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 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.     

Crop rotation and tillage systems as a proactive strategy in the control of peanut fungal soilborne diseases

Soil management practices can affect the population dynamics of soil microbial communities. Cultural practices can be adequately combined to benefit natural populations of microorganisms that may have a role in biological control (actinomycetes, Trichoderma spp., and Gliocladium spp.), thus contributing to the management of peanut fungal soilborne diseases in a sustainable manner within ecological boundaries. During six agricultural cycles, rhizosphere soil samples were taken from a field subjected to crop rotation (soybean, peanut, and maize), peanut being under two tillage systems (no till, reduced tillage) with the aim of quantifying populations of soil microorganisms. The incidence of diseases caused by soilborne fungi in peanut was determined at harvest. The highest amount of actinomycetes, Trichoderma spp., and Gliocladium spp. were recorded when maize was the preceding crop. Regarding tillage systems, the populations of the three groups of microorganisms were higher in peanut under no tillage than under reduced tillage. Under these conditions, the lowest incidence of peanut blight (Sclerotinia minor) and root rot (strains of Fusarium solani) was observed, suggesting a possible natural control of peanut soilborne pathogens. The quantification of actinomycetes, Trichoderma spp., and Gliocladium spp. was used as a tool to explore the impacts of different management systems on microbial groups that may be involved in the biological control of soilborne diseases, with the aim of combining those practices that improve native populations of possible beneficial microorganisms. This manipulation can provide sustainable management strategies in the control of soilborne diseases, avoiding the use of artificial inoculations of microorganisms, and reducing agrochemical application.     

Evaluation of innovative products to reduce copper applications to control potato late blight in organic production systems

The main objective of this project, VETAB project, is to determine alternatives to massive copper utilization to control potato late blight (Phytophtora infestans (Mont.) de Bary) in organic systems. To reach such a target, we first performed a screening of candidate products and additives based on their efficiency in the laboratory, under controlled conditions. We evaluated a wide range of products: formulations with a low level of copper, antagonists suspensions, aminoacid extracts, plants extracts, potassium salts, sulphur formulation, organically stabilised peroxide and rhamnolipids. The product's suspensions were applied by vaporization on potato plants. Two different protocols of application were elaborated. To test the fungicide protection action, the product was applied four days before inoculation of the pathogen. To evaluate the defence stimulating effect, the product was applied several times during the plant growth before inoculation of the pathogen. The last vaporization was performed 4 days before inoculation. We also evaluated the resistance of the product to washing risk. Pathogen suspension was applied as droplets of 5 x 10(4) spo/ml on detached leaves. The leaves were then incubated (18 degrees C, RH > 90%, 6 days) in order to record symptoms development. The best results were obtained with formulations integrating reduced doses of copper and with potassium salts. In conclusion, a wide range of products and additives are proposed on the market but very few of those have a real efficiency. The performance of the most efficient products has to be confirmed in field trials.     

The sweet potato sporamin promoter confers high-level phytase expression and improves organic phosphorus acquisition and tuber yield of transgenic potato

The sweet potato sporamin promoter was used to control the expression in transgenic potato of the E. coli appA gene, which encodes a bifunctional enzyme exhibiting both acid phosphatase and phytase activities. The sporamin promoter was highly active in leaves, stems and different size tubers of transgenic potato, with levels of phytase expression ranging from 3.8 to 7.4% of total soluble proteins. Phytase expression levels in transgenic potato tubers were stable over several cycles of propagation. Field tests showed that tuber size, number and yield increased in transgenic potato. Improved phosphorus (P) acquisition when phytate was provided as a sole P source and enhanced microtuber formation in cultured transgenic potato seedlings when phytate was provided as an additional P source were observed, which may account for the increase in leaf chloroplast accumulation (important for photosynthesis) and tuber yield of field-grown transgenic potato supplemented with organic fertilizers. Animal feeding tests indicated that the potato-produced phytase supplement was as effective as a commercially available microbial phytase in increasing the availability of phytate-P to weanling pigs. This study demonstrates that the sporamin promoter can effectively direct high-level recombinant protein expression in potato tubers. Moreover, overexpression of phytase in transgenic potato not only offers an ideal feed additive for improving phytate-P digestibility in monogastric animals but also improves tuber yield, enhances P acquisition from organic fertilizers, and has a potential for phytoremediation.     

