Innovative propagation methods in seed tuber multiplication programmes

Summary The production of large volumes of vitroplantlets and greenhouse tubers for increasing the rate of multiplication at the start of seed programmes provides the opportunity of reducing the total number of field generations grown before the seed moves into commerce. This implementation is especially useful for countries where high quality potato seed tubers cannot be produced because there are no vector-free production areas. This review covers the following steps: a) laboratory production of microplantlets and microtubers; b) minituber production in the glasshouse; c) storage and dormancy of micro- and minitubers; d) field performance of micro- and minitubers compared with conventional seed tubers; e) incorporation of the mentioned propagules in seed production systems. Many optimized protocols are already available for propagating plantlets, inducing microtubers and obtaining minitubers in the glasshouse at all periods of the year. Advanced molecular approaches techniques (RFLP and RAPD) to detect genetic variation in the progeny of these propagules have been described. Investigations carried out in this field have shown genetic stability, with the propagules usually reproducing plants true-to-type and tubers without deviants. By contrast, variations were demonstrated in DNA extracted from old suspension cell culture. Field trials assessed a lower yield potential crops from in vitro propagules compared with conventional seed tubers., mainly due to slow early crop development and the failure of plants caused by early stress after emergence. This may cause problems when the growing season is short because of the necessity for planting late to avoid night frosts and the mandatory haulm killing dates, common in many seed producing areas. Strategies for improving the field performance of micro- and minitubers are discussed. The most promising crop husbandry techniques appear to be: a) using tubers of a suitable physiological age, properly presprouted and encapsulated; b) optimizing the time application of fertilizer and irrigation, and c) using floating films. Outside the classical seed tuber areas of Northern Europe where the length of the growing period for pre-basic seed is usually not more than 80 days, the growing season is long enough to obtain reasonable yields even from micro- and minitubers.     

Potato Cultivar and Seed Type Affect the Development of Systemic <Emphasis Type="Italic">Potato virus Y</Emphasis> (PVY<Superscript>N-Wi</Superscript>) Infection

Potato virus Y (PVY) infection is one of the greatest challenges to seed potato production in the United States. To determine how cultivar and seed type affect the development of systemic PVY infection, Russet Burbank and Russet Norkotah Colorado 3 cultivars were grown from two types of pre-nuclear seed (i.e., plantlets and minitubers) and Generation 3 (G3) tubers and challenged with PVY strain Wilga (PVY^N-Wi). Systemic PVY infection was measured by assaying spread of virus from the inoculation site to upper non-inoculated leaves. The Burbank cultivar had a lower incidence of systemic PVY infection compared to the incidence of systemic PVY that developed in the Colorado 3 cultivar. Furthermore, Burbank plants grown from G3 tubers had a lower incidence of systemic PVY infection, as compared to Burbank plants grown from plantlets. Together our results indicate that both cultivar and seed type affect the development of systemic PVY^N-Wi infections post-inoculation.     

Growth and yield of potato plants grown from microtubers in fields

Despite many reports of thein vitro production of microtubers, little is known about plant growth and yield from microtubers planted in the field. This study clarified differences in growth and yields between potato plants grown in the field from microtubers and from conventional seed tubers. The experiments were performed at Hokkaido University, Japan, over four years. Conventional seed tubers of about 50 g and microtubers of two sizes (0.5–1.0 g and 1.0–3.0 g) of the latematurity cultivar Norin 1 were planted, and plant growth and tuber yields were analyzed. The microtuber plants had a lower initial increase in root and leaf area index than conventional seed tuber plants, but had the same leaf area index after about 40 days from emergence. The first tuber formation in microtuber plants was about 7 days later than in conventional seed tuber plants, while tuber bulking occurred about 14 days later in microtuber plants. Consequently, the onset of tuber weight increase was later in microtuber plants, but the rate of increase thereafter was similar between conventional seed tuber and microtuber plants. At harvest the tuber fresh weight of microtuber plants was 82% that of conventional tuber plants, suggesting a potential for using microtubers for field planting.     

