Potato Seedlings Research Articles

Nematicidal influence of <i>P.tuberreguim</i> and neem extract on the incidence of root-knot nematode on hausa potato (<i>Solenostemon rotundifolius Poir</i>).

Efficacy of Pleurotus tuberregium, Neem-leaf ash, carbofuram and combination of the three above were tested in the control of root-knot nematode (Meloidogyne incognita) on Hausa potato. In the green house, twenty-five polythene bags were filled with 10kg of steam-sterilized sandy loam soil and Hausa potato seedlings were planted in each of them. Four weeks after planting 5000 eggs of (Meloidogyne incognita) were inoculated round the plants in each of the bag. The treatments which included Pleurotus tuberregium, Neem-leaf ash, Carbofuran (a synthetic nematicide), and a combination of the three treatments above as a combined approach treatment were applied into the bags around the plants to ascertain the nematicidal influence of each. A control plot where nematode eggs were not inoculated and no treatment application was maintained and observed. Influence of these treatment were further observed in the field which is naturally infested with nematode (Meloidogyne incognita.) The field study was laid out in a Randomized Complete Block Design (RCBD) replicated five times. Both the green house study and the field study shows that all the materials used as treatments in this study have nematicidal influence as they significantly (P=0.05) reduced nematode population and their damaging effects. Combined approach treatment (i.e. P. tuberregium, plus Neem-leaf ash, plus carbofuran) gave better result than the single treatments.Keywords: Root-Knot nematode, control, Hausa potato.

Investigation of biological behavior of Iranian indigenous phosphate solubilizing bacteria and determinant of colonization ability of potato roots by these bacteria isolation

The ability of a few soil microorganisms to convert insoluble forms of phosphorus (P) to an accessible form is an important trait in plant growth-promoting bacteria for increasing plant yields. The use of phosphate solubilizing bacteria as inoculants increases the P uptake by plants. In this study, isolation and characterization of 3 strains of phosphate solubilizing bacteria (PSB) from Central province of Iran were carried out. Identification of three isolates was carried out by 16S rDNA sequencing. Three strains namely Bacillus lentus strain PS5, Bacillus Licheniformis strain PS7 and Pseoudomonas putida strain PS13 were isolated from the rhizospere of Beta vulgaris and solanum tuberosom. All of the three strains were selected in vitro for their phosphate solubilizing abilities from alkaline soils. Among the three strains, PS5 and PS7 were the most efficient strains in terms of their capabilities to grow and solubilize phosphorus in the presence of 5% NaCl and 42°C. Root colonization analyses were performed to determine the distribution and metabolic activity of the strains in the potato rhizosper. The soil containing potato seedling was treated with all strains marked with lux genes for bioluminescence, as well as resistance to kanamycin and rifampin prior to planting in non-sterile natural soil. The introduced bacteria were quantified on roots by dilution plating on antibiotic media along with observation of bioluminescence. Results demonstrated the strains could survive in the potato root system under stress conditions. The significance of this study lies in the fact that the bacterial strains isolated from alkaline soils have ability to solubilize phosphate in high salt, pH and temperature conditions.

Hydrogen Sulfide Promotes Root Organogenesis in Ipomoea batatas, Salix matsudana and Glycine max

In this report, we demonstrate that sodium hydrosulfide (NaHS), a hydrogen sulfide (H(2)S) donor, promoted adventitious root formation mediated by auxin and nitric oxide (NO). Application of the H(2)S donor to seedling cuttings of sweet potato (Ipomoea batatas L.) promoted the number and length of adventitious roots in a dose-dependent manner. It was also verified that H(2)S or HS(-) rather than other sulfur-containing components derived from NaHS could be attributed to the stimulation of adventitious root formation. A rapid increase in endogenous H(2)S, indole acetic acid (IAA) and NO were sequentially observed in shoot tips of sweet potato seedlings treated with HaHS. Further investigation showed that H(2)S-mediated root formation was alleviated by N-1-naphthylphthalamic acid (NPA), an IAA transport inhibitor, and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), an NO scavenger. Similar phenomena in H(2)S donor-dependent root organogenesis were observed in both excised willow (Salix matsudana var. tortuosa Vilm) shoots and soybean (Glycine max L.) seedlings. These results indicated that the process of H(2)S-induced adventitious root formation was likely mediated by IAA and NO, and that H(2)S acts upstream of IAA and NO signal transduction pathways.

