Growth Cabinet Experiments Research Articles

Evaluation of nematicides for Meloidogyne enterolobii management in sweetpotato.

Sweetpotato is an important crop whose roots are consumed by people worldwide. Meloidogyne enterolobii stands out as a highly deleterious variant among the species of root-knot nematode that causes significant damage in sweetpotato. In the present study, the activity of four nematicides against M. enterolobii was assessed both in vitro and in growth cabinet experiments. After 48 hours of exposure, fluopyram and cyclobutrifluram had a greater negative effect on the motility of M. enterolobii second-stage juveniles (J2s) compared to fluensulfone and hymexazol, with respective median effective concentration (EC50) values of 0.204, 0.423, 22.335 and 216.622 mg L-1. When M. enterolobii eggs were incubated for 72 hours at the highest concentration of each nematicides, the inhibitory hatching effect of cyclobutrifluram (2.5 mg L-1), fluopyram (1.25 mg L-1) and fluensulfone (80 mg L-1) surpassed 85%, whereas hymexazol (640 mg L-1) was only 67%. Similar results were observed in growth cabinet experiments as well. The disease index (DI) and gall index (GI) were significantly decreased by all four nematicides compared to the control. However, the application of hymexazol did not yield a statistically significant difference in the egg masses index compared to the control, a finding which may be attributed to its potentially limited penetrability through the eggshell barrier. Overall, this study has demonstrated that all four nematicides effectively suppress M. enterolobii in sweetpotato, and this is the first report on the nematicidal activity of cyclobutrifluram and hymexazol against M. enterolobii.

Sensitivity of Meloidogyne enterolobii and M. incognita to fluorinated nematicides.

Meloidogyne enterolobii (Yang and Eisenback) was recently introduced into Louisiana on contaminated sweetpotato planting material. Given the known variation in sensitivity to nematicides within the genus Meloidogyne, there is question as to whether fluorinated nematicides will be as efficacious toward M. enterolobii as they are with M. incognita (Chitwood). Using a series of in vitro and growth cabinet experiments, this study compared the sensitivity of M. enterolobii and M. incognita to four synthetic non-fumigant nematicides (fluopyram, fluensulfone, fluazaindolizine, and oxamyl). Meloidogyne enterolobii had lower sensitivity to nematicides than M. incognita in the majority of the in vitro exposure assays. Similar levels of reduction in root infectivity were observed after nematicide exposure among both nematode species. Fluopyram showed high hatching inhibition for both Meloidogyne species at low concentrations [median effective concentration (EC50 ) values of 0.273 to 0.018 mg L-1 ], whereas fluensulfone showed high root penetration inhibition at low concentrations (EC50 values of 0.151 to 0.065 mg L-1 ) relative to that of other evaluated nematicides. For both Meloidogyne species, each of the four non-fumigant nematicides reduced root galling (58-96% reduction for M. enterolobii, 71-100% reduction for M. incognita) and egg production (63-99% reduction for M. enterolobii, 58-96% reduction for M. incognita) on sweetpotato when applied at the label recommended rate. Fluorinated nematicides and oxamyl show capacity to suppress M. enterolobii on sweetpotato. © 2021 Society of Chemical Industry.

Establishing miscanthus x giganteus crops in Ireland through nodal propagation by harvesting stems in autumn and sowing them immediately into a field

Miscanthus can help achieve renewable energy and GHG mitigation targets but establishment costs of rhizome systems are high. The objective of this study was to examine if stem material could be used to establish field miscanthus crops. Field trials were established to investigate the optimum sowing time for miscanthus stem segments. In two planting seasons, stem segments of miscanthus were cut in September, October or March and either planted immediately or placed in cold storage. These stem segments of 1.8 m length were planted horizontally underneath the ground at a depth of 100 mm. In a separate set of experiments conducted under control conditions, stem segments were harvested each month and placed in a growth cabinet for sixty days. Basal stem pieces of 650 mm length were harvested from a rhizome crop established in 1994 and 2010 and these stems were either stripped of leaves or left with leaves attached to the stem. The growth cabinet experiments showed that the age of the mother crop or leaf removal had no effect on shoot or root formation but that both root and shoot formation were at a maximum in September and decreased thereafter. Establishment rates, average height, stem numbers and biomass yield in the field trials was maximised through a September harvest and planting date in both trial years (P < 0.0001). Treatments which were stored exhibited reduced or no establishment. There was a residual effect of treatment in the second growing season (P < 0.0001). This study demonstrates that miscanthus crops can be established successfully from stem segments.

