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Sacha Buller, Debra Inglis, and Carol Miles

. Romano and Paratore (2001) found that grafting tomato with ‘Beaufort’ rootstock increased plant vigor and yield, but there was no effect on fruit quality. Verticillium wilt is a soilborne disease caused by Verticillium dahliae Kleb. that impacts

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G.E. Vallad, Q.M. Qin, R. Grube, R.J. Hayes, E. Ryder, and K.V. Subbarao

Since its appearance in 1995, Verticillium wilt of lettuce has spread through the Salinas River Valley, where nearly 60% of California's lettuce acreage is located. A replicated field trial was conducted to assess various modern and heirloom lettuce (Lactuca sativa) cultivars, plant introductions, and L. virosa lines for resistance to Verticillium wilt. Based on horticultural type, lettuce plants were destructively sampled at harvest maturity and assessed for the incidence of Verticillium wilt. Of the L. sativa cultivars, only the iceberg type displayed pronounced foliar symptoms of stunting and wilting. Disease incidence based on root symptoms ranged from 0% to 100%, with continuous variation found across and within lettuce types. Most cos, crisphead, and leaf cultivars exhibited 20% or greater disease incidence. Butter cultivars exhibited the lowest disease incidence among the major lettuce types examined, and Latin and Batavia type cultivars exhibited the lowest disease incidence overall. Disease progression was further monitored for 10 select lettuce cultivars for 2 weeks past harvest maturity. Disease intensity increased over the 2-week period for some cultivars, demonstrating the need to assess plants for Verticillium wilt past harvest maturity to avoid misclassifying plants. The L. sativa plant introduction lines tested, predominantly stem and oil-seed horticultural types, were quite susceptible and exhibited distinct symptoms of wilt and defoliation, possibly due to their elongated growth habit. The variation in disease incidence among the L. virosa lines tested was discontinuous, with discrete differences in susceptibility. Overall, the results reflected trends found in previous greenhouse and field trials.

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Max M. González-Salán and Paul W. Bosland

A Verticillium wilt-resistant population of pepper (Capsicum) is being developed from the USDA P.I. 215699 accession. Three selfing cycles with disease screening and selection have been done. The disease screen was conducted at a soil temperature of 25 ± 1°C and at an inoculum level of 2000 microsclerotia per gram of soil. Sixty days after inoculation, individual plants were scored using an interaction phenotype scale (IP), ranging from 1 to 9, where 1= no aerial symptoms, and 9=death. Plant shoot height was also measured. Even after three selfing cycles, P.I. 215699 segregates for Verticillium wilt resistance. The percentage of resistant plants at S3, is 75%. Another cycle of selection (S4) was done and the progeny are being tested. The S4 progeny data, interaction phenotype, shoot height, and percentage of resistant plants, will be analyzed by using standard analysis of variance followed by appropriate means separation. An analysis of correlation for shoot height by interaction phenotype variables will also be conducted.

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Ryan J. Hayes, Karunakaran Maruthachalam, Gary E. Vallad, Steven J. Klosterman, Ivan Simko, Yaguang Luo, and Krishna V. Subbarao

breeding lines with resistance to verticillium wilt caused by V. dahliae . They were selected from the cross ‘Tiber’ × (‘La Brillante’ × ‘Pacific’). Resistance is derived from ‘La Brillante’, a Batavia-type lettuce cultivar with resistance to Race 1

Open access

R. Alconero, R. W. Robinson, B. Dicklow, and J. Shail

Abstract

No significant resistance to verticillium wilt (Verticillium dahliae Kleb) was found in 59 eggplant (Solanum melongena L.) accessions, in a sexual hybrid between S. melongena and S. integrifolium, or in eight somatic hybrid clones between S. melongena and S. sisymbriifolium. A relatively high degree of resistance was observed in accessions of S. aculeatissimum, S. scabrum, and S. sisymbriifolium. All 58 accessions of S. gilo tested were susceptible, as were all accessions of S. incanum, S. integrifolium, S. laciniatum, S. macrocarpum, S. mammosum, and S. nodiflorum.

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Max M. González-Salán and Paul W. Bosland

The segregation ratios for verticillium wilt resistance in PI 215699 suggests that verticillium wilt resistance is a quantitative trait. Additive and dominance genetic variance effects were studied. The F1, F2, F1 B Cr, and F1 B Cs, using the resistant parent (Pr) and the susceptible parent (Ps), PI 215699, and BG. 1668, respectively, were accomplished. The plants were grown in soil temperature tanks with a 25 ± 1C soil temperature, an inoculum level of 2000 microsclerotia of Verticillium dahliae Kleb. per gram of soil, and 18 hours of 250 umol·m-2 · s-1 light. The experiment consisted of four replications with 30 plants per replication for each generation. The seedlings were individually scored 70 days after sowing for an interaction phenotype score (IP) using a scale ranging from 1 to 9 in which 1 = no aerial symptoms and 9 = death. Means, variance, and standard deviations for the percentage of resistant plants (IP = 1) were calculated. A joint three-factor scaling test to estimate the parameters [mid-parent value (m), additive effects (d), and dominance effects (h)] revealed that the data did not fit a simple additive-dominance model. Epistasis was suspected to be present and a joint six-factor model was therefore tested. The joint six-factor model estimates m, d, h, and three epistatic interactions parameters [additive × additive (i), additive × dominance (j), and dominance × dominance (1)]. All epistatic interactions parameters were significant. These results indicate that additive and epistasis effects were involved in the genetic control of verticillium wilt resistance in PI 215699. Broad-sense and narrow-sense heritabilities for percentage of resistant plants in population PI 215699 were estimated to be 0.81 and 0.48 after 70 days of sowing, respectively.

