Reduced Tuber Yield Research Articles

MicroRNA156: A Potential Graft-Transmissible MicroRNA That Modulates Plant Architecture and Tuberization in Solanum tuberosum ssp. andigena

MicroRNA156 (miR156) functions in maintaining the juvenile phase in plants. However, the mobility of this microRNA has not been demonstrated. So far, only three microRNAs, miR399, miR395, and miR172, have been shown to be mobile. We demonstrate here that miR156 is a potential graft-transmissible signal that affects plant architecture and tuberization in potato (Solanum tuberosum). Under tuber-noninductive (long-day) conditions, miR156 shows higher abundance in leaves and stems, whereas an increase in abundance of miR156 has been observed in stolons under tuber-inductive (short-day) conditions, indicative of a photoperiodic control. Detection of miR156 in phloem cells of wild-type plants and mobility assays in heterografts suggest that miR156 is a graft-transmissible signal. This movement was correlated with changes in leaf morphology and longer trichomes in leaves. Overexpression of miR156 in potato caused a drastic phenotype resulting in altered plant architecture and reduced tuber yield. miR156 overexpression plants also exhibited altered levels of cytokinin and strigolactone along with increased levels of LONELY GUY1 and StCyclin D3.1 transcripts as compared with wild-type plants. RNA ligase-mediated rapid amplification of complementary DNA ends analysis validated SQUAMOSA PROMOTER BINDING-LIKE3 (StSPL3), StSPL6, StSPL9, StSPL13, and StLIGULELESS1 as targets of miR156. Gel-shift assays indicate the regulation of miR172 by miR156 through StSPL9. miR156-resistant SPL9 overexpression lines exhibited increased miR172 levels under a short-day photoperiod, supporting miR172 regulation via the miR156-SPL9 module. Overall, our results strongly suggest that miR156 is a phloem-mobile signal regulating potato development.

Effects of dynamic and static deficit and partial root zone drying irrigation strategies on yield, tuber sizes distribution, and water productivity of two field grown potato cultivars

New strategies of partial root-zone drying (PRD) and deficit irrigations (DI) were studied on potatoes in a semi-arid area of Iran. A factorial experiment was conducted as a complete randomized design in three replications. The potato cultivar treatments were Agria and Ramos. The whole growth period of both cultivars was divided into three stages based on the BBCH scale. There were five furrow irrigation treatments. The full irrigation treatment (FI) received 100% of potential evapotranspiration (ET); static deficit irrigation (SDI) received 75% of ET during the growth period; dynamic deficit irrigation (DDI) received 90% of ET in the first one-third of growth period, 75% of ET in the second one-third of growth period, and 50% of ET in the last one-third of growth period; static partial root zone drying irrigation (SPRD) received 75% of ET during the growth period; dynamic partial root zone drying irrigation (DPRD) received 90% of ET in the first one-third of growth period, 75% of ET in the second one-third of growth period, and 50% of ET in the last one-third of growth period. Analysis showed that there were significant differences between irrigation strategies as DI did outperform PRD in tuber production. The SDI, DDI, SPRD, and DPRD irrigation treatments decreased the potato tuber yield by 4%, 7%, 56%, and 52% compared to FI, respectively. SPRD and DPRD decreased potato tuber yield by 54% and 48% compared to SDI and DDI, respectively. Results also showed that there were no significant differences between cultivars. Interaction between irrigation strategies and cultivars was not significant. Furthermore, water productivities (WP) were significant among irrigation strategies. Compared to FI, the SDI and DDI increased WP by 28% and 34%, respectively, but SPRD and DPRD decreased WP by 40% and 31%, respectively. In general, the DI strategy (SDI, DDI) is recommended in the study area due to the slight fresh tuber yield reduction (4%, 7%) and considerable increase (28%, 34%) in WP relative to FI. Furthermore, the dynamic irrigation strategies led to higher WP than the static ones. It was also found that Agria outperformed the Ramos because of higher fresh tuber yield under water-saving irrigation strategies. Under non-limiting water conditions, Ramos produced higher fresh tuber yield. Furthermore, it is required to decrease the duration of wet/dry cycle under PRD strategy to guarantee efficient PRD and cope with extra water stress and hot weather in the region.

