Subterraneum Cv Research Articles

Large variation in waterlogging tolerance and recovery among the three subspecies of Trifolium subterranean L. is related to root and shoot responses

Tolerance to waterlogging and recovery ability was compared among the three subspecies of subterranean clover (Trifolium subterraneum L.) to identify tolerance mechanisms, in order to guide future subclover breeding activities. Three cultivars each of ssp. yanninicum, subterraneum and brachycalycinum were grown in a controlled environment glasshouse with T. michelianum as a waterlogging-tolerant control. After 28 days of growth two treatments were imposed for 35 days: free-draining (control) and waterlogged. A 21-day recovery period followed. After 35 days, waterlogging reduced shoot dry weight (DW) to 58–27% and root DW to 35–21% of respective controls in each subspecies. Shoot relative growth rate (RGR) of yanninicum was least affected (78–104% of control), compared to subterraneum (51–100%) and brachycalycinum (45–69%). The subterraneum cv. Denmark had a similar response to subspecies yanninicum. Shoot RGR of T. michelianum was 138% of its control. After recovery, all traits (except tap root length) recovered to control values. Up to 21 days, the main traits associated with waterlogging tolerance (shoot and root growth) were high petiole length, less petiole anthocyanin pigmentation and high leaf chlorophyll content, but by 35 days these were a high proportion of leaf biomass, high stomatal conductance and enhanced root porosity. Average root diameter and nodulation rates were unrelated to waterlogging tolerance. Subspecies yanninicum had superior waterlogging tolerance. Priority traits for easily-assessed indicators of waterlogging tolerance are less reduction of leaf size and high stomatal conductance.

Legume Ecotypes and Commercial Cultivars Differ in Performance and Potential Suitability for Use as Permanent Living Mulch in Mediterranean Vegetable Systems

Weed control in organic conservative vegetable systems is extremely challenging and the use of legume permanent living mulches (pLM) presents an interesting opportunity. The successful use of pLM is largely determined by the choice of appropriate legumes which are able to combine adequate weed control with a marginal competitive effect on the cash crop(s). However, the availability of legumes for such systems is limited and their characterization based on growth traits can support the selection of suitable legumes for conservation organic vegetable systems. The current study investigated weed control capacity and variability in morphological and phenological traits relevant in inter-plant competition among a range of 11 commercial cultivars of legumes and seven ecotypes of Medicago polymorpha (bur medic). For commercial cultivars, Lotus corniculatus (bird’s-foot trefoil) and Trifolium repens (white clover) showed the best weed control capacity, while Trifolium subterraneum (subterranean clover) and Medicago polymopha had more suitable characteristics for a rapid and complete establishment of the pLM. Overall, legume mulches appear more effective in dicotyledonous than in monocotyledonous weed control. Trifolium subterraneum cv. Antas and T. repens cv. Haifa were identified as the potentially most suitable legumes for use as pLM and their use in mixtures could be a promising solution. In addition, the ecotypes of Medicago polymorpha Manciano and Talamone proved to be well adapted for local environmental conditions and they showed a better weed suppression than the commercial cultivars of Medicago polymorpha.

Evaluation of pasture legumes in northern New South Wales, Australia

Spring herbage mass of 80 mostly annual and biennial legumes was evaluated regionally on the North-West Slopes of New South Wales, Australia in ungrazed plots at three sites (Curban, Terry Hie Hie and Moree) in 1998 and 1999. Of the cultivars tested, Trifolium vesiculosum cvv. ‘Cefalu’ and ‘Zulu’ and T. resupinatum cv. ‘Prolific’ at the Moree and Terry Hie Hie sites, and T. resupinatum cv. ‘Nitro’ at the Curban site generally performed better than the standard ‘test’ cultivars of T. subterraneum cv. ‘Junee’ and T. brachycalycinum cv. ‘Clare’ and Medicago sativa cvv. ‘Aquarius’ and ‘Aurora’. T. michelianum (5) and (11), T. isthmocarpum (SA 8410) and T. glanduliferum (CPI 87182) also had superior performance to many of the other entries and could be considered for further testing and evaluation in this region.

