Seed potato quality as influenced by high temperatures during the growth period. 1. Effect of storage temperature on sprout growth

Summary In the Negev area of Israel potatoes are grown in two seasons of the year: spring and autumn. Locally grown seed of cv. Up-to-Date prepared for the autumn season are grown in the spring under high-temperature conditions during the last part of the growth period. The response to storage temperature treatments consisted of different degrees of sprouting. Temperatures that encouraged bud development (12–22°C) shortened the dormant period of the tubers by about a month, and usually there is clear apical dominance. However, increasing length of the apical bud was positively correlated with storage temperature. Partial loss of apical dominance was obtained when the tubers were held at a low temperature (4°C) for at least two months after lifting. After transfer of the tubers to high temperatures for another month, there were 3 or 4 sprouts per tuber. The physiological age of seed tubers developing in the semi-arid region is discussed. Contribution from the Agricultural Research Organization, Beit Dagan, Israel 1979 Series, No 300.     

Changes in endogenous abscisic acid,soluble sugars and proline levels during tuber dormancy inSolanum tuberosum L.

Abscisic acid (ABA), sucrose, reducing sugars and proline contents were monitored over an eleven-month period in tubers of three potato cultivars that varied in tuber dormancy. ABA and proline levels increased after top pulling the haulms and were not affected by harvest date. Proline did not change in either a storage temperature or cultivar-specific manner. The highest concentrations of ABA were found in tubers stored at 2°C while the lowest concentrations occurred in tubers stored at 20°C. At 10°C, the end of tuber dormancy in the cultivars Kennebec and Nooksack (but not Sebago) coincided with the decline in ABA content. There was no evidence of a threshold concentration of ABA below which sprouting would occur. Tuber samples of 10 different cultivars were removed from 10°C and placed in 20°C storage (in darkness). Initial ABA concentrations (i.e., at the time of removal from 10°C storage) were positively correlated with duration of dormancy and negatively correlated with subsequent rates of sprout elongation at 20°C. Sucrose content was negatively correlated with duration of dormancy. Reducing sugars responded primarily to storage temperature and did not appear to be related to dormancy or sprouting.     

Advancing growth vigor of seed potatoes by a haulm application of gibberellic acid and storage temperature regimes

Seed tubers that are planted soon after their harvest give low yields because of dormancy and low growth vigor. In the research reported in this paper, we investigated the advancing effect of a haulm application of gibberellic acid (750 g GA/ha) 6 days before haulm pulling and its interaction with storage temperature regimes on the growth vigor of immaturely harvested seed tubers of three cultivars. The effects on tuber yield were also examined in one experiment. The storage regimes were: 18 C continuously, hot pre-treatments of different duration (different periods at 28 C and subsequently 18 C) and a cold pre-treatment (20 days at 2 C and subsequently 18 C). Both a foliar spray with GA and storage at 28 C enhanced physiological aging of the tubers and greatly advanced the growth vigor, without negative effects on the morphology of the plants. There was a clear interaction between the GA treatment and the storage temperature regime. At early planting, the effect of the treatments on tuber yield were small for Diamant (short dormancy), but strongly positive for Désirée and Draga (long dormancy).     

Shortening dormancy of seed potatoes by storage temperature regimes

Summary Four experiments (three with four cultivars, one with twenty cultivars) investigated the effect of different storage temperature regimes on the duration of dormancy of seed potatoes harvested immature. Regimes included constant temperatures (18 and 28°C), hot pre-treatments (20 days at 28°C and subsequently 18°C) and cold pre-treatments (20 days at 2°C and subsequently 18°C). Compared with 18°C, storage at 28°C slightly prolonged dormancy of some cultivars with a genetically short dormancy and shortened dormancy by up to 45 days in cultivars with a long dormancy. Some tubers of one cultivar lost their ability to sprout after storage at 28°C for 90 days. A hot pre-treatment shortened dormancy by 2–3 weeks on average, for all cultivars examined. A cold pre-treatment shortened dormancy by 2 weeks on average in some cultivars with a short dormancy and in all cultivars with a long dormancy.     

