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Tuber dormancy and sprouting are commercially important potato traits as long-term tuber storage is necessary to ensure year-round availability. Premature dormancy release and sprout growth in tubers during storage can result in a significant deterioration in product quality. In addition, the main chemical sprout suppressant chlorpropham has been withdrawn in Europe, necessitating alternative approaches for controlling sprouting. Breeding potato cultivars with longer dormancy and slower sprout growth is a desirable goal, although this must be tempered by the needs of the seed potato industry, where dormancy break and sprout vigour are required for rapid emergence. We have performed a detailed genetic analysis of tuber sprout growth using a diploid potato population derived from two highly heterozygous parents. A dual approach employing conventional QTL analysis allied to a combined bulk-segregant analysis (BSA) using a novel potato whole-exome capture (WEC) platform was evaluated. Tubers were assessed for sprout growth in storage at six time-points over two consecutive growing seasons. Genetic analysis revealed the presence of main QTL on five chromosomes, several of which were consistent across two growing seasons. In addition, phenotypic bulks displaying extreme sprout growth phenotypes were subjected to WEC sequencing for performing BSA. The combined BSA and WEC approach corroborated QTL locations and served to narrow the associated genomic regions, while also identifying new QTL for further investigation. Overall, our findings reveal a very complex genetic architecture for tuber sprouting and sprout growth, which has implications both for potato and other root, bulb and tuber crops where long-term storage is essential.

During long-term storage of apples, detection of low O2 stress is used to optimise low O2 storage regimes for dynamic controlled atmosphere (DCA) storage. Monitoring respiratory characteristics, specifically the respiratory quotient (RQ), provides a tool to achieve this. The objectives of this study were to evaluate protocols to monitor response of apple consignments to low O2 using a respiration chamber, the SafePod, designed for use in commercial stores and research laboratories, and to compare the RQ response to changes in chlorophyll fluorescence (CF) yield from the fruit skin as used in DCA-CF. Protocols to identify the lowest oxygen limit (LOL), the O2 concentration below which RQ rises, were tested using ‘Braeburn’ (sensitive to low O2) and ‘Gala’ (less sensitive to low O2). A protocol that allows fruit to acclimatise at each O2 concentration takes several weeks and is therefore not practical for commercial use. A rapid profile without fruit acclimatisation can be completed in 2–3 days. Although this underestimates RQ values, and results in an increase in RQ at a higher O2 concentration than observed for acclimatised fruit, the rapid RQ protocol provides a practical method to compare response of apple consignments between cultivars, orchards and seasons. By the rapid protocol, the LOL of ‘Braeburn’ consignments was near 0.6 kPa and of ‘Gala’ consignments was near 0.2 kPa, consistent with detection of alcoholic taints below the LOL in each case. The RQ response using the SafePod was consistent with increase in CF yield using HarvestWatch™. Fruit respiration rates change through the storage season, including a substantial decrease over the first 2 months after harvest. As RQ response is affected by respiration rate, accurate comparison of consignments depends on profiles being measured at the same stage in the storage season. It is more difficult to determine the LOL by RQ profiling later in the season when respiration rates are lower.

