Levels Of Antibiosis Research Articles

Categories of Resistance to Greenbug and Yellow Sugarcane Aphid (Hemiptera: Aphididae) in Three Tetraploid Switchgrass Populations

Switchgrass, Panicum virgatum L., has been targeted as a bioenergy feedstock. However, little is currently known of the mechanisms of insect resistance in this species. Here, two no-choice studies were performed to determine the categories (antibiosis and tolerance) and relative levels of resistance of three switchgrass populations (Kanlow–lowland ecotype, Summer–upland ecotype, and third generation derivatives between Kanlow × Summer plants, K×S) previously identified with differential levels of resistance to the greenbug, Schizaphis graminum (Rondani), and yellow sugarcane aphid, Sipha flava (Forbes). No-choice studies indicated that Kanlow possessed multi-species resistance, with high levels of antibiosis to both aphid species, based on aphid survival at 7 and 14 days after aphid introduction and cumulative aphid days, while K×S possessed low-to-moderate levels of antibiosis to S. flava. Further, functional plant loss indices based on plant height and biomass indicated that tolerance is an important category of resistance for Summer plants to S. graminum. These studies also indicated that Summer lacks both tolerance and antibiosis to S. flava, relative to the other switchgrasses tested, whereas K×S lack tolerance and antibiosis to S. graminum. These studies are the first attempt to analyze the categories of resistance in switchgrass and provide critical information for characterizing the biological mechanisms of resistance and improving our knowledge of the plant–insect interactions within this system.

Resistance of Sugarcane Cultivars to Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae).

The spittlebug Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) is one of the most important pests of the sugarcane crop in Brazil. Despite of its importance, there is currently a lack of information regarding sugarcane cultivars' resistance to the spittlebug. Therefore, our objective was to evaluate the response of sugarcane genotypes to this species. Two experiments were carried out under laboratory conditions using a random block design with treatments in a factorial arrangement of 2 × 13 (experiment 1) and 2 × 12 (experiment 2), with six replicates. The first factor included two levels of infestation (infested and noninfested plants with spittlebugs), while the second consisted of the cultivars. Nymph survival varied from 47.9 to 84.5%, indicating that there are different levels of antibiosis to M. fimbriolata among the tested cultivars. The highest degree of antibiosis was found in cultivars IACSP96-7586 and IACSP96-2008, in which nymph survival was close to 48%. IACSP96-7586 also presented some degree of tolerance, but IACSP96-7569 and IACSP97-6682 stood out as the most tolerant cultivars to the pest, showing the lowest reduction in weight of aboveground biomass. On average, spittlebug infestations caused a significant reduction in relative leaf chlorophyll content and aboveground biomass weight.

Life Table and Population Parameters ofSchizaphis graminum(Rondani) (Hemiptera: Aphididae) on Six Wheat Genotypes

ABSTRACT: Biological parameters of Schizaphis graminum (Rondani) reared on an ancient wheat species (Einkorn) from England and five Iranian wheat genotypes (Azadi, Ommid, Marvdasht, Pishtaz and Moghan 2) were studied under controlled conditions at 22 ± 1°C, 65 ± 5% RH, 16:8 (L:D) h. The lowest rm value (0.261± 0.002 females/female/day) and net reproductive rate (R0) (28.747± 0.369) were recorded on Einkorn. The highest and the lowest finite rates of increase (λ) were on Moghan 2 and Einkorn, respectively. Also, the longest mean generation time (T) and doubling time (DT) with the lowest percentages of nymphal survival (79.5%) and fecundity over developmental time (35.739± 0.378 nymphs/female/day) were obtained on Einkorn. Adult longevity varied from 10.72± 0.123 days on Einkorn to 18.04± 0.212 days on Moghan 2. Therefore, our results showed that Einkorn, exerting a high level of antibiosis compared to other tested genotypes, may decrease the population density of the greenbug.

New sources of resistance to lettuce aphids in Lactuca spp.

