Potato minitubers: Technology validation in Mexico

The effects of four previously reportedin vitro tuber-inducing modified culture media on the potato cultivars Atzimba and Juanita were studied under three illumination regimes. Tuberization from stem segments started 7–18 days after transfer for all the cultivar-light-medium combinations, but this early start was not related to tuber yield. Atzimba tuberized more than Juanita (1.0 and 0.8 tubers/plant respectively), and 8 h light was optimal. The medium by Wang Hu (WH) promoted the greatest tuberization for cultivar Atzimba (1,198 mg/plant) and that by Palmer-Smith (PS) for Juanita (290 mg/plant). The modified Stallknecht’s (ST), on the contrary, slightly stimulated tuberization under all illumination conditions. The presence of cytokinins and light favored the tuberization process. Dormancy was not observed in any of the microtubers, regardless of the tuber-inducing treatment.     

Kinetin,thermotherapy, and tissue culture to eliminate potato virus (PVX) in potato

PVX infected plantlets from two potato cultivars grownin vitro with 0.3, 3, 30 or 300 ppm kinetin were exposed to temperatures of 28 or 35 C. After 3 wk, axillary buds were isolated and grown aseptically in organogenic media, followed by PVX testing by ELISA. The serological test was also run on whole plantlets at the end of the kinetin-temperature exposure. No donor plants exposed to 28 C nor the plantlets derived from their buds gave an ELISA (-) reaction, regardless of the kinetin content of the media or that of the cultivar. At 35 C the virus was suppressed to undetectable levels in several whole plantlets. In the cultivar Alpha, 2 out of 6 resulting plantlets after isolation of buds were virus-free in the presence of 3.0 mg/1 kinetin during the treatments. From Atzimba, about 15–40% of the regenerated plants were ELISA (-), without any relationship to the cytokinin content in the media. Heat had a stronger influence on virus elimination than kinetin and the results varied with the cultivar.     

Eradication of potato virus X from potato by ribavirin treatment of cultured potato shoot tips

Ribavirin treatment of cultured potato shoot tips was tested as a means of eradicating potato virus X (PVX) from two potato cultivars. Shoot tips were cultured on liquid medium containing 0, 1, 10 or 100μg/ml ribavirin. Cultures were evaluated periodically for viability, and scored for vigor on a relative growth scale. Developed plantlets were assayed for PVX by transmission tests toGomphrena globosa. Ribavirin treatment was phytotoxic at all tested concentrations, and lethal to all cultivars treated at 100 μg/ml. Treatment also delayed plantlet development by up to 2 months at 1 and 10 μg/ml as compared with nontreated controls. PVX assays indicated that 80 and 83% of the plantlets were free of PVX following treatment with 10 μg/ml for cultivars Russet Burbank and Red McClure, respectively. Five and 6% of the plantlets developed from the 1 μg/ml treatment were PVX-free, whereas 0 and 2% of the controls were PVX-free for the same cultivars. Six to 8 months were required to develop plants from shoot-tip cultures treated with 10 μg/ml ribavirin.     

General characteristics of coumarin-induced tuberization of axillary shoots ofSolanum tuberosum L. culturedin vitro

Coumarin readily stimulates tuberization of cultured axillary shoots obtained from etiolated potato sprouts. Adequate concentrations of coumarin must be continuously present in the medium to effect tuber initiation. High nitrogen, gibberellic acid, abscisic acid, indole acetic acid, or naphthalene acetic acid reduced or inhibited coumarin-induced tuberization. Gibberellic acid and high concentrations of nitrogen in medium inhibited the uptake of coumarin-3-14C by the. axillary shoot. Based on the data of physiological activities by coumarin in other plant species and our data on tuberization, we propose that coumarin may represent in part the unknown inhibitor responsible for tuber initiation with reference to the inhibitor/gibberellic acid ratio theory of tuberization.     

