Stem rust resistance in wheat is suppressed by a subunit of the mediator complex

Stem rust is an important disease of wheat that can be controlled using resistance genes. The gene SuSr-D1 identified in cultivar 'Canthatch' suppresses stem rust resistance. SuSr-D1 mutants are resistant to several races of stem rust that are virulent on wild-type plants. Here we identify SuSr-D1 by sequencing flow-sorted chromosomes, mutagenesis, and map-based cloning. The gene encodes Med15, a subunit of the Mediator Complex, a conserved protein complex in eukaryotes that regulates expression of protein-coding genes. Nonsense mutations in Med15b.D result in expression of stem rust resistance. Time-course RNAseq analysis show a significant reduction or complete loss of differential gene expression at 24h post inoculation in med15b.D mutants, suggesting that transcriptional reprogramming at this time point is not required for immunity to stem rust. Suppression is a common phenomenon and this study provides novel insight into suppression of rust resistance in wheat. Stem rust is an important disease of wheat and resistance present in some cultivars can be suppressed by the SuSr-D1 locus. Here the authors show that SuSr-D1 encodes a subunit of the Mediator Complex and that nonsense mutations are sufficient to abolish suppression and confer stem rust resistance

Allelopathic potential of rice residues of selected rice varieties (Oryza sativa L.) against Echinochloa crus-galli

Selection of rice varieties with greater allelopathic potential can be used as a tool in sustainable weed management. Exploitation and implementation of this technology in weed management has been considered as ecologically sound, resource conserving and economically viable method. The objective of this study was to assess the allelopathic traits of rice residues of selected rice cultivars (Bg 359, Ld 365, Bg 407, At 401, Bg 358, At 362, At 402, Bg 450, Bg 300, Herathbanda and Handiran) to suppress barnyard grass (Echinochloa crus-galli) seed germination, growth and development which is one of the most destructive weeds in Sri Lankan paddy ecosystem. Completely Randomised Design was used with three replicates for each cultivar. According to the research findings, significant differences (p≤0.05) were observed among cultivars and amount of residue mixed with sand (2, 4, 6 g of ground residue per 500 g of sand) in terms of barnyard grass plant height, number of leaves, germination and total dry weight. Among those measured variables germination and dry matter accumulation of barnyard grass showed significant reduction when increasing amount of rice residues. Among different cultivars used Ld 365 showed the highest inhibition % for all above measured variables and the lowest was the Herathbanda. As an example the inhibition percentages of plant height, seed germination and shoot dry weight of barnyard grass grown in 6 g of Ld 365 rice residue mixture were 72.7%, 74.2% and 82.6% respectively. In contrast, residues of rice variety Herathbanda caused 36.6%, 37.9% and 40.5% inhibition respectively for above mentioned parameters. When comparing three levels of rice residue mixture suppression ability of barnyard grass seed germination was increased. Therefore, it could be suggested that the allelopathic potential of rice residue significantly changes with cultivar and amount of residue incorporated with soil. Knowledge of rice allelophathic properties of rice residue will offer several possibilities for ecological management of weeds in paddy fields in Sri Lanka