An Emerging Potato Purple Top Disease Associated with a New 16SrIII Group Phytoplasma in Montana.

Potato purple top (PPT) is a devastating disease that occurs in the United States, Canada, Mexico, Russia, and elsewhere causing great economic loss to the potato industry through substantially reduced tuber yield and quality. Chips and fries processed from infected tubers often develop brown discoloration, greatly reducing their marketability. At least seven distinct phytoplasma strains belonging to five different phytoplasma groups (16SrI, 16SrII, 16SrVI, 16SrXII, and 16SrXVIII) have been reported to cause purple top and related symptoms in potato (3). During an unusual drought in 2007, a newly emerging potato disease with extensive yellowish or reddish purple discoloration of terminal shoots and leaves, similar to PPT symptoms, was observed in isolated potato fields in Montana where over 50% of plants exhibited symptoms. Shoot tissues were collected from three symptomatic plants and 17 tubers randomly collected from 17 other symptomatic plants. The tubers were cold treated to induce sprouting and then planted in the greenhouse. All tubers produced plants of which seven exhibited PPT symptoms including severe stunting. Total nucleic acid was extracted from leaf veinal tissue, stolons, or tubers of 10 symptomatic and 10 asymptomatic plants (both field-collected and greenhouse samples) as previously described (3). A nested-PCR assay, using universal primer pair P1/16S-SR followed by R16F2n/R16R2n, was performed as previously described (2,3) to detect phytoplasmas in these samples. Phytoplasma strains were detected in all symptomatic plants. Restriction fragment length polymorphism (RFLP) analyses of nested-PCR products (approximately 1.2 kb) with seven key restriction enzymes (AluI, MseI, HhaI, Tsp509I, HpaII, RsaI, and BfaI) indicated that all samples contained a very similar or identical phytoplasma most closely related to reference strain MW1 (belonging to subgroup 16SrIII-F) (1). Analysis of cloned 16S rDNA sequences confirmed the identity of this new phytoplasma and sequences of three representative PPT-MT strains were deposited in GenBank with Accession Nos. FJ226074-FJ226076. Computer-simulated RFLP analyses of 1.2-kb 16S rDNA sequences of this new phytoplasma and representative members in the peach X-disease phytoplasma group (16SrIII) available in GenBank indicated the strain is distinct and represents a new subgroup, 16SrIII-M (4). This study also indicated that the phytoplasma is tuber transmissible since approximately 35% of plants produced from infected tubers collected in this study developed symptoms. Transmission via infected tubers may pose a potential threat for disease spread by planting uncertified seed potatoes. To our knowledge, this is the first report of 16SrIII group phytoplasmas-associated diseases in potato. A phytoplasma closely related to the PPT-MT strains has recently been detected in potato seedlings exhibiting purple top, rosette, and stunting in Alaska (GenBank Accession No. FJ376628).

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.

