Perennial ryegrass (Lolium perenne L.) is a popular cool-season forage and turfgrass in temperate regions. Due to its self-incompatible and out-crossing nature, perennial ryegrass may show a high degree of heterozygosity. Perennial ryegrass generally is susceptible to drought stress, but variations of drought response of individual genotypes within a particular accession or cultivar are not well understood. The objective of this study was to characterize phenotypic diversity of drought tolerance within and among accessions in relation to genetic diversity in perennial ryegrass. Five individual genotypes from each of six accessions varying in origin and growth habits were subjected to drought stress in a greenhouse. Leaf wilting, plant height, chlorophyll fluorescence (Fv/Fm) and leaf water content (LWC) differed significantly among accessions as well as among genotypes within each accession under well-watered control and drought stress conditions. Fv/Fm was highly correlated with LWC under drought stress. Genetic diversity among and within accessions were identified by using previously characterized 23 simple sequence repeat markers. Across accessions, the mean major allele frequency, gene diversity, and heterozygosity values were 0.66, 0.43, and 0.66, respectively. Accessions with closer genetic distance generally had similar drought responses, while accessions with greater genetic distance showed distinct drought tolerance. Significant differences in drought tolerance among and within accessions, especially for individual genotypes within one accession, indicated that variations of drought response could be used for enhancing breeding programs and studying molecular mechanisms of stress tolerance in perennial ryegrass.
Perennial ryegrass (Lolium perenne) is an important cool-season forage and turfgrass species. Growth and physiological responses of perennial ryegrasses to chronic deficit irrigation (DI) and recovery following a water deficit event are not well understood. The objective of this study was to characterize plant growth, water status, and gene expression in response to DI and recovery of perennial ryegrass. Two accessions, PI598453 (drought tolerant) and PI403847 (drought susceptible), were subjected to irrigation treatments with 100% evapotranspiration (ET) replacement every other day as the control (100% ET) and 70% ET replacement as DI treatment for 21 days in a greenhouse. After the treatment period, the DI-treated plants were shifted back to 100% ET for 7 days for recovery. The grasses were cut every 7 days, for a total of three times. Leaf relative water content (LRWC) significantly decreased at 21 days of 70% ET for both accessions, compared with the control; but to a greater extent in the more susceptible PI403847. Water-use efficiency (WUE) significantly increased 1.6-fold for PI598453 and 1.3-fold for PI403847 under 70% ET, whereas 33% reduction of leaf dry weight (LDW) was found only in PI403847. Plant height (HT) and leaf length (LL) were unaffected by 70% ET after the first two cuttings, but decreased after the third cut and did not recover to the control level for both accessions. Reductions in leaf width (LW) under 70% ET were found at 8 and 6 days after cutting for PI598453 and for PI403847, respectively. The transcript levels of heat shock protein (HSC70), iron superoxide dismutase (FeSOD), and plasma membrane intrinsic protein type 1 (PIP1) in both leaves and stems were generally downregulated during 70% ET treatment with a few exceptions but fully recovered to 100% ET after rewatering. The expression levels of cytosolic copper/zinc superoxide dismutase (cyto Cu/Zn SOD) and light-harvesting Chl a/b-binding proteins (LHCB) did not alter under 70% ET for both accessions. Differential growth and physiological responses of perennial ryegrass accessions to DI could be used for further studying of molecular mechanisms of drought tolerance in perennial ryegrass.
The autotoxicity of root exudates and the change of rhizosphere soil microbes are two important factors that affect the quality and yield of Lanzhou lily (Lilium davidii var. unicolor). Phthalic acid (PA) is a major autotoxin of the root exudates in Lanzhou lily. In this study, we treated plants with different concentrations of PA from the Lanzhou lily root exudates and then analyzed the effects of autotoxins on fresh weight, shoot height, root length, and Oxygen Radical Absorbance Capacity in root. The diversity of soil fungi in Lanzhou lily soil was analyzed using MiSeq. The results showed that PA induced oxidative stress and oxidative damage of Lanzhou lily roots, improved the level of the membrane lipid peroxidation, reduced the content of antioxidant defense enzyme activity and the nonenzymatic antioxidant, and eventually inhibited the growth of the Lanzhou lily. We found that continuous cropping of Lanzhou lily resulted in an increase in fungal pathogens, such as Fusarium oxysporum in the soil, and reduced the size of plant-beneficial bacteria populations. The results in this study indicate that continuous cropping would damage the regular growth of Lanzhou lily.