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.     

Isozyme and quantitative traits polymorphisms in European provenances of perennial ryegrass (Lolium perenne L)

Twenty populations of Lolium perenne originating from a range of habitats in Europe were compared for isoenzyme polymorphisms and agronomically important quantitative traits in order to establish relationships of the levels of diversity with the origin of each population and to assess their suitability to be included in the European core collection of Lolium germplasm. Forty genotypes from each of the twenty populations and each genotype represented by three clonal propagules, were field planted in a fully randomized spaced plant design and fifteen quantitative characters including yield, persistency, reproductive and disease resistence characters were evaluated over a period of two years. Seven putative isozyme loci were assayed to compare the allozyme divergence of populations. The results of the isozyme survey indicate that 71–100% of the loci were polymorphic, 2.3–3.0 alleles/locus and the gene diversity was varying from 0.234–0.410. Of the total allelic diversity 94% remained within populations (H_s) whilst only 6% was distributed among populations (D_st). The differences between populations were determined on the basis of allele frequencies and multivariate analyses of quantitative characters. Populations significantly differed in their allele frequencies at all loci analysed. Random mating was predominant in all populations at most of the loci. The study revealed that the German accession BA 10998 was clearly distinct from the rest both in quantitative characters and allele frequencies. German accession BA 11015 with the lowest gene diversity showed the highest genetic variation for quantitative characters. However, no strict relationship was found between the genetic distance and the geograpical distribution of the populations. Among the quantitative characters, flowering time showed a strong relationship with the type of management practised at the collection site than their place of origin. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seed yield related to crop development and to yield components in nine cultivars of perennial ryegrass (Lolium perenne L.)

Summary We had previously found differences for seed yield among nine perennial ryegrass cultivars which were not associated with variation for seed weight. To detect the physiological basis of these genetic differences for seed yield, growth analyses were carried out. We related crop development and components of seed yield to seed yield during three years on clay and sandy soil. No significant differences occurred among cultivars for accumulation and partitioning of dry matter or the pattern of tiller production. Seed yield of the cultivars was not associated with ear number or total dry matter yield of the seed crop. Seed yield was more correlated with the number of seeds per unit area than with seed weight. The number of seeds as calculated after harvest from seed yield and seed weight was much lower than the number of seeds as estimated prior to harvest from seed yield components. The number of spikelets differed significantly among the cultivars, but the ranking was different from that for seed yield. The physiological basis of the genetic differences for seed yield is not clear. Implications for breeding perennial ryegrass are discussed.     

Comparison of predicted and observed response to selection in two breeding populations of perennial ryegrass

To predict any genetic response to selection, two breeding populations of perennial ryegrass, consisting of half-sib families, were evaluated as spaced plants from 1987 to 1989 for several agronomical traits. In each population, the best plants selected through a multitrait Smith and Hazel's index were planted in a polycross to produce the second generation half-sib families. Both generations were evaluated together from 1991 to 1993 as spaced plants. The difference between generations was the observed genetic response, which was compared to that predicted. Rust tolerance, aftermath heading and persistence were significantly improved in both populations. In trial plots used to assess the yield, no effect of mass selection was noticed. Thus, it is concluded that mass selection failed to increase productivity but produced some improvements in disease tolerance and aftermath heading.     

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.     

Variation in digestibility in nine populations of perennial ryegrass (Lolium perenne) and its genetic basis

Summary Thirty five individuals from each of nine perennial ryegrass populations were sampled from set-stocked and zero-grazed swards and from an old permanent pasture. The swards were 6, 18, 30 months and 11 years old when sampled. The permanent pasture was at least 40 years old.Dry matter digestibility (DMD) and organic matter digestibility (OMD) were determined for green leaf material harvested 4 days after ear emergence. Significant differences were found between the populations, but genotypic differences were found only for OMD. The largest proportion of the total variation was due to differences between blocks. In the zero-grazed populations, DMD and OMD declined significantly with increasing sward age. This was not found for the set-stocked swards. Two sets of pair crosses, from which mid-parent, progeny regressions could be determined, were carried out.The regressions of offspring on mid-parent for set-stocked and zero-grazed swards were used to assess the presence of additive genetic variation and to estimate narrow sense heritability of DMD. The coefficients of correlation, 0.122 and 0.226 respectively, were non-significant, indicating an absence of additive genetic variation.     

