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.     

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.     

Effects of shoot,root and stolon temperature on the development of the potato (Solanum tuberosum L.) plant. III. Development of tubers

Summary The cultivars Bintje and Désirée were growth with their shoots, roots and stolons at different temperatures, to study the effects on tuber development. More tuber sites were initiated in ‘Bintje’ when the air, root or stolon temperature was increased but a combined increase of air and root temperature greatly reduced the number of sites. In contrast, each temperature increase reduced the number of tuber sites in ‘Désirée’ but an increase in temperature in one compartment usually increased the number of tubers set. The relative tuber set was enhanced by a combination of high stolon temperature and low root temperature. Especially an increase in air temperature reduced tuber yield and tuber dry-matter content, but increasing stolon temperature had the largest effects on the induction of second growth. Stolon and tuber development, dry-matter partitioning and initiation of second growth responded differently to variation in temperature around different plant parts suggesting that these processes are affected by different regulation mechanisms.     

Heat stress and the tuberization stimulus

Heat stress may lower potato tuber yields through reduction in the net amount of photosynthate available for total plant growth and through reduced partitioning to the tubers. The latter effect is generally more serious and is the main subject of this paper. High temperatures have much the same effect on partitioning as do long days, and there are significant genetic differences in response to both factors. Both affect the total morphology of the plant. A cutting technique may be used to rapidly screen seedling populations for reaction to temperature or photoperiod. Although progress has been made in studying the nature of the hypothetical “tuberization stimulus”, more needs to be done to clarify the physiological and biochemical changes involved during tuber induction.     

The dependence of internal brown spot development upon calcium fertility in potato tubers

Summary To determine calcium fertility and high temperature effects on internal brown spot development in potato, cv. Russet Burbank plants were fertilised with Hoagland's nutrient solution with or without calcium. Prevalence and severity of internal brown spot were greatest in tubers receiving no calcium fertilisation during growth. Internal brown spot was evident as early as tuber initiation. A high growth medium temperature (32°C) at tuber maturity with a lack of calcium increased internal brown spot incidence and severity. No tubers subjected to the high temperature and fertilised with calcium developed internal brown spot. Peel calcium concentration of tubers receiving no calcium fertilisation was lower (0.5–0.8 g/kg) than tubers receiving calcium (1.2–1.9 g/kg). Medullary tissue calcium concentration was similar under both calcium regimes. Calcium availability during early tuber growth was an influential factor in internal brown spot development, however high temperature effects may not be discounted in exacerbating the disorder. H/LA Paper No. 95-7. Project No. 1984, College of Agriculture and Home Economics Research Center, Pullman WA 99164, USA     

Utilization of potatoes for life support systems II. The effects of temperature under 24-H and 12-H photoperiods

The growth and tuberization of Norland potatoes were studied under five different temperatures and two photoperiods. Treatment levels included 12, 16, 20, 24, and 28 C with either a 24-h (continuous light) or a 12-h photoperiod at 400 μmol m^-2 s^-1 PPF. Plants were grown in 6-liter containers and harvested at 56-days-age. Stem length increased with increasing temperature under both photoperiods. The highest tuber yield occurred at 16 C under the 24-h photoperiod (755 g/plant) and at 20 C under the 12-h photoperiod (460 g/plant). Little or no tuber formation occurred at 28 C under either photoperiod or at 24 C under continuous light. As with tuber yield, the highest total plant dry weights also occurred at 16 C under the 24-h photoperiod and at 20 C under the 12-h photoperiod. Harvest index (tuber dry weight to total dry weight ratio) decreased with increasing temperatures and with continuous light. Results indicate that good growth and tuberization can occur under continuous light, and that increasing the photoperiod from 12 to 24 h effectively decreased the optimal temperature for tuber formation from near 20 C to 16 C. Alternatively, the results imply that at cooler temperatures, the potato becomes less obligate for dark period stimulation of tuberization.     