Physiological, biochemical and molecular responses of the potato (Solanum tuberosum L.) plant to moderately elevated temperature

Although significant work has been undertaken regarding the response of model and crop plants to heat shock during the acclimatory phase, few studies have examined the steady-state response to the mild heat stress encountered in temperate agriculture. In the present work, we therefore exposed tuberizing potato plants to mildly elevated temperatures (30/20 °C, day/night) for up to 5 weeks and compared tuber yield, physiological and biochemical responses, and leaf and tuber metabolomes and transcriptomes with plants grown under optimal conditions (22/16 °C). Growth at elevated temperature reduced tuber yield despite an increase in net foliar photosynthesis. This was associated with major shifts in leaf and tuber metabolite profiles, a significant decrease in leaf glutathione redox state and decreased starch synthesis in tubers. Furthermore, growth at elevated temperature had a profound impact on leaf and tuber transcript expression with large numbers of transcripts displaying a rhythmic oscillation at the higher growth temperature. RT-PCR revealed perturbation in the expression of circadian clock transcripts including StSP6A, previously identified as a tuberization signal. Our data indicate that potato plants grown at moderately elevated temperatures do not exhibit classic symptoms of abiotic stress but that tuber development responds via a diversity of biochemical and molecular signals.

Potato Crop Response to Genotype and Environment in a Subtropical Highland Agro-ecology

Potato response to environment, planting date and genotype was studied for different agro-ecological zones in Lesotho. Field experiments were conducted at four different sites with altitudes ranging from 1,655 to 2,250 m above sea level during the 2010/2011 and 2011/2012 summer growing seasons. Treatments consisted of three cultivars that varied in maturity type, two planting dates and four sites differing in altitude and weather patterns. Various plant parts were measured periodically. To understand and quantify the influence of abiotic factors that determine and limit yields, the LINTUL crop growth model was employed which simulated potential yields for the different agro-ecological zones using weather data collected per site during the study period. Observed actual crop yields were compared with model simulations to determine the yield gap. Model simulations helped to improve our understanding of yield limitations to further expand potato production in subtropical highlands, with emphasis on increasing production through increased yields rather than increased area. Substantial variation in yield between planting date, cultivar and site were observed. Average tuber dry matter (DM) yields for the highest yielding season were above 7.5 t DM ha−1 or over 37.5 t ha−1 fresh tuber yield. The lowest yield obtained was 2.39 t DM ha−1 or 12 t ha−1 fresh tuber yield for cultivar Vanderplank in the 2011/2012 growing season at the site with the lowest altitude. Modelled potential tuber yields were 9–14 t DM ha−1 or 45–70 t ha−1 fresh yield. Drought stress frequently resulted in lower radiation use efficiencies and to a lesser degree harvest indices, which reduced tuber yield. The site with the lowest altitude and highest temperatures had the lowest yields, while the site with the highest altitude had the highest yields. Later maturing cultivars yielded more than earlier maturing ones at all sites. It is concluded that the risk of low yields in rain-fed subtropical highlands can be minimised by planting late cultivars at the highest areas possible as early as the risks of late frosts permit.

Cytokinins: Determinants of Sink Storage Ability

A new study demonstrates that storage organ formation can be induced in the axillary meristem of non-tuberizing plants by ectopic expression of the cytokinin biosynthetic gene LONELY GUY (LOG1).

Effect of partial root-zone drying irrigation timing on potato tuber yield and water use efficiency

Partial root-zone drying (PRD) is an irrigation technique which has shown increased water use efficiency (WUE) without yield reductions in potato and other crops. However, questions remain as to the effect of the water restriction initiation timing and the level of alternate water restriction on the response of the potato crop. In this study, we tested: two PRD treatments with 25% (PRD25) and 50% (PRD50) of total water used in full irrigation (FI, as control), and a deficit irrigation treatment with 50% of water restriction (DI50). Two water restriction initiation timings were tested at: 6 weeks (WRIT6w) and 8 weeks (WRIT8w) after planting. Osmotic potential (π), osmotic adjustment, relative water content and chlorophyll concentration were assessed in four dates during the growing period. PRD50 initiated at WRIT6w showed the highest WUE without a tuber yield reduction respect to the control. While plants under PRDs and DI50 showed lower π than FI, PRDs treatments promoted higher osmotic adjustment particularly in WRIT6w. Our study suggests that early PRDs with mild water restriction allow drought hardiness (improving water stress response) and water saving avoiding a dramatic yield tuber reduction.

