Muhammad, I. | Search bioRxiv

bioRxiv2019

Marker-assisted introgression of multiple resistance genes confers broad spectrum resistance against bacterial leaf blight and blast diseases in Putra-1 rice variety

This experiment was conducted with the aim of introgressing multiple resistance genes against bacterial leaf blight (BLB) and blast diseases through marker-assisted backcross breeding. Two dominant (Xa4 and Xa21) and two recessive (xa5 and xa13) BLB resistance genes were introgressed into a Malaysian elite rice variety Putra-1 with genetic background of three blast resistance (Piz, Pi2 and Pi9) genes and high yielding. Eight polymorphic tightly linked functional and SSR markers were used for foreground selection of target genes. 79 polymorphic SSR markers were used in background selection. The plants were challenged at initial stage of breeding and challenged again at BC2F2 with the most virulent Malaysian pathotypes of Xoo (P7.7) and Magnaporthe oryzae (P7.2) to test their resistance. Results obtained from foreground marker analysis showed that the BC1F1 and BC2F1 both fitted into the Mendels single gene segregation ratio of 1:1 for both Xoo and blast resistance. At BC2F2, result obtained indicated that foreground marker segregation fitted into the expected Mendelian ratio of 1:2:1 for blast resistance only. Marker-assisted background selection revealed high percentage of recurrent parent genome recovery (95.9%). It was concluded that resistance to Xoo pathotype P7.7 in IRBB60 was neither due to two independent gene action nor epistasis but substantially due to single nuclear gene action. Also, the inheritance of blast resistance in the pyramided lines to pathotype P7.2 was also attributed to single gene action. The incorporation of four bacterial leaf blight and three blast resistance genes (Xa4+xa5+xa13+Xa21+Pi9+Pi2+Piz) in the newly developed lines provides for broad spectrum and durable resistance against the two major diseases studied.

genetics↗

bioRxiv2019

Differential detection of Entamoeba species in stool samples collected from children in District Swat, Khyber Pakhtunkhwa Pakistan

BackgroundAmoebiasis is an intestinal disease caused by enteric protozoan called Entamoeba histolytica belongs to the Genus Entamoeba. The main reason of infection is the contamination of food and water due to the poor sanitation. Among Entamoeba species, Entamoeba histolytica is highly pathogenic while the other species are non-pathogenic and needs no medical treatment.\n\nMethodologyA total of 400 stool samples were collected from different areas of district Swat and were processed for screening of amoebic cells. Microscopically identified samples containing amoebic cells were stored at -20 {degrees}C till DNA extraction. Extracted DNA was used in a PCR reaction with specific reference primers to amplify the target DNA.\n\nResultsOut of all 400 stool samples 111 (27.7%) were found positive through microscopy while PCR reaction confirmed 80 out of microscope positive samples. Among 80 PCR positive samples, the infection with Entamoeba dispar was most common (57.5%) followed by E. histolytica (47.5%) and Entamoeba moshkovskii (20%). The positive cases for mono-infection of E. dispar were 33 (41.25%), followed by E.histolytica 25 (31.25%) and E. moshkovskii 7 (8.75%). The co-infection of E. histolytica with E. dispar and E. moshkovskii was 6 (7.5%) and 2 (2.5%), respectively. Similarly the co-infection of Entamoeba dispar with Entamoeba moshkovskii was also 2 (2.5%) while 5 (6.25%) samples were observed with mixed infection of E. histolytica, E. dispar and E. moshkovskii.\n\nSignificance of the studyThe aim of the study was to detect and differentiate the E. histolytica, Entamoeba dispar and Entamoeba moshkovskii using conventional microscopy and polymerase chain reaction. The results suggested that the use of PCR is necessary to differentiate E. histolytica from E. dispar and E. moshkovskii and therefore, to avoid unnecessary treatment the present study recommend the use of PCR for the routine diagnosis of amoebiasis in the study area. It is also suggested that further studies from this area may also facilitate the understanding of genetic diversity of these pathogens.

microbiology↗