The effect of some environmental factors on potato tuber numbers

Summary Five experiments studied the effects of shading, temperature and stolon growth medium on stolon and tuber formation. The lowest numbers of stolons and tubers were produced at the higher and lower nodes. Numbers of primary stolons and tubers were relatively stable across nodes and treatments and variation in total numbers was largely due to changes in numbers of lateral and branch stolons. In the field, 70% shading reduced numbers of stolons and tubers by reducing lateral and branch stolons, while in hydroponics, 45% shading and temperatures at initiation had no effect on tuber numbers. In both environments later planting tended to reduce numbers of stolons and tubers. There were large effects of the physical environment, with compost producing three times as many tubers as dry vermiculite. The potential number of tubers may be determined by the number of stolons and the environmental conditions affecting stolon formation and development.     

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.     

Reduction of potato damage during grading by radiant heating

Summary The effect of using radiant heat to quickly warm potatoes and reduce damage in handling after cold storage was investigated. Two treatments were investigated: tubers dropped 350 mm with no radiant heat applied, and tubers dropped with radiant heat applied. Both treatments were compared with a control set of tubers which were taken directly out of store. The mean damage index per tuber was significantly reduced following radiant heat treatment although there were cultivar and size variations. The temperature profile under radiant heat was also measured which showed an increase in the outside flesh temperature of 8–12°C depending on tuber colour.     

Influence of heat stress on dry matter production and photo-assimilate partitioning by four potato clones

Partitioning patterns of¹⁴C labeled assimilates were studied to determine their relationship to dry matter accumulation and distribution in four potato clones (Desiree, DTO-28, LT-1 and Russet Burbank). Plants placed in growth chambers at 35/25 C day/night temperature and 12-hour photo-period two weeks after tuber initiation were compared with plants grown continuously at 25/12 C. Two weeks after temperature treatments were begun, the most recently expanded leaf was labeled with¹⁴CO₂ for 30 minutes, and plants were harvested 20 hours or 15 days later. High temperature reduced total dry matter production and altered dry matter distribution in favor of vines at the expense of tubers. Partitioning of¹⁴C assimilates generally followed the pattern of dry matter distribution. Potato clones exhibited variation in¹⁴C assimilate export from labeled leaves and in partitioning to vines and tubers. Assimilate partitioning to tubers was not consistently higher in clones considered heat tolerant.     

Diurnal temperature fluctuation effects on potatoes grown with 12 hr photoperiods

This study was designed to characterize the growth responses of potato (Solanum tuberosum L.) to diurnal temperature fluctuations. Potato plants of two cultivars, Norland and Denali, were grown for 90 days under 12 hr photoperiod in walk-in growth rooms at the University of Wisconsin Biotron. The alternating temperature was 22 C light/14 C dark and compared to a constant 18 C as control. At all temperature regimes vapor pressure deficit was maintained at 0.62 kPa (70% relative humidity [correction of humdidity] at 18 C). Plant height, plant dry weight, tuber dry weight, and harvest index were overall greater under the warm light/cool dark alternating temperatures than under the constant temperature. The differences between temperature treatments were greater for Denali than for Norland. Alternating temperatures increased Denali tuber weights by 25%, but no significant increase was found with Norland. Also the total plant weight was increased over 20% with Denali, but increased with Norland in only one of the two replications of the experiment. This study documents that alternating temperatures are a benefit to some cultivars but may not be of benefit to all cultivars.     

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).     

Comparative performance of three small seed tuber sizes and standard size seed tubers planted at similar stem densities

Summary Small seed tubers of 1–5 g, 5–10 g and 10–20 g were planted at the same sprout densities as standard size seed tubers of 40–60 g in order to give similar stem densities. Early ground cover by foliage, total yield, and yield of tubers >45 mm were consistently greater in plots planted with larger seed tubers. The effect of seed tuber size on yield and tuber number per stem varied between years but 1–5 g seed tubers always gave lower yields per stem than larger seed tubers. Reducing the spacing between rows from 90 cm to 60 cm and maintaining the same sprout density was more effective in increasing yields from small seed tubers than increasing sprout density from 20 to 40 sprouts per m² by reducing plant spacing within the row.     

