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.     

Effect of gibberellic acid and multiple harvests on production and reproductive value of seed potatoes produced above ground on stem cuttings

Summary Potato plants of cvs Eersteling and Bintje were grown from stem cuttings and induced to form aerial tubers for use as seed. Spraying the plants with gibberellic acid in concentrations of 10, 25 and 50 mg/l to induce stolon formation in the leaf axils led to a decrease in the number of tubers formed per plant. Multiple harvesting of the largest tubers from plants treated with gibberellic acid or not, approximately doubled the number of tubers formed but halved their individual weight compared with only one harvest at plant senescence. After a storage period of about 1 year, with their vigour declining, the aerial tubers were planted in the field. Aerial seed tubers taken from multiple harvests during the previous year produced the same number of tubers as plants grown from above-ground tubers harvested at plant senescence only, but the tuber yields declined with earlier harvesting when small (5–13 mm) aerial tubers were used, compared to larger (14–19 mm) tubers.     

Early potatoes in Italy with particular reference to Sicily

Summary In Italy, the early potato cultivars of greatest economic significance are those grown off-season, in a cycle which is generally much earlier than the typical spring-summer cycle. Of the area given over to early potatoes in Italy, more than 90% is in the southern regions. The economic value of this production is due to its extraseasonality, which allows much of the early potato harvest to be sold on foreign markets. In Sicily, more than 5000 ha of potato are grown, with a high frequency of potato crops on small plots. Early potatoes are often rotated with various fruits and vegetables, and the length of the cycle is variable, from 100 to 140 days. Choosing the most suitable cultivar is the most complex aspect of early potato growing. Of the criteria used, tuber growth rate has shown most validity. In Sicily two cultivars are mainly grown: Sieglinde and the more recent but well-established Spunta. Agricultural techniques used for early potato cultivation vary depending on the area. An overview of the agronomic practices used in different areas is given in this paper.     

Patterns of stem water potential in field grown potatoes using stem psychrometers

Summary The first large scale outdoor measurements of potato (Solanum tuberosum L.) stem water potential (SWP) usingin situ temperature-corrected stem psychrometers were performed on three cultivars common to Ontario, Canada (Atlantic, Monona and Norchip). Potato plants were examined under three soil water treatments which included rainfed, irrigated and stressed through the use of rain shelters. Cultivar variations in SWP under both irrigated and rainfed conditions were slight (P>0.05), although some significant (P<0.05) differences in mid-day SWP were evident, especially under conditions conducive to high atmospheric water demand. Under these conditions. cv. Atlantic maintained the lowest SWP with cv. Monona highest and cv. Norchip was intermediate. Few differences in pre-dawn SWP were detected between the three cultivars under well watered and rainfed conditions. Under low soil water, significant differences (P<0.05) were observed. The similar trend of Atlantic maintaining the lowest SWP with Monona the highest was consistent.     

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.     

Application of Soluble Chitosan in vitro and in the Greenhouse to Increase Yield and Seed Quality of Potato Minitubers

The aim of this work was to investigate whether the application of soluble chitosan in potato micropropagation can improve microplant quality in vitro, help acclimatisation ex vitro, and increase yield and seed quality of minitubers. Potato cv. Désirée microplants were treated in vitro with soluble chitosan added to the semisolid tissue culture medium in different concentrations. Microplants were subsequently transferred to the greenhouse and sprayed with chitosan solutions or remained unsprayed. Untreated microplants were also established ex vitro and sprayed with chitosan, or left unsprayed as a control. Morphological and physiological parameters of plant growth were assessed in vitro and ex vitro. Plantlet quality was evaluated using a ranking system. Minitubers derived from greenhouse plantlets were planted in the field in subtropical conditions, and growth and yield parameters evaluated. The chitosan concentration most beneficial to the in vitro growth of microplants varied between years. In treatments with the best in vitro growth, minituber number and yield in the greenhouse was also increased. Foliar chitosan application at the acclimatisation phase stabilised the effect of in vitro treatment on yield parameters. The seed quality of minitubers derived from chitosan treatments in vitro alone and in combination with foliar treatment at acclimatisation was improved, giving rise to field plants with increased tuber numbers and yields. The combination of chitosan in vitro and foliar application during the acclimatisation phase ex vitro had a greater effect on minituber seed quality than the concentration applied in vitro.     