Effect of thiacloprid against the potato tuber moth Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae)

The effect of the chloronicotinyl insecticide (thiacloprid 480 SC) was evaluated to determine its potential in controlling the potato tuber moth, Phthorimaea operculella. Application of thiacloprid at various concentrations (0.1–0.4 ml/l) on different age groups of eggs (1–4.5 day-old) had no effect on egg hatchability. However, slight embryocidal effect was noted in all egg age groups exposed to 0.4 ml/l concentration. Egg incubation period was increased (20%) when 4–4.5 day-old eggs were treated with thiacloprid at a rate of 0.4 ml/l compared with the untreated control. Thiacloprid was effective in reducing larval survival on potato seedlings or adults emergence from potatoes, exhibiting activity for at least 14 days after application. When already infected potato seedlings or tubers were treated with thiacloprid at a rate of 0.4 ml/l, adult emergence was decreased. Larvae that hatched from thiacloprid-treated eggs and fed, untreated tubers, encountered some difficulties in surviving and emerging as adults. Our data suggest that potato plants or tubers treated with thiacloprid at a commonly used rate (0.4 ml/l) should be well protected from the possibility of infestations by the potato tuber moth.

Variation of GFP expression in diploid and tetraploid transgenic potato

A diploid potato seedling derived from a cross between a haploid-inducing pollinator and a highly regenerable clone ofSolatium phureja was transformed usingAgrobacterium tumefaciens LBA4404 with a construct bearing kanamycin resistance (hptII) and theS- GFP (green fluorescent protein) gene. From three leaf disks, 17 diploid and 12 tetraploid T0 plants were regenerated. GFP expression was observed in leaves, tubers, flowers and embryos of transformed plants. After self-pollination of T0 diploids, 879 T1 were found to express GFP over a wide continuous range, based on measurements using a GFP meter. Segregation of GFP expression in the T1 indicated that the diploid primary transformants likely contained two copies of the GFP gene. For three of five tetraploid T0, 15:1 segregation ratios of GFP expression:wild type in the T1 supported double copy simplex insertion of the transgene. A segregation ratio of 35 GFP:1 wild type in a fourth tetraploid T1 family supported the likelihood of a single copy duplex insertion. The potential of using GFP as a marker to select against transgenic hybrid seeds following attempted haploid extraction depends upon facile visualization of GFP positive seeds so that the relatively few nontransgenics can be screened for haploidy. Stable GFP expression was found in various tissues of six transgenic diploids; however, visualization of GFP in dry seed was hampered by autofluorescence.

Densidade de plantas e métodos de colheita na multiplicação de batata-semente em vasos

Por apresentar volume limitado de substrato, o plantio em vasos pode levar a uma reduzida taxa de multiplicação de tubérculos de batata. Objetivou-se estudar a multiplicação de tubérculos-semente pré-básicos de batata em vasos, em função da densidade de plantas e dos métodos de colheita. Os ensaios foram conduzidos em ambiente protegido com tela antiafídeo, em vasos de 3 L. Em ambos os ensaios foram utilizadas plântulas livres de vírus. No primeiro ensaio foram avaliadas as cultivares Monalisa e Ágata e dois métodos de colheita (única e escalonada, com colheitas a cada 30 dias), em um fatorial 2 x 2 em delineamento inteiramente ao acaso, com seis repetições e parcelas de quatro vasos, com uma plântula por vaso. No segundo ensaio, foi utilizada apenas a cultivar Monalisa e foram avaliadas cinco densidades de plantio, de 1 a 5 plantas por vaso (25 a 125 plantas m-2) nas épocas de primavera/verão e outono/inverno. Estes ensaios foram conduzidos em delineamento inteiramente ao acaso, com quatro repetições de quatro vasos cada. Não houve efeito significativo do método de colheita sobre o número total de brotos. Ao contrário, maior comprimento e massa fresca de tubérculos foram obtidos na colheita única. A cultivar Ágata produziu significativamente mais tubérculos por planta que a cultivar Monalisa, embora esta tenha produzido tubérculos de maior comprimento e massa. Em relação à densidade de plantio, na primavera/verão cada planta adicionada ao vaso (0,04 m² para cada planta adicionada) proporcionou um incremento de 2,69 tubérculos por vaso (67,25 tubérculos m-2), enquanto, no inverno, o incremento foi de 4,36 tubérculos por vaso (109 tubérculos m-2). Por outro lado, o aumento na densidade levou à redução em média de 3,20 g na massa fresca dos tubérculos para cada planta adicionada ao vaso no experimento de inverno. No experimento conduzido na primavera/verão a densidade de plantio não influenciou o peso fresco dos tubérculos.

