Daughter Tubers Research Articles

Ralstonia solanacearum (phylotype II) isolated from Rosa spp. in the Netherlands is closely related to phylotype II isolates from other sources in the Netherlands and is virulent on potato

AbstractIn 2018, during an annual survey in the Netherlands, Ralstonia solanacearum phylotype II (phy II) was found in asymptomatic greenhouse rose plants at three geographic locations. These findings were remarkable, since previous findings of Ralstonia sp. in rose always concerned Ralstonia pseudosolanacearum phylotype I (phy I). Therefore, no information was available on the virulence of R. solanacearum phy II on rose. In this study, R. solanacearum phy II isolates PD 7421 and PD 7394, isolated in 2018 from asymptomatic ornamental rose (Rosa spp.), were assessed for their virulence in two rose cultivars (“Armando” and “Red Naomi”) at two temperatures. No typical symptoms were observed for PD 7421 and PD 7394 on the two rose cultivars, irrespective of the temperature. However, latent infections upon inoculation of these isolates on rose did occur. R. solanacearum phy II is known as a major potato pathogen, where it causes brown rot. Whole genome multilocus sequence typing analysis demonstrated that the isolates from rose were closely related to R. solanacearum phy II isolates previously found in seed potato and surface water in the Netherlands. Because of this close genetic relatedness, the virulence of PD 7421 and PD 7394 was also assessed in potato plants, where both isolates caused severe disease symptoms on the shoots as well as the daughter tubers. This implies that rose can act as a reservoir for R. solanacearum phy II and, in this way, can potentially be involved in spreading this bacterium.

Seed tuber imprinting shapes the next-generation potato microbiome.

Potato seed tubers are colonized and inhabited by soil-borne microbes, that can affect the performance of the emerging daughter plant in the next season. In this study, we investigated the intergenerational inheritance of microbiota from seed tubers to next-season daughter plants under field condition by amplicon sequencing of bacterial and fungal microbiota associated with tubers and roots, and tracked the microbial transmission from different seed tuber compartments to sprouts. We observed that field of production and potato genotype significantly (P < 0.01) affected the composition of the seed tuber microbiome and that these differences persisted during winter storage of the seed tubers. Remarkably, when seed tubers from different production fields were planted in a single trial field, the microbiomes of daughter tubers and roots of the emerging plants could still be distinguished (P < 0.01) according to the production field of the seed tuber. Surprisingly, we found little vertical inheritance of field-unique microbes from the seed tuber to the daughter tubers and roots, constituting less than 0.2% of their respective microbial communities. However, under controlled conditions, around 98% of the sprout microbiome was found to originate from the seed tuber and had retained their field-specific patterns. The field of production shapes the microbiome of seed tubers, emerging potato plants and even the microbiome of newly formed daughter tubers. Different compartments of seed tubers harbor distinct microbiomes. Both bacteria and fungi on seed tubers have the potential of being vertically transmitted to the sprouts, and the sprout subsequently promotes proliferation of a select number of microbes from the seed tuber. Recognizing the role of plant microbiomes in plant health, the initial microbiome of seed tubers specifically or planting materials in general is an overlooked trait. Elucidating the relative importance of the initial microbiome and the mechanisms by which the origin of planting materials affect microbiome assembly will pave the way for the development of microbiome-based predictive models that may predict the quality of seed tuber lots, ultimately facilitating microbiome-improved potato cultivation.

Virulence of Novel Ralstonia pseudosolanacearum (Phylotype I) Strains from Rose, Blueberry, and Mandevilla on Seed Potato.

