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.     

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。     

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.     

Comparison of inoculation methods on ring rot development in potatoes

Symptoms of bacterial ring rot (Corynebacterium sepedonicum) developed earlier and were more severe in root-inoculated potato plants grown from stem cuttings treated with indole-3-butyric acid (IBA) than in those grown from stem cuttings not so treated or from tuber seed pieces. Disease expression was more rapid and severe in root-inoculated plants than in plants from inoculated seed pieces. The use of IBA-treated stem cuttings provided uniform plant material for ring-rot studies.     

Freeing Russet Burbank potato plants from ring rot by stem cutting and tuber propagation

Apical stem cuttings removed from potato plants (cv. Russet Burbank) infected withCorynebacterium sepedonicum and expressing mild symptoms of bacterial ring rot were demonstrated to be free from the pathogen. This material remained free of ring rot through two additional stem cutting generations and when grown in the field for four successive tuber generations.     

Defender: A high-yielding, processing potato cultivar with foliar and tuber resistance to late blight

The potato cultivar Defender is high-yielding, white-skinned, and notable for having foliar and tuber resistance to late blight infection caused byPhytophthora infestans (Mont.) de Bary. It was released in 2004 by the USDA-ARS and the agricultural experiment stations of Idaho, Oregon, and Washington. Defender is suitable for processing into french fries and other frozen potato products directly from the field or from storage. Defender also may be used for fresh markets in regions such as California, where cultivars with long tubers and white skin are traditionally grown. Resistances to late blight and other potato diseases make Defender an ideal candidate for organic potato production. Defender consistently produced greater total and U.S. No. 1 yields than ‘Russet Burbank’ in Idaho trials. In early harvest trials conducted in the western U.S., average total yields of Defender were 17% and 23% greater than yields for ‘Ranger Russet’ and ‘Shepody’, respectively. In full-season trials conducted in the western U.S., Defender averaged 10% and 15% higher yields than Ranger Russet and Russet Burbank, respectively. Specific gravity of Defender is consistently high, with values comparable to those of Ranger Russet; tuber ascorbic acid (Vitamin C) levels are also high. In addition to late blight, Defender also is resistant to tuber early blight (Alternaria solani, (Ellis & G. Martin), L.R. Jones & Grout), potato virus X, and net necrosis; it has moderate levels of resistance to Verticillium wilt (Verticillium dahliae, Kleb), pink rot, foliar early blight, corky ringspot, and Erwinia soft rot. Defender is susceptible to scab (common and powdery) and potato leafroll virus; it has moderate susceptibility to dry rot (Fusarium spp.) and potato virus Y. Susceptibilities to internal necrosis, tuber greening, and blackspot bruise also have been noted, but may be minimized through cultural and harvest practices.     

Transgenic potatoes expressing anErwinia pectate lyase gene — results of a 4-year field experiment

Summary Four potato lines of cv. Désirée that express the pectate lyase (PL) isoenzyme 3 ofErwinia carotovora subsp.atroseptica were examined in a 4-year field experiment with respect to plant development, tuber yield and resistance of tuber tissue toErwinia soft rot. The PL3 degrades plant cell wall pectin into unsaturated oligogalacturonates eliciting plant defence responses. In one line, enzyme expression was controlled by the CaMV 35S promoter (C) and in three lines it was driven by the potato patatin B33 promoter (D). Plant development of the D-lines in field plots was not distinguishable from that of the non-transgenic counterpart. Also tuber yield was not too different. By contrast, plants of the C-line were smaller than those of the nontransformed counterpart and also showed reduced tuber yield. There were no significant differences in dry mass, starch and protein content of tuber tissue between PL transgenic and non-transgenic potatoes. But compared with the latter, field-grown tubers expressing the PL displayed an enhanced resistance toErwinia soft rot. Thus, average rotting caused byEc-bacteria was diminished in tubers of PL-transgenic lines by 34.1%. The resistance of tubers toEc soft rot was significantly correlated with the PPO activity in tuber tissue.     

Resistencia de tuberculos a las fusaria que afectan papa en el Peru

Fungi of the genusFusarium Link isolated in Perú from potatoes (Solanum tuberosum L. subsp.andigena Juz. & Buk.) affected by: i) wilt, ii) dry rot of stored tubers, iii) secondary rot in tubers affected by “cork” disease (potato mop-top virus?), caused dry rot when inoculated to tubers of Renaacimiento variety. The identification of some of theseFusaria suggests thatFusarium solani Snyder & Hansen is associated with wilt and dry rot, andFusarium oxysporum Snyder & Hansen with rot secondary to cork disease. Tubers of eight potato varieties inoculated with fourFusaria representative of those isolated showed a great range in levels of susceptibility to colonization by theseFusaria, Sapa being the most susceptible variety, and Mantaro appearing to be the most resistant. These results suggest that useful levels of resistance toFusarium tuber rot are available in the Peruvian germ-plasm.     

