A market survey of Australian leafy vegetables and a winter and spring experiment with Swiss chard were conducted to examine nitrate and nitrite levels in leaves. The relationship between growth response to nitrogen (N) supply and light level and accumulation of N in leaves was of particular interest. The survey that included 7 types of lettuce and endive (Asteraceae), 6 leafy Asian vegetables (Brassicaceae), and Swiss chard and spinach (Amaranthaceae) showed that fresh leafy vegetables available during a 6-month period on the Australian market can range in nitrate-N from 12 to 1400 mg/kg fresh weight and nitrite-N from 0 to 37.5 mg/kg. Some samples exceeded the limits for nitrate and nitrite based on international food safety standards. The response of Swiss chard to N supply and light was investigated. The accumulation of nitrate in Swiss chard was primarily influenced by increasing N supply and not by light level. Light conditions for all treatments in both the winter and spring experiments exceeded the critical level (~200 μmol/m2.s) required to increase leaf nitrate. Growth and leaf nitrate concentration were higher for spring, associated with average minimum to maximum temperatures of 18–39°C, compared with 14–28°C for winter. Treatment effects on nitrite-N in Swiss chard could not be determined because nitrite was only detected in one-third of plants. The importance of N supply in affecting nitrate accumulation in vegetables is highlighted by the Swiss chard experiments. It confirmed that nitrate accumulation occurs at optimal to supra-optimal nitrate supply, emphasising for growers the undesirable effect of excessive fertiliser use.
As part of a project exploring the potential for using leaf physiological traits to improve drought tolerance in soybean, studies were conducted to explore whether epidermal conductance (ge), osmotic potential (π), and relative water content (RWC) influenced turgor maintenance and ultimately the survival of droughted plants. In a glasshouse study, plants of 8 soybean genotypes that showed different expression of the traits were grown in well watered soil-filled beds for 21 days and then exposed to terminal water deficit stress. The trends in each trait were then monitored periodically until plant death. Genotypic differences were observed in the rate of decline in RWC as the soil dried, in the temporal patterns of change in ge and π, in the duration of survival after watering ceased, and in the critical relative water content (RWCC) at which plants died. In general, ge became smaller and π became more negative as RWC declined and plants acclimated to the increasing stress. Genotypic differences in ge remained broadly consistent as RWC declined. In contrast, the genotypic rankings for π in stressed plants were poorly correlated with those for well watered plants, indicating differential genotypic capacity for osmotic adjustment (OA) in response to stress. Survival times among genotypes after stress commenced ranged from 27 to 41 days, while RWCC ranged from 49% down to 41%. The differences in survival time among the genotypes were able to be explained by genotypic differences in the rate of decline in RWC and in the RWCC, using a multiple linear regression relationship (R 2 = 0.94**). In turn, genotypic differences in the rate of decline in RWC were positively correlated (r = 0.75*) with ge at 70% RWC, and with OA over the drying period (r = 0.98**). In a second study in a controlled environment facility, leaf area retention at 90% soil water extraction was greatest in the one genotype that combined low ge, high OA, and low RWCC. Overall, the responses from the two studies were consistent with the hypothesis that turgor maintenance and ultimately leaf and plant survival of different genotypes during advanced stages of drought stress are enhanced by low ge, high OA capacity, and low RWCC.