The power of the transplant: direct assessment of climate change impacts

Understanding the factors that limit species distributions has become increasingly important in the face of rapid climate change. Many approaches have been used to predict responses of species and communities to new environmental challenges, including species distribution modelling, glasshouse and growth cabinet experiments, and small-scale field manipulations, all of which have both advantages and limitations. Here, we review the use of a powerful, direct method to predict how species and communities will respond to the changing climate: the field transplant experiment. We discuss how transplant experiments can elucidate the factors that limit species distributions; disentangle the role of genetic change vs. phenotypic plasticity in species’ responses; and improve understanding of the role of species interactions in driving community change. Several generalisations about potential species’ responses to climate change are emerging from these studies, including the critical role of specific life stages in response to warming trends, the role of natural enemies and new hosts in limiting or promoting adaptive capacity, and the role of niche saturation in conferring community stability at a functional guild level. Transplant experiments have also confirmed likely mechanisms of recent range shifts and highlighted the potential for some modelling exercises to overestimate future range changes. With the prospect that accelerating warming over the next few decades will increase extinction rates and accelerate ecosystem degradation, we urge researchers to utilise this powerful but underused method more widely.

Effects of Fungicide Treatments for the Control of Epidemic and Exotic Calonectria Diseases in Italy.

The efficacy of 11 fungicides was evaluated for the control of Calonectria infections on bottlebrush (Callistemon "Masotti") and feijoa (Acca sellowiana), with special emphasis on Calonectria pauciramosa and C. morganii, which are the most destructive species in Italian ornamental nurseries. Three nursery experiments were performed with the selected fungicides in order to determine their ability to prevent leaf spot caused by C. morganii on bottlebrush and leaf spot and crown and root rot caused by C. pauciramosa on bottlebrush and feijoa. All fungicides were effective in reducing disease infections, except for cyproconazole, propamocarb + fosetyl-Al, and K phosphite that were the least effective in reducing C. morganii leaf spot. In contrast, K phosphite proved more effective in reducing crown and root rot caused by C. pauciramosa. Fungicides were also evaluated in growth-cabinet experiments for their ability to reduce incidence and severity of leaf spot on bottlebrush caused by the exotic pathogens C. pseudomexicana, C. tunisiana, C. polizzii, and C. mexicana. Copper hydroxide, fosetyl-Al, prochloraz, prochloraz + cyproconazole, and tebuconazole were always effective in reducing Calonectria leaf spot on bottlebrush. However, some differences in levels of control might be attributable to Calonectria isolate. Overall, this study clearly indicates that new fungicides can be employed for chemical management of Calonectria infections in ornamental nurseries.

Effect of temperature on growth ofColletotrichum lupiniand on anthracnose infection and resistance in lupins

The impact of temperature was assessed on mycelial growth of Colletotrichum lupini on agar and on anthracnose expression in lupin cultivars with varying degrees of resistance. Growth rate of C. lupini was determined at temperatures from 5 to 3°C. Fungal growth was observed at temperatures from 10 to 30°C with maximum growth rate occurring at 25°C. In growth cabinet experiments, the impact of temperatures ranging from 10 to 26°C was observed on anthracnose development in the Lupinus angustifolius cultivars Myallie (susceptible), Merrit (moderately susceptible) and Wonga (resistant) and the L. albus cultivar Kiev Mutant (extremely susceptible). At 10°C, disease incidence was very low (0–12%) in all cultivars, reflecting the slow in vitro growth of the fungus at this temperature. Increasing temperature from 12 to 26°C reduced the latent period by more than 50% and increased disease incidence, sporulation incidence and lesion severity. Latent period response to temperature was independent of cultivar resistance. However, cultivar×temperature interactionswere evident for disease incidence, sporulation incidence and lesion severity responses. Anthracnose resistance in cv.Wonga was temperature sensitive. At 12 and 18°C, disease incidence and severity inWonga were significantly lower than other L. angustifolius cultivars tested but at 26°C disease incidence and severity were similar to other cultivars.