Narrow rows reduce biomass and seed production of weeds and increase maize yield

Smallholder farmers in southern African countries rely primarily on cultural control and hoe weeding to combat weeds, but often times, they are unable to keep up with the weeding requirements of the crop because of its laboriousness, causing them to incur major yield losses. Optimisation of crop planting pattern could help to increase yield and suppress weeds and to reduce the critical period of weed control and the weeding requirements to attain maximum yield. Experiments were carried out in Zimbabwe during two growing seasons to assess the effect of maize density and spatial arrangement on crop yield, growth and seed production of weeds and to determine the critical period for weeding. Planting maize at 60 cm row distance achieved higher yields and better weed suppression than planting at 75 or 90 cm row distance. Increasing crop densities beyond the customary three to four plants m⁻² gave modest reductions in weed biomass but also diminished crop yields, probably because of increased competition for water and nutrient resources. Maize planted in narrow rows (60 cm) intercepted more radiation and suffered less yield reduction from delaying hoe weeding than those planted in wider rows (75 or 90 cm), and the duration of the weed-free period required to attain maximum grain yield was 3 weeks shorter in the narrow spacing than that in the 75- and 90-cm row spacings. Weeding was more effective in curtailing weed seed production in the narrow row spatial arrangements than in the wide row planting. The results of these studies show that narrow row spacings may reduce weeding requirements and increase yields.     

Antitranspirant-induced increases in leaf water potential increase tuber calcium and decrease tuber necrosis in water-stressed potato plants

Experiments were undertaken with field-grown potato (Solanum tuberosum L.) plants to test the hypothesis that altering leaf:tuber water potential gradients within a plant subjected to low soil moisture will allow greater Ca accumulation in tubers and reverse Ca deficiency-related tuber necrosis. Antitranspirant formulations containing a wax emulsion and a spreader/sticker surfactant increased leaf water potential during a drought episode, significantly reducing the potential gradient that develops between leaf and tuber during a period of stress. Increased leaf water potential in treated plants was associated with decreased leaf Ca and increased tuber Ca. Tuber necrosis was found to be reduced in treated plants, thus increasing tuber quality.     

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.     

Evaluation of organic,conventional and intensive beef farm systems: health,management and animal production

The overall aim of the present study was to analyse and compare organic beef cattle farming in Spain with intensive and conventional systems. An on-farm study comparing farm management practices and animal health was carried out. The study also focussed on a slaughterhouse analysis by comparing impacts on the safety and quality of the cattle products. Twenty-four organic and 26 conventional farms were inspected, and farmers responded to a questionnaire that covered all basic data on their husbandry practices, farm management, veterinary treatments and reproductive performance during 2007. Furthermore, data on the hygiene and quality of 244, 2596 and 3021 carcasses of calves from organic, intensive and conventional farms, respectively, were retrieved from the official yearbook (2007) of a slaughterhouse. Differences found between organic and conventional farms across the farm analysis did not substantially reflect differences between both farm types in the predominant diseases that usually occur on beef cattle farms. However, calves reared organically presented fewer condemnations at slaughter compared with intensive and to a lesser extent with conventionally reared calves. Carcass performance also reflected differences between farm type and breed and was not necessarily better in organic farms.     

Natural DNA variation at candidate loci is associated with potato chip color, tuber starch content, yield and starch yield

Complex characters of plants such as starch and sugar content of seeds, fruits, tubers and roots are controlled by multiple genetic and environmental factors. Understanding their molecular basis will facilitate diagnosis and combination of superior alleles in crop improvement programs (“precision breeding”). Association genetics based on candidate genes is one approach toward this goal. Tetraploid potato varieties and breeding clones related by descent were evaluated for 2 years for chip quality before and after cold storage, tuber starch content, yield and starch yield. Chip quality is inversely correlated with tuber sugar content. A total of 36 loci on 11 potato chromosomes were evaluated for natural DNA variation in 243 individuals. These loci included microsatellites and genes coding for enzymes that function in carbohydrate metabolism or transport (candidate loci). The markers were used to analyze population structure and were tested for association with the tuber quality traits. Highly significant and robust associations of markers with 1–4 traits were identified. Most frequent were associations with chip quality and tuber starch content. Alleles increasing tuber starch content improved chip quality and vice versa. With two exceptions, the most significant and robust associations (q < 0.01) were observed with DNA variants in genes encoding enzymes that function in starch and sugar metabolism or transport. Comparing linkage and linkage disequilibrium between loci provided evidence for the existence of large haplotype blocks in the breeding materials analyzed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effects of pruning,fertilizers, and organic amendments on lowbush blueberry production

