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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 In addition, the main chemical sprout suppressant chlorpropham has been withdrawn in Europe, necessitating alternative approaches for controlling sprouting.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.

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.

The fresh produce industry is constantly growing, due to increasing consumer demand. The shelf-life of some fruit, however, is relatively short, limited by microbial contamination or visual, textural and nutritional quality loss. Thus, techniques for reducing undesired microbial contamination, spoilage and decay, as well as maintaining product’s visual, textural and nutritional quality are in high demand at all steps within the supply chain. The postharvest use of signalling molecules, i.e. jasmonates and salicylates, seems to have unexplored potential. The focus of this review is on the effects of treatment with jasmonates and salicylates on the fresh produce quality, defined by decay incidence and severity, chilling injury, maintenance of texture, visual quality, taste and aroma, and nutritional content. Postharvest treatments with jasmonates and salicylates have the ability to reduce decay by increasing fruit resistance to diseases and reducing chilling injury in numerous products. These treatments also possess the ability to improve other quality characteristics, i.e. appearance, texture maintenance and nutritional content. Furthermore, they can easily be combined with other treatments, e.g. heat treatment and ultrasound treatment. A good understanding of all the benefits and limitations related to the postharvest use of jasmonates and salicylates is needed, and relevant information has been reviewed in this paper.

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.

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.

Five sweet potato cultivars (Kemb10, SPK004, KSP20, Yan Shu 1 and Zapallo) were analysed for their sensory characteristics and changes herein during storage under tropical conditions. Nine descriptors for sweet potato were derived after brainstorming and quantitative descriptive analysis (QDA). These were: floury, smooth, soft, chestnutty, sweet, fibrous, grainy, moist and discoloration. Significant differences were observed among the cultivars profiles. A principal component analysis (PCA) revealed two principal components (PC1 and PC2) explaining in total 68% of the variation. PC1 explained 52% and correlated with textural properties, and PC2 explained 16% of the variation and correlated with flavour components. The results suggest that differences between sweet potato cultivars are mainly determined by textural components. Storage had most effect on the sweet and chestnutty characteristics, and did not affect the texture characteristics. Overall the changes during storage were less significant than the differences between the 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.

Sweetpotato weevils ( Cylas spp.) constitute a major constraint upon sweetpotato production and utilization world-wide. Attempts to breed for resistance to Cylas spp. have had limited success. However, there are reports of variation in the susceptibility to weevil attack in the field among cultivars in East Africa. Field trials were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine the extent to which sweetpotato cultivars presently available in East Africa consistently differ in their susceptibility to field infestation by Cylas spp. and to identify the plant factors that determine the levels of susceptibility. Several methods to assess levels of field infestation were tested, and their relative merits are discussed. Significant cultivar differences in susceptibility to Cylas spp. infestation were observed for four out of six trials carried out over 2 years. The exceptions were cases where infestation levels were either very low or very high. Linear...

The response of the sweetpotato weevil Cylas puncticollis (Coleoptera: Brentidae) to roots of different sweetpotato cvs was investigated as part of a project to examine the factors that affect susceptibility of sweetpotato cvs to weevil infestation in the field. Laboratory experiments were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine if the harvested storage roots of sweetpotato cvs differed in their acceptability to C. puncticollis or if any root antibiosis towards C. puncticollis existed. For all experiments cultivar effects for the total number of emerging adults were significant to at least 10% and in most cases were much more significant. At Ukiriguru and Kibaha, the results showed reasonable consistency between years, and of the four cultivars used at both sites, fewer C. puncticollis adults emerged from roots of Sinia and Budagala than from SPN/0 and Mwanamonde on all occasions. A relationship between laboratory experiments and crown dama...

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.