Effect of Potato/Maize Intercropping on Photosynthetic Characteristics and Yield in Two Potato Varieties

The intercropping of potato and maize is widely practiced in China. In the potato/maize system, competition for light is an issue as the leaves of potato and maize become different strata within the canopy. The potato/maize intercropping trials using two potato varieties including Zhongshu 5 (early-maturing variety with erect branches) and Mila (mid-late maturing variety with spread branches) with the sole cropping potato as contro1 were carried out to determine the dynamic changes of LAI, SLW, Chl a+b, Chl a/b ratio, photosynthetical active radiation (PAR), gas exchange attributes in leaves at three position levels at tuber initiation stage and tuber expanding stage and yield. The results indicated that intercropping led to decrease LAI, SLW and Chl a/b ratio and increase Chl a+b. In addition, the gradual decrease in PAR, water use efficiency (WUE), stomatal limitation (L s =1–C i /C a , C a : ambient CO 2 concentration) and the increase in net photosynthetic rate (P n ), stomatal conductance (G s ), intercellular CO 2 (C i ) and transpiration rate (T r ) were observed from tuber initiation stage to tuber expanding stage. There was a continuous significant reduction in PAR, P n , G s and T r from the upper leaves to the middle and lower leaves in all treatments, with a lower reduction under intercropping than under sole cropping. The variations in P n , G s , C i , and L s indicated the decreased photosynthetic activity in the middle and lower leaves pertaining, to both stomatal and non-stomatal mechanisms. Intercropping also declined P n in the upperleaves and elevated P n in the middle and lower leaves. Furthermore, there were higher Chl a+b in vegetative growth stage and tuber initiation stage and lower Chl a+b in tuber expanding stage and starch accumulation stage in Zhongshu 5/maize than in Mira/maize system, with the opposite changing trend for SLW. Higher LAI and Chl a/b ratio at all developmental stages, higher PAR in the upper leaves and lower PAR in the middle and lower leaves were observed, and higher P n in the middle and lower leaves in Zhongshu 5 than in Mira in intercropping systems but the similar Pn in the upper leaves. In comparison with Mira, there were lower Gs , Ci , and T r and higher WUE and L s in leaves at the same position levels in Zhongshu 5. In summary, intercropping led to substantial reduction in tuber yield at harvest time due to the change on the light environment and the photosynthetic characteristics of potato in potato/maize systems. Nonetheless, intercropping deteriorated the light environment for Zhongshu 5/maize system while improved the light environment for Mira/maize system, which led to lower LER in the former (1.24) than in the latter (1.40), showing the stronger intercropping superiority for Mira/maize system in the production.

First Report of Rhizoctonia solani AG4 HG-II Infecting Potato Stems in Idaho.

The fungus Rhizoctonia solani is the causal agent of stem canker and black scurf of potato (Solanum tuberosum). R. solani is a species complex consisting of 13 anastomosis groups (AGs) designated AG1 to 13 (2, 3). Stems of potato (cv. Russet Norkotah) with brown lesions were recovered from one field in Kimberley, Idaho, in August 2011. Using previously described methods (3), R. solani was recovered from the symptomatic stems and one representative isolate (J15) was selected for further characterization. Sequencing of the rDNA ITS region of isolate J15 was undertaken as previously described (3) and the resulting rDNA ITS sequence (HE667745) was 99% identical to sequences of other AG4 HG-II isolates in GenBank (AF354072 and AF354074). Pathogenicity of the isolate was determined by conducting the following experiment. Mini-tubers of cv. Santé were planted individually in 1-liter pots containing John Innes Number 3 compost (John Innes Manufacturers Association, Reading, UK). Pots were either inoculated with J15, an isolate of AG3-PT (Rs08), or were not inoculated. Each treatment was replicated four times. Inoculum consisted of five 10-mm-diameter potato dextrose agar plugs, fully colonized by the appropriate isolate, placed in the compost approximately 40 mm above each seed tuber. Pots were held in a controlled environment room at 21°C with 50% relative humidity and watered as required. After 21 days, plants were assessed for disease. No symptoms of the disease were present in non-inoculated plants. In the Rs08 (AG3-PT) inoculated plants, all stems displayed large brown lesions and 20% of the stems had been killed. No stem death was observed in J15 (AG4 HG-II) inoculated plants. However, brown lesions were observed in three of the four J15 (AG4 HG-II) inoculated plants. These lesions were less severe than in plants inoculated with the Rs08(AG3-PT) inoculated plants and were present in 40% of the main stems. In the J15 (AG4 HG-II) inoculated pots, R. solani AG4 HG-II was reisolated from the five symptomatic stems, thereby satisfying Koch's postulates. To our knowledge, this is the first report of AG4 HG-II causing disease on potatoes in Idaho. AG4 has been isolated from potato previously from North Dakota, although the subgroup was not identified (1). The only previous report where AG4 HG-II was specifically determined to cause disease on potato was in Finland, but the isolate could not be maintained and Koch's postulates were not completed (3). The present study shows that AG4 HG-II can cause stem disease in potatoes, although disease does not develop as severely or as consistently as for AG3-PT. However, as demonstrated with isolates of AG2-1 and AG5, even mild stem infection can reduce tuber yield by as much as 12% (4). AG4 HG-II is a pathogen of sugar beet in Idaho, which was grown previously in this field. This history may have contributed to high levels of soilborne inoculum required to produce disease on potato.