马铃薯微型薯田间繁殖的研究

以马铃薯晚熟品种“下寨６５”为试验材料,研究了离体诱导微型薯直播田间繁殖块茎繁殖脱毒田间１～５代种薯的质量和效率。结果表明,生育阶段比同品种网室繁殖脱毒小薯同代脱毒种薯略迟;生长势、株高、茎粗、主茎分枝数、单株叶面积、根系数、匍匐茎数和匍匐茎长度等生长发育指标,ＰＶＸ、ＰＶＹ、ＰＬＲＶ和ＰＶＡ等重要病毒害发病率及病情指数,干腐病和软腐病发病率,晚疫病发病率和叶面枯死率相同;未发现环腐病和黑经病。单薯重量平均４５．１ｇ,随田间种植代数增加而增大;单株结薯数、单位面积结薯数逐代减小,脱毒田间１～４代单株产量和单位面积产量逐代增加,繁殖效率与脱毒小薯相同,故离体诱导微型薯田间繁殖块茎繁殖脱毒种薯是经济有效且切实可行的。     

Use of jasmonate for conditioning of potato plantlets and microtubers in greenhouse production of minitubers

A two-year study was conducted to determine the effects of (1) jasmonic acid (JA) pre-treatment, (2) JA supplement in culture media, (3) cultivar (Amisk, Atlantic, Russet Burbank, Shepody, and Umatilla Russet), (4) light (0 h, 8 h), and (5) dormancy breaking treatment (Rindite, gibberellic acid) on greenhouse production of minitubers from microtubers andin vitro plantlets. The microtubers were produced under short day (8 h) light conditions and in darkness, from stock plantlets pre-treated with JA and untreated, and on tuberization media with or without JA.In vitro plantlets (the industry choice in nuclear seed potato production) of all five cultivars performed well, meeting the standard criteria for greenhouse production of minitubers. Production of minitubers from microtuber-derived plants of cvs Amisk, Russet Burbank, and Umatilla Russet was similar to that of plantlet-derived plants with regard to number of minitubers. Yields (weight), however, were lower than those from plantlets. Microtuber responses to JA varied with cultivar. Amisk produced the highest number of minitubers per plot from microtubers derived from JA pre-treated plantlets. Jasmonic acid-pretreated microtubers also gave significantly more minitubers in Russet Burbank and Umatilla Russet than the microtubers from other treatments. Shepody did not benefit from JA treatments and JA pre-treated Atlantic microtubers performed poorly, producing significantly lower yields of minitubers than other cultivars. Independently of cultivar, microtubers produced under 8-h photoperiod gave significantly higher yields of minitubers than microtubers produced in the dark. Dormancy release was the key factor influencing microtuber performance. Rindite proved to be a much more effective dormancy breaking treatment than gibberellin. JA conditioning of stock plants prior to tuberization is being proposed as a treatment in production of microtubers for greenhouse production of minitubers.     

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.     

Potato Plants Grown from Minitubers are Delayed in Maturity and Lower in Yield,but are not at a Higher Risk of <Emphasis Type="Italic">Potato virus Y</Emphasis> Infection than Plants Grown from Conventional Seed

Potato virus Y (PVY) is the most important virus in North American seed potato (Solanum tuberosum L.) production. Planting virus-free minitubers in place of field-grown seed, which usually has a low PVY incidence, reduces initial PVY inoculum in the field. However, plants grown from minitubers are smaller and emerge later than those grown from conventional seed, which could make them more likely to become infected with PVY. We tested the effects of seed type of three potato cultivars (Dark Red Norland, Goldrush, and Red La Soda) on PVY incidence, tuber yield, and flowering time. The incidence of PVY in plants grown from minitubers did not differ from that of plants grown from conventional seed. Minituber-grown plants produced lower tuber yields than plants grown from conventional seed. Plants from minitubers also emerged and flowered later, but this did not increase their incidence of PVY. Cultivar-specific differences were observed in tuber yield and flowering times, suggesting that this variation may influence PVY incidence more than seed type.     

