Effects of inoculum density and cultivar resistance on common scab of potato and population dynamics ofStreptomyces scabies

The interaction ofStreptomyces scabies, causal agent of common scab, and its potato host was examined under scab-conducive conditions in the greenhouse. Three potato cultivars with different levels of resistance to common scab were inoculated with four levels of two rifampin-resistant strains ofS. scabies. In general, scab severity increased linearly with an increase in log₁₀ of the inoculum, but both cultivar resistance and strain ofS. scabies affected the slope of the regression line. Rhizosphere and rhizoplane populations ofS. scabies also increased with increasing soil population. One strain ofS. scabies consistently had higher rhizosphere and rhizoplane populations than the other strain. However, rhizosphere population was not consistently related to scab severity, scab incidence, cultivar resistance, or strain virulence.     

内蒙古马铃薯疮痂病发生与防治途径

2011～2012年对内蒙古自治区18个种薯生产单位和11个马铃薯县(旗、市)进行了马铃薯疮痂病(Streptomyces spp.)实地访问和调查。结果被调查的18个种薯生产单位有疮痂病率83.0%,病薯率0.0%～100.0%,11个县(旗、市)商品薯有疮痂病率100.0%,病薯率0.1%～38.0%。重复使用蛭石生产种薯、商品薯生产田轮作少、发病重。种薯较商品薯疮痂病问题更为严重。品种感病、条件适宜、重复使用蛭石、轮作少和缺乏有效杀菌剂是病害严重的主要因素。分析认为,使用效果显著的蛭石消毒剂或种薯处理剂是内蒙古马铃薯疮痂病防治的最佳途径。     

Management Effects of Disease-Suppressive Rotation Crops on Potato Yield and Soilborne Disease and Their Economic Implications in Potato Production

Soilborne potato diseases are persistent problems in potato production. Use of disease-suppressive rotation crops, such as Brassica spp. (mustards, rapeseed) and sudangrass, has shown potential for management of soilborne diseases and enhanced yield in various crop production systems. However, how to best implement these crops into productive potato cropping systems has not yet been determined. In this research, potential disease-suppressive crops were evaluated under four different types of production management (as a cover crop, green manure, harvested crop-residue incorporated, and harvested crop-residue not incorporated) in potato rotation field trials, and their effects on disease, yield, and economic viability determined. Mustard blend, sudangrass, and rapeseed rotations reduced the tuber disease black scurf (by 16–27 %) and increased yield (by 6–11 %) relative to a barley rotation control, but only mustard blend consistently reduced common scab (by 11 %). All rotation crops managed as green manures produced lower disease (by 15–26 %) and higher yields (by 6–13 %) than other management practices. Overall, the combination of mustard blend managed as a green manure was most effective, reducing scurf by 54 % and increasing yield by 25 % relative to a soybean cover crop. The use of mustard or rapeseed as a harvested crop with incorporation provided the best economic return, increasing net income by more than $860/ha relative to the standard barley rotation, but mustard blend grown as a green manure or non-incorporated harvest crop also substantially increased net income ($600 to $780/ha).     

Alasclear: A high quality scab resistant potato

Alasclear was released from the breeding program at Palmer to provide Alaskan potato growers with a variety as resistant to potato scab as Ontario and of much better quality than that variety. Alasclear has a clear skin and is very acceptable at harvest for chip manufacture. Ninety days from planting it accumulated high dry matter as indicated by 1.089 specific gravity. It continues to increase to 1.102 specific gravity over a period of 120 days.     