Potato (Solanum tuberosum L.) ranks fourth among the most important staple food in the world. Ralstonia solanacearum (phylotype [phy] IIB, sequevar [seq] 1 and 2), also known as R3B2, the causal agent of brown rot disease on potato, is extremely damaging, causing great economical losses to potato in temperate regions. It is thought that members of Ralstonia pseudosolanacearum (phy I) are not pathogenic at low temperatures and are usually found in warmer climates. R. pseudosolanacearum strain PD 7123 (seq 33) isolated from roses in the Netherlands, strain P824 (seq 13) isolated from blueberry, and strain P781 (seq 14) from mandevilla in Florida are phylogenetically closely related and could share the same host. The virulence and ability of these novel strains to multiply latently in potato in temperate regions is unknown. The objective of this work was to assess the virulence and presence of latent infections of the mentioned R. pseudosolanacearum strains on three commercial seed potato cultivars under warmer (28°C) and temperate (20°C) temperatures. At 28°C, all three R. pseudosolanacearum strains caused severe symptoms on all potato cultivars. Overall disease severity on potato was lower at 20°C than 28°C, but major differences in virulence of the three strains were observed at 42 days postinoculation (dpi) among potato cultivars. All asymptomatic potato plants and most of their daughter tubers had latent infections at 20°C. Altogether, these results show that the phy I strains from rose, blueberry, and mandevilla may pose a threat to potato production in temperate climates and the worldwide movement of seed potatoes.[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Infection Dynamics of Potato Virus Y Isolate Combinations in Three Potato Cultivars.

The United States potato industry has recently experienced a strain shift; recombinant potato virus Y (PVY) strains (e.g., PVYNTN) have emerged as the predominant strains over the long dominant ordinary strain (PVYO), yet both are often found as single infections within the same field and as mixed infections within individual plants. To understand mixed infection dynamics in potato plants and in daughter tubers, three potato varieties varying for PVY resistance, 'Red Maria', 'CalWhite', and 'Pike', were mechanically inoculated either at the pre- or postflowering stage with all possible heterologous isolate combinations of two PVYO and two PVYNTN isolates. Virus titer was determined from leaves collected at different positions on the plant at different times, and tuber-borne infection was determined for two successive generations. PVYNTN accumulated to higher levels than PVYO at nearly all sampling time points in 'Pike' potato. However, both virus strains accumulated to similar amounts in 'Red Maria' and 'CalWhite' potato early in the infection when inoculated preflowering; however, PVYNTN dominated at later stages and in plants inoculated postflowering. Regardless of inoculation time, both virus strains were transmitted to daughter plants raised from the tubers for most isolate combinations. The relative titer of PVYNTN and PVYO isolates at the later stages of mother plant development was indicative of what was found in the daughter plants. Although virus titer differed among cultivars depending on their genetics and virus isolates, it did not change the strain outcome in tuber-borne infection in subsequent generations. Differential virus accumulation in these cultivars suggests isolate-specific resistance to PVY accumulation.

Protection of Potatoes and Mortality of Wireworms (Agriotes obscurus) With Various Application Methods of Broflanilide, a Novel Meta-Diamide Insecticide.

Wireworms are primary pests of potatoes in Canada. Presently, the highly toxic organophosphate phorate (i.e., Thimet 20G) is the only effective insecticide in use in Canada. As such, there is an urgent need for novel alternative treatments that provide competitive tuber blemish protection and wireworm reduction with a safer human and environmental portfolio. Herein we evaluated broflanilide, a novel meta-diamide insecticide for both tuber protection and wireworm mortality. When evaluated in field trials in Agassiz, British Columbia over 6 yr, broflanilide applied as a seed piece treatment (SPT) to mother tubers at 1.5-2.0 g AI/100 kg seed (approx. 50 g AI/ha), or as an in-furrow spray (IFS) at 0.23-0.25 g AI/100 m row (approx. 25 g AI/ha) was as effective at reducing blemishes to daughter tubers by wireworms (Agriotes obscurus) as phorate (Thimet 20G at 3230 g AI/ha), bifenthrin (Capture 2EC IFS at 300 g AI/ha) and clothianidin (Titan ST at 312.5 g AI/ha). In addition, broflanilide SPT and IFS applied at the above rates reduced resident wireworms (in the field at the time of planting) by 95.4-99.0% and neonate wireworms (produced from eggs laid during the growing season) by 98.1-100%. Similar results were obtained when broflanilide IFS (nonsystemic) was paired with clothianidin SPT (systemic) for broad-spectrum potato insect pest control. Strategies for the use of broflanilide on wheat (e.g., Teraxxa F4) in rotation with potatoes (Cimegra), both registered in Canada in 2020 are discussed.