Consequences of soil compaction for seedling establishment: Implications for natural regeneration and restoration

Abstract Soil compaction can affect seedling root development by decreasing oxygen availability and increasing soil strength. However, little quantitative information is available on the compaction tolerances of non‐crop native species. We investigated the effects of soil compaction on establishment and development of two New Zealand native species commonly used in restoration programmes; Cordyline australis (Agavaceae) (cabbage tree) a fleshy rooted species, and Leptospermum scoparium (Myrtaceae) (manuka) a very finely rooted species. Seedlings were grown in a range of soil compaction levels in growth cabinet experiments. Low levels of soil compaction (0.6 MPa) reduced both the number and speed of C. australis seedlings penetrating the soil surface. In contrast, L. scoparium seedlings showed improved establishment at an intermediate compaction level. Root and shoot growth of both species decreased with increasing soil strength, with L. scoparium seedlings tolerating higher soil strengths than did C. australis. Despite these results, soil strength accounted for only a small amount of variation in root length (R2 &lt; 0.25), due to greater variability in growth at low soil strengths. Soil strengths of 0.6 MPa are likely to pose a barrier to C. australis regeneration. This is consistent with adaptation to organic and/or soft, waterlogged soils. Active intervention may be necessary to establish C. australis from seed on many sites previously in farmland.

Relative tolerances of wild and cultivated barleys to infection by Blumeria graminis f.sp. hordei (Syn. Erysiphe graminis f.sp. hordei). I. The effects of infection on growth and development

The two lines of wild barley, B19909 and I-17-40 and the cultivated barley, cv. Prisma used in this investigation were found to be the most susceptible to infection of 25 wild and four cultivated barley lines when exposed to the local population of Blumeria graminis f.sp. hordei. All three lines were susceptible during the early stages of growth but expressed some level of adult plant resistance although this level of resistance was significantly higher in line I-17-40 than in either of the other two. The relative tolerances of the lines to the mildew were determined by comparing the effects of infection on their growth and development in growth cabinet experiments. Mildew developed more slowly on line I-17-40 than on the other two lines and by the third week after inoculation, when mildew cover on B19909 and cv. Prisma had reached about 27%, only about 15% of the green leaf area of line I-17-40 was covered. Mildew continued to increase on line B19909 and cv. Prisma so that 6 weeks after inoculation it covered 40% of their leaf-blades. On line I-17-40 30% of the green leaf area was colonised by 4 weeks after inoculation but because of adult plant resistance coupled with the loss of the earlier infected leaves through senescence mildew cover then reduced falling to 15% by 6 weeks. Although total mildew biomass, measured as conidial production was higher on line B19909 than on cv. Prisma all its growth parameters were reduced less indicating that it was the more tolerant line. Conidial production on the lower susceptible leaves of line I-17-40 was slightly lower than on cv. Prisma yet the reaction of these leaves to infection was the same on both lines indicating that tissues of I-17-40 were slightly less tolerant than those of the cultivated barley. However, during the later stages of growth when its upper leaves expressed high levels of ‘adult plant resistance’ dry matter production in this line increased to levels higher even than in the controls. This capacity for compensatory photosynthesis ensured that by the end of growth few differences in any of the measured growth parameters between infected and uninfected plants of line I-17-40 were significant. The greater tolerance of line B19909 over the other two lines and of cv. Prisma over line I-17-40 during the early stages of growth appears to be due to a lower sensitivity to infection of those processes which regulate dry matter accumulation and its distribution around the plant.