Seedling competition of lucerne in mixtures with temperate and tropical pasture species

Two replacement series studies were conducted to quantify the competitive ability of seedlings of Medicago sativa (lucerne) sown in mixtures with temperate and tropical species. A temperate mixtures study (Expt 1) consisted of lucerne cv. Genesis sown with each of Phalaris aquatica (phalaris) cv. Atlas PG, Lolium arundinaceum (tall fescue) cv. Resolute MaxP, Cichorium intybus (chicory) cv. Puna, Trifolium subterraneum (subterranean clover) cv. Clare, Austrodanthonia richardsonii (wallaby grass) cv. Taranna and Avena sativa (forage oats) cv. Eurrabie. There was also an additional mixture of chicory and subterranean clover. A tropical grass mixtures study (Expt 2) included Genesis lucerne sown with each of Panicum coloratum var. makarikariense cv. Bambatsi, Dicanthium aristatum cv. Floren, Chloris gayana (Rhodes grass) cv. Katambora, Digitaria eriantha subsp. eriantha cv. Premier and Bothriochloa bladii subsp. glabra cv. Swann. In Expt 1, lucerne-phalaris mixtures were equally competitive, whereas lucerne-tall fescue mixtures over-yielded. Chicory was aggressive in mixtures with lucerne and subterranean clover; similarly forage oats was more competitive than lucerne. Subterranean clover was competitive against lucerne at harvest 1, but by harvest 2 the low cutting height had reduced its competitiveness. Lucerne was more aggressive than wallaby grass. In Expt 2, all tropical grass-lucerne mixtures over-yielded; however, lucerne was generally more competitive than the grasses, except for Rhodes grass at harvest 1. While our study indicated that mixtures of lucerne seedlings with phalaris or tall fescue may be compatible, mixtures with tropical grasses were more likely to result in lucerne seedling dominance. This competitiveness may be overcome by either spatial or temporal separation and we discuss the concept of using mixtures to exploit environmental niches.

Study of ambient ozone phytotoxicity in Ukraine and ozone protective effect of some antioxidants

The aim of the study was to assess ambient ozone phytotoxicity in Kyiv (Ukraine) using bioindicator clover plants ( Trifolium subterraneum cv. Geraldton) and to test some natural and synthetic antioxidants as ozone protectants. The results obtained showed that ambient ozone concentrations were high enough to cause visible leaf injury in clover. All used substances showed partial ozone protective effect on clover. Water extracts from the leaves of plants, known to contain flavonoids–antioxidants showed weaker ozone protective effect and were less stable in the field conditions than synthetic antioxidants. Among the studied extracts, those from Ocimum basilicum and Tagetes patula were more effective as ozone protectants than the one from Salvia sclarea.

The Rhizobium leguminosarum biovar trifolii ANU794 Induces Novel Developmental Responses on the Subterranean Clover Cultivar Woogenellup

The clover-nodulating Rhizobium leguminosarum bv. trifolii ANU794 initiates normal root-nodule development with abnormally low efficiency on the Trifolium subterraneum cv. Woogenellup. The cellular and developmental responses of Woogenellup roots to the site- and dose-defined inoculation of green fluorescent protein (gfp)-labeled cells of ANU843 (nodulation proficient) and ANU794 was investigated using light, fluorescence, and confocal microscopy. Strain ANU794-gfp induced three primordia types and four developmental responses at the inoculation site: true or aberrant nodules (on 5 and 25% of plants, respectively), hybrid structures (20% of plants), or lateral roots (50% of plants). The novel hybrid structures possessed nodule and lateral root-like features and unusual vascular patterning. Strain ANU794-gfp induces lateral root formation by stimulating pericycle cell divisions at all nearby protoxylem poles. Only true nodules induced by ANU794-gfp contained intracellular bacteria. In contrast, strain ANU843-gfp induced nodules only and lateral root formation was suppressed at spot inoculation sites. Primordium types were distinguishable by the emission spectrum characteristics of phenolic UV-absorbing and fluorescent compounds that accumulate in primordium cells. Hybrid primordia contained (at least) two fluorescent cell populations, suggesting that they are chimeric. The results suggest that ANU794 may produce both nodule- and lateral root-generating signals simultaneously.

