Lily Ouyang

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.

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.

Comparisons between wild populations and bred perennial ryegrasses for root growth and root/shoot partitioning.

Abstract Root and shoot dry weights (DW), and root DW depth distribution were determ ined for wild type perennial ryegrass, breeding lines and cultivars. The plants were grown in 1 m deep tubes of sand culture in a glasshouse experiment. There were significant differences in shoot DW among accessions in the wild types but not within the bred material, and the wild types had more accessions with low shoot DW. Root DW varied significantly among accessions in both the bred material and the wild types. There were significant differences in root/shoot DW ratios among accessions, and between pools in the breeding lines, but no differences within the wild types. Root/ shoot ratios in the wild types had a much narrower and generally higher range of values than those in the bred lines. The percentage of root DW in the top 10 cm of sand did not vary significantly in the bred lines but it did in the wild types. Variation was recorded in root DW depth distribution at both the accession and genotype levels. We concluded that selection for merit based on shoot performance does not necessarily result in large root systems, and better plant performance might result from an increase in root system size in perennial ryegrass.

Phosphate responses of some Trifolium repens × T. uniflorum interspecific hybrids grown in soil

Abstract. Previous studies in sand culture suggested that some white clover (Trifolium repens) × T. uniflorum interspecific hybrids were more tolerant than white clover of low external phosphate (P) supply. Here, P acquisition and growth responses were determined in soil for two T. repens × T. uniflorum backcross hybrids and their parental white clover cultivar, grown in a glasshouse pot experiment at Olsen P of 6, 7, 9, 14, or 20 mg P kg–1 soil. Growth of all of the clover entries responded strongly to increasing soil P levels, and one hybrid clover grew, on average, 17% better than the white clover control cultivar at Olsen soil P 9–20 mg kg–1. Internal P concentrations and shoot growth per unit P absorbed did not differ among the clovers. Instead, improved growth of the hybrid resulted from a greater ability to acquire soil P. This hybrid had the longest, most frequently branched roots. Frequent branching and growth of root tips into fresh soil would reduce the limitations to P uptake imposed by slow diffusion of P to the root surface. The results confirm previous observations that interspecific hybridisation is a useful strategy for increasing the range of P responsiveness in breeding populations for white clover.

Loss of weight in ryegrass and clover roots preserved in ethanol prior to image analysis for root traits.

The dry weight content of root samples from perennial ryegrass and white clover decreased significantly over a week’s storage in 70% ethanol, but did not change further with longer storage times. Ryegrass roots lost on average 22.4% of the original dry weight, and clover roots lost 29.2%. Storage of roots in ethanol prior to image analysis of root traits could introduce significant error in the calculation of parameters involving root dry weight. Determination of root fresh weights, and dry weight for a subsample prior to preservation would allow calculation of a correction factor for dry weights obtained from preserved samples.

Evaluation of aluminium‐tolerant white clover (Trifolium repens) selections on East Otago upland soils

Abstract Growth of 15 legumes was monitored for 3 years on 3 Otago upland soils with 11, 45, or 70 μg g‐1 extractable soil aluminium (Al). Lotus pedunculatus and L. corniculatus produced the greatest dry matter over the 3 years, with L. pedunculatus producing superior yields at intermediate and high soil Al sites. Within white clover, types selected for Al tolerance produced similar yields to types selected for Al susceptibility, and four commercial white clover cultivars and an alsike clover (Trifolium hybidum). Caucasian clover (T. ambiguum) spread by rhizomes at the high Al site, but neither Lotus species spread from the planted row. Some white clovers showed limited spread. It is concluded that optimising performance of Lotus and Caucasian clover on these soils will be a more productive strategy than breeding for Al‐tolerance in white clover.

Root morphology and architecture, and internal phosphate use efficiency, in related white clover cultivars of different ages

Root morphology and architecture were determined for four related white clover (Trifolium repens L.) cultivars—Huia, Pitau, Kopu II and Mainstay, released 57, 36, 15 years and 1 year ago, respectively. The plants were grown in soil maintained at a range of available phosphate (P) levels in a glasshouse pot experiment. Root samples for analysis were obtained from plants growing in the 17 and 62 mg P kg−1 soil treatments. There were no statistically significant (P < 0.05) effects of cultivar age or soil P level on root morphology or architecture. The inherently efficient herringbone branching pattern of white clover root systems has apparently been able to support ongoing improvements in shoot system performance during cultivar development, without changing. There was a significant increase in shoot dry weight yields per unit plant P absorbed, as cultivar age decreased. This is evidence that repeated selection for shoot traits has resulted in an increase in internal P-use efficiency.

Effect of clover root weevil larval feeding on growth of clover progenies from parents selected for tolerance in field trials

Abstract The effects of larval herbivory by clover root weevil (CRW, Sitona lepidus) on seven white clover (Trifolium repens) and two red clover (Trifolium pratense) progenies from plants showing tolerance of CRW in field trials were tested in two controlled glasshouse experiments. CRW larvae recovered from red clover plants were, on average, fewer (6.3 larvae/g root dry weight) and shorter (5.7 mm/g root dry weight) than those from white clover (16.7 larvae, 7.1 mm length).This confirmed previous findings that red clover is an inferior host for this pest. In the first experiment, progeny of four of the white clover selections for CRW tolerance showed high tolerance (shoot dry weights −2.9% to +3.1% different from their respective weevil-free controls) compared with a 13–24% shoot weight loss for two white clover cultivars. These results confirm field trial observations that there is variation for CRW tolerance in white clover and also that CRW tolerance is hereditable in at least some populations. The second experiment, on a smaller subset of white clovers, showed little effect of CRW on either the tolerant clover selections or the cultivar controls. An index of larval feeding pressure (larval numbers×larval projected areas/root dry weight) gave much lower values for the second experiment (12–78 mm2/g) than for the first (69–102 mm2/g). The absence of negative effects of CRW on the cultivar controls in experiment 2 was assumed to result from low CRW feeding pressure, allowing compensatory growth responses. A small but consistent increase in shoot: root ratio in the +CRW treatment in experiment 1 provided supporting evidence for increased allocation to shoots as a mechanism for plants to reduce the impact of root herbivory.

Variation in cadmium concentrations in shoots of chicory (Cichorium intybus L.)

ABSTRACT Fifty plants from each of eight chicory (Cichorium intybus L.) populations were screened for foliar cadmium (Cd) concentrations using soil containing 1.2 mg Cd kg−1. There was substantial variation in Cd concentrations in all the populations and no relationship between Cd level and plant size. Two polycrosses were done with plants selected for lower Cd and one polycross with plants selected for higher Cd, and the progenies tested for foliar Cd and growth rate. Progenies from parents selected for higher Cd averaged 15.1 mg Cd kg−1 and the progenies from those selected for lower Cd averaged 8.1 mg Cd kg−1. The % realised heritabilities for shoot Cd concentrations ranged from 0.6 to 1.0. This means that it should be possible to breed productive, low Cd chicory for use as a forage on soils with elevated Cd, as well as hyper accumulating types for phytoremediation of contaminated soils.