The persistence of a diverse group of lucerne (Medicago sativa sspp.) germplasm was evaluated under farmer management across a range of acidic and neutral-alkaline soils at 8 sites in South and Western Australia. Dryland field trials were sown in parallel with commercial lucerne paddocks being grown in rotation with cereal crops, remaining unfenced and under management by the farmer for the life of the stand. The combined differences in soil type, grazing management, and low rainfall contributed to large differences in average lucerne persistence between sites in South Australia and Western Australia. After 3 years, plant frequency (a measure of plant density used to monitor persistence) averaged 17% (at least 17 plants/m(2)) on the strongly acidic soils in Western Australia and 30% on the neutral-alkaline soils in South Australia (at least 30 plants/m(2)). Differences in persistence were attributed to the combined stresses of soil pH, drought conditions, and grazing management. Genetic correlation analyses between sites failed to show any clear patterns in the performance of entries at each site, except for a high correlation between 2 South Australian sites in close proximity. Highly winter-active germplasm was less persistent than other winter activity groups, but was higher yielding when assessed in an additional trial at Katanning, WA. Highly winter-active lucerne (class 9-10) should continue to be recommended for short (2-4 year) phases in rotation with cereals, and winter-active groups (6-8) should be recommend for longer (4-7 year) phases in rotations. The results of this evaluation are also being used to identify broadly adapted, elite genotypes in the breeding of new lucerne cultivars for the southern Australian cropping districts.
Phosphorus efficiency (PE), and its relationship with intracellular (APase) and secreted (S-APase) acid phosphatases, anthocyanin accumulation, and calcium and zinc nutrition, were compared among 8 cultivars of each of wheat, sunflower, chickpea, and lentil grown under greenhouse conditions with low and high rates of P supply in a P-deficient calcareous soil. Except for the chickpea cultivars, deficiency of P resulted in significant decreases in shoot dry weight of all the crop cultivars and led to significant decreases in root dry weight in wheat and sunflower, significant increases in root dry weight in chickpea, and no significant difference in root dry weight in lentil. PE differed greatly among species and their cultivars. On average, shoot P concentration in cultivars of wheat, sunflower, chickpea, and lentil increased by 44%, 54%, 47%, and 8%, respectively, with P supply, and the increases in P concentration differed greatly among cultivars of all species. Intracellular leaf APase activity of wheat and lentil cultivars was slightly decreased by P supply, while it was unchanged in sunflower and chickpea cultivars. However, root-secreted acid phosphatase (S-APase) activity was significantly reduced by P supply in wheat, sunflower, and chickpea cultivars. Under low-P conditions, S-APase activities of all species except sunflower were negatively correlated with PE. Phosphorus deficiency increased the anthocyanin concentration of the cultivars of wheat and sunflower, whereas it was usually decreased in cultivars of the P-efficient species chickpea and lentil. In general, concentration of Ca was found to be lower, but Zn concentration was higher, in P-efficient cultivars than in P-inefficient cultivars. The results demonstrated that PE of the cultivars clearly depends on their ability to take up P and Zn, and on secretion of acid phosphatases from their roots under P deficiency. The results also suggest that characteristics of Zn and Ca nutrition should be taken into consideration when screening cultivars of crop species for their P efficiency.
There is increasing interest in the use of organic amendments in the Australian cotton (Gossypium hirsutum L.) industry because of perceived benefits to soil health and the environment. A 2-year field experiment was conducted at the Australian Cotton Research Institute (ACRI), near Narrabri, NSW, using three locally available organic amendments applied at typical farmers’ rates to irrigated cotton. The amendments used were cattle manure (10 t/ha), composted cotton gin trash (7.5 t/ha), and a commercial liquefied vermicompost (50 L/ha), and their effects on soil quality characteristics were compared with those of control soil where no amendment was added. The soil (0–0.10 m) was sampled on six occasions and analysed for selected chemical and microbiological properties. The physiological characteristics and nutrient uptake of mature cotton plants were also examined. The organic amendments did not have a significant effect on microbiological properties as measured by microbial biomass and respiration. Of the chemical properties measured, manure-amended plots showed higher nitrate-nitrogen, available phosphorus, and exchangeable potassium (K) concentrations over 2 years. Exchangeable K was 28% higher where cattle manure was applied than in control plots during the active growth stage of cotton in the first year of experiment. Higher nutrient uptake by mature cotton plants and lower nutrient concentration in soil were observed in the second year. Cotton physiological properties and lint yield were not significantly affected by the application of organic amendments. Seasonal parameters had a strong effect. The results suggest that there are few short-term benefits to be gained in terms of soil quality from application of organic amendments to Vertosols at the rates used in these trials.