The use of resistant cultivars is one of the best ways to protect lettuce from aphid pests. At present, there are cultivars available with nearly complete resistance to Nasonovia ribisnigri biotype Nr:0 (based on the Nr gene) and partial resistance to Macrosiphum euphorbiae. Nevertheless, a new biotype of N. ribisnigri (Nr:1) able to overcome the resistance based on the Nr gene is expanding around Europe and has become a major threat of lettuce. In the present work, we report the presence of this new biotype in southeastern Spain, a major lettuce-producing region. Furthermore, a pool of 264 germplasm accessions belonging to Lactuca genus was tested in a greenhouse assay to search for new resistance sources to N. ribisnigri. The most promising accessions were retested in the laboratory to characterize the resistance by means of free-choice and antibiosis assays against biotypes Nr:0 and Nr:1 of N. ribisnigri and against a clone of M. euphorbiae. Three accessions of L. virosa showed resistance against the target aphid species and could be of interest for ongoing breeding programs. The accessions CGN16272 and CGN13361 were both partially resistant to the Nr:1 biotype of N. ribisnigri and to M. euphorbiae, and CGN13355, in spite of not being resistant to N. ribisnigri, showed a near complete resistance to M. euphorbiae. The study of the feeding behavior of N. ribisnigri biotypes showed that the Nr:1 biotype is able to maintain a similar phloem feeding ingestion pattern on genotypes bearing the Nr gene and on N. ribisnigri-susceptible lettuce genotypes. Moreover, as aphids rejected L. virosa as a feeding source due to superficial factors (high level of antixenosis), no differences in the level of antibiosis between such genotypes were detected. A second set of screening assays were conducted on 40 accessions of L. virosa in order to select for resistance against the Nr:1 biotype. The results showed three accessions with high levels of resistance (CGN05148, CGN21399 and CGN16274) against Nr:1 that could be of interest in lettuce breeding programs.

Characterization of Mycolytic Enzymes of Bacillus Strains and Their Bio-Protection Role Against Rhizoctonia solani in Tomato

Four antagonists bacteria namely, Bacillus megaterium MB3, B. subtilis MB14, B. subtilis MB99 and B. amyloliquefaciens MB101 were able to produce chitinase, β-1,3-glucanase and protease in different range with the presence of Rhizoctonia solani cell wall as a carbon source. Amplification of chitinase (chiA) gene of 270 bp and β-1, 3-glucanase gene of 415 bp was given supportive evidence at molecular level of antibiosis. After in vitro screening, all antagonists were tested against R. solani under greenhouse conditions. Root treatment of Bacillus strains showed superior defense during pathogen suppression in terms of chitinase, glucanase, peroxidase, poly phenol oxidase, phenylalanine ammonia-lyase activity and total phenolic content in leaves of tomato. All these enzymes accumulated high in tomato leaves as compared to roots. Pathogenesis-related proteins and defense-related enzymes accumulation was directly correlated with plant protection and greenhouse results indicated that B. amyloliquefaciens MB101- and B. subtilis MB14-treated plants offered 69.76 and 61.51 % disease reductions, respectively, over the infected control. These results established that these organisms have the potential to act as biocontrol agents. This study could be highlighted a mutual importance of liquid formulation of antagonistic Bacillus spp. against root associated sclerotia former pathogen R. solani.

Identification of antibiosis and tolerance in rice varieties carrying brown planthopper resistance genes

Brown planthopper (BPH) [Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)] is a major pest in rice [Oryza sativa L. (Poaceae)] production. Identification of resistance genes and development of BPH-resistant varieties is an economical and effective way to control this pest. In this study, BPH honeydew excretion, survival rate, and emergence rate were used as indicators to detect the antibiotic level, whereas the relative growth rates of plant height (RH) and fresh weight (RW), and the number of days until yellowing were used to identify the level of tolerance to BPH in rice varieties. Rice varieties Swarnalata and B5, which showed high levels of antibiosis and tolerance to BPH, thus were highly resistant in the seedling bulk test; Mudgo and T12, which showed moderate resistance to the insects, had a high level of tolerance and moderate antibiosis to BPH. Varieties Rathu Heenati, ARC 10550, and Chin Saba were identified to be susceptible to BPH, showing a moderate level of tolerance and no antibiosis. In comparison to the evaluation methods of BPH resistance, the honeydew excretion and survival rate could be used to detect the antibiotic level, and the RH, RW, or leaf yellowing days could be employed as indicators to evaluate the rice varieties’ tolerance. Overall, a combined application of these indicators can effectively identify the levels of antibiosis and tolerance to BPH in rice varieties, and BPH-resistance levels of the varieties were mainly determined by the antibiosis level. The results should help in understanding BPH-resistance categories of rice varieties and for resistance breeding.

