J. R. Crush

Effect of irrigation with lake water containing microcystins on microcystin content and growth of ryegrass, clover, rape, and lettuce.

The effect of irrigation with lake water containing a variety of microcystins on accumulation of toxins, or toxin metabolites, and plant growth in ryegrass, clover, rape, and lettuce, was investigated in a glasshouse experiment. The plants were grown in sand culture and received either three or six applications of lake water, which was applied either directly to the sand surface or to the plant shoots. As determined by LC–MS, each plant received 170 μg of a mixture of 10 different microcystins per application. Microcystins in plant samples were extracted with 70% methanol and analyzed by Adda‐specific ELISA. For the shoot application treatment, microcystins were not present at measurable levels in shoots of ryegrass or rape, but were present in lettuce [0.79 mg/kg dry weight (DW)] and clover (0.20 mg/kg DW). Total microcystin concentration in roots did not vary greatly depending on whether treatment water was applied directly to the sand, or reached the roots via run‐off from the shoots. Microcystins in roots were highest in clover (1.45 mg/kg DW), intermediate in lettuce (0.68 mg/kg DW) and low in ryegrass (0.20 mg/kg DW), and rape (0.12 mg/kg DW). There was no evidence for root‐to‐shoot translocation of microcystins. Three applications of microcystins reduced shoot DW of ryegrass, rape and lettuce, and increased root DW of ryegrass and lettuce. Clover DW was not changed by treatment with microcystins. The results show that irrigation with water containing microcystins has the potential to move microcystins into farm animal and human food chains at concentrations that can exceed recommended tolerable limits.

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...

Growth and milksolids production in pastures of older and more recent ryegrass and white clover cultivars under dairy grazing

Abstract Dairy milksolids (MS) production rates were measured in pastures consisting of different age‐classes of perennial ryegrass and white clover cultivars. There were four pasture treatments consisting of factorial combinations of ryegrasses representative of those available to farmers in the 1980s and 1998, and clovers available in the 1960s and 1998. The pasture treatments were grown in self‐contained, replicated 4 ha farmlets and rotationally grazed at a stocking rate of three Friesian cows per hectare. The 1998 ryegrass and clover cultivars were more competitive than the older cultivar types, and tended to form a higher proportion of the sward at the end of the trial. This did not translate into significant cultivar age group effects on short‐term pasture growth rates or annual pasture dry matter (DM) yields which averaged 17.2 ± 0.9 t DM/ha over years 2–4 of the trial. The 1980s ryegrasses had faster growth rates in spring than the 1998 ryegrasses. Consequently, more silage was made on average on farmlets sown with the 1980s ryegrasses (230 kg silage DM/cow per yr), than with the 1998 ryegrasses (150 kg silage DM/cow per yr), although the yield increase was statistically significant only in the 2001–02 year. Herbage chemical profiles and feeding quality were similar in all treatments. Nitrogen fixed per unit clover grown did not vary with clover types. There was a very strong linear correlation between annual clover yields and annual N fixation. Annual N fixation totals varied substantially from the mean value of 157 kg N/ha, as clover annual DM yields changed. Total annual milksolids (MS) production ranged from 811 kgMS/haperyrto 1250kgMS/ha per yr, with no consistent pasture treatment effects. There was no significant effect of ryegrass type on milk production per cow or milksolids production per hectare in any year. Clover type had an effect on production only in 2001/02, with higher milk production per cow and total milksolids production per hectare on the 1998 clover treatments, due to the higher clover content of pastures in this treatment. We suggest that annual pasture production from these well‐managed ryegrass‐white clover pastures is very close to the practical limit achievable in this region. Any major increases in herbage yield will require novel plant germplasm.

Effect of different Neotyphodium endophytes on root distribution of a perennial ryegrass (Lolium perenne L.) cultivar

Abstract Plants of perennial ryegrass either endophyte‐free or infected with Neotyphodium lolii endophyte strain AR1, AR37 or wild‐type, were grown in 105‐mm‐diameter tubes of sand in a glasshouse. Root angles were determined by counting root intercepts on semi‐circular stainless steel mesh transects running from near the edge of the tube at the sand surface to directly under the plant. The average number of root intercepts did not vary between endophyte strains or between their average and the endophyte‐free treatment. However, the linear decline of root intercept frequency with depth varied according to the endophyte status of the ryegrass. Endophyte‐infected plants had fewer roots close to the surface. This effect of shoot endophytes on root distribution patterns in ryegrass may improve the plants tolerance of moisture stress.

Nutrient responses and macronutrient composition of some Trifolium repens×Trifolium uniflorum interspecific hybrids

Abstract. Interspecific hybridisation is being utilised in white clover (Trifolium repens L.) breeding programs to overcome factors currently restricting productivity and persistence. Valuable new traits that may be introduced from the wild relative T. uniflorum include root characteristics and other adaptations to its natural, Mediterranean habitat. This study examined the effect of hybridisation on growth and macronutrient composition of white clover compared with T. uniflorum and T. repens × T. uniflorum backcross 1 (BC1) hybrids in two glasshouse sand culture experiments. Shoot and root dry weights of BC1 hybrids were greater than of white clover in low-concentration nutrient treatments but not in a more concentrated treatment. Decreases in dry weight with decreasing nutrient treatment strength were also smaller for some BC1 hybrids compared with white clover and other hybrid families. Most foliar macronutrient levels were adequate for white clover growth, but mean shoot or leaf phosphorus (P) concentrations were below published critical levels. Higher dry matter production under these low internal P concentrations suggests that some T. repens × T. uniflorum BC1 hybrids may be more tolerant of lower soil P levels than white clover. Such adaptations are likely to have been inherited from T. uniflorum. However, transgressive segregation may also be occurring, as T. uniflorum was larger than white clover in some, but not all, cases of low nutrient supply.