Light effects on the growth and morphogenesis of potato(Solanum tuberosum) in vitro: A review

Growth, morphogenesis, and tuberization of potato tissuesin vitro are affected by light. Measurements of the various aspects of light that control development and growth of potato are outlined. Physical parameters like light sources, delivery of the light source, and the degradation of culture media by light are discussed. Irradiance, photoautotrophic growthin vitro, spectral wavelength, and photoperiod modify the responses of potato tissues in culture. Acclimatization of tissue culture plantlets, vegetative growth, and the production, quality, and dormancy of microtubers are modified by light. New light sources such as light-emitting diode (LED) lamps are becoming available forin vitro research and for micropropagation of potato. Pulsed or chopper light has the potential to save energy costs. Light effects on potato protoplasts, anther culture, virus eradication, andin vitro conservation are discussed. Potential new research areas are the effect of the spectral quality of light on regeneration of shoots and somatic embryosin vitro, end-of-day red and far-red light treatments, axillary shoot formation in cultured plantlets, and the use of LEDs. The influence of monochromatic spectral filters on growth and development of potatoes in tissue culture could potentially lead to improvements in productivity. The relationship between daily quantum light integral and photoperiod and their effects on growth and morphogenesis of the potato will provide some useful areas of research.     

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.     

Variability for photoperiodic reaction among diploid and tetraploid potato clones from three taxonomic groups

The photoperiodic behaviour of 18 potato clones from three taxonomic groups (Andigena, Phureja, and Tuberosum diploid and tetraploid) was studied under controlled environments. Day lengths of 11, 13, 15, and 17 hours were provided with all other environmental conditions common. Six characters were studied: tuber formation, stem height, haulm weight, tuber number, tuber weight, and tuberization efficiency (tuber weight/haulm weight). All clones showed well defined critical daylength values at which tuberization was either absent or irregular. A wide variability for critical day length was observed among clones, the higher values corresponding to Tuberosum tetraploid and the lower values to the Phureja group. Stem height and haulm weight increased as photoperiod increased. Tuber number remained practically the same for all groups but Phureja which showed an inverse relationship. Tuber weight decreased as daylength increased for the groups Andigena, Phureja, and Tuberosum diploid which on the average showed a short day reaction for tuber yield. Tuberosum tetraploid did not show any significant change, behaving as a day neutral type. Tuberization efficiency was, in general, decreased as daylength increased suggesting a short day behaviour for all groups. A regression analysis of tuber yield and tuberization efficiency on photoperiod indicated that, in general, tetraploid genotypes were less sensitive to drastic increases in daylength than diploids.     

The effect of nitrogen on the coumarin-induced tuberization of potato axillary shoots culturedin vitro

Coumarin-induced tuberization was studied on axillary shoots excised from etiolated potato sprouts each of which was cultured in vitro. Sprouts grown on culture medium with high nitrogen concentrations produced axillary shoots which elongated and would not readily tuberize. Sprouts cultured on medium low in nitrogen produced axillary shoots which tuberized with limited elongation. Carbohydrate concentration of the culture medium for the excised axillary shoot could significantly modify the nitrogen effect of the potato sprout medium. Axillary shoots growing on high nitrogen medium did not tuberize except in cases where the carbohydrate concentration was increased.     

Effect of inoculum concentration ofPhytophthora infestans on potato late blight

Zoospore suspensions ofPhytophthora infestans applied to potato cultivars in the field with an exponential inoculum sprayer resulted in defoliation within a range of severity that was log-normal with respect to inoculum concentration. Regression lines for different cultivars differed in position and, depending upon moisture conditions, slope, indicating that the cultivars differed in resistance to penetration and to invasion of tissue by the pathogen.     

Characterization of a new gibberellin related dwarfing locus in potato (Solanum tuberosum L.)