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Douglas V. Shaw and Thomas R. Gordon

Strawberry (Fragaria ×ananassa Duch.) genotypes retained for resistance to Verticillium wilt (Verticillium dahliae Kleb.) after two cycles of a two-stage (TS) selection procedure consisting of full-sib family selection followed by within-family selection of individuals, and genotypes retained for resistance using genotypic mass (GM) selection were crossed to a common set of moderately susceptible genotypes. The relative resistance of the seedlings from these progenies was compared using a resistance score and the percentage of stunted plants. Although the two sets of resistant parents had performed similarly in genotypic comparisons, those genotypes selected using the TS procedure yielded test cross offspring with significantly higher resistance scores (X̄ = 3.84 ± 0.09 vs. X̄ = 3.46 ± 0.09, t = 3.11**) and significantly lower rates of plant stunting (X̄ = 38.1% ± 3.1 vs. X̄ = 50.2% ± 2.9, t = 2.87**) than the parents chosen using GM selection. Further resolution using analysis of variance and general combining ability (GCA) estimates showed that these between-set differences resulted from higher resistance breeding values for parents selected using the TS procedure. The five genotypes with largest GCA for resistance score and four of the five genotypes with minimum GCA for percentage stunting were obtained by TS selection.

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Gloria María García-Ruiz, Carlos Trapero, and Francisco Javier López-Escudero

effect on the economy of the country. Verticillium wilt of Olive (VWO), caused by Verticillium dahliae Kleb., is currently the most destructive and threatening disease of olive in the Mediterranean region ( Bubici and Cirulli, 2011 ; Hiemstra and

Open access

John O’Sullivan and Andres A. Reyes

Abstract

The effects of soil fumigation with Telone C-17 on yield, petiole NO3-N levels and verticillium wilt (incited by Verticillium albo-atrum Reinke & Berth and V. dahliae Kleb.) of potatoes (Solanum tuberosum L.) grown continuously and in a 2-year rotation with corn since 1972 at 8 rates of nitrogen were studied in 1978 and 1979. Soil fumigation resulted in significant yield increases where potatoes were grown continuously. Potatoes grown in rotation responded to fumigation only in 1979. Continuous culture of potatoes resulted in reduced yields in both years. Nitrate-N levels were substantially lower in petioles from fumigated plots than in non-fumigated plots. Yield responses from fumigation and rotation were the result of reduced severity of verticillium wilt infestation. Soil fumigation and rotation had equal effects on yield and verticillium wilt, particularly in 1979.

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Fotios Bletsos, Costas Thanassoulopoulos, and Demetrios Roupakias

Eggplant (Solanum melongena L.) seedlings (`Tsakoniki') were grafted by hand on the Verticillium dahliae Kleb. resistant wild species Solanum torvum Sw. (GST) and Solanum sisymbriifolium Lam. (GSS). Grafted and nongrafted eggplants were transplanted to a fumigated soil with methyl bromide and to infested soil with microsclerotia of V. dahliae. Grafted plants were more vigorous, as measured by plant height, main stem diameter, and root system weight, than the nongrafted `Tsakoniki'. This resulted in an increased early production (GST, 45.5%; GSS, 18.4%) and late production (GST, 69.3%; GSS, 59.2%) as compared to the noninfected controls. The mean yield reduction (over years) in early production caused by the disease, as compared to the controls grown in fumigated soil, was 29.4%, 36.6%, and 77.9% for eggplant grafted on S. torvum, S. sisymbriifolium, and nongrafted plants, respectively. This yield reduction in total production was 6.9%, 20.5%, and 56.8%, respectively. The disease incidence in ungrafted plants was 96% and 100% during early and late harvest periods. In contrast, the disease incidence in grafted plants was significantly lower, averaging 28.1% (GST) and 52.6% (GSS) in early production, and 37.6% and 79.3%, respectively, in late production. Solanum torvum was found more resistant than S. sisymbriifolium, because grafted infected plants developed mild symptoms, as indicated by significantly lower leaf symptom index (average value 1.2 and 2.22) and disease index (average value 1.55 and 3.38), respectively. In conclusion, grafting of eggplant on either wild species had positive effects on growth, production, and verticillium wilt control.