Morphological changes in tuber buds during dormancy and initial sprout growth of seed potatoes

Summary Potato tuber dormancy is usually defined as lasting from tuber initiation until a sprout of 2 mm long has been formed under storage conditions optimal for sprouting. We tried to find out whether there is a period during which buds of seed tubers do not grow and whether different batches of seed take the same time to grow sprouts 2 mm long. We measured changes in number of leaf primordia and length of tuber buds of cvs Diamant and Désirée over two years. After early haulm pulling, buds did not grow for at least 60 days (‘Diamant’) or 95 days (‘Désirée’). Buds in both cultivars and two tuber weights of ‘Diamant’ took about 20 days from the estimated onset of sprouting to grow 2 mm long. We question whether this period is always similar and thus whether the moment sprouts 2 mm long have formed is a good criterion for the end of dormancy.     

Effects of a short period of drought on changes in tuber volume and specific leaf weight. I. Long-term changes

Summary Single-stemmed potato plants, cv. Bintje, were grown on a nutrient solution under controlled conditions. They were exposed to a short drought stress, or remained untreated. Long-term measurements of tuber volume were carried out with a non-destructive volume-meter. Specific leaf weight was monitored with a β-gauge. Tubers from the same plant varied in rate and duration of growth. The relative growth of stressed tubers was 43–54% less than that of the control tubers. The hierarchy of tubers from one stem changed over time in plants that were exposed to the stress. Specific leaf weight declined during the stress period but there was a prompt recovery after the relief from drought. This response was similar to the response of the average rate of volume increase of the tuber.     

Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 2. Tuber yield and dry matter accumulation and other tuber properties

Summary The effect of repeated short periods of water stress during the hot season on six potato cultivars was investigated. The number of tubers per plant tended to decrease in response to water stress in cultivars which had more than 9.8 tubers per control plant (Désirée, Alpha, Elvira). In the other cultivars, no consistent effect of water stress on tuber number per plant was observed. Except for Spunta, the percentage of large tubers (>60 g/tuber) was reduced in the water-stressed plants. Consequently, the average weight of these tubers was greater than that of tubers harvested from the unstressed plants, indicating that the sink force of the individual tuber was not impaired by drought. However, tuber yield per plant was reduced due to drought in all cultivars tested. The smallest decrease in dry matter accumulation as well as the greatest lowering of the osmotic potential in the tuber tissue was found in Alpha. No consistent effect of water stress on the percentage of misshapen and sprouting tubers was observed, indicating the marked effect of the high temperature on these traits. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No 310-E, 1981 series. This investigation was sponsored by a grant from the Ministry for Development Cooperation of the Netherlands.     

Estimating tuber dry matter concentration from accumulated thermal time and soil moisture

Summary The tuber dry matter concentration, [DM], of crops of potato (Solanum tuberosum L.) was related using regression analysis, to time, thermal time, incident radiation accumulated from plant emergence, and soil moisture deficit (SMD). Variation in [DM] was best accounted for by the regression model that was a function of thermal time above a base of 0 °C accumulated from plant emergence, and SMD. When validated against an independent data set, there was good agreement between observed and estimated [DM] with a linear relation accounting for 79.3% of the variance.     

Observations on the bulking and development of tuber size distribution in maincrop potatoes at Rothamsted in 1964–75

Summary Tuber samples taken at 2-week intervals from plots of cvs King Edward, Majestic and Pentland Crown in 1964–75 showed that the maximum bulking rates ranged from 1 to 5 tonnes/hectare/week. Maximum tuber numbers were usually produced by 11 weeks after planting and thereafter numbers declined. In September, about 70% of the tubers initiated were recovered, and between 24 and 52% of the tubers had reached marketable size (>4 cm). Tuber size distributions developed similarly in all years with all cultivars. During tuber initiation the distributions appeared as one population, and usually between 9 and 11 weeks after planting a second population of larger tubers developed. The population of small tubers later declined although in most years it was still present in September. This development fitted a model based on a mixture of two normal distributions and was determined by five parameters; the proportion of tubers in the small population and the means and standard errors of both populations.     