Fecundity and development rate of the bird cherry-oat aphid, Rhopalosiphum padi (L) (Hom.: Aphididae) on six wheat cultivars

Rhopalosiphum padi is a polyphagous species with a nearly worldwide distribution. Biological parameters of this aphid on six commonly grown wheat cultivars in the Fars province including Chamran, Darab2, Shiraz, Ghods, Marvdasht and Niknezhad were investigated at the two-leaf stage of wheat. The experiments were carried out at 24 ± 5°C, 65 ± 5% R.H. and a photoperiod of 14:10 h (L:D) in a greenhouse. The number of nymphs per female of R. padi was 62.05, 55.84, 49.89, 47.63, 42.76 and 40.65 (nymphs/female) on Niknezhad, Shiraz, Ghods, Marvdasht, Chamran, and Darab2, respectively. Also, the highest and the lowest r<sub>m</sub> values of this aphid were obtained on Niknezhad (0.381 per day) and Darab2 (0.328 per day), respectively. In addition, other population growth indices were estimated. In general, a high level of antibiosis in Darab2 compared with the other tested cultivars may decrease the population density of R. padi on wheat and also cause a suppression of cereal viruses (e.g. BYDV) and reduce the pesticide application to wheat fields of Iran.  

Characterization of antibiosis and antixenosis to the whitefly silverleaf Bemisia tabaci B biotype (Hemiptera: Aleyrodidae) in several squash varieties

The objective of this study was to investigate the potential resistance mechanisms to Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) B biotype, in eight Cucurbita pepo varieties. Attractivity, oviposition preference, and nymphal development were evaluated under greenhouse and laboratory conditions. Variety Bianca was the least attractive to adult whiteflies in multi-choice tests. The whiteflies showed oviposition nonpreference (antixenosis) for Novita Plus, Bianca and Sandy in multi-choice test, and similar results were observed in no-choice tests with varieties Bianca, Novita, Caserta Cac and Sandy. Sandy expressed high antibiosis levels against whitefly nymphs, leading to 63.9% mortality. The high level of resistance in variety Sandy can serve as base for genetic improvement of C. pepo focusing on the development of resistant varieties to B. tabaci B biotype.

Resistance of squash cultivars to Aphis gossypii

The Cucurbitaceae plants are damaged by attack of a wide spectrum of insects and microorganisms. Among the sucker insects causing damages on squash Cucurbita pepo (L.), the aphid Aphis gossypii (Glover) (Hemiptera: Aphididae) is pointed as one of the most important, once their nymphs and adults suck the sap of the leaves continuously, besides being potential vector of virus. The present research evaluated different cultivars, aiming to identify the resistance against this aphid. The cultivars Novita, Sandy, Caserta Cac Melhorada, Novita Plus, Samira, AF-2858 and Caserta TS were used in laboratory assays (T= 25±2ºC; RH= 70±10% and fotophase= 12 h). In the immature phase the duration of nymphal instars was evaluated, the total duration and their viability, confining individuals on leaf disks from cultivars. In the adult phase the duration of reproductive period, the fecundity and the biological cycle were observed. The cultivar 'Sandy' expressed high level of antibiosis and feeding non-preference against A. gossypii, increasing the nymphal stage and causing mortality near to 70%. Besides, this cultivar reduced the production of nymphs and the longevity of the insects. The 'Novita Plus' cultivar also induced significant nymphal mortality, however in lower levels than those verified in 'Sandy', indicating a moderate resistance.