Control of soilborne potato diseases using Brassica green manures

Brassica crops used in crop rotations and as green manures have been associated with reductions in soilborne pests and pathogens. These reductions have been attributed to the production of volatile sulfur compounds through a process known as biofumigation, and to changes in soil microbial community structure. In this study, selected Brassica crops, including canola, rapeseed, radish, turnip, yellow mustard, and Indian mustard, were evaluated for control of various soilborne potato pathogens and diseases in culture, in greenhouse trials, and in field trials on commercial potato farms. In in vitro assays, volatiles released from chopped leaf material of Brassica crops and barley inhibited growth of a variety of soilborne pathogens of potato, including Rhizoctonia solani, Phytophthora erythroseptica, Pythium ultimum, Sclerotinia sclerotiorum, and Fusarium sambucinam, with Indian mustard resulting in nearly complete inhibition (80–100%). All Brassica crops and barley reduced inoculum levels of R. solani (20–56% reduction) in greenhouse tests, and radish, rapeseed, and Indian mustard reduced subsequent potato seedling disease by 40–83%. In an on-farm field trial at a site with a substantial powdery scab problem, Indian mustard, rapeseed, canola, and ryegrass grown as green manure rotation crops reduced powdery scab in the subsequent potato crop by 15–40%, and canola and rapeseed reduced black scurf by 70–80% relative to a standard oats rotation. At another field site where common scab was the primary disease problem, an Indian mustard green manure reduced common scab by 25%, and rapeseed, yellow mustard, and ‘Lemtal’ ryegrass also reduced black scurf relative to a standard ryegrass rotation. Disease reductions were not always associated with higher glucosinolate-producing crops, and were also observed with non- Brassica crops (barley and ryegrass), indicating other mechanisms and interactions are important, particularly for control of R. solani. Overall, Indian mustard was most effective for reducing powdery scab and common scab diseases, whereas rapeseed and canola were most effective in reducing Rhizoctonia diseases. These results indicate that Brassica crops have potential for use as green manures for the control of multiple soilborne disease problems.

First Record of Verticillium dahliae on Potato in Malta.

Potato is an important and highly valued crop throughout the Maltese Archipelago. Much of the production is exported to Holland. In January 2005, minor wilts and chlorosis of potato plants were observed in a field at Hal-Farrug, Luqa (Malta). Verticillium dahliae Kleb (1) was isolated on potato dextrose agar (PDA) from vascular tissue excised from the base of the plants. Three different isolates were obtained, all of which were typically distinguished by verticillately shaped conidiophores and the abundant production of microsclerotia on PDA. In May 2005, colonies of these three isolates were cultured in potato dextrose broth (PDB), from which conidial suspensions of each isolate were prepared with sterile distilled water to a concentration of 107 ml-1. For each isolate, 10 7-day-old potato seedlings were inoculated via root immersion in the inoculum suspension and transplanted to 20-cm diameter plastic pots containing a soil/peat mixture (1:1 [v/v]). Seedlings treated in the same way with sterile distilled water were used as a control. All plants were kept under controlled glasshouse conditions (20 ± 3°C) and watered to field capacity as required. Minor chlorosis and wilt of the pair of lower-most leaves was noted 7 days after inoculation. During subsequent weeks, wilt began to appear in the typical half-leaf form, while chlorosis was noted on all organs of the plants, including the principal stem (3). Symptoms were absent on the control plants. Measuring the weight of the new tubers produced by each plant revealed no apparent difference between inoculated and healthy plants; nevertheless, inoculated plants resulted in more tubers with a smaller diameter in respect to those of the uninoculated plants. V. dahliae was never isolated from tubers. Little to no variation in symptom severity was noted among plants inoculated with the three individual isolates. At the end of June, V. dahliae was reisolated on PDA from all inoculated plants, in particular, from vascular tissues originating from principal and lateral stems, crowns, and roots. All attempts to isolate the pathogen from control plants were unsuccessful. Molecular detection of the pathogen by using species-specific primers and real-time Scorpion PCR (2) confirmed the results obtained by the classical isolation method. The low symptom severity observed by the growers in the field, usually mistaken for normal dieback of aged plants, might explain why V. dahliae was never reported before on potatoes in the Maltese Archipelago.