The role of hydraulic lift in nutrient uptake from dry topsoil is unclear. Vertically-split root systems were used to measure hydraulic lift and phosphorus (P) and potassium (K) uptake at the rosette and flowering stages of two canola (Brassica napus L.) cultivars (Trigold and Boomer with small and large root systems, respectively) grown in soil low in P and K. Rubidium (Rb) was used as a tracer to examine K uptake from K fertiliser banded in dry topsoil. During vegetative growth, statistically significant hydraulic lift was measured, irrespective of cultivar root size or a specific nutrient (P or K) placed in the topsoil. The Rb tracer revealed significant amounts of K were absorbed from the dry soil, but at rates five-fold lower than from the moist soil. The water lifted could not prevent cessation of P uptake by Boomer and a reduction in P uptake by Trigold. During mid to late flowering, ion uptake from the dry topsoil was impeded despite the continuation of hydraulic lift up to 28 days after the topsoil was dried. Minimal fine root growth following topsoil drying (and reduction in fine root biomass in some treatments) appeared to be the primary cause of impeded nutrient uptake.
Root-lesion nematodes (Pratylenchus thornei Sher and Allen and P. neglectus ( Rensch) Filipijev and Schuurmans Stekhoven) cause substantial yield loss to wheat crops in the northern grain region of Australia. Resistance to P. thornei for use in wheat breeding programs was sought among synthetic hexaploid wheats (2n= 6x = 42, AABBDD) produced through hybridisations of Triticum turgidum L. subsp. durum ( Desf.) Husn ( 2n= 4x = 28, AABB) with Aegilops tauschii Coss. ( 2n= 2x = 14, DD). Resistance was determined for the synthetic hexaploid wheats and their durum and Ae. tauschii parents from the numbers of nematodes in the roots of plants grown for 16 weeks in pots of pasteurised soil inoculated with P. thornei. Fifty-nine (32%) of 186 accessions of synthetic hexaploid wheats had lower numbers of nematodes than Gatcher Selection 50a (GS50a), a partially resistant bread wheat. Greater frequencies of partial resistance were present in the durum parents (72% of 39 lines having lower nematode numbers than GS50a) and in the Ae. tauschii parents (55% of 53 lines). The 59 synthetic hexaploids were re- tested in a second experiment along with their parents. In a third experiment, 11 resistant synthetic hexaploid wheats and their F-1 hybrids with Janz, a susceptible bread wheat, were tested and the F(1)s were found to give nematode counts intermediate between the respective two parents. Synthetic hexaploid wheats with higher levels of resistance resulted from hybridisations where both the durum and Ae. tauschii parents were partially resistant, rather than where only one parent was partially resistant. These results suggest that resistance to P. thornei in synthetic hexaploid wheats is polygenic, with resistances located both in the D genome from Ae. tauschii and in the A and/or B genomes from durum. Five synthetic hexaploid wheats were selected for further study on the basis of ( 1) a high level of resistance to P. thornei of the synthetic hexaploid wheats and of both their durum and Ae. tauschii parents, ( 2) being representative of both Australian and CIMMYT ( International Maize and Wheat Improvement Centre) durums, and ( 3) being representative of the morphological subspecies and varieties of Ae. tauschii. These 5 synthetic hexaploid wheats were also shown to be resistant to P. neglectus, whereas GS50a and 2 P. thornei-resistant derivatives were quite susceptible. Results of P. thornei resistance of F(1)s and F(2)s from a half diallel of these 5 synthetic hexaploid wheats, GS50a, and Janz from another study indicate polygenic additive resistance and better general combining ability for the synthetic hexaploid wheats than for GS50a. Published molecular marker studies on a doubled haploid population between the synthetic hexaploid wheat with best general combining ability ( CPI133872) and Janz have shown quantitative trait loci for resistance located in all 3 genomes. Synthetic hexaploid wheats offer a convenient way of introgressing new resistances to P. thornei and P. neglectus from both durum and Ae. tauschii into commercial bread wheats.
