Mitochondrial Genome Recombination in Somatic Hybrids of Solanum Commersonii and S. Tuberosum

Interspecific somatic hybridization has been performed in potato breeding experiments to increase plant resistance against biotic and abiotic stress conditions. We analyzed the mitochondrial and plastid genomes and 45S nuclear ribosomal DNA (45S rDNA) for the cultivated potato (S. tuberosum, St), wild potato (S. commersonii, Sc), and their somatic hybrid (StSc). Complex genome components and structure, such as the hybrid form of 45S rDNA in StSc, unique plastome in Sc, and recombinant mitogenome were identified. However, the mitogenome exhibited dynamic multipartite structures in both species as well as in the somatic hybrid. In St, the mitogenome is 756,058 bp and is composed of five subgenomes ranging from 297,014 to 49,171 bp in St. In Sc, it is 552,103 bp long and is composed of two sub-genomes of 338,427 and 213,676 bp length. StSc has 447,645 bp long mitogenome with two subgenomes of length 398,439 and 49,206 bp. The mitogenome structure exhibited dynamic recombination mediated by tandem repeats; however, it contained highly conserved genes in the three species. Among the 35 protein-coding genes of the StSc mitogenome, 21 were identical for all the three species, and 12 and 2 were unique in Sc and St, respectively. The recombinant mitogenome might be derived from homologous recombination between both species during somatic hybrid development.

EVALUASI KETAHANAN HIBRIDA SOMATIK NILAM TERHADAP PENYAKIT LAYU BAKTERI (Ralstonia solanacearum)