Wild relatives of sorghum as sources of resistance to sorghum shoot fly, Atherigona soccata

AbstractThe levels of resistance to shoot fly, Atherigona soccata in sorghum germplasm are low to moderate and therefore, we evaluated 17 wild relatives of sorghum under field and greenhouse conditions as an alternate source of genes for resistance to this pest. Thirty‐two accessions belonging to Parasorghum, Stiposorghum and Heterosorghum did not suffer any shoot fly damage under multi‐choice conditions in the field, while one accession each of Heterosorghum (Sorghum laxiflorum) and Chaetosorghum (S. macrospermum) suffered very low shoot fly damage. Accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399) and S. matarankense (TRC 243576) showed absolute non‐preference for oviposition under no‐choice conditions. Accessions belonging to Heterosorghum, Parasorghum and Stiposorghum were preferred for oviposition, but suffered low deadheart formation. Manual infestation of seedlings with shoot fly eggs did not result in deadheart formation in some of the accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399), S. matarankense (TRC 243576) and S. purpureosericeum (IS 18944). Larval mortality was recorded in main stems of the Parasorghums. Within section Sorghum, accessions belonging to S. bicolor ssp. verticilliflorum were highly susceptible to shoot fly, as were those of S. halepense. However, a few accessions such as IS 18226 (race arundinaceum) and IS 14212 (S. halepense) resulted in reduced survival and fecundity. Wild relatives of sorghum exhibited very high levels of antibiosis to A. soccata, while only low levels of antibiosis have been observed in the cultivated germplasm. Therefore, wild relatives with different mechanisms of resistance can be used as a source of alternate genes to increase the levels and diversify the basis of resistance to shoot fly, A. soccata.

Resistance of stored bean varieties to Acanthoscelides obtectus (Coleoptera: Bruchidae)

AbstractDuring bean seed storage, yield can be lost due to infestations of Acanthoscelides obtectus Say, the bean weevil. The use of resistant varieties has shown promising results in fighting these insects, reducing infestation levels and eliminating chemical residues from the beans. The expression of resistance to A. obtectus in bean varieties is frequently attributed to the presence of phytohemagglutinins, protease inhibitors and alpha‐amylase, and especially to variants of the protein arcelin, which reduce the larval viability of these insects. To evaluate the effect of bean seed storage time on the resistance expression of bean varieties to A. obtectus, tests with seeds of three ages (freshly‐harvested, 4‐month‐old, and 8‐month‐old) were conducted in the laboratory, using four commercial varieties: Carioca Pitoco, Ipa 6, Porrillo 70, ônix; four improved varieties containing arcelin protein: Arc.1, Arc.2, Arc. 3, Arc.4; and three wild varieties also containing arcelin protein: Arc.1S, Arc.3S, and Arc. 5S. The Arc.5S, Arc.1S, and Arc.2 varieties expressed high antibiosis levels against the weevil; Arc.1 and Arcs expressed the same mechanism, but at lower levels. The occurrence of oviposition non‐preference was also observed in Arc.5S and Arc.1S. The Arc.3 and Arc. 4 varieties expressed low feeding non‐preference levels against A. obtectus. The expression of resistance in arcelin‐bearing, wild or improved varieties was affected during the storage of seeds, and was high under some parameters but low in others. The results showed that addition of chemical resistance factors such as protein arcelin via genetic breeding may be beneficial in improving the performance of bean crops.

Aspectos biológicos de Dione juno juno (Cramer) (Lepidoptera: Nymphalidae) em genótipos de maracujazeiro

Avaliou-se o efeito de genótipos de maracujazeiro no desenvolvimento de Dione juno juno (Cramer) (Lepidoptera: Nymphalidae). O experimento foi conduzido em laboratório, sob condições ambientais controladas (temperatura de 26 ± 1ºC, U. R. de 60 ± 10% e fotofase de 14 horas). Lagartas recém-eclodidas foram alimentadas com folhas de genótipos de maracujazeiro: Passiflora edulis Sims., P. alata Dryand., P. serrato-digitata L., P. edulis f. flavicarpa Deg. ('Sul Brasil'), P. edulis f. flavicarpa, P. edulis f. flavicarpa ('Maguary FB-100') e P. foetida L. Para cada genótipo estudado, utilizaram-se 50 lagartas, provenientes de ovos coletados no campo. Essas lagartas foram mantidas em ramos de maracijazeiro, no interior de tubos de PVC até a pupação. Observações e reposição do alimento (ramos), diárias, foram realizadas. Os parâmetros avaliados foram duração e viabilidade das fases larval e pupal, peso das lagartas, peso das pupas e longevidade do adulto. O delineamento experimental foi o de blocos casualizados, com sete tratamentos e dez repetições. Os dados obtidos foram submetidos à análise de variância, e quando observadas diferenças, as médias foram comparadas pelo teste de Tukey, a 5% de probabilidade. Os genótipos P. alata, P. serrato-digitata e P. foetida não são adequados ao desenvolvimento de D. juno juno, impossibilitando a sobrevivência das lagartas, o que mostra o alto grau de antibiose desses materiais. Entre os demais, P. edulis, P. edulis f. flavicarpa, Maguary FB-100 e Sul Brasil foram mais adequados.