Gibberellins have been shown to be involved in such important processes as seed germination, flowering, maturation and tuberization in potato. Parents fromSolanum tuberosum Groups Andigena and Tuberosum were found to produce progeny containing dark green, rosette dwarf individuals which could be completely restored to normal appearance by exogenous GA₃. Test crosses indicated that this phenomenon can be explained by the action of a single locus, the dwarfing characteristic being conferred by the nulliplex condition. The gene symbol “ga₁” is proposed. Group Andigena dwarfs demonstrated much greater tuberization compared to their normal full sibs or dwarfs restored to normal phenotype by exogenous GA₃. The possibility that such gibberellin mutants may be involved in the long day adaptation of Gp. Tuberosum is discussed. This character may also be a useful tool for investigating various aspects of the gibberellin status of the potato.     

Effect of time of inoculation with potato leafroll virus on development of net necrosis and stem-end browning in potato tubers

The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed.     

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.     

Aggressiveness of Phytophthora Infestans Genotypes on Potato Stems and Leaves at Three Temperatures

Epidemics of late blight on potato in the semiarid Pacific Northwest since 1991 have been characterized by a prevalence of stem lesions in relation to leaf lesions. This study was conducted in 1997 to test the hypothesis that isolates representing immigrant strains of Phytophthora infestans were more adapted at causing stem lesions and more aggressive at higher temperatures than isolates representing the relatively older US-1 strain. A total of 23 Phytophthora infestans isolates representing US-1, US-8, and a new A1 compatibility type strain were tested for aggressiveness on leaflets and stems of whole potato plants (cv. Russet Burbank) in 11 trials. Plants in one set of trials were incubated at constant temperatures of 18, 23, and 28 °C for six days with a 16 h photoperiod. Plants in the second set of trials were incubated at the same three day temperatures but the night temperature in all treatments was reduced to 16 °C. Lesion establishment was recorded, and daily severity readings were used to calculate the area under the lesion expansion curve (AULEC). Lesion area, sporulation frequency, sporulation time, and sporulation capacity were also measured. Lesion establishment was higher on stems than on leaves for isolates of all strains. Isolates representing US-8 and new A1 strains often had higher AULEC values but had similar lesion establishment, sporulation frequency, sporulation time, and sporulation capacity values as US-1 isolates. A reduction in components of aggressiveness for all strains was noted at 28 °C, with leaflets being more affected than stems. Sporulation rarely occurred at 28 °C. Few differences in components of aggressiveness were observed between 18 and 23 °C. These findings indicate that isolates from the relatively newer strains (US-8 and new A1) were not better adapted in causing lesions on potato stems than isolates from the old US-1 strain, nor were they better adapted to higher temperatures. The relatively newer strains, however, were generally more aggressive as indicated by higher AULEC on stems and leaflets over the range of temperatures used in this experiment.     

Reinfection of potato seed stocks with potato virus S and potato virus X in Wisconsin

Reinfection of potato seed stocks with the potato viruses S (PVS) and X (PVX) varied with cultivar, virus, and grower. Rapid recontamination was observed for the cultivars Norgold Russet and Ontario with PVS and for the cultivars LaChipper, Norchip, and Norgold Russet with PVX. Recontamination was low for the cultivars LaChipper and Monona with PVS and for the cultivars Kennebec, Monona, Norland, and Superior with PVX. Survey results suggest that PVS and/or PVX can be eliminated from cultivars which appear to possess field resistance to infection, but that further evaluation of cultivars which are very susceptible to reinfection will be necessary.     

In vitro mass tuberization and virus-free seed-potato production in Taiwan

This is the first report ofin vitro tuberization becoming feasible for agriculture in seed-potato production. The optimum condition forin vitro mass tuberization of virus-free potatoes were: 10 mg/1 BA, 8% sucrose. 20°C incubating temperature, and eight hours of 100 lux incubation photoperiod. An estimated 36,000 dormant, miniature tubers were harvested from the aseptic containers incubated on a 10m² bench area in a fourmonth period. After three successive plantings in soil, 1,800 kgs of virusfree seed-potatoes were obtained.     

