Peter Stephen Kettlewell

Film-forming antitranspirants may help potatoes tolerate moderate drought, but their effects on early tuberisation and tuber size distribution remain unclear. Two pot experiments were conducted in a polytunnel (late summer) and a glasshouse (winter–spring), with moderate drought imposed during tuber initiation and early bulking, alone (DT) or combined with an antitranspirant (di-1-p-menthene; VGDT). Leaf relative water content (RWC), stolon traits, and tuber yield and size distribution were measured. Moderate drought reduced RWC, stolon number, and tuber set, which indicates the sensitivity of early tuber development to water deficit. VGDT increased leaf RWC under drought from 55% to 71% in Experiment 1 and from 62% to 73% in Experiment 2, while the total tuber number under moderate drought increased from 5.2 to 11.7 tubers plant⁻¹ in Experiment 1 and from 6.1 to 10.7 tubers plant⁻¹ in Experiment 2. VGDT also increased the number of large (≥9 cm) tubers, shifting size distribution towards marketable classes. Although Vapor Gard improved plant water status and tuber number under drought, it did not restore performance to irrigated levels. These findings indicate its value as a complementary tool to mitigate drought-related losses during tuberisation, not a substitute for irrigation.

Potatoes (Solanum tuberosum L.) are highly sensitive to water deficits, which compromise both yield and tuber quality, with russeting representing a major disorder that limits marketability. Film-forming antitranspirants, such as Vapor Gard (VG; di-1-p-menthene), may alleviate these effects by reducing transpirational water loss, but their effectiveness under different stress intensities remains uncertain. This study investigated the impacts of moderate and severe drought (targeted at 30% and 20% available water content, respectively) on plant water status, yield, and tuber physiological disorders in two varieties (Challenger and Russet Burbank), and assessed the extent to which VG could mitigate these impacts. Two pot experiments were conducted in a polytunnel using a factorial combination of soil–water regime and VG application. Drought reduced relative water content (RWC) by 30–36% and tuber yield by 29–61%, compared with irrigated plants. Under moderate drought, VG improved leaf RWC by 14–27% and increased yield by 37–67% relative to untreated drought-stressed plants across the two experiments, approaching levels achieved with irrigation. VG’s influence on stomatal conductance was small and inconsistent. VG also consistently reduced russeting in the susceptible Challenger variety, while reductions in necrosis and jelly end rot were observed in Russet Burbank, indicating that disorder responses were variety dependent. Under severe drought conditions, VG provided little additional benefit for plant water status, yield, or disorder incidence. Overall, the results suggest that VG has potential as a management tool for reducing drought-related yield and quality losses in potatoes, particularly under moderate soil water deficit. However, further optimisation of application strategies is required to enhance consistency across environments.

From a perspective of food security, the agricultural sector worldwide has a responsibility to improve crop yields. Wheat yield in Japan is about half that of high‐yielding countries in Northwest Europe. Explanations offered so far—such as high temperatures and a rainy summer season shortening wheat's growth period, or comparatively underdeveloped breeding and cultivation techniques—remain speculative. This lack of clarity risks misdirecting research efforts on wheat cultivation in Japan and possibly other parts of the world. To address the issue, the present study focused on the efficiency of yield formation, rather than yield itself, across Japan and Northwest Europe. The efficiency of yield formation, derived from the division of actual yield by sunshine hours during the specific growth period from ear emergence to maturity, was compared between two geographical regions while factoring in climate variables. Despite the large yield difference, there was no significant difference in the efficiency of yield formation of wheat between the two regions. This indicates that Japan's low yield is largely due to climatic adversity for wheat, that is, high temperature, high precipitation and short sunshine hours during the critical growth phase for yield formation of the crop. The implication is that improvements in breeding and cultivation techniques alone are not likely to significantly increase wheat yield in Japan. A fruitful direction for future research endeavors in wheat production in monsoon Asia was discussed.