Screening of Arbuscular Mycorrhizal Fungi for Symbiotic Efficiency with Sweet Potato

ABSTRACT A greenhouse study was conducted to study the efficiency of 14 isolates of arbuscular mycorrhizal (AM) fungi isolated from a local agricultural soil on the productivity of sweet potato (Ipomoea batatas). The different AM fungi enhanced the biomass and nutritional status of sweet potato seedlings to different extents. The genus Glomus was more effective than Acaulospora or Scutellospora. Efficiency also varied among isolates of Glomus irrespective of individual host plant or location of origin. Intraspecific differences were sometimes greater than interspecific differences. Benefits deriving from fungal isolates were positively correlated with the root-colonization rate and the abundance of extraradical propagules of the AM fungi. Taking plant yield parameters, nutritional status of the plants, and fungal attributes into consideration, GEGM (Glomus etunicatum together with Glomus mosseae) and GE6 (Glomus etunicatum) were the most effective AM symbionts for sweet potato under the experimental conditions.

Pathogenicity of the root‐knot nematode Meloidogyne javanica on potato

Host–parasite relationships and pathogenicity of Meloidogyne javanica on potatoes (newly recorded from Malta) were studied under glasshouse and natural conditions. Potato cvs Cara and Spunta showed a typical susceptible reaction to M. javanica under natural and artificial infections, respectively. In potato tubers, M. javanica induced feeding sites that consisted of three to four hypertrophied giant cells per adult female. Infection of feeder roots by the nematode resulted in mature large galls which usually contained at least one mature female and egg mass. In both tubers and roots, feeding sites were characterized by giant cells containing granular cytoplasm and many hypertrophied nuclei. Cytoplasm in giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density (P) [0–64 eggs + second‐stage juveniles (J2s) per cm3 soil] and growth of cv. Spunta potato seedlings was tested under glasshouse conditions. A Seinhorst model [y = m + (1 − m)z(P−T)] was fitted to fresh shoot weight and shoot height data of nematode‐inoculated and control plants. Tolerance limits (T) for fresh shoot weight and shoot height of cv. Spunta plants infected with M. javanica were 0·50 and 0·64 eggs + J2s per cm3 soil, respectively. The m parameter in that model (i.e. the minimum possible y‐values) for fresh shoot weight and shoot height were 0·60 and 0·20, respectively, at P = 64 eggs + J2s per cm3 soil. Root galling was proportional to the initial nematode population density. Maximum nematode reproduction rate was 51·2 at a moderate initial population density (P = 4 eggs + J2s per cm3 soil).

The protective effects of cobalt on potato seedling leaves during osmotic stress

The protective effects of cobalt on potato seedling leaves during osmotic stress were reported and discussed in this paper. The results showed that the membrane damage was significantly alleviated after 24 h of osmotic stress when cobalt of appropriate concentrations was added in PEG solutions. During -1.0 MPa PEG osmotic stress cobalt of 25 μmol L^(-1) inhibited ethylene production rate significantly. Cobalt of 25 μmol L^(-1) had no significant influence on the content of thiobarbituric acid reacting substances or chlorophyll in the first 16 h. When the stress lasted 20 h and 24 h, treatment with cobalt effectively restrained the increment in the levels of reactive oxygen species, hampered the decline in the content of putrescine, spermidine and spermine. The decline in the activities of antioxidative enzymes, thus inhibited the accumulation of thiobarbituric acid reacting substances and alleviated the reduction of chlorophyll content. It can be concluded that when the potato leaves were deeply stressed and damaged, through the inhibition of ethylene production, cobalt alleviated the decline in polyamine content and the activities of anti-oxidative enzymes, and hence alleviated the increment in reactive oxygen species levels and membrane damage and showed protective effects on the leaves.

