Tuberization in potato at high temperatures: response of physiologically young plants to disbudding and growth inhibitors

Summary In physiologically young plants (Solanum tuberosum L., cv. Sebago), abscisic acid (ABA) and chlorethyltrimethylammonium chloride (CCC) promoted tuberization at day/night temperatures of 32°/18°C, but not at 32°/28°C, in contrast to earlier experiments with physiologically old plants. Disbudding promoted tuberization at both temperatures. These results suggest that physiologically young plants have a greater capacity for increased gibberelling synthesis in the buds at high temperatures.     

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 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.     

The effect of temperature on the development of wilting and on progeny tuber infection of potatoes inoculated with South African strains of biovar 2 and 3 ofPseudomonas solanacearum

Summary Potato plants, after inoculation with a South African strain of biovar 2 or a strain of biovar 3 ofPseudomonas solanacearum were grown in growth chambers at temperatures ranging from 14/16°C (dark/light) up to 25/30°C. When grown at 14/16°C or higher, plants inoculated with the biovar 2 strain developed wilting symptoms and internal symptoms on progeny tubers and the disease was transmitted by the progeny tubers. When the plants were inoculated with the biovar 3 strain, wilting symptoms developed from 18/20°C, internal symptoms on progeny tubers from 20/22°C and the disease was transmitted by progeny tubers from plants grown at 16/18°C or higher.     

Internodal elongation: A potential screening technique for heat tolerance in potato

Summary In pot culture experiments over 2 consecutive years, 20 potato genotypes of varying heat tolerance were grown under long day conditions and heat stressed by being exposed to high (38 °C/21 °C mean day/night) temperature. The percent increase in mean internode length of heat stressed plants over those grown at normal temperatue (25°C/16°C day/night) was correlated with the percent tuber dry matter yield of the heat stressed plants (r=0.618, P=0.01). In the same 20 genotypes, grown under short day conditions at normal temperature, the fraction of leaf bud cuttings exposed to high night temperature (23°C) that produced tuber initials correlated with the percentage increase in internode elongation in stem cuttings exposed to 25°C compared with those exposed to 15°C (r=0.680. P=0.01). Thus the relative changes in internode elongation are related to thermal tolerance, and it is suggested that this can be used as a selection criterion for heat tolerance.     

Reduction in potato growth at high temperature: role of photosynthesis and dark respiration

The relationship of photosynthesis and dark respiration to reduced potato growth at temperatures above 20°C was determined. Ten potato clones were propagated in vitro from sterile plandets and grown in a growth chamber at 20/15°C and 30/25°C (day/night) with an 18 hr. daylength. Plants were harvested 26 to 30 days after transplanting. Daylength was decreased to 12 hrs. to induce tuberization and plants were harvested at 45-51 and 75-79 days after transplanting. At each harvest one plant from each cultivar was chosen from each of five blocks and selected growth (tuber number and dry weight of leaves, stems, roots and stolons, and tubers) and physiological variates [leaf area, net photosynthesis, maintenance dark respiration, and chlorophyll fluorescence parameters 0 (Initial), P (Peak), T (Terminal), P-O (Variable fluorescence) and P-T (Fluorescence quenching)] were measured. The high temperature decreased root and stolon, tuber and total dry weight and increased stem dry weight. Amongst physiological variates, the higher temperature decreased leaf area, net photosynthesis and maintenance dark respiration. The chlorophyll fluorescence parameter 0 significantly increased, which also increased the P and T parameters. Variable fluorescence (P-O) and fluorescence quenching (PT) were not significantly affected by the growth temperature. The analyses of covariance, in which physiological variates were used as covariates to remove significant differences in growth variates, indicated that the most effective covariate was the T chlorophyll fluorescence parameter. The least effective covariates were leaf dark respiration and the chlorophyll fluorescence parameters P-O and P-T. The changes in 0 fluorescence suggest that reduced photosynthetic efficiency, particularly in Photosystem II, plays a major role in reduced potato production at high temperatures.     

