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.     

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.     

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.     

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.     

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.     

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.     

Overexpression of jasmonic acid carboxyl methyltransferase increases tuber yield and size in transgenic potato

Jasmonates control diverse plant developmental processes, such as seed germination, flower, fruit and seed development, senescence and tuberization in potato. To understand the role of methyl jasmonate (MeJA) in potato tuberization, the Arabidopsis JMT gene encoding jasmonic acid carboxyl methyltransferase was constitutively overexpressed in transgenic potato plants. Increases in tuber yield and size as well as in vitro tuberization frequency were observed in transgenic plants. These were correlated with JMT mRNA level––the higher expression level, the higher the tuber yield and size. The levels of jasmonic acid (JA), MeJA and tuberonic acid (TA) were also higher than those in control plants. Transgenic plants also exhibited higher expression of jasmonate-responsive genes such as those for allene oxide cyclase (AOC) and proteinase inhibitor II (PINII). These results indicate that JMT overexpression induces jasmonate biosynthesis genes and thus JA and TA pools in transgenic potatoes. This results in enhanced tuber yield and size in transgenic potato plants.     

Influence of high temperature on carbon assimilation,enzymatic antioxidants and tuber yield of different potato cultivars

High temperature is one of the major limiting factors for cool season crops like potato in many parts of the world. This problem is more aggravated in early season planting of potato crop. This study was conducted to evaluate the performance of five potato cultivars (Solanum tuberosum L. cultivars Kufri jyoti, Kufri megha, Kufri pokraj, Rangpuria and Badami) under normal (mid October–mid January) and early season (mid August–late October) conditions during two consecutive years in terms of carbon assimilation, activities of antioxidant enzymes and tuber yield. Temperature during growth of early season crop remained 2–14°C higher than in the normal season crop, which imposed severe heat stress on early season crop. However, this heat stress in early season crop caused several folds increase in the activity of antioxidant enzymes, which had strong positive correlation with tuber yield. Although tuber yield of all tested cultivars was less in early season than in normal season; nonetheless cultivars Kufri megha and Rangpuria performed better in early season planting owing to higher net photosynthesis, carotenoid contents, membrane stability, and activities of enzymatic antioxidant enzymes. In crux, carotenoids, activities of enzymatic antioxidants, carbon assimilation and membrane stability may be used as physiological markers in future breeding programs aimed to improve the heat resistance in potato.     

Stem canker (Rhizoctoniu solani) on three early and three maincrop potato cultivars: effects of seed tuber size on growth and yield

Large seed tubers (mean 134 g) and small seed tubers (50 g) of three early and three maincrop potato cultivars, spaced respectively 48 and 30 cm apart within rows, were inoculated with Rhizoctonia solani at planting in 1985 and 1986. All seed of early cultivars was sprouted and maincrop seed was either sprouted or not sprouted. In all cultivars, plant emergence was slower from small than large seed and with both was delayed by inoculation. From 11 wk after planting numbers of stems and tubers and weights of foliage and tubers/m² were usually similar from small and large seed when not inoculated, but inoculating delayed plant growth and decreased tuber numbers and yield more from small than large seed. Inoculating decreased mean yields from large and small seed of early cultivars at 11 wk by respectively 24% and 31% (Arran Comet), 12% and 18% (Estima) and by 10% and 28% (Wilja) and losses were greatest with saleable sized tubers (3–4 cm). When grown to maturity inoculating decreased yields by 7% (Arran Comet), 5% (Estima) and 14% (Wilja). With maincrop cultivars, yields in October from large and small seed were decreased by respectively 4% and 10% (DCsirke), 9% and 12% (Maris Piper) and by 14% and 22% (Pentland Squire). In all cultivars yields of tubers < 44 mm and 44–70 mm were decreased and, with Pentland Squire, tubers > 82 mm were increased. The incidence of stem canker and of black scurf on progeny tubers was not affected by seed size but in all cultivars the percentage of greened tubers was slightly increased by inoculation.     

A survey of black dot and other fungal tuber blemishing diseases in British potato crops at harvest

Black dot and other fungal blemishing diseases were assessed on tubers from crops in eastern England in 1987 and 1988, and in 1989 and 1990 from crops throughout Great Britain. Black dot was found on tubers in crops from all areas of the country, and was most common in those from eastern and southern England. The disease was scarce on most Scottish crops, but occasionally some were severely affected. In 1988 there was no consistent relationship between the amounts of disease on the seed and subsequent ware crop. On average, the disease was more prevalent in irrigated crops and where the interval between successive potato crops was short. In 1990 treating seed tubers with fungicide had no effect on subsequent levels of disease. Few crops were unaffected by silver scurf, and it was most common in crops from southern and eastern England. In the national survey common scab was the most prevalent disease, black scurf was less common and skin spot and powdery scab uncommon except in some Scottish crops.     

Promotive effects of 5-aminolevulinic acid on the yield of several crops

The role of 5-aminolevulinic acid (ALA) as a precursor of chlorophyll or a herbicide is well documented. In the present report, to elucidate the physiological effects of ALA, this compound was applied to the foliage of radish at 0.06, 0.18, 0.6, 1.8 and 6 mM. ALA at 0.06ndash;1.8 mM increased the dry weight of radish root (underground part), but injured radish seedlings at 6 mM. Also, the application of ALA at 0.18 and 0.6 mM increased fixation of CO₂ in light and decreased release of CO₂ in darkness.Furthermore, the effects of foliar treatment of ALA on the yield of several crops were also evaluated. The results showed that an application of ALA at low concentrations increased the growth and yield by 10ndash;60percnt; over the control on kidney bean, barley, potato and garlic.These results suggest that ALA has plant growth regulating properties at low concentrations and may enhance agricultural productivity.     

Toxicity of MCPA on non-green potato tuber calli

Growth of potato tuber calli cells (non-green) is inhibited by 4-chloro-2-methylphenoxyacetic acid (MCPA) as a consequence of perturbation of membrane integrity. MCPA also depresses ATP content with simultaneous increase of ADP and AMP, i.e., the energy charge is severely compromised. Cell redox state is also affected by MCPA, as a function of concentration. Up to 60 μM, MCPA stimulates glutathione reductase and glutathione transferase, whereas superoxide dismutase and catalase activities are not affected. However, 120 μM MCPA inhibits all these activities. Cell death challenged by MCPA is putatively related to disturbance of membrane integrity responsible for mitochondrial uncoupling with decrease of the energy charge and subsequent loss of ions and metabolites.