(342) Cool-season Living Mulchesfor Florida

Living mulches between beds of polyethylene-mulched vegetable crops may suppress weeds and decrease surface and ground water contamination by pesticides. They should be either low growing or amenable to mowing and should withstand traffic. Twelve winter cover crops were planted in north (N.) and north central (N.C.) Florida in Fall 2004: black oats (Avena strigosa cv. Soilsaver), annual ryegrass (Lolium multiflorum cv. Gulf), rye (Secale cereale cv. Wrens Abruzzi), hard fescue (Festuca longifolia cv. Oxford), white clover (Trifolium repens cvs. Dutch white and New Zealand white), berseem clover (T. alexandrinum cv. Bigbee), crimson clover (T. incarnatum cv. Dixie), subterranean clover (T. subterraneum cv. Mt. Barker), arrowleaf clover (T. vesiculosum cv. Yuchi), a barrel medic (Medicago trunculata cv. Parabinga), and a disc × strand medic (M. tornata × M. littoralis cv. Toreador). Black oats, rye, and annual ryegrass established quickly and suppressed winter annual weeds. Canopy development of the other species was poor. Shoot biomass was greater in N. Florida than in N.C. Florida. The highest shoot biomass occurred with black oats. By 8 weeks after planting (WAP) rye and annual ryegrass had similar amounts of biomass, but by 16 WAP the yield of rye was greater. At some harvests, biomass with wheel traffic or mowing was lower than without, but black oats, rye, and ryegrass did not succumb to these treatments. Of the legumes, only crimson clover and `Toreador' medic in N. Florida produced sufficient biomass by 16 WAP to permit a harvest. Black oats, rye, and annual ryegrass appear to be the best living mulch candidates; however, black oats would require more frequent mowing.

The role of fractures and lipids in the seed coat in the loss of hardseededness of six Mediterranean legume species

Changes in the seed coat morphology of 12 annual legumes were studied using environmental scanning electron microscopy (ESEM). The seeds of Biserrula pelecinus L. cv. Casbah, Ornithopus sativus cv. Cadiz, Trifolium clypeatum L., T. spumosum L., T. subterraneum L. cv. Bacchus Marsh, Trigonella balansae Boiss. & Reuter., Trigonella monspeliaca L. and Vicia sativa subsp. amphicarpa Dorthes (morthes.) were examined by ESEM after exposure to field conditions for 6 months, while those of Medicago polymorpha L. cv. Circle Valley, Trifolium clypeatum L., T. glanduliferum Boiss., T. lappaceum L., T. spumosum L., and T. subterraneum L. cv. Dalkeith, were examined after 2 years' exposure. The entry of water into seeds was followed by covering various parts of the seed coat with petroleum jelly and soaking the treated seeds in dyes.As the seeds softened over time, more and larger fractures appeared on the seed coat. Water entered the seed either through fractures, over the seed coat as a whole or through the lens. It is hypothesized that the formation of fractures occurs after physicochemical changes in the seed coat, probably associated with changes in the amount and nature of seed coat lipids.The newly matured whole seeds of M. polymorpha cv. Circle Valley, T. clypeatum, T. glanduliferum, T. lappaceum, T. spumosum, and T. subterraneum cv. Dalkeith were analysed for lipid content in 1997. The seed coats of T. subterraneum cv. Dalkeith and T. spumosum were separated from the cotyledons and examined in detail for lipid content.The lipid content of whole seeds ranged from 48 (T. lappaceum) to 167 mg/g (T. subterraneum cv. Dalkeith). Total lipid of the whole seeds of T. subterraneum cv. Dalkeith and T. glanduliferum declined by about 9 mg/g over 2 years, while in T. spumosum it declined by about 17 mg/g.In contrast, the major fatty acids in the seed coat declined by 0·67 mg/g over the 2 years. Change in seed coat lipids showed a marked similarity to changes in hardseededness for both T. subterraneum cv. Dalkeith and T. spumosum. The results strongly suggest that seed softening is associated with loss of lipids in the seed coat, because lipids have physical characteristics that are altered at temperatures experienced in the field.

