Stewart S. Higgins

Comparative gas exchange characteristics of potted, glasshouse-grown almond, apple, fig, grape, olive, peach and Asian pear

Abstract Net photosynthesis (Pn), dark respiration (Rd), transpirational flux density (TFD) and leaf conductance (kl) on glasshouse-grown plants of almond, apple, fig, grape, olive, peach and Asian pear were examined under various laboratory environmental conditions. Grape and almond had the highest light-saturated photosynthetic rates, greater than 20 μmol CO2 m−2 s−1. Apple had the lowest temperature optimum for Pn, 20°C. Almond had the highest Rd rate between 10 and 50°C, but grape had the highest Q10 for respiration, a value of 2.5. Apple, olive and grape stomata were most sensitive to the leaf-to-air vapor pressure difference. Apple had the greatest sensitivity of Pn to the vapor pressure difference.

Diurnal water relations of apple, apricot, grape, olive and peach in an arid environment (Jordan)☆

Abstract Selected water-relations parameters were examined on a diurnal basis for apple, apricot, grape, olive and peach grown under common conditions in Amman, Jordan. The study objective was to determine if there were differences in water-relations characteristics that could be useful for the prediction of water use by these crop plants at various sites in Jordan or in similar arid areas with limited water. Transpiration was greatest in apple, followed by peach. Apricot, olive and grape had similar transpiration rates, and these species lost less water per unit leaf area than peach or apple. Apple and olive reached maximum leaf conductance in the afternoon, while peach and apricot had maxima at mid-day; grape had the earliest maximum leaf conductance. Grape had the highest midday xylem pressure potential and olive the lowest, with apple, apricot and peach being intermediate. Apple and olive appeared to have the most rapid return to pre-dawn xylem pressure potential. Estimates of the liquid pathway resistance to water flow were lowest in apple and highest in olive. Results suggest that these species represent alternative plant strategies in response to a common moisture regime.

Rootstock influence over 25 years on yield, yield efficiency and tree growth of cultivars ‘delicious’ and ‘golden delicious’ apple (Malus domestica Borkh.)☆

Abstract The influence of nine rootstocks on growth and production of cultivars ‘Goldspur’ (GS) and ‘Wellspur Delicious’ (WS) and of three rootstocks on growth and production of cultivars ‘Red King Delicious’ (RK) and ‘Golden Delicious’ (GD) apple was evaluated. With spurred scions (WS and GS), the largest trees were on seedling (sdlg), Malling Merton (MM) 104 and MM 109 roots, and the smallest were on Malling (M) 26. Annual yields of most combinations had reached a plateau but none showed significant signs of decline after 25 years. WS cumulative yields were not significantly greater than RK (non-spur). GD produced greater cumulative yields than GS. When cumulative yields among nine stocks within spurred scions were compared, GS/MM 106 and MM 104 and WS/MM 109 and MM 106 ranked highest. Yield efficiencies were superior with M 26, spurred growth habit and clonal stocks.

Nitrogen fixation potential in global chickpea mini-core collection

Biological nitrogen fixation (BNF) is a sustainable alternative for nitrogen supply to agriculture worldwide. One approach to increasing BNF in agriculture is to breed and use legumes with greater BNF capacity. To assess the capacity for BNF in chickpea (Cicer arietinum) global germplasm, a genetically diverse subset from the USDA global chickpea core collection was assayed for BNF potential. The greenhouse experiment assayed 39 global accessions and commercial cultivar UC-5, inoculated with Mesorhizobium ciceri. Plant height, branch number, nodule number, shoot weight, root weight, nodule weight, proportion of nitrogen fixed, and total nitrogen fixation were determined. All characteristics varied significantly among the accessions. Proportion of plant nitrogen fixed ranged from 47% to 78% and was correlated with shoot weight (r = 0.21, P < 0.01) and total plant weight (r = 0.20, P < 0.01), but not with nodule number or weight. Accession 254549 from Iraq produced the greatest total fixed nitrogen, more than any other accession and 121% more than that fixed by UC-5. The variation among BNF capacities of the accessions supports the preservation and use of global germplasm resources and suggests that nitrogen fixation in commercial chickpea varieties may be improved by introgressing positive alleles from the global chickpea germplasm collections.

