Deficit irrigation based on drought tolerance and root signalling in potatoes and tomatoes

Agriculture is a big consumer of fresh water in competition with other sectors of the society. Within the EU-project SAFIR new water-saving irrigation strategies were developed based on pot, semi-field and field experiments with potatoes (Solanum tuberosum L.), fresh tomatoes (Lycopersicon esculentum Mill.) and processing tomatoes as model plants. From the pot and semi-field experiments an ABA production model was developed for potatoes to optimize the ABA signalling; this was obtained by modelling the optimal level of soil drying for ABA production before re-irrigation in a crop growth model. The field irrigation guidelines were developed under temperate (Denmark), Mediterranean (Greece, Italy) and continental (Serbia, China) climatic conditions during summer. The field investigations on processing tomatoes were undertaken only in the Po valley (North Italy) on fine, textured soil. The investigations from several studies showed that gradual soil drying imposed by deficit irrigation (DI) or partial root zone drying irrigation (PRD) induced hydraulic and chemical signals from the root system resulting in partial stomatal closure, an increase in photosynthetic water use efficiency, and a slight reduction in top vegetative growth. Further PRD increased N-mineralization significantly beyond that from DI, causing a stay-green effect late in the growing season. In field potato and tomato experiments the water-saving irrigation strategies DI and PRD were able to save about 20-30% of the water used in fully irrigated plants. PRD increased marketable yield in potatoes significantly by 15% due to improved tuber size distribution. PRD increased antioxidant content significantly by approximately 10% in both potatoes and fresh tomatoes. Under a high temperature regime, full irrigation (FI) should be undertaken, as was clear from field observations in tomatoes. For tomatoes full irrigation should be undertaken for cooling effects when the night/day average temperature >26.5 °C or when air temperature >40 °C to avoid flower-dropping. The temperature threshold for potatoes is not clear. From three-year field drip irrigation experiments we found that under the establishment phase, both potatoes and tomatoes should be fully irrigated; however, during the later phases deficit irrigation might be applied as outlined below without causing significant yield reduction:

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Potatoes

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After the end of tuber initiation, DI or PRD is applied at 70% of FI. During the last 14 days of the growth period, DI or PRD is applied at 50% of FI.

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Fresh tomatoes

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From the moment the 1st truce is developed, DI is applied at 85-80% of FI for two weeks. In the middle period, DI or PRD is applied at 70% of FI. During the last 14 days of the growth period, DI or PRD is applied at 50% of FI.

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Processing tomatoes

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From transplanting to fruit setting at 4th-5th cluster, the PRD and DI threshold for re-irrigation is when the plant-available soil water content (ASWC) equals 0.7 (soil water potential, Ψ_soil = −90 kPa). During the late fruit development/ripening stage, 10% of red fruits, the threshold for re-irrigation for DI is when ASWC = 0.5 (Ψ_soil = −185 kPa) and for PRD when ASWC (dry side) = 0.4 (Ψ_{soil, dry side} = −270 kPa).

The findings during the SAFIR project might be used as a framework for implementing water-saving deficit irrigation under different local soil and climatic conditions.     

Multi-model comparison on the effects of climate change on tree species in the eastern U.S.: results from an enhanced niche model and process-based ecosystem and landscape models

Context

Species distribution models (SDM) establish statistical relationships between the current distribution of species and key attributes whereas process-based models simulate ecosystem and tree species dynamics based on representations of physical and biological processes. TreeAtlas, which uses DISTRIB SDM, and Linkages and LANDIS PRO, process-based ecosystem and landscape models, respectively, were used concurrently on four regional climate change assessments in the eastern Unites States.

Objectives

We compared predictions for 30 species from TreeAtlas, Linkages, and LANDIS PRO, using two climate change scenarios on four regions, to derive a more robust assessment of species change in response to climate change.

Methods

We calculated the ratio of future importance or biomass to current for each species, then compared agreement among models by species, region, and climate scenario using change classes, an ordinal agreement score, spearman rank correlations, and model averaged change ratios.

Results

Comparisons indicated high agreement for many species, especially northern species modeled to lose habitat. TreeAtlas and Linkages agreed the most but each also agreed with many species outputs from LANDIS PRO, particularly when succession within LANDIS PRO was simulated to 2300. A geographic analysis showed that a simple difference (in latitude degrees) of the weighted mean center of a species distribution versus the geographic center of the region of interest provides an initial estimate for the species’ potential to gain, lose, or remain stable under climate change.

Conclusions

This analysis of multiple models provides a useful approach to compare among disparate models and a more consistent interpretation of the future for use in vulnerability assessments and adaptation planning.