Effects of gypsum,sulfur, terraclor and terraclor super-x for potato scab control

An investigation was made to determine possible effects of gypsum and sulfur for control of common scab of potato [Streptomyces scabies (Thaxt.) Waksman and Henrici] in a highly buffered calcareous soil. This investigation included a comparison of the effectiveness of gypsum and sulfur with Terraclor and Terraclor Super-X. Both gypsum and sulfur reduced potato scab and measurements indicate that change of soil pH was slight (0.1–0.4 pH reduction). Band applications of sulfur in the sulfate (gypsum) or elemental form were effective at 600 lbs/A (672.5 Kg/ha) but not at lower rates. The weight of tubers thrown out of grade with scab was reduced by 53% with the effective sulfur rate. Treatment effects of gypsum (600 lb S/A-672.5 Kg/ha) were not significantly different from sulfur dust (600 lb/A-672.5 Kg/ha), Terraclor or Terraclor Super-X (both at 25.0 lb PCNB/A-28.0 Kg/ha). Tissue analyses of tuber peelings showed a significant reduction in calcium from treatments involving sulfur and gypsum, indicating that calcium levels in tuber peelings were positively correlated with scab susceptibility.     

Review: Powdery Scab of Potato—Increased Knowledge of Pathogen Biology and Disease Epidemiology for Effective Disease Management

The importance of the potato tuber disease powdery scab, caused by the zoosporic pathogen Spongospora subterranea f. sp. subterranea, has increased worldwide, and the disease is one of the most important problems facing potato production in some regions. This soilborne pathogen produces many resting spores which can remain dormant for long periods, are highly resistant to environmental stresses and can spread the disease on seed potatoes and in contaminated soil. The enigmatic nature of this organism exacerbates the development of effective powdery scab control methods. Substantial knowledge has been gained in the last decade on the biology of the pathogen and the epidemiology of the disease, but no single effective control measure is, or is likely to be, available. An integrated approach to powdery scab management is the aim, with host resistance as a substantial and sustainable component. Further research on the epidemiology of powdery scab and population genetics of the pathogen is urgently required. All stakeholders involved in the potato industry must become aware that solution of the powdery scab problem is likely to be a long-term goal. When resistant cultivars with all the other characteristics demanded for marketing high-quality potatoes are available, and when disease risk from the pathogen on seed and/or in soil can be accurately determined, then the mission to develop effective powdery scab control will become achievable.     

Relationship Between Tuber Storage Proteins and Tuber Powdery Scab Resistance in Potato

The potato genotypes (Solanum tuberosum L.) with russet tuber skin are generally resistant to powdery scab (Spongospora subterranea f.sp. subterranea or Sss). Lipoxygenase (LOX; EC 1.13.11.12) and patatin are two key storage proteins that are known to offer resistance to several diseases and insects. The objective of this study was to find out the relationship of these proteins in stored tubers with potato tuber powdery scab resistance, especially in russet skinned potatoes. An evaluation of potato germplasm with different tuber characteristics in a greenhouse environment over several years (2006–’11) suggests that russet skinned tuber genotypes (Mesa Russet, Centennial Russet and Russet Nugget) with negligible tuber disease severity index (DSI) and 100 % marketability were resistant to powdery scab. Higher physiological levels of LOX protein (on a dry weight basis) were negatively correlated with tuber DSI and positively correlated with tuber russet skin. Tuber total protein and patatin-lipase levels did not have a significant relationship with tuber powdery scab resistance. The proposed role of LOX protein in suberin- and/or non-suberin-mediated mechanisms of powdery scab resistance in russet skinned tubers are discussed here. The physiological levels of LOX protein can be considered as a useful marker for powdery scab resistance in potato breeding programs.     

Transmission of Scab Resistance to Tetraploid Potato Via Unilateral Sexual Polyploidization

Resistance to common scab continues to be a high priority trait for potato breeders. We have identified a source of resistance in the diploid wild potato relative Solanum chacoense and have introgressed it into cultivated potato by crossing it to a dihaploid. A clone generated by crossing two full-sib hybrids is highly resistant and produces both 2n pollen and 2n eggs. This clone, named 4–48, is homozygous for a major QTL for scab resistance derived from S. chacoense. Clone 4–48 was reciprocally crossed to three round white cultivars Megachip, Pike, and White Pearl. Common scab resistance was transferred to tetraploid offspring, with transmission through the male parent generally more effective than through the female parent. The majority of progeny (70%) exhibited stability for resistance to common scab across environments. This germplasm will be useful for breeding new resistant cultivars.     

