Proposed vector candidate: Leptotrombidium palpale for Shimokoshi type Orientia tsutsugamushi

To identify the vector species for Shimokoshi type Orientia tsutsugamushi, a survey of larval trombiculid mites was conducted in Yamagata Prefecture, Japan from April to May 2012. In all, 2889 larval trombiculid mites were obtained from 21 Apodemus speciosus rodent hosts, 2600 of which were morphologically classified into eight species in three genera. After screening of O. tsutsugamushi DNA in individual larval trombiculid mites using real‐time PCR targeting the 16S ribosomal RNA gene, serotype‐specific nested PCRs targeting the 56 kDa protein gene were performed, followed by sequencing analysis. As a result, Shimokoshi type O. tsutsugamushi DNA was identified from 3 (1.9%) of 157 Leptotrombidium palpale. This is the first study to identify Shimokoshi type O. tsutsugamushi DNA in L. palpale. The results indicate that L. palpale is a possible vector for Shimokoshi type O. tsutsugamushi.     

Seroepidemiological Survey of Zoonotic Diseases in Small Mammals with PCR Detection of Orientia tsutsugamushi in Chiggers,Gwangju, Korea

Serosurveillance for zoonotic diseases in small mammals and detection of chiggers, the vector of Orientia tsutsugamushi, were conducted from September 2014 to August 2015 in Gwangju Metropolitan Area. Apodemus agrarius was the most commonly collected small mammals (158; 91.8%), followed by Myodes regulus (8; 4.6%), and Crocidura lasiura (6; 3.5%). The highest seroprevalence of small mammals for O. tsutsugamushi (41; 26.3%) was followed by hantaviruses (24; 15.4%), Rickettsia spp. (22; 14.1%), and Leptospira (2; 1.3%). A total of 3,194 chiggers were collected from small mammals, and 1,236 of 3,194 chiggers were identified with 7 species of 3 genera: Leptotrombidium scutellare was the most commonly collected species (585; 47.3%), followed by L. orientale (422; 34.1%), Euchoengastia koreaensis (99; 8.0%), L. palpale (58; 4.7%), L. pallidum (36; 2.9%), Neotrombicula gardellai (28; 2.3%), and L. zetum (8; 0.6%). L. scutellare was the predominant species. Three of 1,236 chigger mites were positive for O. tsutsugamushi by PCR. As a result of phylogenetic analysis, the O. tsutsugamushi strain of chigger mites had sequence homology of 90.1-98.2% with Boryong. This study provides baseline data on the distribution of zoonotic diseases and potential vectors for the development of prevention strategies of vector borne diseases in Gwangju metropolitan area.     

Serosurveillance of Scrub Typhus in Small Mammals Collected from Military Training Sites near the DMZ, Northern Gyeonggi-do, Korea, and Analysis of the Relative Abundance of Chiggers from Mammals Examined

Comprehensive quarterly serosurveillance on scrub typhus in small mammals collected from military training sites located near the Demilitarized Zone (DMZ), northern Gyeonggi-do (Province), ROK was conducted to determine the potential rodent-borne and associated ectoparasite disease risks to military personnel. A total of 1,196 rodents and insectivores representing 8 species, Apodemus agrarius (87.3%, n = 1,044), Mus musculus (5.4%, n = 65), Crocidura lasiura (3.3%, n = 40), Microtus fortis (2.6%, n = 31), Micromys minutus (0.3%, n = 4), Tscherskia triton (0.3%, n = 4), Rattus norvegicus (0.3%, n = 4), and Myodes regulus (0.3%, n = 4) were assayed for the presence of antibodies to Orientia tsutsugamushi. O. tsutsugamushi antibodies were detected in 6 of 8 species and seroprevalence determined; A. agrarius (45.6%), M. musculus (23.1%), M. fortis (48.4%), M. minutus (50.0%), T. triton (50.0%), and R. norvegicus (25.0%). A total of 31,184 chigger mites collected from 508 rodents and insectivores were slide-mounted and 10 species belonging to 4 genera were identified. Leptotrombidium pallidum (53.4%) was the most frequently collected, followed by L. palpale (15.7%), Neotrombicula tamiyai (14.3%), L. orientale (10.7%), L. zetum (3.1%), Walchia fragilis (2.1%), and L. gemiticulum (0.8%), while the remaining 3 species, L. subintermedium, N. gardellai, and Euschoengastia koreaensis were rarely observed (prevalence < 10%). In contrast to previous surveys, higher chigger indices of the primary scrub typhus vectors, L. pallidum (165.4), L. orientale (45.0), and L. palpale (21.4), were observed during the spring season.     