Exposure of chromatophores of Rhodobacter capsulatus to a high light intensity (10 000 μE m −2 s −1 ) in the presence of oxygen results in non-photochemical quenching of bacteriochlorophyll fluorescence and a decrease in the quantum yield of charge separation at the reaction centre. Several observations support the hypothesis that this is due to the formation of a quencher in the light-harvesting antennae. The relationship between quenching of the maximum fluorescence yield F m and the dark-level fluorescence yield F o fits theoretical predictions for antenna quenching, while the decrease in photochemical quantum yield is proportional to the decrease in F v / F m (where F v = F m — F o ). The number of functional reaction centres appears to be unchanged. No change in redox dependence of charge separation can be detected, suggesting that no damage of the reaction centre occurs. It is suggested that the quencher is formed by the oxidation of some species. Consistent with this, quenching is inhibited by the removal of oxygen. Aerobic quenching can be observed in mutants lacking either the outer light-harvesting complex LHII or both the reaction centre and the inner light-harvesting complex LHI indicative of quenching throughout the light-harvesting apparatus. Under anaerobic conditions there is still some light-dependent inhibition of quantum yield of charge separation by a distinct process that does not effect F v / F m . The mechanism of this process is unknown

A new hypothesis is presented to explain the major molecular process that regulates the efficiency of light harvesting by chloroplast membranes. It is proposed that in excess light the decrease in the thylakoid lumen pH causes an increase in aggregation of the light harvesting complexes of photosystem II resulting in formation of an efficient pathway for non-radiative dissipation of excitation energy. The aggregation is potentiated by the conversion of violaxanthin to zeaxanthin. This hypothesis is based upon (i) similarity between the spectroscopic changes associated with energy dissipation and those observed upon aggregation of isolated light harvesting complex; and (ii) the link between changes in light scattering and increased energy dissipation.

Thylakoids isolated from light-treated spinach leaves (‘light’ thylakoids) which contain significant zeaxanthin levels show amplification of high-energy-state chlorophyll fluorescence quenching (qE) with respect to the transthylakoid pH gradient, when compared to thylakoids from dark-adapted leaves (‘dark’ thylakoids) which contain no zeaxanthin. In 77 K fluorescence emission spectra q E in ‘dark’ thylakoids shows maximal quenching with respect to fluorescence yield near 680 nm, whereas in ‘light’ thylakoids additional quenching occurs near 700 nm, which is associated with the appearance of a chlorophyll species absorbing at long wavelengths. It is suggested that this long-wavelength species is associated with an aggregated state of LHC II.

The quenching of variable fluorescence yield (qN) and the quenching of dark level fluorescence yield (q0) directly atributable to high-energy-state fluorescence quenching (qE) was studied to distinguish between energy dissipation in the antenna and light harvesting complexes (antenna quenching) and energy dissipation at the reaction centres (reaction centre quenching). A consistent relationship was obtained between qN and q0 in barley leaves, the green alga Dunaliella C9AA and in pea thylakoids with 2,3,5,6-tetramethyl-p-phenylene diamine (DAD) as mediator of cyclic electron flow around PS 1. This correlated well with the relationship obtained using m-dinitrobenzene (DNB), a chemical model for antenna quenching, to quench fluorescence in Dunaliella C9AA or pea thylakoids. The results also correlated reasonably well with theoretical predictions by the Butler model for antenna quenching, but did not correlate with the predictions for reaction centre quenching. It is postulated that qE quenching therefore occures in the antenna and light harvesting complexes, and that the small deviation from the Butler prediction is due to PS 2 heterogeneity.

Although sweetpotato is primarily grown for home consumption, marketing is becoming increasingly important, and in this case, short shelf-life of the roots is a major constraint. An assessment of the levels of damage of sweetpotatoes when they arrive at urban markets indicated that between 49% and 93% roots exhibited some form of damage. The major types of damage noted were breakages, cuts, infestation by weevils (Cylas spp.), rotting and superficial scuffing. All forms of damage, except superficial scuffing, lead to a shortened shelf-life due to both increased fresh weight loss and rotting. Superficial scuffing increased the rate of rotting but not of weight loss. It was estimated, based on the six cases considered, that the damage resulted in a reduction of shelf-life of between 23% and 47%. Key Words: Ipomoea batatus, post-harvest losses, Tanzania (African Crop Science Journal 2001 9(1): 301-308)