Effects of continuous and seasonal grazing strategies on the herbage mass, persistence, animal productivity and soil water content of a Sirosa phalaris - subterranean clover pasture, North-West Slopes, New South Wales

An experimental site was established in 1997 on the North-West Slopes of New South Wales to further investigate the use of strategic grazing management to improve the persistence of phalaris (Phalaris aquatica cv.�Sirosa) and subsequent effects on animal production and soil water content. The pasture was sown in 1992 to Sirosa phalaris, subterranean clover (Trifolium subterraneum var. subterraneum cv. Seaton Park) and lucerne (Medicago sativa cv. Aurora). Four grazing treatments were applied in a randomised 3-replicate design. Treatments consisted of continuous grazing at 12.3 sheep/ha (C12 or control); continuous grazing at 6 sheep/ha (C6), and 2� spring and autumn strategies of either resting from grazing for 6 weeks in each season (SAR0), or reducing stocking rate from 12.3 to 4.0 sheep/ha (SAR4). Despite annual applications of fertiliser and high clover content, Sirosa phalaris herbage mass in plots continuously grazed at 12.3 sheep/ha declined from a mean of 3300 kg DM/ha in spring 1997 to < 700 kg DM/ha by May 1998. At the end of the study (February 2001), Sirosa mean herbage mass in these plots was 670 kg DM/ha and lower (P < 0.05) than for the other treatments (mean value 5400 kg DM/ha). These marked changes in herbage mass, and the degradation of the Sirosa-based pasture to an annual pasture by continuous grazing at 12.3 sheep/ha, were not generally reflected in either short-term animal production or substantial differences in soil water content. Wool production (kg/head) was not significantly different among treatments each year. Compared with continuous grazing at 12.3 sheep/ha, sheep liveweights were higher (P < 0.05) in plots continuously grazed at 6.1 sheep/ha from November 1997 to February 1999. However, from February 1999 to 2001, sheep liveweights in the 2 treatments with the highest Sirosa phalaris content were lower (P < 0.05) than those continuously grazed at 12.3 sheep/ha. Only the soil water content for the C6 and SAR4 treatments at 0–30�cm was significantly different to the control treatment, but the differences were predicted to be < 2.5 mm/year. In the root zone (0–90 cm), mean soil water content ranged from 159 to 309 mm (mean 220 mm), while plant available water (soil water content – soil water content at –1500 kPa) was a mean of 79 mm, ranging from 11 to 168 mm.

Injury and growth response of subterranean clover to ambient ozone as assessed by using ethylenediurea (EDU): Three years of plant monitoring at four sites in The Netherlands

To assess injury and growth responses to ambient ozone, ethylenediurea (EDU) and non-EDU-treated plants of subterranean clover ( Trifolium subterraneum cv. Geraldton) were exposed to ambient air at four rural sites in the Netherlands during the growing seasons of 1994–1996. In each of two successive experiments of 8 weeks, harvests were performed after four (cutting) and 8 weeks of exposure (final harvest). Characteristic ozone symptoms were always observed at each site until mid September and EDU protected the plants almost completely. Injury generally depended on site and year and increased significantly with increasing accumulated exposure to ambient ozone (AOT40) with a maximum of 31%. Injury response to ozone increased with increasing daily mean vapour pressure deficit (VPD). Each increase in VPD of 0.1 kPa would result in an additional increase in injury of ca. 2% given a fixed ozone exposure level. Ozone-induced injury was observed on several occasions where maximal 5-day AOT40 values in the week prior to injury were well below 200 nl l −1 h, the proposed short-term critical level for injury development when VPD is below 1.5 kPa. Leaf biomass response of the plants to EDU was highly variable and biomass reduction was not correlated with AOT40. The EDU method was not useful to validate the proposed long-term critical level (3000 nl l −1 h for 3 months) to protect crops against growth and yield reductions by ambient ozone.