Role of seed tubers in the spread of plant pathogenicStreptomyces and initiating potato common scab disease

The influence of tuber-borne pathogenicStreptomyces on potato common scab incidence in daughter tubers was examined under micro-plot conditions. Visually healthy tubers, surface-disinfested healthy tubers, and tubers with 25% scab coverage were planted in pasteurized soil. At 30, 57, and 93 days after planting, soil and belowground plant parts were sampled from various zones around the mother tuber. The total population of actinomyctes was determined by plating on a semiselective medium, and colonies of pathogenicStreptomyces were identified using polymerase chain reaction (PCR) targeting thetxtA gene. At day 30, pathogenicStreptomyces populations were below detectable levels, whereas by day 93, measurable levels were present on the belowground plant parts and in soil adjacent to scabby mother tubers at 10⁴ to 10⁵ CFU g^?1 soil. Incidence of scab in the progeny tubers was 89% at harvest. Progeny tubers produced by visually healthy seed tubers had an incidence of 60% scab and substantial populations of pathogenicStreptomyces were present in the zone near the mother tuber (10⁴ CFU g^?1 soil). Plots planted with surface disinfested seed tubers had a very lowStreptomyces population in the tuber zone and yielded 100% marketable tubers. A perfect correlation (r = 1.00) was found between the population densities of pathogenicStreptomyces in the root zone and daughter tuber disease incidence indicating that measurement of such populations in the field can serve as an excellent predictor of scab disease. After harvest, populations of pathogenicStreptomyces (10⁶ to 10⁷ CFU g^?1 lesion tissue) remained high on the mother tubers.     

Incidence and severity of powdery scab on potatoes in Pennsylvania

Studies were conducted in Potter Co., Pennsylvania to investigate the effect of powdery scab (Spongospora subterranea) on five potato cultivars (Norchip, Rosa, Kennebec, Katahdin, and Monona) at two planting dates. Soil temperature was within the range of 15–18 C and soil moisture was within 15–19% based on dry weight throughout the season. The effect of planting date was significant at each disease assessment, except for the severity on the fourth assessment. By the end of the season, incidence of scab was 66% or more for all cultivars. Rosa, Kennebec and Katahdin had a greater scab incidence over both planting dates and a greater severity at the first planting date than Monona and Norchip.     

Evidence for a relationship between certain soil arthropods and acid scab development

Springtails and mites have been found consistently in acid scab lesions and studies have shown that these arthropods carryStreptomyces spp. both on and in their bodies. Tests with several soil-applied, systemic insecticides have shown significant control of acid scab despite having little effect on the acid scab pathogen in culture. Diazinon, a long residual insecticide, gave acid scab control as good as the best fungicides thus far tested as seed or soil treatments. This insecticide also was found to be almost nontoxic to the acid scab pathogen. We suggest that soil arthropods appear to be a factor in acid scab development and present circumstantial evidence suggestive of their involvement in all potato scab development.     

Characterization,Pathogenicity and Chemical Control of <Emphasis Type="Italic">Streptomyces acidiscabies</Emphasis> Associated to Potato Common Scab

The pathogenicity of 10 bacterial isolates was investigated on potato, radish, carrot and beet, including sensitivity and pathogen control efficacy. The isolates were identified by morphological, biochemical and molecular methods. All isolates were pathogenic on radish, carrot, and beet, and were highly virulent on potato. Although the isolates were obtained from different locations in the El Fuerte Valley (Sinaloa, Mexico), they were similar in their morphological, physiological and biochemical characteristics. Sequences of the 16S rRNA gene obtained by PCR were identical for all isolates. These results indicate that the bacterial isolates from potato scabby tissue belong to S. acidiscabies. Furthermore, the effectiveness of fluazinam, both in vitro and under greenhouse and field conditions, represents a possibleoption for chemical control of potato common scab disease. While our results suggest that spraying at seeding is effective in controlling common scab, future studies to combine this treatment with seed dressing before planting will be conducted to determine if there is an increase in disease control.     

