多年生黑麦草收获时间对种子发芽特性及其活力的影响

本文研究了多年生黑麦草(Lolium perenne L.)收获时间对种子千粒重、发芽率、发芽势、出苗率和成苗率的影响.结果表明,多年生黑麦草盛花后不同时间收获的种子,千粒重大的出苗迅速整齐,有明显的出苗高峰,且幼苗生长快,幼苗素质好.千粒重越大,发芽率、出苗率和成苗率越高,三者之间的差异越小;多年生黑麦草种子的发芽率、出苗率与成苗率之间呈显著的正相关关系.     

Prospects for applications of genomic tools in registration testing and seed certification of ryegrass varieties

The ryegrass (Lolium) species, perennial ryegrass (Lolium perenne L.) and Italian ryegrass (Lolium multiflorum Lam.), are the two most important pasture grass species for global temperate regions and are also useful for amenity purposes. Due to an outbreeding reproductive habit, high levels of genetic heterogeneity are present within cultivated varieties. A continual increase in delivery of new cultivars to the marketplace, along with limited capacity to discriminate on the basis of morphological characteristics in a grow‐out test, has caused difficulties for distinctness, uniformity and stability (DUS) testing in the current plant variety protection (PVP) system. A range of genomic tools and resources have been generated for ryegrasses, which provide new opportunities and challenges to the current PVP system. In this review, the currently available genomic tools and resources are described, along with prospects for applications to the PVP system and testing for seed certification and purity accreditation.     

Path and correlation analysis of perennial ryegrass (Lolium perenne L.) seed yield components

Maximum perennial ryegrass seed production potential is substantially greater than harvested yields with harvested yields representing only 20% of calculated potential. Similar to wheat, maize and other agriculturally important crops, seed yield is highly dependent on a number of interacting seed yield components. This research was performed to apply and describe path analysis of perennial ryegrass seed yield components in relation to harvested seed yields. Utilising extensive yield components which included subdividing reproductive inflorescences into five size categories, path analysis was undertaken assuming a unidirectional causal‐admissible relationship between seed yield components and harvested seed yield in six commercial seed production fields. Both spikelets per inflorescence and florets per spikelet had a significant (p < .05) direct effect on the overall seed yield; however, total path correlation coefficients showed that inflorescence size had the largest positive influence on seed yield via its indirect effects on other seed yield components. Our results will allow seed producers, seed production researchers and plant breeders alike to more efficiently increase harvested seed yield.     

Spaced-plant traits related to seed yield in plots of perennial ryegrass (Lolium perenne L.)

Summary Seed yield in perennial ryegrass is low and selection criteria for high seed production are lacking. Indirect selection in spaced plants would be efficient, but spaced-plant traits need to be identified that correlate with seed yield in drilled plots. Spaced plants were studied of nine perennial ryegrass cultivars with a different seed production when grown in plots. Genotypic variation within cultivars for seed yield components and other traits was assessed in four environments in replicated clonal experiments. Extensive genotypic variation for most traits was present within each cultivar. Based on cultivar means of 25 or 50 genotypes, significant differences among cultivars were found for most traits. Cultivar-year interactions were found for most traits, but no significant cultivar-location interactions were generally found. Spaced-plant traits in general showed poor correlation to corresponding traits in drilled plots. Cultivars with contrasting seed yield in plots could not be distinguished on the basis of their spaced-plant traits and therefore no criteria for indirect selection for seed production in drilled plots could be identified in spaced plants.     

Improved seed yield in perennial ryegrass (Lolium perenne L.) from two generations of phenotypic selection

Two generations of recurrent phenotypic selection for seed yield per plant under controlled pollination were carried out to combine improved seed yield with improved forage grass performance in perennial ryegrass (Lolium perenne L.). Selected and unselected varieties (AberDartand AberElan respectively) and control varieties were grown for seed in pots in a glasshouse experiment and in two field plot experiments over 5 harvest years. Seed yield components and seed yield were measured. Significant improvements in seed yield of the selected AberDart over the unselected AberElan were observed both in individual plants grown in the glasshouse and in field plots. Detailed observations of the individual components of seed yield showed that the increased seed yield of AberDart can be attributed to a higher proportion of ovules forming seeds (% seedset), greater seed number per tiller and more reproductive tillers per plant. This improvement in seed yield of AberDart was also observed when it was grown in field plots with AberElan, experimental selection lines and commercial varieties. AberDart produced more seeds per tiller than the other commercial varieties and selection lines studied. The implication of this approach for the breeding of perennial ryegrass varieties that combine good agronomic performance and acceptable seed yields is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytology of seed development related to floret position in perennial ryegrass (Lolium perenne L.)