Drought severely impacts crop yields, especially wheat. Antitranspirants, which reduce water loss, have been shown to improve crop yield under drought, possibly by increasing pollen viability. To understand the mechanisms, transcriptomic responses were studied in early meiotic wheat anthers extracted from polytunnel-grown plants: well-watered, droughted unsprayed, and droughted plants treated with antitranspirants. Film (Vapor Gard (VG), di-1-p-menthene) and metabolic (Abscisic Acid (ABA), 20% S-ABA) antitranspirants were applied at the flag leaf stage (GS39). Well-watered (WW) plant anthers had more upregulated genes (626 genes) than downregulated ones (226 genes) when compared to droughted unsprayed ones. Most of the differentially expressed genes (DEGs) were transcriptionally downregulated (3959 genes) in droughted, treated-plant anthers (ABA and VG) compared with unsprayed (US), and the number of genes with upregulated expression was lower (830 genes). VG-treated plant anthers had more downregulated genes (3325 genes) than ABA-treated ones (634 genes). Carbohydrate or sugar metabolism and related processes were affected in antitranspirant-treated plant anthers with significant downregulation of genes compared to droughted unsprayed ones; in contrast, these processes were upregulated in well-watered anthers, suggesting broad differences in the transcriptional response. However, antitranspirants did not significantly affect pollen viability or yield in treated plants compared to unsprayed plants, suggesting that anthers are more sensitive at the transcriptomic level than subsequent physiological processes determining yield.

Stomatal blockers are hydrophobic polymers applied to leaves to physically block stomatal pores and restrict gas exchange, and which have potential as plant growth regulators to retard growth. Three experiments in a heated glasshouse, one sown in autumn and two sown in winter, were conducted with pot-grown rapeseed plants at the four-leaf stage to evaluate retardant potential of two bio-based polymers: di-1-p-menthene (DPM) and extracted cauliflower leaf wax. Both stomatal blockers reduced stomatal conductance and plant dry weight in the autumn-sown experiment, when solar radiation was high during leaf development and stomatal conductance of water-treated plants was relatively high. Wax was more effective than DPM at reducing plant dry weight, despite no difference in stomatal conductance. In the two winter-sown experiments, when solar radiation was lower during leaf development, stomatal conductance in water-treated plants was less than in the autumn-sown experiment. Stomatal conductance was reduced by the blockers in the winter-sown experiments, but plant dry weight was unaffected. It was concluded that stomatal blockers may have potential to act as plant growth regulators to retard growth in rapeseed, but further research is necessary to define the circumstances when a response will occur.

Drought severely impacts crop yields, especially wheat. Antitranspirants, which reduce water loss, have been shown to improve crop yield under drought, possibly by increasing pollen viability. To understand the mechanisms, transcriptomic responses were studied in early meiotic wheat anthers extracted from polytunnel-grown plants: well-watered, droughted unsprayed, and droughted plants treated with antitranspirants. Film (Vapor Gard (VG), di-1-p-menthene) and metabolic (Abscisic Acid (ABA), 20% S-ABA) antitranspirants were applied at the flag leaf stage (GS39). Well-watered (WW) plant anthers had more upregulated genes (626 genes) than downregulated ones (226 genes) when compared to droughted unsprayed ones. Most of the differentially expressed genes (DEGs) were transcriptionally downregulated (3,959 genes) in droughted, treated-plant anthers (ABA and VG) compared with unsprayed (US), and the number of genes with upregulated expression was lower (830 genes). VG-treated plant anthers had more downregulated genes (3,325 genes) than ABA-treated ones (634 genes). Carbohydrate or sugar metabolism and related processes were affected in antitranspirant-treated plant anthers with significant downregulation of genes compared to droughted unsprayed ones; in contrast, these processes were upregulated in well-watered anthers, suggesting broad differences in the transcriptional response. However, antitranspirants did not significantly affect pollen viability or yield in treated plants compared to unsprayed plants, suggesting that anthers are more sensitive at the transcriptomic level than subsequent physiological processes determining yield.

Strawberries have a short shelf-life leading to food loss and waste when production unexpectedly exceeds demand. PGRs may have potential to delay production and reduce food loss and waste, but no PGRs are available for delaying strawberry production. The aim of this preliminary study was to investigate re-purposing a stomatal blocking film antitranspirant polymer as a PGR to temporarily delay production. Poly-1-p-menthene or water was applied during early fruit ripening in two glasshouse experiments, one on a June-bearer cultivar and one on an everbearer cultivar. Ripe strawberries were harvested during the next 23 days, the cumulative yield was recorded, and the production curves were fitted using polynomial regression in groups. The statistical analysis showed that cubic polynomial regression curves could be fitted separately to each treatment. Application of the blocker delayed the production of both cultivars by 1–2 days during the period of rapid berry production. The delay diminished and cumulative yield returned to the water-treated value by 13 and 18 days after application in the June-bearer and everbearer cultivars, respectively. At 23 days after application, the blocker gave 8% greater cumulative yield in the June-bearer, but not in the everbearer. It was concluded that, if a greater delay could be achieved, there may be potential to use stomatal blockers as PGRs in some cultivars of strawberry to delay production and reduce food loss and waste when unanticipated lower demand occurs.

