Gelling agent and light effects onin vitro tuberization of potato cultivars

The effects of Gelrite and agar onin vitro tuberization of six potato cultivars, Atlantic, Chaleur, Cherokee, Desiree, Kennebec and Red Pontiac under low light intensity and in the dark were examined. The medium consisted of MS salts, vitamins, 6% sucrose, 2.5 mg/l kinetin and either 2 g/l Gelrite or 6 g/l agar. The cultures were kept either under diffused light with a 16 h photoperiod or in darkness at 22/19 C day/night temperatures for eight weeks. Tuberization was earlier and more uniform (a higher proportion of tubers ≥ 5 mm) on Gelrite than on agar solidified medium and earlier in the darkness than in the light. Light effects varied from cultivar to cultivar. The slowest to tuberize in light were Atlantic and Red Pontiac, the fastest, Chaleur and Cherokee. Chaleur, Cherokee and Kennebec produced significantly more large tubers and higher total tuber mass under low light than in darkness. Atlantic and Red Pontiac reacted in the opposite way. Desiree produced significantly more large tubers in the dark, but the differences in tuber mass between the dark and light conditions were not significant. Light also stimulated shoot and root growth in most of the cultures. No relation was observed between the relative maturities of the tested cultivars and their tuberization responsesin vitro.     

A comparison of variability in storage behaviour of seed tubers from true potato seed and clonal tubers

Summary The tuber-to-tuber variability in storage behaviour of seed tubers from true potato seed was compared with that in clonal seed tubers after storage in the dark, in diffused light, or in diffused light with a single desprouting. The variability was estimated by calculating standard deviations of length, number and weight of sprouts, and tuber weight loss. After dark storage, the variability of these variables was greater in seed tubers from true potato seed than in clonal seed tubers. After storage in diffused light with a single desprouting, the variability of number, length and weight of sprouts of seed tubers from true seed was not statistically different from that observed in clonal seed tubers. All storage treatments resulted in a greater variability of tuber weight loss in seed tubers from true potato seed than in clonal tubers.     

Change in Some Glycoalkaloids of Potato under Different Storage Regimes

The potato (Solanum tuberosum L.) is an important food crop worldwide. Potato tubers can be stored to provide continuity of supply between production seasons, but it is important that they be stored under appropriate conditions as incorrect storage will result in deterioration in end user quality and may increase glycoalkaloid levels. We have investigated the effects of types of household storage on potato glycoalkaloid content (total glycoalkaloids [TGA]; α-solanine; α-chaconine) in Turkey. Tubers of potato cultivars (cvs.) Agria and Bettina were stored under four types of storage conditions (indirect sunlight for 10 h per day and dark storage for the remaining 14 h per day; storage under continuous fluorescent light; storage in constant darkness; storage in the dark in a refrigerator) for 56 days. Samples of tubers were taken at the beginning of the storage period and after 14, 28 and 56 days of storage for tuber glycoalkaloid measurement. Tubers stored in the three light environments showed an increase in glycoalkaloid levels; however, none of the cv. Agria tubers reached the critical level of 200 mg/kg tuber. On day 56 the TGA level of cv. Bettina tubers stored under fluorescent light reached 234.31 mg/kg.     

Area control of the green peach aphid on peach and the reduction of potato leaf roll virus

Peach trees in a 500-mile² (1295 sq. K) area were sprayed during April and May each year from 1966 to 1969 to control the wingless fundatrix form ofMyzus persicae (Sulzer) after the overwintering eggs had hatched and before subsequent generations of the aphids had developed wings and migrated to summer host plants. The results were monitored from 1966 to 1971 by using about 60 yellow water trap pans each year to collect winged aphids in the control area. Also, aphids were counted weekly in about 30 potato fields each year. Samples of potato tubers collected from the 30 fields (and from 34 other fields in 1965) were indexed for net necrosis and then planted and indexed for chronic leaf roll. The early spraying reduced the populations of winged aphids collected in traps in May and early June 1966–1969 by about 60% compared with the post-spray years (1970–1971). The amount of net necrosis found in potato tubers from the control area was reduced from 11 % in 1965 to slightly more than 3% from 1967 through 1969 and the chronic leaf roll in plants was reduced from 43% in 1965 to about 10% for the same years. Only after two years of spraying was there evidence of a significant reduction in the spread of the virus; similarly, not until 2 years (1970 and 1971) following the end of the spray program did the virus increase significantly.     