An investigation into the factors influencing sugar levels in UK grown potatoes (cv. Record)

Summary Reducing sugar and sucrose content of potato tubers (cv. Record) grown in Tayside (northern United Kingdom (UK)) and Lincolnshire (southern UK) were monitored during the 1984 growing season and after two months storage at 10°C. Neither latitude nor agronomic factors were shown to affect sugar content. Significant correlations were found between the post storage reducing sugar content and the sugar contents measured at harvest. Regression analyses indicated that in immature tubers sucrose breakdown was responsible for reducing sugar accumulation during storage.     

Influence of cultivar and prewarming on texture retention of thermally processed potatoes

Summary Potato cubes (2.5 cm) of six cultivars were soaked in CaCl₂ solution (0.004% calcium) at 4°C for 21 h, prewarmed at 75°C for 30 min, and boiled (20 min) or microwaved (2 min, 15 sec). Prewarming treatment significantly retained fracturability (g force at first break point) of boiled samples over non-treated controls. Thirty min prewarming at 75°C gave maximum fracturability retention for boiled samples; prewarming time had no effect on texture of microwaved samples. Cultivar differences in fracturability correlated with inherent tuber calcium content.     

Discovery of an atypical strain ofBurkholderia solanacearum affecting potatoes in India

Summary An atypical strain ofBurkholderia solanacearum was isolated from potato. Characters examined were colony shape, size, colouration, pathogenicity to susceptible hosts, vascular discolouration and biovar features. In contrast to normal white-coloured colonies, this atypical strain produced cream coloured, fluidal colonies on tetrazolium chloride medium. It did not cause disease symptoms in eggplant, datura and pepper but was slightly to highly pathogenic on tomato and potato respectively but caused no discolouration of vascular tissues. This atypical strain from potato also differed from established biovars in its ability to produce acid only from mannitol and maltose, a combination which has not been previously reported. This is believed to be the first report of the presence of an atypical strain ofB. solanacearum from India.     

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.     

Compatibility of potatoes to contrasting seasonal conditions,to high temperatures and to water deficit: The association with time of maturation and yield potential

Summary Genotypic variation in the adaptation of potatoes of several maturity classes to the specific climatological conditions of the autumn season, to the high summer temperatures and to water deficit, was studied. Late-maturing cultivars exhibited the highest yielding potential both in the spring and autumn seasons but specific compatibility of cultivars to the autumn was detected. The late-maturing cultivars were more susceptible to high temperatures than were the early ones. However, there were significant differences in susceptibility to high temperatures among cultivars of the same maturity class. Susceptibility to water deficit was similar in the various maturity classes, but there were differences in the susceptibility to drought among cultivars of the same maturity class. High yielding potential generally resulted also in acceptable tuber yields under conditions of water deficit. High temperatures in combination with a water deficit aggravated yield losses, especially in the late-maturing cultivars. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 2782-E, 1989 series.     

Inheritance of tolerance ofGlobodera pallida and the relationship between tolerance and resistance toG. pallida in potatoes

Summary The tolerance of and resistance toGlobodera pallida of two potato progenies which segregated for these characteristics were assessed in pots in the glasshouse. The level of tolerance varied widely between genotypes within the progenies, with several genotypes being significantly more tolerant than the intolerant parent. The levels of resistance and tolerance in the progenies were not significantly correlated. No indications were obtained that the ranking of genotypes for tolerance is influenced by the density ofG. pallida in the soil. The results confirm that selection for tolerance in aG. pallida resistance breeding programme is useful and feasible.     

Salinity stress and sodium-potassium interactions in micropropagated potatoes

Summary Increased potassium (K) fertilization of saline soils has been implicated in alleviating salt stress in plants. We examined whether varying K concentrations in Murashige & Skoog (MS: 1962) basal medium could affect salt (NaCl) stress in micropropagated potatoes. Plantlets of cvs Sierra and Russet Burbank were evaluated after 1 month of growth in a medium containing 0. 40, or 80 mM NaCl and 6,20, or 30 mMK. The medium K was adjusted using KNO₃ while total nitrogen was kept constant using NH₄NO₃. Growth parameters were less affected in Sierra than Russet Burbank, and roots were less affected than shoots, as the medium salinity increased. Tissue Na levels were greater when the medium K was 6 mM compared with 20 mM MS control. The medium K concentration 50% greater than MS control did not promote growth and did not limit tissue Na levels. While this should be confirmed by field assessment, our results suggest that while K deficiency promotes salt damage, its addition beyond the usual fertilizer recommendations is not beneficial in alleviating salinity stress.     