Introgression of heat shock protein (Hsp70 and sHsp) genes into the Malaysian elite chilli variety Kulai (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) through the application of marker-assisted backcrossing (MAB)

Backcrossing together with simple sequence repeat marker strategy was adopted to improve popular Malaysian chilli Kulai (Capsicum annuum L.) for heat tolerance. The use of molecular markers in backcross breeding and selection contributes significantly to overcoming the main drawbacks such as increase linkage drag and time consumption, in the ancient manual breeding approach (conventional), and speeds up the genome recovery of the recurrent parent. The strategy was adopted to introgress heat shock protein gene(s) from AVPP0702 (C. annuum L.), which are heat-tolerant, into the genetic profile of Kulai, a popular high-yielding chilli but which is heat sensitive. The parents were grown on seed trays, and parental screening was carried out with 252 simple sequence repeat markers. The selected parents were crossed and backcrossed to generate F₁ hybrids and backcross generations. Sixty-eight markers appeared to be polymorphic and were used to assess the backcross generation; BC₁F₁, BC₂F₁ and BC₃F₁. The average recipient allele of the selected four BC₁F₁ plants was 80.75% which were used to produce the BC₂F₁ generation. BC₁-P₇ was the best BC₁F₁ plant because it had the highest recovery at 83.40% and was positive to Hsp-linked markers (Hsp70-u2 and AGi42). After three successive generations of backcrossing, the average genome recovery of the recurrent parent in the selected plants in BC₃F₁ was 95.37%. Hsp gene expression analysis was carried out on BC₁F₁, BC₂F₁ and BC₃F₁ selected lines. The Hsp genes were found to be up-regulated when exposed to heat treatment. The pattern of Hsp expression in the backcross generations was similar to that of the donor parent. This confirms the successful introgression of a stress-responsive gene (Hsp) into a Kulai chilli pepper variety. Furthermore, the yield performance viz. plant height, number of fruits, fruit length and weight and total yield of the improved plant were similar with the recurrent parent except that the plant height was significantly lower than the Kulai (recurrent) parent.     

Geographical Distribution and Relative Abundance of Vectors of Scrub Typhus in the Republic of Korea

A survey to determine the geographical distribution and relative abundance of potential vectors of scrub typhus was conducted from October to November 2006 at 13 localities throughout the Republic of Korea. Apodemus agrarius accounted for 97.6% (80/82) of all rodents, while only 2 Myodes regulus (2/82) were collected. A total of 10,860 chiggers were collected from A. agrarius belonging to 4 genera and 8 species, while only Walchia fragilis (40) was collected from Myodes regulus. Leptotrombidium pallidum (8,137; 74.9%), a vector of scrub typhus, was the predominant species collected from A. agrarius followed by Leptotrombidium scutellare (2,057, 18.9%), Leptotrombidium palpale (279; 2.7%), Leptotrombidium orientale (232; 2.1%), and Leptotrombidium zetum (79; 0.7%), Neotrombicula tamiyai (58; 0.5%), Euschoengastica koreaensis (16; 0.1%), and Cheladonta ikaoensis (2; < 0.1%). L. pallidum was the predominant chigger collected at collection sites in Gangwon (100%), Gyeonggi (87.2%), Chungnam (100%), Chungbuk (100%), Jeonbuk (73.9%), Jeonnam (77.0%), and Gyeongbuk (66.1%) provinces, whereas L. scutellare was the predominant chigger collected in Gyeongnam province (77.9%) and Jeju Island (62.3%). Data suggest a correlation between chigger population abundance and human cases of scrub typhus in Korea.     