The effect of NaCl on antioxidant enzyme activities in potato seedlings

The effect of NaCl on the growth and activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were investigated in the seedlings of four potato cultivars (Agria, Kennebec; relatively salt tolerant, Diamant and Ajax; relatively salt sensitive). The shoot fresh mass of Agria and Kennebec did not changed at 50 mM NaCl, whereas in Diamant and Ajax it decreased to 50 % of that in the controls. In Agria and Kennebec, SOD activity increased at 50 mM NaCl, but no significant changes observed in Diamant and Ajax. At higher NaCl concentration, SOD activity reduced in all cultivars. CAT and POD activities increased in all cultivars under salt stress. Unlike the other cultivars, in Ajax seedlings, APX activity increased in response to NaCl stress. We also observed new POD and SOD isoenzyme activities and changes in isoenzyme compositions under salt stress. These results suggest that salt-tolerant potato cultivars may have a better protection against reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes (especially SOD) under salt stress.

The effect of NaCl on proline accumulation in potato seedlings and calli

The effects of salt stress were studied on the accumulation and metabolism of proline and its correlation with Na+ and K+ content in shoots and callus tissue of four potato cultivars, viz., Agria, Kennebec (relatively salt tolerant), Diamant and Ajax (relatively salt sensitive). Na+ and proline contents increased in all cultivars under salt stress. However, K+ and protein contents decreased in response to NaCl treatments. The activities of enzymes involved in proline metabolism, Δ1-pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (ProDH) increased and decreased, respectively, in response to elevated NaCl concentrations. The changes of P5CS and ProDH activities in more salt sensitive cultivars (Diamant, Ajax) were more than those in the tolerant ones. Then the stimulation of synthesis in combination with a partially increase of protein proteolysis, a decrease in proline utilization and inhibition of oxidation resulted in high proline contents in seedlings and calli under salt stress. In callus tissue, reduced growth and cell size may be partially responsible for high proline accumulation in response to high NaCl levels. However, although the basic proline contents in the seedlings of more salt tolerant cultivars were higher than the sensitive ones, a clear relationship was not generally observed between accumulation of proline and salt tolerance in potato.

Influence of nitrogen form on yield and nitrate content of subirrigated early potato

AbstractPotato is classified among the vegetables with low nitrate content but, in diet, it contributes most to the daily intake of nitrate, because of its high per capita consumption. Two trials were carried out in winter–spring and autumn–winter cycles using a trough bench subirrigation system. Potato seedlings were transplanted into pots containing peat, pumice and vermiculite in a 3:1:1 volume ratio. Both trials were carried out to compare three nutrient solutions having the same nitrogen concentration (6.4 mM), but different ammonium:nitrate (NH4‐N:NO3‐N) percentage ratios (100:0, 50:50 and 0:100). In the winter–spring cycle, tubers were lower in weight and were more numerous than in the autumn–winter cycle. The tuber yield of ammonium‐fed plants was lower than with the mixed form and 100% NO3‐N, but only in the trial carried out in the winter–spring period. Nitrate‐fed plants yielded a number of tubers almost 3‐fold higher than ammonium‐fed plants. The NO3 content of tubers harvested in spring in the presence of 100% NH4‐N in the nutrient solution was a 25% of that in nitrate‐fed plants (44 vs 169 mg kg−1 of fresh mass); in tubers harvested in winter, with worse light conditions, nitrate content increased with increasing NO3‐N in the nutrient solution (26, 109, and 225 mg kg−1 of fresh mass with NH4‐N:NO3‐N 100:0, 50:50 and 0:100, respectively). The substrate electrical conductivity increased with increasing ammonium concentration in the nutrient solution, and was higher in the upper layer of the substrate. Copyright © 2004 Society of Chemical Industry

