D. Waterer

Tomato Ve disease resistance genes encode cell surface-like receptors

In tomato, Ve is implicated in race-specific resistance to infection by Verticillium species causing crop disease. Characterization of the Ve locus involved positional cloning and isolation of two closely linked inverted genes. Expression of individual Ve genes in susceptible potato plants conferred resistance to an aggressive race 1 isolate of Verticillium albo-atrum. The deduced primary structure of Ve1 and Ve2 included a hydrophobic N-terminal signal peptide, leucine-rich repeats containing 28 or 35 potential glycosylation sites, a hydrophobic membrane-spanning domain, and a C-terminal domain with the mammalian E/DXXXLφ or YXXφ endocytosis signals (φ is an amino acid with a hydrophobic side chain). A leucine zipper-like sequence occurs in the hydrophobic N-terminal signal peptide of Ve1 and a Pro-Glu-Ser-Thr (PEST)-like sequence resides in the C-terminal domain of Ve2. These structures suggest that the Ve genes encode a class of cell-surface glycoproteins with receptor-mediated endocytosis-like signals and leucine zipper or PEST sequences.

Uptake, Movement, Activity, and Persistence of an Abscisic Acid Analog (8′ Acetylene ABA Methyl Ester) in Marigold and Tomato

ABSTRACTThe abscisic acid (ABA) analog 8′ acetylene ABA methyl ester (PBI 429) was evaluated for its potential to alter the growth and moisture use of bedding plants during nursery production. Treating seedlings with the ABA analog as a root-dip slowed moisture use and growth of tomato seedlings under greenhouse conditions. In marigolds, comparable ABA analog treatments had no effect on growth and limited effects on plant moisture use. To determine whether these differences in response to treatment with the ABA analog were associated with differences in absorption of the analog and/or its persistence, the ABA analog was applied either as a foliar spray or root-dip, and the resulting concentrations of the ABA analog were monitored over a 10-day interval in both the roots and the leaves. In both crops, the ABA analog was detected in both leaf and root tissues irrespective of the mode of application, suggesting systemic movement of the analog. Tissue concentrations of the ABA analog were consistently lower in the foliar treatment than in the root-dip. The uptake and the retention of the ABA analog over time was similar in leaves of the two test crops, but less of the ABA analog was absorbed and retained in the roots of marigold plants than in the tomatoes. This suggests that the observed differences in responses of these two plant species to application of ABA analogs may be related to differences in retention or accumulation of ABA in the roots rather than to differences in the total amount of ABA analog absorbed or its movement and retention in the plant system. Levels of endogenous ABA were not significantly altered by application of the ABA analog.

The Method of ABA Application Affects Salt Stress Responses in Resistant and Sensitive Potato Lines

The phytohormone abscisic acid (ABA) has been proposed to act as a mediator in plant responses to a range of stresses, including salt stress. Most studies of ABA response apply ABA as a single dose. This may not resemble the prolonged increasing endogenous ABA levels that can occur in association with slowly increasing salinity stresses in nature or field situations. Salt stress response based on method of ABA application was examined in four potato genotypes of varying salt stress resistance: the sensitive ABA-deficient mutant and its normal sibling, a resistant genotype line 9506, and commercial cultivar ‘Norland’ of moderate resistance. ABA was applied by root drench at 0, 50, 75, or 100 μM concentrations through a single dose, or by slowly increasing multiple ABA doses in a sand-based growing system under greenhouse conditions. Salt tolerance was then evaluated after 2 weeks of exposure to 150–180 mM NaCl stress. The method of ABA application had a marked effect on the responses to salt stress. Plant responses to the method of ABA application were differentiated according to (1) growth rate, (2) root water content, and (3) apparent shoot growth response. Under a single dose, growth rate increased in all genotypes under salt stress, whereas slowly increasing multiple ABA applications generally maintained stable growth rates except in the ABA-deficient mutant where there was an upward growth trend. Percent root water content was elevated only under slowly increasing multiple ABA doses in two genotypes, whereas none of the single-dose treatments induced any change. The single ABA dose enhanced vertical growth, whereas the slowly increasing multiple ABA dose applications enhanced lateral shoot growth. Because exogenous application is still an artificial system, endogenous ABA was supplied through grafting of ABA-deficient mutant scions onto rootstocks with known elevated ABA levels. Multiple exogenous ABA applications as low as 50 μM elicited similar shoot water content responses as grafting treatments without ABA application in the mutant genotype but had no effect on the ABA normal sibling. Shoot dry weight was significantly increased through grafting over all exogenous ABA treatments. Our study further indicates that the method of ABA application regime in itself can alter plant responses under salt stress and that certain application regimes may reflect responses to elevated endogenous levels of ABA.