Larval Chigger Mites Collected from Small Mammals in 3 Provinces,Korea

A total of 9,281 larval chigger mites were collected from small mammals captured at Hwaseong-gun, Gyeonggi-do (Province) (2,754 mites from 30 small mammals), Asan city, Chungcheongnam-do (3,358 mites from 48 mammals), and Jangseong-gun, Jeollanam-do (3,169 for 62 mammals) from April-November 2009 in the Republic of Korea (= Korea) and were identified to species. Leptotrombidium pallidum was the predominant species in Hwaseong (95.8%) and Asan (61.2%), while Leptotrombidium scutellare was the predominant species collected from Jangseong (80.1%). Overall, larval chigger mite indices decreased from April (27.3) to June (4.9), then increased in September (95.2) and to a high level in November (169.3). These data suggest that L. pallidum and L. scutellare are the primary vectors of scrub typhus throughout their range in Korea. While other species of larval chigger mites were also collected with some implications in the transmission of Orientia tsutsugamushi, they only accounted for 11.2% of all larval chigger mites collected from small mammals.     

Susceptibility of Oncomelania hupensis formosana recombinants and hybrids with Oncomelania hupensis nosophora to infection with Schistosoma japonicum

Chiu J.-K., Ong S.-J., Yu J.-C., Kao C.-Y. and Iuima T. 1981. Susceptibility of Oncomelania hupensis formosana recombinants and hybrids with Oncomelania hupensis nosophora to infection with Schistosoma japonicum. International Journal for Parasitology11: 391–397. Three generations of Oncomelania hupensis formosana recombinants were produced by mating the Kaohsiung race with the Ilan and Changhua races of the snails. F₂ and F₃ recombinants were produced by back-crossing F₁ and F₂ with Kaohsiung O. h. formosana. Subsequently, susceptibility of recombinants to infection with the original strain of Schistosoma japonicum, Ilan or Changhua strain, was investigated. Results indicated that susceptibility of recombinants declined steadily generation by generation. Marked decline of infectivity was observed for Kaohsiung-Ilan recombinants as compared with Kaohsiung-Changhua recombinants. For example, the overall infection rate of Kaohsiung-Ilan F₁ recombinants was 7.3 % with a 51.4 % of control snails. The same figures for F₂ were 4.2 and 52.6%, and 1 and 40.3 % for F₃. On the other hand, the overall infection rate of Kaohsiung-Changhua F₁ recombinants was 21.9% with a 46.9% of control snails; and 11.9 and 50.3 % for F₂; and 7.6 and 33.2% for F₃. The F₃ hybrids of Oncomelania hupensis nosophora from Japan and O. h. formosana from Kaohsiung and Ilan were also produced, and susceptibility with the Japanese strain of S. japonicum was studied. A highly significant decline of susceptibility was observed among hybrids (4.4%) in contrast with control snails (85.6 %).Feasibility of applying O. h. formosana in biological control of S. japonicum was discussed. One must determine in the laboratory, prior to application, which race of O. h. formosana should be used depending on the Oncomelania snails of an endemic area. For S. japonicum prevalent in Yamanashi, Japan, the Ilan race of O. h. formosana was found to be better choice than the Kaohsiung race of the snails.     

Breeding Potential of Introgression Lines Developed from Interspecific Crossing between Upland Cotton (Gossypium hirsutum) and Gossypium barbadense: Heterosis,Combining Ability and Genetic Effects

Upland cotton (Gossypium hirstum L.), which produces more than 95% of the world natural cotton fibers, has a narrow genetic base which hinders progress in cotton breeding. Introducing germplasm from exotic sources especially from another cultivated tetraploid G. barbadense L. can broaden the genetic base of Upland cotton. However, the breeding potential of introgression lines (ILs) in Upland cotton with G. barbadense germplasm integration has not been well addressed. This study involved six ILs developed from an interspecific crossing and backcrossing between Upland cotton and G. barbadense and represented one of the first studies to investigate breeding potentials of a set of ILs using a full diallel analysis. High mid-parent heterosis was detected in several hybrids between ILs and a commercial cultivar, which also out-yielded the high-yielding cultivar parent in F₁, F₂ and F₃ generations. A further analysis indicated that general ability (GCA) variance was predominant for all the traits, while specific combining ability (SCA) variance was either non-existent or much lower than GCA. The estimated GCA effects and predicted additive effects for parents in each trait were positively correlated (at P<0.01). Furthermore, GCA and additive effects for each trait were also positively correlated among generations (at P<0.05), suggesting that F₂ and F₃ generations can be used as a proxy to F₁ in analyzing combining abilities and estimating genetic parameters. In addition, differences between reciprocal crosses in F₁ and F₂ were not significant for yield, yield components and fiber quality traits. But maternal effects appeared to be present for seed oil and protein contents in F₃. This study identified introgression lines as good general combiners for yield and fiber quality improvement and hybrids with high heterotic vigor in yield, and therefore provided useful information for further utilization of introgression lines in cotton breeding.     

