Genetic variation and heritability of forage yield in Mediterranean tall fescue

The genetic control of tall fescue forage yield has been poorly investigated. Full‐sib families from diallel crosses of Mediterranean germplasm were evaluated for forage yield over 34 months in a Mediterranean environment with severe drought stress (diallel 1, with 20 parents) and over 16 months under irrigation in a heated greenhouse simulating the Mediterranean temperature pattern (diallel 2, with 15 parents). Genetic parameters were estimated for fresh biomass in diallel 1 and dry‐matter yield in diallel 2. Additive genetic variance was always larger than non‐additive (dominance) variance. Narrow‐sense heritability was fairly high (h² = 0.61) in diallel 1 and moderate (h² = 0.45) in diallel 2. Predicted yield gains from one selection cycle were larger in the former diallel (23.9%) than in the latter (10.5%), suggesting that gains can be enhanced by selection under severe drought stress and over a time span sufficient to allow the variation in persistence to fully emerge. General combining ability effects of eight parents that were common to both diallel crosses were highly correlated (r = 0.94) across the contrasting evaluation environments. The extent and consistency of additive genetic effects across environments suggest that rapid improvement of forage yield is possible.     

Cytogenetic and isozymic characterization of anther-panicle culture derived tall fescue aneuploids

Summary Chromosome associations of 44 tall fescue (Festuca arundinacea Schreb., 2n=6x=42) plants derived from anther-panicle culture of Kentucky 31 were evaluated to determine if new genetic stocks could be identified. Seventeen of the plants were euploids (21 II), two were monosomic (20II+1I), 22 were double monosomic (19II+2I) and three were triple monosomic (18II+3I). Zymograms were obtained for phosphoglucoisomerase (PGI), glutamate oxaloacetate transaminase (GOT), acid phosphatase (ACPH), malate dehydrogenase (MDH) and 6-phosphogluconate dehydrogenase (6-PGD). The zymograms were identical for GOT, ACPH, and 6-PGD but different patterns were found for MDH and PGI in some of the double monosomics and euploids from a different piece of callus than the majority of the plants.Contribution of the USDA-ARS in cooperation with the Kentucky Agricultural Experiment Station. Scientific Journal Series No. 86-3-61.     

Genetic variation, heritability and genetic correlations for forage quality and yield traits of Mediterranean tall fescue germplasm

Higher ruminant intake potential and in vivo digestibility as indicated by lower neutral and acid detergent fibre (NDF and ADF), respectively, and higher crude protein (CP), may be valuable targets in tall fescue breeding. Some 105 full‐sib families from a diallel cross of Mediterranean parent germplasm were grown in a heated greenhouse simulating the temperature pattern of a Mediterranean environment, to estimate genetic parameters for NDF, ADF, CP and dry matter (DM) yield in one autumn and one winter harvest. Family x harvest interaction was large for NDF and ADF, moderate for CP and absent for DM yield. Additive genetic variance was mostly larger than specific genetic variance, and tended to be small for quality traits and large for DM yield. Narrow‐sense heritability was low for CP and ADF in autumn and moderate to fairly high in the remaining cases. Predicted gains per selection cycle never exceeded 5% for quality traits while being greater than 10% for DM yield. An inverse genetic correlation between DM yield and any quality trait emerged in the presence of sizeable genetic variation.     

Heritabilities of nutritive quality factors and interrelationships with yield in selected progenies of tall fescue

Nine polycross (PX) and nine different self (S₁) progenies were randomly chosen from 43 selected tall fescue genotypes and evaluated for in vitro digestible organic matter (IVDOM), crude protein, neutral detergent fibre, acid detergent fibre and acid detergent lignin of whole plants, leaf blades and stems (stem plus leaf sheath) at each of four harvest dates in 1991 and 1992. Significant variation for all whole‐plant and leaf quality traits occurred among the PX progenies at the May harvest. Variation among S₁ progenies was significant for almost all of the stem traits. Genetic variance components for both progeny groups were significant for almost all of the traits, confirming the presence of additive genetic variation. Heritability estimates on a progeny‐mean basis ranged from medium to high for almost all the traits of the whole‐plant and the leaf and stem fractions. The results suggest that spring would be the time at which direct selection for high IVDOM or low fibre content would be successful and that selection for leaf or stem quality traits improves whole‐plant quality. Selection for quality traits in the summer or in the autumn would be difficult since no significant genetic variability was found.     

Comparison of the isozyme variation in tall fescue parents and their somaclones

Summary This study was conducted using the isozymes ACP-1, ADH-1, GOT-2, GOT-3, MDH, 6-PGD-1 and PGI-2 to: a) compare isozyme banding patterns of tall fescue somaclones with parents and b) correlate tissue culture-induced chromosome abnormalities with variant banding patterns. The 174 somaclones were grouped into seven categories based on their meiotic analyses and time of regeneration from culture. Differences in isozyme frequency between categories compared by chi-square tests were greatest for MDH, 6-PGD-1 and PGI-2, and least for ACP-1. The most significant differences in frequency were found between somaclones and parents. In comparisons of somaclone categories, the most different isozyme distributions were between the early vs. late regenerated somaclones. No significant differences in isozyme frequencies were found between all 42-chromosome somaclones vs. aneuploid somaclones and the three somaclone groups (42-normal, 42-abnormal, aneuploid) compared to each other. This study suggests that culture-induced isozyme variation alters the distribution of the isozyme phenotypes, but is not directly correlated with chromosome abnormalities.     