Curing of freshly harvested yams (Dioscorea spp.) is a process for wounded yams during harvest to heal. In this work the effectiveness of straw, polypropylene and jute sack on curing of seven key farmers’ yam varieties over a duration of 7, 14 and 21 days was studied. Seven key farmers’ yam varieties identified as Pona, Lariboko, Dente, Mutwumudoo, Serwah belonging to D. rotundata, Matches and Akaba belonging to D. alata were studied under different curing treatments. The percentage weight loss of yam tubers varied among the treatments over curing period. Curing under jute sack showed all yam varieties had weight losses less than 2.0%, within 7 days of curing. Five different varieties had weight loss less than 2.0% except Dente under the straw treatment. Mutwumudoo variety showed the highest water loss (8.4%) for polypropylene sheet and 6.9% for Lariboko in the control treatment. During 7 days curing the control and polypropylene treatment did not support yam curing. After 14 days of curing of tubers, similar tends were observed as in 7 days curing. After 14 days of curing under jute sack, percentage weight loss of the tubers ranges from 2.0% - 3.7%. In the straw treatment, the percentage weight loss ranges between 1.0% - 4.7% in all other varieties except Dente (D. rotundata) (8.2%). Polypropylene sheet treatment showed the highest percentage weight loss in Mutwumudoo variety (18.4%). A similar trend was observed for the yam tubers cured for 21days as percentage weight loss of tubers under jute sacks was 2.5 – 9.8%. Curing temperature and humidity ranged between 27&degC - 40&degC and 87% - 100% rh for yam tubers under the three different treatments of polypropylene, jute and straw. However, the control treatment recorded lower humidity of 60% - 80% rh. Curing material, duration, climatic conditions and yam varieties influenced curing and Serwah variety, which is a D. rotundata is the best bet yam variety to cure under jute sack for 7, 14 and 21 days of curing.

Exogenous ethylene is commonly used as a commercial sprouting inhibitor of potato tubers. The role of ethylene in the control of sprouting of sweetpotato roots, however, is not known. The aim of this study was to investigate the role of ethylene in control of sprouting in sweetpotato roots by observing the effect of an ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), and the ethylene antagonist, 1-methylcyclopropene (1-MCP), in the presence and absence of exogenous ethylene on root sprouting and associated sugar accumulation. Continuous exposure to 10 μl L−1 ethylene, 24 h exposure to 625 nl L−1 1-MCP or dipping in 100 μl L−1 AVG all inhibited sprout growth in sweetpotato roots of two varieties over 4 weeks of storage at 25 °C. The observations that both ethylene on its own and 1-MCP, which inhibits ethylene action, inhibit sprout growth indicate that while continuous exposure to exogenous ethylene leads to sprout growth inhibition, ethylene is also required for sprouting. In potato tubers ethylene is required to break dormancy, while continuous exposure inhibits sprout growth. Monosaccharide concentrations in ethylene, 1-MCP or AVG treated roots were lower than in untreated roots, and for ethylene treated roots this was associated with higher respiration rates. This is consistent with the activation of some additional process by ethylene which uses energy through sugar metabolism. 1-MCP and AVG both inhibited this increase in respiration rate and counteracted the decrease in monosaccharide concentrations. 1-MCP presumably counteracts the ethylene stimulation of this process, while the effect of AVG is attributed to its possible inhibitory effects on protein synthesis.

Two hot pepper hybrids; 'Wonder King' and 'P-6' were grown under high plastic tunnels and fruits were picked at their horticultural maturity stage i.e., full green color with uniform size and shape. The study was conducted to determine the best polyethylene packaging material and low temperature treatment to maximize the shelf life of green hot peppers. Freshly harvested fruits were stored at a range of temperatures; 7, 14 and 21°C in a range of packaging; 7, 15 and 21 µm thick polyethylene bags or unpacked (control) and their post harvest quality was assessed. Minimum weight loss for 'P-6' was observed for fruits stored at 7°C in 7 µm thick polyethylene bags, whereas for 'Wonder King' minimum weight loss was for fruits stored at 7°C in 21 µm thick polyethylene bags. Maximum ascorbic acid in 'P-6' was 53 mg 100 g-1 when stored at 14°C packed in 15 µm thick polyethylene bags whereas in the case of 'Wonder King' maximum ascorbic acid was 107 mg 100 g-1 at 7°C with 7 µm thick polyethylene bags. Total phenolic compounds were 53.62 mg 100 g-1 for 'P-6' when stored at 7°C unpacked while no significant differences were found in 'Wonder King'. No significant carotenoid differences were recorded for 'P-6' whereas maximum total carotenoids (5.93 mg 100 g-1) were found for fruits stored at 7°C with 7 µm thick polyethylene bags. Total sugars, reducing sugars and non reducing sugars in 'P-6' were estimated at 9.16, 2.71 and 2.59% whereas in the case of ‘Wonder King’ these were 6.53, 1.37 and 1.27% at 21°C in open conditions, respectively. Maximum shelf life (20 days) was recorded for 'P-6' at 7°C in 15 µm thick polyethylene bags while in 'Wonder King' maximum shelf life was 10 days at 7°C using 15 µm thick polyethylene bags.