Evaluating opportunities for an increased role of winter crops as adaptation to climate change in dryland cropping systems of the U.S. Inland Pacific Northwest

The long-term sustainability of wheat-based dryland cropping systems in the Inland Pacific Northwest (IPNW) of the United States depends on how these systems adapt to climate change. Climate models project warming with slight increases in winter precipitation but drier summers for the IPNW. These conditions combined with elevated atmospheric CO2, which promote crop growth and improve transpiration-use efficiency, may be beneficial for cropping systems in the IPNW and may provide regional opportunities for agricultural diversification and intensification. Crop modeling simulation under future climatic conditions showed increased wheat productivity for the IPNW for most of the century. Water use by winter wheat was projected to decrease significantly in higher and intermediate precipitation zones and increase slightly in drier locations, but with winter crops utilizing significantly more water overall than spring crops. Crop diversification with inclusion of winter crops other than wheat is a possibility depending on agronomic and economic considerations, while substitution of winter for spring crops appeared feasible only in high precipitation areas. Increased weed pressure, higher pest populations, expanded ranges of biotic stressors, and agronomic, plant breeding, economic, technology, and other factors will influence what production systems eventually prevail under future climatic conditions in the region.

Calibration and validation of APSIM-Wheat and CERES-Wheat for spring wheat under rainfed conditions

Phenology, the first step of calibration of models.Robustness of APSIM-Wheat and CERES-Wheat in simulating spring wheat phenology, LAI, biomass and yield.Calibration is necessary to minimize uncertainty.Models as decision support tools in agriculture under climate variability. Crop growth in process based crop models is controlled by different parameters. Model calibration is necessary for application to new cultivars and environment. We applied a manual method to calibrate APSIM-Wheat and CERES-Wheat for the flowering day, maturity day, leaf area index, biomass and grain yield of five spring wheat cultivars under rainfed conditions in Pakistan. Five wheat cultivars of diverse origin namely Tatara, NARC-2009, Sehar-2006, SKD-1 and F-Sarhad were planted on 19th November, at Islamabad during the years 2007-2011. The experiments were laid out in Randomized Complete Block Design (RCBD) replicated four times with individual plot size of 5m?3m. APSIM-Wheat and CERES-Wheat were calibrated for all five wheat cultivars using genetic coefficients estimated based upon measured data during 2008-09 cropping year and validated with independent data sets (experimental data of 2009-10 and 2010-11 cropping seasons) which were not used for models calibration. Both models were able to accurately simulate anthesis and maturity days, maximum leaf area index, biomass and grain yield, with normalized root mean square error (RMSE) less than 10%, D-index greater than 0.80 and model efficiency above 80% in most cases. The temporal changes in maximum LAI accumulation for all cultivars indicate that both measured and simulated values match each other. Evaluation with the measured data showed that performance of both models was realistic as indicated by the accurate simulation of crop phenology, LAI, biomass and grain yield against measured data. Climate variability results depicted that an increase in temperature from 0?C to 5?C resulted in a 60% average decline in the yield of wheat cultivars while increased CO2 increased yield similar to the combined effect of increased temperature and CO2. We concluded that to bring accuracy in the simulation outcomes of models, new cultivars should be calibrated to minimize uncertainty to allow judicious recommendations in response to climate variability.

Scion/interstock/rootstock effect on sweet cherry yield, tree size and yield efficiency

Abstract Yield and trunk cross-sectional area of ‘Bing’ and ‘Chinook’ cherries were measured on four tart cherry interstocks, ‘Kansas Sweet’, ‘Northstar’, ‘Montmorency’ and ‘Redrich’, and on four rootstocks, Mahaleb 4, Mahaleb 900, F 12-1 Mazzard and New York Mazzard, over a 20-year period. Additional treatments included both scions on either mahaleb or mazzard rootstocks without interstocks. Fifty-seven percent of total mortality was associated with ‘Redrich’ interstock, with no other single treatment showing disproportionately high mortality. After 20 years, cumulative yield was highest on Mahaleb rootstocks, but there were no significant differences in cumulative yield among interstocks. Trees lacking interstocks had significantly lower cumulative yield than trees with interstocks. Trunk cross-sectional area of ‘Bing’ was smaller than ‘Chinook’, and ‘Northstar’ produced smaller trunks than other interstocks tested. However, trees without interstocks tended to have smaller trunks than those with interstocks, although not significantly smaller than those with ‘Northstar’ interstocks. Trunk cross-sectional area was not affected by rootstock. Yield efficiency of ‘Bing’/‘Northstar’/Mahaleb 4 was the highest of the combinations tested.