Introgression and stabilization oferwinia tuber soft rot resistance into potato after somatic hybridization ofsolanum tuberosum ands. brevidens

Resistance to potato tuber soft rot caused byErwinia carotovora was transferred fromSolanum brevidens to the cultivated potato over the course of four backcross generations originating from a somatic hybrid. Soft rot reactions were determined via a tuber plug inoculation method developed during the course of these experiments. Soft rot resistance was highest in the somatic hybrid (only ca. 20% of tubers and plugs showed evidence of severe rotting) and lowest among progeny of control potato x potato crosses (ca. 80% of tuber plugs showed severe rot). Backcross generations involving somatic hybrids were intermediate in their reaction, and resistance stabilized to about 60% of tuber plugs showing severe rot in the BC₂ through the BC₄. Reciprocal crosses showed no difference in the inheritance of soft rot resistance, indicating that neitherS. brevidens norS. tuberosum donor cytoplasm had a significant effect on the expression of resistance. Crosses between BC₃ siblings where noS. brevidens genetic markers were detected but resistance was segregating demonstrated a dosage effect for soft rot resistance. We conclude that introgression of soft rot resistance has occurred and that at least one locus responsible for resistance inS. brevidens now resides in theS. tuberosum genome.     

Resistance to soft rot (Erwinia carotovora subsp.atroseptica) in tetraploid potato families obtained from 4x-2x crosses

Diploid potato clones, interspecific hybrids ofSolanum species, having in their originS. tuberosum,S. chacoense, S. yungasense, S. phureja, S. gourlayi, andS. demissum, with resistance to soft rot, were crossed to tetraploid potato clones in 4x-2x crosses. The 24 tetraploid families obtained in a North Carolina II design were examined for tuber resistance to soft rot in a laboratory test and for basic agronomic traits in field trials conducted for two consecutive years. In addition, one family originating from a 4x-2x cross of two susceptible parents was tested. Statistical analysis of the data revealed significant general (GCA) and specific combining ability (SCA) effects, year, GCA (female) × year, GCA (male) × year, and SCA × year upon the inheritance of resistance to soft rot. About 35% of the progeny was selected as resistant to tuber soft rot, and of these 11% showed high resistance combined with good tuber yield, tuber weight, and tuber appearance. The relationships between resistance to soft rot and chosen agronomic traits were not noted or were weakly significant and sporadic. The resistance to tuber soft rot found in diploid potato hybrids can be transferred to the cultivated tetraploid pool through 4x-2x crosses, and a high frequency of offspring posses resistance.     

Contamination of soil and transmission of seedborne potato dry rot fungi (Fusarium spp.) to progeny tubers

A survey of selected potato soils in Maine was made to determine the species and populations ofFusarium spp. present.Fusarium solani ‘Coeruleum’ was most often isolated butFusarium roseum ‘Sambucinum’ was not recovered from any soil. Crops or cropping sequences in general showed no direct relationship to observed Fusaria populations or tuber dry rot. Field studies were conducted to determine the effect ofFusarium contaminated seed on soil and daughter tuber contamination. Whole and cut seed were inoculated withFusarium roseum ‘Sambucinum’ and half of each lot treated with thiabendazole (1500 ppm) to controlFusarium seed decay. Soil populations ofF. roseum ‘Sambucinum’ were higher near plants produced from non-treated, cut seed tubers. No increase inFusarium populations was found between plants or near plants produced from whole or thiabendazole treated seed. Daughter tuber contamination was greatest from plants produced from non-treated contaminated cut seed, and lowest from whole or treated seed. Whole non-treated seed produced daughter tubers with contamination equal to treated whole seed. This indicates that the use of whole seed could be a method to reduce daughter tuber contamination and reduce reliance on chemical treatments. Cut seed contaminated withFusarium spp. is an important source of daughter tuber contamination which can result in a high amount of tuber dry rot in storage.     

Extraction ofclaviba cter michiganensis subsp.sepedonicus from composite samples of potato tubers

The presence ofClavibacter michiganensis subsp.sepedonicus was detected by immunofluorescence and ELISA in diluent in which cores from 200 potato tubers had been incubated on a rotary shaker. By this procedure the ring rot pathogen was detected in composite samples from naturally infected tubers and tuber samples “spiked” with infected tissue or a pure culture of the pathogen. Populations of saprophytic bacteria increased about 100-fold in the diluent during 18 h of incubation but did not interfere with serological detection of C.m. sepedonicus. Some of the results suggest thatC. m. sepedonicus cells multiply during incubation of tuber samples. Extraction of ring rot bacteria from potato tuber tissue by incubation on a rotary shaker requires little work and minimizes the amount of plant tissue in the extract compared to the standard extraction procedure involving maceration and differential centrifugation.     

