J. R. Caradus

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.

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...

Genecology of white clover (Trifolium repens L.) from wet and dry hill country pastures.

Abstract Populations of white clover were collected from north-facing and south-facing aspects of dry and wet hill country farms and compared in a uniform, spaced plant environment. Root systems were compared in another study where plants were grown in field tiles. These populations were also compared with the cultivars Grasslands Huia, Grasslands Tahora, and Whatawhata Early Flowering in both studies. The dry hill country populations as a group were more cyanogenic, larger-leaved, taller, and had larger tap-root diameters and different leaf mark characteristics, than the wet hill country populations. Tahora and Whatawhata Early Flowering both resembled the “dry” populations more than the “wet” populations, except that Whatawhata Early Flowering had a higher percentage of plants flowering early than either collected population group. Huia was larger-leaved, more erect, and had thicker taproots than all other lines in the study. Within dry farms, populations from north-facing aspects had a higher percentag...

Response of white clover cultivars to fertiliser nitrogen

Abstract Fifteen white clover (Trifolium repens L.) cultivars were grown with perennial ryegrass to determine their tolerance to fertiliser nitrogen (N) application. There were four N treatments (0, 25, 100, and 225 kg N/ha per year) and the trial was mob-stocked by sheep 8 times a year for 3 years. N applied at 25 kg N/ha per year had no significant effect on either clover or total sward yield. However, 225 kg N/ha per year depressed clover yield by 38% and clover proportion in the sward by 45% but increased total sward yield by 27%. There was no significant cultivar × N interaction for clover yield or proportion of clover in the sward. However, there was a significant difference among cultivars for N tolerance ratio in spring, calculated as N225 divided by the mean of N0 and N25 of clover yield. Cultivars with the highest N tolerance ratio were Huia, Kopu, Bianca, and Crau; those with the lowest were Menna, Aran, Katrina, and N-line. Spring N tolerance ratio was not correlated with spring yield or any o...

Adaptation to low fertility hill country in New Zealand of white clover lines selected for differences in response to phosphorus.

Abstract White clover breeding lines developed as high and low P‐responsive, in glasshouse selection trials, were compared, over three years, with 17 other breeding lines and cultivars for growth in four soil‐fertility treatments under two defoliation treatments on a hill‐country farm. Differences between P‐response groups were transitory and biologically insignificant. Selection for differences in response to P in a controlled environment was not successful in identifying white clover germ‐plasm adapted to low P hill‐country soils. White clover breeding lines and cultivars that achieved high growth over the 3‐year duration of the trial had New Zealand parentage and were all medium to small leaf types.

Breeding and description of ‘Grasslands Sustain’, a medium‐large‐leaved white clover (Trifolium repens L.) cultivar

Abstract ‘Grasslands Sustain’ white clover was bred to break the negative relationship between yield potential and persistence, by combining medium—large leaf size with high stolon growing point density. It is expected to grow and persist well under a range of stock classes and management systems. Winter growth is similar to that of ‘Grasslands Kopu’ but autumn, spring, and summer growth is improved. Depending on the trial, 50–60% of genotypes were cyanogenic. Peak flowering occurred 2 weeks after the longest day irrespective of closing date.

Frost tolerance of Trifolium species

Abstract Thirteen Trifolium species were artificially frosted at ‐4, ‐8, ‐12, and ‐16°C in controlled environment rooms. This was carried out in such a way that soil freezing was avoided and only shoots were frosted. Frost tolerance was primarily assessed as the percentage of dead to total leaf dry weight present 1 week after frosting. Trifolium arvense, T. dubium, and T. hybridum were the most frost‐tolerant, whereas T. ambiguum, T. subterraneum, T. glomeratum, T. vesiculosum, and T. cernuum were the most frost‐sensitive, based on the temperature required to kill 50% of leaves. Trifolium ambiguum may have been particularly sensitive to frosting because of its poor vigour (size).

Morphological variation among white clover (Trifolium repens L.) populations collected from a range of moist hill country habitats

Abstract Genotypes of white clover were collected from a range of hill country habitats defined by aspect, slope, fertiliser input, management, and stock class, and grown as spaced plants in a uniform environment. Few morphological differences were found among genotypes that could be related to habitat of origin. However, genotypes from rotationally grazed cattle pastures were taller than those from rotationally grazed sheep pastures. Effects of fertiliser input level on plant height and on leaf/flower height ratio, and effect of slope on leaf and flower heights and growth, were inconsistent. Hill country genotypes had characters intermediate between ‘Grasslands Tahora’ and ‘Grasslands Huia’. Genotypes with (a) high and low proportions of nodes branching, (b) long and short internodes, and (c) large and small leaf sizes were selected and crossed in isolation. Comparison of progeny with parents showed that differences in nodal branching frequency and internode length observed in the field were environmenta...

Effect of different aluminium and phosphorus levels on aluminium-tolerant and aluminium-susceptible genotypes of white clover (Trifolium repens L.)

Abstract Two genotypes of white clover (Trifolium repens L.) selected for either tolerance or sensitivity to soil aluminium (Al), were grown in an acid soil with factorial combinations of four Al and four phosphorus (P) levels. Plants of the Al-tolerant genotype were larger and leafier than the susceptible plants despite containing more Al. Shoot Al concentrations were lower in the tolerant plants. Al x P interactive effects on growth were normal, with P ameliorating the effects of increased Al. Shoot and root magnesium (Mg) levels were much higher in the tolerant plants suggesting that in white clover, as for some other species, Mg plays a key role in Al tolerance. Increasing Al application rates from 20 to 50 (μg Al/g soil stimulated several of the plant growth parameters that were recorded but the mechanism was not apparent. The Al-tolerant genotype had a lower shoot P concentration and shoot P content and was more responsive to applied P than the susceptible genotype. These characteristics which are a...

Growth of United States versus New Zealand white clover cultivars in diverse grasses in Mississippi, USA

Abstract The use of plant material outside the country of development is common, but whether such material is superior to existing types of the same species is questionable. Seven United States and eight New Zealand white clover (Trifolium repens) cultivars, germplasms, or breeding populations were evaluated for plant spread and dry matter yield for two years at Mississippi State, Mississippi, USA, when grown in monoculture or with grasses having differing seasonal growth patterns, viz tall fescue (Festuca arundinacea) and bermudagrass (Cynodon dactylori). Plant material originating in the United States had 49–53% greater plant spread and 79–222% greater clover dry matter yield in monoculture or in association with either grass than the New Zealand material. Osceola, SRVR, and Brown Loam Syn#2 white clover had greater plant spread than all New Zealand material at 9 of 11 sampling dates. White clover spread and yield under monoculture showed a closer correlation with growth in association with common bermu...