Evidence for Systemic, Cross-resistance in White Clover ( Trifolium repens ) and Annual Medic ( Medicago truncatula var truncatula ) Induced by Biological and Chemical Agents

Soil-based growth cabinet and greenhouse experiments were designed to determine whether a resistance response previously noted in Trifolium repens to the clover cyst nematode Heterodera trifolii was systemic and also effective against a pest from a different taxon. Root applications of benzo(1,2,3)thiadiazole-7-carbothioic acid-S-methyl ester (BTH) or a Pseudomonas -like bacterial strain P29 to white clover seedlings induced resistance to the blue-green aphid, Acyrthosiphon kondoi . A similar response was observed in the annual medic, Medicago truncatula var truncatula . Estimation of lignin and callose content of whole plants at the termination of the bioassay showed no differences between treated and control plants. The significance of these findings is discussed.

Koeleria macrantha: performance and distribution in relation to soil and plant calcium and magnesium.

• The reported sensitivity of Koeleria macrantha (Poaceae) to soil magnesium, resulting in its absence from South Wales dolomitic limestone, was examined here in relation to varying ionic Ca to Mg ratios, and by cultivation in different limestone soils. • In a growth cabinet experiment, shoot and root Ca and Mg concentration and dry weight yield were determined for five edaphically varied populations of K. macrantha grown from tillers, over a range of Ca:Mg concentrations. The influence of relative concentrations of other nutrients was also investigated. In addition, K. macrantha plants were cultivated on Carboniferous, Magnesian and dolomitic limestone soils. • Total plant Ca: Mg ranged from 0.3 to >20 mille-equivalents. Optimal substrate ratios (from 25:1 to 0.1:1), and response to different concentrations of nutrients varied between the populations. Cultivation on dolomitic limestone soil produced the highest yields. • The adverse effect on yields of all populations with low substrate Ca: Mg was much lower than predicted. Results suggest K. macrantha has a higher substrate Mg tolerance than other members of the Poaceae: its reported absence from the South Wales dolomitic limestone is unlikely to be due to soil magnesium sensitivity.

Acclimation of plants to light gradients in leaf canopies: evidence for a possible role for cytokinins transported in the transpiration stream.

The mechanism of response of plants to vertical light intensity gradients in leaf canopies was investigated. Since shaded leaves transpire less than leaves in high light, it was hypothesized that cytokinins (CKs) carried by mass transport in the transpiration stream would be distributed over the leaf area of partially shaded plants parallel to the gradient in light intensity. It was also hypothesized that this causes the distribution of leaf growth, leaf N and photosynthetic capacity, and possibly chloroplast acclimation as observed in plants growing in leaf canopies. In a field experiment, the distribution of Ca, N and CKs in a bean leaf canopy of a dense and an open stand supported the concept of a role for CKs in the response of N allocation to the light gradient when a decreasing sensitivity for CKs with increasing leaf age is assumed. Both shading of one leaf of the pair of primary bean leaves and independent reduction of its transpiration rate in a growth cabinet experiment caused lower dry mass, N and Ca per unit leaf area in comparison to the opposite not treated leaf. Shading caused a parallel reduction in CK concentration, which supports the hypothesis, but independent reduction of transpiration rate failed to do the same. Application of benzylaminopurine (BA) counteracted the reduction caused by shade of leaf N, photosynthetic capacity and leaf area growth. The experiments show an important role for the transpiration stream in the response of plants to light gradients. Evidence is presented here that CKs carried in the transpiration stream may be important mediators for the acclimation of plants to leaf canopy density.