In seed crops of perennial ryegrass, Lolium perenne L., yields are low and only 15 to 20% of the florets produce a harvestable seed. This study was conducted to determine if seed abortion was a major cause of low floret site utilization (FSU) and therefore of low seed yield in spaced plants. Spikes of four spaced-planted genotypes of perennial ryegrass were harvested and fixed at one-week intervals one to five weeks after the beginning of anthesis. Of a total of 74 spikes, over 13,000 florets were examined with a binocular microscope and 66 whole spikelets were microtome sectioned. The histology of the pro-embryo is presented in relation to the development of the endosperm. In one low yielding, two intermediate and one high yielding genotype, biological FSU was 8, 72, 73 and 63%, respectively. In all genotypes, 90% of the unproductive florets showed ovule degeneration within a few days after flowering. A few florets were sterile or contained a degenerated embryo sac already before flowering and about 5% of the unproductive florets showed seed abortion later than one week after flowering. Within a spikelet, successful fertilization did not decline from the basal to the distal floret. Although in later stages distal florets had slightly less seeds, unproductive florets were found at all floret positions. Biological FSU decreased mainly by ovule degeneration shortly after flowering. In spaced plants, seed abortion was not important to low seed yield.     

Tetraploid Westerwolths ryegrass

Summary Germinated seeds of the annual Westerwolths ryegrass were treated with colchicine-solutions of 0.05 to 0.4% at a temperature of 29°C in order to obtain autotetraploids. The best results were obtained after treatment for 2 hours with 0.1 and 0.2% solutions or 4 hours with 0.05%. By these procedures about 8% of the treated seeds produced mixoploid or tetraploid mature plants. A preliminary progeny test was performed with seed of outstanding C₁-plants.In spaced plants and in drilled rows the dry matter production of these C₂-families was on average equally as high as that of the most productive original diploid variety. The proportion of leaves was higher in both the first and in the second cut, while drought resistance was considerably better. The tetraploids came later into ear, tillering ability was smaller and mildew attack was slightly heavier. In samples from drilled and from space-planted rows seed production per inflorescence was found to be higher in the tetraploids than in the diploids. The seed of the tetraploids was larger.From the data available it is concluded that chromosome doubling offers favourable possibilities for the improvement of Westerwolths ryegrass. Some suggestions for a breeding programme are given.     

Breeding perennial ryegrass for agriculture

Summary Perennial ryegrass has become the most widely sown perennial forage grass in temperate regions due to its combination of high digestibility and tolerance of grazing. The primary objectives in breeding for agricultural use are to improve total and seasonal dry matter production over a range of fertiliser inputs, digestibility, persistency, freezing tolerance and drought or heat tolerance. Adequate seed production and resistance to a wide range of diseases and pests is also necessary. Improvements in productivity and persistency so far have been achieved mainly by hybridisation and recurrent selection using the polycross method and by the use of polyploidy. Further improvements in freezing tolerance, drought and heat tolerance and, for some localities, resistance to pests and snow moulds are required to extend the geographic range of the species. Modern cultivars show little improvement in leaf or stem digestibility but a high magnesium variety is now available. Perennial ryegrass breeding is at an early stage and prospects for further progress appear good.     

Colchicine induced polyploids in ryegrass

Studies on induction, isolation and stabilization of tetraploids in Lolium perenne L. (2n=14) are reported. These investigations revealed that:

1. 1.
   The different varieties of ryegrass responded differentially to colchicine treatment.     
   
   

Stability of esterases and total proteins during seed storage of perennial ryegrass (Lolium perenne L.) and their use for cultivar discrimination

Polymorphisms in electrophoretic patterns obtained by isoelectric focusing (IEF) were examined to evaluate their suitability for cultivar identification in perennial ryegrass (Lolium perenne L.). It was possible to discriminate 64 (94%) of 68 cultivars by combining results from esterase and total protein analysis. Discrimination was based on quantitative differences (relative band intensity) rather than on qualitative differences (presence or absence of bands). Esterase patterns from different recent (fresh to seven years old) seed lots of the same perennial ryegrass cultivars were very stable. Occasionally, minor differences in band intensity were observed between recent and old (up to 30 years old) seed lots of a cultivar. Storage of meal samples up to two years at −20 ^°C had no effect on the total protein patterns. No correlation was found between esterase patterns and ploidy level, cultivar type (pasture or turf), heading date or breeding company. Esterase patterns appeared to be unsuitable markers for the selection of reference cultivars for distinctiveness, uniformity, and stability (DUS) testing, because no correlation was found between cultivars on the basis of esterase banding patterns and morphological characteristics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Germination in vitro of ryegrass pollen grains

Summary Pollen grains of diploid and tetraploid Italian, perennial and hybrid ryegrass (Lolium spp.) germinated on 20% sucrose solution with 10 ppm each of CaCl₂, H₃BO₃ and EDTA. Pollen tubes emerged within 2–3 minutes after sowing and completed full growth within 1 1/2 hours. The tube elongation showed the expected linear growth rate. The tubes of the haploid pollen grains grew faster (3.9 m/minute) than that of the diploid (3.3 m/minute). Diploid pollen grains germinated better on 25% than on 20% sucrose solution. Up to 25% of the diploid pollen produced two tubes.     