<p>ABSTRAK</p><p>Penelitian evaluasi ketahanan hibrida somatik nilam terhadappenyakit layu bakteri (Ralstonia solanacearum) telah dilaksanakan dilaboratorium dan rumah kaca KP Laing Solok dari bulan Januari sampaiDesember 2007. Penelitian bertujuan untuk mendapatkan nomor hibridasomatik nilam yang tahan terhadap penyakit layu bakteri. Kegiatanpenelitian meliputi pengambilan sampel tanaman nilam terinfeksi penyakitlayu bakteri di lapangan, dan isolasi dan perbanyakan isolat bakteripatogen di laboratorium. Uji patogenisitas isolat bakteri patogen pada bibitnilam dilaksanakan di rumah kaca. Selanjutnya perbanyakan bibit nilamhibrida somatik, inokulasi bibit dengan bakteri somatik, dan inkubasi bibittersebut dilaksanakan di rumah kaca. Penelitian ini menggunakan beberapanomor nilam hibrida somatik sebagai perlakuan yang disusun dalamrancangan acak lengkap (RAL) dengan tiga ulangan. Parameter yangdiamati adalah masa inkubasi menunjukkan gejala awal penyakit untuk ujipatogenisitas isolat bakteri patogen. Masa inkubasi menunjukkan gejalaawal penyakit dan kematian serta intensitas penyakit. Selanjutnya jugadiamati pertumbuhan tanaman dan produksi daun basah untuk pengujianketahanan nomor hibrida somatik nilam terhadap bakteri patogen. Hasilpenelitian menunjukkan bahwa hibrida somatik 2IV/4 dan 9II/21 sertavarietas Girilaya sampai akhir pengamatan tidak menampakkan gejalapenyakit. Sementara itu hibrida somatik 2IV/6; 9II/34; 2IV/9; 9IV/3; dan9IV/6 menunjukkan gejala awal penyakit (118,5 – 133,6 hari setelahinokulasi ”HSI”) dan kematian bibit (130,5 – 182,2 HSI) paling lamadengan intensitas penyakit (29,6 – 48,2%) lebih rendah dibandingkandengan hibrida somatik lainnya. Selanjutnya, penyumbatan pembuluhkayu sangat rendah yaitu 5,20 – 9,50% pada bagian akar, tetapi padabagian pangkal batang dan pucuk tidak ada penyumbatan. Pertumbuhandan produksi daun basah lebih tinggi dibandingkan dengan hibrida somatiklainnya, yakni tinggi tanaman 78,00 – 104,00 cm; jumlah daun 66 – 112daun, dan produksi daun basah 55,00 - 99,19 g. Sebaliknya hibridasomatik 9IV/4; 9II/23; 9II/33; 9IV/14; dan 2IV/1 memperlihatkan gejalaawal penyakit (32,3 -105,84 HSI) dan kematian bibit nilam (41,5 – 125,0HSI) lebih cepat, dan intensitas penyakit lebih tinggi (75 – 100%)dibandingkan hibrida somatik lainnya termasuk varietas Sidikalang.Penyumbatan pembuluh kayu oleh bakteri patogen sebesar 12,46 – 31,25%pada bagian akar, 6,10 – 22,50% pada bagian batang, dan 4,17 – 6,25%pada pucuk. Begitu juga dengan pertumbuhan dan produksi daun basahlebih rendah dibandingkan dengan hibrida somatik lainnya, dengan tinggitanaman 42,20 – 61,85 cm, jumlah daun 24 - 37 daun, dan produksidaun basah 18,00 - 41,20 g. Berdasarkan hasil penelitian ini terpilih duanomor hibrida somatik yaitu (2IV/4 dan 9 II/21) yang tahan terhadappenyakit layu bakteri, dan lima nomor hibrida somatik yaitu (9IV/6, 9IV/3,9II/34, 2IV/9, dan 2IV/6) yang toleran terhadap penyakit layu bakteri dirumah kaca.</p><p>Kata kunci : Pogostemon cablin Benth., nilam, penyakit layu bakteri,evaluasi ketahanan, hibrida somatik</p><p>ABSTRACT</p><p>Evaluation on the Resistance of Hybrid Somatic PatchouliPlant to Bacterial Wilt Disease (Ralstonia solanacearum)</p><p>The study on the resistance evaluation of somatic hybrid patchouliplant to bacterial wilt disease (Ralstonia solanacearum) had beenconducted in green house KP.Laing Solok from January to December2008. The objective of this study was to find the somatic hybrid numbersof patchouli plants resistant to bacterial wilt disease. The studied activitieswere collection of patchouli plant that was infected by bacterial wiltdisease in the field. Isolation and culture of the pathogen bacterial wereconducted in the laboratory and virulence test of pathogen bacterial onpatchouli plant was in the green house. In addition, sub culture of thesomatic hybrid seeds of patchouli plants, inoculation of these seeds bybacterial pathogen, and incubation of them were done at green house. Thestudy used some numbers of somatic hybrid as treatments that werearranged in completely randomized design (CRD) with three replicates. Asparameters were incubation period showing the first disease symptom forpathogenicity test of bacterial pathogen. Incubation period showed thefirst symptom died plant and diseases intensity. Plant growth and leafproduction were also observed for the study of number resistance ofsomatic hybrid patchouli plant to bacterial pathogen. The results showedthat somatic hybrid 2 IV/4 and 9 II/21 and Girilaya varieties did not showany symptoms. However, somatic hybrid 2IV/6, 9II/34, 2IV/9, 9IV/3, and9IV/6 showed the first symptom (118.5 – 133.6 days after inoculation”DAI”) and dead period (41.5 – 125.0 DAI) were the longest and thedisease intensity (29.6 – 48.2%) was lower than other somatic hybrid.Occluded xylem vessel by pathogen bacterial on root was lowest 5.20 –9.50%, but it was not found on base and young stems. They are alsohigher in the growth and leaf production than another somatic hybridpatchouli plant with 75.00 – 104.00 cm plant height, 66 -112 leaves/plant,and fresh leaf production of 55.00 – 99.19 g/pot. However, somatic hybrid9 IV/4, 9 II/23, 9 II/33, 9 IV/14, and 2 IV/1 showed earlier diseasesymptom, quicker seed death and higher disease intensity (75 -100%) thanother somatic hybrid patchouli plants including Sidikalang variety. Inaddition they had occluded xylem by bacterial pathogen 12.46 - 31.25% onthe root, 6.10 - 22.50% on the stem, and 4.17 – 6.25% on young stem.Plant growth and leaf production were lower than other somatic hybridpatchouli plants as of was 42.20-61.85 cm plant height; 24-37 leaves/plant,and fresh leaf production 18.00-41.20 g/pot. According to these results,experiment selected two numbers of somatic hybrid (2IV/4 and 9II/21)which were resistant to bacterial wilt disease, and five numbers of somatichybrid (9 IV/6, 9IV/3, 9II/34, 2IV/9, and 2IV/6) that were tolerant tobacterial wilt disease in the glass house.</p><p>Key words: Pogostemon cablin Benth., patchouli, bacterial wilt disease,resistant evaluation, somatic hybrid patchouli plant</p>

Genomic signatures of somatic hybrid vigor due to heterokaryosis in the oomycete pathogen, Bremia lactucae

Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce globally. This oomycete pathogen is highly variable and has rapidly overcome resistance genes and fungicides deployed in attempts to control it. The described high-quality genome assembly of B. lactucae provides the foundation for detailed understanding of this economically important pathogen. The biotrophic nature of B. lactucae coupled with high levels of heterozygosity and the recently expanded repeat content made genome assembly challenging. The combined use of multiple read types, including synthetic long reads, single molecule sequences, and Hi-C, resulted in a high-quality, chromosome-scale, consensus assembly of this diploid organism. Phylogenetic analysis supports polyphyly in the downy mildews consistent with the biotrophic mode of pathogenesis evolving more than once in the Peronosporaceae. Flow cytometry plus resequencing of 30 field isolates as well as sexual offspring and asexual derivatives from multinucleate single sporangia demonstrated a high incidence of heterokaryosis in B. lactucae. Heterokaryons have phenotypic differences and increased fitness compared to homokaryotic derivatives. Consequently, B. lactucae exhibits somatic hybrid vigor and selection should be considered as acting on a population of nuclei within coenocytic mycelia. This provides evolutionary flexibility to the pathogen enabling rapid adaptation to different repertoires of host resistance genes and other challenges. The advantages of asexual persistence of heterokaryons may have been one of the drivers of selection that resulted in the loss of uninucleate zoospores in multiple downy mildews.