Trophic interactions between three species of cereal aphid (Hemiptera: Aphididae) and spring wheat (Poaceae): implications for pest management

AbstractThe susceptibilities of genetically diverse Canadian spring wheats, Triticum aestivum L. and Triticum durum Desf., to three aphid species, Rhopalosiphum padi (L.), Sitobion avenae (Fabricius), and Schizaphis graminum (Rondani), were investigated. Trophic interactions measured as changes in biomass of aphids and wheat plants were used to quantify levels of resistance, components of resistance, and impact of aphids on yield. Plants in field cages were infested with small numbers of aphids for 21 days at heading. These plants were usually more suitable for the development of S. avenae and S. graminum than of R. padi. Partial resistance, measured as seed production by infested plants as a proportion of that by a control, varied from 11% to 59% for different aphid species and wheat classes when all wheat plants were infested at the same stage. Cultivars within wheat classes responded similarly to each of the aphid species. None of the wheat cultivars showed agriculturally effective levels of antibiosis. The specific impact of each aphid species and wheat class varied from 5 to 15 mg of plant biomass lost for each milligram of biomass gained by the aphids. Canadian Western Red Spring wheat had a lower specific impact and therefore was more tolerant to aphids than the other two classes, but not tolerant enough to avoid economic damage at the aphid densities observed. Plants did not compensate for feeding damage after aphid feeding ceased, based on the higher specific impacts observed for mature plants than for plants that were heading. The interactions between aphids and plants show that current economic thresholds probably underestimate the damage caused by cereal aphids to Canadian spring wheat.

Characterization of Oryza rufipogon-Derived Resistance to Tungro Disease in Rice.

Rice tungro disease (RTD) is caused by the interaction between Rice tungro spherical virus (RTSV) and Rice tungro bacilliform virus (RTBV), both of which are transmitted by green leafhoppers (GLH). In order to define the resistance against RTD in rice cv. Matatag 9 which was developed by interspecific hybridization between RTD-susceptible cv. IR64 and Oryza rufipogon, the reactions of Matatag 9 to the viruses and GLH were evaluated in comparison with RTD-susceptible and -resistant rice cultivars. The incidences of infection with RTSV and RTBV in Matatag 9 were significantly lower than those in the susceptible parent cv. IR64; however, no substantial differences in virus accumulation were observed between IR64 and Matatag 9 once infected with the viruses. Symptoms in Matatag 9 infected with RTBV and RTSV were milder than those observed in IR64. A higher level of antixenosis to GLH was observed in Matatag 9 compared with IR64. The levels of antibiosis against GLH in Matatag 9 were comparable with those in another GLH-resistant cultivar, and significantly higher than those in RTD-susceptible cultivars. Collectively, these results suggest that tolerance to tungro viruses and resistance to GLH both contribute to the apparent resistance to RTD in Matatag 9, although possible involvement of other resistance mechanisms cannot be excluded.

Antibiosis in Soybean Breeding Lines for the Management of Corn Earworm for Sustainable Soybean Production

ABSTRACT Corn earworm (Helicoverpa zea Boddie), is one of the major insect pests of soybean in many soybean growing areas. A study was conducted during three soybean growing seasons to evaluate the antibiosis type of resistance in soybean breeding lines which were grown in replicated field trials. A plant introduction, ‘PI 229358’, with a known antibiosis type of resistance against corn earworm was included as a resistant check and four commercial varieties including Hutcheson, Stalwart, Charleston and Croton also were included in the experiments for comparison. The results of antibiosis tests showed that some breeding lines such as ‘E3582019’ and ‘D6874003’ provided level of antibiosis to corn ear-worm comparable to that found in the commercial variety Stalwart. Also, ‘M3583009’ and ‘D358B3010’ provided antibiosis to corn earworm which was similar to a commercial variety, Stalwart. However, none of the breeding lines provided the resistance which was similar to ‘PI 229358’. The intermediate antibiosis found in some of the breeding lines could play an important role in the management of corn earworm and other insect pests coupled with other desirable agronomic traits such as higher seed yield.