Variation in the duration of tuber dormancy within a seed potato lot

Summary The variation in duration of dormancy within a seed tuber lot was studied over three years by harvesting individual plants of cvs Diamant and Désirée from field plots and by storing the tubers at 18°C. The variation in dormancy within a tuber lot was large (especially for cv. Diamant) and was mainly caused by variation within plants. For cv. Diamant there was a close negative relation between dormancy and the cube root of tuber weight, whereas for cv. Désirée a relation with tuber weight was almost absent. The duration of dormancy of a seed lot comprising tubers with a narrow range in weight can be well described by two parameters. It is proposed to maintain the moment of 80% sprouting as the criterion for the end of dormancy of a tuber lot and to characterize the spread in dormancy duration by the time lapse between 10% and 90% sprouting.     

Influence of post harvest temperature treatments,storage period and harvest date on development of spraing caused by tobacco rattle virus and potato mop-top virus

Summary The frequency of PMTV-spraing and TRV-spraing increased during storage in several cultivars. The only exception was cv. Saturna, where a decrease was observed in 1992. A spraing inducing treatment of one week at 18 °C followed by one week at 8 °C immediately after an early harvest increased the frequency and provided a rough estimate of the development of spraing in untreated tubers during storage. Under most circumstances wound healing at 25 °C compared with 15 °C resulted in a lower frequency of spraing during the storage period. The date of harvest had an important influence on development of spraing during storage and on the effect of post harvest temperature treatments. Therefore, physiological processes that induce or erase spraing are strongly related to tuber maturity. The mechanisms controlling development of symptoms seemingly are identical for the two spraing inducing vira.     

Relation between growth conditions and dormancy of seed potatoes. 3. Effects of light

Summary The effects on the dormancy of progeny tubers of the timing and level of shading during plant growth were investigated in three field experiments. The tubers were harvested while immature. Shading (50–75%) the crop shortly before haulm pulling shortened dormancy by 5–7 days in two experiments. However, dormancy was hardly affected by 50% shading in one experiment, carried out in a sunny dry period. The effects of the photoperiod during tuber bulking on dormancy were studied in two indoor experiments. Plants were grown at 18/12°C (day 12h/night) and a 12 h photoperiod. Shortly after tuber initiation, the photoperiod was extended to 18 h for 4–6 weeks by photosynthetically inactive incandescent light, or kept at 12 h. The effects of the photoperiod on dormancy were up to 9 days, but differed between the cultivars and experiments. Generally, the effects on tuber dormancy of differences in growth conditions, as reported in this series of papers, were limited.     

Seed Potato Performance after Storage in Light at Elevated Temperatures

In regions with short growth seasons, it is of great importance to use potato (Solanum tuberosum L.) seed tubers with a high growth vigour and a short growth cycle. Such qualities may be obtained by treatments advancing the physiological age of the seed tubers. In this study, we have exposed tubers from four cultivars to various combinations of temperature and light conditions (green-sprouting) for 3–7 months in controlled climate. Subsequent sprout quality, seed tuber health and performance were studied in laboratory, greenhouse and field trials. Satisfactory short, sturdy and leafy sprouts were produced even after 7 months storage at 15 °C under light exposure. An assay of black scurf (Rhizoctonia solani) on the tuber skin showed that light exposure significantly reduced the occurrence compared with dark-stored tubers, while the average effect of storage temperatures was insignificant. In general, green-sprouting advanced emergence and plant growth by 1–2 weeks, and showed early tuber initiation and growth, compared to untreated material. Yields, 107 days after planting in the field trial, did not deviate significantly from untreated tubers. However, plant development at harvest was in accordance with general responses to physiological ageing of potato seed tubers, i.e. still tall and immature plants from untreated tubers, and short and mature plants from aged tubers. Results demonstrated the possibility of successful long-term storage of potato seed tubers in light at elevated temperatures and a potential for earlier harvests and higher early yields from such treatments.     