In the present study we tested how assimilate availability per kernel at different grain-filling stages may affect maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) individual kernel weight (KW). These two species have shown a contrasting KW response to increased assimilate availability at similar seed developmental stages. Plant growth rate (PGR) per kernel was used to estimate the assimilate availability per kernel at two stages: around the early grain-filling period when kernel number per plant is also being established, and around the effective grain-filling period. We tested 3 commercial genotypes from each species, and modified the PGR by thinning or shading the stand at different developmental stages. In both species, each genotype showed a particular relationship between PGR around flowering and kernel number, which gave a range of responses in the PGR per kernel set around flowering. Final KW always increased whenever PGR per kernel around flowering was enhanced. Only sorghum showed a consistent KW increase when PGR per kernel during the effective grain-filling period was enhanced. Results confirmed that increasing assimilate availability per kernel will affect maize kernel size only if the potential set early in development is altered. Most important, we showed that linking specific KW sensibility across species at different seed developmental stages using a simple estimate of assimilate availability per seed (i.e. PGR per kernel) at each grain-filling stage helped explain most of the explored genotypic and environmental variability in final kernel size.
Winter cover crops are beneficial, especially legumes that can supply nitrogen (N) to the next crop. The purpose of this study, involving separate experiments carried out at 2 different locations in north-eastern Slovenia, was to determine the most appropriate sowing time (early, early autumn SD1; late, mid autumn SD2; very late, late autumn SD3) for winter legumes (Trifolium subterraneum L., T. incarnatum L., T. pratense L., and Vicia villosa Roth) for the optimal yield of beneficial dry matter and soil N cycling. The control treatment used Lolium multiflorum Lam. For legume cover crops in SD1, from 915.0 (T. subterraneum) to 2495.0 (V. villosa) kg herbage dry matter yield (HDMY)/ha, 52.3 (T. pratense) to 148.4 (T. incarnatum) kg accumulated N (AN)/ha, and 14.5 (T. pratense) to 114.5 (T. incarnatum) kg symbiotically fixed N (Nsymb)/ha was obtained to the end of autumn. Until the spring ploughing-in, which was before maize sowing, legume cover crops in SD1 yielded 1065.0 (T. subterraneum) to 4440.0 (T. incarnatum) kg HDMY/ha, 74.9 (T. subterraneum) to 193.0 (V. villosa) kg AN/ha, and 4.7 (T. subterraneum) to 179.0 (V. villosa) kg Nsymb/ha. All parameters in SD2 were significantly lower than in SD1, whereas the SD3 sowing was not suitable for the legumes. The benefits of legume winter cover crops with regard to symbiotic N fixation were achieved only by early sowing; however, the amount of soil mineral N in late autumn and in early spring was decreased under L. multiflorum more than under the legumes.
Fusarium wilt disease of watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai), caused by Fusarium oxysporum f. sp. niveum (FON), is one of the limiting factors of worldwide watermelon production. In this study, a Fusarium wilt resistant watermelon JSB, which was derived from a spontaneous mutation of the susceptible Sugar Baby (SB), was used to investigate histopathology. The number and diameter of xylem vessels in the root (10 mm below the shoot base) of resistant JSB plants were significantly higher than those in susceptible SB plants. At 9 days post inoculation (dpi), using the plate assay on Nash-PCNB media, FON could be recovered from 86% of the roots in the symptomless plants of both watermelon lines, and from 55% and 64% of the stem segments (5 mm above the shoot base) in resistant and susceptible plants, respectively. In paraffin and free-hand tissue sections, at 8, 13, and 35 dpi, the xylem of roots and stems close to the soil surface in resistant watermelon JSB plants was also colonised by FON, but to a much lower percentage than the susceptible SB ones. No colonisation below the middle of stems was observed in the resistant JSB plants. The susceptible plants grown in infested soil were all dead by 35 dpi, while the resistant plants remained healthy. These observations suggest that reducing FON colonisation in the vascular systems of the host may contribute to the resistance in JSB. Furthermore, the higher expression of the phenylalanine ammonia lyase (PAL) gene in JSB induced by FON and the effects of PAL inhibitor on the resistance of JSB suggested that PAL is involved in resistance of watermelon to Fusarium wilt pathogen.