The inheritance of host plant effect on latency period of wheat leaf rust in spring wheat. II: Number of segregating factors and evidence for trangressive segregation in F3 and F5 generations

Summary The dry matter yields of four varieties of Lolium perenne with similar flowering dates (Ba 10761, cv. Talbot, cv. S.321 and cv. Tove) were compared during two harvest years in an orthogonal plot trial with two contrasting harvesting frequencies, three levels of applied nitrogen (200, 400 and 600 kg N/ha/yr) and two wear treatments (with and without wear). Frequent harvesting, reduction of applied nitrogen from 600 to 200 kg/ha, and wear reduced mean annual yield by 6.49, 5.13 and 0.65 t/ha respectively. Differences between varieties in mean annual dry matter yields over all treatments were 0.52 t/ha in the first harvest year and 1.49 t/ha in the second harvest year. Over both harvest years, Ba 10761 outyielded Talbot by 15% under frequent harvesting but by only 5% under infrequent harvesting. This variety/harvesting frequency interaction was due to relatively poor growth of Ba 10761 during the reproductive phase of growth, reproductive growth accounting for a larger proportion of total annual yield under infrequent harvesting than under frequent harvesting. Talbot gave relatively low yields at the lowest level of nitrogen. Genotype/harvesting management interactions arising from genetic independence of productivity during vegetative and reproductive growth can be predicted from results of single-management trials but such predictions of genotype/nitrogen level interaction are not yet possible.     

Factorial regression analysis of genotype by environment interaction in ryegrass populations, using both isozyme and climatic data as covariates

A sample of 58 natural ryegrass populations (Lolium perenne L.) from the French and Spanish oceanic coast was evaluated for three seasonal growth traits (i.e. spring, autumn and winter vigour traits) in 5 evaluation sites (three in France and two in Spain). This sample showed a high level of genotype (population) × environment (evaluation sites) interactions for the three agronomic traits. A factor regression analysis, using both isozyme frequencies of populations and climatic factors of evaluation sites as covariates, was carried out on a sub-sample of 30 populations in order to explain these interactions. This method succeeded in explaining most population × location interactions by the product of two covariates. For instance, for spring vigour trait, 72.8% of the interaction term could be explained by the use of two covariates: the PGI2-20 allelic frequency of populations and the minimum temperature of the coldest month of evaluation sites. This study shows the advantage of such a method for plant breeders who need to identify promising ryegrass populations for their breeding objectives. A number of genetic and evolutionary hypotheses are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of water deficit and plant interaction on morphological growth parameters and yield of white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) mixtures

The effects of soil water deficit and interspecific plant interaction were studied on the dry matter (DM) yield of white clover and ryegrass and on the morphogenesis of white clover. Plants were grown either: (1) individually (no interaction); or in a mixture of equal plant numbers with either (2) just shoot interaction, or (3) both shoot+root interaction. Plants were subjected to soil water deficits corresponding to no (0 MPa), moderate (−0.5 MPa) or severe (−1.0 MPa) water deficit. Ryegrass had higher above- and below-ground DM yields than white clover. The above- and below-ground DM yield for ryegrass, and the above-ground DM yield, stolon growth and relative growth rate (RGR), and leaf appearance rate (LAR) for white clover decreased as soil water deficit increased. In shoot+root interaction at no and moderate soil water deficit levels, white clover had the highest proportion of above-ground growth in the leaf form (69%) and had, respectively, 11% and 32% more above-ground DM yield than when grown in just shoot interaction; ryegrass had, respectively, 20% and 25% more above-ground DM yield than ryegrass grown in just shoot interaction. In shoot+root interaction at severe soil water deficit, ryegrass had twice as much above-ground DM yield as white clover (3.50 g per plant versus 1.59 g per plant, respectively) and white clover had 60% less above-ground DM yield than when grown in just shoot interaction. In a soil column of restricted depth (30 cm) at no and moderate soil water deficit levels, remarkable increases in shoot biomass yield were observed for both white clover and ryegrass grown in shoot+root interaction. The increased shoot biomass yield of ryegrass can be attributed to benefits from white clover's N fixing ability, whereas the causes for increased white clover biomass yield need to be studied further. However, at severe soil water deficit, ryegrass had a competitive advantage over white clover when grown in shoot+root interaction. This was due to the larger root system of ryegrass and its ability to control transpirational losses more efficiently, thus prolonging its growth period compared with white clover.     