Microtuber and minituber production and field performance compared with normal tubers

Summary Microtuber and minitubers of cv. Monalisa were produced in the laboratory and compared with normal seed tubers in a field experiment. These tubers were planted at similar plant densities (13.6 sprouts per m²) with two distances between rows (60 and 90 cm). Final ground cover was almost complete only in the plots derived from normal tubers and decreased with the size of the mother tubers. Normal seed, mini- and microtubers yielded respectively 50.8, 31.7, and 17.0 t/ha (means of two spacings). At close and wide spacing between rows, microtubers yielded respectively 27.3 and 6.7 t/ha, and minitubers 38.9 to 24.4 t/ha. Row spacing did not influence the yields from normal seed tubers. Total number of tubers per m² was also affected and, as means of the two spacings, ranged from 107.8 with microtubers, 122.1 with minitubers, to 142.9 with normal tubers. Mother tuber type also affected the yield distribution in three tuber grades (<36, 36–55, and 55–80 mm) and micro and minitubers produced many small tubers. Multiplication rates and the possible use of different propagation sources are discussed.     

改进生产马铃薯种薯技术的研究

我国于１９７５年已利用马铃薯茎尖组织培养获得无病种薯．相继在马铃薯主要产区的许多省份内均取得显著的增产就地留种的效应．但获得的无病毒种薯并不是一劳永逸的，因此必须采用综合措施防止无病毒种薯再侵染病毒和其它病原。例如，应用蚜虫飞迁资料控制传播病毒以及将微型薯和小薯种植在防虫温室和防虫网棚内．在种薯检验过程中应利用酶联免疫和往返凝胶电泳跟踪检测，以便在防虫网棚群内采取局部控制，对脱毒小薯进行无性繁系选择．     

Comparison of Mineral Oil and Rapeseed Oil Used for the Protection of Seed Potatoes against PVY and PVM Infections

The aim of this research was to compare the effectiveness of mineral oil with rapeseed oil in the protection of potato seeds against Potato virus Y (PVY) and Potato virus M (PVM) infection. The research was carried out under field conditions in the north of Poland, in the Department of Potato Protection and Seed Science of the Plant Breeding and Acclimatization Institute??National Research Institute at Bonin. The effects of oil protection on potato seed infection by viruses, yield, and its structure and phytotoxity were assessed. Two rapeseed oils and one mineral oil were used: Olejan 85 EC (85% of natural rapeseed oil), alimentary oil Marlibo (100% of natural rapeseed oil) and Sunspray 850 EC (98.8% mineral oil+1.2% emulsifier). The effectiveness of oils in protection against PVY and PVM tuber infection was tested on two cultivars (Clarissa and Rosalind), which have a different level of resistance to the two viruses. The assessment of phytotoxicity was carried out on 10 potato cultivars from different earliness groups (Augusta, Bryza, Cekin, Clarissa, Impala, Krasa, Rosalind, Satina, Velox). Two oil concentrations, 2% and 4% were applied. During the growing period, eight to nine oil treatments were applied at 7-day intervals. The effectiveness of rapeseed oils against PVY and PVM was much weaker than that of the mineral oil and for the susceptible cultivar the percentage infected tubers did not differ significantly from untreated crops. However, Olejan 85 EC deserves attention as it significantly reduced PVY infection across years in the more resistant cultivar, especially in the case of a lower concentration (2% vs. 4%). When there are no other means of protection to use on organic seed plantations, this oil can be used as an alternative, especially in the case of cultivars which are moderately resistant to PVY. A disadvantage of its application may be the fact that in some years symptoms of phytotoxicity on potato plants were recorded and a lowering of tuber yield.     