Breeding Potential of Potato Somatic Hybrids: Evaluations for Adaptability,Tuber Traits,Late Blight Resistance,Keeping Quality and Backcross (BC<Subscript>1</Subscript>) Progenies

Ten tetraploid interspecific potato somatic hybrids developed earlier through protoplast fusion between the dihaploid Solanum tuberosum L. ‘C-13’ and the diploid wild species Solanum pinnatisectum Dun. were used in this study. Somatic hybrids and standard control cultivars were evaluated for adaptability, tuber traits, late blight resistance and keeping quality attributes (dormancy, sprouting, weight loss and appearance after 75 days of storage) during two successive winter crop seasons (short-days) in the sub-tropical plains of India, where nearly 90% of India’s potatoes are grown. Somatic hybrids showed medium to good plant vigour and late to very late plant maturity. Though none of the somatic hybrids produced equal or higher tuber yield than the control cultivars, except clone P7, all other somatic hybrids produced significantly higher marketable and total tuber yield after a 90-day growth than the parent C-13. Most of the somatic hybrids possessed higher tuber dry matter concentration, resistance to late blight and better keeping quality attributes than the control cultivars. Notably, the tubers of somatic hybrids showed a tendency for colour change from white to purple on exposure to sunlight. Breeding potential of somatic hybrids was further assessed by crossing them with commonly grown local potato cultivars for the development of backcross (BC₁) progenies. In the hybridization programme, berries were formed while somatic hybrids were used either as male or female parents with common cultivars. Our results revealed that the use of bulk pollen of somatic hybrids not only resulted in higher pollination success but also helped to achieve higher numbers of true potato seeds (TPS) per berry. Despite the formation of berries, TPS was absent in 22 crosses using somatic hybrids as a female or male parent which may be due to ovule or embryo abortions. Segregating BC₁ generations were evaluated under the same sub-tropical conditions for further exploitation in potato breeding. Based on our study, the somatic hybrids P4, P8 and P10 can be utilized for the introgression of important characters such as high tuber dry matter concontration, resistance to late blight and excellent keeping quality attributes into the cultivated potato via conventional breeding methods for cultivar development in the sub-tropical plains of India.     

Sensitivity of Pectobacterium carotovorum to hydroxytyrosol-rich extracts and their effect on the development of soft rot in potato tubers during storage

A hydroxytyrosol-rich olive mill wastewater (HROMW) (29.3% weight:dry weight) and a hydroxytyrosol-rich extract (HRE) (52.7% weight:dry weight) were prepared from the fresh olive mill wastewater (OMW) using hydrolysis and post-hydrolysis purification processes. The minimal bactericidal concentrations of HROMW and HRE against Pectobacterium carotovorum subsp. carotovorum were 72 and 40 g L⁻¹, respectively. According to the European standard method (EN 1276: 1997), HROMW and HRE showed powerful disinfectant properties and reduced the viability of P. carotovorum by more than 5 log units after a contact time of 5 min at 2% dry weight:volume. Curative and preventive controls of potato soft rot were obtained by treatment of tubers with HROMW or HRE 3 days before or 3 days after their infection with P. carotovorum, respectively. The soft rot development during potato tuber storage was significantly reduced by treatment with HRE. This extract could be used in eco-friendly strategies of post-harvest disease control and could substitute for chemical pesticides.     

Carbon Disulphide (CS<Subscript>2</Subscript>) Promotes Sprouting and Affects the Metabolism of Harvested Minitubers Grown from True Potato Seed

Chemical agents may be used to overcome dormancy in potato tubers so as to permit early planting. In this paper, the effect of carbon disulphide on sprouting and related metabolic processes in potato tubers grown from true potato seed (TPS) was investigated. Carbon disulphide was applied to potato tubers derived from TPS, at a rate of 20 ml m^?3 container volume for 72 h. It accelerated tuber sprouting and increased tuber weight loss. It also caused an increase in the respiration rate, as well as ethylene emission from the tubers during the first 6 days after treatment. The respiration rate of carbon disulphide-treated tubers remained at a higher level than that of untreated controls for 35 days after treatment. In addition, carbon disulphide increased the concentrations of the soluble sugars sucrose and fructose, but not glucose, in the tuber tissues (buds, parenchyma). These findings suggest that carbon disulphide releases potato minitubers from dormancy and that dormancy breakage is associated with changes in tuber metabolism prior to the visible sprouting.     