Molecular and Serological Typing of Potato virus Y Isolates from Brazil Reveals a Diverse Set of Recombinant Strains.

In Brazil, Potato virus Y (PVY) currently presents a significant problem for potato production, reducing tuber yield and quality. Recombinant tuber necrotic isolates of PVY had been reported to occur in the country but no systematic study of the PVY isolate diversity was conducted thus far. Here, a panel of 36 PVY isolates, randomly collected in Brazil from potato between 1985 and 2009, was subjected to a systematic molecular and serological typing using reverse-transcription polymerase chain reaction and a series of PVYO- and PVYN-specific monoclonal antibodies. The data collected were combined with biological characterization of the same isolates in tobacco. Of the 36 isolates tested, 3 were typed as PVYO, 10 as PVYN:O/N-Wi, 21 as PVYNTN, and 2 as "unusual" or inconclusive. Of the 10 isolates from the recombinant PVYN:O/N-Wi strain group, 1 isolate, MAF-VOY, was found to have an unusual serological profile identical to the nonrecombinant PVYO-O5 strain group. The 21 tested PVYNTN isolates included 1 isolate that did not induce vein necrosis in tobacco and 2 isolates with an unusual serological profile (i.e., displaying negative reactivity to one commercial PVYN-specific monoclonal antibody). Whole genome sequences were determined for four PVY isolates from Brazil, representing PVYO, PVYNTN, and PVYN-Wi strains. The genome of the MAF-VOY isolate was found to be recombinant, having characteristic N-Wi structure with two recombinant junctions and carrying a single mutation in the capsid protein at position 98, which led to an unusual O5 serological reactivity. Taken together, the data obtained suggest that the two recombinant strains, PVYNTN and PVYN:O/N-Wi, now are apparently dominant in the Brazilian potato crop. The data also suggest that recombinant isolates in Brazil often have unusual serological reactivity which may hamper their correct identification by conventional typing based on enzyme-linked immunosorbent assay.

Ontogeny of the tuber crop Plectranthus edulis (Lamiaceae)

Plectranthus edulis (Lamiaceae) is one of the economically important tuber crops of the genus Plectranthus. It is grown in mid and high altitude areas in parts of Ethiopia. The structure of this plant and its development in time has not been described in detail. Two similar experiments were carried out at Awassa and Wondogenet (Southern Ethiopia) with two cultivars (Lofuwa and Chankua) and 20 harvest dates [from 14 to 280 days after planting (DAP)]. The plants were grown from seed tuber pieces and attained a maximum height of about 1.5 m. Plants produced main stems and primary, secondary and tertiary branches, with primary and secondary branches and their leaves constituting the main part of the canopy. Plant components were the seed tuber pieces, sprouts, main stems, branches, leaves, flowers, fruits, seeds, roots, stolons and tubers. Five, partly overlapping, ontogenetic vegetative phases were observed during one crop cycle: emergence, canopy development, stolon initiation and development, tuber initiation and growth, and a phase of canopy senescence. Stolons were formed on main stems and primary branches and originated below ground or above ground (aerial stolons). Aerial stolons were initiated later than below-ground stolons and were much longer (up to 2.5 m). Tubers usually were produced as a swelling on the tip of the stolon and sometimes as a swelling of the middle part of stolons. Tubers were stem tubers with pairs of ''eyes'' (compound buds) being arranged in the same decussate pattern as the axillary buds on stolons and stems. Tubers of cv. Lofuwa were up to 25 cm in length, those of cv. Chankua up to 20 cm, and both with a diameter of about 2 cm. The tubers in the middle of the stolon were longer than the ones at the tip. After tuber initiation, the total number of tubers increased almost linearly during 12 to 14 weeks, and maximum numbers of tubers were attained around 238 DAP, at crop senescence. Also, the number of smaller tubers (< 10 or 20 g) increased until 238 DAP. In the period of tuber initiation, the average weight per tuber increased up to 20 to 25 g per tuber. The increase in tuber fresh weight with time was therefore realized by an increase in both tuber number and in average weight per tuber. After crop maturity, farmers keep the tubers unharvested in the soil until they need them. This practice dramatically reduces tuber yield and number, because decreases of 36 to 59% were found in total tuber fresh weight and of 18 to 48% in number of tubers when tubers were kept in the soil in the 6 weeks period between 238 and 280 DAP.

