Effects of plastic film covers on dry-matter production and early tuber yield in potato crops

Three experiments, conducted in 1988, 1989 and 1990, examined the effects of date of removal of a clear, perforated (200 X 10 mm holes m^-2), plastic film cover on the growth and early yield of potato crops. Results confirmed that the highest early yields were achieved when the cover was removed 2 wk after 50% crop emergence and the resulting yield increase over a non-covered control varied from 6–14 t ha^-1. Later removal reduced the benefit from covering and in some cases eliminated any advantage. Covering increased mean soil and air temperatures 2.9°C and 3.2°C respectively (mean of three experiments), thereadvancing crop emergence between 3 and 5 days. The number of day-degrem accumulated between planting and emergence was very similar in covered and non-covered treatments within a season but varied between seasons from 190°C to 293°C day (> 0°C). Delaying removal resulted in an increased physical restriction to canopy expansion and reduced the capacity of the crop to intercept solar radiation. Total dry-matter yield was determined largely the amount of radiation intercepted crops (R²= 0.98). Plastic covering had relatively little effect on partitioning of dry matter to tubers but reduced tuber dry-matter percentage at early harvests when removal occurred later than 3 wk after crop emergence.     

CONSTANS delays flowering and affects tuber yield in potato

CONSTANS (CO) has a central role in the photoperiodic regulation of flowering in Arabidopsis thaliana. We show here that potato (Solanum tuberosum ssp. andigena) plants constitutively expressing Arabidopsis CO (pACo plants) flower late under all photoperiodic conditions tested. Exogenous application of gibberellic acid to pACo plants corrected their short stem phenotype but not their late flowering. To further understand the effect of CO in potato, we used three photoperiodic conditions: short days (SD), which strongly induce tuberisation of wild type plants, SD supplemented with a night break (SD+NB), which are moderately inductive, and tuberisation-inhibiting long days. Tuberisation of pACo plants was delayed under SD and very strongly delayed or completely inhibited under SD+NB, suggesting that CO affects an autonomous pathway controlling potato tuberisation. In addition, tuber yield, a trait of high agronomic relevance, was significantly increased in pACo plants expressing moderate CO levels. Our results indicate that CO affects flowering and stem elongation through distinct mechanisms and suggest that its effects on flowering and tuberisation in potato are photoperiod-independent.     

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.     

Control of tuberisation in potato by gibberellins and phytochrome B

Phytochrome B-deficient plants exhibit increased gibberellin (GA) levels or responsiveness, which may contribute to their elongated growth and reduced chlorophyll levels. We have investigated the effects of applications of gibberellic acid and an inhibitor of gibberellin biosynthesis, ancymidol, on wild-type and phytochrome B-antisense potato (Solanum tuberosum ssp. andigena) plants. The results showed that some phenotypes of the phytochrome B-antisense plants, i.e. increased stem length and reduced chlorophyll, can be mimicked by treating wild-type plants with gibberellic acid. However, another phenotype, i.e. tuberisation response in long days, is mimicked by application of a GA biosynthesis inhibitor ancymidol, thus appearing to be the result of a reduction in the gibberellin levels. A simple increase in gibberellin levels or sensitivity is, therefore, not sufficient to explain the phenotype of the antisense plants.     

Effect of canopy size and shape on the tuber yield of sixteen potato genotypes

An experiment was conducted to evaluate the utility of visual assessment of canopy characteristics in the selection of high-yielding clones for the southern Canadian Prairies. Over a 3-yr period the yield development characteristics of 16 genotypes, selected to represent a range of canopy types, both in size and shape, were studied by destructive sampling at five stages during the growing season. While the response over harvest dates was not consistent for the canopy size or shape groups for most yield variables, it was demonstrated that under the short season growing conditions in southern Alberta, canopies intermediate in size and degree of upright growth habit appear to be most efficient in terms of maximising tuber bulking rates. It was concluded that for the southern Canadian Prairies, selection of genotypes with these types of canopy structure is consistent with the objective of developing early-maturing cvs with high tuber yield.     