Effects of continuous grazing and seasonal closures on the performance and persistence of some sown temperate perennial grasses, North-West Slopes New South Wales

A split-plot experiment was sown at Tamworth in 1992 to examine the effects of continuous sheep grazing and seasonal closures (autumn, spring, spring + autumn, and summer + winter) on the herbage mass, plant frequency and basal cover of 5 perennial grasses, when sown as monocultures or with a perennial (Trifolium repens cv. Haifa) or annual legume (Trifolium subterraneum var. subterraneum cv. Seaton Park). Plant basal area and crown density data were also collected. The perennial grasses were Phalaris aquatica cv. Sirosa, Festuca arundinacea, cv.� Demeter, Lolium perenne cv. Kangaroo Valley, Austrodanthonia richardsonii (syn. Danthonia richardsonii) cv.�Taranna, and A. bipartita (syn. D. linkii) cv. Bunderra. There was no significant effect of legume presence on the herbage mass or persistence of the perennial grasses. The only treatment that had a significant effect (P< 0.05) on either herbage mass, plant frequency or basal cover data was the grazing treatment × perennial grass interaction in each of the years 1993-98, except for herbage mass in December 1993 and basal cover in October 1998. In all of the grazing treatments examined, Kangaroo Valley ryegrass failed to persist after spring 1994; Demeter fescue had failed by spring 1997 and Sirosa phalaris by spring 1998. Six years after sowing the only temperate grass cultivars that were persisting in all grazing treatments were the native perennials, Taranna and Bunderra. Hence, the data represent the entire stand life from sowing to eventual failure for the 3 introduced cultivars. While grazing treatment effects within years for individual species were significant, overall grazing had little effect on the rate of decline in herbage mass and persistence of Kangaroo Valley, Demeter and Sirosa. By 1998, grazing treatment had no significant effect on the herbage mass and basal cover of Taranna and Bunderra, but their plant frequencies were lowest in the spring rest and summer + winter rest treatments.

Water use, competition and a temperate-zone C4 grass (Eragrostis curvula (Schrad.) Nees. complex) cv. Consol

The effects of a perennial C4 grass (Eragrostis curvula [Schrad.] Nees. complex cv. Consol) and winter-growing annual pasture on the soil water deficit (SWD) was assessed at 2 sites near Wagga Wagga, NSW. At Site A, newly sown E. curvula-Trifolium subterraneum L. pasture was compared with an annual pasture containing Lolium rigidum Gaud. and T. subterraneum. A mature E. curvula pasture sown 10 years previously was compared with an adjacent volunteer annual pasture at Site B. The annual pasture at Site A had little effect on the SWD at 120 cm depth, but it developed an appreciable SWD at 60 cm on 2 occasions when spring rainfall was well below average. This deficit was not evident the following autumn. When E. curvula was present in the pasture, it developed a substantial SWD at 120 cm in summer and autumn. This represented a significant realignment of the water balance that had the potential to reduce deep drainage. The size of the SWD in autumn determined how rapidly soils reached field capacity in winter. At Site B, E.�curvula consistently created a deficit of between 108 and 124 mm to 100 cm depth in autumn, compared with 2-106 mm for the annual pasture. The soil profile under E. curvula did not reach field capacity until 60-100 days later than the annual pasture. The annual pasture at Site B had a minimal effect on the SWD at 100 cm in 3 of the 4 years of the study. The camping behavior of sheep at Site A caused E. curvula to succumb to competition from T. subterraneum, Hordeum leporinum Link, and Cryptostemma calendula (L.) Druce. Competitive interactions between T.�subterraneum cv. Junee and Eragrostis curvula cv. Consol were therefore investigated in a glasshouse study using the de Wit replacement series methodology. Pots were watered to weight and water usage was recorded under 2 levels of watering [low (restricted watering) and high (watered to field capacity)] that were applied after an establishment period of 6 weeks. Pots were harvested after a further c.12 weeks and above- and below-ground yield of each species determined. T. subterraneum tended to use water up to the limit of its supply, and as water became less available and in response to increasing atmospheric water demand in spring, it frequently wilted. E. curvula rarely wilted; it exhibited water-saving strategies, including leaf waxing and leaf rolling in the heat of the day in response to increasing water demand without necessarily exhausting its water supply. Both species used water more efficiently (dry matter/kg water used) when its supply was limited. The water use efficiency of monoculture T. subterraneum was greater than that of slowly growing E. curvula, and both species used water most efficiently when growing alone. T. subterraneum was highly competitive against E. curvula. Competition resulted from its out-of-phase growth compared with E. curvula. E. curvula has the potential to markedly affect on the water balance. However, it is vulnerable to competition. Managing the flush of growth in spring is an important issue in maintaining a balance between E. curvula and winter-growing annual species.

