The Effect of Gamma-Irradiation on the Sucrose Content in Sweet Potato Roots and Potato Tubers

The sucrose content in both potato tubers and sweet potato roots was considerably increased by gamma-irradiation. The maximum increase was achieved by an irradiation dose of 3 to 4 kGy for potatoes and 0.8 to 2 kGy for sweet potatoes. Cooling treatment (15°C, 2 weeks) for sweet potato roots also enhanced the sucrose content (almost 2 times) but was not additive to the irradiation treatment; the maximum sucrose content in irradiated sweet potato roots was in the range of 7 to 12% irrespective of the cooling treatment, depending on the variety of sweet potatoes. Irradiation made the sucrose content in the roots 2 to 4 times higher.     

In vitro culture of the obligate parasite Spongospora subterranea (cercozoa; plasmodiophorida) associated with root-inducing transferred-DNA transformed potato hairy roots

Spongospora subterranea is a soil-borne, obligate parasitic protist that causes powdery scab of potatoes. In this study, an in vitro culture system was developed for the maintenance and proliferation of the protist in potato hairy roots. The hairy roots of potato were induced in vitro with Agrobacterium rhizogenes. Cystosori of S. subterranea from potato scab lesions were surface disinfested and used to inoculate potato hairy roots. Plasmodia, zoosporangia, and cystosori were observed microscopically in the hairy roots within 6 wk after inoculation, indicating the completion of the life cycle of S. subterranea in vitro. This is the first in vitro culture system for S. subterranea, and will be a valuable tool to study fundamental and practical aspects of the biology of the parasite.     

Preferential Colonization of Solanum tuberosum L. Roots by the Fungus Glomus intraradices in Arable Soil of a Potato Farming Area

The symbiosis between plant roots and arbuscular mycorrhizal (AM) fungi has been shown to affect both the diversity and productivity of agricultural communities. In this study, we characterized the AM fungal communities of Solanum tuberosum L. (potato) roots and of the bulk soil in two nearby areas of northern Italy, in order to verify if land use practices had selected any particular AM fungus with specificity to potato plants. The AM fungal large-subunit (LSU) rRNA genes were subjected to nested PCR, cloning, sequencing, and phylogenetic analyses. One hundred eighty-three LSU rRNA sequences were analyzed, and eight monophyletic ribotypes, belonging to Glomus groups A and B, were identified. AM fungal communities differed between bulk soil and potato roots, as one AM fungal ribotype, corresponding to Glomus intraradices, was much more frequent in potato roots than in soils (accounting for more than 90% of sequences from potato samples and less than 10% of sequences from soil samples). A semiquantitative heminested PCR with specific primers was used to confirm and quantify the AM fungal abundance observed by cloning. Overall results concerning the biodiversity of AM fungal communities in roots and in bulk soils from the two studied areas suggested that potato roots were preferentially colonized by one AM fungal species, G. intraradices.     

Role of Surface Substances on Germinated Spores of Ceratosystis fimbriata,Black Rot Fungus,in Host-parasite Interaction

Surface substances were isolated by sonication from the germinated spores of various strains of Ceratocystis fimbriata and characterized in relation to host-parasite specificity. The substances from the sweet potato strain, compatible with sweet potato, potently inhibited the spore agglutination of various strains by spore-agglutinating factor from sweet potato roots, while the substances from incompatible strains, that is, coffee, taro, and almond strains, weakly inhibited this agglutination. The substances from the sweet potato strain increased ethylene production from sweet potato roots infected by all strains tested, sweet potato, coffee, taro, and almond strains, which was possibly an index of pathogenicity. On the other hand, the substances from incompatible strains, coffee, taro, and almond strains, suppressed the ethylene production from the tissue infected by all four strains except the substances from almond strains on almond strain. Heat and trypsin treatments inactivated the spore agglutination inhibitory activity of the surface substances. Coincidently, these treatments extinguished the effect of the surface substances on pathogenicity of C. fimbriata on sweet potato roots.     