Given the increasing importance of organic produce, a study was carried out to find out how organic production methods affect postharvest and storage quality of ‘Conference’ pears (Pyrus communis). When fruit were taken out of cold storage and artificially infected either with Monilinia fructigena or Penicillium expansum disease development was significantly slower in organic pears than in conventional pears. The effects were more marked for M. fructigena which is the more aggressive pathogen (about 20% inhibition of lesion growth rate), compared with a smaller, but significant effect on P. expansum (5-10% inhibition of lesion growth rate). Organic pears had higher dry matter content (15.6% compared with 14.7%) and were firmer than conventionally-produced fruit, which may affect the rate of pathogen growth. Analysis of total phenols indicated an increase induced by infection by either pathogen, but no significant differences either before or after infection between organically and conventionally-produced pears.

Chlorophyll fluorescence has been tested by many researchers as a non-invasive method to assess physiological damage in chlorophyll containing fruits and vegetables. The characteristic Fv/Fm is most commonly considered. One draw-back of this method is that the fluorescence signal is affected primarily by the state of photosystem II, which is one of the components most sensitive to stresses, including heat, chilling and oxidative stress, so that the Fv/Fm may be more sensitive than the overall tissue. A more reliable strategy may be to look at the ability of the tissues to resynthesise photosystem II after damage, by looking at the rate of Fv/Fm recovery. This strategy shows promising results in predicting chilling injury in peppers and cucumbers, and heat stress in asparagus. Trials are also reported that attempt to predict low temperature injury in apples, but the results are not definitive.

Alternative methods for disinfestation of asparagus against thrips (Thrips tabaci) need to be developed for the Thai export trade, ensuring efficient thrips’ mortality, while maintaining quality and environmental safety. Hot air/water using temperatures of 40-60°C and high CO2 treatments were studied at laboratory level. An appropriate treatment involving hot water at 45°C for 15 min, with or without high CO2 treatment, followed by hydro-cooling with water at ambient temperature (~20°C) was identified. Methods to assess quality, such as objective tests (% mass loss, force measurement, colour measurement) and subjective tests (appearance, decay, off-odour, snap-test for texture) gave no indication of significant quality deterioration. Chlorophyll fluorescence and ion leakage measurements were used to assess physiological stress. The Fv/Fm ratio which indicates the intactness of photosystem II was shown to decrease immediately after all heat treatments tested, but recovered over 24h for non-damaging heat treatments (42.5 and 45°C). A rise in % K+ leakage was observed that increased with treatment temperature but recovered over 24h following treatment at 45°C. High CO2 showed neither significant detrimental effect nor indication of physiological stress, and could kill thrips although not at a sufficiently high rate. Confirmatory trials to demonstrate the efficacy of these treatments in Thailand using naturally infested asparagus were carried out. The mortality rate of thrips was as high as when this method was tested in the UK. Adoption of the selected disinfestation method into existing process lines in Thailand would not be too complicated.

An understanding of the control of sprouting of sweetpotatoes (Ipomoea batatas) is important, both for marketing of sweetpotatoes in the developed world and for the role of the crop for food security in the developing world. Long-term storage of sweetpotatoes requires inhibition of sprouting, while stimulation of sprouting is necessary for the production of planting material. Many studies have been conducted on the control of sprouting/dormancy of potatoes whereas sprouting in sweetpotatoes is less studied. Recently, exposure to ethylene has been introduced as a commercial method for controlling of sprouting in potatoes. Data presented here show that 20 ppm ethylene is effective in controlling sprouting in sweet potato over 4 weeks of storage at 25°C. Gibberellins appear to have a key role in stimulating sprout growth in potato. Trials using gibberellins and gibberellin synthesis inhibitors suggest that gibberellins are likewise involved in the stimulation of sprouting in sweetpotatoes.