Photoperiodin vitro affects subsequent yield of Greenhouse-grown potato tubers

In vitro potato plantlets of cultivar (cv.) Shepody (Solatium tuberosum L.) were exposed to 12-or 16-hr photoperiods for 8 weeks. Plantlets were acclimatized to the greenhouse and grown under 14-hr photoperiods until they senesced, and minitubers were harvested. Greenhouse-grown potato plants developed from tissue-culture plantlets exposed to a 16-hr photoperiod were taller and had more nodes than plants developed from plantlets exposed to 12-hr photoperiods. However, yield data of minitubers from greenhousegrown plants indicated that the 12-hr photoperiodic treatment increased the numbers, dry weight and specific gravity of minitubers. A further advantage of the 12-hr photoperiodic treatment was the greater numbers of minitubers in the 15–40 g size class compared with tubers in the <15 g and >40 g size classes. Thus, for the cv. Shepody, plant height and node number of greenhouse-grown plants were not good indicators of minituber yield from that crop. Seed potato nuclear stock facilities producing minitubers should investigate the possibility of optimizing minituber production by exposing multiplication cultures to shorter daylengths.     

马铃薯脱毒原原种微型化生产和微型薯应用

马铃薯脱毒原原种微型化生产的技术关键在于控制植株个体生长;而其首要条件是种苗基础和营养水平.利用普通日光温室,在瓶苗假植或使用已有的微型薯育苗的基础上,采取砂床剪枝扦插和高密度少肥栽培生产微型薯,比移栽瓶苗或直播微型薯的办法更好.即在剪枝扦插后40天收获,平均获得单薯重1～5克的微型薯个数占总数的(76.0～91.6%,最高达100%.单薯重1克以上的4个规格1～3克、大于3克、大于5克、大于10克)微型薯直播亩产达1806～2194公斤,接近或超过大薯切块直播(1962公斤/亩),但4个规格微型薯的含量不呈规律性差异.单薯重小于1克的微型薯育苗移栽亩产达2299公斤,略高于大规格微型薯直播产量.但考虑其利用价值,将单薯重小于1克的微型薯作为脱毒原原种微型化生产的基础种苗使用更合适.     

内蒙古西部区马铃薯脱毒种薯快速繁育的研究——Ⅱ.脱毒种薯生产技术及其良种繁育体系的研究

在内蒙古乌兰察布盟后山地区武川原种基地，对各级种薯生产技术及其良繁体系进行了系统的研究。现已明确：在开放条件下生产脱毒小薯（原原种），产量可达８０７３～９４６５ｋｇ／ｈｍ２，种薯产量和质量不低于温、网室生产的脱毒小薯；不同薯重的脱毒小薯旱坡地直播效果，以１０ｇ和８～１０ｇ薯重的效果好，产量和商品率均高；１级种薯在不同旱地类型种植的增产效果，以旱滩地的产量最高，其次为旱坡地，分别比对照（未脱毒）增产７１．２８％、１７１．２８％；８月上旬为有翅桃蚜迁飞盛期，从７月上旬迁飞初期开始喷药防蚜，防治效果显著；在乌盟后山半农半牧地区以原原种、原种、１、２级种薯建立的３级脱毒良种繁育体系符合该地区的生产实际，能达到留种和保种的快速、优质、高产、低成本的效果。经过６年示范推广，现已在武川等３个旗县普及，累计各级种薯种植面积达到２．３２万ｈｍ２，平均单产３万ｋｇ／ｈｍ２左右，生产出各级种薯及商品薯６９８５万ｋｇ，累计创造社会财富７１５０万元。     

Production of seed potatoes in Cyprus: incidence and economic importance of virus diseases