Light and genotype effects on in vitro tuberization of potato plantlets

Summary In vitro tuberization responses of eleven clones of potato were evaluated under different photoperiods and light intensities. No growth regulators were added to the medium to avoid the potential modification of the response to the environmental stimuli. Plantlets were grown on MS medium containing 3% sucrose for four weeks under long days (16 h). Tuberization was induced by short days (8 h). Five photoperiodic combinations and three light intensity treatments were applied. Light applied after the tuber induction phase delayed or inhibited tuber initiation (at proper photoperiods both at 111 and 55 μmol m⁻² s⁻¹ light intensities at 24/15 °C day/night temperature). Darkness following the induction stage accelerated and synchronized tuber initiation after high light intensity. However, these effects of dark treatment depended on light intensity applied in short days before dark treatment. There was an interaction between the duration of darkness applied in photoperiodic treatments and the light intensity applied in short days on tuber initiation. No relationship was observed between the maturity groups of clones tested and their tuber initiation responses. Tight interaction (P≤0.01) of treatments and clones was proved by statistical analysis. Reliable tuberization and high rate of tuberization (1.20–1.52) can be reached using these hormon-free systems.     

Comparison of the growth of potato crops grown in autumn and spring in North Africa

Summary The relationships between intercepted solar radiation and dry matter production (total and tubers) were established for four cultivars of different maturity classes and using seed tubers of two physiological ages. The crops were grown in an autumn and a spring season in Tunisia. Radiation use efficiencies were lower in autumn than in spring and the quantity of intercepted radiation at tuber initiation was more than two times greater in autumn than in spring due to retarded tuberization in the autumn caused by the relatively high temperatures. In addition, tuber dry matter, number of stems per plant, tubers per stem and harvest indices were all lower in the autumn than in the spring season which explained why tuber yields in the spring season were higher than in the autumn.     

Effects of temperature pre-treatment of transplants from in vitro produced potato plantlets on transplant growth and yield in the field

Summary In vitro produced potato plantlets, cvs Gloria and Spunta were planted in soil and exposed to day/night temperatures of 18/12 or 26/20°C for 14 days. They were then transplanted into the field in two experiments to assess after-effects of temperature on the performance of short-cycle crops. Accumulated intercepted radiation (AIR) was calculated from ground cover and incoming radiation, and dry matter production and fresh tuber yield were frequently recorded. Pre-treatment at 26/20°C caused higher leaf area at the end of the transplant production phase and resulted in a higher AIR at the end of the field phase than pre-treatment at 18/12°C. Higher AIR, however, was not associated with significantly higher yield. Initially, the proportion of dry matter partitioned to tubers was lower after 26/20°C, but this effect did not persist. High temperature pre-treatment may improve the performance of plantlets, especially of very early potato cultivars.     

Effect of weight of potato minitubers on sprout growth,emergence and plant characteristics at emergence

Summary The behaviour of minitubers in five weight classes, having mid-point values between 0.19 and 3.00 g, was studied during sprouting and emergence under controlled conditions. Lighter tubers took longer to produce sprouts of 2 mm, and their sprouts grew more slowly between 2 and 4 mm and 4 and 6 mm. As sprouts lengthened their rate of growth increased. The influence of tuber weight was less for heavier tubers and also decreased as the sprouts grew longer. When tubers with sprouts of the same length were planted in pots, sprouts from lighter tubers took longer to emerge. Emergence was later and differences between weight classes were larger when tubers were planted deeper (6 or 9 cm) or when they had shorter sprouts at planting (2 or 4 mm). At emergence, plants from lighter tubers had thinner stems and lower stem and root weights, but higher stem weights proportional to tuber weights and higher shoot:root ratios.     