Lipopolysaccharides of Rhizobium etli strain G12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode Globodera pallida

Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml(-1). Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction of G. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots.     

THE INFECTION OF PLANTS BY VIRUSES THROUGH ROOTS

Roots of young tomato plants became infected when inoculated with tomato bushy stunt, tobacco mosaic, and potato X viruses. Root infections also occurred when these viruses were added to soil or culture solutions in which plants were growing.
The viruses were sometimes localized around their initial entry points in roots; sometimes they invaded the root system but not the shoots, and sometimes they produced full systemic infection of roots and shoots. In some experiments, but not all, systemic infections were more frequent when the upper tap root or superficial roots were inoculated than when fibrous roots were inoculated.
In both tomato and potato, virus X spread from diseased to healthy plants sharing the same culture solution, if their roots were in contact, but not otherwise. Infection of the roots of potato plants by inoculation, produced only one plant with virus-infected haulms, although several had infected tubers.     

Sucrose Phosphate Synthetase from Various Plant Origins

Some properties of sucrose-P synthetases obtained from various plant tissues, including sweet potato roots, potato tubers and leaves of barley, rape and ladino clover were studied. The specific enzyme activity of the sucrose-P synthetase from sweet potato roots was much lower than that of the sucrose synthetase of the other tissues. The enzyme activity decreased gradually as the roots developed. The optimum pH did not differ between enzyme preparations from sweet potato roots and barley leaves. Manganese chloride exhibited a marked stimulative effect on the sucrose-P synthetase from sweet potato roots and potato tubers, whereas it was inhibited the barley leaf enzyme.

Kinetic studies of sucrose-P synthetase showed that the behavior of the enzyme to the substrates did not differ in the enzyme sources examined. The substrate saturation curve of the enzyme with respect to fructose-6-P was sigmodal in shape, giving a straight line with a slope of 1.35~1.5 (n value) in a plot of the data using the empirical Hill equation. On the other hand, enzymes from all the various tissues exhibited a hyperbolic substrate saturation curve for UDP-glucose, obeying the ordinary Michaelis-Menten type reaction. Manganese chloride had no effect on the Km for UDP-glucose, the S_0.5 for fructose-6-P and the n value of the enzyme from potato tuber tissues.     

类芽孢杆菌QHZ11-gfp在马铃薯植株上的定殖特征及促生效果

[背景] 生防菌在作物根系的有效定殖是其功能发挥的前提,而直观的跟踪技术和有效的定量方法是研究生防菌根系分布规律的重要工具。[目的] 研究马铃薯黑痣病病原菌立枯丝核菌（Rhizo ctonia solani） JT18的拮抗菌QHZ11在马铃薯植株上的定殖特征及对马铃薯的促生效果。[方法] 采用绿色荧光蛋白（Green Fluorescent Protein,GFP）对QHZ11进行标记,将标记菌株菌悬液、生物有机肥和无菌水分别接种至灭菌土壤,通过激光共聚焦显微技术和实时荧光定量PCR等方法观察和测定标记菌株在马铃薯植株不同部位的定殖特征、数量变化及对马铃薯的促生效果。[结果] pHAPII质粒成功导入QHZ11并可稳定遗传40代,记为QHZ11-gfp;菌株标记前后的菌落形态、生长曲线和对R.solani JT18的拮抗能力等基本一致。从第7天开始,相继在马铃薯芽上和根上发现了绿色荧光,说明QHZ11-gfp成功定殖到了马铃薯的芽、根等部位。QHZ11-gfp在根系和匍匐茎的定殖数量均呈现先升高至块茎形成期达到峰值后下降的趋势,并且在整个生育期根系的定殖数量始终大于匍匐茎。菌悬液和生物有机肥处理均显著促进了马铃薯根系的生长,并通过增加株高等农艺性状提高了块茎产量。其中,生物有机肥处理在各部位的荧光强度、定殖数量和对马铃薯的促生效果均显著优于菌悬液。[结论] QHZ11-gfp可在马铃薯植株上成功定殖并对马铃薯有良好的促生效果,将其制成生物有机肥促进了其定殖,使促生效果也更好。     