Occurrence rates of wild rodent hosts and chigger mites and the infection rate of Orientia tsutsugamushi in the central region of South Korea from 2015 to 2018

Outbreaks of vector‐borne diseases are dramatically increasing because of climate change, consequently increasing the importance of surveillance of endemic disease vectors. In this study, we surveyed chigger mites, vectors for Orientia tsutsugamushi—the bacteria that causes Tsutsugamushi disease—, and their rodent hosts in Gimcheon, central South Korea, in 2015–2018. A total of 225 rodents were collected, with trap rate and percentage of rodents infected by chigger mites of 9.8 and 72.4%, respectively. Six species of rodents from five genera were collected, the most common rodent being Apodemus agrarius (n = 153, infection rate = 90.8%). The highest number of rodents was collected in spring (trap rate = 10.3), but the rate of infected rodents was higher in fall (81.5%) than in spring (61.3%). Trap rate was highest for bank near waterway (17.9), but the chigger index (CI) was highest in hill (224.1). A total of 20,534 (CI 126.0) chigger mite individuals from 10 species and three genera were found on the collected rodents. The most common species was Leptotrombidium pallidum (n = 7,982, 83.6%, CI 49.0), followed by L. palpale and L. scutellare. Chigger mites were most frequent at banks near waterway (n = 11,093, CI 152.0) and hill (n = 2,017, CI 224.1). To detect O. tsutsugamushi in chigger mites, 450 pools of chigger mites (n = 10,991) were analyzed; 24 pools were positive—23 of A. agrarius, the most frequently collected species in South Korea, 1 of Micromys minutus—and the minimum positive rate (MPR) was 0.22. The detected strain types included Boryong (dominant in all years, seasons, and habitats), Jecheon, 07–489, and IIOC1202.     

Morphological characteristics and chromosome behaviour in F1, F2 and BC1 progenies between Chrysanthemum × morifolium and Ajania pacifica

The garden chrysanthemum (Chrysanthemum × morifolium) variety ??Aoyunhuoju?? (2n = 6x = 54) was crossed as female with Ajania pacifica (2n = 10x = 90) to produce intergeneric F1 hybrids, which were used both as the source of F₂ generation and as the parent for a first back-cross with ??Aoyunhuoju??. The morphology of all of the F₁ hybrids and hybrid derivatives was intermediate with respect to the two parents, although the BC₁ progenies resembled ??Aoyunhuoju?? more closely than any of the F₁ and F₂ progenies did. In the F₁ generation, the density of silvery hairs on the lower leaf surface and along the margin of the leaf was lower than in A. pacifica, while that in the BC1 generation, this trait was less prominent than in the F₁. The somatic chromosome number of the F₁, F₂ (with an exception of F₂-6 of a mainly 63) and BC1 generations was 2n = 8x = 72, 2n = 8x = 72 and 2n = 7x = 63 respectively, as expected. The hybrids and their derivatives retained a variable degree of fertility. There was a low frequency of meiotic chromosome pairing failure in all three hybrid generations, with most of the chromosomes involved as bivalents. Some BC₁ individuals show potential for commercialization thanks both to their flower shape and the inheritance of the silvery leaf trait from A. pacifica.     

