Ian L. Gordon

The Richards function and quantitative analysis of germination and dormancy in meadowfoam ( Limnanthes alba )

While investigating germinability in the new-crop meadowfoam ( Limnanthes alba Benth.), it was desired to gain maximum information despite minimal seed material and prior knowledge. Extended use of the Richards function in a factorial germination experiment proved very powerful. The functions yielded estimates of four correlated coefficients, requiring multivariate analysis of variance (MANOVA) to provide valid F -tests among germination profiles. These germination functions provided more rigorous discrimination among treatments than the univariate final germination level. The functions for the imbibants KNO 3 and GA 4+7 , in darkness at 10/5°C, were best, being characterized by high mean absolute germination rate, relatively short duration, and high final germination (upper asymptote). The results provided insights into possible dormancy mechanisms.

Quantitative genetics of intraspecies hybrids

Quantitative genetics generally is based on the properties of the randomly fertilized (RF) population or inbred derivatives of it. Simple hybrids and hybrid swarms do not conform to this model; and only some properties of hybrid means appear to have been available. In this paper, several genetical properties are derived, including genotype and allele frequencies, genotypic variance, broad-sense heritability, and outbreeding coefficient. The earlier mean is confirmed, and hybrid vigour is examined critically. These results make it possible to evaluate quantitatively both natural selection and forward selection (in plant breeding) from hybrids. An important finding is that hybrids with maximum hybrid vigour do not maximize genetic advance from forward selection, i.e. evolution is unlikely to enhance hybrid vigour. Another finding is that the concepts of additive genetic variance and narrow-sense heritability are inappropriate for hybrids, owing to the genetic disequilibrium inherent from their origin, and to the ephemeral nature of their population structure.

Estimates of genetic variability and heritability for vegetative and reproductive characters of kiwifruit (Actinidia deliciosa)

The results of this study indicated a great deal of genetic variation in a number of characters of horticultural interest in kiwifruit seedling populations, and therefore, a potential to improve kiwifruit by vine selection. High narrow sense heritability was shown for pedicel length(0.62) and flowering duration (0.50) in male vines, and pedicel length (0.67),floral shoot percentage (0.54), leaf length-width ratio (0.64), fruit elongation (0.64) and fruit weight (0.52) in female vines. For these traits, selection of superior seedlings should lead to rapid genetic improvement in these populations.

A comparative study of herbage intake, ingestive behaviour and diet selection, and effects of condensed tannins upon body and wool growth in lambs grazing Yorkshire fog (Holcus lanatus) and annual ryegrass (Lolium multiflorum) dominant swards

SUMMARY An experiment was carried out from August to early November 1994 to examine dierences in diet selection, herbage intake, grazing behaviour and animal performance between weaned lambs rotationally grazing swards of annual ryegrass (Lolium multiflorum)}white clover (Trifolium repens) and Yorkshire fog (Holcus lanatus)}T. repens with or without Lotus corniculatus. There were four replicate groups of six lambs per treatment. The eects of condensed tannins (CT) on lamb production were assessed by twice-daily oral administration of 10 g polyethylene glycol (PEG; molecular weight 4000) to half the lambs on each sward. The Lotus content of all swards was very low, and results are presented here for main sward comparisons meaned over lotus treatments. Overall mean estimates of pre-grazing herbage mass and sward surface height for the annual ryegrass and Yorkshire fog swards respectively, were 5820 v. 4360‡190 kg DM}ha (P ! 0‐001) and 29 v. 21‡0‐ 6c m (P ! 0‐001). The coecient of organic matter digestibility (OMD) of the diet selected and herbage intake were higher on Yorkshire fog than on annual ryegrass (0‐78 v .0 ‐74‡0‐080 g}kg; P ! 0‐05, and 1070 v. 860‡57 g OM per lamb per day, P ! 0‐05 respectively), reflecting the higher content in the diet of grass green leaf (980 v. 930 g}kg‡14 g}kg, P ! 0‐05) and the lower content of dead material (80 v. 110‡15 g}kg, P ! 0‐08). Lambs grazing on Yorkshire fog swards had higher clean wool growth rate (1470 v. 1280‡30 mg}cm per day, P ! 0‐01) and greater fibre diameter (31 v. 29‡0‐2 l, P ! 0‐001), greater liveweight gain (152 v. 108‡5‐ 5g }day, P ! 0‐001), final weight (42 v. 38‡0‐5 kg, P ! 0‐001), carcass weight gain (89 v .6 9‡2‐ 5g }day, P ! 0‐001), carcass weight (19 v. 17‡0‐3 kg, P ! 0‐001) and soft tissue thickness (GR value 11 v .8 ‡0‐5 mm, P ! 0‐01), and lower faecal egg counts (FEC; square root transferred values 9‐2 v .1 1‐0‡0‐4 eggs}g fresh faeces, P ! 0‐01) than lambs grazing annual ryegrass swards. Similar dietary concentrations of condensed tannins (CT) between Yorkshire fog and annual ryegrass swards (4‐2 v .3 ‐ 7D M‡0‐ 2g }kg, P ! 0‐08) increased clean wool growth (1440 v. 1310‡32 mg}cm# per day, P ! 0‐05), fibre diameter (30‐7 v .2 9‐5‡0‐21 l, P ! 0‐01) and liveweight gain (141 v. 120‡4‐3 g per lamb per day, P ! 0‐01), although dierences in carcass weight (17‐9 v .1 8‐2‡0‐3 kg) and FEC transformed values (9‐6 v .1 1‐0‡0‐6 eggs}g fresh faeces) were not significant. The eects of CT on animal performance were greater in Yorkshire fog swards. CT had no significant eects on diet selection, herbage intake and grazing behaviour patterns.