Enzyme-linked immunosorbent assay (ELISA) for the detection of potato leafroll virus and potato virus Y in potato tubers after artificial break of dormancy

Summary Conditions necessary for the detection of potato leafroll virus (PLRV) and potato virus Y (PVY) in tubers from primary and secondary infected plants were investigated. Tubers were analysed before and after breaking dormancy by rindite treatment. PLRV was reliably detected indormant tubers whereas PVY was readily detected only when tubers had been rindite-treated and held for two to three weeks at 22°C and high humidity in the dark. PLRV occurred in higher concentration at the heel end than at the rose end of infected tubers and the concentration remained nearly unchanged during the experimental period of 35 days, whereas PVY was found to be more concentrated at the rose end and was rapidly accumulating in the tubers after the break of dormancy. In dormant tubers PVY concentration dropped during storage at 22°C. The use of ELISA for tuber indexing is discussed.     

Changes in the potato (Solanum tuberosum L.) tuber at the onset of dormancy and during storage at 23°C and 3°C. I. Biochemical and physiological parameters

Summary In the last 30 d of potato (Solanum tuberosum L.) tuber growth metabolic activity decreased. Levels of glucose-6-P and sucrose in whole tuber tissues declined and in tuber slices there was a decrease in the uptake from the medium and in the incorporation into macromolecules of [U-¹⁴C]sucrose. During storage at 23°C only the uptake of [U-¹⁴C]sucrose increased concomitant with tuber sprouting, indicating a possible involvement of the transport mechanisms in dormancy breaking. At 3°C, levels of reducing sugars and sucrose increased in response to the low temperature and increased release of K⁺ and malondialdehyde levels indicated cell membrane damage. The cell membrane functionality was restored at sprouting. The sprouting potential of the tubers was evaluated using the sprouting ability of single-bud explants (“seedcores”) in response to water, GA₃ or ABA dips. This sprouting potential of tubers changed with stage of tuber growth and storage duration and temperature, indicating that the tissue hormonal state changed strongly throughout tuber life, probably in relation with the “sink” to “source” transition.     

Effect of Storage and Pre-sprouting Regimes on Seed Potato Performance in Norway

Physiological quality affects vigour and yield potential of potato seed tubers. Under short-season conditions, a seed tuber should preferably produce a short cycle and mature crop. The aim of the current studies was to assess how various storing and pre-sprouting treatments affect growth vigour and yield formation. Results showed that different low-temperature storage regimes before pre-sprouting treatments had no clear effects although some minor differences between treatments occurred. For pre-sprouted (‘green’-sprouted) seed tubers, results from field trials in southern Norway (2007–2008) showed that emergence of cvs Asterix and Saturna improved significantly compared to unsprouted seed. Total yields increased significantly for both cultivars in 1 out of 2?years. For Saturna, a major increase in number of tubers per plant resulted in larger proportions of smaller-size grades and thus lower marketable yields. In other trials (northern Norway, 2006–2007), varying duration of pre-sprouting did not affect growth vigour and yield. For number of tubers and size grades, the results varied significantly between pre-sprouting durations, but differently among trials, so no clear conclusions can be drawn. In one of the two trials, increased duration of pre-sprouting resulted in higher proportions of the smaller sizes at the expense of large tubers. Different levels of temperature sums during pre-sprouting (ca. 200 or 400?day-degrees >4?°C) did not affect seed performance. In conclusion, our studies showed that pre-sprouting may improve growth vigour and increase the proportion of smaller grade sizes.     

The effect of temperature and light during storage of young seed potatoes on initial plant development at early plantings

Summary Young seed tubers of several cultivars were exposed to storage temperatures of 4–24°C in light and dark intended to optimise their growth vigour following early plantings. In five experiments during four autumn and winter periods, the effects of storage conditions on subsequent initial plant development in the glasshouse were studied. Storage of seed potatoes for 2 months at temperatures of 12°C or higher greatly increased early plant development of five cultivars following early plantings. Light during storage had a favourable effect, but desprouting before planting was greatly disadvantageous.     