Effects of essential oils on biological attributes of Trichogramma galloi adults

Bioactivity of nine essential oils (EOs) was studied on Anagasta kuehniella eggs in relation to the longevity of females, parasitism and emergence rates and sex ratio in the generations parental, F₁ and F₂ of Trichogramma galloi in comparison to a trade formulation of Azadirachta indica. There was no F₁ and F₂ progeny with Zingiber officinale being the most harmful. The greatest reductions in the parasitism rates (57, 43 and 28%) in the parental generation was caused by Allium sativum, Carapa guianensis and A. indica, respectively. In addition, A. sativum reduced the longevity (4.7 days) in the parental generation and emergence (33%) of F₁. Tested EOs did not affect the sex ratio in the generations F₁ and F₂ and emergence in the F₂. Allium sativum and Z. officinale were non-selective to T. galloi; while A. indica, C. guianensis and P. nigrum oils may compromise the progeny; therefore, their use must be avoided. Citrus sinensis, Mentha piperita, Origanum vulgare, Syzygium aromaticum and Thymus vulgare were selective to T. galloi, and these EOs are promising for IPM programs.     

Coincidence between Geographical Distribution of Leptotrombidium scutellare and Scrub Typhus Incidence in South Korea

To clarify the geographical distribution of scrub typhus vectors in Korea, a survey of larval trombiculid mites was conducted from 2005 to 2007 by collecting wild small mammals twice a year (spring and autumn) at 24 sites nationwide. A total of 67,325 mites representing 4 genera and 14 species were collected from 783 trapped rodents, corresponding to a chigger index (number of chigger mites per rodent) of 86.0. The predominant mite species were Leptotrombidium pallidum (52.6%), Leptotrombiduim scutellare (27.1%), Leptotrombidium palpale (8.2%), Leptotrombidium orientale (5.6%), and Neotrombicula tamiyai (1.7%). However, the proportions of L. scutellare in southern areas, including endemic provinces such as Jeollabuk-Do (34.3%), Jeollanam-Do (49.0%), and Gyeongsangnam-Do (88%), were relatively higher than in central Korean regions where L. pallidum was predominant. In autumn, the ratio of L. scutellare increased to 42% while the ratio of L. pallidum decreased. The geographical distribution map of the L. scutellare chigger index was identical to the incidence pattern of scrub typhus, whereas those of overall mites and L. pallidum showed no relationship with case incidence patterns. Distribution mapping analysis shows an identical geographical distribution of L. scutellare and epidemic incidence of scrub typhus in South Korea. L. pallidum could be another vector at all other parts of the Korean peninsula, including the eastern and northern regions that have a low level of scrub typhus incidence.     

Francisella tularensis: No Evidence for Transovarial Transmission in the Tularemia Tick Vectors Dermacentor reticulatus and Ixodes ricinus

Background

Tularemia is a zoonosis caused by the Francisella tularensis, a highly infectious Gram-negative coccobacillus. Due to easy dissemination, multiple routes of infection, high environmental contamination and morbidity and mortality rates, Francisella is considered a potential bioterrorism threat and classified as a category A select agent by the CDC. Tick bites are among the most prevalent modes of transmission, and ticks have been indicated as a possible reservoir, although their reservoir competence has yet to be defined. Tick-borne transmission of F. tularensis was recognized in 1923, and transstadial transmission has been demonstrated in several tick species. Studies on transovarial transmission, however, have reported conflicting results.

Objective

The aim of this study was to evaluate the role of ticks as reservoirs for Francisella, assessing the transovarial transmission of F. tularensis subsp. holarctica in ticks, using experimentally-infected females of Dermacentor reticulatus and Ixodes ricinus.

Results

Transmission electron microscopy and fluorescence in situ hybridization showed F. tularensis within oocytes. However, cultures and bioassays of eggs and larvae were negative; in addition, microscopy techniques revealed bacterial degeneration/death in the oocytes.

Conclusions

These results suggest that bacterial death might occur in oocytes, preventing the transovarial transmission of Francisella. We can speculate that Francisella does not have a defined reservoir, but that rather various biological niches (e.g. ticks, rodents), that allow the bacterium to persist in the environment. Our results, suggesting that ticks are not competent for the bacterium vertical transmission, are congruent with this view.     