Evidence that thaxtomin C is a pathogenicity determinant of streptomyces ipomoeae, the causative agent of streptomyces soil rot disease of sweet potato

Streptomyces ipomoeae is the causal agent of Streptomyces soil rot of sweet potato, a disease marked by highly necrotic destruction of adventitious roots, including the development of necrotic lesions on the fleshy storage roots. Streptomyces potato scab pathogens produce a phytotoxin (thaxtomin A) that appears to facilitate their entrance into host plants. S. ipomoeae produces a less-modified thaxtomin derivative (thaxtomin C) whose role in pathogenicity has not been examined. Here, we cloned and sequenced the thaxtomin gene cluster (txt) of S. ipomoeae, and we then constructed targeted txt mutants that no longer produced thaxtomin C. The mutants were unable to penetrate intact adventitious roots but still caused necrosis on storage-root tissue. These results, taken in context with previous histopathological study of S. ipomoeae infection, suggest that thaxtomin C plays an essential role in inter- and intracellular penetration of adventitious sweet potato roots by S. ipomoeae. Once inside the plant host, the pathogen uses one or more yet-to-be-determined factors to necrotize root tissue, including that of any storage roots it encounters.     

Potato-associated arbuscular mycorrhizal fungal communities in the Peruvian Andes

The world's fourth largest food crop, potato, originates in the Andes. Here, the community composition of arbuscular mycorrhizal fungi (AMF) associated with potato in Andean ecosystems is described for the first time. AMF were studied in potato roots and rhizosphere soil at four different altitudes from 2,658 to 4,075 m above mean sea level (mamsl) and in three plant growth stages (emergence, flowering, and senescence). AMF species were distinguished by sequencing an approx. 1,500 bp nuclear rDNA region. Twenty species of AMF were identified, of which 12 came from potato roots and 15 from rhizosphere soil. Seven species were found in both roots and soil. Interestingly, altitude affected species composition with the highest altitude exhibiting the greatest species diversity. The three most common colonizers of potato roots detected were Funneliformis mosseae, an unknown Claroideoglomus sp., and Rhizophagus irregularis. Notably, the potato-associated AMF diversity observed in this Andean region is much higher than that reported for potato in other ecosystems. Potato plants were colonized by diverse species from 8 of the 11 Glomeromycota families. Identification of the AMF species is important for their potential use in sustainable management practices to improve potato production in the Andean region.     

基于发根培养体系的甘薯品种抗线虫特性鉴定研究

利用发根农杆菌诱导的甘薯发根体系,鉴定甘薯品种抗线虫的特性。试验在甘薯品种徐薯18、栗子香和鲁78066诱导的发根体系上,接种马铃薯腐烂线虫,六周后调查发根繁殖线虫情况及线虫侵染发根情况,然后评价它们的抗线虫特性。结果表明:培养六周后,线虫在徐薯18、栗子香和鲁78066发根上繁殖倍数分别为8.82,0.76和0.70;在徐薯18发根上观察到多处线虫侵入位点,在栗子香和鲁78066发根上只观察到一处线虫侵入位点;基于以上结果,鉴定徐薯18为易感线虫病品种,栗子香和鲁78066为抗线虫病品种,徐薯18和鲁78066的鉴定结果和发病地自然诱发鉴定结果相一致,栗子香不同于发病地自然诱发鉴定结果。鉴定结果表明:用不同品种的甘薯发根作鉴定其抗线虫特性,具有体系简单、直观方便、重复性好以及不受自然环境影响等优点,进一步完善可以作为植物对线虫病抗性鉴定新的体系。     

Interaction between rhizobia and potato tissues10

Several cultivars of Solanum tuberosum L., the potato, weregrown on tissue culture media and their roots inoculated withstrains of rhizobia known to infect legumes at root junctionsor between epidermal cells. Infection incidence and severityshowed considerable cultivar/bacterial strain interaction. Bacteriaspread through intercellular spaces and invaded cells in a non-structuredway: some infections penetrated to the root xylem. There wasno evidence that potato root cells produced nod-inducing factorsand nitrogenase activity was not detected. In some host/rhizobialcombinations outgrowths were formed on roots. These varied fromloose infected callus tissue at the junctions of lateral roots,to modified lateral roots of limited growth which showed somecolonization by rhizobia. Key words: Solarium tuberosum L, potato, glycoprotein, immunogold labelling, rhizobia, flavonoids     