新型水溶微肥“丰钛宝”在马铃薯上施用示范

试验研究在马铃薯苗期、现蕾期、开花期叶面喷施丰钛宝水溶微肥的效果。结果表明:丰钛宝对马铃薯的生长有明显的促进作用,喷施后叶色黑绿、有光泽、叶片厚、植株长势旺盛,绿叶保持时间比对照延长11 d,还能促进成熟。无论是现代化栽培还是传统种植都表现增产,增产幅度11%～16%,大薯率增加,并有解毒降低除草剂残留对马铃薯危害程度的作用,施用丰钛宝的效益较高,投入产出比达到1:18以上。     

The effect of netted scab (Streptomyces spp.) andVerticillium dahliae on growth and yield of potato

Summary The effect ofStreptomyces spp. (netted scab) on the growth of potato was investigated in three pot experiments, in two of which the effect ofVerticillium dahliae was also assessed. The netted scab organisms attacked all underground plant parts of susceptible potato cultivars early in the growing season; the roots were especially seriously attacked, markedly reducing tuber yield and number but prolonging the duration of the growing season. The nematicide oxamyl had little effect on the incidence of netted scab. Repeated growing of the susceptible cv. Bintje greatly increased soil contamination with the netted scab pathogens. V. dahliae reduced haulm growth before wilt symptoms were evident and it reduced tuber yield but not number. Oxamyl delayed infection byV. dahliae by controlling parasiticPratylenchus nematodes (mainlyP. thornei).     

浅谈云南豆科牧草的应用前景

简介豆科牧草作为畜牧饲草、培肥农田地力、生态复绿、水土保持的功能特点,浅析了豆科牧草在云南的广阔应用前景。     

Germplasm Release: Three Tetraploid Potato Clones with Resistance to Common Scab

Common scab caused by the soil-borne bacterium Streptomyces scabies is a serious disease for the potato industry. We have identified a strong source of resistance in the diploid wild relative Solanum chacoense. This resistance has been introgressed into tetraploid cultivated potato via unilateral sexual polyploidization. This paper describes three hybrid clones (M8, M16, M17) for use by potato breeding programs to enhance resistance to common scab. They were created by crossing a diploid clone (50% S. tuberosum, 50% S. chacoense) to tetraploid cultivars, producing hybrids with 75% cultivated and 25% wild germplasm. The clones are male and female fertile, and are adapted to temperate zone production environments.     

Use of Biocontrol Organisms and Compost Amendments for Improved Control of Soilborne Diseases and Increased Potato Production

Soilborne potato diseases are persistent problems in potato production and alternative management practices are needed. In this research, biocontrol agents (Bacillus subtilis GB03 and Rhizoctonia solani hypovirulent isolate Rhs1A1) and compost amendments (from different source material), were evaluated alone and in combination, for their potential to reduce soilborne diseases and increase tuber yield over three field seasons in Maine. Both biocontrol organisms reduced multiple soilborne diseases, stem and stolon canker by 20–38 %, black scurf by 30–58 %, and common scab by 10–34 % relative to the nontreated control treatment, and the combination treatment of both biocontrol organisms together provided nominally better control than individual treatments. However, biocontrol treatments had no direct effect on tuber yield. Compost amendments from different sources all increased total and marketable tuber yield substantially (11–37 % and 17–51 %, respectively) relative to nontreated controls. However, except for some reduction of Rhizoctonia canker, compost amendments did not reduce soilborne diseases (black scurf and commons scab) in any year, and resulted in increased levels of common scab in some years (20–45 % increase). The combination compost-biocontrol treatment, although did not perform significantly better than individual component treatments, still provided indications of combined beneficial effects from both component treatments. This research demonstrated the usefulness of these approaches and combinations as additional options for reduction of soilborne diseases and increased tuber yield and can be implemented for enhanced sustainability and productivity in potato production systems.     

