Direct and indirect responses to divergent phenotypic selection for fiber traits in timothy (Phleum pratense L.)

Genetic improvement of timothy digestibility by breeding requires an effective and reliable selection procedure. The general objective of this study was to evaluate the concentrations of four fiber components (neutral detergent fiber, acid detergent fiber, acid detergent lignin, hemicellulose, and cellulose) and four ratios involving these concentrations (acid detergent lignin over hemicellulose, acid detergent lignin over cellulose, acid detergent lignin over the sum of hemicellulose and cellulose and hemicellulose over cellulose) as selection criteria to improve timothy digestibility without affecting plant biomass. Selected genotypes and populations derived from them were evaluated in a field experiment. Significant variability was observed among genotypes for all nine traits. Divergent phenotypic selection for seven of the traits (all except hemicellulose and hemicellulose over cellulose) produced groups of genotypes that consistently differed for the trait used as the selection criterion. Selection criteria that involved acid detergent lignin were the most effective in identifying genotypes with consistent differences in in vitro true digestibility. Genotypes selected for high or low values of each criterion were intercrossed to produce progeny populations. Five of the nine pairs of divergent populations were consistently different for the trait used as the selection criterion. Selection for acid detergent lignin over cellulose was the most effective in producing populations with consistent differences (22 to 32 g kg-1 DM) in in vitro true digestibility, with reduced values of this ratio associated with increased digestibility. This was mainly due to a reduction of the concentrations of lignin and neutral detergent fiber, particularly in the stem fraction, resulting in greater stem digestibility. Among the criteria examined here, the ratio of acid detergent lignin over cellulose therefore seems to be the most promising for phenotypi

Estimating the yield potential of short-rotation willow in Canada using the 3PG model

The ability to predict short-rotation coppice (SRC) willow productivity for a given region would be very helpful for large-scale deployment of this crop. The objectives of this study were to calibrate and validate the 3PG model for two commonly used clones (SX64 and SX67) and to provide yield potential estimates for 16 sites across Canada. One dataset for each clone, including leaf area index (LAI) and stem biomass was used for calibrating parameters controlling leaf and stem growth. All other datasets, coming from 8 different willow plantations, were used for model validation. Model performance was good in predicting stem biomass for the SX64 (normalized mean error [NME] = -8%, normalized root mean square error [NRMSE] = 22%) and SX67 (NME = -3%, NRMSE = 16%) clones. Predictions were more scattered for LAI, with NRMSE close to 35% and 33% and NME of 1% and 8% for SX64 and SX67, respectively. The simulation results show that the highest yields were obtained with the three-year rotation for the SX67 clone, whereas a two-year rotation seemed to be more appropriate for the SX64 clone. The simulation results also show that growing degree-days had a significant impact on yield potential which varied from 10.5 to 16.5 t DM haâ 1 for SX64 and from 7.5 to 11.5 t DM haâ 1 for SX67.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Leaf nitrogen concentration as an indicator of corn nitrogen status

International audiencePlant-based measurements can be used to diagnose the in-season N status of corn (Zea mays L.). Our objective was to assess the relationship between the corn nitrogen nutrition index (NNI), an index based on whole plant N concentration, and leaf nitrogen concentration of the uppermost collared leaf expressed on the basis of dry matter (DM; N-L) or area (N-LA). Three to seven N fertilization treatments were used in this study conducted at eight site-years in Canada and two site-years in France. Leaf N concentrations were measured from the uppermost collared leaf on three to five sampling dates along with NNI determinations. At all sites and most sampling dates, N-L, N-LA, and NNI increased with increasing N rates. With data from all sampling dates, N-L and N-LA were related to NNI, but the intercept of the response curves varied with site-year. These site-specific relationships should be used with caution for the in-season evaluation of corn N status. At stage of development similar to V12, however, N-L was strongly related to NNI (NNI = -0.035 + 0.028 N-L; R-2 = 0.82) and the response curve was not affected by site, year, nor cultural practice; N-LA was also related to NNI, but the intercept of the response curve varied with site-year. Determining N concentration (DM basis) of the uppermost collared leaf at, or near, the V12 stage of development is an alternate method for assessing NNI, hence eliminating the need to measure shoot biomass

Selection of rhizobial strains differing in their nodulation kinetics under low temperature in four temperate legume species

Abstract Background Winter climate change including frequent freeze‐thaw episodes and shallow snow cover will have major impacts on the spring regrowth of perennial crops. Non‐bloating perennial forage legume species including sainfoin, birdsfoot trefoil, red clover, and alsike clover have been bred for their adaptation to harsh winter conditions. In parallel, the selection of cold‐tolerant rhizobial strains could allow earlier symbiotic nitrogen (N) fixation to hasten spring regrowth of legumes. Methods To identify strains forming nodules rapidly and showing high N‐fixing potential, 60 rhizobial strains in association with four temperate legume species were evaluated over 11 weeks under spring soil temperatures for kinetics of nodule formation, nitrogenase activity, and host yield. Results Strains differed in their capacity to form efficient nodules on legume hosts over time. Strains showing higher nitrogenase activity were arctic strain N10 with sainfoin and strain L2 with birdsfoot trefoil. For clovers, nitrogenase activity was similar for control and inoculated plants, likely due to formation of effective nodules in controls by endophyte rhizobia present in seeds. Conclusions Selection based on nodulation kinetics at low temperature, nitrogenase activity, and yield was effective to identify performant rhizobial strains for legume crops. The use of cold‐tolerant strains could help mitigate winter climatic changes