Biocontrol of Fusarium sambucinum, dry rot of potato, by Serratia plymuthica 5–6

Abstract Serratia grimesii 4–9 and Serratia plymuthica 5–6, isolated from the rhizosphere of pea, Pisum sativum (L), were evaluated for their potential to suppress growth of Fusarium sambucinum in vitro and to reduce Fusarium dry rot in stored potatoes (Solanum tuberosum L). In vitro studies indicated that these bacterial isolates suppressed growth of F. sambucinum by 60% or more at both 15 and 25°C. In a potato tuber slice assay the number of infection sites in potato slices exposed to F. sambucinum and treated with S. grimesii 4–9 and S. plymuthica 5–6 was reduced by 96 and 97%, respectively, at 15°C. The diameter (mm) of the infection sites was reduced 91 and 96%, respectively, when compared to slices treated with F. sambucinum alone. Studies with Fusarium-infected whole potato tubers also showed significant reduction in dry rot formation following treatment with the bacterial isolates or the fungicide thiabendazole. When applied simultaneously with the pathogen, S. grimesii 4–9 and S. plymuthica 5–6 suppressed development of Fusarium dry rot by 60 and 77%, respectively, at 15°C and by 63 and 84%, respectively, at 25°C compared to tubers inoculated with the pathogen alone. Thiabendazole suppressed development of Fusarium dry rot by 66 and 81% at 15 and 25°C, respectively, compared to tubers inoculated with the pathogen alone. These studies demonstrate the potential of soil bacteria as biofungicides for managing post-harvest crop diseases. Due to the potential risks to human health associated with S. grimesii 4–9, S. plymuthica 5–6 is recommended for further study for biofungicide development.

Impact of high soil pH on potato yields and grade losses to common scab.

The influence of soil pH on yields and grade-out due to tuber damage by common scab (Streptomyces scabies) was evaluated over multiple cropping seasons for potato (Solanum tuberosum) grown on land heavily infested with S. scabies. Soils with a native pH of 8.0 were adjusted to pH 7.0 to 9.0 using elemental sulfur as an acidulant and calcitic lime as the liming agent. There was little change in total tuber yields over this pH range, but the incidence and severity of scab lesions declined as the pH increased above 8.5. Marketable yields after grade-out to scab were highest at pH 9.0. This study demonstrates that in alkaline soils losses due to potato common scab may be managed by adjusting the soil pH to a point unfavorable to the scab organism. The economics of this type of pH change and its impact on subsequent crops need to be considered. Key words: Common scab, Streptomyces scabies, Solanum tuberosum, liming

Effect of Pot Size and Timing of Plant Growth Regulator Treatments on Growth and Tuber Yield in Greenhouse-Grown Norland and Russet Burbank Potatoes

Abstract. The effects of pot size, timing of the application of paclobutrazol (PTZ) and gibberellic acid (GA3), and the counteractive effect of these two compounds on growth and tuber yield of greenhouse-grown Norland and Russet Burbank potatoes were investigated. Plants were grown either in 1.5-liter pots (15 cm deep) or 3.0-liter pots (18 cm deep) and received a foliar application of either 1.5 mm PTZ or 9 × 10−3 mm GA3 at early or late stolon initiation. Some plants that had been foliar treated with 1.5 mm PTZ at early stolon initiation were foliar treated with 9 × 10−3 mm GA3 at late stolon initiation. PTZ reduced haulm length in both cultivars significantly, particularly when the treatment was applied at early stolon initiation, but the late treatment reduced haulm length only when growing in 3.0-liter pots. Irrespective of the timing of treatment, GA3 increased haulm length in Norland growing in both pot sizes, but the treatment increased haulm length in Russet Burbank only when applied at late stolon initiation. GA3 applied after PTZ did not overcome the growth-inhibiting effect of the PTZ treatment. The PTZ treatment effectively increased usable tuber number/plant (UTN) in Norland, but PTZ had no effect on UTN in Russet Burbank. PTZ reduced usable tuber weight/plant (UTW) only in Norland growing in 1.5-liter pots. By contrast, GA3 increased UTN only when treated at late stolon initiation of 1.5-liter pot-grown Norland, whereas the same treatment was effective when applied only at early stolon initiation for Russet Burbank. For Norland, the increase in UTN by early applied PTZ was reduced by the subsequent application of GA3. The use of 3.0-liter pots for minituber production in both Norland and Russet Burbank appears to have no advantage over growing in 1.5-liter pots, particularly when PTZ or GA3 is used to enhance tuberization.

Field evaluation of doubled haploid plants in the Apiaceae: dill (Anethum graveolens L.), caraway (Carum carvi L.), and fennel (Foeniculum vulgare Mill.)

The Apiaceae family includes vegetables, as well as herb and spice crops. Compared to major crops, there have been few breeding or genetic improvement programs for any of the Apiaceae, especially the herb and spice species. Haploidy technology can be used to develop uniform, true-breeding lines, as well as to accelerate breeding programs. Field trials of dill (Anethum graveolens L.), caraway (Carum carvi L.), and fennel (Foeniculum vulgare Mill.) doubled haploid (DH) lines were conducted over 2–5 cropping seasons. Several of the DH dill lines had desirable agronomic characteristics such as short uniform stature along with early maturity that would be useful for crop improvement. Seed yields and the essential oil content of the seed harvested from the best performing DH dill lines were either equal to or higher than the parental line. A DH annual caraway line was identified that produced higher seed yields than the industry standard. The main constituents of the essential oil for the DH lines of both dill and caraway were similar to the parental lines. Fennel DH lines exhibited differences in height but were too late in maturity for seed production under prairie conditions. The results indicate that not only were we able to generate DH lines that could be used in a crop improvement program, but we developed DH lines that could be used directly as cultivars as these lines performed better than the industry standard (parental line).