Tillering, Internode Development, and Dry Matter Partitioning in Creeping Bentgrass

High tiller density and stolon development are critical to wear tolerance and persistence of creeping bentgrass (Agrostis palustris Huds. synonym A. stolonifera L.). A better understanding of creeping bentgrass growth and development would be helpful in screening germplasm for improved turf characteristics. The objectives of this study were to determine tiller appearance and main stem elongation and development, and to determine above ground dry matter partitioning, in high and low tillering populations of creeping bentgrass grown under low light (150 μmol m−2 s−1). Individual, pregerminated seeds of cv. Emerald and germplasm UM67‐10 were transplanted into 10‐cm pots containing an 80:20 (v/v) sand:peat media. Two growth cabinet experiments were conducted under 16‐ and 8‐h photoperiod and 20/15°C day/night temperatures. Phenological development was monitored through 35 d after transplanting (DAT). Dry weight per tiller was correlated to tiller age for main stem and primary tillers (r = 0.98 and r = 0.99) and secondary tillers (r = 0.93 and r = 0.99) for UM67‐10 and Emerald, respectively, at 35 DAT. Dry weight per tiller was related to tiller elongation. Population differences for dry weight accumulationper day were significant (P = 0.05) for lower order tillers. The germplasm UM67‐10 initiated tillering earlier and main stem elongation later than Emerald. Tillers per plant were correlated to tiller appearance date. Elongating tiller weight within populations was related to main stem elongation date and its final length. Late season planting, when daylight is decreasing, will result in a bentgrass stand with fewer tillers per plant and with little elongated stem growth. Screening germplasm for tiller production in a growth cabinet may facilitate identifying grasses with high tiller density and improved wear tolerance.

Cocksfoot mottle virus spreads to the South Island of New Zealand

In previous surveys of New Zealand cocksfoot (Dactylis glomerata L.) pastures, Cocksfoot mottle virus (CoMV) was detected at only one site near Taupo on the North Island. However, we have recently found CoMV at two sites near Dunedin on the South Island. Isolates from these sites, associated with mild and severe symptoms in cocksfoot (CoMV-Wa and CoMV-Ok, respectively), were partially characterised. In agarose gels, the virions of the two isolates had slightly different mobilities when subjected to an electric field, indicating a difference in net surface charge. However, both isolates produced similar leaf mottle symptoms in wheat, their capsid proteins had similar molecular weights (Mr = ca. 31 kDa) as determined by SDS-polyacrylamide gel electrophoresis and they were serologically indistinguishable in double-diffusion tests using 17 antisera to 10 sobemoviruses. CoMV-Ok and CoMV-Wa were serologically related to Lucerne transient streak virus but not to eight other sobemoviruses. Further surveys using DAS-ELISA showed variable incidences of CoMV (range 0–80%) at nine South Island sites. The beetle vectors of CoMV have not been introduced into New Zealand. At two sites where CoMV was found, we observed severe feeding damage from armyworms (Persectania aversa Walker). However, in growth-cabinet experiments this species failed to transmit the virus. Incidences were significantly higher at mown sites (39%) than at unmown sites (11%), suggesting that mechanical transmission is responsible for spread. In view of the increased use of cocksfoot on New Zealand farms, the impact of CoMV on cocksfoot productivity now needs to be assessed and current levels of resistance to CoMV in commercial cultivars need to be evaluated.

Germination and dormancy of grassy woodland and forest species: effects of smoke, heat, darkness and cold

The germination requirements of a broad spectrum of common species found in grassy woodlands and forests in the New England region of northern New South Wales were tested in a series of replicated growth-cabinet experiments. The effects of dark/diurnal light and smoke/no smoke were measured on 65 species in an orthogonal experiment, 21 of which were retested after storage for 12 months. The effect of storage for several years was also assessed under a diurnal light regime. In addition, the effects of preimbibition heat (80˚C), and chilling on germination were also measured. A single temperature regime (15˚C night/25˚C day) was used in all treatments for comparative purposes. Most species had high viability and germinability under a diurnal light regime. Small shrub species included, however, a large proportion of species with entrenched dormancy. Light enhanced germination of 21 species significantly, whereas dark stimulated germination of only eight species. Heat and cold treatments also stimulated some germination but more often inhibited germination or produced no effect. Smoke stimulated germination, relative to other cues, in only one species (Ajuga australis) and more often inhibited germination or produced no effect. The relationship between variation in germination (stimulation, no effect or inhibition) of species in six growth-form classes was tested by using contingency tables for each treatment. No significant relationship between growth form and the effects of light, smoke or chilling was detected. Preimbibition heat effects were, however, significantly different among growth forms. Subshrubs showed a higher than expected proportion of species with a heat stimuli while herbaceous species showed a higher than expected proportion of species inhibited by preimbibition heat. Germinability generally increased in herbaceous species when stored at ambient temperatures while it remained relatively constant in woody species. Conversely, viability decreased in herbaceous species but remained relatively more constant in woody species. The effects of seed storage and high germinability suggest that most perennial herbaceous species have transient or short-term persistent seed banks. Germinability, with and without cues, was also negatively correlated with increasing seed size and larger growth forms. These traits might be related to the need for woody species, with soil-stored seed banks, to spread establishment risks in an environment where herbaceous competition and herbivory are likely to be important selection factors.