Efficacy assessment of some Trichogramma species (Hymenoptera: Trichogrammatidae) in controlling the potato tuber moth Phthorimaea operculella Zell. (Lepidoptera: Gelechiidae)

Laboratory studies were conducted to assess several life-history characteristics of three Trichogramma species—T. cacoeciae, T. evanescens, and T. principium—reared on potato tuber moth eggs. The effects of host age, parasitoid age, and different temperatures on the mean number of parasitized eggs and the percentage of emerged progeny were determined. The age of both Trichogramma and host eggs significantly affected the number of eggs parasitized by the wasps, but did not affect the percentage of parasitoids emerging from parasitized eggs. No intraspecific differences for potato tuber moth eggs were found among the tested Trichogramma species. However, T. principium proved to be more effective than T. cacoeciae and T. evanescens in parasitizing host eggs at high temperatures (>33 °C). Trichogramma significantly decreased the number of potato tuber moth F1 emerged progeny when they were released with moths in small cages either over potatoes or potato seedlings.

Clover Proliferation Group (16SrVI) Subgroup A (16SrVI-A) Phytoplasma is a Probable Causal Agent of Potato Purple Top Disease in Washington and Oregon.

An epidemic of purple top disease of potato (Solanum tuberosum) occurred in the Columbia Basin Region of Washington and Oregon in 2002 and 2003, causing great economic loss in the potato industry (1). Symptoms of potato purple top (PPT) were characterized by upright terminal shoots, upward leaf rolling, chlorosis, red or purplish discoloration of new leaves, proliferation of axillary shoots with basal swelling, and the formation of aerial tubers. Preliminary studies on PPT disease suggested phytoplasma as a possible cause (1). In this study, 78 potato samples (including five asymptomatic) were collected from five fields throughout the region. A nested polymerase chain reaction (PCR) with primer pair P1/P7 in the first amplification followed with primer pair R16F2n/R16R2 was performed to detect the presence of phytoplasmas in infected plants (2). Restriction fragment length polymorphism (RFLP) and phylogenetic analyses of amplified 16S rDNA sequences were used for phytoplasma identification. Eighty-four percent (63% in the first amplification) of the symptomatic samples and 60% (0% in the first amplification) of the asymptomatic samples tested positive. Low phytoplasma titers and the presence of PCR inhibitors accounts for the low detection rate in the first PCR amplifications. RFLP analyses of 16S rDNA with enzymes MseI, AluI, HhaI, RsaI, and HpaII indicated that the phytoplasma associated with PPT belonged to the clover proliferation (CP) group (16SrVI) subgroup A (16SrVI-A) (2). 16SrVI-A currently consists of three members, CP (GenBank Accession No. AY500130), potato witches'-broom (GenBank Accession No. AY500818), and vinca virescence (VR) (GenBank Accession No. AY500817), a strain of beet leafhopper-transmitted virescence agent (BLTVA) phytoplasma (2). The taxonomic affiliation of PPT phytoplasma was confirmed by phylogenetic analysis of cloned 16S rDNA (GenBank Accession Nos. PPT4, AY496004; PPT8, AY496005). The 16S rDNA sequences of the PPT strains were closely related to VR with 99.7% sequence homology compared with 99.2% with CP. A high correlation between the symptoms and the presence of 16SrVI-A phytoplasmas in the potato plants suggests that these phytoplasmas play an etiological role in PPT disease. To gain further evidence, a modified test of Koch's postulates was conducted. Infected tissues from four phytoplasma-positive potato samples (including PPT4 and PPT8) were grafted onto healthy potato seedlings. Within 60 days after grafting, the potato seedlings developed symptoms similar to those in the original diseased samples. The newly infected plants were maintained through cuttings. RFLP analysis of 16S rDNA indicated that the phytoplasmas detected in each of the seedlings and cuttings were identical to those in the scions. These results confirmed the probable etiological role of CP group, subgroup 16SrVI-A phytoplasma strains in PPT disease in Washington and Oregon. There are two other confirmed cases of phytoplasmas (BLTVA and aster yellows phytoplasma) associated with PPT disease in Utah (4) and Mexico (3).