Yield, water use efficiency and nitrogen uptake in potato: influence of drought stress

Summary A lysimeter experiment was performed to study the optimal allocation of limited water supply in potatoes. Irrigation regimes equal to 40, 60 and 80% of maximum evapotranspiration (ET) were evenly applied over the crop cycle. Other treatments involved withholding 80 mm of irrigation, based on ET, beginning at each of three designated growth stages (tuber initiation, early and late tuber growth). An irrigated control treatment, restoring the entire ET, was included for comparison. Continuous drought stress reduced photosynthesis as irrigation volumes were reduced. Plant biomass and tuber yield decreased almost proportionally to water consumption, so that WUE was roughly constant. N uptake was highest in the control and in 80% ET treatment. Withholding water during tuberisation severely hindered plant physiological processes and penalized tuber yield. Reductions in photosynthesis, total biomass and yield were the greatest when drought was imposed during tuber initiation. The earliest stress resulted in the lowest WUE and N uptake. A new crop water stress index (SI) was proposed, which combines atmospheric demand for water and canopy temperature.     

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.     

Effects of a short period of drought on changes in tuber volume and specific leaf weight. II. Diurnal changes

Summary Single-stemmed potato plants, cv. Bintje, were grown on a nutrient solution under controlled conditions. They were exposed to a short drought stress, or remained untreated. Short-term changes in tuber volume and in specific leaf weight were measured non-destructively. Tubers from control plants increased rapidly in volume during the night and did not grow, or even shrivelled during the day. Tubers of stressed plants did not show a uniform response; some tubers markedly declined in volume during the day. The patterns of volume increase of stressed plants became erratic after the stress, mainly because some plants never fully recovered. Patterns of diurnal fluctuation in tuber volume were similar to diurnal changes in specific leaf weight; tubers within the same stressed plant sometimes reacted differently. In these cases the effects on the diurnal fluctuation partly reflected the long-term effects, reported in an earlier paper.     

Intercellular spaces enhance potato tuber elasticity

Summary The intercellular volume within tuber tissue increases with tuber maturation. At the same time, both tuber injury after mechanical load and lentical perforation after water uptake by tubers in wet peat decreases. The degree of tuber injury is correlated with intercellular space (r=−0.667,n=16) and with water saturation of tissue (r=0.697,n=16). The tubers lose water during storage. In wet soil wilted tubers take up significantly higher amounts of water than turgid tubers, and lenticel perforation is much more frequent. Tuber maturation in autumn and low water loss during storage enhance the cushioning effect of the intercellular gas volume of tuber tissue against outside mechanical load and internal tension after water uptake.     

Osmotic potential of potatoes subjected to a single cycle of water deficit

Summary Potato plants (Solanum tuberosum L.) of the cultivars Alpha, Cara, Blanka, Désirée and Idit, were exposed to a transient water deficit during tuber growth. Drought stress increased the concentration of solutes as assessed by refractometry and lowered the osmotic potentials as assessed by cryoscopy in both leaf and tuber tissues of the five cultivars. Differences among cultivars, as well as between leaf and tuber tissue of the same cultivar, could indicate variability of the soluble components contributing to the osmotic potential. Differences were noted in the response of the cultivars to the environment in terms of osmotic potentials. Essentially, two types of responses were identified: transient maintenance of lower osmotic potential for 24–48 h after stress relief; and inherently high concentration of solutes and low osmotic potential. The possible advantage of sensitivity to environmental changes is also considered. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 3010-E, 1990 series. This study was supported by the Ministry of Foreign Affairs, Technical Assistance Department, the Netherlands.     

Genetic variation in the response of andigena potatoes to inorganic fertilizers

Summary Tuber yield, dry matter and true protein content were studied in 24 andigena potato genotypes. Their performance and response differed greatly and significantly when grown at three levels of inorganic N, P and K fertilizer application. In general, tuber yield and protein content increased with increased fertilizer level, whereas dry matter content initially decreased but then increased significantly with fertilizer additions. For all three characteristics, genotype x fertilizer interaction was significant, and although there was a wide genetic variability for relative responsiveness of different genotypes, no significant undesirable association was detected for performance. The genotypes JEX/A 674, 706 and 744 are most promising and could be used for wide-scale cultivation and for breeding.     

