Improvement of two traditional Basmati rice varieties for bacterial blight resistance and plant stature through morphological and marker-assisted selection

Bacterial blight (BB) is a major production threat to Basmati, the aromatic rice prized for its unique quality. In order to improve the BB resistance of two elite, traditional BB-susceptible Basmati varieties (Taraori Basmati and Basmati 386), we utilized the strategy of limited marker-assisted backcrossing for introgression of two major BB resistance genes, Xa21 and xa13, coupled with phenotype-based selection for improvement of their plant type and yield. Improved Samba Mahsuri, an elite high-yielding, fine-grain-type BB-resistant rice variety served as donor for BB resistance. Backcross-derived improved Basmati lines at BC1F5 possessing a single resistance gene (i.e. either Xa21 or xa13) displayed moderate resistance to BB, while lines possessing both Xa21 and xa13 showed significantly higher levels of resistance. Two-gene pyramid lines (Xa21 + xa13) possessing good grain and cooking quality similar to their respective traditional Basmati parents, short plant stature (<110 cm plant height) and higher grain yield than the recurrent parent(s) were identified and advanced. This work demonstrates the successful application of marker-assisted selection in conjunction with phenotype-based selection for targeted introgression of multiple resistance genes into traditional Basmati varieties along with improvement of their plant stature and yield

Systems-Based Analysis of the \u3cem\u3eSarcocystis neurona\u3c/em\u3e Genome Identifies Pathways That Contribute to a Heteroxenous Life Cycle

Sarcocystis neurona is a member of the coccidia, a clade of single-celled parasites of medical and veterinary importance including Eimeria, Sarcocystis, Neospora, and Toxoplasma. Unlike Eimeria, a single-host enteric pathogen, Sarcocystis, Neospora, and Toxoplasma are two-host parasites that infect and produce infectious tissue cysts in a wide range of intermediate hosts. As a genus, Sarcocystis is one of the most successful protozoan parasites; all vertebrates, including birds, reptiles, fish, and mammals are hosts to at least one Sarcocystis species. Here we sequenced Sarcocystis neurona, the causal agent of fatal equine protozoal myeloencephalitis. The S. neurona genome is 127 Mbp, more than twice the size of other sequenced coccidian genomes. Comparative analyses identified conservation of the invasion machinery among the coccidia. However, many dense-granule and rhoptry kinase genes, responsible for altering host effector pathways in Toxoplasma and Neospora, are absent from S. neurona. Further, S. neurona has a divergent repertoire of SRS proteins, previously implicated in tissue cyst formation in Toxoplasma. Systems-based analyses identified a series of metabolic innovations, including the ability to exploit alternative sources of energy. Finally, we present an S. neurona model detailing conserved molecular innovations that promote the transition from a purely enteric lifestyle (Eimeria) to a heteroxenous parasite capable of infecting a wide range of intermediate hosts. IMPORTANCE Sarcocystis neurona is a member of the coccidia, a clade of single-celled apicomplexan parasites responsible for major economic and health care burdens worldwide. A cousin of Plasmodium, Cryptosporidium, Theileria, and Eimeria, Sarcocystis is one of the most successful parasite genera; it is capable of infecting all vertebrates (fish, reptiles, birds, and mammals—including humans). The past decade has witnessed an increasing number of human outbreaks of clinical significance associated with acute sarcocystosis. Among Sarcocystis species, S. neurona has a wide host range and causes fatal encephalitis in horses, marine mammals, and several other mammals. To provide insights into the transition from a purely enteric parasite (e.g., Eimeria) to one that forms tissue cysts (Toxoplasma), we present the first genome sequence of S. neurona. Comparisons with other coccidian genomes highlight the molecular innovations that drive its distinct life cycle strategies

Local Admixture of Amplified and Diversified Secreted Pathogenesis Determinants Shapes Mosaic \u3cem\u3eToxoplasma gondii\u3c/em\u3e Genomes

Toxoplasma gondii is among the most prevalent parasites worldwide, infecting many wild and domestic animals and causing zoonotic infections in humans. T. gondii differs substantially in its broad distribution from closely related parasites that typically have narrow, specialized host ranges. To elucidate the genetic basis for these differences, we compared the genomes of 62 globally distributed T. gondii isolates to several closely related coccidian parasites. Our findings reveal that tandem amplification and diversification of secretory pathogenesis determinants is the primary feature that distinguishes the closely related genomes of these biologically diverse parasites. We further show that the unusual population structure of T. gondii is characterized by clade-specific inheritance of large conserved haploblocks that are significantly enriched in tandemly clustered secretory pathogenesis determinants. The shared inheritance of these conserved haploblocks, which show a different ancestry than the genome as a whole, may thus influence transmission, host range and pathogenicity

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Not AvailableRice blast is one of the most devastating diseases affecting the rice crop throughout the world. In molecular breeding for host plant resistance, functional markers are very useful for enhancing the precision and accuracy in marker-assisted selection (MAS) of target gene(s) with minimum effort, time and cost. Pi54 (which was earlier known as Pik h) is one of the major blast resistance genes and has been observed to show resistance against many isolates of the blast pathogen in India. The gene has been cloned through map-based strategy and encodes a nucleotide-binding site–leucine-rich repeat (NBS–LRR) domain-containing protein. In the present study, we carried out allele mining for this gene and identified a 144-bp insertion/deletion (InDel) polymorphism in the exonic region of the gene. A PCR-based co-dominant molecular marker targeting this InDel, named Pi54 MAS, was developed. Pi54 MAS was observed to perfectly co-segregate with blast resistance in a mapping population with no recombinants. Validation of this marker in 105 genotypes which are either susceptible or resistant to rice blast disease showed that the marker is polymorphic in most of the resistant–susceptible genotype combinations and is more accurate than the earlier reported markers for Pi54. Hence this functional, co-dominant marker is suggested for routine deployment in MAS of Pi54 in breeding programs.Not Availabl

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Not AvailableBacterial blight (BB) is a major production threat to Basmati, the aromatic rice prized for its unique quality. In order to improve the BB resistance of two elite, traditional BB-susceptible Basmati varieties (Taraori Basmati and Basmati 386), we utilized the strategy of limited marker-assisted backcrossing for introgression of two major BB resistance genes, Xa21 and xa13, coupled with phenotype-based selection for improvement of their plant type and yield. Improved Samba Mahsuri, an elite high-yielding, fine-grain-type BB-resistant rice variety served as donor for BB resistance. Backcross-derived improved Basmati lines at BC1F5 possessing a single resistance gene (i.e. either Xa21 or xa13) displayed moderate resistance to BB, while lines possessing both Xa21 and xa13 showed significantly higher levels of resistance. Two-gene pyramid lines (Xa21 + xa13) possessing good grain and cooking quality similar to their respective traditional Basmati parents, short plant stature (<110 cm plant height) and higher grain yield than the recurrent parent(s) were identified and advanced. This work demonstrates the successful application of marker-assisted selection in conjunction with phenotype-based selection for targeted introgression of multiple resistance genes into traditional Basmati varieties along with improvement of their plant stature and yield.Not Availabl