Simple sequence-repeat (SSR) and sequence characterised amplified regions (SCARs) have been used to characterise the genetic diversity of chickpea germplasm. A set of 48 genotypes comprising cultigen, landraces, and wild relatives important for breeding purposes was used to determine the genetic similarity between genotypes and to assess the association between ascochyta blight (AB) and SCAR phenotypes. The 21 SSR markers amplified a total of 370 alleles, with an average of ~17 alleles per SSR locus among the 48 genotypes. Polymorphic information content (PIC) values ranged from 0.37 for the XGA13 locus to 0.93 for the XGA106. Principal coordinate analysis (PCO) of genetic similarity (GS) estimates revealed a clear differentiation of the chickpea genotypes into 5 groups, which were generally consistent with available pedigree information. Comparison of SCAR and AB phenotypes enabled us to tag the common source(s) of AB resistance in the breeding collection. Based on the SCAR phenotypes, it was evident that the studied chickpea genotypes, including worldwide-known AB-resistant lines (ICC12004, ILC72, ILC3279), carry at least one common source of resistance to AB. Since SSR markers are polymerase chain reaction (PCR)-based markers, highly polymorphic, and amenable to high-throughput technologies, they are therefore well suited for studies of genetic diversity and cultivar identification in chickpea. The broad level of genetic diversity detected in the chickpea germplasm should be useful for selective breeding for specific traits such as AB, backcrossing, and in enhancing the genetic base of breeding programs.
DairyMod, EcoMod, and the SGS Pasture Model are mechanistic biophysical models developed to explore scenarios in grazing systems. The aim of this manuscript was to test the ability of the models to simulate net herbage accumulation rates of ryegrass-based pastures across a range of environments and pasture management systems in Australia and New Zealand. Measured monthly net herbage accumulation rate and accumulated yield data were collated from ten grazing system experiments at eight sites ranging from cool temperate to subtropical environments. The local climate, soil, pasture species, and management (N fertiliser, irrigation, and grazing or cutting pattern) were described in the model for each site, and net herbage accumulation rates modelled. The model adequately simulated the monthly net herbage accumulation rates across the range of environments, based on the summary statistics and observed patterns of seasonal growth, particularly when the variability in measured herbage accumulation rates was taken into account. Agreement between modelled and observed growth rates was more accurate and precise in temperate than in subtropical environments, and in winter and summer than in autumn and spring. Similarly, agreement between predicted and observed accumulated yields was more accurate than monthly net herbage accumulation. Different temperature parameters were used to describe the growth of perennial ryegrass cultivars and annual ryegrass; these differences were in line with observed growth patterns and breeding objectives. Results are discussed in the context of the difficulties in measuring pasture growth rates and model limitations.