Nematodes as a Limiting Factor in Potato Production in Scandinavia

Plant parasitic nematodes associated with potato feed on roots and/or tubers. About 70 species, representing 24 genera, have been reported from potato. Since nematodes attack underground plant parts, there are no reliable foliar symptoms to show that nematodes may be the major cause of poor growth and reduced tuber yields. Potato roots damaged by nematodes may show lesions, abnormal proliferation of lateral roots, emerging white females and brown cysts. Nematode attacks may render plants vulnerable to other pathogens, so disease caused by microorganisms may have nematodes as an etiological component. Therefore, nematode damage may often have been attributed to other factors. In Scandinavia, potato cyst nematodes (Globodera rostochiensis and Globodera pallida) are by far the most important nematodes on potato. In Norway, the cost of compensations schemes due to imposed statutory regulations of potato cyst nematodes may some years exceed the compensation for any other pests or diseases organism in agriculture. Other important nematodes include root lesion nematodes (Pratylenchus spp.), stubby root nematodes (Trichodorus spp. and Paratrichodorus spp.), and potato rot and stem nematodes (Ditylenchus spp.). Root knot nematode Meloidogyne hapla is considered less important. Meloidogyne chitwoodi and Meloidogyne fallax are not known to be present in Nordic countries. In the control, crop rotations using non-host crops, alternating susceptible and resistant potato cultivars, are an important control measure. However, the use of resistant potato cultivars requires knowledge of the species and pathotypes present in the field.

Impact of Deficit Irrigation on Tuber Yield and Quality of Potato Cultivars

Potato (Solanum tuberosum L.) tuber yield and quality are impacted by irrigation and nitrogen (N) management. This study was conducted in the Pacific Northwest (PNW) region of United States to evaluate the effects of deficit irrigation (DI) and rates of pre-plant and in-season N applications on Ranger Russet and Umatilla Russet cultivars. In 2004, with Ranger Russet only, DI with 20% lower total irrigation for the entire growing period resulted in 28% tuber yield reduction compared to that of plants irrigated to replenishment full evapotranspiration (ET), i.e., full irrigation (FI). A subsequent study in 2006 and 2007 with DI (14% to 17% deficit) resulted in tuber yield reduction of 7% to 10% in both cultivars compared to full ET irrigation. Yield reduction in DI was generally attributed to reduction in large weight tubers, >0.227 kg/tuber, in both cultivars across three years. Petiole NO3-N concentrations were greater in plants grown under DI as compared to those of plants in full ET irrigation across all years and cultivars, particularly during tuber maturation stage. This is an important consideration as increased N availability during the late growing season adversely affects tuber quality. Petiole NO3-N concentrations increased with increased in-season N rates. In 2007, 112 kg·ha−1 in-season N resulted in petiole NO3-N concentrations below desirable concentrations across most of the growing season in both cultivars. This, in turn, contributed to a significant reduction in tuber yield as compared to the 224 kg·ha−1 in-season N rate. Continuous DI with 14% to 20% reduction in water as compared to irrigation to replenish full ET, begun three to four weeks after seedling emergence, had significant negative effects on tuber yields of both cultivars in high-production irrigated growing conditions. Application of N up to 112 kg ha−1 as pre-plant soil applied plus 224 kg ha−1 of in-season fertigation in five applications at two-week intervals beginning four weeks after seedling emergence appears to be adequate to support high yields of high-quality tubers.

Epitope Mapping for Monoclonal Antibodies Recognizing Tuber Necrotic Isolates of Potato Virus Y

