Response of broomcorn millet(Panicum miliaceum L.)genotypes from semiarid regions of China to salt stress

Salt tolerance of crops is becoming more and more important, owing to the constant increase of salinity in arid and semi-arid regions. Broomcorn millet(Panicum miliaceum L.),generally considered tolerant to salinity, can be an alternative crop for salt affected areas.To assess genotypic variation for vegetative-stage salinity tolerance, 195 broomcorn millet accessions from a core collection were evaluated for germination percentage, shoot length,and root length during germination in 8 m L of deionized water(control) or 8 m L of a120 mmol L-1salt solution(treatment). Six genotypes with different levels of salt tolerance were selected based on the growth parameters and ion concentrations in plant at the seedling stage and used for confirmation of the initial salinity response. Substantial variation for salinity tolerance was found on the basis of salt damage index [(germination percentage under control- germination percentage under salinity) / germination percentage under control × 100, SDI] and 39 accessions exhibited strong salt tolerance with SDI lower than 20%. The salt tolerance performance of the genotypes was generally consistent across experiments. In the seedling growth study, seedling number, root length and belowground biomass were adversely affected(showing more than 70%, 50%, and 32%reduction, respectively) in sensitive genotypes compared to tolerant genotypes(35%, 31%,and 3% reduction, respectively) under 160 mmol L-1Na Cl treatment. In general,whole-plant salinity tolerance was associated with increased Na+concentration and Na+/K+ratio, and salt-tolerant genotypes often had higher root and lower shoot Na+concentration than sensitive ones. Na+concentration in root was closely related to salt tolerance and may be considered as a selection criterion for screening salt tolerance of broomcorn millet at the seedling or vegetative stages.

Heterosis in root microbiota inhibits growth of soil-borne fungal pathogens in hybrid rice

In nature,plants are colonized by various microbes that play essential roles in their growth and health.Heterosis is a natural genetic phenomenon whereby first-generation hybrids exhibit superior phenotypic performance relative to their parents.It remains unclear whether this concept can be extended to the“hybridization”of microbiota from two parents in their descendants and what benefits the hybrid microbiota might convey.Here,we investigated the structure and function of the root microbiota from three hybrid rice varieties and their parents through amplicon sequencing analysis of bacterial 16S ribosomal DNA(rDNA)and fungal internal transcribed spacer(ITS)regions.We show that the bacterial and fungal root microbiota of the varieties are distinct from those of their parental lines and exhibit potential heterosis features in diversity and composition.Moreover,the root bacterial microbiota of hybrid variety LYP9 protects rice against soil-borne fungal pathogens.Systematic analysis of the protective capabilities of individual strains from a 30-member bacterial synthetic community derived from LYP9 roots indicated that community members have additive protective roles.Global transcription profiling analyses suggested that LYP9 root bacterial microbiota activate rice reactive oxygen species production and cell wall biogenesis,contributing to heterosis for protection.In addition,we demonstrate that the protection conferred by the LYP9 root microbiota is transferable to neighboring plants,potentially explaining the observed hybrid-mediated superior effects of mixed planting.Our findings suggest that some hybrids exhibit heterosis in their microbiota composition that promotes plant health,highlighting the potential for microbiota heterosis in breeding hybrid crops.