J. R. Caradus

Bio: J. R. Caradus is an academic researcher from AgResearch. The author has contributed to research in topics: Trifolium repens & Cultivar. The author has an hindex of 15, co-authored 48 publications receiving 788 citations.

Past lessons and future prospects: plant breeding for yield and persistence in cool-temperate pastures

Abstract: Pastoral-based animal production systems are under increasing pressure to provide the high quantity and quality of feed needed for optimal ruminant performance. The capacity of farmers to increase forage yield further, solely by increasing fertilizer inputs or through improved pasture management, is limited. Emerging requirements to balance industry production targets against the need to reduce greenhouse gas emissions and N losses pose further challenges. Plant breeding is being asked to deliver results more urgently than at any time previously, and this review attempts to highlight issues that might limit the prospects for future progress by seeking lessons from four past examples: (i) white clover breeding gains and the need to consider the complexity of the grazed grass-clover mixed sward, with its tendency for cycling in plant species composition; (ii) a systems field trial of new and old grass ⁄ clover cultivars, and how the complexity of growth of perennial forage crops, and the dynamic optimality required for sustainable harvesting might limit our ability to breed for ‘yield’ per se; (iii) the manipulation of a physiological trait (low ‘maintenance’ respiration) and the implications of such changes for plant fitness and G · E interactions; and (iv) an hypothesis-driven development of a trait (high-sugar grasses) and the value of ‘proof of concept’ studies, the requirement of scientific understanding of the mechanisms of trait expression, and how one might in future go about assessing breeding achievements. We discuss the general ecological considerations around shifts in the frequency distribution of traits in new populations, whether altered conventionally or by genetic modification, and how selection for a particular trait might inadvertently reduce both fitness and persistence. A major priority for breeding, we propose, might be to revisit previously abandoned traits that affected the physiological performance of forage species, armed now with a capacity to monitor gene expression at the molecular level, and so unravel ⁄ control the G · E interactions that limited their benefits. We also discuss how a ‘loss of yield advantage’ of new cultivars, seen when tested several years after sowing, requires urgent investigation and propose this might be associated with fitness costs of perenniality. Finally, we argue for a careful reconsideration of what are realistic expectations for systems field trials and that focus on forage breeding might be shifted more to ‘proof of concept’ studies, critical experimental design, comparing ‘traits’ rather than ‘cultivars’, and the wider ecological assessment of fitness and function of traits in the plant, community and ecosystem.

Review: World checklist of white clover varieties II

Abstract: The checklist presents a summary of information published since 1985 on the origin, breeding, and characteristics of white clover (Trifolium repens L.) varieties. This complements the previous checklist (Caradus 1986). Origin and breeding history, agronomic potential, disease susceptibility, and the maintenance of a cultivar are listed where known.

Classification of a world collection of white clover cultivars

Abstract: Morphology, flowering, cyanogenesis and leaf markings of 109 white clover (Trifolium repens L.) cultivars, grown as spaced plants and in small plots, were measured. Principal component analysis and cluster analysis were used to compare cultivars. Cultivars were classified into four broad groups. The most important criteria for distinguishing between groups were leaf size, cyanogenesis and combinations of these. Group I, termed small, included small-leaved, prostrate cultivars; Group II, termed intermediate, included the majority of the cultivars which were characterised by medium sized leaves and relatively low cyanogenesis levels; Group III, termed large, included the large-leaved highly cyanogenic cultivars; and Group IV, termed ladino, included large-leaved acyanogenic cultivars.

Cyanogenesis potential and iodine concentration in white clover (Trifolium repens L.) cultivars

Abstract: Hydrogen cyanide (HCN) and iodine (I) concentrations in the herbage were determined for 51 white clover (Trifolium repens L.) cultivars that had been grown under uniform conditions in a glasshouse. HCN contents ranged from 120 to 1110ngHCN/g dry matter (DM). Cultivars that are agronomically successful in New Zealand, and cultivars of New Zealand origin, were mainly highly cyanogenic. There was evidence in ‘Grasslands Kopu’ and ‘Aran’ of a decline in cyanide content in plants raised from first generation seed, compared to plants from Breeders or Basic seed. This decline may result in part from contamination of seed crops by low HCN resident clovers. Iodine concentration in the white clovers ranged from 0.08 to 0.21 μg I/g DM with 77% of values being below 0.12 μg I/g DM. There was no correlation between I and HCN concentrations. It seems there is little potential to improve the I nutrition of stock by selecting for increased I content in white clover. The influence of cyanogenic clover on the meta...

Human biochemical genetics

Abstract: So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Plant and microbial strategies to improve the phosphorus efficiency of agriculture

Abstract: Background Agricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. In fertilised and intensive systems, P-efficient plants are required to minimise inefficient use of P-inputs and to reduce potential for loss of P to the environment.

Morphological plasticity in clonal plants: the foraging concept reconsidered.

Abstract: 1 Studies of morphological plasticity in clonal plants have analysed responses to habitat quality in terms of spacer (stolon or rhizome internode) length and branching intensity. The capacity for these parameters to respond to environmental quality has been interpreted as an expression of foraging behaviour, as it confers the potential to intensify the placement of ramets in the more favourable microhabitats (patches) of a heterogeneous environment. This plasticity in clonal morphology is compared with similar responses of individual shoots and roots to habitat quality that have also been accepted as manifestations of foraging behaviour. 2 The most consistent morphological response shown by clonal species is a higher branching intensity an increased propensity of lateral meristems to grow out and form lateral rhizomes and stolons under conditions of higher resource supply. In contrast, spacer lengths show a variety of responses to light and nutrient availability, and many species exhibit no significant response. Even in stoloniferous species, where stolon internodes tend to shorten under higher photon flux densities, the degree of shortening may often be insufficient to elicit a significant concentration of ramets in favourable habitat patches. 3 Many clonal and nonclonal species have however, been shown to be very efficient in placing leaves and roots in areas of high resource supply within their environment. This is achieved by a high level of morphological plasticity of the shoot and root branches. 4 We therefore suggest that it is the highly plastic changes in the morphology of individual ramets that enable effective exploitation of local concentrations of essential resources once they have been located. The unresponsive spacer lengths of many clonal species may permit a continuous search of habitat space by the plant, rather than a selective placement of ramets. 5 The foraging concept is reformulated in more general terms relating to resourceacquisition strategies, so that it is applicable to both clonal and nonclonal species of plants.