An account is given of the possible time(s) and place(s) of the origin of hexaploid wheat from natural hybridisation between Triticum tauschii (Ae. tauschii) and both wild and cultivated forms of tetraploid wheat. A recapitulation is presented of the likely genotypic and phenotypic status of the newly arisen natural hexaploid and the likely path of hybridisation from whence it arose. Recent substantial contributions of T. tauschii to wheat improvement indicate the likelihood that introgession en masse from T. tauschii has not occurred throughout its natural and agricultural associations with wheat. This has been substantiated in comparative studies revealing higher levels of genetic variation in T. tauschii compared with the D genome of hexaploid wheat. A case is made for a widening of the concept of the gene pool of T. tauschii for wheat improvement and the notion of a secondary gene pool is proposed to include variation in T. tauschii as it occurs in several polyploid forms of ‘grass Triticum’. The likely differentiation of growth habit forms, conditioned by vernalisation (i.e. vrn) genes, in hexaploid wheat synthesis, including the interaction of these genes in hexaploid wheat, is discussed. It is speculated that growth habit differentiation was of significance to the hexaploid’s yield contribution and survival in tetraploid-hexaploid mixtures (likely to be a common constitution of wheat crops of early agriculture), and in the Neolithic spread of agriculture to the higher latitude, and colder environments of NW Europe and central Asia. The significance of the contribution of T. tauschii to the unique milling and bread-making properties of hexaploid wheat is discussed in the light of Roman discernment of its closer fulfilment of the requirements of leavened bread-making compared with tetraploid wheat. The significance of the contribution of T. tauschii to the evolution of wheat appears to have been much delayed (by ~6500 years) in that hexaploid wheat did not receive singular attention and cultivation until during the Roman era, from whence it gradually rose in popularity to eventually achieve its current pre-eminent status. Continuing systematic evaluation of genetic variation in both the primary and secondary gene pools of T. tauschii for wheat improvement, using both conventional and genetic analysis and contemporary genomic tools, is advocated. The latter approach is particularly important for quantitative traits in the light of wide divergence in plant phenotype of their representatives from that of hexaploid wheat.
Nitrogen (N) and phosphorus (P) are the 2 most limiting nutrients for grain production within the northern grains region of Australia. The response to fertiliser N and P inputs is influenced partly by the age of cultivation for cropping, following a land use change from native pasture. There are few studies that have assessed the effects of both N and P fertiliser inputs on grain yield and soil fertility in the long term on soils with contrasting ages of cultivation with fertility levels that are running down v. those already at the new equilibrium. Two long-term N × P experiments were established in the northern grains region: one in 1985 on an old (>40 years) cultivation soil on the Darling Downs, Qld; the second in 1996 on relatively new (10 years) cultivation on the north-west plains of NSW. Both experiments consisted of fertiliser N rates from nil to 120 kg N/ha.crop in factorial combination with fertiliser P from nil to 20 kg P/ha.crop. Opportunity cropping is practiced at both sites, with winter and summer cereals and legumes sown. On the old cultivation soil, fertiliser N responses were large and consistent for short-fallow crops, while long fallowing reduced the size and frequency of N response. Short-fallow sorghum in particular has responded up to the highest rate of fertiliser N (120 kg N/ha.crop). Average yield increase with fertiliser N compared with nil for 5 short-fallow sorghum crops was 1440, 2650, and 3010 kg/ha for the 40, 80, and 120 kg N/ha, respectively. Average agronomic efficiency of N for these crops was 36, 33, and 25 kg grain/kg fertiliser N applied. This contrasts with relatively new cultivation soil, where fertiliser N response was generally limited to the first 30 kg N/ha applied during periods of high cropping intensity. Response to P input was consistent for crop species, VAM sensitivity, and starting soil test P level. At both the old and new cultivation sites, generally all winter cereals responded to a 10 kg P/ha application, and more than half of long-fallow sorghum crops from both sites had increased grain yield with P application. At the old cultivation site, average yield gain for 10 kg P/ha.crop treatment was 480 kg/ha for all winter cereal sowings, and 180 kg/ha for long-fallow sorghum. Short-fallow sorghum did not show yield response to P treatment.