Potato virus Y (PVY) is an important viral pathogen of potato responsible for reducing tuber yield and quality across the globe. The PVYN and PVYNTN strains, the latter of which induces potato tuber necrotic ringspot disease (PTNRD), are regulated for international potato trade, and have been routinely detected using monoclonal antibodies (MAbs) that discriminate between PVYN and PVYO serotypes. Here, we identify the distinct binding sites in the capsid protein of PVY for three of the four main PVYN-specific MAbs, Bioreba-N, SASA-N, and Neogen-N, available commercially. These binding domains were mapped through a combination of TAS-ELISA testing of MAbs on multiple reference isolates of PVY, sequence analysis, heterologous expression of capsid protein fragments, and synthetic peptide binding experiments. All three MAbs were found to bind linear epitopes located within the first 31 N-terminal amino acids of the capsid protein. Bioreba-N MAb epitope spanned aa 1-17 and included three positions, aa 1, aa 11, and aa 17, which differ between PVYN and PVYO serotypes. Both SASA-N and Neogen-N epitopes spanned aa 22-30, and included two positions, aa 24 and aa 29, which differ between PVYN and PVYO serotypes. Epitopes for SASA-N and Neogen-N MAbs are likely to be identical or overlapping. Examination of available sequences for tuber necrotic isolates of PVY that do not react with PVYN-specific MAbs SASA-N and Neogen-N indicated possible selection for substitutions in corresponding epitopes leading to the loss of reactivity towards these antibodies. The data obtained suggested that testing with more than one PVYN serotype-specific MAb could assure a reliable serological identification of a PVYN or PVYNTN isolate.

Effects of Liberibacter-Infective Bactericera cockerelli (Hemiptera: Triozidae) Density on Zebra Chip Potato Disease Incidence, Potato Yield, and Tuber Processing Quality

In plant pathosystems involving insect vectors, disease spread, incidence, and severity often depend on the density of the vector population and its rate of infectivity with the disease pathogen. The potato psyllid, Bactericera cockerelli (Sulc), has recently been associated with zebra chip (ZC), an emerging and economically important disease of potato in the United States, Mexico, Central America, and New Zealand. "Candidatus Liberibacter solanacearum," a previously undescribed species of liberibacter has been linked to the disease and is transmitted to potato by B. cockerelli. Experiments were conducted under laboratory and field conditions to determine the impact of B. cockerelli density on ZC incidence, potato yield, and tuber processing quality. Insect densities ranging from one to 25 liberibacter-infective psyllids per plant were used during the experiments. Results showed that a single adult potato psyllid was capable of inoculating liberibacter to potato and causing ZC disease after a 72-h inoculation access period and was as damaging as 25 psyllids per plant. In addition, ZC-diseased plants showed a sharp reduction in tuber yield but the disease response was independent of the density of psyllids. Furthermore, both glucose and sucrose were found to have highly elevated concentrations in ZC-diseased potato tubers compared with noninfected ones and psyllid density did not vary the response. The high reducing sugar concentrations found in ZC-infected potato tubers are believed to be responsible for browning and reduced quality in processed ZC-infected tubers. This information could help ZC-affected potato producers in making effective management decisions for this serious disease.

Tuber yield, water and fertilizer productivity in early potato as affected by a combination of irrigation and fertilization

Excessive amounts of irrigation water and fertilizers are often utilized for early potato cultivation in the Mediterranean basin. Given that water is expensive and limited in the semi-arid areas and that fertilizers above a threshold level often prove inefficacious for production purposes but still risk nitrate and phosphorous pollution of groundwater, it is crucial to provide an adequate irrigation and fertilization management. With the aim of achieving an appropriate combination of irrigation water and nutrient application in cultivation management of a potato crop in a Mediterranean environment, a 2-year experiment was conducted in Sicily (South Italy). The combined effects of 3 levels of irrigation (irrigation only at plant emergence, 50% and 100% of the maximum evapotranspiration – ETM) and 3 levels of mineral fertilization (low: 50, 25 and 75 kg ha−1, medium: 100, 50 and 150 kg ha−1 and high: 300, 100 and 450 kg ha−1 of N, P2O5 and K2O) were studied on the tuber yield and yield components, on both water irrigation and fertilizer productivity and on the plant source/sink (canopy/tubers dry weight) ratio. The results show a marked interaction between level of irrigation and level of fertilization on tuber yield, on Irrigation Water Productivity and on fertilizer productivity of the potato crop. We found that the treatments based on 50% ETM and a medium level of fertilization represent a valid compromise in early potato cultivation management. Compared to the high combination levels of irrigation and fertilization, this treatment entails a negligible reduction in tuber yield to save 90 mm ha−1 year−1 of irrigation water and 200, 50 and 300 kg ha−1 year−1 of N, P2O5 and K2O, respectively, with notable economic savings for farmers compared to the spendings that are usually made.

Altering trehalose-6-phosphate content in transgenic potato tubers affects tuber growth and alters responsiveness to hormones during sprouting.