Biological control of fusarium dry rot of potato tubers under commercial storage conditions

Lack of effective chemicals impedes control of Fusarium dry rot of stored potato tubers destined for processed and table stock use. Biological control of dry rot incited byGibberella pulicaris (anamorph=Fusarium sambucinum) has been demonstrated in laboratory studies but not in commercial storage environments. Several Gram-negative bacterial strains that were efficacious and amenable to production in liquid culture in laboratory studies were selected for pilot studies in Idaho and for bin trials at commercial storage houses in Idaho and North Dakota. In the first year of pilot studies,Pseudomonas fluorescens S22:T:04 (≈1 x 10⁸ cfu/ml) decreased dry rot caused byG. pulicaris by 19% when coinoculated with the pathogen compared to controls and to the fungicide thiabendazole (TBZ) applied at label rates. In second year pilot studies,P. fluorescens P22:Y:05 andEnterobacter cloacae S11:T:07 (≈4 x 10⁸ cfu/ml) reduced the severity of disease incited byG. pulicaris (25% and 17% average disease decrease, respectively) when antagonists were applied after pathogen inoculum. Treatment effects on dry rot that developed from inoculation withNectria haematococca (anamorph=Fusariumsolani var.coeruleum) were variable and influenced by interactions between antagonists, a wetting agent, and TBZ. In commercial storage bin trials,E. cloacae S11:T:07 reduced naturally occurring levels of dry rot by an average of 21% compared to 14% for TBZ, demonstrating that this antagonist was effective when produced using a liquid culture medium and methodology that approximates commercial practices for producing biomass.     

Inheritance of a pectate lyase mediated soft rot resistance in crosses between transgenic potato lines of cv. désirée andS. tuberosum cultivars

Summary Expression of the pectate lyase (PL) isoenzyme 3 in transgenic potato lines of cv. Désirée mediates an enhanced resistance of tuber tissue toErwinia carotovora (Ec) soft rot due to a pre-activation of plant defence mechanisms. Therefore, theSolanum tuberosum cvs Agave and Adretta with a moderate level of soft rot resistance were crossed with such PL-expressing potato lines. The resulting progenies were assessed with respect to plant/tuber characteristics over a period of four years and then tested for PL3-expression as well as for soft rot resistance. 71% of the selected progeny lines exhibited a stable production of the PL3 enzyme. Statistical analysis revealed differences between the transgenic and the non-transgenic progeny concerning the soft rot resistance of tuber tissue. Compared with the PL-inactive progeny, extension of Ec-rotting on the wound surface of PL-transgenic potatoes was diminished on average by 51.8%. Similarly, the degree of cell lysis caused by bacterial maceration was significantly (P<0.05) reduced in tuber tissue of PL-expressing progeny lines. The latter also revealed an enhanced PPO and PAL activity in their tuber tissue indicating an active plant defence. It is concluded therefore that the PL-mediated soft rot resistance introduced into potatoes by means of molecular techniques is heritable.     

Application of a PCR-based test for detection of potato late blight and pink rot in tubers

A polymerase chain reaction (PCR)-based test for potato late blight (Phytophthora infestans) and pink rot (P.erythroseptica, P. nicotianae) diseases has been developed for use with potato tuber tissue. Primers based on sequence analysis of the ITS2 region of ribosomal DNA of late blight and pink rot pathogens were utilized in PCR assays of inoculated tubers and tubers harvested from plots known to have late blight and/or pink rot. Assays of artificially inoculated Kennebec and Russet Burbank tubers revealed thatP. infestans was detected by PCR as early as 72 h after inoculation and in the absence of visible symptoms. Much higher detection frequencies were obtained by PCR compared with plating on selective medium or placement of tissue in moist chambers. Tubers from plots known to have late blight and/or pink rot were tested using the PCR assay. Assay of late blight lesions showed ca. 80% recovery for late blight-infected tubers from the field. Results indicate that the PCR assay provides a rapid and accurate test for diagnosis of late blight and pink rot in potato tubers.     

Potato minituber production using aeroponics: Effect of plant density and harvesting intervals

To optimize minituber production through aeroponics some horticultural management factors should be studied. Potato plantlets, cv Zorba, were grown aeroponically at two different plant densities (60 and 100 plants/m²). Plants showed an extended vegetative cycle of about 5 months after planting. A higher number of stolons was obtained at low plant densities. Tuber formation hastened when supplied N was reduced. Experiments on harvesting intervals (7, 10, and 14 days) indicated that for a density of 60 plants/m², both number of minitubers and yield increased as harvesting interval decreased. Best results were achieved harvesting every 7 days: a total tuber yield of 118.6 g per plant was obtained (four times higher than for 100 plants/m²). Such a yield was composed, on the average, of 13.4 tubers with a mean tuber weight of 8.1 g. Harvesting intervals did not have an effect on the number of minitubers and yield for a density of 100 plants/m². The best productivity obtained in this study was 800 minitubers/m² for weekly harvests and a low plant density (60 plants/m²). We also studied the field performance of aeroponically produced minitubers vs those produced by hydroponics. Minituber behavior under field conditions was independent from the technique used for its production.     

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.