Impact of the potato inoculation date on potato virus Y load and viral distribution in daughter tubers at harvest

AbstractAged plants are more difficult to infect than young plantlets. This modification of susceptibility is described as mature plant resistance (MPR). For potato virus Y (PVY), MPR is known to lead to low infection rates of plants inoculated at the postflowering stage and a decrease in the number of infected daughter tubers. However, the impact of inoculation date on the capacity of PVY to accumulate in daughter tubers has not been studied so far. Field and greenhouse experiments were carried out to better understand PVY epidemiology and to help potato growers to evaluate consequences of early/late infections on the quality of their crops. In field trials, potato plants (cv. Bintje) were covered by insectproof nets from planting to harvest except for a 14‐day period to expose plants to natural PVY infections. Under controlled conditions, potato plants were mechanically inoculated with PVY at different dates from preflowering stages (early inoculations) to postflowering stage (late inoculations). At harvest, daughter tubers were individually collected and analysed to define proportions and viral load of infected tubers according to the time between virus inoculation and harvest. Our results showed that although the age of plants at the time of inoculation can modify their susceptibility to PVY infection, in return, early and late PVY inoculations lead to similar rates of infected tubers at the plant scale and equivalent viral accumulation in infected tubers. All together, these data revealed that both early/late infections are high risks for the sanitary quality of potato tubers.

High-Quality Complete Genome Resource of Pectobacterium parvum Isolate FN20211 CausingAerial Stem Rot of Potato.

High-Quality Complete Genome Resource of Pectobacterium parvum Isolate FN20211 CausingAerial Stem Rot of Potato.

ATIVISA (ACONITUM HETEROPHYLLUM WALL EX. ROYLE): A COMPREHENSIVE REVIEW ON PROPAGATION, TRADITIONAL USES AND PHARMACOLOGY

Aconitum heterophyllum Wall ex. Royle is considered an important medicinal plant in traditional system of medicine as the tuberous roots are used for curing different ailments. But over grazing, prolong seed dormancy and many other reasons have led to the exploitation of this plant, so conservation through various modes is the need of the hour. Aims: The present review aims for accounting extensive information on different methods of propagation, traditional uses and pharmacological activities of Aconitum heterophyllum. Review Methods: A literature search was done on Aconitum heterophyllum using relevant Ayurvedic and contemporary texts. Different scientific databases such as Pubmed, Scopus, EBSCO, Google Scholar Information were used to collect all information regarding propagation and pharmacology of this plant. Results: Available data has reported that this endangered plant can be propagated through various methods such as raising propagules from seeds and daughter tubers, and other plant tissue culture techniques. Plant has reported to have 0.79% of total alkaloids in roots, out of which Atisine (0.4%), Heteratisine (0.3%), histisine, heterophyllisine, heterophylline, heterophyllidine are some major alkaloids. It also possesses important pharmacological activities like anti-bacterial activity, anti-diarrhoeal activity, enzyme-inhibition activity, anti-inflammatory activity, hepato-protective activity and anti-spasmodic activity. Conclusion: The results of this review clearly suggests about the valuable traditional use of Aconitum heterophyllum in curing various ailments like diarrhoea, dysentery, bilious complaints, intermittent fever and diseases of children. Further research: Different traditional uses mentioned in Āyurveda texts need further validation through different experimental and clinical studies which is a recommendation of this review.

Influence of abiotic factors, inoculum source, and cultivar susceptibility on the potato tuber blemish diseases black dot (Colletotrichum coccodes) and silver scurf (Helminthosporium solani)

AbstractBlack dot and silver scurf are potato blemish diseases whose economic impact has increased in recent years. Because their symptomatology on tubers is visually similar, disease assessment does not usually differentiate between the two pathogens, which share the same ecological niche. The epidemiology of black dot has been extensively studied, especially in the UK, but the factors that influence silver scurf have been less investigated. In this study, the influence of cultivar, source of inoculum, and environmental conditions on both diseases was studied in field trials over a three‐year period (2016–2018) in Switzerland. Planting minitubers did not prevent either disease in daughter tubers, indicating the contribution of soil as an inoculum reservoir. An arbitrary threshold of Colletotrichum coccodes soil inoculum could be set to discriminate between low and high disease risk. For the first time, Helminthosporium solani DNA was detected in stolons, and infections appeared earlier in stolons than in tubers. H. solani stolon and tuber infections usually appeared later in the season than those of C. coccodes. Black dot severity correlated positively with precipitation, while silver scurf severity correlated positively with temperature. Table potato cultivars commonly grown in Switzerland exhibited significant differences in susceptibility to both diseases, and cultivars with low susceptibility to both silver scurf and black dot were identified. These results gave new insights into understanding the factors driving the epidemiology of potato blemish diseases and may contribute to building a risk assessment scheme to manage both diseases simultaneously.