Phytochrome B mediates the photoperiodic control of tuber formation in potato

To determine whether phytochrome B is involved in the response of potato plants to photoperiod, a potato PHYB cDNA fragment was inserted in the antisense orientation behind the 35S CaMV promoter in Bin19 and this construct was transformed into Solanum tuberosum ssp. andigena plants which normally require short days for tuberization. Two independent transformants were obtained that had much lower levels of PHYB mRNA and protein, and which exhibited phenotypes characteristic of phyB mutants, for example, elongated stems and decreased chlorophyll content. The level of phyA, and of several phytochrome A-controlled responses, was unaffected in these plants. The photoperiodic control of tuberization in these antisense PHYB plants was abolished, the plants tuberizing in short day, long day, or short day plus night break conditions. This result shows that phytochrome B is required for the photoperiodic control of tuberization in potato ( Solanum tuberosum ssp. andigena ) and that it regulates this developmental process by preventing tuber formation in non-inductive photoperiods rather than by promoting tuberization in inductive photoperiods.     

The effects of arbuscular mycorrhizal fungi and chitosan sprays on yield and late blight resistance in potato crops from microplants

The established microplants, mycorrhized and non-mycorrhized controls, were planted in the field and unsprayed (controls), sprayed with a conventional fungicide (Ridomil), with Ridomil alternating with N,O-carboxymethyl chitosan (NOCC — a soluble chitosan) or sprayed only with NOCC. The effects of the treatments on late blight progression in the crop were monitored throughout the season and yield measured. In a preliminary study on the inoculation of detached leaves from unsprayed plants and plants sprayed with Ridomil and NOCC, respectively, NOCC was shown to delay disease development. In the field, late blight development was most rapid in the unsprayed controls, delayed in the Ridomil-treated plants and disease progression was slowed in the other treatments (AMF-inoculation, AMF-NOCC sprayed, NOCC-sprayed and Ridomil-NOCC sprayed). It was shown that plant chitinase activity increased in the AMF, AMF-NOCC and NOCC treatments. At harvest, yields for the Ridomil-NOCC, NOCC and AMF-NOCC treatments were significantly higher than the un-sprayed, non-mycorrhizal control and were not significantly different to the Ridomil-sprayed control. The results are discussed in relation to the production of seed potatoes for organic (ecological) growers.     

Effect of chitosan and a biocontrol streptomycete on field and potato tuber bacterial communities

Four treatments applied on potato seed tubers i.e. talc only, chitosan only, Streptomyces melanosporofaciens strain EF-76 in talc and S. melanosporofaciens strain EF-76 in chitosan were compared for their efficiency to reduce common scab incidence. As previously reported the joint application of the geldanamycin-producing S. melanosporofaciens strain EF-76 and chitosan was effective to control common scab of potato. Nevertheless, field application of S. melanosporofaciens EF-76 did not allow the selection of geldanamycin-resistant actinomycetes (GRA) in the bulk soil during the potato growing season. The number of GRA on harvested potato tubers was, however, significantly higher in treatments that contained chitosan than in other treatments suggesting that chitosan might promote the establishment of the antagonistic actinomycete on progeny tubers. Biolog EcoPlates were used to determine the metabolic profiles of the bacterial soil communities. A permutation MANOVA analysis detected significant differences within the metabolic profiles of the bacterial communities at the potato flowering period but not at the beginning of the season or a week before harvest. A combination of S. melanosporofaciens EF-76 and chitosan thus represents a promising tool against common scab, with low short-term impact on soil bacterial communities.     

Synergistic effects of repellents and attractants in potato tuber moth control

Pest management strategies aimed at reducing pesticide input often rely on behaviour-modifying stimuli to manipulate the distribution and abundance of pests and/or beneficial insects. However, the combined effect of more than one stimulus has rarely been tested. Here we show that the combination of two stimuli has a synergistic effect that controls herbivore damage and increases potato yield, despite the fact that each stimulus alone has no effect. A main potato pest in Colombia is the Guatemalan potato moth (Tecia solanivora) whose larvae specialize on potato tubers. To control this pest we tested the oviposition interference (repellence) of eight aromatic plants and the oviposition stimuli (attractiveness) of eight potato varieties. In the field we tested the effectiveness of the single and combined use of repellent and attractive stimuli on herbivore damage and tuber production of potato plants and compared the efficacy of these treatments to conventional management systems that employed insecticides. Although there was no effect of the attractive and repellent stimuli in the field when used alone, the combined use reduced the number of damaged tubers and increased the weight of undamaged tubers relative to the untreated plots, thus demonstrating a synergistic effect. Productivity in the conventionally treated plots was similar to plots treated with the combined stimuli. We demonstrate that the simultaneous use of garlic–pepper extracts and intercropping with S. tuberosum cv Roja Nariño are an effective strategy for the management of T. solanivora. This strategy maintains the productivity attained with conventional management practices, but without the health, environmental and ecological costs associated with the use of insecticides.     