The Effect of Day to Night Temperature Variation on Leaf Development in Wheat

Summary

The rate of leaf development in wheat is related to time and temperature in units of degree-days (DD) leaf^?1 (phyllochron). Experiments were conducted in controlled environment chambers to study the effect of day to night variation in temperature on leaf development in two wheat cultivars, Penawawa and Stephens. Plants were grown at constant 20°C, and in eight day/night temperature ranges as wide as 8/32°C to 32/8°C, all with a mean temperature of 20°C. The leaf number on the main stems was counted (in Haun units) every other day, from the emergence of the 2nd leaf until the emergence of the 5th leaf. Leaf phyllochron values were derived from the inverse of the slopes of the linear regression of leaf number on DD. Phyllochron values ranged from 99 to 153 DD leaf^?1. The phyllochron values were greater when higher temperatures were imposed at night under extreme day to night temperature treatment.     

The relationship between temperature and sprout growth in stored seed potatoes

Summary Sprout growth in a range of European cultivars was studied over two seasons at constant temperatures from 2 to 25°C, with an additional 33 (day)/22°C (night) treatment in the second season. There were only minor differences in the response of the cultivars and the optimum for sprout growth was at 15–18°C in all cases, when measured over an extended period, but initially sprout growth was more rapid at 23–25°C. Sprout growth at 23–25°C was frequently arrested by sub-apical necrosis, and at these temperatures the sprouts remained short enough for the tubers to be planted by hand without desprouting.     

Differential sensitivity to temperature of cuphea vegetative and reproductive growth

Cuphea (Cuphea viscosissima Jacq. x C. lanceolata W.T. Aiton; PSR23) is a new oilseed crop rich in medium-chain fatty acids similar to tropical palms. Agronomic studies suggest that temperature is a key determinant of cuphea seed yields. However, little is known about the growth and photosynthesis response of cuphea to temperature. The following study is the first of its kind to evaluate cuphea's growth and photosynthesis response to temperature. Cuphea was grown under day/night temperature regimes of 18/12, 24/18, and 30/24 °C and regression analysis was used to assess its responses of growth and photosynthesis and determine their optimum temperature range. Vegetative growth and leaf photosynthesis adapted well over the temperature range studied. However, reproductive growth was more sensitive showing a decline with increasing temperature. Reproductive growth rate was greatest under the lowest (18/12 °C) temperature treatment and declined by 43% at the highest growth temperatures. In contrast, vegetative growth, which was greatest under the 24/18 °C treatment, declined by just 25 and 10% at the lowest and highest temperatures, respectively. Photosynthesis acclimated to temperature by up-regulation of in vivo Rubisco activity with declining growth temperature. Maximum Rubisco activity (V_cmax) in leaves under the 18/12 °C treatment was 76% greater than that of leaves grown at 30/24 °C. Photosynthetic acclimation permitted cuphea to vegetatively grow well over a wide temperature range, but does not explain the sensitivity of reproductive growth to temperature, which will require further research to elucidate.     

Development during storage of spraing symptoms in potato tubers infected with tobacco rattle virus

Summary In trials with potato tubers infected with tobacco rattle virus (TRV), symptoms of spraing in cvs Bellona, King Edward, Maris Bard, Matilda, Sv 82146 and Sv 82149 increased during storage when the tubers were cut. Storage of intact tubers at a constant temperature of 9°C or at fluctuating temperatures (2 weeks at 18°C, 2 weeks at 9°C and 2 weeks at 18°C) did not increase the frequency of symptoms.     

The effect of night temperature and glasshouse ventilation on the incidence of Botrytis cinerea in a late-planted tomato crop

The incidence of Botrytis cinerea Pers. was assessed on leaves, stems and fruits of tomato grown in night environments of 16°C with or without ventilation at night and 13°C with ventilation. Ventilation and temperatures by day were the same in all treatments. The experiment used nine independent glasshouse compartments in a row and column design. At 16°C, night ventilation gave significant reductions in grey mould on stems, leaves and fruits to c. 25% of that on unventilated plants. With night ventilation and a night temperature of 13°C, the incidence of B. cinerea on stems, leaves and fruit was doubled when compared with ventilated plants at 16°C. These differences could be explained partly in terms of the humidity which prevailed in the crops. No significant differences in yield were detected between treatments.     