A four-year field study was conducted on a Hebert gravelly sandy loam (pH 4.5) in Nova Scotia to assess the effects of pruning management and seven fertility amendments on lowbush blueberry (Vaccinium augustifolium Ait) production (yield, above ground and root tissue composition) and soil fertility. Pruning by oil burning produced higher fruit yields than flail mowing but burning had the opposite effect on the plant N content (with a lesser influence on above ground Mn and Zn). None of the fertility treatments (chicken manure, dairy manure, swine manure, urea, sawdust, NPK, NPK+S+Lime+Micronutrients) produced fruit yields significantly greater than the control. Treatments provided the equivalent of 50kg total N/ha/2-yr cycle. Treatments influenced tissue N, P, K, Ca, Mg, B, Mn, Cu, Zn and Mo levels. In general, the three manure treatments produced the highest levels of plant macronutrients; the urea treatment produced the lowest levels of plant nutrients. In most cases, extractable levels of soil P, K, Ca and Mg were highly correlated with the plant tissue content of these elements. Overall, the dairy manure treated soils were the highest in soil fertility.     

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.     

Immunolocalization of extensin and potato tuber lectin in carrot, tomato and potato

Tissue-specific expression of two members of the cell wall hydroxyproline-rich glycoprotein (HRGP) family, extensin and potato tuber lectin, was examined by immunolocalization at the light microscope level in various organs (leaves, stems, roots, fruit, tuber) of carrot ( Daucus carota cv. Thumbelina), tomato ( Lycopersicon esclentum cv. Pixie Hybrid II), and potato ( Solanum tuberosum cv. Kennebec). Extensin was prominently expressed in vascular tissue, particularly xylem and also phloem, although virtually all cells displayed some degree of staining which varied as a function of the tissue, organ, and plant under study. Antibodies against potato tuber lectin (PTL) displayed a localization pattern similar to that observed for extensin; notably PTL did not stain cambium but did stain epithelial cells lining secretory cavities. These distribution patterns are consistent with a role for extensin, and possibly PTL, in providing mechanical support in tissues subjected to compression or torsional stress imparted by vascular growth, or by similar stress brought about by transport of vascular fluids.     

Altered plastidic ATP/ADP-transporter activity influences potato ( Solanum tuberosum L.) tuber morphology, yield and composition of tuber starch

The metabolic function of the plastidic ATP/ADP transporter (AATP) in heterotrophic plastids was examined in transgenic potato plants that exhibited increased or decreased amounts of the protein. Altered mRNA levels correlated with activities of the plastidic ATP/ADP transporter. Potato tubers with decreased plastidic ATP/ADP transporter activities exhibited reduced starch contents whereas sense lines accumulated increased amounts of tuber starch. Starch from wild-type tubers had an amylose content of 18.8%, starch from antisense plants contained 11.5–18.0% amylose, whereas starch from sense plants had levels of 22.7–27.0%. The differences in physiological parameters were accompanied with altered tuber morphology. These changes are discussed with respect to the stromal ATP supply during starch biosynthesis.     

Effects of rotation length and oxamyl on potato yield and the potato cyst-nematode, Globodera rostochiensis, in a sandy loam soil

In sandy loam infested with golden potato cyst-nematode, Globodera rostochiensis, oxamyl at 5.6 kg a.i. ha^-1 incorporated in the top 15 cm of the soil just before planting potatoes greatly reduced nematode population increase on susceptible cv. Désirée grown six, seven or eight years after the last susceptible potato crop, but did not significantly increase tuber yields. In four-course and two-course rotations, oxamyl also controlled increase of G. rostochiensis and greatly increased yields of both cv. Désirée and resistant cv. Maris Piper. Oxamyl maintained tuber yields in a four-course rotation at the same level as in a six to eight-course rotation. Decline of G. rostochiensis in the soil was much faster under barley in some two-course rotations than under barley in four-course rotations.     