Relation between growth conditions and dormancy of seed potatoes. 2. Effects of temperature

Summary In two indoor experiments under short day conditions, the effect of temperature during tuber bulking on dormancy of tubers was investigated for cvs Diamant and Désirée. Temperature treatments started after tuber initiation and lasted for 4 weeks, after which the haulm was removed. In Experiment 1, the day/night temperature regimes 18/12, 22/22, 26/18 and 32/12 °C (T18/12 etc.) were compared. In Experiment 2, three day temperatures (18, 24 and 30 °C) were combined with three night temperatures (12, 18 and 24 °C), resulting in nine treatments. The dormancy of cv. Diamant was shortest after very high day temperatures (30–32 °C), but intermediate day temperatures (22–26 °C) had no shortening effect compared to T18/12. Dormancy of cv. Désirée was not shortened, but rather tended to be prolonged by high temperatures (22–32 °C) during growth. High temperatures during growth resulted in more sprouts per tuber after dormancy had ended.     

Seed potato quality as influenced by high temperatures during the growth period. 2. Sprouting pattern in several cultivars in response to storage temperature

Summary Locally grown seed tubers of nine varieties developing in spring or in autumn in a semi-arid region were examined for length of dormancy and for sprouting response. In spring, high temperatures during the last part of tuber development markedly shortened the dormant periods of tubers in comparison with tubers of the same varieties developing in autumn. The sprouting behaviour of tubers indicated that it is a varietal characteristic influenced by the change in environmental conditions during tuber development and storage. On tubers developing in spring and stored at high temperatures, three sprouting patterns were defined: a) apical dominance, characterized by the evident development of the apical sprout and less than 10% sprouting of the non-apical buds; b) apical influence, the apical sprout well developed and 10–20% sprouting of the non-apical buds; and c) simultaneous sprouting of 3 or 4 sprouts of similar size per tuber. It is suggested that apical dominance is a relative rather than an absolute phenomenon. The extent of dominance depends upon the variety's response to the high temperatures during tuber growth and storage. Contribution from the Agricultural Research Organization, Beit Dagan, Israel, 1979 Series, No 301.     

Growth rate and carbohydrate metabolism of potato tubers exposed to high temperatures

Summary The effect of high tuber temperature (30 °C) on the growth rate and carbohydrate metabolism of tubers was studied with 3 cultivars differing in heat tolerance. Subjecting individual tubers to 30°C for 6 days caused cessation of tuber growth. During this period, non-treated tubers (20°C) on the same plant increased in volume. At 30°C, incorporation of¹⁴C-labelled assimilates into the ethanol-insoluble fraction (mainly starch) as well as the starch content was significantly reduced. In contrast, the incorporation of¹⁴C-labelled assimilates into the sugar fraction was not affected by high tuber temperature. At 30°C the activity of some of the enzymes involved in starch metabolism was depressed. Varietal differences in responses of tuber growth rate and carbohydrate metabolism to high tuber temperature were insignificant. From these preliminary results it is concluded that high soil temperatures may decrease starch content of potato tubers directly by inhibition of the conversion of sugars into starch.     

Relation between growth conditions and dormancy of seed potatoes. 1. Effects of nitrogen

Summary The duration of dormancy of seed potatoes varies between years and between origins. Therefore, the effects of conditions during crop growth on dormancy of progeny tubers were studied. The effect of nitrogen during tuber bulking on the duration of dormancy was investigated in three field experiments with two cultivars. In addition to an application of 125 kg N/ha at planting, top dressings of 0–150 kg N/ha were given about 2 weeks after tuber initiation. Haulm was pulled about 4 weeks later. The effect of nitrogen rate at planting was also examined in one experiment. Nitrogen top dressings shortened dormancy in all experiments by 5–8 days. An increased nitrogen rate at planting resulted in a shorter dormancy when the duration of dormancy was expressed in days after tuber initiation, but not when it was expressed in days after haulm pulling, probably because extra nitrogen also delayed tuber initiation.     

Effects of Foliar and Tuber Sprout Suppressants on Storage of Ware Potatoes under Tropical Conditions