Monthly Occurrence of Vectors and Reservoir Rodents of Scrub Typhus in an Endemic Area of Jeollanam-do, Korea

Monthly surveys were conducted to investigate the occurrence of chigger mites and seroprevalence of scrub typhus among small mammals in Jeollanam-do, the southwestern part of Korea, from November 2006 through October 2007. Fifty-eight small mammals, including 57 Apodemus agrarius (98.3%) and 1 Crocidura lasiura (1.7%), were captured, and a total of 4,675 chigger mites representing 4 genera and 8 species were collected from them. The chigger infestation rate among small mammals was 69.0%. The most predominant species in A. agrarius was Leptotrombidium scutellare (54.0%), followed by Leptotrombidium pallidum (39.4%), Leptotrombidium orientale (4.4%), Leptotrombidium palpale (1.1%), Neotrombicula tamiyai (0.6%), Eushoengastia koreaensis (0.3%), Neotrombicula gardellai (0.3%), and Cheladonta ikaoensis (<0.1%). The chigger index of A. agrarius was the highest in October (740.0), followed by November (242.0), September (134.6), March (98.3), February (38.2), January (35.3), December (34.5), April (30.8), and May (1.7). The average antibody positive rate of scrub typhus in wild rodents was 50.0%. The seropositive rates were high in October (100.0%) and November (83.3%), whereas those in other months were relatively low (28.6-57.1%). The chigger index of L. scutellare rapidly increased in September to form an acuminate peak in October, followed by a gradual decline. These results suggest that the outbreak of scrub typhus in the southwestern part of Korean peninsula is mostly due to L. scutellare.     

The falcifolia syndrome of Oenothera: III. The general pattern of its non-Mendelian inheritance

Summary The falcifolia (fal) syndrome is a malformation characterized by shoot sectors with sickle-shaped leaves, which appears in hybrids between Oenothera suaveolens and O. lamarckiana and shows a non-chromosomal inheritance of a previously undescribed type. The determinants, their location in the cell, and the mechanism of their expression are unknown. The defect is the result of a cross in which mixing of two different cytoplasms occurs, without the usual predominantly maternal inheritance. F₁ progeny of reciprocal crosses show a quantitative difference in the frequency and degree of expression of the fal character. When the F₁ progeny are backcrossed to the parents, the percentage of fal is high in crosses to O. suaveolens and low in those to O. lamarckiana. This manner of transmission is observed regardless of whether the hybrid is used as seed or pollen parent or shows a normal or fal phenotype. F₂ generations from F₁ plants having either a normal or a fal phenotype always include a certain percentage of fal plants, although the latter generally produce a higher percentage of fal progeny. If a second backcross is carried out, plants that produce normal progeny on self-pollination behave differently from those that produce some fal off-spring when selfed. The latter are similar to the F₁ with regard to the transmission of the fal trait. Plants of the F₁B₁ yielding normal progeny upon selfing produce normal progeny in the F₁B₂ if the parent to which they are backcrossed is the same as in the first backcross; if the parents of the first and second backcross differ, a high percentage of fal offspring is obtained. Again, whether the hybrid is used as seed or pollen parent is not relevant. Exceptions to this behaviour have been observed only rarely in that the character of the penultimate cross is retained. There is some evidence of somatic segregation of the fal determinants, since sister plants may react differently; this suggestion is supported by comparing the progenies of different branches of a self-pollinated fal plant of the F₁ generation.Abbreviations F₁, F₂, F₃, F₄ First through fourth filial generation, obtained by self-pollination - F₁B₁ First backcross generation, i.e. the F₁ was backcrossed to one of the original parents - F₁B₂ Second backcross generation, i.e. the F₁B₁ was backcrossed to one of the original parents - F₁B₃ Third backcross generation, i.e. the F₁B₂ was backcrossed to one of the original parents - (F₁B₁)D₁ Descendants obtained by self-pollination of a F₁B₁ plant; further generations obtained by self-pollination are designated as D₂, D₃, D₄ - (F₁B₁)D₁B₁ Descendant or generation obtained by a backcross of the D₁ of an F₁B₁. Backcrosses of the D₂ and D₃ are designated mutatis mutandis - (F₁B₁)D₁B₂ Generation obtained by a backcross of the (F₁B₁)D₁B₁     

Inheritance of components of partial resistance of barley to Rhynchosporium secalis with particular reference to race specificity