Role of root disease in the poor establishment of Medicago pastures after cereal cropping in South Australia

Field experiments were conducted in 1991, 1992 and 1994 at three locations in South Australia to investigate the involvement of root pathogenic fungi in the poor establishment and growth of annual medics (Medicago spp.) in naturally regenerating pastures. The severity of root disease across the three sites, rated on a 0–4 scale, was 2·4 (1991), 2·7 (1992) and 1·7 (1994). Medicago emergence and/or herbage production increased in the presence of potassium phosphonate applied as a soil drench or as a postemergence spray at 1·0 kg to 3·0 kg a.i. ha−1 in every year and with metalaxyl applied as a postemergence spray (0·83 kg a.i. ha−1) in 1992 and as a soil drench (5 kg a.i. ha−1) in 1994. The severity of root disease was reduced in the presence of both fungicides. Metalaxyl specifically reduced root infection of Medicago by Pythium spp. whilst potassium phosphonate showed a broader spectrum activity, reducing infection by Fusarium spp., Phoma spp., Pythium spp. and Rhizoctonia solani. Fungal isolates showing pathogenicity towards Medicago littoralis cv. Harbinger in growth cabinet experiments included Fusarium acuminatum, F. avenaceum, F. culmorum, F. crookwellense, F. equiseti, F. graminearum, Phoma medicaginis, Pythium irregulare and Rhizoctonia solani.

Knowledge-based and inductive modelling of rough fescue ( Festuca altaica, F. campestris and F. hallii) distribution in Alberta, Canada

The distribution of three rough fescue species ( Festuca altaica, F. campestris and F. hallii) in Alberta was modelled using knowledge-based and inductive approaches. The first used differences in temperature responses defined in growth cabinet experiments, and simple logical algorithms operating on monthly mean climate surfaces. The second used a point database of surveyed botanical composition to define relationships between the species location and climatic factors. Agreement between the zones defined by knowledge-based logical modelling, inductive modelling from points and interpolation of botanical composition was generally good. Botanical composition was used as an abundance measure to enhance estimates of conditional probability of presence in inductive modelling. Additional peaks in the distribution of conditional probability of presence with certain climate variables allowed the identification of a sub-zone attributable to F. campestris which was smaller than that produced by logical modelling. Modelled zones from both methods agreed with published descriptions of distribution and intergrading between species. Choice of method depends on the relative availability of site data versus the amount of knowledge of species behaviour.

Seed-to-seedling transmission of Botrytis cinerea in chickpea and disinfestation of seed with moist heat

Summary. Chickpea crops in south-eastern Australia are affected in some seasons by poor emergence and seedling soft rot. Botrytis cinerea was isolated on a semi-selective agar medium from diseased seedlings and from samples of seed submitted by growers. The frequency of isolation from seed harvested in 1993–94 ranged from 0 to 95%. Higher isolation rates were associated with reductions in seedling establishment in 1994 estimated at 30–75%. Surface sterilisation studies showed that infection was largely external on the seed. In growth cabinet experiments at 8–18°C, seedlings grown from infected seed or from seed inoculated with B. cinerea developed soft rot, and sporulation of the pathogen on the basal stem lesions was observed. Treatment of moist seed at 50°C for 5 min or storage of seed at 20°C for 12 months reduced the frequency of isolation of B. cinerea to 0 and 2%, respectively, with no adverse effect on germination. Heat treatment of freshly harvested seed reduced the isolation frequency from 98 to 18%. The applicability of heat treatment for seed disinfestation by chickpea growers is discussed.