Manipulation of microtubers for direct field utilization in seed production

A two-year field study was conducted to determine the effects of jasmonic acid (JA), light (duringin vitro explant production andin vitro tuberization phases), and dormancy-breaking treatment on performance of microtubers in the production of seed tubers (pre-elite) in five potato cultivars. Microtubers were produced under short day (8-h) conditions and in darkness, from stock plantlets pre-treated with JA and untreated, and on tuberization media with or without JA. Microtuber performance was compared to invitro plantlets transplanted directly to the field. Yields of tubers from microtubers were 30% to 40% of those from plantlets. Microtubers of cultivars Amisk and Russet Burbank produced the highest yields of pre-elite tubers. Atlantic microtubers performed poorly in the field. JA pre-treatment of stock plantlets, prior toin vitro tuberization, enhanced seeds tuber production from microtubers in Russet Burbank and lowered in Shepody. JA presence in media duringin vitro tuberization significantly lowered production of tubers while exposure to 8-h light resulted in microtubers performing significantly better in the field than microtubers produced in the dark. Dormancy release was the key factor influencing microtuber performance. Unlike greenhouse studies, gibberellic acid (GA₃) was more effective than Rindite. A further refinement of the production and handling methods is required before microtubers can be recommended for field production of seed tubers.     

The effects of ozone and 1,8-cineole on sprouting,fry color and sugars of stored Russet Burbank potatoes

Ozone and 1,8-cineole were investigated as alternatives to isopropyl-n-(3-chloro-phenyl)carbamate (CIPC) to control sprout development of potato (Solatium tuberosum) tubers cv Russet Burbank during long-term storage. Sprout development was similar in ozone-treated and air-stored tubers, but both had much larger and more numerous sprouts than CIPC-treated tubers. Sucrose and reducing sugars in ozone-treated tubers were similar to levels in air-stored potatoes. Fry color was not different among potatoes stored in ozone, air and CIPC. Conversely, potatoes treated with 1,8-cineole did not produce any sprouts during the 25 week study. The fry color of tubers exposed to cineole was darker than either air-stored or CIPC-treated tubers. Sucrose and reducing sugar levels were higher in cineole-treated tubers than in tubers treated with CIPC.     

Factors influencing incidence of internal brown spot in Russet Burbank potatoes

Studies were conducted to determine factors influencing incidence of internal brown spot (IBS) in Russet Burbank potatoes. A significant decrease in the incidence of IBS occurred as planting date was delayed from March 31 to May 12. IBS increased during storage particularly at the higher storage temperature and in larger tubers. Foliar application of maleic hydrazide (MH) significantly reduced IBS from a high of 33% of tubers to less than 10%. The incidence of IBS in tubers was lower in the field as well as in storage from plants sprayed with MH. Tubers with high specific gravity had greater incidence of IBS than low gravity tubers. Results indicate that IBS is a physiological disorder influenced by factors affecting growth of tubers.     

Effects of spraying mefluidide onto potato foliage

Summary Spraying the growth regulator mefluidide onto potato foliage at 500 or 1000 g/ha on two dates in July after tubers had been initiated did not affect the number, size and yield of tubers or the extent of injuries after mechanical harvesting. The skin of some tubers from sprayed plants was brown and this was more common from plants sprayed on 15 July than on those sprayed two weeks earlier. Spraying at 1000 g/ha decreased the severity of black scurf but increased gangrene.     

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.     

