Phenotyping Winter Dormancy in Switchgrass to Extend the Growing Season and Improve Biomass Yield

Switchgrass is a prominent bioenergy crop. Like most perennial warm season species, switchgrass undergoes growth suspension in winter as a surviving strategy in temperate climates to protect their meristems from cold injuries and dehydration, while storage organs below ground drive spring regrowth when conditions become favourable. In this paper, we describe a reliable phenotyping method for winter dormancy in switchgrass using various traits including regrowth height after clipping in early fall (FRH), senescence percentage, date of spring regrowth (SRD), and flowering date (FD). FRH and senescence percentage appear to be reliable indicators of the onset of winter dormancy, whereby accessions that initiated dormancy early have a low FRH and a high senescence percentage. Even though it is difficult to have an exact assessment of the duration of dormancy because it is hard to determine with precision the date of growth suspension, SRD can be used as a surrogate indicator of the duration. Flowering date showed low correlations with all the traits and biomass yield suggesting that it may not be a reliable indicator for winter dormancy in switchgrass. Combining the variables FRH, senescence, and SRD in a selection index may provide a reliable tool to phenotype winter dormancy in switchgrass. The strong correlation of these variables with biomass yield makes them useful candidates for the manipulation of the duration of dormancy to increase the growing season and consequently improving biomass production. In southern regions with mild winters, it might be possible through intense selection to develop germplasm with much reduced dormancy or even non-dormant switchgrass germplasm.

Effect of Plant Growth Stimulants on Alfalfa Response to Salt Stress

Salinity is a major impediment to crop production. This study was undertaken to compare the effect of seaweed extract, humic acid, and potassium sulfate nanoparticles in alleviating salt stress in Alfalfa (Medicago sativa L.). Seeds of ten alfalfa genotypes were germinated in a growth chamber at five salt concentrations (0%, 0.5%, 1.0%, 1.5%, and 2.00%). Salt concentrations above 1% reduced seed germination by more than 70% in most genotypes. One salt tolerant genotype (Mesa-Sirsa) and one salt sensitive (Bulldog 505) were selected and planted in greenhouse pots containing 2 kg of sand and subjected to two salt levels (10 and 15 dS· m-1). Four treatments consisting of 1) control (Hoagland solution, no-salt), 2) seaweed extract at 4 Kg·ha-1, 3) humic acid at 28 L· ha-1, and 4) potassium sulfate at 300 Kg· ha-1. Plant biomass was reduced under both salt concentrations in both genotypes, with a greater magnitude in the salt sensitive genotype. Application of seaweed extract resulted in higher relative water content and proline under both salt concentrations (10 and 15 dS·m-1) in the salt sensitive genotype, and lower electrolyte leakage in both salt tolerant and salt sensitive genotypes, under both salt concentrations. Seaweed extract also resulted in higher catalase and SOD activities in both genotypes under 10 dS·m-1. Catalase and SOD activities were associated with significantly (p < 0.01) reduced electrolyte leakage and increased shoot dry weight. Overall, seaweed extract seemed to have a positive effect in alleviating salt stress in alfalfa.

Allelopathic Effects of Cereal Rye on Weed Suppression and Forage Yield in Alfalfa

Cereal rye (Secale cereale L.) is widely used as cover crop because of its allelopathic effects and effectiveness in weed suppression. In the Southeastern US, rye is traditionally grown for winter grazing in dormant bermudagrass pastures, where alfalfa (Medicago sativa L.) is increasingly planted as a companion crop. The effect of cereal rye on alfalfa as a succeeding crop is not known. Therefore, the objective of this study was to evaluate the effect of cereal rye on alfalfa seedling emergence, growth, forage yield, and weed suppression in field conditions. Rye was planted in the fall (mid-October) and the biomass was harvested in spring (March) followed by disking and incorporation of the remaining stubble in the soil. Alfalfa seed was planted four weeks later. The experiment design was a split-plot design with the main plots being no-rye and after-rye and the sub-plots being alfalfa cultivars. Ten alfalfa cultivars were planted in three replications after-rye and three replications with no-rye as a previous crop. In the establishment year, weed density was significantly (p < 0.01) lower in the after-rye alfalfa plots by nearly 77%. Alfalfa seedling counts were also significantly lower (p 0.01) among the cultivars planted in the after-rye block compared to the no-rye, with a seedling count reduction between 35% and 64%. Reduction in total dry biomass yield varied from 15% to 43% among the cultivars planted in the after-rye block. The results of this study also suggest that the allelopathic effect of rye on alfalfa may not persist beyond the establishment season, but the enormous yield reduction in the first production season may constitute a costly economic penalty in terms of forage production. There was variation in the response of different alfalfa cultivars to the effect of rye residue as indicated by the variation in the magnitude of reduction in stand count and forage yield. This warrants more research in multi-location trials with and without rye in order to establish whether there is genetic variation in alfalfa germplasm in their tolerance to cereal rye allelopathy.

Determining the earliest growth stage to detect the presence of endophytes in tall fescue and perennial ryegrass seedlings using molecular markers

Background:Tall fescue(Festuca arundinacea[Schreb.],Lolium arundinaceum[Schreb.]Darbysh)and perennial ryegrass(Lolium perenne)are important cool-season forage and amenity grasses that have a mutualistic association with an endophytic fungus.Endophytes confer insect and drought resistance to plants but can produce mammalian toxins.Novel endophytes that do not produce mammalian toxins have been introduced to elite cultivars for commercial production.Seed companies need to maintain adequate levels of novel endophytes within the elite forage cultivars.Endophyte detection is performed using immunochemical and molecular techniques because of their speed and reliability.Early detection in seedlings is essential to evaluate the viability of the endophyte within seed lots.Methods:This research aimed to identify the earliest growth stage in which immunochemical and molecular methods can detect viable endophyte in seedlings of tall fescue cultivars BarOptima(e34),Texoma MaxQII(584),and Jesup MaxQ(542),as well as the perennial ryegrass cultivar Remington(NEA2).Results:Immunochemical testing detected endophytes in seedlings 14 days after germination(DAG),but the detection rate increased until 42 DAG in some cultivars tested.The molecular marker Tef1exon detected endophytes at a lower rate than the immunochemical method at 28–42 DAG.However,there was insufficient DNA to detect endophytes in 14 DAG seedlings using markers.Conclusions:We conclude that the most accurate detection of viable endophytes in seedlings was 42 DAG,at which sufficient and consistent endophyte colonization occurred.