The effect of seed weight and coleoptile tiller development on seedling vigour in tall fescue,Festuca arundinaceaSchreb.

Summary Two characters, previously shown to influence the rate of seedling growth in tall fescue, were studied in detail in three distinct populations as part of a programme to improve seedling vigour in the species. The effect of seed weight was found to be confined to the very early stages of growth and was apparent in seedling dry matter yield but not in tiller number. The development of a tiller in the axil of the coleoptile, which varied significantly between populations, had a far greater and more permanent effect both in terms of dry matter yield and tiller number. The increase in tiller number attributable to the coleoptile tiller and its derivatives increased geometrically in step with the total tiller number, so that the intitial difference of 28% in the first harvest remained practically unchanged in the subsequent three harvests. Similarly, the percentage difference in dry matter yield between plants with and without a coleoptile tiller remained more or less constant at about 22% from the second harvest onwards.It is concluded that the development of a coleoptile tiller may prove to be a useful selection criterion in the breeding of this species.     

Genetic analysis of in vitro plant tissue culture responses and regeneration capacities

Summary The in vitro development of a whole plant from a single cell (eg microspore or somatic cells) is a characteristic feature of plants. The amenability of a plant to in vitro culture is influenced by the genotype, which is thus of major importance in the plant tissue culture response. The differences observed between different cultivars during in vitro tissue culture with respect to embryogenesis and regeneration result from quantitative or qualitative genetic differences. We describe results obtained from quantitative genetic studies, from Mendelian genetic analysis and from gene mapping. It is less easy to study the influence of cytoplasmic genomes. Moreover, it is necessary to discriminate between maternal effects and cytoplasmic inheritance. A conclusion from this review is that the choice of parental strains for a breeding program should be realized on agronomic criteria rather than on compatibility with the tissue culture technique used. Fortunately, it is relatively easy to incorporate short-term tissue culture capacity into agronomically valuable genotypes. This is of major interest since tissue culture remains necessary for most aspects of crop plants biotechnology. Very little is known about the molecular events that trigger in vitro embryogenesis and regeneration. It is clear that genes involved in the tissue culture response are not specialised tissue culture genes.     

Development of high-gossypol cotton plants with low-gossypol seeds using trispecies bridge crosses and in vitro culture of seed embryos

The objective of this work is to develop an upland cotton, Gossypium hirsutum L. [2n = 4x =52, 2(AD)h], having a reduced level of gossypol in the seeds for food and feed uses, and a high level of gossypol in the remaining organs to limit pest incidence. Using G. sturtianum Willis (2n = 2x = 26, 2C1) as donor and G. thurberi Torado (2n = 2x = 26, 2D1) or G. raimondii Ulbrich (2n = 2x = 26, 2D5) as bridge species, two trispecies hybrids G. thurberi– G. sturtianum– G. hirsutum and G. hirsutum– G. raimondii– G. sturtianum were synthesized. Both trispecies hybrids were male sterile. Recurrent backcrossing to G. hirsutum as pollinator and selfing of the second backcross (BC) progenies resulted in seeds which were rescued by in vitro culture. In total, 1208 flowers of the trispecies hybrids and their BC progenies yielded 192 seed embryos from which 62 plants were obtained. Cytogenetic analyses indicated a relatively high frequency of chromosome pairing and chiasmata. The gland levels in backcross seeds ranged from glandless seeds to normally glanded seeds. All vegetative parts of those hybrids were glanded, but a wide range of variability for gland density was observed on leaf, stem, bract and calyx. Plants derived from seeds having a reduced level of gossypol constitute very interesting germplasm to develop a cultivated glanded cotton with low-gossypol seeds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nutrient culture medium components affecting plant recovery from immature embryos of three Glycine genotypes and an interspecific hybrid grown in vitro

Summary Immature embryos of Glycine max (L.) Merr. cv. Bay, G. tabacina (Labill.) Benth. and G. tomentella Hayata were cultured on 72 media combinations to identify a nutrient medium which would allow a greater percentage of interspecific plants to be recovered from cultured embryos of G. max × various perennial Glycine species. The highest mean plant recovery rate of 79% was from a medium containing B5 nutrient salts as reported by Gamborg et al. (1968), vitamin components according to Williams (1978) and 30 g/l sucrose. This is as compared with 25% from a medium used previously. In an additional test, 67% of hybrid embryos of G. max × G. tomentella were recovered from the same medium, from which G. tomentella was most effectively recovered in all testing.Contribution No. 89-276-J of the Kansas Agric. Exp. Stn., Manhattan.