Effects of ethylene on potato tuber respiration

Treatment of potato tubers (Solanum tuberosum L.) with ethylene gas causes a rapid rise in their respiration rate, reaching 5 to 10 times the rate of untreated tubers over 30 hours of treatment and then falling slowly. The response shows a lag of 8 hours, and more than 24 hours of exposure is required for maximum effect; the temperature optimum is near 25 C. In sensitivity to low concentrations and dependence on temperature, the phenomenon is similar to the effect of ethylene on the respiration of climacteric and nonclimacteric fruits. Treated potato tubers returned to air recover their sensitivity to ethylene more slowly than do nonclimacteric fruits (e.g., mature green oranges). It is proposed that the respiratory rise characteristic of ripening in climacteric fruits and of the wound response in plant tissues is induced by a rise in endogenous tissue ethylene.     

Use of a stress inducible promoter to drive ectopic AtCBF expression improves potato freezing tolerance while minimizing negative effects on tuber yield

Solanum tuberosum is a frost-sensitive species incapable of cold acclimation. A brief exposure to frost can significantly reduce its yields, while hard frosts can completely destroy entire crops. Thus, gains in freezing tolerance of even a few degrees would be of considerable benefit relative to frost damage. The S . tuberosum cv. Umatilla was transformed with three Arabidopsis CBF genes ( AtCBF1-3 ) driven by either a constitutive CaMV35S or a stress-inducible Arabidopsis rd29A promoter. AtCBF1 and AtCBF3 over-expression via the 35S promoter increased freezing tolerance about 2 °C, whereas AtCBF2 over-expression failed to increase freezing tolerance. Transgenic plants of AtCBF1 and AtCBF3 driven by the rd29A promoter reached the same level of freezing tolerance as the 35S versions within a few hours of exposure to low but non-freezing temperatures. Constitutive expression of AtCBF genes was associated with negative phenotypes, including smaller leaves, stunted plants, delayed flowering, and reduction or lack of tuber production. While imparting the same degree of freezing tolerance, control of AtCBF expression via the stress-inducible promoter ameliorated these negative phenotypic effects and restored tuber production to levels similar to wild-type plants. These results suggest that use of a stress-inducible promoter to direct CBF transgene expression can yield significant gains in freezing tolerance without negatively impacting agronomically important traits in potato.     

Simultaneous boosting of source and sink capacities doubles tuber starch yield of potato plants

An important goal in biotechnological research is to improve the yield of crop plants. Here, we genetically modified simultaneously source and sink capacities in potato (Solanum tuberosum cv. Desirée) plants to improve starch yield. Source capacity was increased by mesophyll‐specific overexpression of a pyrophosphatase or, alternatively, by antisense expression of the ADP‐glucose pyrophosphorylase in leaves. Both approaches make use of re‐routing photoassimilates to sink organs at the expense of leaf starch accumulation. Simultaneous increase in sink capacity was accomplished by overexpression of two plastidic metabolite translocators, that is, a glucose 6‐phosphate/phosphate translocator and an adenylate translocator in tubers. Employing such a ‘pull’ approach, we have previously shown that potato starch content and yield can be increased when sink strength is elevated. In the current biotechnological approach, we successfully enhanced source and sink capacities by a combination of ‘pull’ and ‘push’ approaches using two different attempts. A doubling in tuber starch yield was achieved. This successful approach might be transferable to other crop plants in the future.     

Changes in GA 20-oxidase gene expression strongly affect stem length, tuber induction and tuber yield of potato plants

Gene StGA20ox1 encoding potato GA 20-oxidase is expressed to relatively high levels in leaves and regulated by daylength. To investigate whether this gene is involved in photoperiodic regulation of tuber formation, we have obtained transgenic potato plants expressing sense and antisense copies of the StGA20ox1 cDNA. Over-expression of this cDNA resulted in taller plants that required a longer duration of a short day photoperiod (SD) to tuberize. Tubers from these plants had a decreased time of dormancy and developed sprouts with elongated internodes. Plants expressing antisense copies of the StGA20ox1 cDNA had shorter stems, a decreased length of the internodes and tuberized earlier than control plants, showing increased tuber yields. Antisense inhibition of this gene had no visible effect on the time of dormancy of the tubers, although at the end of dormancy these formed sprouts with shortened internodes. Decreased levels of endogenous GA20 and GA1 were detected in the apex and first leaves of the antisense lines. These results demonstrate the involvement of the GA 20-oxidase activity encoded by StGA20ox1 in the control of stem elongation and in tuber induction but not in tuber dormancy, indicating that the latter may be regulated by another member of the gene family.