ABSTRACT
Symptomless fungal endophytes in the genus Epichloë are repeatedly mentioned to increase tolerance of cool-season grasses to a wide range of environmental stress factors, mainly drought. However, the generality of this idea is challenged because (i) most studies have been conducted on two economically important forage grasses {tall fescue [Festuca arundinacea (Schreb.) Dumort] and perennial ryegrass (Lolium perenne L.)}, (ii) endophyte-mediated mechanisms and effects on plant responses to drought have shown to be highly variable across species, and that (iii) symbiosis incidence in plant populations occurring in extremely arid environments is usually low. We question this idea by reviewing the existing information about Epichloë fungal endophyte effects on drought tolerance in cool-season grasses. We combined standard review, vote counting, and calculation of effect sizes to synthesize the literature, identify information gaps, and guide future research. The total number of studies was higher for domesticated than for wild species, a ratio that was balanced when papers with data quality for effect size calculus were considered. After the drought, endophyte-infected plants accumulated more aboveground and belowground biomass than non-infected counterparts, while no effect on tillering was observed. However, these effects remained significant for wild (even on tillering) but not for domesticated species. Interestingly, despite the continuous effort in determining physiological mechanisms behind the endophyte effects, no studies evaluated plant fecundity as a measure of ecological fitness nor vital rates (such as survival) as to escalate individual-level variables to population. Together with the high variability in results, our work shows that generalizing a positive effect of fungal endophytes in plant tolerance to drought may be misleading. Future studies combining field surveys with manipulative experiments would allow us to unravel the role of fungal endophytes in plant adaptation by considering the evolutionary history of species and populations to the different ecological contexts.
ABSTRACT
Herbaceous winter-hardy Hibiscus spp. in the section Muenchhusia, also known as rosemallows, are attractive ornamental plants found in temperate environments. These should not be confused with woody winter-hardy hibiscus (Hibiscus syriacus L. and related species) which have also been intensively used as ornamental shrubs. During the past 70 years, breeders have attempted to create winter-hardy hibiscus hybrids with novel flower colors resembling the distantly related tropical Chinese hibiscus, Hibiscus rosa-sinensis L. Although direct attempts to hybridize winter-hardy hibiscus with the tropical hibiscus have been unsuccessful, new interspecific herbaceous winter-hardy hibiscus hybrids with a palette of novel flower colors commonly found in tropical hibiscus have been recently introduced. In this review, we outline the historic perspective on interspecific hybridizations in woody and herbaceous winter-hardy hibiscus and discuss breeding approaches to develop herbaceous winter-hardy hibiscus hybrids with novel flower colors and shapes resembling tropical hibiscus cultivars. By creating a broad genetic variability in herbaceous winter-hardy hibiscus hybrids we found a successful approach to increase the range of flower colors and shapes in these species and made them look very like their distant tropical relatives.
ABSTRACT
Summer dormancy is an evolutionary response that some perennial cool-season grasses adopted as an avoidance strategy to escape summer drought and heat. It is correlated with superior survival after severe summer droughts in many perennial grass species originating from Mediterranean environments. Understanding the genetic mechanism and environmental determinants of summer dormancy is important for interpreting the evolutionary history of seasonal dormancy and for the development of genomic tools to improve the efficiency of genetic selection for this important trait. The objectives of this research are to assess morphological and biochemical attributes that seem to be specific for the characterization of summer dormancy in tall fescue, and to validate the hypothesis that genes underlying stem determinacy might be involved in the mechanism of summer dormancy. Our results suggest that vernalization is an important requirement in the onset of summer dormancy in tall fescue. Non-vernalized tall fescue plants do not exhibit summer dormancy as vernalized plants do and behave more like summer-active types. This is manifested by continuation of shoot growth and high root activity in water uptake during summer months. Therefore, summer dormancy in tall fescue should be tested only in plants that underwent vernalization and are not subjected to water deficit during summer months. Total phenolic concentration in tiller bases (antioxidants) does not seem to be related to vernalization. It is most likely an environmental response to protect meristems from oxidative stress. Sequence analysis of the TFL1 homolog CEN gene from tall fescue genotypes belonging to summer-dormant and summer-active tall fescue types showed a unique deletion of three nucleotides specific to the dormant genotypes. Higher tiller bud numbers in dormant plants that were not allowed to flower and complete the reproductive cycle, confirmed that stem determinacy is a major component in the mechanism of summer dormancy. The number of variables identified in these studies as potential players in summer dormancy in tall fescue including vernalization, TFL1/CEN, water status, and protection from oxidative stress are a further confirmation that summer dormancy is a quantitative trait controlled by several genes with varying effects and prone to genotype by environment interactions.
ABSTRACT
Rumen bacterial communities in forage-fed and grazing cattle continually adapt to a wide range of changing dietary composition, nutrient density, and environmental conditions. We hypothesized that very distinct community assemblages would develop between the fiber and liquid fractions of rumen contents in animals transitioned from bermudagrass hay diet to a grazed wheat diet. To address this hypothesis, we designed an experiment utilizing a 16S-based bTEFAP pyrosequencing technique to characterize and elucidate changes in bacterial diversity among the fiber and liquid rumen fractions and whole rumen contents of 14 (Angus x Hereford) ruminally cannulated steers sequentially fed bermudagrass hay (Cynodon dactylon; 34 days) and grazing wheat forage (28 days). Bermudagrass hay was a conserved C4 perennial grass lower in protein and higher in fiber (11% and 67%, respectively) content than grazed winter wheat (Triticum aestivum), a C3 annual grass with higher protein (20%) and a large (66%) soluble fraction.Significant differences in the OTU estimates (Chao1, Ace,and Rarefaction) were detected between fractions of both diets, with bermudagrass hay supporting greater diversity than wheat forage. Sequences were compared with a 16S database using BLASTn and assigned sequences to respective genera and genera-like units based on the similarity value to known sequences in the database. Predominant genera were Prevotella (up to 33%) and Rikenella-like (upto 28%) genera on the bermudagrass diet and Prevotella (upto 56%) genus on the wheat diet irrespective of the fractions. Principle component analyses accounted for over 95% of variation in 16S estimated bacterial community composition in all three fractions and clearly differentiated communities associated with each diet. Overall, bermudagrass hay diets clustered more clearly than wheat diets.These data are the first to explore bacterial diversity dynamics in a common population of animals in response to contrasting grass forage diets.