Assessment of drought resistance in 20 accessions of Triticum aestivum and related species I. Total dry matter and grain yield stability

Summary Interspecific hybridisation has been suggested to improve the resistance of crops to biotic and abiotic stresses. To identify sources of resistance to drought which could be used in a breeding programme, an assessment of a large number of wheat species was carried out. The evaluation was based on the estimation of a drought susceptibility index and stability in total dry matter and grain yields of various species grown across a range of soil moisture conditions. On the basis of stability in total dry matter yield, T. aestivum was relatively more drought resistant. However, on the basis of grain yield stability, T. sphaerococcum, T. vavilovii and T. aestivum cv. C 306 exhibited better yield stability and drought resistance than the other species tested. It is suggested that the above species could be utilized as parental material in a hybridisation programme aimed at improving the drought resistance of wheat.     

Influence of Rhizosphere Ionic Strength on Mineral Composition, Dry Matter Yield and Nutritive Value of Forage Chicory

Animal manure and urine deposition can cause localized patches of high ionic strength (IS) soil in pastures, influencing plant production, nutritive value and sward composition. Chicory (Cichorium intybus L.) appears to thrive in high‐nutrient input situations, but no information is available on chicory response to increasing IS. In a greenhouse experiment, we evaluated the effect of rhizosphere ionic strength (0.9, 4.0, 8.0 and 12.0 dS m^?1) on productivity and nutritive value of chicory. Dry matter production decreased linearly as IS increased. Shoot concentrations for Ca, Na and Cl increased as IS increased. All mineral concentrations, except Cu, were substantially higher than or equal to the highest concentrations reported for forages. At all IS, nitrate‐N and K exceeded maximum recommendation for ruminant diets. The sodium level could be high enough to reduce dry matter intake at the highest IS level. Crude protein and energy estimates indicate chicory would support production levels equivalent to those of other high‐quality forages. In vitro organic matter disappearance increased as IS increased. Chicory as a component of a forage mixture could help stabilize forage yield in pastures and also shows promise for use as a nutrient mop in feedlot areas, where excess soil nutrients are a problem.     

Effect of generation of inbreeding, cutting treatment and year on agronomic traits in berseem populations

The selfing effect in berseem clover (Trifolium alexandrinum L.) was analysed by comparing generation means for nine agronomic traits (dry matter yield, plant height, leaf-stem ratio, harvest index, seed yield and its components). Parents, S₁, S₂, S₃, and S₄ generations of six populations of different geographical origin (3 from Egypt and 3 from southern Italy) were investigated to estimate the relative changes with increasing homozygosity and to prove the effectiveness of selfing in a breeding program. The experiment was carried out at Foggia (Italy) under field conditions for two years (1995 and 1996) adopting two cutting treatments: at fifth internode elongation (A) and flowering (B). The mean values decreased with the advancement in selfing generations in both years and cutting treatments for the most of the traits. Treatment B yielded more biomass and seed yield than treatment A in both years. Cutting treatments did not affect the adaptability of the selfed progenies of populations with different geographical origin, in fact, the Italian populations were more productive for dry matter under both cutting treatments (856.6 g m^-2 on average), whereas Egyptian populations proved superior for seed yield particularly under treatment B (62.5 g m^-2 on average). Inbreeding depression was greater for forage dry matter and seed yield (−62and −79% on average, respectively), whereas the plant height and 1000-seed weight were the least susceptible traits (−26 and −19% on average, respectively). Estimates of the parameters of the stability analysis showed that not all populations responded to inbreeding level and environment variations to the same degree. Differences were evident under treatment A, only. Development of self-fertile, relatively vigorous inbred lines of berseem clover with different degrees of homozygosity appears possible. Genotypes tolerant to selfing from Egyptian and Italian groups have been obtained by inbreeding and selection for self-fertility; they could be utilised as basis for producing new breeding activities. This revised version was published online in July 2006 with corrections to the Cover Date.