Summary Since 1981 seed potatoes have been produced on a semi-commercial scale in Cyprus by single multiplication of imported class A stocks. The main virus in these locally produced seed potatoes was potato leaf roll virus (PLRV) which was detected in 369 of 658 seed crops examined, at an average incidence of ca 1.5% (range 0.1%–15%). Tuber infections were detected in 203 of 223 samples tested, at an average incidence of ca 6.8% (range 1–32%), indicating a considerable spread of the virus during local seed multiplication. Potato viruses Y, X and A, and alfalfa mosaic virus occurred at much lower incidence than PLRV. The effect of secondary PLRV infection on ware-potato yield was determined in the cultivars Spunta and Cara, each planted on two different dates. In all four cultivar-planting date combinations there was a very close negative correlation between yield and virus incidence. At 100% infection, losses in total yield varied from 46% (later planting of Cara) to 72% (earlier planting of Spunta). The threshold level of infection for significant losses was ca 10%.     

Field performance of peat-lite mix encapsulated small minitubers

Small minitubers (1.3 to 1.9 cm diameter), produced in the greenhouse from tissue culture plantlets are usually discarded because they are undersized for field planting. They have potential as a means of expanding the production of basic nuclear potato seedstocks. Field trials were conducted to evaluate the performance of greenhouse-produced minitubers at 15 and 30 cm spacings, with one or two minitubers/hill, and with or without encapsulation in a moist ball of artificial greenhouse peat-lite mix. All minitubers were green-sprouted for about two weeks under 16 hr/day fluorescent lighting before planting. Encapsulation in moist peat-lite mix significantly increased total yield by an average of 44% over minitubers without the soil mix. Independent of encapsulation, closer seed spacing and two minitubers/hill increased yields by an average of 35% and 20%, respectively, compared to wider spacing and one minituber/hill. Yields of encapsulated minitubers compared favorably with cut (50 gm) and whole (80 gm) seed, averaging 103% of the cut and 87% of the whole seed yields, respectively. These results indicate that small minitubers can be used effectively to expand production of basic nuclear seedstocks.     

马铃薯试管薯的诱导和应用

试管薯与试管苗一样是马铃薯脱毒原原种薯生产的基础。研究从诱导试管薯形成的最佳接种密度、利用试管薯生产脱毒种薯和保存种质资源的优越性3个方面进行。结果表明,进行试管薯诱导时每瓶接种10个茎切段能获得较多数量和较高质量的试管薯。利用试管薯生产脱毒种薯,可以提高脱毒苗的成活率,保证了脱毒薯的产量和质量,是比较优良的生产方式。运用试管薯保存种质资源,可以减少转接次数,降低病毒病的累加机率,提高了苗源质量,是一种较为实用和保存时间长的方法。     

Disease eradication and propagation of the initial seed potato material in Estonia

Summary The EVIKA Research Centre has developed a disease eradication system for the initial material of seed potato, which consists of 1. Selection of the initial material for eradication, plant thermotherapy, meristem tip cultivation and testing for viruses; 2. Re-eradication (thermotherapy of test-tube plants, cultivation of meristem tips, testing for viruses, testing of varietal quality and yield of disease-free meristem clones, and the selection of meristem clones with best varietal characteristics; 3. Renewing of the initial material (all processes as above, but the initial material is selected from the seed potatoes grown for at least 3 years in the field). Field trials were conducted after the second cycle of eradiaction to determine whether the plantlets were true-to-type and to assess the yield, disease resistance and tuber dry matter. Recently we have also started in vitro testing of meristem plants resistance to late blight, hoping that this approach will improve the selection efficiency. Propagation and growing of the seed tubers consists of 3 main steps: 1. Plantlet propagation in vitro; 2. Greenhouse propagation in plastic rolls; and 3. Planting the first generation tubers in the field. Under our conditions it is the cheapest, simplest and most effective way. Multiplication of the meristem-derived plants is done by shoot tip cuttings in a greenhouse in plastic rolls with peat as the growing medium. The first generation of seed tubers is grown in the field. In our trials plant productivity was affected by the method of multiplication, growing conditions and genotype. The highest yield per hectare was obtained with plants multiplied in plastic rolls. The in vitro plants had more tubers per plant than plants multiplied in plastic rolls. In seed production fields the productivity of plants was more influenced by following our instructions than by multiplication and growing methods. The number of tubers per plant obtained with over 0.5 million plants was 6.5–9.0. In the second generation of seed tubers, grown under equal density, the greater-sized tubers gave more tubers with lower weight than the smaller-sized tubers. Cutting tubers had no effect on the plant development and tuberization.     