Fungi associated with Collembola and mites isolated from scabby potatoes

Collembola and mites from the lesions of tubers infected with the acid scab organism were tested for the presence of fungal potato pathogens.Streptomyces spp. were found on and in the bodies of these arthropods.Verticillium albo-atrum was present on the external surface and in the body of the Collembola. Various other soil-inhabiting fungi which are not known to be potato pathogens and which were found on and in the bodies of these arthropods are noted.     

Detection of potato viruses X and S in tissue culture plantlets

The latex agglutination test (LAT) and enzyme-linked immunosorbent assay (ELISA) were evaluated in separate studies for their ability to detect potato virus X (PVX) and potato virus S (PVS) in tissue culture plantlets. Healthy and infected clonal lines of several potato cultivars were used. LAT was unsatisfactory because only low levels of agglutination were obtained with infected samples, and because variable and inconsistent results were obtained with both healthy and infected clones. ELISA, however, consistently gave high spectrophotometric readings and intense visual reactions for infected but not for healthy clones. The results indicate that ELISA can be used to detect PVX and PVS in tissue culture plantlets, and in programs where tissue culture is employed, early detection and elimination of infected plantlets is possible.     

Eradication of potato virus Y and S from potato by chemotherapy of cultured axillary bud tips

Ribavirin (virazole) treatment of cultured axillary bud tips (3-4 mm) was tested as a method of eradicating potato virus Y (PVY) and potato virus S (PVS) from two potato cultivars, Norchip and Desiree. Ribavirin treatment was phytotoxic at all concentrations tested, but cultivars treated at 5 mg/1 were visually similar to the nontreated control cultures after 20 weeks. The buds treated with ribavirin at 20 mg/1 had a survival rate of only 30–40%. Virus assays indicated that 2,74,82, and 89% of the plants were free of PVY, and 1, 71, 83 and 90% were free of PVS, 20 weeks following treatment with 0, 5, 10, and 20 mg/1, respectively. Virus assays indicated that 2, 74, 82, 89% of the plants were free of PVY, and 1, 71, 83 and 90% were free of PVS, 20 weeks following treatment with 0, 5, 10, and 20 mg/1 ribavirin treatment respectively for cultivar Norchip. Desiree cultivar assayed 2, 69, 80 and 86% free of PVY and 2, 74, 85 and 93% free of PVS, 20 weeks following treatment with 0, 5, 10, and 20 mg/1 ribavirin treatment respectively.     

Protein in potato flakes: Evaluation by the meadow vole (Microtus pennsylvanicus)

Th protein content of six potato cultivars, Russet Burbank and the numerically designated 58, 709, 711–3, 321–65 and 322–6, ranged from 5.5 to 8.7 g per 100 g. Similar results were obtained by both Kjeldahl and Biuret procedures. Amino acid analyses with a Beckman model 120C showed methionine to be the low level amino acid. Glutamic and aspartic acids were in higher amounts than the essential amino acids. The Chemical Score was similar to data of bio-assays by the meadow vole,Microtus pennsylvanicus. Cultivar 58 produced the greatest weight gain, but was only significantly higher than cultivars 709 and 711–3. Both weight gains and digestibility were increased by the inclusion of methionine in the diet.     

Effect of gelling agents onin vitro tuberization of six potato cultivars

The gelling agent Phytagel? was compared with Difco Bacto-agar forin vitro tuberization of six potato cultivars (Jaerla, Blanka, Claustar, Kennebec, Désirée, and Baraka). On a culture medium with 6% sucrose but lacking growth regulators, tuberization was higher when Phytagel? was used rather than Difco Bacto-agar, regardless of the photoperiodic regime used. Chemical analyses of the gelling agents revealed a higher mineral content and organic impurities in Bacto-agar than in Phytagel?, which is therefore recommended for microtuber production. The same gelling agent should be used in all treatments of microtuberization experiments in order to draw meaningful physiological conclusions.