Elkton: A New Potato Variety with Resistance to Internal Heat Necrosis and Hollow Heart and Suitable for Chipping Directly from the Field in the Southern United States

Elkton is a medium to medium-late maturing potato variety with tan netted-skin, round-oval tubers, and white-flesh. Average marketable yields ranged from 76 % to 113 % of Atlantic and average specific gravities ranged from ?0.002 to ?0.006 less than Atlantic depending on location. Chip color processed directly from the field in southern locations or from storage in the northern locations is equivalent to Atlantic. Elkton is resistant to internal heat necrosis and hollow heart. Color and texture ratings of Elkton following baking, boiling and microwaving have been similar to Atlantic. Elkton is moderately resistant to early blight and Verticillium wilt; moderately susceptible to foliar late blight and susceptible to tuber late blight; moderately susceptible to powdery scab; and, susceptible to potato virus Y and potato virus S. Its reaction to common scab has been inconsistent. Plant Variety Protection has been requested for Elkton.     

免耕套种与秸秆还田对水稻生长和稻米品质的影响

在稻麦两熟条件下,研究了麦田免耕套种水稻与秸秆还田对水稻生长和稻米品质的影响。与移栽稻相比,免耕套种水稻株高较低,单茎叶面积略小,生物量低,但生育后期干物质累积量增加迅速。第1年免耕套种秸秆还田的产量最高,翻耕移栽秸秆还田的产量略高于移栽秸秆不还田的产量,但随着连续免耕时间的延长,第2年免耕套种的产量降低。在单位面积穗数相差不大的情况下,免耕套种水稻每穗实粒数较少,千粒重较高,套种水稻可获得较高产量。水稻免耕套种可明显改善稻米的加工品质和外观品质,提高出糙率、精米率和整精米率,降低垩白率和垩白度。翻耕移栽秸秆还田也能提高整精米率,降低垩白率和垩白度。水稻免耕套种和秸秆还田可提高稻米蛋白质含量,降低直链淀粉含量,使胶稠度变软,稻米品质变优;而水稻移栽秸秆还田条件下蛋白质含量提高,直链淀粉含量略增,胶稠度变硬,食味品质有变劣的趋势。     

The Suppression of Verticillium Wilt of Potato Using Corn as a Green Manure Crop

Field studies involving the effects of growing sweet corn (Zea mays var. Jubilee sweet corn and var. Jubilee super-sweet corn) as a green manure for 2 or 3 seasons demonstrated both suppression of verticillium wilt by 60–70% (Verticillium dahliae Kleb.) and increased potato yields. Although these treatments showed no direct effect on V. dahliae soil populations, the colonization of V. dahliae on potato feeder-roots and in potato tissue of stem apices were reduced. Feeder-root colonization by V. dahliae was positively correlated with verticillium wilt incidence (P?≤?0.05 to P?≤?0.01) and negatively correlated with yield (P?≤?0.05). Corn green manures additionally increased populations of several soilborne fungi which included Ulocladium, and Fusarium equiseti. Specific nutritional and microbial effects were secondary to the effects of cropping practices. When compared with the fallow treatments for 1994, 1995, and 1997, the percentage yield increases for 1994 were: +34% for total yield, +57% for U.S. #1’s, and +127% for tubers >280 g; for 1995 (a year of reduced degree-days and decreased verticillium incidence): +14% for total yields, +15% for U.S. #1 yields, and +21% for tubers >280 g; for 1997: +24% for yield totals, +74% for U.S. #1’s and +179% for tubers >280 g. For establishing these yield benefits, stalks with and without ears of corn were used as green manures. Corn varieties differed for effectiveness as a green manure, which could be accounted for by differences of biomass. When compared with the super-sweet corn, the sweet corn produced an increase (>2-fold) of biomass with less than half of the resulting wilt incidence. When potato was grown consecutively for 2 years, the benefits from green manures became mostly eliminated. However, following 2 consecutive years of potato, a single green manure of sweet corn was sufficient to return the potato crop to the original benefits of verticillium suppression and increased yields. This occurred even though soilborne V. dahliae inoculum levels had increased by >4-fold from 45 to 182 cfu g^?1 of soil. Results of this study demonstrate the importance of green manures and soil-ecology to the management of the Russet Burbank potato.