Six spring barley cultivars with no known genes for resistance to specific virulences but varying in partial resistance to Rhynchosporium secalis, were crossed in all combinations (6 × 6 diallel including reciprocals). In addition to seeds from naturally selfed plants, seeds of all parent cultivars were also produced by artificial selfing (emasculation followed by pollination using pollen from the same cultivar). This ensured comparability between seeds of parents and F₁. Both sets of parents, F₁ and F₂ families were grown in the field as single spaced plants and inoculated at Zadoks growth stage 49 with spore suspensions (2 × 10⁶ spores ml^-1) of three races (pathotypes) of R. secalis (Zadoks, Chang & Konzak, 1974). Components of partial resistance, incubation period (ICP), infection frequency (IF) and spore production per lesion (SP/L) were assessed on each plant. There were highly significant differences for all three components of partial resistance in both sets of parent cultivars but rank order in both sets was similar as evidenced by correlation coefficients, r= 0.96 for ICP and IF and r= 0.87 for SP/L. All three components of partial resistance were strongly correlated with NIAB (National Institute of Agricultural Botany, Cambridge, UK) resistance ratings. Means of F₁ and F₂ families were correlated with mid-parent values for ICP and IF but not SP/L. No difference in aggressiveness was found between races but for each component of partial resistance there was a significant interaction between race and parent cultivar (artificial selfs) and, for IF and ICP, a significant interaction between race and F₁ family. There was no evidence of interaction between parent (natural selfs) and race nor between race and F₂ family. Examination of genetic control of resistance showed evidence of strong additive effects (combining ability) in both F₁ and F₂ for ICP and IF but not for SP/L. There was no evidence for maternal or reciprocal differences, but there was evidence for dominance effects although their nature differed between components of partial resistance and between F₁ and F₂ generations. In the F₁, but not the F₂ generation, several elements of dominance (direction, distribution of dominant genes between parent cultivars, specific combining ability) showed for ICP or IF (but not SP/L) significant interaction with race.     

B型烟粉虱对寄主转换的适应性

将B型烟粉虱分别从嗜性较强的番茄上转移到嗜性相对较弱的国抗22棉花、泗棉3号棉花和辣椒上, 以及从嗜性较弱的辣椒上转移到嗜性相对较强的番茄、国抗22棉花和泗棉3号棉花上, 观察寄主转移后的F₁代、F₂代、F₃代烟粉虱产卵效应和寄主适应度的变化;将F₄代烟粉虱再转移到原寄主, 观察烟粉虱产卵效应和寄主适应度的恢复情况。结果表明, 烟粉虱在不同嗜性寄主上的产卵效应存在明显的差异。在不同嗜性的寄主之间转移, 烟粉虱的寄主适应度变化趋势不同, 从嗜性较强的寄主转移到嗜好性相对较弱的寄主上, 烟粉虱的寄主适应度迅速下降;从嗜性较弱的寄主向嗜性较强的寄主转移后, 烟粉虱的适应度则会迅速提高。烟粉虱对新寄主的适应速度与其对原寄主和新寄主之间的嗜性差异程度有关, 但一般经过1-2个世代后, 产卵效应会逐渐恢复到烟粉虱在该寄主上的正常水平。从过渡寄主转移到原寄主, 烟粉虱的寄主适应度变化符合一般的寄主转移规律, 但嗜性相对较强的过渡寄主可以刺激烟粉虱提高寄主适应性。     

Urbanization of Scrub Typhus Disease in South Korea

Background

Scrub typhus is an endemic disease in Asia. It has been a rural disease, but indigenous urban cases have been observed in Seoul, South Korea. Urban scrub typhus may have a significant impact because of the large population.

Methods

Indigenous urban scrub typhus was epidemiologically identified in Seoul, the largest metropolitan city in South Korea, using national notifiable disease data from 2010 to 2013. For detailed analysis of clinical features, patients from one hospital that reported the majority of cases were selected and compared to a historic control group. Chigger mites were prospectively collected in the city using a direct chigger mite-collecting trap, and identified using both phenotypic and 18S rDNA sequencing analyses. Their infection with Orientia tsutsugamushi was confirmed by sequencing the 56-kDa antigen gene.