The broad-sense heritability of 3 traits related to leaf survival in severely stressed plants was studied in several hybrid soybean populations. The 3 traits were epidermal conductance (ge), osmotic potential (π), and relative water content (RWC). The populations were generated by hybridising unrelated parental genotypes previously shown to differ in the 3 traits. ge (mm/s) was measured on well watered plants from 10 populations involving all combinations of 5 parental lines, grown in soil-filled beds in the glasshouse. π (MPa) and RWC (%) were measured on severely stressed plants of 3 populations involving all combinations of 3 different parents, growing into a terminal water deficit under a rainout shelter in the field. Broad-sense heritability for ge was significantly different from zero (P < 0.05) in all 10 populations and ranged from 60% to 93%. Heritability estimates for π70 (the tissue osmotic potential at 70% RWC) ranged from 33% to 71%. Only two estimates were statistically significant (P < 0.05) because of large standard errors and the fact that parental differences were smaller than previously observed. Broad-sense heritability for RWC of severely stressed plants ranged from 40% to 74%, and was statistically significant (P < 0.05) for 2 of the 3 populations. For all 3 traits, F2 progeny distributions were consistent with quantitative inheritance with a high degree of additive gene action. It was concluded that capacity exists to breed varieties with low ge, low π70, and high RWC in stressed plants. However, in the case of osmotic potential, genotypes with lower π70 combined with greater precision of measurement would be needed than proved possible in these studies. Further, specific strategies would be needed to select for the critical RWC, the minimal RWC at which leaf tissues die and which provides a measure of tissue dehydration tolerance. More research is also needed to characterise the dynamic relations between ge, π, and RWC in influencing leaf survival in soybean, before they could be confidently used in a breeding program to improve drought tolerance.
In the olive breeding program of Córdoba, Spain, the first 15 obtained selections have recently been tested in a comparative field trial, including their genitors, ‘Arbequina’, ‘Frantoio’ and ‘Picual’, as a control. In this work, we report the evaluation of the fruit characteristics and ripening time of those selections. Average data recorded in the comparative field trial orchard in two consecutive harvest seasons were used for statistical analysis. A high degree of variability and significant differences between genotypes were obtained for all the fruit characteristics analysed, and for ripening time and extractability index. For most of those parameters, selections showing better values than the genitors have been found. In particular, many of the selections had higher oil content than the genitors. Data for seedling plants evaluation was significantly correlated with data of the reported field trial for fruit weight, fruit removal force/fruit weight ratio and oil content. This indicates that selection in the seedling stage for these characters can be efficiently performed, even when only the first year of agronomic evaluation of the seedling is considered. On the contrary, seedling selection for fruit moisture, fruit removal force and ripening date seems to be difficult to perform. In summary, the results of the agronomic evaluation suggest that some of the selections could be released as new olive cultivars in the near future, for first time in Spain.
We report exceptional productivity and associated water-use efficiency across seasons for commercial crops of rainfed spring wheat and grain sorghum growing on stored soil water in Vertosols on the Liverpool Plains, central-eastern Australia. Agreement between the independently measured terms of evapotranspiration (ET) and the soil water balance (in-crop rainfall + δsoil water) was achieved within acceptable uncertainty across almost all measurement intervals, to provide a reliable dataset for the analysis of growth and water-use relationships without the confounding influence of water outflow either overland or within the soil. Post-anthesis intrinsic transpiration efficiency (kc ) values of 4.7 and 7.2 Pa for wheat and sorghum, respectively, and grain yields of 8 and 7 t/ha from ET of 450 and 442 mm (1.8 and 1.6 g/m2.mm), clearly demonstrate the levels of productivity and water-use efficiency possible for well-managed crops within an intensive and productive response cropping sequence. The Vertosols in which the crops were grown enabled rapid and apparently unconstrained delivery of significant quantities of subsoil water (34% and 51% of total available) after anthesis, which enabled a doubling of pre-anthesis standing biomass and harvest indices of almost 50%. Durum wheat planted into only 0.30 m of moist soil and enduring lower than average seasonal rainfall, yielded less biomass and grain (2.3 t/ha) with lower water-use efficiency (0.95 g/m2.mm) but larger transpiration efficiency, probably due to reduced stomatal conductance. We argue that crop planting in response to stored soil water and management for high water-use efficiency to achieve high levels of average productivity of crop sequences over time can have a significant effect on both increased productivity and enhanced hydrological stability across alluvial landscapes.
