Suleiman S. Bughrara

Inheritance of glyphosate resistance in rigid ryegrass (Lolium rigidum) from California

Abstract Glyphosate resistance was found in a rigid ryegrass population in northern California. A sample of the resistant plants were collected and grown under greenhouse conditions. The objective of this study was to evaluate glyphosate resistance in the progeny of the collected plants by recurrent selection, obtain the homozygous resistant and sensitive lines to establish dose-response curves, and to determine the inheritance of glyphosate resistance in rigid ryegrass. Diverse levels of resistance were observed in the first generation with survival of 89, 59, 45, and 9% from glyphosate at 1x, 2x, 4x, and 8x respectively, where x = 1.12 kg ha−1 isopropylamine salt of glyphosate. Clones of plants that died from 1x were allowed to produce seed and were further subjected to recurrent selection to generate the most sensitive plants (S lines), which died from 0.125x glyphosate. The most resistant plants (R lines) were generated from the survivors receiving 8x glyphosate. The ratio between I50 rates for the glyphosate resistant and the glyphosate sensitive plants was > 100-fold. The R and S lines were crossed reciprocally and F1 progeny of both (R × S) and (S × R) showed intermediate resistance. These survived up to 2x glyphosate. The F2 progeny were generated by intercrossing of F1 plants. The ratio of sensitive, intermediate, and resistant plants in the F2 population before the treatment of glyphosate at 0.125x followed by 8x was 1 : 16, 14 : 16, and 1 : 16 respectively, which corresponded to the Mendelian segregation ratio of two genes. The results indicated that the inheritance of glyphosate resistance in rigid ryegrass from California appeared to be nuclear, incompletely dominant, multigenic, and pollen-transmitted with no indication of maternal inheritance. Nomenclature: Glyphosate; rigid ryegrass, Lolium rigidum Gaud. LOLRI.

Monitoring of gene expression profiles and identification of candidate genes involved in drought responses in Festuca mairei.

To understand the molecular genetic basis underlying drought tolerance in grasses, the cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique was applied for identification of genes responding to drought stress in a xerophytic adapted plant, Festuca mairei. A total of 11,346 transcript derived fragments (TDFs) were detected, and 464 (4.1%) TDFs were identified as differentially expressed fragments (DEFs) during the drought treatment of the plant. The expression patterns of these DEFs included up-regulated (∼30%), down-regulated (∼54.3%), and the remainder (∼16.7%) showing transient changes. The differential expression patterns of 171 DEFs were further confirmed by macroarray hybridization analysis. Sequences had been obtained for 163 DEFs, and 62 sequences had no significant hits to sequences currently in public databases. Predicted functions of remaining 101 sequences were subdivided into 17 categories. Down-regulated genes were highly represented by metabolism and cellular biogenesis. Up-regulated DEFs were enriched in genes involved in transcription, defense, cell cycle and DNA processing. Analysis of the 163 DEFs provides a first glimpse into the transcripts of F. mairei during drought stress treatment. The combination of data from studies on genetic model plants and on diverse plant species will enhance understanding of the drought tolerance mechanisms in plants.

Evaluation of drought tolerance for Atlas fescue, perennial ryegrass, and their progeny

Perennial ryegrass (Lolium perenne L.) has good turf quality but low drought tolerance. Atlas fescue (Festuca mairei) has exceptional drought tolerance but poor turf quality. Intergeneric hybridization between the two grasses would have the potential to develop a plant combining the important turf traits of perennial ryegrass and the improved drought tolerance of Atlas fescue. The objectives of this study were to (1) investigate drought tolerance of progeny from the crossing of perennial ryegrass with Atlas fescue and (2) identify characteristics for screening under drought stress. A total of 19 genotypes were exposed to a 14-week drought treatment. Soil water content, leaf elongation, leaf water content, and leaf water potential were measured weekly, and root length and biomass were recorded after the treatment. Based on the weekly measurements of leaf elongation, leaf water content, and leaf water potential to drought stress, the plants were classified into four groups. Leaf elongation was a sensitive and helpful parameter for screening drought tolerant plants. Three groups were identified with high, moderate, and low drought tolerance based on a decrease in leaf elongation in response to declining soil water content. Some progeny in a high drought tolerant group rated better than the Atlas fescue parent. The results suggested that an improved drought tolerant perennial ryegrass could be developed through intergeneric hybridization by inheriting drought tolerance of Atlas fescue.

Cytology and pollen grain fertility in creeping bentgrass interspecific and intergeneric hybrids

Creeping bentgrass (Agrostisstolonifera L. or A. palustris Huds.) is a highly outcrossing allotetraploid species. It can form hybrids with a number of other Agrostis species and Polypogon genus. However, cytology and pollen grain fertility of the creeping bentgrass interspecific and intergeneric hybrids are not well known. In this research, chromosome pairing behaviors during meiosis I in F1 and pollen viability of F1 hybrids, as well as seed set rate and seed germination rate of backcrosses were studied in hybrids between creeping bentgrass, and other bentgrass species and three species of Polypogon genus. Abnormal chromosome pairing, laggard chromosomes, and premature segregation in F1 hybrids were found. Pollen viability ranged from 1.6 to 48.5% amongst F1 hybrids, significantly lower than that of the parents (85.5–94.1%). Some hybrids produced pollens of different sizes within the same anther. Seed set following backcrosses using F1 hybrids as the male parent and creeping bentgrass as the recurrent parent was significantly lower than their parents. The study of chromosome paring behaviors and progeny fecundity are important in utilizing the alien genes to improve bio-stress and abio-stress resistance, and in assessing the potential transgene risks of creeping bentgrass.

Parental genome composition and genetic classifications of derivatives from intergeneric crosses of Festuca mairei and Lolium perenne

Intergeneric hybridization between Festuca and Lolium has been a long-term goal of forage and turfgrass breeders to generate improved cultivars by combining stress tolerance of Festuca and rapid establishment of Lolium. However, wide-distance hybridizations usually result in the wild genome being eliminated from the hybrid due to incomplete chromosome pairing and crossovers. In this study, random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to detect the parental genome composition of F1 hybrids and backcross, generated from crosses between Festuca mairei St. Yves (Fm) and Lolium perenne L. (Lp). Each of the hybrids exhibited integration of Fm and Lp genomes with varying levels of Fm/Lp genome ratios. However, cluster and principle component analyses of the progeny consistently revealed four groups depending on the amount of genome introgression from both parents. The parental genome composition and classifications of intergeneric progeny would be useful for breeding material selection.