     

Chilling Tolerance of 10 Maize Genotypes as Related to Chilling-induced Changes in ACC and MACC Contents

We studied chilling-induced changes of 1-aminocydopropane-1-carboxylic acid (ACC) and of 1-(malonylamino) cyclopropane-1-carboxylic acid (MACC) contents in seedlings of ten maize genotypes with different chilling tolerance. Seedlings at the third leaf stage were chilled at 5°C and at 65% RH. Immediately before and after two and five days of chilling the contents of ACC and of MACC in the third leaf were measured. Water content and – after recovery – the degree of necrotic injuries and the percentage of seedling survival were also determined.
After 2 days of chilling, the ACC content increased in all genotypes investigated. The increase was significantly higher in the sensitive genotypes than in the tolerant ones. There was a significant correlation between ACC content and necrotic injuries of seedlings. Chilling for 5 days increased the ACC content further and the difference between the two groups of genotypes still existed.
The MACC content increased after 5 days of chilling in all genotypes investigated. The increase was greater in the tolerant genotypes than in the sensitive ones. However, the difference in MACC accumulation between the two groups of genotypes investigated was not significant, and thus no correlation between MACC accumulation and chilling susceptibility was found.
The possible causes for the increase of ACC and MACC contents under chilling conditions and the possibility of using the ACC content as an indicator of chilling tolerance in maize breeding are discussed.     

Plant age and in vitro or in vivo propagation considerably affect cold tolerance of Miscanthus × giganteus

The aims of the study were to determine why young Miscanthus × giganteus plants are more frost sensitive during the first winter than older plants, to compare cold tolerance of plants propagated in in vivo and in vitro conditions, and to select plants with higher cold tolerance. The study was performed in three experiments in which plants were prehardened at 12 °C for 2 weeks, hardened at 5 °C for 3 weeks and next chilled at 0 °C or ?3 °C for 3 or 14 days. Afterwards shoot regrowth from rhizomes was evaluated. In Experiment 1 frost tolerance of young plants obtained from a horticultural farm and plants that had already survived the first winter in the field was compared on the basis of LT₅₀ coefficient. In Experiment 2 frost tolerance of plants obtained in vivo and in vitro was compared. Experiment 3 was performed on four groups of plants: in vivo and in vitro obtained plants which were twice selected in cold, as well as in vivo and in vitro obtained plants which were cold treated once. Plants of all these groups were analysed with respect to their frost tolerance. They were prehardened, hardened and subjected to a temperature of 0 °C or ?3 °C for 14 days. The changes in processes accompanying cold acclimation occurring in the rhizomes or leaves of these plants were investigated. The content of abscisic acid, low-molecular antioxidants and phenolics, as well as catalase and non-specific peroxidase activities were analysed.Young commercially obtained plants were more frost sensitive than plants which had survived the first winter in the field. This effect could be caused by a small amount of storage compounds accumulated in finely divided rhizomes produced in a horticultural farm. Prehardening temperature of 12 °C caused more considerable changes in cold acclimation processes in Miscanthus rhizomes than hardening temperature of 5 °C. Plants propagated by in vitro culture were more cold tolerant but only in the first vegetative season compared to plants obtained in vivo. Plants chilled twice demonstrated a higher low-molecular antioxidant level, as well as a greater capability of phenolic accumulation compared to plants which were once cold stressed. Regardless of the recurrence of cold acclimation, ABA level was significantly increased in leaves by prehardening and in rhizomes by hardening. Each repetition of cold acclimation increased cold tolerance and shoot regeneration ability of M. × giganteus rhizomes.     

Lethal temperature for pinewood nematode, Bursaphelenchus xylophilus, in infested wood using radio frequency (RF) energy

We evaluated radio frequency (RF) dielectric heating for eradication of pinewood nematodes (PWN) in infested wood. Thirteen temperatures were tested (from ambient to 70 °C) on small wood samples (2.5 × 3.8 × 0.64 cm) to determine the minimum lethal temperature (100 % mortality), which was 56 °C [based on infra-red (IR) thermal images data 55.5–57.4 °C] with a 1 min hold time. We also used thermal probes inside the wood to confirm that temperatures were ≥56 °C. Thirty additional samples were tested bracketing the minimum lethal temperature using 54, 56 and 58 °C with additional replications to produce the minimum sample size equivalent of 100 % mortality of at least 93,616 nematodes to satisfy the Probit 9 efficacy requirement. This minimum lethal temperature was further verified by treating infested large wood blocks (10.2 × 10.2 × 25.4 cm). All samples that met or exceeded the 56 °C lethal temperature for the required 1 min hold time (as measured by probes inserted in the wood and on the wood surface by IR) produced 100 % mortality. The sample size required to show Probit 9 efficacy was also satisfied. This study supports the consideration of RF in addition to microwave (MW) dielectric heating as alternative treatments of wood packaging material for inclusion in ISPM No. 15, provided the treatment delivers the target lethal temperature throughout the profile of the material in industrial scale operations.     