Erratum to: Two novel chromosomal loci influence cultivar-specific nodulation failure in the interaction between strain ANU794 and subterranean clover cv. Woogenellup.

The nodulation failure resulting from the interaction between Rhizobium leguminosarum biovar trifolii strain ANU794 and the Trifolium subterraneum cv. Woogenellup was examined by transposon mutagenesis to resolve whether multiple determinants were involved in cultivar-specificity. Three new transposon-induced mutants of ANU794 (W72, W78 and W710) with significantly enhanced nodulation ability on cv. Woogenellup were identified. The W72 and W78 mutations are chromosomally-located, whereas the W710 mutation isplasmid-located. The ethylene synthesis inhibitor, aminoethoxyvinylglycine, fails to enhance the nodulation ability of ANU794, ANU7943 (csn1::Tn5) and W78 on cv. Woogenellup, but enhances the nodulation ability of W72,W710 and ANU7941 (nodM::Tn5). DNA sequencing of the W78 locus reveals strong homology to an unknown Mycobacterium open reading frame, and to several bacterial non-haem chloroperoxidases. The previously identified csn1 locus showed homology to the 50S ribosomal protein, L9, with the Tn5 insertion being located in the 5'-untranslated region. The results suggest that cultivar-specificity is mediated by at least two independent mechanisms or determinants, and not by a simple gene-for-gene interaction. The role of ethylene in cultivar specificity is discussed. Cultivar-specific interactions may prove useful in identifying pathways involved in efficient nodule formation and plant-microbe interactions.

Two novel chromosomal loci influence cultivar-specific nodulation failure in the interaction between strain ANU794 and subterranean clover cv. Woogenellup.

The nodulation failure resulting from the interaction between Rhizobium leguminosarum biovar trifolii strain ANU794 and the Trifolium subterraneum cv. Woogenellup was examined by transposon mutagenesis to resolve whether multiple determinants were involved in cultivar-specificity. Three new transposon-induced mutants of ANU794 (W72, W78 and W710) with significantly enhanced nodulation ability on cv. Woogenellup were identified. The W72 and W78 mutations are chromosomally-located, whereas the W710 mutation isplasmid-located. The ethylene synthesis inhibitor, aminoethoxyvinylglycine, fails to enhance the nodulation ability of ANU794, ANU7943 (csn1::Tn5) and W78 on cv. Woogenellup, but enhances the nodulation ability of W72,W710 and ANU7941 (nodM::Tn5). DNA sequencing of the W78 locus reveals strong homology to an unknown Mycobacterium open reading frame, and to several bacterial non-haem chloroperoxidases. The previously identified csn1 locus showed homology to the 50S ribosomal protein, L9, with the Tn5 insertion being located in the 5'-untranslated region. The results suggest that cultivar-specificity is mediated by at least two independent mechanisms or determinants, and not by a simple gene-for-gene interaction. The role of ethylene in cultivar specificity is discussed. Cultivar-specific interactions may prove useful in identifying pathways involved in efficient nodule formation and plant-microbe interactions.

Lupins, a New Host of Phytophthora erythroseptica.