Analysis of Branching in Spring-sown White Lupins ( Lupinus albusL.): The Significance of the Number of Axillary Buds

Plant density and sowing date were shown to affect branching in spring-sown white lupin ( Lupinus albusL.), but the response varied among environments. The patterns of primary and secondary branching in the cv. Lublanc were studied as a function of both the number of axillary buds and the plant growth rate. Field experiments that used a wide range of sowing dates and plant densities to alter plant architecture were conducted over 5 years, and these were supplemented with data from additional glasshouse and growth cabinet experiments. The number of axillary buds on the main stem or primary branches, which determined the potential number of branches, increased linearly with the number of nodes. In situations where all axillary buds did not produce branches, it was found that the number of primary and secondary branches produced was related to the plant growth rate at the beginning of branch elongation. Knowledge of the number of axillary buds improved the analysis of the interaction between cultural practices and environmental conditions on plant architecture. The variability of branching potential among genotypes was discussed.

Effects of photoperiod on leaf appearance rate and leaf dimensions in winter and spring wheats

Research on genotypic variation in the response of leaf-area production and expansion to photoperiod in wheat is limited. Growth-cabinet experiments using four spring and four winter wheat (Triticum aestivum L.) cultivars and four photoperiod (8, 12, 16 and 20 h) treatments were thus conducted with the objective of investigating the effect of photoperiod on leaf appearance rate and leaf dimensions. Winter wheats were grown without vernalization. In the spring wheats, flag leaves and spikes were formed under the longer photoperiod (16 and 20 h) treatments, and leaf number increased linearly with time. At the shorter photoperiods, flag leaves and spikes appeared in some cultivars only, and the rate of increase in leaf number decreased in the later stages. Final leaf number was greater at shorter photoperiods. In the winter cultivars, more leaves appeared than in the spring types under the longer photoperiods. For leaves 3–7, leaf number was a linear function of time, with photoperiod and cultivar effects. For one of four spring cultivars, the rate of leaf appearance was greater at 8 h than at 20 h, whereas for three of the winter cultivars the reverse was true. Leaf length increased with leaf number up to at least nodes 5–6 for both spring and winter types but decreased for the later-formed leaves for the spring but not for the winter types. Leaves of plants grown under photoperiods longer than 8 h were longer and broader than those grown under the short photoperiod, and the effect was more pronounced in winter than in spring cultivars. Such genotypic differences in the direct effects of photoperiod on leaf dimensions, which could influence the rates of leaf-area production and dry-matter accumulation under field conditions, emphasize that future studies should incorporate genotypes from different eco-physiological regions and that simulation models of wheat growth and development may need to account for variability in the control of vegetative growth. Key words: Wheat, photoperiod, leaf appearance rate, leaf length, leaf width

Influence of soil-water matric potential on the control of Pythium root infection of wheat with metalaxyl in two contrasting soils of South Australia

Under prevailing climatic conditions, treatment of winter-sown wheat with metalaxyl (seed dressing, granule, or soil drench applications) significantly limited seed infection by Pythium species but did not give a significant yield response in separate field trials conducted on 2 contrasting soil types in South Australia. However, following irrigation of trial plots (which raised the soil-water matric potential from about -0.09 MPa to -0.02 MPa) during the first 3 weeks of wheat growth in 1989, metalaxyl granule treatment was effective in limiting seed and root infection by the 2 dominant Pythium species present, P. irregulare and P. echinulatum, and gave a significant increase in grain yield on both soil types. This effect of soil-water matric potential was confirmed in growth cabinet experiments in which metalaxyl was shown to be more effective in controlling infection of wheat by P. irregulare in both soil types when the soil-water matric potential was maintained at -0.02 MPa than at a soil-water matric potential of -0.1 MPa.