Effect of pre-planting temperature and light treatments of seed tubers on potato yield and tuber size distribution

Summary From 1985 to 1987 field experiments were caried out to test the influence of different pre-planting storage treatments on yield and size distribution of potato crops. The storage treatments included 4, 8 and 12°C in the light and in the dark, for different periods before planting. Subjecting the seed tubers to light at low temperatures induced crops to produce a larger proportion of smaller sized tubers while storing seed tubers at higher temperatures in the dark led to an increase of tubers >55 mm. These observations were confirmed in five field experiments with two cultivars at two sites and in three growing seasons.     

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.     

Management of silver scurf (Helminthosporium solani) with fungicide seed treatments and storage practices

Thiabendazole insensitive strains ofHelminthosporium solani, the causal agent of silver scurf, make controlling the disease with seed treatment difficult. Potato tuber seed treatments and environmental storage management practices were investigated as means to minimize silver scurf. Fungicide seed treatments were evaluated for control ofH. solani; disease was evaluated during the growing season, at harvest, and after 5 months of storage. Silver scurf was observed on progeny tubers eleven weeks after planting. Fungicides that reduced silver scurf incidence and severity on the seed resulted in reduced incidence and severity of the disease in the progeny tubers at harvest and significantly lower disease ratings after storage. Only small increases in disease incidence (0-8%) were seen after storage. Thiophanate-methyl with mancozeb, Captan with mancozeb, and fludioxonil were among the most effective in reducing the incidence and severity of silver scurf on seed and in progeny tubers (Incidence on progeny tubers at harvest for these three treatments were 3%, 9%, and 8% respectively). Thiophanatemethyl alone was not effective for control of silver scurf (48% incidence compared to 43% incidence for the untreated control). Environmental conditions in storage affected disease development. Reduced humidity (85%) during the curing period (0–3 weeks after harvest) significantly reduced (11%) the surface area of tubers infected with silver scurf. Free moisture on the tuber surfaces during storage significantly increased (15%) tuber surface area infection.H. solani was shown to survive in soil and on some potato storage building materials for up to 9 months. The silver scurf disease of potatoes can be suppressed using effective seed treatment and storage management.     

Spraying potatoes to prevent leaf roll spread by the green peach aphid

Studies were made at Presque Isle, Maine, 1962–1966, to determine the suppressive effects of several materials against spread of the potato leaf roll cirus,Corium solani Holmes, transmitted by the green peach aphid,Myzus persicae (Sulzer), when applied as foliar sprays to Kennebec, Green Mountain, or Chippewa potatoes in field cages or in field plots. The early cage tests showed that spray mixtures containing 1% of the systemic plant growth regulant chlorocholine chloride (2-chloroethyltri-methylammonium chloride) or 1% of mineral oil were more effective than the insect antifeeding compound AC-24,055^® (=ENT-25,651), the aphid-repellent compounds ENT 20,430 or ENT 21,178, or the surfactants Sarkosyl-O^® (bis (2-ethylhexyl) sodium sulfosuccinate) or Aerosol-OT^® (CH₃ (CH₂)_n CON (CH₃) CH₂ COOH). Field tests disclosed that chlorocholine chloride at 5.2 lb or 2.6 lb/a/a was more effective when healthy green peach aphids were placed on infector plants in the plots soon after the plants were sprayed, 1 week later, or soon after the 2nd of 2 weekly applications than when the aphids were introduced before spraying. The difference in leaf roll suppression at these two dosages was not significant at the 5% level; as high as 90% control of leaf-roll spread was obtained. When only natural infestations of aphids were involved and field spread of the virus was light, the 86% control of leaf roll spread that was obtained from 4 weekly applications made in late June and in July was not significantly different (P=0.05) from the 79% control obtained from 2 biweekly applications made during the same period of time. The potato plants soon recovered from the slight chlorosis resulting from the spray treatment and there was no reduction in weight of US 1 tubers at harvest. Aphid population trends in treated plots were not affected.     