It has previously been shown that sweetpotato cultivars differ in the efficiency by which their roots can heal wounds at low humidity, although this does not appear to relate to rate of wound-healing at high humidity. It has also been shown previously that there is a negative relationship between cultivar root dry matter (DM) content and efficiency of root wound-healing at low humidity (assessed by a lignification score; LS). Root DM content tends to be negatively related to root sugar levels. The study presented here was undertaken to examine further the role of carbohydrates in root response and ability to heal wounds in the presence of water stress. Data from 17 cultivars confirmed the negative correlation between LS and DM and the positive correlation between LS and root sugar levels. Measurement of sugar levels at the root surface both at the time of wounding and after complete healing (5 days) for 10 cultivars indicated a stronger relationship of LS with final sugar levels than initial DM content. This was confirmed in further experiments using a system of adjacent tissue cuboids cut from the parenchyma which were able to exhibit lignification almost as efficiently as whole roots. With this system it was also possible to demonstrate a relatively rapid accumulation of sugars within 24 h of healing. The data were examined further by the development of linear regression models of LS. Comparison of the levels of variance accounted for by the models indicates that LS is strongly cultivar dependent, and most of the cultivar effect is related to cultivar differences in sugar levels during wound-healing. Differences in sugar levels between roots/cuboids of each cultivar also have an effect. Further, the similarity of the models for the whole roots and cuboids gives us confidence in the validity of using the cuboids to investigate wound-healing of whole roots.

The effect of continuous exposure to ozone on quality changes during the storage of red bell peppers, cucumbers and zucchini was investigated. Peppers were stored at 14 °C and were exposed to ozone at 0.1 and 0.3 μmol mol−1, while cucumbers and zucchini were stored at 12 and 8 °C, respectively, and exposed to ozone at 0.1 μmol mol−1. The content of fructose (2.75 g/100 g FW) and glucose (2.00 g/100 g FW) in red bell peppers exposed to ozone at 0.1 μmol mol−1 was increased by 8 and 7%, respectively, when compared to controls. Continuous exposure to ozone at 0.3 μmol mol−1, on the other hand, had no effect on fructose (2.52 g/100 g FW) and glucose (1.88 g/100 g FW) content. The content of vitamin C was significantly enhanced in red bell peppers exposed to ozone at 0.1 and 0.3 μmol mol−1 after 7 d of storage, however, this effect was not maintained. After 14 d, vitamin C content in peppers exposed to ozone at 0.1 μmol mol−1 was not significantly different from the control, whereas it was reduced at 0.3 μmol mol−1. Total phenolics content was increased in peppers exposed to ozone at 0.1 μmol mol−1, but was unaffected at 0.3 μmol mol−1. Continuous exposure of red bell peppers to ozone at 0.1 and 0.3 μmol mol−1 had no significant effect on weight loss, texture and colour. In cucumbers and zucchini, continuous exposure to ozone at 0.1 μmol mol−1 reduced weight loss by more than 40% and improved texture maintenance, while having no significant effect on their biochemistry. The findings from this study suggest that continuous exposure to ozone at 0.1 μmol mol−1 is a promising method for shelf-life extension of cucumbers and zucchini. Even though in red bell peppers continuously exposed to ozone at 0.1 μmol mol−1 sugars and phenolics content was increased, further work is still needed to better understand the exact mechanism of ozone action and its potential for the industrial use.

This paper presents a study on the wound healing processes in sweetpotatoes ( Ipomoea batatas Lam.) when exposed to tropical conditions typical for marketing (RH 50–73%, T 25–30 °C). The physiological processes during healing were revisited. At low humidities (65% ± 10) the depth of the lignified layer i.e. the thickness of the desiccated cell layers was affected by both cultivar and humidity. Some cultivars consistently failed to produce a lignified layer and for others the layer was often not continuous. The continuity of the lignified layer was more important for effectiveness of wound healing than the actual thickness. A method for assessing efficiency of wound healing based on assessing the continuity of lignified layers was developed, and called the lignification score. Wound healing efficiency as measured by the lignification score was found to be a major factor for the shelf-life of sweetpotato cultivars. Lignification of wounds correlated with reduced rate of weight loss and reduced susceptibility to microbial infection. A high dry matter content in cultivars correlated with a low lignification score. This relationship was consistent for five trials, including 34 cultivars.