Characterization of pectic substances from two potato cultivars with different sensitivities to prewarming

Summary Potato cultivars Chieftain and Kennebec were prewarmed at 70°C for 15 min. prior to heating at 100°C for 18 min. in a water bath. Chieftain exhibited a large increase in fracturability upon treatment while Kennebec showed a smaller increase. Pectic substances of the two cultivars were sequentially extracted in water, sodium hexametaphosphate (0.5%), hydrochloric acid (0.05M, 50°C), and sodium hydroxide (0.05M, 5°C). The largest fraction isolated from both cultivars consisted of hydroxide-soluble pectic substances, and was followed by the acid-soluble fraction. Chieftain contained significantly greater amounts of the hydroxide-soluble fraction than Kennebec. Ion exchange chromatography revealed that the extracted pectic substances from the two major fractions consisted of a charged pectin chain with attached neutral sugars. Gel filtration chromatography revealed wide molecular size distributions for the isolated pectic substances. Pectic neutral sugar content for the hydroxide-soluble fraction (50% of total pectic substances) was greater for Chieftain than for Kennebec.     

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.     

Effects of Age and Pretreatment of Tissue-Cultured Potato Plants on Subsequent Minituber Production

Potato (Solanum tuberosum L.) plantlets were conditioned in tissue culture to produce more minitubers when planted in a greenhouse. Tissue-cultured potato plantlets, varieties Coliban and Russet Burbank, were grown for 4, 10, or 12 weeks under three temperature regimes (22/18 °C, 16/10 °C, and 10/2 °C day/night) and a photoperiod of 16, 12, or 8 h in different stages of growth. Duration, temperature, and photoperiod of the in vitro period affected plantlet morphology and the total number of minitubers produced per plant in a greenhouse. Extending the growing period and introducing a hardening period with low temperatures (16/10 °C) during the in vitro production stage resulted in 97% more minitubers (4.94 vs 2.50 minitubers per plant for the control) in variety Coliban and up to 71% (6.50 vs 3.80 minitubers per plant for the control) in variety Russet Burbank. The total number of minitubers produced per plant did not change significantly for both varieties when a shorter photoperiod was used instead of the standard 16-h day during the growing period in vitro. Results presented in this experiment demonstrate that the number of minitubers can be substantially increased through the introduction of an induction period as an interstage between the in vitro stages of potato plantlet production and minituber production.     

Effect of storage temperature and duration on quality and survival of potato transplants

Potato transplants (Solanum tuberosum) were harvested and stored at 1.7, 7.2, 12.8, 15.6 and 18.3°C between 4 and 8 days. The transplants were evaluated after storage for leaf color and drop, wilt, tuberization, and stolonization. After transplanting, the plants were evaluated for survival. At 1.7 and 7.2°C storage, the leaves were greener with less drop than at the higher temperatures. During storage above 7.2°C, the development of tubers and stolons continued. Plant survival was generally higher at 1.7, 7.2 and 12.8°C than at 15.6 and 18.3°C.     

Carbon dioxide enrichment and temperature effects on cotton canopy photosynthesis,transpiration, and water-use efficiency

The objectives of this study were to evaluate effects of ambient and double ambient [CO₂] at a range of growing temperatures on photosynthesis, respiration, transpiration, water-use efficiency and dry matter accumulation of cotton plants (Gossypium hirsutum L., cv. DPL 50). In Experiment I, plants were grown outdoors until first bloom, then transferred into naturally lit growth chambers and grown for 22 days at 30/18°C with five CO₂ concentrations varying from 350 to 900 μl l⁻¹. In Experiment II, air temperatures were maintained at 20/12, 25/17, 30/22, and 35/27°C day/night during a 70-day experimental period with [CO₂] of 350 and 700 μl l⁻¹ at each temperature. Photosynthesis increased with [CO₂] from 350 to 700 μl l⁻¹ and with temperature. Plants grown at 35/27°C produced fewer bolls due to abscission compared with plants grown at optimum temperatures (30/20°C). At higher [CO₂], water-use efficiency increased at all temperatures due mainly to increased canopy photosynthesis but also to more limited extent to reduced canopy transpiration. Increased photosynthesis at higher [CO₂] resulted in greater dry matter accumulation at all temperatures except at 20/12°C. Respiration increased as dry matter and temperature increased. Plants grown at higher [CO₂] had less respiration per unit dry matter but more per unit area. These results indicate that future increases in [CO₂] are likely to benefit cotton production by increasing carbon assimilation under temperatures favorable for cotton growth. Reduced fruit weights at higher temperatures indicate potential negative effects on production if air temperatures increase as projected in a high-CO₂ world.     