Efficiency of Xenorhabdus bovienii in protecting potato (Solanum tuberosum L.) against Rhizoctonia black scurf

This research evaluated the efficiency of metabolism products of entomopathogenic nematode symbiotic bacteria (MPEPNSB) of Xenorhabdus bovienii (Enterobacteriaceae) against Rhizoctonia black scurf on potato and effect of MPEPNSB treatment alone and in combination with NPK fertilizers on emergence of plants, yield and biochemical indicators of daughter tuber quality. The field experiment was carried out in 2016 under natural conditions of the Northwest region of Russia on the sod-podzolic loamy soil. The application of MPEPNSB (aqueous suspension, 30 mL/L of water) for the treatment of soil (1000 L/ha), seed tubers (10 L/t) and potato plants in the emergence phase (200 L/ha) inhibited the severity of black scurf by 97 %, the incidence of the disease reduced by 97.6 %. The complex treatment increased the potato plant emergence by 13.8%, yield by 22 %, starch content by 5 % and vitamin C content by 9.3 %. Combined application of MPEPNSB and mineral fertilizers improved yield and tuber quality indicators in potato. Application of MPEPNSB with fertilizers (MPEPNSB + N60P60K90 and MPEPNSB + N90P90K120) increased the potato yield by 55-58 %, starch content by 7.8 % and vitamin C content by 14.5-13.1 %. This study provides a perspective for the use of MPEPNSB for Rhizoctonia black scurf control in potato protection systems. Application of MPEPNSB produced high quality potato tubers.

Potato virus Y and Potato leafroll virus management under climate change in sub-Saharan Africa

Potato has increased in importance as a staple food in sub-Saharan Africa, where its production is faced with a multitude of challenges, including plant disease development and spread under changing climatic conditions. The economically most important plant viruses affecting potatoes globally are Potato virus Y (PVY) and Potato leafroll virus (PLRV). Disease management relies mostly on the use of insecticides, cultural control and seed certification schemes. A major obstacle in many sub-Saharan Africa countries is the availability of disease-free quality seed potatoes. Establishment and implementation of quality control through specialised seed production systems and certification schemes is critical to improve seed potato quality and reduce PVY and PLRV sources. Seed could be further improved by breeding virus-resistant varieties adapted to different environmental conditions combined with management measures tailored for smallholder or commercial farmers to specific agricultural requirements. Innovative technologies – including more sensitive testing, remote sensing, machine learning and predictive models – provide new tools for the management of PVY and PLRV, but require support for adoption and implementation in sub-Saharan Africa.&#x0D; Significance:&#x0D; &#x0D; Potato virus Y (PVY) and Potato leafroll virus (PLRV) are the two major potato viruses threatening profitable seed potato production.&#x0D; High-quality seed shortage in many sub-Saharan Africa countries has been identified as a constraint to increasing yield.&#x0D; Specialised seed grower or seed certification programmes should be implemented to prevent virus transmission from seed to daughter tubers.&#x0D; Sustainable PVY and PLRV management in seed potatoes requires specific regional approaches to growth, farming and climatic conditions.&#x0D; Future research should include predictive models and new innovative technologies such as more sensitive testing, machine learning and remote sensing.&#x0D;