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.     

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.     

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.     

Aspects of nitrogen fertilizer rate on tuber dry-matter content of potato cv. Record

Summary Effects of three rates of fertilizer nitrogen, viz. 80, 160 and 240 kg N/ha, on tuber yield and dry-matter percentage in potato cv. Record were compared in two experiments. Crop nitrogen uptake increased with application rate but total uptake differed between experiments. Tuber yield was highest following application of 160 or 240 kg N/ha but differences between these two rates were not significant. Tuber dry-matter percentage was reduced in one experiment with increasing nitrogen rate, but in the second experiment final dry- matter percentage was highest following application of 240 kg N/ha. In all treatments, positive linear relationships were found between dry matter percentage and mean fresh weight of tubers >30 mm, but within experiments, the regression coefficients were generally reduced by increased crop nitrogen uptake.     

Seed tuber production from true potato seed (TPS) in Egypt and the influence of environmental conditions in different growing periods

Summary The effect of environmental conditions on seed tuber production from true potato seed (TPS) in nurseries was evaluated in different growing periods during two seasons in Egypt. In the autumn season, high soil and air temperatures reduced emergence and initial foliage development of early-sown seedlings, and decreased tuber yields. In late-sown seedlings low night temperatures and short daylengths caused early tuberization, poor foliage development and low tuber yields. In the spring season, low temperatures and short daylengths resulted in a slow initial foliage development and early haulm-tuber competition for assimilates in early-sown seedlings. However, tuber yields were higher than for late-sown seedlings, presumably because net assimilation and assimilate partitioning to the tubers were impaired by above optimum air and soil temperatures in May and June. Slow development of true seed-sown plants caused a high sensitivity towards adverse environmental conditions and would limit yielding ability in Egypt.     

Sporulation ofPhytophthora infestans (Mont.) de Bary on the surface of diseased potatoes and tuber to tuber spread of infection during handling

Summary Laboratory experiments and observations in commercial stores showed that viable sporangia ofPhytophthora infestans can be produced on infected potato tubers of different cultivars. Infection was also found to spread from diseased to healthy tubers during handling.     

Water loss from potato tuber discs: a method for assessing wound healing

Summary A rapid and simple method for assessing wound healing in dises of potato tuber tissue has been developed. The rate of water loss is measured when batches of six dises are briefly exposed in a stream of air. The rate of water loss shows little change during the early stages of wound healing but decreases rapidly later.     

Diel changes in tuber volume

Summary The long-term and short-term changes in volume of tubers from plants grown under controlled conditions, when assessed by an accurate, non-destructive tuber-volume meter, showed sigmoid increases in volume. The diel changes were remarkable: the rate of volume increase was very high shortly after the onset of the dark phase, but it declined sharply directly after the onset of the light phase; it was much faster during the night than during the day, especially in the later stages of growth. The nocturnal rate of volume increase was greatest when the tubers showed their greatest overall rate of growth. The daytime increases in volume were fastest during the early stages of tuber development. The key process underlying these phenomena seems to be the movement of water out of and into the tuber.     

Somaclonal variation in tuber traits of potato

Summary About 13,000 somaclones of 17 cultivars and clones of potato were obtained from in vitro callus cultures and individually planted in a greenhouse, followed by tuber generations grown in the field. These plants were subjected to the multistage selection procedure commonly used in potato breeding. Over a period of five years and three field generations the tuber number, size, shape, eye depth, starch content, starch yield and tuber appearance of these somaclones were assessed and compared with that of the controls. These characters varied depending on donor genotype and trait. The frequency of variants was assessed and there were acceptable proportions of desirable abberrants and invariants among the somaclones. Depending on trait the average gain rate for all donor genotypes ranged between 0.2 and 2.3% for-deviants, between 12.2 and 15.5% for invariants and between 0.1–1.4% for +deviants. It is concluded that this technique should be used into potato breeding programmes to improve commercially important characteristics of specific cultivars and breeding clones.