Adventitious root mass distribution in progeny of four perennial ryegrass (Lolium perenne L.) groups selected for root shape

Abstract The effects of one cycle of selection for adventitious root system shape (i.e. percentage of total root mass in successive depth increments) were investigated in progeny of four perennial ryegrass pools with contrasting rooting patterns: (1) low surface (0–10 cm) root mass and roots to 1 m; (2) high surface root mass and roots to 1 m; (3) high root mass 10–20 cm and roots to 1 m; (4) high surface root mass, shallow rooting. Ten half-sib families were selected from each of the root type progenies, and five seeds from each family were sown and raised as stock plants. Tiller cuttings of each plant were planted into individual 1 m deep root screening tubes of sand and irrigated with nutrient solution After 115 days, the shoots were cut off, the sand/root column cut into 10 cm increments and the roots washed free of sand. The shoots and root samples were oven-dried and weighed. The four root shape progeny groups did not differ significantly for shoot or root dry weight (DW), or root/shoot DW ratio. Root type 2 (high surface root mass and roots to 1 m) progeny had a significantly higher percentage of total root mass between 0 and 10 cm than did root type 1 (low surface root mass and roots to 1 m) but none of the other differences were significant for percentage roots 0–10 cm. The root type 2 progeny had a lower percentage of total root DW between 10 and 20 cm than all the other root types, none of which differed and had a significantly lower percentage of root DW 20–30 cm than types 1 and 4 but did not differ at this depth from type 3 progeny. The probability of root type 4 (high surface root mass, shallow rooting) plants having roots at 1 m depth was 0.67; this was significantly lower than for the other selections, none of which varied significantly. These results indicate that it should be possible to change root system shape in perennial ryegrass using conventional breeding techniques.

Root growth patterns of perennial ryegrasses under well-watered and drought conditions

Abstract A boroscope and mini-rhizotrons were used to explore root growth patterns in five different ryegrasses grown outdoors under simulated field edaphic conditions including drought. Few major differences in root counts were found among the ryegrasses. The seasonal patterns of root counts in well-watered treatments showed an autumn peak that was later (or even suppressed) as autumn soil temperatures increased in consecutive years. Seasonal patterns were not measurable at more than 7 cm depth down the profile. The summer drought resulted in an increase in root counts right down the profile, which started about a month after the drought began. This was followed by rapid death of roots in the top 15 cm of soil but lower death rates deeper in the soil. After rewetting of the soil, there was a delay of approximately 1 month before a rapid increase in root production occurred. This overcame the apparent high soil temperature inhibition of autumn root growth in the well-watered control treatment.

Phosphate uptake by white clover (Trifolium repens L.) genotypes with contrasting root morphology

Abstract Phosphorus (P) response curves were established for white clover genotypes with either relatively long, fine roots (LFR), or relatively short, thick roots (STR) in a glasshouse experiment. The LFR genotype had smaller average root diameter, greater specific root length (SLR, cm mg‐1 root dry weight), longer roots and more branched roots than the STR genotype. Root dry weight of the genotypes was identical across all P levels. P uptake per unit root mass was higher in the LFR genotype, resulting in greater P acquisition and higher shoot dry weight yields than for the STR genotype. We concluded that development of white clovers with high SRL and frequent root branching could contibute to an improvement in the efficiency of phosphate use in pastoral farming.

The role of C4 grasses in New Zealand pastoral systems

Abstract As agricultural scientists in temperate regions search for the next revolution in pasture productivity, C4 grasses often appear in the literature as “having potential” to push through the ceiling of production. This potential has yet to be realised in high producing pastures in New Zealand, despite investigations in the 1970s, and ongoing suggestions (a) that research would enable the full value to be exploited and (b) that the advent of genetic technologies could provide the answer. This paper reviews the New Zealand and Australian literature on C4 grasses, identifies the difficulties with incorporating them into high producing temperate grazing systems, and makes suggestions for their use in the future.

Root growth media effects on root morphology and architecture in white clover

Abstract Root morphological and architectural parameters were recorded for Trifolium repens L. cv. ‘Grasslands Huia’, inbreds of cv. ‘Huia’ and cv. ‘Crau’, and selections within ‘Huia’ for contrasting root morphology. The plants were grown in sand and solution culture in a glasshouse experiment. Images of roots were made using a flat‐bed scanner and analysed using WinRhizo™ image analysis software. Mean root topological indices of 0.95 for solution culture and 0.93 for sand culture indicated that root media had little effect on the herringbone pattern of white clover roots. There were root media effects on five root architectural parameters, all explicable as the result of roots branching more frequently in sand. There were clover type × root media type interactions for five root parameters. These were caused by the inbred clovers being less responsive to a change in root medium than the other three clovers. Differences between roots grown in sand or solution culture were relatively small, but we recommend using sand for screening white clover for root parameters when the physical effects of a solid medium on roots is important.