Changes in abscisic acid, salicylic acid and phenylpropanoid concentrations during cold acclimation of androgenic forms of Festulolium (Festuca pratensis × Lolium multiflorum) in relation to resistance to pink snow mould (Microdochium nivale)

We investigated changes in concentrations of abscisic (ABA) and salicylic acid (SA), phenolic compounds and phenylalanine ammonia-lyase (PAL) activity in relation to cold-induced tolerance of four androgenic genotypes of Festulolium ( Festuca  ×  Lolium hybrids ) to frost and to the snow mould fungus Microdochium nivale . Cold acclimation increased frost tolerance and resistance to snow mould. Resistant genotypes were characterized by higher ABA concentrations during the first 54 h of cold acclimation and lower concentrations of SA than susceptible genotypes. After cold acclimation, the content of phenolics was significantly lower in genotypes tolerant to frost and M. nivale infection than in susceptible genotypes, while PAL activity was significantly higher. Signalling networks controlling cold acclimation to frost (abiotic) and mould infection (biotic) appears to involve increases in foliar concentrations of ABA and decreases in the SA level during successful cold acclimation. Higher PAL activity and lower concentrations of phenolic compounds also appear to be associated with enhanced tolerance to frost and fungal attack.     

Effect of Low Soil Temperature on Weight Increase, Gas Exchange and Distribution of 14C-Assimilates in Seedlings of a Maize Hybrid

Seedlings of a maize hybrid sensitive to chilling initially grew in the growth chamber of the phytotron at 20/ 17°C (day/night) and after the formation of the fourth leaf, the soil temperature was lowered to 5°C. Under such growth conditions the dynamics of dry weight change, gas exchange and the distribution of ¹⁴C-assimilates in seedlings were examined. The low soil temperature inhibited daily growth of dry weight of whole seedlings more than their photosynthesis. Simultaneously, it was also responsible for a greater increase in dissimilative losses.
During 37 hours (day-night-day), following exposure to ¹⁴CO₂, dissimilation in seedlings in cool soil (5°C) and in non-chilling conditions amounted to 35.1 % and 23.4 % of assimilated ¹⁴C (AC), respectively. At lower soil temperature relatively high dissimilative losses were observed on the first day after exposure (23.5 %), lower at night (9.9 %) and the lowest on the following day - merely 1.7 % AC. Higher losses of ¹⁴C under chilling conditions occurring on the first day were a result of limited photosynthetic refixation of ¹⁴CO₂ At night, however, they were associated with a prolonged period of intensive translocation of assimilates to the stem. It was assumed that an excessive accumulation of assimilates in leaf blades might be an additional factor responsible for increased dissimilative losses at low temperature during the first twenty-four hours. In the third period of measurements, as a result of a limited transport of ¹⁴C, dissimilative losses were lower than in previous ones and were not dependent upon soil temperature.     

Physiological Effects of Winter Rape (Brassica napus var. oleifera) Prehardening to Frost. I. Frost Resistance and Photosynthesis during Cold Acclimation

The objective of the research was to define the changes in photosynthetic activity induced by prehardening and to determine their involvement in frost tolerance of winter rape.
Prehardening of winter rape, consisting of keeping the plants at + 12°C during the light periods from sprouting until the beginning of the 1st stage of cold hardening, contributed to increasing its effectiveness. After 42 days of hardening at + 2°C the resistance of the prehardened plants equalled that attained by winter rape in the most favourable seasons of vegetation in the field. Prehardening stimulated the efficiency of photosynthesis at chill temperatures (+ 2–5°C). Differences in photosynthetic efficiency, like those in frost resistance, increase with successive weeks of hardening. They also concern the leaves already developed at the hardening temperature. A prehardened photosynthetic apparatus is less susceptible to the progress of photoinactivation taking place when the seedlings are kept at + 2°C. It also demonstrated greater activity even during the first hour of hardening or in the newly expanding leaves, and also at higher temperatures, most probably because of the more efficient progress of the dark, processes. The described changes in the functioning of the photosynthetic apparatus induced by prehardening were thus qualitatively very similar to those observed during long-term growth at + 5°C. already described in the literature.     

Role of the maternal effect phenomena in improving water stress tolerance in narrow‐leafed lupine (Lupinus angustifolius)

This paper describes experiments concerning improvement of drought tolerance in narrow‐leafed lupine (Lupinus angustifolius L.) by maternal effects. The first step involved harvesting seeds from plants exposed and not exposed to drought during flowering and seed ripening. The next‐generation plants grown from these seeds were exposed to drought and the effects of this stress on their physiological processes were examined. To find out whether drought applied to parent plants may affect tolerance to this stress in progeny plants such features as plant growth, tissue water content, abscisic acid concentration and yield‐related parameters were assessed. The study revealed that the progeny plants grown from the seeds of drought‐treated plants were more tolerant to this stress than the plants grown from the seeds harvested from optimally watered maternal plants. Drought tolerance was manifested by a reduced concentration of abscisic acid, increased plant height and maintaining high leaf water content. Most importantly, these plants produced significantly higher yield when exposed to drought than the plants grown from the seeds harvested from optimally watered plants.