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Effect of inbreeding on trait stability in Steinernema feltiae

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  1. Tez No: 402611
  2. Yazar: SEVGİ TÜRKÖZ
  3. Danışmanlar: DR. OLAF STRAUCH
  4. Tez Türü: Yüksek Lisans
  5. Konular: Biyoloji, Biology
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2013
  8. Dil: İngilizce
  9. Üniversite: Ghent Unıversıty
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

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Özet (Çeviri)

Progress in genetic improvement of beneficial traits of entomopathogenic nematodes {Steinernema and Heterorhabditis) by hybridisation and genetic selection has often been lost again once the selection pressure was released during mass production. Recently, a method was developed for Heterorhabditis bacteriophora to stabilize traits by selection of improved inbred lines. Culturing this nematode in liquid media results in highly homozygous inbred lines, because under these conditions the nematode reproduces exclusively through selfing. This approach is not possible for Steinernema spp. because they are amphimicitic. Therefore, the main objective of this study was to develop a procedure to produce inbred lines of a desiccation tolerant hybrid strain of Steinernema feltiae (HYB13A) and check how inbreeding influences beneficial traits like desiccation tolerance and the virulence. Results were compared with a commercial strain (Com). Inbred lines were produced by culturing single gravid females isolated from infected insects on agar plates seeded with the symbiotic bacterium X. bovienii and continuously transferring those single gravid females up to eight inbreeding steps. Survival of inbred lines was low due to contaminations carried over from insect cadavers. An antibiotic treatment of the females could not solve the problems. Culturing nematodes in monoxenic culture was more successful, mean inbreeding steps imtil lines were lost was 4.5 whereas inbreeding with females originating from insects (in vivo) with or without antibiotic treatment provide mean inbreeding step of 2.5. The desiccation tolerance of the S. feltiae strains was measured by producing dehydrating conditions using different concentrations of polyethleneglycol 600 and the water activity (aw) was measured. Before inbreeding the mean tolerated water activity survived by 50% of the population (WA50) measured after a 48h adaptation to desiccation stress was 0.912 for strain Com and for the HYB strain, which had been selected for enhanced tolerance, 0.835 was assessed without a significant difference between the strains. Significantly more tolerant were S. riobrave strain Sr Lin4 (aw-value= 0.73) and S. yirgalemense (awvalue^ 0.769). Only few inbred lines could be monitored for the development of their desiccation tolerance during inbreeding because many were lost with increasing inbreeding steps. For HYB strain (Line 16 and 17) WA50 significantly decreased from 0.83 to 0.714 and 0.658, respectively. Com strain line 20 also dropped from 0.91 to 0.68. There was a significant correlation between the desiccation tolerance and the inbreeding step for the lines that can be followed for the continuous inbreeding step. The HYB strain was significantly more tolerant than the Com strain for the mean tolerated water activity also when exposed to stress without prior adaptation of the population. Inbred lines with selection pressure was significantly higher tolerant than those without selection pressure. This significance was only for the most tolerant 10% individuals of HYB strain which dropped from 0.9 to 0.734 for the non-adapted populations. The virulence seemed to be negatively affected for the HYB strain. The investigation was the first attempt to try to stabilize beneficial traits of S. feltiae through production of inbred lines. Keywords- Biological control, Steinernema feltiae, desiccation tolerance, inbreeding, selection

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