Potato (Solanum tuberosum L.) is an important source of dietary carbohydrate and cash income generation for farmers in the tropical highlands of Kenya. The feasibility for cold storage at the farm level is limited due to the high costs of maintaining such a facility and there is limited data on the long-term post-harvest storage and quality of tubers of tropical-adapted cultivars. Application of sprout suppressants to control premature sprouting of ware potato is an attractive proposition. The objectives of this study were to evaluate the efficacy of pre-harvest foliar applications of paclobutrazol (PBZ) and ethephon for sprout suppression on ware potato tubers in storage. Post-harvest spray applications of Isopropyl N-(3-chlorophenyl carbamate) chloropropham (CIPC) and 1,4-dimethylnaphthalene (DMN) on tubers as fog was also evaluated. Potato cultivars had varying levels of tuber dormancy. The tubers were stored at ambient temperature (23 C) and evaluated weekly for 24 weeks for percent of tubers sprouting, length of longest sprouts, tuber weight loss and assessed for dormancy for 24 weeks. Paclobutrazol prolonged tuber dormancy by 21–31 days and reduced tuber weight loss. Ethephon treatment had no effect on dormancy and tuber weight loss. Potato tubers treated with CIPC had greater sprout control than the other treatments in storage. Tuber response to DMN treatment varied among the three potato cultivars evaluated. The findings from this study imply that PBZ is effective in prolonging potato tuber dormancy for short-term basis at 23 C, while CIPC applied on tubers was effective for long term storage. Optimization of post-harvest potato storage can improve food security in the highland tropics.     

Changes in the potato (Solanum tuberosum L.) tuber at the onset of dormancy and during storage at 23°C and 3°C. II. Evaluation of protein patterns

Summary The changes in polypeptide profiles (2D-PAGE) occurring in the soluble and microsomal fractions of parenchymatic tissue of potato (Solanum tuberosum L.) tubers were studied during the last 30 d of maturation and during storage at 23°C and 3°C. The major changes were observed in the last period of tuber maturation, when several polypeptides disappeared and new ones appeared. At both 23°C and 3°C specific polypeptides disappeared in dormant tubers and new polypeptides appeared during storage. At 3°C specific changes in protein composition occurred, particularly in the microsomal fraction. The changes in polypeptide profiles are discussed in relation to the transition from “sink” to “source” of the tuber, the onset of dormancy and of sprouting ability and the activation of cold acclimation responses. The results are also discussed on the basis of the physiological and biochemical changes that occur in the parenchymatic tissue.     

A method to assess cultivar differences in rate of physiological ageing of seed tubers

Inter-cultivar differences in rate of physiological ageing of potato tubers were assessed in a laboratory test and field tests. The physiological status of the seed tubers was varied by storing them at 4°C and a range of higher temperatures for 28 weeks (= excluding curing and pre-sprouting periods), after which tubers were desprouted. In a laboratory test, growth vigor was assessed by determining number and weight of sprouts after 28 days of incubation. In a field test, percentage emergence, total plant height, haulm and tuber weights were determined and a stand score was allocated 4 weeks after emergence of the 4°C storage treatment. Ageing indices were calculated by dividing the values for the warm-stored treatments by values for the tubers stored at 4°C. Using the tests the cultivars were scored from 0–10 and ranked accordingly. The indices were more evenly distributed over the range of 0–10 in the field test than in the laboratory test. Fresh haulm yield proved very suitable for calculating ageing indices but it could be replaced by a visual score of the haulm development without a great loss in accuracy     

Changes in ascorbic acid content during growth and short-term storage of potato tubers (Solanum tuberosum L.)

Changes in ascorbic acid levels were followed in apical and basal portions of Russet Burbank and Kennebec tubers during growth and development. Influence of nitrogen fertilization during growth and short-term storage on ascorbic acid level of the tuber was also studied. Changes in ascorbic acid content during growth showed two distinct phases, the first phase being characterized by an increase in ascorbic acid content with growth and development of the tuber, followed by a second phase which showed a decrease in ascorbic acid content with increasing maturity. The shift from the first phase to the second phase occurred earlier for Kennebec than for Russet Burbank. Increased nitrogen fertilization resulted in a delay of this shift from the first to the second phase. The apical portion of the tuber consistently showed higher ascorbic acid content than the basal portion. Kennebec tubers were higher in vitamin C content than tubers of Russet Burbank cultivar. High nitrogen fertilization resulted in less ascorbic acid content during growth. Storage of tubers for four weeks at 5.5°C also resulted in a marked decrease in ascorbic acid content of tubers. Nitrogen fertilizer rate during growth had no influence on the decrease in ascorbic acid content of tubers in storage.