Effect of repeated applications of insecticides to potatoes on numbers of Myzus persicae (Sulzer) (Hemiptera: Aphididae) and on the frequencies of insecticide-resistant variants

Numbers of Myzus persicae on potatoes (Solanum tuberosum) receiving three insecticide regimes were recorded in 1985 and 1986. Frequencies of insecticide-resistant variants were determined using an immunoassay for esterase-4 (E4), the enzyme responsible. M. persicae was more abundant at the end of the season on plots sprayed alternately throughout the experiment with a mixture of pyrethroid with oil and pirimicarb, than on those treated with pirimicarb alone. Frequency distributions of E4 activity showed that very resistant variants intermediate between R₂ and R₃ levels accounted for >50% of the populations. Further samples of aphids, collected on separate farms from defoliated patches in late-growing potato crops where repeated spraying had failed to control aphids, showed that these highly resistant variants had again been selected. Possible reasons for the observed increase in numbers of M. persicae following pyrethroid/oil treatment and consequences for virus control are discussed.     

Preconditioning and storage of chemically immature Russet Burbank and Shepody potatoes

Russet Burbank and Shepody potatoes of different chemical maturities (i.e. varying sucrose concentrations) at harvest were preconditioned by holding at 15 C for various durations to lower the concentration of reducing sugars to levels acceptable for processing as french fries out of 8 C storage. In chemically immature tubers (i.e. those harvested with a high sucrose), sucrose declined after harvest and stabilized in storage regardless of the preconditioning period. However, there was a temporary small increase in sucrose after harvest in more chemically mature tubers. The concentrations of the reducing sugars glucose and fructose were low at harvest, usually < 1.0 mg g^?1, but increased rapidly during the first 30 to 45 d of storage in tubers with more than 2.0 mg g^?1 sucrose at harvest. Preconditioning for up to 70 d at 15 C either limited the increase in reducing sugars or lowered them more rapidly during storage than when preconditioned for only 14 d. Fresh weight loss of Russet Burbank and Shepody was greater in physically and chemically immature tubers compared to more mature tubers. Extended preconditioning of Russet Burbank and Shepody resulted in minimal additional weight loss.     

Relative differences in sugar content of basal and apical portions of Russet Burbank potatoes

Basal and apical portions of mature and immature Russet Burbank tubers stored at 42 F (5.6 C), 45 F (7.2 C), and 48 F (8.0 C) were analyzed for sucrose and reducing sugars at seven monthly intervals for three seasons. Percent relative difference of reducing sugars (between mature and immature tubers) was greater in the apical than the basal portion. On the other hand, seasonal differences in percent reducing sugars were reflected more in the basal portion by greater relative differences among seasons than in the apical portion. Statistical analysis showed no trend or influence of maturity or storage temperature in affecting the relativeratio of reducing sugars between the basal and apical portions. Differences among growing seasons appeared to affect this ratio. Tubers from the 1970–71 season had more equal relative amounts of sugars in the two portions than did the tubers from 1968–69 or 1969–70 seasons. Ratio ofsucrose between the basal and apical portions was not affected appreciably by maturity, storage temperature or season, although immaturity and lower storage temperatures caused slightly greater overall sucrose accumulation. Sucrose and reducing sugar contents were poorly correlated regardless of maturity, storage temperature or different seasons.     

Effects of short periods of chilling and warming on potato sugar content and chipping quality

Two days of chilling (exposure to 1 C) had no detectable effect on chip color or sugar content of potato (Solanum tuberosum L.) tubers. Four days of chilling led to increases in sugars if potatoes were stored at 10 C or 19 C for 3 to 4 days after chilling ended. Longer chilling gave increases in sugars by the end of the chilling period, and returning tubers to 10 C or 19 C magnified the response. Glucose and fructose gave similar increases from chilling treatments, except that glucose levels were consistently greater. Sucrose was increased by chilling, but the response pattern did not always resemble that of the reducing sugars. Twenty-seven days of storage at 19 C after chilling lowered levels of reducing sugars late in the storage season but not in December. Cultivars differed in response to chilling. Kennebec tubers accumulated far more reducing sugars but much less sucrose than did Norchip tubers. Storage at 19 C after chilling lowered the sucrose content of Kennebec and Monona while raising that of Norchip.     