Several lupin (Lupinus) species are native to southern Spain (2). The white lupin, Lupinus albus L., is the most important crop, and its seeds are used for human consumption and animal feed. Accessions of three indigenous species, L. albus, L. angustifolius L., and L. luteus L., and an introduced species from South America, L. mutabilis Sweet, were planted during October in replicated yield trials in acidic soils (pH 6.5) in the Sierra Morena Mountains (elevation 350 m) north of Córdoba. Root and crown rot disease was widespread and very serious on the indigenous lupins, particularly in several patches of white lupin cultivars. Infected plants were devoid of feeder rootlets, and the tap roots, crowns, and lower stems were necrotic and turned dark brown to black. Rotted roots were colonized heavily by fungal oospores. Many affected plants wilted and died before flowering. A Phytophthora sp. was isolated consistently from the necrotic roots and crowns of symptomatic white lupins. The same fungus also was isolated from the necrotic root tissues of the other indigenous lupin species. Isolates of the fungus from diseased white lupins were homothallic and produced oospores rapidly and abundantly on corn meal and V8 agars. Antheridia were amphigynous, and aplerotic oospores ranged from 22 to 32 μm (average 27 μm). Nonpapillate, ovoidobpyriform sporangia were produced only in water on simple sympodial sporangiophores. Cultures on V8 agar grew at 5 to 30°C (optimum ≈25°C). The species was identified as Phytophthora erythroseptica Pethybr. based on morphology of oospores, sporangia, and other cultural characteristics (1). Koch's postulates were fulfilled by planting seeds of white lupin cv. Multulupa in sterile potting soil infested with a blended culture on V8 agar from a white lupin isolate of P. erythroseptica and reisolating the fungus after 28 days from lesions that developed on the roots and crowns of inoculated plants incubated in a greenhouse at 16 to 26°C. The fungus was not isolated from white lupins seeded in potting soil inoculated with sterile V8 agar. In pathogenicity tests, two isolates of P. erythroseptica from white lupins caused severe symptoms on the roots and crowns of inoculated white lupin cv. Multulupa similar to those observed on white lupins naturally infected in field trials. These isolates also caused root and crown rots on inoculated L. luteus and L. angustifolius. The fungus did not infect the roots or crowns of tarwi (L. mutabilis cv. SCG 20), alfalfa (Medicago sativa cv. Moapa), bean (Phaseolus vulgaris cv. Contender), chickpea (Cicer arietinum cv. Blanco Lechoso), faba bean (Vicia faba cv. Arboleda), lentil (Lens culinaris cv. local), pea (Pisum sativum cv. Lancet), soybean (Glycine max cv. Akashi), or subterranean clover (Trifolium subterraneum cv. Seaton-park). The tests were repeated, and the results were similar. This is the first report of P. erythroseptica infecting Lupinus spp.

Interactive effects of arbuscular mycorrhizal symbiosis, intraspecific competition and resource availability on Trifolium subterraneum cv. Mt. Barker

We performed two glasshouse experiments to determine whether the presence of arbuscular mycorrhizal symbiosis reduces the intensity of intraspecific competition at low concentrations of available phosphorus (P), and whether this effect is modified by a reduction in light intensity. In the first experiment, Trifolium subterraneum cv. Mt. Barker was grown at different densities in controlled conditions of light and temperature, and half of the pots were inoculated with spores of the arbuscular mycorrhizal fungus, Gigaspora margarita. In the second experiment, the plants were grown in similar controlled conditions but the light intensity received by half of the pots was reduced by >50%. The biomass and P content of individual mycorrhizal plants and the biomass response to mycorrhizal infection were drastically reduced as plant density increased. The effects of density on percentage infection, shoot and root P concentrations, and root: shoot ratios were inconsistent. Generally reduction in light intensity did not alter these effects. Mycorrhizal symbiosis increased intraspecific competition intensity through an increase in the availability of soil P. This increase in competition was reflected in the greater size inequality of low density mycorrhizal treatments. Our results emphasize that the main effects of mycorrhizas at the individual level cannot be expected to be apparent at the population level, because they are overridden by density‐dependent processes.

Yield losses of white cabbage caused by competition with clovers grown as cover crop

The use of intercropping as an integrated pest management (IPM) tool to reduce population densities of pests of field grown vegetables, and the growth and yields of cabbage and clover cover crops grown in the Netherlands, were investigated. In the first 2 experiments, the clover (Trifolium repens cv. Pertina or T. subterraneum cv. Geraldton) crop significantly reduced pest damage of fresh market cabbage cv. Minicole. The associated yield losses due to competition with the cover crop were 15-24%. In other experiments designed to investigate these yield losses in cabbage for storage (cv. Slawdena), the losses were 18-43%. The decrease in weight/head was reduced by decreasing the row distance from 0.75 to 0.50 m, although yield losses were still high. Delaying the sowing of the clover crop, or transplanting the cabbage into a rotary cultivated strip in the clover stand instead of transplanting in the clover stand itself, did not reduce yield losses. It is suggested that intercropping with clover as an IPM tool is not suitable at present for cabbage crops in the Netherlands.

