The special topic of the two papers is the systemic acquired resistance (SAR) and pathogenesis-related protein genes (PR).  SAR is an enhanced resistance against further potential parasite beyond the initial infection site, which can be induced by either pathogen infection or exogenous inducer, including synthetic chemicals and natural products.  As a “whole-plant” resistance defense, SAR confers broad-spectrum immunity to widely diverse pathogenic microorganisms, such as viruses, bacteria and fungi for a relatively long lasting period.  Convincingly, it is a promising way to prevent crop diseases by activating the plants’ own natural defenses via application of chemical inducers or creating resistant wheat cultivars.  

The first article from Wang et al. (2018) reviewed SAR in wheat and barley, the possible involvement of the master regulator Non-expresser of PR genes 1 (NPR1) and PR genes in the SAR processes.  The author summarized to our current knowledge of the three different types of SAR-like responses in wheat and barley in comparison to Arabidopsis and rice.  Research updates on the wheat and barley NPR1 homologs in SAR, downstream genes of SAR, including PR genes and BTH-induced genes were highlighted, which provided initial clue for understanding the SAR mechanism in these two plant species.  The review is informative in the research advances of SAR in wheat and barley, which would help the readers to obtain an overall understanding of SAR in the resistance of wheat and barley to different pathogens.  

The second article from Farrakh et al. (2018) investigated the roles of different PR protein genes in race-specific resistance and non-race specific high-temperature adult-plant (HTAP) resistance of wheat to wheat stripe rust fungus by profiling the expression of eight different PR genes.  The authors elucidated that different PR genes are involved in different types of resistance and resistance controlled by different Yr genes, owing to the varied expression level of PR genes at different stages of infection and among different Yr gene lines.  The research provides useful and needed information of the function of PR genes in wheat all-stage resistance and HTAP, which greatly improves the understanding of the molecular mechanism underlying race specificity and durability of stripe rust resistance.   

At the molecular level, the findings of the papers deepen our knowledge on the response of crop plant to pathogen invasion.  More importantly, the information obtained give clues for improving plant resistance in novel ways.  I genuinely believe that the findings will inspire the readers of the Journal of Integrative Agriculture for developing future research on the given topics.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an airborne disease. In China, it frequently develops initially in central Shaanxi and southwestern Gansu, and from there, inoculum spreads to the eastern wheat production regions. Field investigations have suggested that Pst could spread from the west to the east within central Shaanxi and that Gansu could serve as the inoculum source for central Shaanxi, but there is no direct evidence for this hypothetical dispersal route. In the current study, 321 Pst isolates collected from central Shaanxi and Gansu in the 2019-2020 and 2020-2021 winter wheat cropping seasons were genotyped using 23 pairs of KASP-SNP markers. The dispersion among subpopulations was analyzed using several approaches, and overall, the populations were found to exhibit high levels of genetic diversity. There was little genetic divergence (0.05 > F_st > 0) within central Shaanxi. However, significant gene flow (Nm > 4) driven by wind-oriented dispersal from west (Baoji) to east (Weinan) occurred. There was also gene flow among the 4 Gansu subpopulations of Tianshui, Longnan, Pingliang, and Qingyang. Migration of the pathogen occurred between central Shaanxi and Gansu. Migration from Gansu to central Shaanxi was major compared with that from central Shaanxi to Gansu that was minor. Genetic variation occurred among isolates, instead of among subpopulations and within isolates. Linkage disequilibrium revealed that there was strong genetic recombination in the subpopulations from Gansu and central Shaanxi. Therefore, the present study provides molecular evidence that Pst spread from west to east in central Shaanxi and showed that Gansu (especially Longnan and Tianshui) was one of the major origins of the pathogen inoculum of wheat stripe rust in central Shaanxi. The results revealed the west-to-east transmission route of wheat stripe rust in central Shaanxi, being used to guide integrated management of the disease.