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.     

The effect of seed-and soilborne inoculum ofColletotrichum coccodes on the incidence of black dot on potatoes

Summary Soil in a potato field naturally infested with black dot (Colletotrichum coccodes) was fumigated with methyl bromide at 126 g m⁻² or left unfumigated. Potato seed tubers (cv. BP1) uninfected, lightly infected (1–25% surface affected), severely infected (26–100% surface affected) and severely infected withC. coccodes but dusted with prochloraz manganese chloride as Octave 2.5% DP at 750 g per 100 kg seed were planted in fumigated and unfumigated soil. When harvested, the incidence of black dot on the progeny of infected seed planted in unfumigated soil was twice that of progeny in fumigated soil, with progeny of uninfected seed having a 68.5 times higher disease incidence in unfumigated soil. Black dot on progeny tubers was reduced by pre-treatment of seed with prochloraz in fumigated soil only. With black dot infested fields, planting disease-free seed or treating seed with fungicides would not decrease disease on progeny tubers.     

Relationships between ground cover,intercepted solar radiation,leaf area index and infrared reflectance of potato crops

Summary In field trials with potato several methods determining the proportion of intercepted solar radiation by the crop were compared. Non-destructive measurement of the proportion of ground cover with the aid of a grid correlated well with the proportion of intercepted photosynthetically active radiation as measured with a tube solarimeter and with the leaf area index. Measurement of the infrared reflectance of the crop proved to be an efficient and objective method to show differences between treatments. Moreover, it showed a good correlation with ground cover and radiation interception until full closure of the canopy. Percentage ground cover is useful for assessing intercepted solar radiation and leads to fewer errors in calculation of efficiency of conversion into dry matter than the other methods.     

The effect of storage conditions on chemical content of raw potatoes and texture of cooked potatoes

Summary Texture of boiled potato tubers (cv. Beate) was studied over several months of storage at either 4 or 8 °C, in relation to dry matter content, non-starch polysaccharides (NSP), methyl groups, glucose, starch and amylose. The dry matter content decreased significantly during storage at 4 °C, but increased at 8 °C due to evaporation. The insoluble NSP contained rhamnose, galactose, arabinose, xylose, mannose, fucose and glucose; the first three sugars decreased significantly after the first 7 weeks of storage. Fracturability and percent compression before break increased during storage at 8 °C, particularly percent compression after 15 weeks. The change in fracturability could partly be explained (R²=43.4%) by the content of the NSP and the increase in percent compression by dry matter (R²=91.8%). Changes in texture during storage at 4 °C, however, were not striking, and could not be explained by changes in the potato components that were analysed.     

Evaluation of treatments with hot water,chemicals and ventilated containers to reduce microbial spoilage in irradiated potatoes

Summary Potatoes irradiated to control sprouting were dipped in: hot water (56°C, 5 min; 52°C, 10, 15 and 20 min); cold (25°C, 5 min) or hot (56°C, 5 min) salicylic acid (1000 and 2000 ppm); or sodium hypochlorite (0.1 and 0.2%, 5 min); or dusted with salicylic acid (1 and 2%), to try to reduce the incidence of bacterial soft rot (Erwinia sp.) during controlled temperature (10°C, 15°C) and ambient temperature (20–34°C) storage. All treatments, particularly hot water and hot salicylic acid dip, increased microbial spoilage, possibly as a result of handling damage during the treatments combined with the inhibition of wound periderm formation as a result of irradiation. Storing irradiated tubers in well ventilated containers reduced soft rot compared to storing them in sacks and after 6 months storage at 10, 15 and 20–34°C, 95, 90 and 77% respectively were healthy and marketable.     

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.     

Effect of haulm treatments on the formation of microsclerotia ofVerticillium dahliae Kleb. on potato

Summary In four pot experiments, potato plants of cv. Element were artificially infected withV. dahliae. At an early and a late harvest haulms were killed chemically, by burning or by various other treatments, including cutting them into pieces of different lengths and keeping the debris on the soil surface or covering with soil. After 4 weeks the plant material was air-dried and the number of microsclerotia per mg was determined. At the early harvest, in two experiments, the chemical treatment yielded more microsclerotia than the cutting treatments. Covering colonised haulm tissue with non-sterilised soil was effective in inhibiting microsclerotia formation. Shorter haulm pieces led to fewer microsclerotia at the later harvest if the material was kept on the soil surface. The variation in microsclerotial yield and in treatment effects among the different experiments was large.