Assessing effects of ambient ozone on injury and growth of Trifolium subterraneum at four rural sites in the Netherlands with ethylenediurea (EDU)

To assess adverse effects of ambient ozone on injury and growth, EDU (ethylenediurea) and non-EDU-treated plants of subterranean clover ( Trifolium subterraneum cv. Geraldton) were exposed to ambient air at four rural sites in the Netherlands. In each of two successive experiments of eight weeks during the 1994 growing season, an intermediate harvest (cutting) was performed after four weeks of exposure. Concentrations of ambient ozone were high in Experiment 1 (June 21–August 16) and relatively low in Experiment 2 (August 23–October 18). Subterranean clover displayed characteristic ozone injury at all sites in Experiment 1 and in Experiment 2 until the intermediate harvest (September 20). The proportion of leaves injured in non-EDU-treated plants was higher than that in plants treated with the antioxidant. Both the degree of injury and the protective effect by EDU differed between sites and were not related to the measured ozone levels. The proposed short-term critical levels for injury development by ozone would not have protected clover against ozone injury in Experiment 2. The site-dependent pattern of injury in non-EDU-treated plants was similar for the various harvests and experiments and a maximal degree of 23% injury was observed after four weeks of exposure. The protective effect by EDU was related positively to the injury intensity in non-EDU-treated plants, irrespective of site, harvest and experiment. EDU caused variable effects on leaf biomass production under conditions of low ozone in Experiment 2 whereas EDU generally increased leaf biomass when the plants were exposed to the relatively high concentrations in Experiment 1. The EDU-induced increase in leaf biomass production in this experiment did not vary between sites and was on average 5–7%, depending on the harvest. The involvement of elevated concentrations of ambient ozone measured at the four sites in the Netherlands in 1994 in the observed increase of leaf biomass by EDU is discussed.

Effectiveness and genetic diversity of Rhizobium leguminosarum bv. trifolii isolates in Portuguese soils polluted by industrial effluents

The effects of heavy metals from industrial effluents on symbiotic nitrogen fixation were studied using soils from an industrial area polluted for nearly 40 y. The work reported here indicated a decrease in effectiveness and genetic diversity of Rhizobium leguminosarum bv. trifolii population present in contaminated soils, although the size of this population was not affected by the presence of heavy metals. Twenty-seven Rhizobium isolates from polluted soil and 32 isolates from unpolluted soil were evaluated for effectiveness by acetylene reduction assay (ARA) determination using Trifolium subterraneum cv. Clare as the host plant and for genetic diversity by examination of the banding patterns of DNA on gel electrophoresis. Only 15% of the isolates from polluted soil were effective. Almost all the isolates (94%) from unpolluted soil were effective showing an ARA activity similar to the standard Rhizobium strain (recommended as inoculant for Trifolium subterraneum). The isolates from unpolluted soil had a greater diversity in terms of the numbers of plasmid types than the isolates from the polluted soil. The plasmids groups dominant in the unpolluted soil were often absent from the isolates from the polluted soil.

Mass rearing Halotydeus destructor (Tucker) (Acari : Penthaleidae) for use in summer screening of Trifolium subterraneum (L.) for mite resistance

Summary. Controlled environment experiments were conducted to establish some of the requirements for successful mass rearing of Halotydeus destructor (redlegged earth mite). Numbers of mites reared on Vicia sativa (common vetch) cv. Blanchefleur grown alone or on a mixture of vetch with Trifolium subterraneum (subterranean clover) cv. Goulburn, were significantly higher than those on subterranean clover or Arctotheca calendula (capeweed) alone. Populations reared on vetch grown in a sandy soil were significantly higher than those reared on vetch grown in a loamy soil, pure sand or pure loam. Covering the soil surface with a natural pasture mulch increased mite numbers compared with leaving the soil bare or placing plant pots inside ventilated cages. Subsequent changes in rearing methodology produced enough mites to enable summer screening of subterranean clover lines for resistance to H. destructorfor the first time. Over 20 000 mites can be produced from vetch at one time for screening tests throughout the year.