Effect of cut seed tubers and pre-germination on potato tuber yield

Potato (Solanum tuberosum L.) is one of the important vegetable crops in Senegal with the potential to improve the national food supply and economic benefits to smallholder producers. Experiment was conducted from November 2015 to March 2016 to assess the impact of cut seed tubers and pre-germination on seed tuber storage conditions on potato tubers yield. Four treatments were used for experiment. Pre-plant seed treatments were (T1) 136 whole seed tubers 45-55 g then pre-germinated; (T2) 68 cutted tubers 22-28 g then pre-germinated; (T3) 68 pre-germinated seed tubers then cut 22-28 g; (T) 136 whole seed tubers 45-55 g not pre-germinated (maintained 4 °C). Plants grown from whole and pre-germinated seed tubers had significantly higher yield and more number of secondary stems per plant, when compared to cut and or no pre-germinated seed (P &lt; 0.001). Daughter tubers produced from cut seed resulted in higher small size potato tubers than those from whole seed (P &lt; 0.001). However, no significant difference was found on potato seed emergence. Our results indicated a clear advantage to plant whole and pre-germinated seed potatoes with the aim of producing healthier daughter tubers and increasing yields.Keywords: Seed potato, whole seed, pre-germination, Niayes, Senegal.

Growth and Yield Performance of Solanum tuberosum Grown from Seed Potatoes Infected with 'Candidatus Liberibacter solanacearum' Haplotypes A and B.

Zebra chip (ZC) disease of potato (Solanum tuberosum) is associated with infection by 'Candidatus Liberibacter solanacearum' (Lso). Two haplotypes of Lso-A and B-occur in the United States. Lso haplotype B is more virulent than haplotype A, causing greater disease incidence in tubers, more severe symptoms, and greater loss in tuber yield. This study assessed whether tubers from infected plants generate new infected plants the following year. The effects of both Lso haplotypes A and B on tuber resprout were examined on five potato cultivars. When compared with noninfected tubers, overall plant emergence rate from Lso A- or B-infected tubers was lower, plants emerged slower, and plants generated lower daughter tuber yields in weight and quantity. Plants generally emerged poorly from Lso B-infected tubers and produced lower daughter tuber yields than Lso A-infected tubers. Regardless of Lso treatment, all daughter tubers were asymptomatic, and only 0.3% tested positive for Lso in experiments conducted over 2 years. This suggests that plants generated from Lso A- and Lso B-infected seed potatoes with severe ZC symptoms are likely not a significant source of Lso in potato fields.

Carrot Pathogen ‘Candidatus Liberibacter solanacearum’ Haplotype C Detected in Symptomless Potato Plants in Finland

‘Candidatus Liberibacter solanacearum’ (CLso) haplotype C, a bacterial pathogen transmitted by the carrot psyllid Trioza apicalis, causes yield losses in carrot production. Due to concerns that this pathogen might also threaten potato (Solanum tuberosum) production, the occurrence of CLso in cultivated and volunteer potatoes in Tavastia Proper and Satakunta regions of Finland was studied. Volunteer potato plants were found in 13 of the 27 inspected carrot fields. Of the 148 potato samples tested by PCR, eight volunteer potato plants and one cultivated potato grown at the edge of a carrot field were found to be CLso positive. The PCR products obtained from these potatoes with primers OA2/OI2c, LpFrag4-1611F/LpFrag4-480R and CL514F/CL514R all showed 100% sequence identity to CLso haplotype C. This is the first observation of CLso haplotype C in field-grown potatoes. In addition, transmission experiments were performed. Attempts to transmit CLso into potato with carrot psyllids were not successful; however, CLso haplotype C was transmitted from infected carrots to potato plants by leaf grafting and by phloem connection formed by dodder, a parasitic plant, and found to survive in the potato plants for several weeks after transmission. However, the bacterial colonisation progressed slowly in the potato phloem and the amount of bacteria detected was low. The plants produced from the daughter tubers of the CLso-positive potato plants were all CLso negative, suggesting that CLso haplotype C was not able to pass to the daughter plants. None of the CLso-positive potatoes inoculated in greenhouse or collected from fields showed symptoms characteristic of zebra chip disease, associated with CLso haplotypes A and B.