Categories of Resistance, Antibiosis and Tolerance, to Biotype I Greenbug (Schizaphis graminum (Rondani) Homoptera: Aphididae) in Four Sorghum (Sorghum bicolor (L.) Moench. Poales:Gramineae) Hybrids

Resistance categories (antibiosis and tolerance) of four sorghum (Sorghum bicolor (L.) Moench) hybrids to biotype I greenbug, Schizaphis graminum (Rondani), were determined in environmental growth chamber and field studies. Greenbug weight and fecundity were lower on ‘Cargill 607E’ compared with ‘Cargill 797’. Percentage of leaf damage area was significantly less on two resistant hybrids (Cargill 607E and Cargill 797) after a 14-d greenbug feeding period compared to two susceptible hybrids (‘Golden Harvest 510B’ and Garst 5715). In growth chamber studies on sorghum seedlings, ‘Cargill 607E’ and ‘Cargill 797’ reduced greenbug weight significantly compared with ‘Golden Harvest 510B’ and ‘Garst 5715’. Greenbug weight was 2.9 mg/25 greenbugs on ‘Cargill 607E’, 3.1 mg/25 greenbugs on ‘Cargill 797’, 3.9 mg/25 greenbugs on ‘Golden Harvest 510B’, and 4.8 mg/25 greenbugs on ‘Garst 5715’. On field grown sorghum plants, ‘Cargill 797’ did not reduce greenbug growth compared with ‘Golden Harvest 510B’. ‘Cargill 607E’ had a negative impact on weight of greenbugs. Greenbug weight was 7.9 mg/25 greenbugs on ‘Cargill 607E’, 9.2 mg/25 greenbugs on ‘Cargill 797’, and 10.0 mg/25 greenbugs on ‘Golden Harvest 510B’. ‘Cargill 607E’ and ‘Cargill 797’ were resistant to biotype I greenbugs compared with susceptible ‘Golden Harvest 510B’ and ‘Garst 5715’. Antibiosis was confirmed as the primary category of resistance in ‘Cargill 607E.’ ‘Cargill 797’ was primarily tolerant but may have some level of antibiosis, because smaller greenbugs developed in some of the studies.

Genetic control of different types of the aphid resistance in cereal crops

Inheritance of the two main types of the plant resistance to insects was investigated in the sorghum-greenbug (Schizaphis graminum Rond.) and wheat-bird cherry-oat aphid (Rhopalosiphon padi L.) interaction systems. The data obtained support the hypothesis that antixenosis (avoiding of the plant by the insect, given a choice) and antibiosis (adverse effect of the plant on the insect feeding on it) are pleiotropic manifestations of the same genes. This is confirmed by the following facts. (1) Identical patterns of segregation for antixenosis and antibiosis in different cases of sorghum resistance to the greenbug: monogenic control (gene Sgr4), digenic control (Sgr1, Sgr2 and Sgr7, Sgr8), and complementary action of the genes (Sgr9 and Sgr10). (2) Correlated changes in the levels of antibiosis and antixenosis during long-term reproduction of a greenbug clone on the resistant sorghum variety k-1206 (resistance controlled by one gene). (3) Simultaneous expression of antixenosis and antibiosis in F3 wheat hybrid families to the bird cherry-oat aphid.