This study compared the relative tolerances of subterranean clover (Trifolium subterraneum L.), balansa clover (T. michelianum Savi.), and gland clover (T. glanduliferum Boiss.) to acid soil conditions. Seed yield, seedling density, herbage production, N2 fixation, and herbage mineral composition of the 3 legumes were assessed when grown on an acid soil (pHCa of 4.3 and 15% exchangeable Al [0–0.10 m]) with and without the addition of lime (CaCO3). Annual legume species were sown in a mixed sward together with burr medic (Medicago polymorpha L.), and in mixtures with either lucerne (Medicago sativa L.), chicory (Cichorium intybus L.), or phalaris (Phalaris aquatica L.). Due to drier than average seasonal conditions, none of the perennial species persisted beyond the first summer. Lime increased the herbage production of annual legumes by 18–22% and total pasture production by 14% in both 2002 and 2003. Subterranean clover was the most tolerant of the annual legumes to acid soil conditions, showing no visible toxicity symptoms and no response to lime in terms of seed yield. In contrast, both balansa and gland clovers exhibited visual symptoms of manganese toxicity in the absence of lime, with Mn concentrations in the shoots of 817 mg/kg and 626 mg/kg, respectively. Both species responded positively to lime with seed yields increasing by 45% and 124%, respectively. Lime increased the proportion of herbage N derived from N2 fixation by subterranean clover from 29 to 40% and by gland clover from 30 to 43%. Lime had no effect on the proportion of N2 fixed by balansa clover (29–31%), suggesting a suboptimal symbiosis of rhizobia with that species. Adding chicory or phalaris to the pasture mix increased sward herbage production in the establishment year by 39% and 21%, respectively. Based on leaf symptoms and herbage yield responses to lime, Mn toxicity was present in lucerne with tissue levels of up to 916 mg/kg, but no symptoms were observed in chicory (1129 mg/kg) or phalaris (403 mg/kg). Chicory and phalaris were more tolerant of acidity and high levels of Mn than lucerne, gland clover, and balansa clover. The study highlighted the value of the small-seeded annual legumes, balansa clover and gland clover, to the production of mixed pasture swards even in drier than average seasonal conditions. Although more sensitive to acid soils than subterranean clover, they set a greater number of seeds and, in the case of balansa clover, a greater weight of seed under moisture stress in the establishment year than the larger seeded subterranean clover.
High sucrose content (SC) in sugarcane stalks is a priority for all sugarcane industries world wide. Partitioning to sucrose in the cane stalk is related to the supply of photo-assimilate and the demand for assimilate by other organs. If photosynthesis could be maintained, but leaf and stalk growth constrained, by genetics or management during the stalk elongation phase, it may be possible to reduce stalk height and to increase both SC and sucrose yield. This paper reports an experiment designed to test this hypothesis and to develop a methodology to assess variation in response to source–sink manipulation in sugarcane clones. The research was conducted on a ‘low’ (Q138) and a ‘high’ (Q183) SC cultivar in two temperature controlled and airtight glasshouses (chambers) at CSIRO’s Davies Laboratory in Townsville, Australia. Potted plants of each cultivar were placed in two chambers of the Tall Plant Facility (TPF). In one chamber, plants were irrigated to minimise water stress while plants in the other chamber were irrigated to reduce plant extension rate (PER) considerably more than photosynthesis. Water stress reduced gain in total biomass by 19% and gain in top mass by 37%, and increased sucrose mass gain by 27%. During the experiment, SC of dry matter increased 37% in the dry treatment and only 8% in the wet treatment and this effect was greater in Q183 than in Q138. Water stress reduced whole plant photosynthesis by 18%, thus largely accounting for the 19% reduction in biomass accumulation and it reduced PER by 41%, corresponding to the 37% reduction in mass of tops. Reduced PER resulted in reduced demand for photo-assimilate by fibre and tops thus allowing excess assimilate to accumulate in the form of sucrose. The techniques developed here to control PER and measure the resulting changes in carbon partitioning now allow further examination of both the control of the balance between growth and sucrose storage and the extent of genotypic variation to the response of reduced PER.