Impact of Seed Cutting and Seed-Borne Inoculum on Daughter Tuber Common Scab and Plant Growth

Common scab (CS), caused primarily by the filamentous, soilborne bacterium Streptomyces scabies, creates significant challenges in the production of quality potato tubers in global growing regions. Over the past several decades, numerous studies been conducted to improve our understanding of the impact of cultural and pesticide treatments for managing the health of progeny daughter tubers. None of the previous studies, however, have addressed differences between the impacts of CS from whole seed vs. cut seed pieces on resulting disease on daughter tubers. A greenhouse trial was conducted during 2013–2014 to assess the impact of seed type and CS severity on plant health and CS on daughter tubers. Cut and suberized ‘Snowden’ seed pieces (~2 oz.) exhibiting 0, 5, and ≥50% CS severity were sown in 3-gal pots containing a 50:50 mix of sterilized sand and field soil. Whole ‘Snowden’ seed tubers (~2 oz.) with the same three levels of CS severity were sown under the same conditions. At harvest, approximately 20% of daughter tubers from asymptomatic seed pieces (both cut and whole) exhibited symptoms of CS. Disease incidence and severity significantly increased for pieces that had 5 and ≥50% CS across both experiments. Plants grown from whole seed had significantly higher yield, on average, when compared to cut seed. Daughter tubers produced from whole seed resulted in higher CS incidence than those from cut seed in one of our two experimental trials. Our results indicated a clear advantage to plant common scab-free seed potatoes with the aim of producing healthier daughter tubers.

Wireworm and Flea Beetle IPM in Potatoes in Canada: Implications for Managing Emergent Problems in Europe

Three species of wireworms (Coleoptera: Elateridae) known to cause severe damage to potatoes in Europe and Asia have been introduced to Canada and are now well established as pests in the westernmost province of British Columbia (BC) (Agriotes obscurus and A. lineatus) and the eastern provinces of Nova Scotia and Prince Edward Island (A. obscurus, A. lineatus and A. sputator). Conventional insecticide-based efforts to control these invasive pests have had serious environmental impacts, or are failing to prevent severe economic damage from occurring to potatoes in some key potato production areas. Research toward developing an IPM programme for these exotic species has been completed or is underway in Canada, including the following: biological and ecological studies, development of monitoring and risk assessment programmes, and development of insecticidal and alternative control strategies. This research is summarized and implications for wireworm management in Europe are discussed. In addition to wireworms, one of the primary economic insect pests of potatoes in BC is the tuber flea beetle, Epitrix tuberis (Coleoptera: Chrysomelidae). The larvae of this beetle feed on developing or mature daughter tubers, producing surface channels or tracks and holes directly into the tuber. In the past, growers would apply 7–10 foliar sprays of broad-spectrum insecticides per growing season, which was not always successful in controlling this pest. In the EU, a newly identified flea beetle, Epitrix papa sp. n., as well as the North American species, E. cucumeris, have been identified as attacking potatoes initially in Portugal (2004) and later also in Spain. The potential spread of these emergent pests to various EU and non-EU countries is of concern, and if established would require the development of management strategies. The former development of a highly effective IPM programme developed in BC for E. tuberis is discussed, as is its potential for E. papa and E. cucumeris management in Europe.

Biocontrol of powdery scab of potato by seed tuber application of an antagonistic fungus, Aspergillus versicolor, isolated from potato roots

An environmentally friendly measure to control potato powdery scab caused by a protozoan pathogen Spongospora subterranea f.sp. subterranea (Sss) was developed by focusing on antagonistic microorganisms that were considered compatible with potato root. Five hundred and eight soil fungi, isolated from potato root cultivated in soil suspensions from four potato fields in Hokkaido, were screened for suppressiveness of root infection by Sss in a hydroponic culture system and for powdery scab severity in greenhouse and field experiments. Antagonistic isolate Im6-50, identified as Aspergillus versicolor, was selected as a potent biological control agent. In a 3-year field test, A. versicolor Im6-50 suppressed powdery scab with a protection value of 54–70 (100 = complete protection) when applied directly on seed tubers compared with a protection value of 77–93 by the synthetic fungicide fluazinam. A. versicolor Im6-50 was detected from the surface of daughter tubers and from the soil in which the inoculated seed tubers were cultivated by PCR using species-specific primers. The establishment of A. versicolor Im6-50 on the stolon of inoculated potato plants and in the rhizosphere is considered to contribute to the mechanism for disease suppression.