First Report of Powdery Mildew on Potato Caused by Golovinomyces cichoracearum in California.

In October 2003, potato plants in three fields (cv. Desiree, Satina, Midas, and Mondial) in Lancaster, California exhibited symptoms and signs of powdery mildew. Disease symptoms were most severe on cvs. Desiree and Santina. Disease expression was greater along sprinkler lines and in localized areas from which the disease spread to surrounding plants. Severely affected plants began collapsing just prior to water cutoff. Early symptoms comprise small dark areas on the adaxial surface of leaves, along the veins, and at the petioles. Dark lesions consisting of mycelia and conidiophores were also visible on the main stems of affected plants. As the disease progressed, leaves were covered by a gray powdery fungal mass, and older leaves became necrotic. Conidial chains arising from the hyaline, epiphytic mycelia consisted of two to eight conidia. The cylindric to doliform conidia measured 16.8 to 22.8 μm wide (mean = 19.2, standard error = 0.36, N = 30) × 28.8 to 45.6 μm long (mean = 32.4, standard error = 0.75, N = 30). No cleistothecia were observed. Identification of the causal agent as Golovinomyces cichoracearum (synonyms G. orontii and Erysiphe cichoracearum) based on morphology was confirmed by internal transcribed spacer (ITS)-polymerase chain reaction (PCR). Conidia were washed off the affected leaves, concentrated by filtration and centrifugation, and sonicated to release genomic DNA. PCR was performed on the sonicated conidia with primers ITS4 and ITS5 (2), and the resulting amplicon was purified and sequenced. BLAST analysis of the ITS sequence revealed a 99% homology to E. cichoracearum from an Ambrosia sp. (GenBank Accession No. AF011292). Pathogenicity was confirmed on potato seedlings cv. Red La Soda. Inoculations were performed twice on six plants (three pots) each time. A sterile brush was used to transfer conidia from the affected leaves to seedlings consisting of two to three fully expanded leaves. A plastic bag was placed around each pot containing two seedlings for 1 to 2 days and then removed. Noninoculated controls were stroked with a sterile brush, placed in a plastic bag for 1 to 2 days, and kept in the greenhouse on a separate bench. Two control plants were included for each inoculation. Plants were maintained in a greenhouse at approximately 25 to 28°C and 40 to 60% relative humidity. After 7 days, dark spots were visible on the leaves of all inoculated plants, and conidiophores with conidia identical to those of the isolate used as the inoculum source were apparent after 10 days. The controls showed no disease symptoms or signs. To our knowledge, this is the first report of powdery mildew caused by G. cichoracearum on potato in California. The first field report of the disease was from Washington in 1950 (1), with subsequent reports from Utah and Ohio.

True Potato Seed

ABSTRACT Delicate nature of potato seedlings is one of the most dominating factors hindering the adoption of True Potato Seed (TPS) for seedlings transplant crop. In the present study, possibilities of developing hardy TPS families were explored wherein hardiness was evaluated in terms of seedlings' transplant survival. Genetic variability and herit-ability were reasonably high for characters contributing to hardiness. Seedlings of cultivated species were hardier and had better performance than those of wild species for characters important to transplant survival. Among various root and shoot characters studied, seedling vigour was the major contributor to hardiness. Circinnate and inverted “U” shaped embryos were present in more than 90% seeds of both hybrid and open-pollinated families, and these two classes of seeds were at par to each other and better than rod shaped embryos for all characters including transplant survival and tuber yield. Though hybrid families were, in general, more productive, sele...