Under marketing conditions in tropical developing countries sweetpotatoes have a shelf-life of only 1 to 2 weeks. Storage trials conducted under simulated tropical marketing conditions showed that root shrivelling due to weight loss and rotting are the two major forms of deterioration. Measurement of respiration rates indicated that under these conditions weight loss is primarily (86%) due to water loss. Under these environmental conditions rotting is promoted by water loss, which is therefore the driving force of deterioration. For the cultivars studied, a large range in rates of weight loss was found, which was consistent between seasons, suggesting that breeding for extended shelf-life is feasible. A range of root quality characteristics were assessed, including dry matter content, sugar content, surface area, initial weight, rough weevil ( Blosyrus spp.) damage, latex production, cortex thickness and hardness of the tissue. Multiple regression models for rates of weight loss indicated that dry matter content and root monosaccharide content were important controlling factors. Cultivars with low dry matter content and with high monosaccharide levels lose less weight. The two characteristics are related, and we do not know which more directly affects rates of weight loss. Other root characteristics were less important, although it was found that root size and pre-harvest rough weevil damage had significant effects.

Grain yields of eight representative semidwarf spring wheat (Triticum aestivum L.) cultivars released in northwest Mexico between 1962 and 1988 have increased linearly across years as measured in this region during 6 yr under favorable management and irrigation. To understand the physiological basis of this progress and possibly assist future selection for grain yield, leaf traits were determined during 3 yr in the same study. Stomatal conductance (g(S)), maximum photosynthetic rate (A(max)), and canopy temperature depression (CTD), averaged over the 3 yr, were closely and positively correlated with progress in the 6-yr mean yield. The correlation was greatest with g(S) (r = 0.94 P < 0.01). Compared with the overall yield increase of 27%, g(S) increased 63%, A(max) increased 23%, and canopies were 0.6 degree C cooler. Carbon-13 isotope discrimination was also positively associated with yield progress (r = 0.71, P < 0.05), but other leaf traits such as flag leaf area, specific leaf weight, percentage N and greeness were not, nor was crop growth rate around anthesis. The causal basis of the leaf activity interrelationships is reasonably clear, with both increased intercellular CO2 concentration and increased mesophyll activity contributing to the increase in A(max). However, causal links to the yield progress, and the accompanying increase in kernels per square meter, are not clear. It is concluded that g(S) and CTD should be further investigated as potential indirect selection criteria for yield.

Sweet potato is an important staple food crop in East Africa, but under local marketing conditions it has a shelf life of generally no longer than 2 weeks. As a result, the potential for marketing over longer distances is limited. The role of changes in sensory properties and weight loss as limiting factors for shelf-life were investigated. The important sensory attributes of five sweet potato cultivars were determined in discussion sessions with four taste panels and were: floury, sweet, chestnutty, grainy, smooth, soft, fibrous, discoloration, and moist. The sensory profiles of the five cultivars (KSP20, Kemb10, Yanshu 1, Pumpkin, and SPK004) differed significantly (P < 0.001). However, after 4 and 8 weeks under simulated tropical storage conditions (26 °C, 80% to 90% RH) no significant changes in the attributes were detected in most cases (P > 0.05). Changes in sensory properties were therefore not considered to limit shelf life. Shelf life experiments in Tanzania under simulated marketing conditions (26 + 5 °C, 50% to 60% RH) with 29 local cultivars revealed that roots with high rates of weight loss also rot rapidly. It was found that weight losses (primarily due to water loss) were high and varied significantly among cultivars (12% to 45% loss in 21 days). Further studies will investigate the structure and strength of the periderm as the main barrier to water loss to facilitate future cultivar selection.