Projected Dryland Cropping System Shifts in the Pacific Northwest in Response to Climate Change

Agriculture in the dryland region of the Inland Pacific Northwest (IPNW, including northern Idaho, eastern Washington and northern Oregon) is typically characterized based on annual rainfall and associated distribution of cropping systems that have evolved in response to biophysical and socio-economic factors. Three agro-ecological classes (AEC) have been proposed for the region: a) crop/fallow (CF), b) annual crop/fallow transition (CCF), and c) continuous cropping (CC). AECs attempt to associate land use into relatively homogeneous areas that result in common production systems. Although there is an interest in sustainable intensification of cropping systems (e.g., reduction of fallow), the question remains whether climate change will preclude intensification or shift the borders of existing AECs toward greater fallow utilization. A simulation study was conducted to address this question, with the aim of classifying 4x4 km pixels throughout the region into one of the three AECs for baseline (1979-2010) and future periods (2030s, 2015-2045; 2050s, 2035-2065; 2070s, 2055-2085). Baseline data were derived from traditional rotations and historical climate records. Data for future projections were derived from atmospheric CO2 concentration considering daily weather downloaded from 12 global circulation models and 2 representative concentration pathways (RCP 4.5 and 8.5). Due to the direct effect of atmospheric CO2 on photosynthesis and stomatal conductance, the transpiration use efficiency of crops (TUE; g above-ground biomass kg water-1) showed an increasing trend, with winter wheat TUE changing from 4.76 in the historical period to 6.17 and 7.08 g kg-1 in 2070s, depending on AEC. Compared to the baseline, total grain yield by the 2070s in the region was projected to increase in the range of 18% to 48% (RCP 4.5) and 30% to 65% (RCP 8.5), depending on AEC. As a consequence of these changes, compared to the historical baseline period, the future fraction of the area classified as CF decreased from 50% to 39-36%, CC increased from 16% to 24-28%, and CCF decreased slightly (~1%), with the greater change projected for the RCP 8.5 scenario.

Rootstock effects on responses of potted ‘Smoothee Golden Delicious’ apple to soil-applied triazole growth inhibitors. I: Shoot and root growth

Abstract Emulsions containing 0, 1, 10 or 100 mg paclobutrazol, uniconazole or triapenthenol in 100 ml water were applied to the soil of potted cultivar ‘Smoothee Golden Delicious’ apple ( Malus domestica , Borkh.) on M 9, M 7a or MM 111 rootstocks (M = Malling, MM = Malling-Merton). Percentage reductions in shoot length were greatest for trees on MM 111 and M 7a, and least for M 9. Mean shoot lengths of treated trees compared to controls were 64% for MM 111, 69% for M 7a and 75% for M 9. Within rootstocks, triapenthenol caused the greatest and uniconazole the least reduction in shoot growth and stem cross-sectional area per unit increase in dosage. The marginal effectiveness for reduction in shoot length and cross-sectional area was greatest for triapenthenol and least for uniconazole, but the reverse was true for a reduction in shoot dry weight. Rootstock effect on root dry weight at the end of the experiment depended on the chemical used and the dosage applied. Total root growth was small in all treatments.

Growth and fruit production of young micropropagated apple (Malus domestica Borkh.) trees

Abstract Tree size, cumulative yield, yield efficiency and anchorage of six micropropagated (MP) apple ( Malus domestica Borkh.) cultivars were determined in 1991 after 5 years of fruit production, as compared with trees budded on domestic seedling (sdlg) or Malling (M) 7a roots. Trees were planted in 1984, with crops harvested from 1987 through 1991. Trees of all scions except cultivar ‘Rome’ were smaller (as determined by trunk cross-sectional area) on M 7a than for MP trees. MP trees of cultivar ‘Delicious’, cultivar ‘Jonathan’, cultivar ‘Rome’ and cultivar ‘Spartan’ were larger than trees on sdlg, while the opposite occurred with ‘Golden Delicious’ (GD). Cumulative yield was affected by a scion × rootstock interaction, with few consistent trends in scion or rootstock effects. Yield efficiency was also affected by a scion × rootstock interaction. In 1991, cumulative yield efficiency on M 7a was superior to other rootstocks with all scions except GD, while the efficiency of sdlg and MP trees was statistically similar with all scions. In general, cumulative yield efficiency for M 7a was twice that for sdlg and MP trees. Nearly all trees leaned in response to prevailing westerly winds, with trees on sdlg generally more upright than MP or M 7a trees.