Some sprouting characteristics of microtubers

Summary Microtubers can be stored longer, transported and handled easier than plantlets, but they have some disadvantages related to long dormancy. Dormancy, number of sprouts per tuber and loss of microtubers under different storage temperatures were studied. Microtubers of four genotypes originated from different tuberization treatments (photoperiod combinations) were observed. We found that dormancy depended on cultivar and — in some cases — on the photoperiod treatment applied during tuberization. Generally, the dormacy was long and was greatly elongated by low storage temperature. One of the photoperiod treatments shortened while the other treatment prolonged the rest-period compared to the control, maybe due to a change in temperature accompanying the change in daily light (photoperiod combination). Besides, these treatments affected the number of sprouts per tuber. There was no significant difference in duration of dormancy between different tuber-size groups, but the loss increased significanctly with a decrease in tuber size. Based on this information we can use microtubers more effectively in the seed potato production programme.     

Tuber growth and biomass partitioning of two potato cultivars grown under different n fertilization rates with and without irrigation

Nitrogen and water deficiencies are known to affect potato yield, but much less is known of their effect on tuber growth and biomass partitioning. The objective of this on-farm study conducted at two sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and N fertilization rates on tuber growth and biomass partitioning of the cultivars Shepody and Russet Burbank. The N fertilization rates were 0,100, and 250 kg N ha^-1in 1995, and 0, 50,100, and 250 kg N ha_?1 in 1996 and 1997. The highest bulking rate observed in our study (7.3 g fresh tubers m^-2 °C^-1) can be considered near the potential bulking rate in New Brunswick. The water deficit in the absence of supplemental irrigation reduced this potential bulking rate by as much as 40%, but this reduction was much less at five of six sites and negligible at two of six sites. Nitrogen deficiency reduced the bulking rate at two of six sites. This negative effect of N deficiency on bulking rate was greater with irrigation than without irrigation at two of six sites; the tuber bulking rate with irrigation was reduced by as much as 50% with no N applied at one site. Shepody had a greater bulking rate than Russet Burbank. The tuber bulking of Russet Burbank, however, started earlier and lasted longer than that of Shepody. Water and N deficiencies increased biomass partitioning to tubers and large roots. Shepody partitioned a greater proportion of its biomass to large roots and had a greater root biomass than Russet Burbank. Our results demonstrate the ability of potatoes to modify biomass partitioning when grown under water and/or N stresses. As a result of this compensation, the reduction in tuber yield due to limited N and water stresses is minimized.     

Carbon dioxide effects on potato growth under different photoperiods and irradiance

Carbon dioxide concentration can exert a strong influence on plant growth, but this influence can vary depending on irradiance. To study this, potato plants (Solanum tuberosum L.) cultivars Norland', Russet Burbank', and Denali' were grown in controlled-environment rooms at different levels of CO2 and irradiance. Carbon dioxide levels were maintained either at 350 or 1000 micromoles mol-1 and applied in combination with 12- or 24-h photoperiods at 400 or 800 micromoles m-2 s-1 photosynthetic photon flux. Air temperatures and relative humidity were held constant at 16 degrees C and 70%, respectively, and plants were harvested 90 d after planting. When averaged across all cultivars, CO2 enrichment increased tuber yield and total plant dry weight by 39 and 34%, respectively, under a 12-h photoperiod at 400 micromoles m-2 s-1; 27 and 19% under 12 h at 800 micromoles m-2 s-1; 9 and 9% under 24h at 400 micromoles m-2 s-1. It decreased dry weights by 9 and 9% under 24 h at 800 micromoles m-2 s-1. Tuber yield of Denali showed the greatest increase (21%) in response to increased CO2 across all irradiance treatments, while tuber yields of Russet Burbank and Norland were increased 18 and 9%, respectively. The results show a pattern of greater plant growth from CO2 enrichment under lower PPF and a short photoperiod.