Effect of Hirsutella rhossiliensis on Infection of Potato by Pratylenchus penetrans

We evaluated the ability of the nematode-pathogenic fungus Hirsutella rhossiliensis (Deuteromycotina: Hyphomycetes) to reduce root penetration and population increase of Pratylenchus penetrans on potato. Experiments were conducted at 24 C in a growth chamber. When nematodes were placed on the soil surface 8 cm from a 14-day-old potato cutting, the fungus decreased the number entering roots by 25%. To determine the effect of the fungus on population increase after the nematodes entered roots, we transplanted potato cuttings infected with P. penetrans into Hirsutella-infested and uninfested soil. After 60 days, the total number of nematodes (roots and soil) was 20 ± 4% lower in Hirsutella-infested than in uninfested soil.     

发根农杆菌介导药用甘薯西蒙1号的遗传转化

用发根农杆菌A4分别感染药用甘薯西蒙1号的叶片、茎切段、叶柄等外植体,诱导出毛状根,并对毛状根进行了离体培养.采用L9(34)正交设计法优化甘薯西蒙1号的毛状根诱导条件;PCR扩增检测转化毛状根;用高效液相色谱仪检测了毛状根中咖啡酸的含量.结果表明:转化中茎切段是最合适的外植体,最佳感染时间20 min,共培养最佳时间为2天;PCR扩增检测表明发根农杆菌Ri质粒的T-DNA片段已整合进植物的基因组中;经高效液相色谱仪证实毛状根中含有咖啡酸,含量为0.03792 mg/g.     

Movement of Potato Root Diffusate Through Soil

Movement of potato root diffusate (PRD) through soil was examined by using the hatch of eggs from Globodera rostochiensis cysts as an indicator. Porous bags containing cysts were placed at increasing distances and depths from potato roots, whose growth was restricted by nylon mesh. Significantly greater hatch was observed up to 50 cm laterally away from potato roots, compared with hatch in fallow soil. Eight weeks after plant emergence, we detected a concentration gradient of PRD, as measured by egg hatch, that decreased with increasing lateral and vertical distance from the root zone. Egg hatch beyond 5 weeks after plant emergence was not attributed to PRD.     

Cd-Binding Complexes from the Root Tissues of Various Higher Plants Cultivated in Cd2+-Containing Medium

Stone parsley, soybean, sunflower, sweet potato, potato, andadlay cultivated in a Cd²⁺-containing medium had Cd-bindingcomplexes with molecular weights of about 4,000 in the roottissues. The complexes were similar to the complex previouslyfound in water hyacinth roots in their absorption and CD spectraand their amino acid compositions. The results indicate thewidespread existence of complexes similar to fission yeast Cd-BPlin roots of various plants. (Received June 30, 1986; Accepted December 18, 1986)     

Lipopolysaccharides of Rhizobium etli Strain G12 Act in Potato Roots as an Inducing Agent of Systemic Resistance to Infection by the Cyst Nematode Globodera pallida

Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml⁻¹. Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction of G. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots.     

Resolution of natural hatching factors for golden potato cyst nematode, Globodera rostochiensis

The hatching responses of Globodera rostochiensis (golden potato cyst nematode) to purified and partially-purified preparations of natural (including the potato glycoalkaloids solanine and α-chaconine) and artificial hatching factors (HFs) were bimodal. At least 10 HFs, mostly anionic, were resolved from potato root leachate by a combination of gel permeation and ion-exchange chromatography. Whereas potato roots were the principal source of HFs, haulm leachate also contained such chemicals. Root leachate from aseptically-grown potato plants lacked several HFs which were present in conventionally-produced leachate.