Ascorbic acid and glycoalkaloid content of Atlantic and Superior potato tubers as affected by supplemental irrigation and soil amendments

Atlantic and Superior potato (Solanum tuberosum L.) tubers were collected at harvest from two field experiments in Maine during 1993 and 1994. Tubers were analyzed for ascorbic acid (ASC) and total glycoalkaloid (TGA) concentration within one month of harvest and after 4 to 5 months of storage at 10 C. ASC concentration was significantly higher in Superior than Atlantic at harvest and after storage. TGA concentration was consistently higher in Atlantic than Superior. Irrigation tended to slightly reduce ASC and increase α-solanine concentrations when applied too late in the season for yield benefits. Storage decreased tuber ASC content, but no specific pattern was observed for TGA changes. Soil amendment programs using compost and manure (22 Mg ha^?1 potato compost + 45 Mg ha^?1 manure) did not dramatically affect tuber ASC or TGA concentrations. ASC content of the tubers declined dramatically in storage, but no consistent pattern was found for tuber TGA changes. We conclude that genotype, growing environment, and storage time play much stronger roles in determining tuber ASC and TGA levels than do irrigation and soil management programs. We observed a negative relationship between the average tuber size of the assayed samples and ASC concentration in fall samplings; however, this relationship was not observed from storage. Average tuber size and TGA content generally displayed a negative relationship.     

The immediate effect of gamma irradiation upon the sugar content of potatoes previously stored at 2, 4.5, 6, 10 and 15.5°C

Summary The sugar content of samples of potatoes, cv. Majestic, was varied by storage for 4 weeks at 2, 4.5, 6, 10 and 15.5°C, before irradiation with 10 krad. With initial sucrose contents of 0.14–0.37% FW (tubers from 4.5–15.5°C) the marked temporary increase in sucrose, as reported previously, was observed, reaching a maximum after 3–7 days before falling rapidly to a level rather higher than in non-irradiated tubers. Tubers from 2°C, with 1.4% sucrose, showed an immediate drop in this after irradiation, succeeded within 3 days by a rise to values not significantly different from the controls. Irradiation caused a significant increase in reducing sugar content, for a period of up to 7 days in sweetened tubers, but for 21 days or more in unsweetened tubers. Previous storage at the different temperatures had some permanent residual effect upon the sugar content of the controls during subsequent storage for up to 90 days at 10°C.     

The effect of potato virus X on susceptibility of potato tubers toFusarium roseum ‘Avenaceum’

Potato virus X (PVX)-free and mild PVX-infected tuber lines originating from the same Katahdin clone were compared for susceptibility to tuber rot incited byFusarium roseum (Lk.) Synd. and Hans. ‘Avenaceum’. The effect of interval between top-kill and harvest on development ofFusarium tuber rot was also determined. A series of tubers from both PVX-free and PVX-infected tuber lines was either (i) mechanically bruised and inoculated by immersion in a spore suspension ofF. roseum ‘Avenaceum’, (ii) mechanically bruised but not inoculated, (iii) inoculated only or (iv) neither bruised nor inoculated. Tubers from all treatments were then stored at temperatures of 18–21 C (65–70 F) for a 3-week period prior to being placed at 4 C (39 F) for the remainder of the storage period. The amount of rot was determined after a 5–6 month storage period at the latter temperature. In a 4-year study PVX-free tubers were significantly (1% level) more susceptible to infection byF. roseum ‘Avenaceum’ than tubers infected with mild PVX. PVX-free tubers left in the ground for 2 or 3 weeks after top-kill were significantly (1% level) more susceptible toFusarium dry rot than those infected with the virus; however, there was no significant difference in disease incidence between PVX-free and PVX-infected tubers when harvested 4–5 weeks after top-kill. Tubers, both PVX-free and PVX-infected, remaining in the ground for a 2 week period following top-kill were significantly (1% level) more susceptible toFusarium tuber rot than those harvested 3 weeks after top-kill; similarly, both PVX-free and PVX-infected tubers harvested 3 weeks after top-kill were significantly (1% level) more susceptible than those left in the ground for a 4–5 week interval.