Standard errors of heritabilities based on perennial observations, with application to Yorkshire Fog grass

SummaryThe variance of heritability ratios are considered for cases where data from perennial genotypes are collected serially over time. A random effect model for randomised complete blocks at a single location is examined. Estimation of the variance of estimates of heritability is presented for three types of heritability definition.Estimators are applied to two characters in a Yorkshire Fog grass germplasm collection evaluated for two years at one site. The precision of such heritability estimates is discussed. Estimators for the multiple sites model are available also, from the author.

Genetic advance estimates for red clover ( Trifolium pratense ) grown under spaced plant and sward conditions

A spaced plant experiment and a sward experiment were conducted at INIA La Estanzuela, Uruguay in 1996 with six red clover ( Trifolium pratense L.) populations, to study the efficacy of selecting genotypes for sward performance in a spaced plant nursery. This was examined through: (a) the ranking of the best linear unbiased predictors (BLUP) of populations and (b) the ratio of the correlated genetic advance in swards by selecting under spaced plant conditions to the direct genetic advance of selecting under sward conditions. From the eight characters analysed, only the rankings of BLUPs for leaf size and flowering were significantly the same between populations. The other six characters performed differently according to the level of competition imposed. Post-grazing leafiness and the difference between pre- and post-grazing leafiness (the two most important characters to measure preferential grazing) achieved greater genetic advance when selection was done as spaced plants: while for pre- and post-grazing height genetic advance was greatest by selecting under sward conditions. For other characters, the best conditions to select depended on the selection intensity achievable.

Quantitative genetics of allogamous F2: an origin of randomly fertilized populations

The quantitative genetic properties are derived for the bulk F2 originating from random fertilization (RF) amongst hybrid (F1) individuals. Only its mean appears to have been derived previously, and that definition is confirmed (by another method). New general equations are found also for all genotype frequencies, allele frequencies, inbreeding coefficient, the genotypic, additive-genetic and dominance variances, and broad-sense and narrow-sense heritabilities. The assumption that such an F2 is a classical RF population is shown to be correct. Indeed, the allogamous F2 is a natural origin for the RF population. The relationships are given between precedent RF populations (parents) and subsequent RF populations following hybridization (allogamous F2). The allogamous F2 is generally inbred with respect to its parental F1, the degree depending on the hybrid’s parents’ allele frequencies. At the same time, it is outbred with respect to those original parents, and not inbred at all with respect to the equivalent RF population. The genotypic variance is generally more than in the F1, and likewise for heritabilities. These findings make it possible to evaluate the genetic advance from selection and hybridization. The results depend on the allele frequencies of the original parents and the degree of overdominance, but generally, selection is more advantageous than hybrid vigour.

Statistical modelling of grazing preference of sheep when presented with a range of plant types

A statistical model of the grazing preference of sheep is presented for the evaluation of spaced plants in small plots for plant-breeding purposes. Plants are located randomly to reduce the effect of external factors on diet selection, and to differentiate between discriminatory and random grazing. Consistency of discrimination among grazings and sites (Massey University, New Zealand and INIA La Estanzuela, Uruguay) was tested. The statistical design and subsequent analyses considered all sources of variation to minimize error, and to separate genetic effects from environment effects. Clonal replicates were used to enhance error-control, and hence the precision of heritability estimates, as most characters are inherited quantitatively. Post-grazing leafiness is considered the best character to select and breed for animal preference in a red clover germplasm.

Patterns of variation in flowering and seed set of meadowfoam

Patterns of flowering and seed set were explored by principal component (PC) analysis of counts of fresh flowers, total flowers and seeds at four observation times. This pattern analysis was attempted because of the complicated rhythms of flowering and seed set over an extended period. The approach was considered superior to regressions (over time) for this data because of these pattern complexities, and because these were few time-nodes. Also it avoided the need to find optimum regression functions. Parsimony was achieved with a two-component ordination based on truncation at 70% of the total variance. The results for all characters showed that the first component concentrated on the middle period of flowering/seed set, and de-emphasized the early phase. The second component emphasized the extremities of the flowering/seed set span. The first component accounted for a large proportion of total variance (45.5% to 69.2%), which indicated its importance. The general meaning of the first component was ‘median flowering’, ‘general flower production’ and ‘median-to-late seed set’ for these characters fresh flowers, total flowers and seed set, respectively. The results showed that PC analysis successfully summarized the complex patterns of flowering/seed set and revealed the pattern differences between plants. It was apparent that no particular pattern of general flowering and seed set could be regarded as ‘typical’ in meadowfoam. It was confirmed that the population was diverse, this being typical of segregating plants within a randomly fertilized population.