Serogroups ofErwinia carotovora involved in systemic infection of potato plants and infestation of progeny tubers

Enrichment techniques and serological strain typing methods were used to determine the source of stem and progeny tuber populations ofErwinia carotovora (Ec) in 1980 and 1981. Plots were established in a field that had been planted with potatoes since 1972. Seed tubers of cultivars Russet Burbank and Norgold Russet were assayed forErwinia carotovora pv.carotovora (Ecc) andErwinia carotovora pv.atroseptica (Eca) by tuber peeling and direct plating and plating following enrichment in a pectate-based broth. Levels of seed tuber infestation ranged from undetectable to 2.4 × 10⁴ colony-forming units per g peel tissue. Prior to planting Ecc was detected in soil samples from field plots by enrichment in a pectate-based broth. Ec was isolated from symptomless plants with increasing frequencies from 8 weeks following planting regardless of the level of Ec populations in seed tubers. At harvest progeny tuber recontamination was low and not related to levels of seed tuber Ec populations. In 1980, serological typing of representative Ecc isolates indicated serogroups III, XXIX, and unknown strains isolated from the soil but not the seed tubers prior to planting were isolated from stems and progeny tubers. Serogroup XXIX was isolated from soil, seed, stems and progeny tubers in 1981. Throughout both years, Ecc was isolated more frequently than Eca from seed, soil, stems, and progeny tubers. These data emphasize the potential for reinfestation of seed stocks and infection of plants by populations of Ecc that overwinter in soil under Wisconsin conditions.     

整薯播种对马铃薯生育及产量的影响

1979～1984年,在黑龙江省北部黑土地区气象条件、生产水平和栽培条件下,通过田间试验,研究了整薯播种对马铃薯生育和产量的影响。结果表明:整薯播种与传统习惯的切块播种相比,6年期间平产出现频率为2次,一般年份整薯播种比切块播种增产9～12%,在春旱严重的1980年,整薯播种表现出非常突出的抗旱保苗效果。在群体叶面积发展进程上,整薯播种表现早发早衰,切块播种晚发晚表,一般年份光合势前者比后者高9.6%,春旱严重的1980年高82.8%。块茎商品率以112.5克为准时,6年平均整薯播种为74.1%,切块播种为80.0%,两者相差5.9%;以50克为准时,整薯播种为97.3%,切块播种为98.2%,两者相差0.9%。     

Volunteer potatoes as a source of potato leafroll virus and potato virus X

Volunteer potatoes were investigated as infection sources for potato leafroll virus (PLRV) and potato virus X (PVX) in a high elevation seed potato growing area of eastern Idaho. Population densities ofMyzus persicae were assessed. Percentage of PLRV and PVX infection of the volunteers and seed potato crops was determined, as well as density of volunteers and certain parameters of volunteer growth and reproduction. Volunteers apparently harbored no more PLRV than the potato crop from which they originated. But they were found to be an important reservoir of PVX with the infection increasing as much as 12.43% in one year. No aphids capable of transmitting PLRV were found although one species that can transmit potato virus Y was recorded. The mean density of volunteers varied from 0 to 84,880 stems/ha. The number of tubers remaining in the field after harvest and winter weather conditions appeared to be the only factors affecting volunteer density. Volunteer plants arising from seed pieces at an average depth of 6.1 cm were found to set an average of 2.1 new tubers per plant at an average depth of 4.0 cm. These results suggest that volunteer potatoes are a significant source of PVX infection in subsequent seed potato crops.