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.     

Responses of sunflower yield and grain quality to alternating day/night high temperature regimes during grain filling: Effects of timing,duration and intensity of exposure to stress

In order to quantify the effects, at different stages during grain filling, of alternating day/night high temperature regimes on sunflower grain yield and quality, heads were exposed to high temperatures during 7 or 6 days starting either 10–12 days after anthesis (daa, HT1), 18 daa (HT2) or 24 daa (HT3). Also, heads were exposed to high temperatures for periods of 2, 4 or 6 days in each of HT1 and HT2. Temperatures covered a range of mean daily grain temperature of 20–40 °C and peak grain temperatures (i.e., those prevailing during the central 5 h of the daylight period) of 26–45 °C. High temperature stress for periods of 4 days or longer produced significant (p < 0.05) reductions in grain yield and grain quality. Early (HT1) exposure to stress reduced yield by 6%/°C above a mean grain temperature threshold of 29 °C; later (HT2 + HT3) exposures reduced yield by 4%/°C above a threshold of 33 °C. These reductions in yield were attributable to reductions in unit grain weight at all positions (periphery, intermediate, central) on the head, and an increase in the proportion of very small (10–30 mg) grains, termed half-full (HF) grains in this paper. In both full and HF grains, stress in either HT1 or HT2 reduced final pericarp weight, associated with fewer number of cell layers and thinner cell walls in the schlerenchyma. High temperatures reduced both the rate and duration of oil deposition in the grain, with the greatest effects being found with early (HT1) exposures. The unsaturation (oleic acid/linoleic acid) ratio of oil from mature grain was altered only when exposure to heat stress overlapped with the cessation of deposition of storage lipids. The effects of duration and intensity of heat stress on relative (to control) grain yield and oil content could be reasonably summarized using a linear response to cumulative hourly heat load calculated with a base temperature of 30 °C. We conclude that: (i) 4 days of alternating day/night temperatures resulting in mean daily grain temperatures of >30 °C can reduce sunflower grain yield and quality; (ii) the magnitude of these effects is strongly dependent on the timing of exposure and their nature on the grain growth processes active at the time of stress; and (iii) an hourly heat load (base = 30 °C) provides a useful integrative estimator of the effects of exposure to heat stress on grain yield and oil content for a given phase of grain filling.     

Promotion of Seedling Growth of Seeds of Rice (Oryza sativa L. cv. Hitomebore) by Treatment with H2O2 before Sowing

Abstract

High germinability of seeds and establishment of young seedlings in rice (Oryza sativa L.) are necessary for direct seeding in paddy fields. We investigated whether germinability and seedling growth were promoted by treatment of rice seeds (cv. Hitomebore) with hydrogen peroxide solution (H₂O₂) during the imbibition for 24 h. H₂O₂ treatment with 50 mM H₂O₂ promoted seed germination, and seedling growth (shoot length, root length and shoot fresh weight) in agar culture under a low temperature condition (18°C day/14°C night). Seedling growth was promoted by H₂O₂ treatment not only under the low-temperature condition but also under a normal (23°C day/18°C night) temperature condition. Furthermore, H₂O₂ treatment promoted seedling growth under a flooding condition in a greenhouse. These results suggest that H₂O₂ treatment of rice seeds during the imbibition is advantageous for direct seeding. We discussed the relation between the promotion of the seed germinability and the seedling growth under a low-temperature condition, and the expression of some genes encoding ROS scavenger enzymes induced by H₂O₂ treatment.     

Influence of daylength and temperature during formation of seed potatoes on subsequent growth and yields under long day conditions

Production of high quality seed potatoes is normally favoured by a cool climate with minor pest problems. Growth chamber studies aimed to reveal if daylengths (12 and 24 hrs) and temperatures (18/12 and 12/9°C day/night) during production also might influence progeny growth. Results showed no significant carry-over effect from daylength conditions, while growth vigour and yields were affected by parent plant growth temperature. Further experiments, including a greater range of temperatures, different cultivars and measurements of physiological age, are required to discuss theoretical and practical implications of the results.