Resistance to Rhopalosiphum padi (Homoptera: Aphididae) in Triticale and Triticale-Derived Wheat Lines Resistant to Diuraphis noxia (Homoptera: Aphididae)

Rhopalosiphum padi (L.) (bird cherry-oat aphid) and Diuraphis noxia (Mordvilko) (Russian wheat aphid) are common aphid pests of wheat and can cooccur at relatively high levels within wheat fields. Resistance to both aphids has been identified in several triticale accessions. We conducted experiments to identify and characterize antibiosis-type resistance to R. padi in additional triticale lines and to test R. padi-resistance levels in several backcrossed, triticale-derived lines of D. noxia-resistant wheat. Triticale accessions ‘6A-558’, ‘H85-734’ and ‘M86-6174’ were identified with moderate levels of antibiosis to R. padi. All three accessions limited R. padi population growth relative to ‘Arapahoe’ over 13 d. 6A-558 increased development time of R. padi compared to that on Arapahoe, and 6A-558, H85-734 and M86-6174 each decreased the number of nymphs produced by R. padi over 7 d. Additional tests confirmed ‘N1185’ triticale as a strong source of resistance to R. padi, and showed that ‘Lamar’ wheat was not resistant to R. padi. Tests of wheat lines derived from crosses between N1185 and Lamar and then selected for resistance to D. noxia showed that three of 13 lines reduced the number of R. padiper plant, with resistance levels comparable to N1185 in two lines. Nymphiposition by R. padi measured over a 24-h period did not differ among any lines in no-choice tests. The results provide further support that triticale is a significant source of resistance to R. padi, but further work is needed to understand transference of R. padi-resistance from triticale to wheat.

Genetic characterization and molecular mapping of a Hessian fly-resistance gene transferred from T. turgidum ssp. dicoccum to common wheat

A gene (temporarily designated Hdic) conferring resistance to the Hessian fly (Hf) [Mayetiola destructor (Say)] was previously identified from an accession of German cultivated emmer wheat [Triticum turgidum ssp. dicoccum (Schrank ex Schübler) Thell] PI 94641, and was transferred to the Hf-resistant wheat germplasm KS99WGRC42. The inheritance of Hdic resistance exhibited incomplete penetrance because phenotypes of some heterozygous progenies are fully resistant and the others are fully susceptible. Five simple sequence repeat (SSR) markers (Xgwm136,Xcfa2153, Xpsp2999,Xgwm33, and Xbarc263) were linked to the Hdic gene on the short arm of wheat chromosome 1A in the same region as the H9, H10, and H11 loci. Flanking markers Xgwm33 and Xcfa2153 were mapped at distances 0.6 cM proximal and 1.4 cM distal, respectively. Marker analysis revealed that a very small intercalary chromosomal segment containing Hdic was transferred from emmer wheat to KS99WGRC42. This is the first emmer-derived Hf-resistance gene that has been mapped and characterized. The Hdic gene confers a high level of antibiosis to biotypes GP and L, as well as to strains vH9 and vH13 of the Hf, which is different from the biotype reaction patterns of the known Hf-resistance genes on chromosome 1A (H5 and H11 susceptible to biotype L, H9 and H10 susceptible to strain vH9). These results suggested that Hdic is either a new gene or a novel allele of a known H gene on chromosome 1A. The broad spectrum of resistance conferred by the Hdic gene makes it valuable for developing Hf resistant wheat cultivars.

Antibiosis to Corn Earworm, Helicoverpa zea Boddie, by Cowpea Genotypes

ABSTRACT Corn earworm (Helicovrpa zea Boddie) is a pest of cow-pea in many regions of the United States. The larvae chew round holes in cowpea pods to feed on the developing grains, and thus, affect the yield and seed quality. Studies were conducted to identify antibiosis to corn earworm (CEW) in diverse cowpea genotypes which had been identified to provide better yields in the Delmarva (Delaware, Maryland and Virginia) peninsula region. A series of bioassays were performed to evaluate the newly formed terminal trifoliolates of field grown cowpea for antibiosis to CEW. Results showed significant differences in larval weights in all bioassays. The genotypes which gave the lowest larval weights were Mississippi Silver and Quick pick Pinkeye, while the genotype, Champion, provided the largest weights of larvae in virtually all tests. Therefore, this genotype could probably be used as a susceptible check for future cowpea antibiosis studies to CEW. Results also indicate that some genotypes of cowpea that provided consistently lower weights of larvae, including Mississippi Silver and Quick pick Pinkeye, have higher levels of antibiosis to corn earworm larvae than genotypes Champion and Dixielee. These superior genotypes need to be evaluated for multiple pest resistance and other desirable agronomic traits. The antibiosis could be integrated with other methods of cowpea pest management to reduce the amount of insecticides for the management of CEW and other insect pests of cowpea.