Trehalose-6-phosphate (T6P) is a signaling metabolite that regulates carbon metabolism, developmental processes, and growth in plants. In Arabidopsis (Arabidopsis thaliana), T6P signaling is, at least in part, mediated through inhibition of the SNF1-related protein kinase SnRK1. To investigate the role of T6P signaling in a heterotrophic, starch-accumulating storage organ, transgenic potato (Solanum tuberosum) plants with altered T6P levels specifically in their tubers were generated. Transgenic lines with elevated T6P levels (B33-TPS, expressing Escherichia coli osmoregulatory trehalose synthesis A [OtsA], which encodes a T6P synthase) displayed reduced starch content, decreased ATP contents, and increased respiration rate diagnostic for high metabolic activity. On the other hand, lines with significantly reduced T6P (B33-TPP, expressing E. coli OtsB, which encodes a T6P phosphatase) showed accumulation of soluble carbohydrates, hexose phosphates, and ATP, no change in starch when calculated on a fresh weight basis, and a strongly reduced tuber yield. [¹⁴C]glucose feeding to transgenic tubers indicated that carbon partitioning between starch and soluble carbohydrates was not altered. Transcriptional profiling of B33-TPP tubers revealed that target genes of SnRK1 were strongly up-regulated and that T6P inhibited potato tuber SnRK1 activity in vitro. Among the SnRK1 target genes in B33-TPP tubers, those involved in the promotion of cell proliferation and growth were down-regulated, while an inhibitor of cell cycle progression was up-regulated. T6P-accumulating tubers were strongly delayed in sprouting, while those with reduced T6P sprouted earlier than the wild type. Early sprouting of B33-TPP tubers correlated with a reduced abscisic acid content. Collectively, our data indicate that T6P plays an important role for potato tuber growth.

PACLOBUTRAZOL, UNICONAZOL Y CYCOCEL EN LA PRODUCCIÓN DE TUBÉRCULO-SEMILLA DE PAPA EN CULTIVO HIDROPÓNICO

Three growth inhibitors (cycocel, uniconazole and paclobutrazol) applied at different concentrations were assessed to determine their ability to produce compact potato (Solanum tuberosum L.) plants with reduced leaf area, but without reduced tuber yield, in an experiment conducted in hydroponic greenhouse conditions. The treatments were: paclobutrazol (50, 100, 150, 200 and 250 mg.L-1), uniconazole (2.5, 5, 10, 20 and 40 mg.L-1), cycocel (200, 400, 800, 1,600 and 2,400 mg.L-1) and a control without regulators, with 10 pots as the experimental unit. A randomized complete block design with 16 treatments and four replications was used. Uniconazole and paclobutrazol were more effective in reducing growth, leaf area and leaf area index compared with cycocel. Uniconazole at concentrations >5 mg.L-1 reduced plant height (23 and 46 %), tuber biomass and total plant biomass compared with the control. Paclobutrazol applications at 100, 200 and 250 mg.L-1 reduced plant height (50 to 64 %), tuber biomass (44 to 69 %) and total plant biomass (45 to 67 %); at 150 mg.L-1, it reduced plant height (42 %) without affecting tuber biomass (47.0 g). Uniconazole at 20 mg.L-1 and paclobutrazol at 150 mg.L-1 produced stunted potato plants and reduced their leaf area index from 13.9 in plants without inhibitors (the control) to 10.93 and 9.34, respectively, without affecting the number of tubers per plant, tuber biomass or harvest index.

Identification of drought-responsive compounds in potato through a combined transcriptomic and targeted metabolite approach

Two potato clones (Solanum tuberosum L.) of the Andean cultivar group, called Sullu and SS2613, with different drought-tolerance phenotypes were exposed to a continuously increasing drought stress in a field trial. At the physiological level, while relative leaf water contents were similar in both clones, osmotic potential was lower in Sullu and declined more strongly during drought compared with SS2613. In the drought-stressed plants, tuber yield was reduced by about 70% compared with control plants in both clones. Potato cDNA microarrays and target metabolite analysis were performed on leaves sampled at several time-points after the onset of drought. At the transcriptomic level, photosynthesis-related genes were already strongly repressed in Sullu after 28 d of withholding irrigation and even more strongly after a longer stress duration, whereas, in SS2613, repression occurred only after 49 d of soil drying; similarly, a strong perturbation of carbohydrate-related genes was observed in Sullu. At the metabolite level, differential accumulation of osmotically active solutes was observed between the two cultivars; indeed, in Sullu, contents of galactose, inositol, galactinol, proline, and proline analogues were higher upon drought stress compared with SS2613. These results point to different drought responses in the cultivars at the leaf level, with, however, similar tuber yield reductions. The previously shown tolerant clone Sullu lost part of its tolerance under the experimental conditions used here; it was, however, able to maintain an absolute yield three times higher than SS2613.