Results

Eighty-eight cases of urban scrub typhus were determined in Seoul. The possible sites of infection were mountainous areas (56.8%), city parks (20.5%), the vicinity of one’s own residence (17.0%), and riversides (5.7%). Eighty-seven chigger mites were collected in Gwanak mountain, one of the suspected infection sites in southern Seoul, and seventy-six (87.4%) of them were identified as Helenicula miyagawai and eight (9.2%) as Leptotrombidium scutellare. Pooled DNA extracted from H. miyagawai mites yielded O. tsutsugamushi Boryong strain. Twenty-six patients from one hospital showed low APACHE II score (3.4 ± 2.7), low complication rate (3.8%), and no hypokalemia.

Conclusions

We identified the presence of indigenous urban scrub typhus in Seoul, and a subgroup of them had mild clinical features. The chigger mite H. miyagawai infected with O. tsutsugamushi within the city was found. In endemic area, urban scrub typhus needs to be considered as one of the differential febrile diseases and a target for prevention.     

Assessment of genetic differentiation in the large yellow croaker, Pseudosciaena crocea Richardson,and its first hybrid filial generations with AFLP markers

The genetic diversity (the digital characteristics) of four populations (120 individuals) of breeding large yellow croakers, Pseudosciaena crocea Richardson, was analyzed with amplified fragment length polymorphism (AFLP) markers. Ten primer combinations amplified 248 bands, of which 39.52% were polymorphic. Shannon's information index of the Daiqv (DQ) population was higher than that of the Minyu (MY) population, at 0.2167 and 0.2074, respectively. Additionally, the Shannon's information index value for the minus-hybrid (DQ population♂ × MY population♀) first hybrid generation was higher than the value for the plus-hybrid (MY population♂ × DQ population♀) first hybrid generation at 0.1687 and 0.1613, respectively. The F_ST of the parental generation was lower than that of the filial generation at 0.0329 and 0.0891, respectively. Gene flow was very high according to F_st values in both parental and filial generations. The UPGMA clustering analysis based on genetic similarity organized the four populations into three groups. The minus-hybrid stock was the most distinct as compared to the other populations.     

Additive transgene expression and genetic introgression in multiple green-fluorescent protein transgenic crop × weed hybrid generations

The level of transgene expression in crop × weed hybrids and the degree to which crop-specific genes are integrated into hybrid populations are important factors in assessing the potential ecological and agricultural risks of gene flow associated with genetic engineering. The average transgene zygosity and genetic structure of transgenic hybrid populations change with the progression of generations, and the green fluorescent protein (GFP) transgene is an ideal marker to quantify transgene expression in advancing populations. The homozygous T₁ single-locus insert GFP/Bacillus thuringiensis (Bt) transgenic canola (Brassica napus, cv Westar) with two copies of the transgene fluoresced twice as much as hemizygous individuals with only one copy of the transgene. These data indicate that the expression of the GFP gene was additive, and fluorescence could be used to determine zygosity status. Several hybrid generations (BC₁F₁, BC₂F₁) were produced by backcrossing various GFP/Bt transgenic canola (B. napus, cv Westar) and birdseed rape (Brassica rapa) hybrid generations onto B. rapa. Intercrossed generations (BC₂F₂ Bulk) were generated by crossing BC₂F₁ individuals in the presence of a pollinating insect (Musca domestica L.). The ploidy of plants in the BC₂F₂ Bulk hybrid generation was identical to the weedy parental species, B. rapa. AFLP analysis was used to quantify the degree of B. napus introgression into multiple backcross hybrid generations with B. rapa. The F₁ hybrid generations contained 95–97% of the B. napus-specific AFLP markers, and each successive backcross generation demonstrated a reduction of markers resulting in the 15–29% presence in the BC₂F₂ Bulk population. Average fluorescence of each successive hybrid generation was analyzed, and homozygous canola lines and hybrid populations that contained individuals homozygous for GFP (BC₂F₂ Bulk) demonstrated significantly higher fluorescence than hemizygous hybrid generations (F₁, BC₁F₁ and BC₂F₁). These data demonstrate that the formation of homozygous individuals within hybrid populations increases the average level of transgene expression as generations progress. This phenomenon must be considered in the development of risk-management strategies.Communicated by J. Dvorak