Management of common scab of potato using planting and harvest dates

The influences of planting and harvest dates on yields and grade-out due to tuber damage by common scab (Streptomyces spp.) were evaluated over three cropping seasons using two cultivars of potato (Solanum tuberosum) grown on land heavily infested with pathogenic Streptomyces species. Early planting and delaying the harvest enhanced yields in both cultivars, but also increased tuber grade-out due to excessive levels of scab. Delaying the harvest reduced marketable yields more than did early planting. The longer harvest was delayed after top-kill, the greater was the grade out due to scab. Increased losses to scab exceeded any increase in tuber yields obtained by delaying harvest. This study demonstrates that common scab of potato may be managed by minimizing the period the crop is in the ground, but that this method of disease management is achieved at the expense of yields. Early planting coupled with timely harvesting after kill-down of the tops appears to be an effective compromise between the objectiv...

Influence of irrigation, nitrogen and seed piece spacing on yields and tuber size distribution of seed potatoes

This study examined the influence of irrigation, soil nitrogen (N) levels and seed piece spacing on the yields and tuber size distribution of Norland, Russet Burbank and Shepody potatoes over three seasons at two sites in central Saskatchewan. The crops were grown under standard irrigated conditions or on dryland with in-row spacings of 15, 23 or 30 cm and total N levels of 200 or 300 kg ha−1 as either preplant or split applications. Irrigation greatly enhanced yields of all tuber size categories in the drier years but had less effect if seasonal precipitation reached or exceeded normal levels. Smaller size tubers formed a greater proportion of the total yield in crops exposed to drought stress. Norland was less affected by drought than the later-maturing cultivars. Yield responses to N were limited to situations where soil moisture was abundant or crop demand for nutrients was increased by close in-row spacings. Close in-row spacing increased total yields in some cases, while in others it resulted in a r...

Northstar: A high-yielding, white cold-storage chipping potato cultivar with attractive oval tubers resistant to late blight

Abstract‘Northstar’ (V0123-25) is a white-skinned, white-flesh, mid-season maturing potato cultivar suitable for cold storage chipping. It was selected from a cross made at the Lethbridge Research Centre of Agriculture and Agri-Food Canada between ‘Niska’ and ND860-2. In trials across western Canada, full season marketable yields of Northstar were 6% to 31% greater than ‘Snowden’ and 11% greater than ‘Norchip’. Specific gravity of Northstar has averaged 0.009 and 0.012, less than Snowden and ‘Atlantic’, respectively. Chip color was superior to Norchip, Snowden and Atlantic. Northstar showed an excellent potential for direct chipping out of a 6 C storage. Tubers of Northstar are uniform, oval, smooth to slightly flaky in texture, with shallow eyes. The incidence of hollow heart and internal necrosis was lower than Atlantic, Norchip and Snowden. Deformed tubers occurred at levels less than Norchip and Snowden. Northstar is resistant to tuber late blight infection, moderately resistant to common scab, Verticillium wilt and Fusarium wilt, and moderately susceptible to foliar late blight. It is susceptible to early blight and shows clear tuber and foliar symptoms when infected with bacterial ring rot.Resumen‘Northstar’ (VO123-25) es un cultivar de papa de piel blanca, pulpa blanca que madura a media estación, adecuado para hojuelas de almacenamiento frío. Fue seleccionado de un cruzamiento entre ‘Niska’ y ND860-2 en el Centro de Investigación Agrícola Lethbridge and Agri-Food Canada. En pruebas a través del Oeste canadiense, los rendimientos comerciables de estación completa de Northstar fueron de 6% a 31% más altos que ‘Snowden’ y 11% mayores que ‘Norchip’. La gravedad específica de Northstar ha promediado 0.009 y 0.012 menos que Snowden y ‘Atlantic’, respectivamente. E1 color de hojuela fue superior que Norchip, Snowden y Atlantic. Northstar mostró un excelente potencial para hacer hojuelas de tubérculos directamente extraídos de almacenamiento de 6 C. Los tubérculos de Northstar son uniformes, ovales, lisos a ligeramente escamosos, con ojos superficiales. La incidencia de corazón vacío y necrosis interna fue menor que en Atlantic, Norchip y Snowden. Los tubérculos deformes se presentan a menores niveles que en Norchip y Snowden. Northstar es resistente a la infección de tizón tardío al tubérculo, moderadamente resistente a sarna común, marchitez por Verticillium y Fusarium y moderadamente susceptible a tizón tardío foliar. Es susceptible al tizón temprano y muestra claros síntomas al tubérculo y al follaje cuando se infecta con pudrición bacteriana en anillo.