Potatoes are highly sensitive to drought, particularly during tuber initiation. This study aimed to evaluate the effectiveness of film-forming (Vapor Gard [VG]) and metabolic (abscisic acid [ABA]) antitranspirants in mitigating drought stress and reducing tuber physiological disorders in four potato varieties. Two experiments examined the effects of VG and ABA antitranspirants on drought-stressed potato plants of four varieties (Challenger, Markies, Nectar, and Russet Burbank) grown in pots in a polytunnel (semi-controlled environment). Experiment 1 imposed severe drought by withholding irrigation until 70% of the available water content was depleted (reaching 15–17% volumetric water content within ~15 days), while Experiment 2 featured gradual drought stress from tuber initiation, with the soil volumetric water content declining to <10% over 30 days. Antitranspirants were applied at the start of the tuber initiation and two weeks later to assess their impact on the soil volumetric water content, stomatal conductance, relative water content, yield, and tuber physiological disorders. Drought significantly reduced the soil and plant water status, tuber yield, and quality across both experiments, with more severe effects observed in Experiment 1. VG and ABA had repeatable effects in both experiments and in all varieties, reducing water stress by preventing a large reduction in the relative water content during the tuber initiation and bulking stages. Both antitranspirants improved the tuber appearance by reducing the tuber skin disorder of russeting in the susceptible Challenger variety in both experiments, with VG being more effective than ABA. Beneficial reductions in the effects of drought from antitranspirants were also recorded in the volumetric water content, stomatal conductance, yield, and jelly end rot but not consistently in all varieties and in both experiments. The results show that antitranspirants have the potential to minimise water stress in droughted potatoes and subsequently reduce the physiological disorder of russeting and improve the tuber appearance of the Challenger variety.

Rapeseed (Brassica napus L.), as one of the most important oil crops around the world, has been affected by drought considerably, particularly at flowering when crops are most sensitive to water stress. It has been shown that film antitranspirant (AT) can effectively reduce the yield loss of droughted crops if applied at the critical stage. However, the mechanism remains unclear by which AT mitigates drought damage to plants under different rates of water depletion. Two experiments in randomised complete block designs were conducted on spring rapeseed with two levels of irrigation, well-watered (WW) and water-stressed (WS), where slow and fast soil water depletion were imposed during the flowering stage in mesocosms (Expt 1_SD) and pots (Expt 2_FD), respectively, and different concentrations of AT, 0, 0.25%, 0.5%, and 1% and 0, 0.5%, and 1%, were applied. Leaf physiological traits, seed yield, and yield components were determined. The results showed that compared to WW, water stress reduced leaf relative water content (RWC) by 2% and 6% in Expt 1_SD and Expt 2_FD, respectively, and had detrimental effects on stomatal conductance, CO₂ assimilation rate, and intrinsic water use efficiency. Following AT application, a positive linear relationship was observed in leaf RWC against AT concentrations, albeit with large variations. In Expt 1_SD, seed dry weight and aboveground biomass increased significantly with increasing AT concentrations, while no yield responses were observed in Expt 2_FD, indicating that soil water status may play an important role in rapeseed responses to AT application regardless of concentrations. Therefore, the timing of AT application needs to consider soil water conditions in addition to the growth development of rapeseed plants.

Wheat and barley yields in Japan are considerably lower than those in the UK, even where similar Climate Zones (CZs) of relatively cold and humid nature are shared. In order to understand this difference, it is first necessary to find out if any common climate–yield relationship exists between the two countries. The Climate Zonation Scheme (CZS) developed in the Global Yield Gap Atlas (GYGA) was used to analyse actual yield (Ya) with three climatic factors of the GYGA-CZS, i.e., growing degree days (GDD), aridity index (AI) and temperature seasonality (TS). A significant relationship was found between AI scores and Ya values across the two countries. Ya values decreased with an increase in AI scores; in other words, lower yields are associated with higher AI scores. In addition, the degree of yield reduction with the rise in AI scores was greater in Japan than in the UK. The present study also proposed a novel method to link CZs of the GYGA-CZS to regional classification units, especially for countries where statistical crop yield data are available only at a coarse scale.