Tuber‐specific cphA expression to enhance cyanophycin production in potatoes

The production of biodegradable polymers that can be used to substitute petrochemical compounds in commercial products in transgenic plants is an important challenge for plant biotechnology. Nevertheless, it is often accompanied by reduced plant fitness. To decrease the phenotypic abnormalities of the sprout and to increase polymer production, we restricted cyanophycin accumulation to the potato tubers by using the cyanophycin synthetase gene (cphA(Te)) from Thermosynechococcus elongatus BP-1, which is under the control of the tuber-specific class 1 promoter (B33). Tuber-specific cytosolic (pB33-cphA(Te)) as well as tuber-specific plastidic (pB33-PsbY-cphA(Te)) expression resulted in significant polymer accumulation solely in the tubers. In plants transformed with pB33-cphA(Te), both cyanophycin synthetase and cyanophycin were detected in the cytoplasm leading to an increase up to 2.3% cyanophycin of dry weight and resulting in small and deformed tubers. In B33-PsbY-cphA(Te) tubers, cyanophycin synthetase and cyanophycin were exclusively found in amyloplasts leading to a cyanophycin accumulation up to 7.5% of dry weight. These tubers were normal in size, some clones showed reduced tuber yield and sometimes exhibited brown sunken staining starting at tubers navel. During a storage period over of 32 weeks of one selected clone, the cyanophycin content was stable in B33-PsbY-cphA(Te) tubers but the stress symptoms increased. However, all tubers were able to germinate. Nitrogen fertilization in the greenhouse led not to an increased cyanophycin yield, slightly reduced protein content, decreased starch content, and changes in the amounts of bound and free arginine and aspartate, as compared with control tubers were observed.

An Emerging Potato Purple Top Disease Associated with a New 16SrIII Group Phytoplasma in Montana.

Potato purple top (PPT) is a devastating disease that occurs in the United States, Canada, Mexico, Russia, and elsewhere causing great economic loss to the potato industry through substantially reduced tuber yield and quality. Chips and fries processed from infected tubers often develop brown discoloration, greatly reducing their marketability. At least seven distinct phytoplasma strains belonging to five different phytoplasma groups (16SrI, 16SrII, 16SrVI, 16SrXII, and 16SrXVIII) have been reported to cause purple top and related symptoms in potato (3). During an unusual drought in 2007, a newly emerging potato disease with extensive yellowish or reddish purple discoloration of terminal shoots and leaves, similar to PPT symptoms, was observed in isolated potato fields in Montana where over 50% of plants exhibited symptoms. Shoot tissues were collected from three symptomatic plants and 17 tubers randomly collected from 17 other symptomatic plants. The tubers were cold treated to induce sprouting and then planted in the greenhouse. All tubers produced plants of which seven exhibited PPT symptoms including severe stunting. Total nucleic acid was extracted from leaf veinal tissue, stolons, or tubers of 10 symptomatic and 10 asymptomatic plants (both field-collected and greenhouse samples) as previously described (3). A nested-PCR assay, using universal primer pair P1/16S-SR followed by R16F2n/R16R2n, was performed as previously described (2,3) to detect phytoplasmas in these samples. Phytoplasma strains were detected in all symptomatic plants. Restriction fragment length polymorphism (RFLP) analyses of nested-PCR products (approximately 1.2 kb) with seven key restriction enzymes (AluI, MseI, HhaI, Tsp509I, HpaII, RsaI, and BfaI) indicated that all samples contained a very similar or identical phytoplasma most closely related to reference strain MW1 (belonging to subgroup 16SrIII-F) (1). Analysis of cloned 16S rDNA sequences confirmed the identity of this new phytoplasma and sequences of three representative PPT-MT strains were deposited in GenBank with Accession Nos. FJ226074-FJ226076. Computer-simulated RFLP analyses of 1.2-kb 16S rDNA sequences of this new phytoplasma and representative members in the peach X-disease phytoplasma group (16SrIII) available in GenBank indicated the strain is distinct and represents a new subgroup, 16SrIII-M (4). This study also indicated that the phytoplasma is tuber transmissible since approximately 35% of plants produced from infected tubers collected in this study developed symptoms. Transmission via infected tubers may pose a potential threat for disease spread by planting uncertified seed potatoes. To our knowledge, this is the first report of 16SrIII group phytoplasmas-associated diseases in potato. A phytoplasma closely related to the PPT-MT strains has recently been detected in potato seedlings exhibiting purple top, rosette, and stunting in Alaska (GenBank Accession No. FJ376628).