Incomplete Infection of Secondarily Infected Potato Plants - an Environment Dependent Underestimated Mechanism in Plant Virology.

The common assumption in potato virus epidemiology is that all daughter tubers produced by plants coming from infected mother tubers (secondary infection) will become infected via systemic translocation of the virus during growth. We hypothesize that depending on the prevalent environmental conditions, only a portion of the daughter tubers of a plant that is secondarily infected by viruses may become infected. To test this hypothesis experimental data from standardized field experiments were produced in three contrasting environments at 112, 3280, and 4000 m a.s.l. in Peru during two growing seasons. In these experiments, the percentage of infected daughter tubers produced by seed tubers that were infected with either potato potexvirus X (PVX), potato Andean mottle comovirus (APMoV), potato potyvirus Y (PVY) (jointly infected with PVX) or potato leafroll luteovirus (PLRV) was determined. Incomplete autoinfection was found in all cases, as the percentage of virus infected daughter tubers harvested from secondarily infected plants was invariably less than 100%, with the lowest percentage of infection being 30%. Changing the growing site to higher altitudes decreased autoinfection for all viruses. Therefore, the assumption of complete autoinfection of secondarily infected plants were rejected, while the hypothesis of environmentally dependent incomplete autoinfection was accepted. The findings help explain the occurrence of traditional seed management practices in the Andes and may help to develop locally adapted seed systems in environments of the world that have no steady access to healthy seed tubers coming from a formally certified seed system. The results obtained almost three decades ago are discussed in light of most recent knowledge on epigenetic regulation of host plant – virus interactions which allow for speculating about the underlying biological principles of the incomplete autoinfection. A research roadmap is proposed for achieving explicit experimental proof for the epigenetic regulation of incomplete autoinfection in the pathosystem under study.

Seed Potato Growth and Yield as Affected by Mother Plant Exposure to Herbicides

In a repeated multi-year study, mother potato plants were exposed to herbicides at rates that simulated off-target application, such as through tank contamination. Following exposure of mother plants to herbicides, seed from mother plants was planted in the following growing season and crop growth, yield and tuber quality were quantified. Visual injury from herbicides was observed both in the mother plant and daughter tuber growing seasons and occasional impacts on tuber yield were noted. However, an inconsistent relationship was observed for herbicide related injury and tuber yield reductions of mother potato plants with daughter tuber growth and yield. The lack of consistency in the relationship between visual potato injury in the mother plant production and adverse daughter tuber growth and yield in the following year challenges traditional crop scouting as a tool to predict off-target herbicide risk near seed potato production.

Yield-enhancing and tuber-downsizing effects of transplantation cultivation method of case-held tuber seedlings in the sweet potato cultivar Beniharuka

We developed transplantation cultivation method of case-held tuber seedlings (CTS), which was derived from direct planting method of seed tubers, and applied this method to the sweet potato cultivar Beniharuka. A plastic case made of polypropylene was designed for cultivation of CTS. Seed tubers of cultivar Beniharuka in the range of 30–80 g were cut in half. The half-cut tubers were placed inside the plastic cases, and the cases were filled with a commercial soil mix. The case-held tubers were incubated under natural sunlight in a glass house. After 3–4 wk, the CTS were transplanted into a field. Mother tuber (seed tuber) enlargement was suppressed by the plastic confinement of the cases, and daughter tubers were formed above the case as vine-root-originated tubers. In the field experiments in 2012 and 2013, daughter tuber yields were increased 19% and 21% by case-held tuber seedling transplanting (CTST) over conventional vine-planting (VP), the number of daughter tubers per plant in CTST were 36 and 68% higher than in VP, and the mother tuber yields were limited to 2.1 and 4.3% of the total fresh yield of mother and daughter tubers, respectively in 2012 and 2013. Application of CTST method to cultivar Beniharuka enhanced tuber yield, increased the number of daughter tubers per plant, downsized daughter tubers compared to VP, and mother tuber enlargement was suppressed by case-holding. The CTST method is expected to produce more and smaller good in shape tubers of cultivar Beniharuka compared to VP.