Flowering time regulation in perennial ryegrass

Flowering in perennial ryegrass (Lolium perenne L.) is induced by a period of short days and low temperatures (vernalisation), followed by long-day photoperiod conditions. Genetic linkage mapping and association genetics studies have collectively identified 36 quantitative trait loci for flowering time which were distributed across all seven linkage groups of perennial ryegrass. Close to 40 genes (or putative orthologues/homologues of genes known from other species) for flowering time regulation have been identified, including central integrators and genes involved in four pathways (vernalisation, photoperiod, gibberellin, and autonomous). The structure and function of these predicted genes remains to be characterised. Although the photoperiod pathway is conserved in comparison to that of other temperate grasses, the vernalisation pathway appears to differ, due to absence of an orthologue of the cereal VRN2 gene. Although putative components from the autonomous pathway were identified, their target is unclear. No counterparts of genes from two other pathways (ageing and ambient temperature) have so far been reported. Given that c. 200 genes for flowering time regulation have been described in the model plant species Arabidopsis thaliana (L.) Heynh., additional genes may be identified from ryegrasses through comparative genomics approaches in the near future.     

Breeding two base populations of perennial ryegrass

Summary A program designed to develop two base populations of perennial ryegrass was initiated in 1985 in Galicia. Multitrait mass selection by a base index was practised in two genetic resources groups of wild Galician populations. Plants selected were intercrossed and the two resulting base populations (F and G) were evaluated in two locations at the spaced plant level and in plot trials with the aim of estimating the genetic parameters and the possibilities for future breeding. The two populations did not show significant differences from commercial cultivars. Production characters had low heritabilities (0.01–0.32) in both locations. Seasonal yields had medium to high family heritabilities (0.36–0.73). For the economic traits chosen, the expected genetic advances were important in both populations for summer and autumn growth in Mabegondo and spring and summer-autumn dry matter yield (1^st and 3^rd year) in Puebla de Brollón. Expected genetic advance for early spring growth was 0.62 in population F. In the autumn of 1991 equal numbers of plants, selected at each location by combined family and mass selection from each of these populations, were planted in two polycrosses with the aim of improving the genetic basis and adaptation of these populations.     

Aneuploids of perennial ryegrass (Lolium perenne)

Summary Aneuploid plants of perennial ryegrass (Lolium perenne L.) with 2n=15 to 30 chromosomes were obtained by crossing a near-triploid (2n=3x+1=22) with a diploid or on open-pollination with diploids and tetraploids. Aneuploids occurred with a frequency of 83% in near triploid × diploid progeny and 92% on open-pollination with diploid and tetraploid plants. Aneuploid plants with 15 to 18 chromosomes resembled diploids in morphology and those with 19 to 30 chromosomes were akin to tetraploids. Meiotic studies suggested that most aneuploid plants resulted from transmission of aneuploid egg cells (n=8 to 23). Aneuploid plants with 2n=27 to 30 chromosomes in the progeny of 22×14 cross originated from unreduced egg cells. Plants with 19 to 21 chromosomes were recovered only by immature seed culture. Aneuploid plants with 26 to 30 chromosomes and triploids (2n=21) had higher pollen fertility and bigger seeds than plants with 15 to 22 chromosomes.     

Mite attack in inbred plants of perennial ryegrass

The writer describes an attack of the mite Tarsonemus spirifex in inbred plants of perennial ryegrass.Parathion, if need be applied repeatedly, restricts the mite activity considerably.     

不同种衣剂处理对玉米丝黑穗病害的防治效果

玉米丝黑穗病是我国各玉米产区普遍存在的病害,对玉米安全生产构成威胁。通过种子包衣剂处理和田间试验,明确了不同种衣剂对玉米丝黑穗病的防治效果。根穗宝(44%氟唑环菌胺悬浮种衣剂,先正达作物保护有限公司)0.9mL/kg处理种子对玉米丝黑穗病的防治效果最好,达到96.53%,玉米增产16.5%。     

Origin of Westerwolths ryegrass (Lolium multiflorum westerwoldicum)

Summary In the past century, all the grass seed required for the Netherlands was imported.About 1900, however, the seed production of the annual Westerwolths ryegrass (Lolium multiflorum westerwoldicum) was introduced. The local variety was probably obtained by harvesting seed producing plants from Italian ryegrass, sown in spring and sowing again in the next year in spring. In this way a local variety of the seed type originated.     

Breeding perennial ryegrass with better crown rust resistance

Improving rust resistance is one of the main goals in our breeding programme with perennial ryegrasses. We have studied the behaviour of our breeding material over several years in several locations under natural and artificial infection conditions. The narrow sense heritability of crown rust resistance is fairly high (0.46), providing scope for improving resistance, but this optimism is reduced by the negative correlation with yield. The most resistant material yielded 4% less than the most susceptible material. No decline in digestibility is expected when improving the disease resistance. The incidence of crown rust is very variable between years, locations and between spontaneous and artificial infections, creating constraints in selection. Observations for several years and at several locations appear to be the best way to improve rust resistance in perennial ryegrass.