Functional and structural microbial diversity in organic and conventional viticulture: organic farming benefits natural biocontrol agents

Statistically significant differences in the structure and function of above-ground grapevine-associated microorganisms from organically and conventionally managed vineyards were found. Aureobasidium pullulans, a copper-detoxifying fungus and biocontrol agent, plays a key role in explaining these differences. The black fungus was strongly enriched in the communities of organically managed plants and yielded a higher indigenous antiphytopathogenic potential.     

Evaluating soil rhizobacteria for their ability to enhance plant growth and tuber yield in potato

The objectives of this study were to identify promising microorganisms to improve potato productivity in low-input systems of tropical highlands and to compare results from in vitro, greenhouse and field experiments to advance the development of a screening method for rhizobacteria and develop an efficient assessment of their effect on plant growth in field conditions. A total of 150 bacterial strains were screened in vitro, in greenhouse and field trials. The series of experiments confirmed the plant growth-promoting ability of a range of rhizobacteria. Although in vitro and greenhouse results were promising, the field experiment showed variability and the results require further verification. The in vitro tests might have limited value for screening as no correlation could be found between in vitro tests and pot trial results. However, trials in controlled conditions produced insights into the mechanisms causing better plant growth in potato, such as early tuberisation, fast development of leaf area and probably greater photosynthetic rates.     

Influence of fertilization on the Colorado potato beetle, Leptinotarsa decemlineata, in organic potato production

The abundance of the Colorado potato beetle, Leptinotarsa decemlineata (Say), in organically grown potato did not change significantly in response to increasing rates of dehydrated poultry manure. However, peaks of abundance of larvae were shifted forward in time in response to the high rate of organic fertilizer. Tests using excised foliage showed that the shift was not caused by differential larval mortality or longer developmental times. Time allocation to resting, walking, and feeding by adults was similar regardless of fertilizer rate. Adult foliage consumption was unaffected by organic fertilizer rates in no choice tests and significantly affected in few choice tests. A 22% longer larval development time on plants treated with low fertilizer rate than on plants with high rate was the most significant effect. Even though maximum plant height, canopy, biomass, and yield were significantly smaller in the organic than in conventional plots, the suitability of the plants was not affected except for reduced feeding by summer beetles. Summer adults spent less time feeding and consumed two to five times less foliage on organic potato than on inorganically fertilized and conventionally produced plants. The overall influence of fertilizer on Colorado potato beetle populations was limited and therefore can only play a secondary role in management strategies for organic potato. Avoidance of excessive organic fertilizer that promotes short larval development time and extension of the period over which large Colorado potato beetle larvae are present should be recommended.     

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.     

Effects of potato genotype, oxamyl and the numbers of potato cyst-nematodes, Globodera rostochiensis or G. pallida on tuber yields and nematode increase

A new technique is described for establishing different numbers of the potato cyst-nematode Globodera rostochiensis in field soil, which leaves the soil homogeneous in nutrient status. Field plots established in this way were used to compare yield losses in four potato cultivars (Maris Piper, Pentland Crown, Pentland Dell and Désirée) associated with different numbers of G. rostochiensis. Over the range of 7.4 to 148.4 eggs g^-1 soil at planting, yield losses were 18.7% (Maris Piper), 53.2% (Désirée), 55.7% (Pentland Crown) and 63.5% (Pentland Dell). Similar results were obtained in another experiment on the same field in a different year using only lightly and heavily infested plots. Treating the seedbed soil with oxamyl before planting prevented significant injury to potatoes by G. rostochiensis but increased the yield of Pentland Dell and perhaps Désirée (but not Maris Piper or Pentland Crown) more than expected from nematode control alone. Treating heavily infested soil with such a nematicide cannot therefore be recommended as part of a valid procedure for establishing lightly and heavily infested plots for comparing tolerances of attack by potato cyst-nematodes in a range of potato genotypes. In peaty loam soils moderately or heavily infested with G. pallida, oxamyl at 5.6 kg a.i. ha^-1 incorporated into the seedbed before potatoes were planted generally increased tuber yields, though the effects varied considerably with the cultivar grown. Increase of G. pallida in these soils was controlled better by growing potatoes bred for resistance to it (ZB 35 – 29, Caxton, Santé, Morag, 11233 ab 22, Fingal, A27/23, Cromwell). Increase of G. pallida on susceptible cultivars varied greatly and Romano increased G. pallida no more than the resistant Morag. G. pallida is probably controlled best in peaty loam by growing a resistant cultivar in soil treated with a granular (non-fumigant) nematicide.