Comparison of the genetic basis of salt tolerance at germination, seedling, and reproductive stages in an introgression line population of rice.

BACKGROUND: Salinity is a major limitation for rice farming due to climate change. Since salt stress adversely impact rice plants at germination, seedling, and reproductive stages resulting in poor crop establishment and reduced grain yield, enhancing salt tolerance at these vulnerable growth stages will enhance rice productivity in salinity prone areas. METHODS AND RESULTS: An introgression line (ILs) population from a cross between a high yielding cultivar 'Cheniere' and a salt tolerant donor 'TCCP' was evaluated to map quantitative trait loci (QTLs) for traits associated with salt tolerance at germination, seedling, and reproductive stages. Using a genotyping-by-sequencing based high density SNP linkage map, a total of 7, 16, and 30 QTLs were identified for five germination traits, seven seedling traits, and ten reproductive traits, respectively. There was overlapping of QTLs for some traits at different stages indicating the pleiotropic effects of these QTLs or clustering of linked genes. Candidate genes identified for salt tolerance were OsSDIR1 and SERF for the seedling stage, WRKY55 and OsUBC for the reproductive stage, and MYB family transcription factors for all three stages. Gene ontology analysis revealed significant GO terms related to nucleotide binding, protein binding, protein kinase activity, antiporter activity, active transmembrane transporter activity, calcium-binding protein, and F- box protein interaction domain containing protein. CONCLUSIONS: The colocalized QTLs for traits at different growth stages would be helpful to improve multiple traits simultaneously using marker-assisted selection. The salt tolerant ILs have the potential to be released as varieties or as pre-breeding lines for developing salt tolerant rice varieties.

Genetics of yield component traits under salt stress at flowering stage and selection of salt tolerant pre-breeding lines for rice improvement.

Rice is highly vulnerable to salt stress at both seedling and flowering stage. While research efforts largely focused on seedling stage salinity tolerance, flowering stage salt tolerance studies are limited. Development of rice cultivars with salt tolerance at both stages will enhance rice productivity in salt affected farmlands. In the present study, two introgression line (IL) populations of a salt-tolerant landrace 'Nona Bokra (N)' were developed in the genetic backgrounds of two U.S. cultivars 'Cheniere (C)' and 'Jupiter (J)' and were evaluated for elucidation of the genetic basis of agronomically important traits at flowering stage and development of salt tolerant pre-breeding lines. Evaluation of both sets of ILs (JN-ILs and CN-ILs) under saline (EC = 8 dSm-1) environment led to identification of a total of 33 QTLs for seven different yield and yield component traits impacted by salt stress. Majority of large-effect QTLs for traits such as panicle length (qPL1.1JN), spikelet sterility (qSS1.1JN), thousand-grain weight (qTGW1.1JN), days to flowering (qDFF1.1CN), and plant height (qPH1.1CN) were located on chromosome 1. Some candidate genes present within the major effect QTL regions include potassium channel OsKAT1, NAC domain-containing protein, potassium transporters, and photosensitive leaf rolling 1. Comparison of the results with earlier reports on seedling stage suggested a different set of genes controlling salt tolerance at both stages. In addition, pre-breeding lines with improved flowering stage salinity tolerance were identified. These pre-breeding rice lines will accelerate fine mapping, map-based cloning, and pyramiding of desirable alleles for both flowering and seedling stage salt tolerance through marker assisted selection.

Multidrug-Resistant Extended-Spectrum ß-Lactamase-Producing Escherichia coli Pathotypes in North Eastern Region of India: Backyard Small Ruminants-Human-Water Interface.

A total of 648 diarrheagenic Escherichia coli (DEC) were isolated from calves (n = 219), lambs (n = 87), kids (n = 103), human (n = 193), and water (n = 46) samples. The presence of enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), and shigatoxigenic E. coli (STEC) was confirmed by PCR-based detection of the Shiga toxin, intimin, hemolysin, and enterotoxin genes. All the isolates were tested for antimicrobial resistance (AMR) by disc diffusion assay. Extended-spectrum ß-lactamase (ESBL), carbapenemase, and metallo-beta-lactamase production were determined by double-disk synergy test, modified Hodge test, and combined disk test assays. AMR genes (blaTEM, blaSHV, blaCTX-M, blaCMY-2, blaNDM, blaKPC, blaVIM, and blaIMP) were detected by PCR using specific primers. Majority of the isolates from human and water exhibited resistance (>80%) against amoxicillin, ampicillin, aztreonam, cefotaxime, cefixime, gentamicin, ceftazidime, and cefalexin, and against imipenem (70.98%), doripenem (70.47%), and ertapenem (60.62%). Bovine isolates were sensitive to carbapenems. Many isolates (5.75-24.35%) from human, water, calves, kids, and lambs were multidrug resistant (MDR), with resistance against three or more classes of antimicrobials. A total of 170/648 (26.23%) isolates were classified as STEC (9.88%), EPEC (4.32%), and ETEC (12.04%). The AMR genes, including blaTEM, blaCMY2, blaCTX-M, and blaSHV were detected in the E. coli from all sources. but blaNDM and blaKPC were detected only in the isolates from human and water. Three STEC isolates from human origin possessed multiple ESBLs, carbapenemase and metallo-beta-lactamase genes reported for the first time. ESBLs producing EPEC and ETEC in lambs and kids are also reported under this study. Presence of MDR-DEC in domestic animals and common potable water poses public health concern in this region.

Coinfection of diarrheagenic bacterial and viral pathogens in piglets of Northeast region of India.

AIM: This study aimed to study the prevalence of the coinfection of enteric bacterial and viral pathogens, namely Escherichia coli, Salmonella, Rotavirus, and Picobirnavirus from fecal samples of pre-weaned piglets in Northeast region of India. MATERIALS AND METHODS: A total of 457 fresh fecal samples were collected from piglets under 9 weeks old during 2013-2015 from organized (n=225) and unorganized (n=232) farms of Manipur, Meghalaya, Mizoram, and Nagaland. Samples were collected from diarrheic (n =339) and non-diarrheic (n=118) piglets including local indigenous (n=130) and crossbreed (n=327) piglets in different seasons during the study period. The samples were processed for the isolation of E. coli and Salmonella and detection of their putative virulence genes by polymerase chain reaction (PCR). Samples were also processed for the detection of Rotavirus and Picobirnavirus by RNA-polyacrylamide agarose gel electrophoresis and reverse transcriptase-PCR (RT-PCR). RESULTS: A total of 11 (2.40%) samples were found positive for two or more coinfecting enteric bacterial and viral pathogens. All the 11 positive fecal samples were recovered from diarrheic piglets. Salmonella Typhimurium (enterotoxin, stn gene) and Picobirnavirus genogroup 1 were found to be more frequent as coinfecting agents. Coinfection was recorded higher in unorganized (3.87%) compared to organized farm (0.88%). Again, higher detection was recorded in crossbreed (2.75%) than local indigenous piglets (1.53%). The occurrence of coinfection was found to be more common during summer (4.68%) followed by winter (2.27%) season. CONCLUSION: The present study highlighted the significance of E. coli, Salmonella, Rotavirus, and Picobirnavirus as important diarrheagenic pathogens causing coinfection in piglets in Northeast region of India. Probably, this is the first systematic study of the coinfection of four important diarrheagenic bacterial and viral agents associated with piglet diarrhea in India.