Studies were carried out in the field at Serere Agricultural and Animal Production Research Institute (SAARI), Eastern Uganda, to establish whether the existing sweetpotato germplasm in Uganda has cultivars resistant to the sweetpotato weevils, Cylas spp. The trials were conducted during the two growing seasons of 1997. Root size was the only sweetpotato rooting characteristic that significantly influenced tuber infestation (P=0.009) and damage (P=0.049). Root size was positively correlated to tuber infestation by Cylas spp. (Y=0.0456x + 21.206; R2 = 0.2731) and negatively correlated to damage by Cylas weevils (Y=-0.027x + 29.684, R2=0.1647). A laboratory study demonstrated the effect of temperature on oviposition, survival and developement of Cylas puncticollis (Boheman). The variety 'Tanzania' that was used as the susceptible check registered the highest weevil emergence under both wet and dry weather conditions while varieties 'Kasira' and 'Akere-Ikokolak' registered the least emergence of adult C. puncticollis. These results indicate that the latter two varieties posses considerable levels of resistance to sweetpotato weevils. Key Words: Germplasm, resistance, sweetpotato weevils, Uganda (African Crop Science Journal 2001 9(1): 165-174)

The yield of photosynthetic O2 evolution was measured in cultures of Dunaliella C9AA over a range of light intensities, and a range of low temperatures at constant light intensity. Changes in the rate of charge separation at Photosystem I (PS I) and Photosystem II (PS II) were estimated by the parameters ΦPS I and ΦPS II . ΦPS I is calculated on the basis of the proportion of centres in the correct redox state for charge separation to occur, as measured spectrophotometrically. ΦPS II is calculated using chlorophyll fluorescence to estimate the proportion of centres in the correct redox state, and also to estimate limitations in excitation delivery to reaction centres. With both increasing light intensity and decreasing temperature it was found that O2 evolution decreased more than predicted by either ΦPS I or ΦPS II. The results are interpreted as evidence of non-assimilatory electron flow; either linear whole chain, or cyclic around each photosystem.

31P nuclear magnetic resonance (NMR) saturation transfer has been used to measure enzymatic flux through the creatine phosphokinase reaction in the direction of ATP synthesis in the human forearm muscle flexor digitorum superficialis. Modification of the ratio method for measurement of spin-lattice relaxation (R. Freeman, H. D. W. Hill, and R. Kaptein, J. Mags. Reson. 7, 82 (1972) was tested and used to appreciably shorten the duration of the measurement. Under conditions of steady state work intracellular pH decreased slightly by 0.06 units and the spin-lattice relaxation time of phosphocreatine in muscle was unchanged, while flux from phosphocreatine to ATP was 64 ± 10% of the resting value. This is contrary to the increase in flux of 155% predicted from previous saturation transfer studies carried out in vitro on rabbit skeletal muscle creatine phosphokinase using metabolite concentrations to mimic those in vivo (E. A. Shoubridge, J. L. Bland, and G. K. Radda, Biochim. Biophys. Acta 805, 72 (1984). This discrepancy could be accounted for by an underestimation of the ADP concentrations to which the enzyme is exposed due to inaccurate assumptions about the total metabolite concentrations, or possibly by compartmentation of creatine phosphokinase and its reactants. © 1989 Academic Press, Inc.

The thylakoid membranes of higher plants possess several mechanisms that control both the distribution and rate of dissipation of absorbed light. These mechanisms, which allow regulation of photosynthetic electron transport in response to alteration in external and internal factors, can be observed as the various processes that quench chlorophyll fluorescence. By using the 'light-doubling techniques’, together with analysis of quenching relaxation, it is possible to assess quantitatively the extents of these regulatory processes and to allow their interrelations to be studied. These techniques can be applied to in vitro systems or to leaves, and can be particularly useful when applied with electron-transport measurements and when models are used to aid interpretation. Results of quenching analysis at different light intensities in isolated thylakoids, intact chloroplasts, protoplasts, algae and leaves of a variety of species are presented.

The relaxation of the non-photochemical quenching of chlorophyll fluorescence has been investigated in cells of the green alga Dunaliella following illumination. The relaxation after the addition of DCMU or darkening was strongly biphasic. The uncoupler NH4Cl induced rapid relaxation of both phases, which were therefore both energy-dependent quenching, qE. The proportion of the slow phase of qE increased at increasing light intensity. In the presence of the inhibitors rotenone and antimycin the slow phase of qE was stabilised for in excess of 15 min. NaN3 inhibited the relaxation of almost all the qE. The implications of these results are discussed in terms of the interpretation of the non-photochemical quenching of chlorophyll fluorescence in vivo and the mechanism of qE.