremely low application rates. Synthetic analogs have been prepared and examined to evaluate structural requirements for inducing this unusual neoplastic response. Chain length (optimum length C22–C24) is important, whereas unsaturation within the chain is relatively unimportant. Difunctionality is required for maximum activity, but the α,ω-diols themselves are inactive. Most critical is the ester portion(s) of the molecules; 3-hydroxypropanoate esters are far more active than any analogs examined.

Screening ornamental lilies for resistance to Botrytis elliptica

Abstract The screening of ornamental lilies for resistance to fire, a disease caused by Botrytis elliptica (Berk.) Cooke, is discussed. Detached leaves from greenhouse-grown lilies were inoculated with spores of B. elliptica and incubated at 20°C and 100% relative humidity for 48 h. After incubation, the leaves were transferred to a growth-chamber. Percentage infection and lesion size, which were assessed 1 week after inoculation, varied with the fungal isolate used and with spore concentration. When 20 ornamental lily clones were tested for resistance, clones derived from Lilium longiflorum Thunb. (Easter Lilies) showed less variability in resistance than the more genetically diverse colored lily clones. A study carried out in the field generally confirmed results obtained with green-house-grown plants.

Composition of essential oils of some lipidote Rhododendrons

Abstract Essential oils from leaves of 43 species of Rhododendron comprising 21 subsections were generally complex, and contained a number of compounds that were not identified. Caryophyllene, humulene, and one or more eudesmol isomers were the most commonly identified constituents. α-Pinene was the major component in eight of the oils, and germacrone was the major component in five of the oils. Monoterpenes were the major components of the oils in eight of the 12 species of subsection Triflora that were examined. Sesquiterpenes were major components in about 80% of the other 31 species.

Role of glandular scales of lepidote rhododendrons in insect resistance

Glandular scales on selected lepidote rhododendron species varied in density from 109 ± 13 to 4180 ± 60/cm2 of leaf surface. Globules contained within the scales stained with Sudan IV, a lipophilic dye. Essential oil contents of the scales varied with species from 24 ± 8 to 151 ± 35 ng/scale. Black vine weevil [(Otiorhynchus sulcatus (F.)] feeding on leaves from a sample of rhododendron species was inversely related to leaf essential oil content, and weevil feeding on membrane filters was inhibited by application of essential oil extracts from leaves of most lepidote rhododendrons tested. Results suggest that the glandular scales of the lepidote rhododendrons function, at least in part, in plant defense against insects.

(Z)-oxacyclotridec-10-en-2-one does not appear to be responsible for resistance to adult alfalfa weevil feeding exhibited byMedicago rugosa.

Steam distillate prepared from leaves ofMedicago rugosa Desr. could inhibit feeding by adult alfalfa weevils (Hypera postica (Gyll.) on membrane filters, whereas an equivalent amount of steam distillate prepared usingM. sativa L. had no effect on weevil feeding. Earlier work established that a 12-carbon lactone, (Z)-oxacyclotridec-10-en-2-one, was responsible for the feeding deterrent properties of the steam distillate fromM. rugosa. The concentration of this volatile varied with plant age and leaf position. The maximum concentration in leaves ofM. rugosa (area basis) was estimated, on the basis of tests using an inert substrate, to be too low to cause a detectable inhibition of feeding. No correlation between lactone content and weevil feeding was detected when leaves from similar positions on plants of different ages were used in a multiple choice bioassay. Although small amounts (< 12.5μg) of (Z)-oxacyclotridec-10-en-2-one can inhibit adult alfalfa weevil feeding on 13-mm-diameter membrane filters, because leaf concentrations (area basis) of this compound are lower than required to cause a detectable inhibition of feeding on the inert substrate, and because concentrations do not correlate with weevil feeding, it is unlikely that this lactone is responsible for resistance to adult alfalfa weevil feeding exhibited byM. rugosa.