Sweetpotato Resistance Research Articles

Resistance of Sweetpotato Genotypes to Adult <I>Diabrotica</I> Beetles

Production of sweetpotatoes, Ipomoea batatas (L.) Lam. (Convolvulaceae), is limited by several insect pests, including Diabrotica spp. (Coleoptera: Chrysomelidae), and new integrated pest management (IPM) techniques for this crop are needed. Host plant resistance is one attractive approach that fits well into IPM programs. A host plant resistance research program typically depends on reliable bioassay procedures to streamline evaluation of germplasm. Thus, a bioassay technique was developed for evaluating sweetpotato germplasm by using adults of the banded cucumber beetle, Diabrotica balteata LeConte, and spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber. A single beetle was placed on a piece of sweetpotato peel (periderm and cortex with stele removed) that was embedded periderm-side up in plaster in a petri dish. Feeding and longevity of insects on 30 sweetpotato genotypes were evaluated in two experiments by using this procedure. Adult longevity ranged from 7 to 11 d for starved individuals to 211 d for beetles fed a dry artificial diet. Longevity of banded cucumber beetles that fed on sweetpotato peels ranged from 12 d for the most-resistant genotype to 123 d for SC1149-19, a susceptible control cultivar. Longevity of spotted cucumber beetles was slightly shorter than longevity of banded cucumber beetles. For the most resistant sweetpotato genotypes, both Diabrotica species exhibited a significant delay in initiation of feeding, and more beetles died on these genotypes before they had fed. Both antibiosis and nonpreference (antixenosis) are important mechanisms of resistance in sweetpotato genotypes. This bioassay was consistent with field results, indicating that this technique could be useful for evaluating resistance to Diabrotica spp. in sweetpotato genotypes.

Molecular marker variability for southern root-knot nematode resistance in sweetpotato

Amplified fragment length polymorphism (AFLP) marker profiles for individuals in two F1 populations of sweetpotato [Ipomoea batatas (L.) Lam] were used in association studies to identify AFLP markers suitable for identification of plants possessing a resistant reaction to southern root-knot nematode race 3 [Meloidogyne incognita (Kofoid and White) Chitwood]. Population one consisted of 48 half-sib genotypes developed at the Louisiana State University (LSU) AgCenter. The second population consisted of 54 full-sibs developed by the East African and International Potato Center (CIP) sweetpotato breeding programs. Results for plant nematode resistance indicate a bimodal distribution among the genotypes for the LSU population and a normal distribution for the CIP population. Using analysis of molecular variance (AMOVA) at P < 0.001 and two multivariate analysis techniques i.e logistic regression and discriminant analysis, 5 and 4 AFLP markers that had a strong and significant association with respect to the resistance trait were selected for the LSU and CIP populations, respectively. A comparative analysis of the power of discriminant analysis models for southern root-knot nematode resistance class prediction achieved 88.78% (LSU) and 88.04% (CIP) classification efficiencies.

United States Department of Agriculture-Agricultural Research Service research on natural products for pest management.

Recent research of the Agricultural Research Service of USDA on the use of natural products to manage pests is summarized. Studies of the use of both phytochemicals and diatomaceous earth to manage insect pests are discussed. Chemically characterized compounds, such as a saponin from pepper (Capsicum frutescens L), benzaldehyde, chitosan and 2-deoxy-D-glucose are being studied as natural fungicides. Resin glycosides for pathogen resistance in sweet potato and residues of semi-tropical leguminous plants for nematode control are also under investigation. Bioassay-guided isolation of compounds with potential use as herbicides or herbicide leads is underway at several locations. New natural phytotoxin molecular target sites (asparagine synthetase and fructose-1,6-bisphosphate aldolase) have been discovered. Weed control in sweet potato and rice by allelopathy is under investigation. Molecular approaches to enhance allelopathy in sorghum are also being undertaken. The genes for polyketide synthases involved in production of pesticidal polyketide compounds in fungi are found to provide clues for pesticide discovery. Gene expression profiles in response to fungicides and herbicides are being generated as tools to understand more fully the mode of action and to rapidly determine the molecular target site of new, natural fungicides and herbicides.

Effects of Previous Insect Feeding Injury to Sweet Potato on Resistance to Sweet Potato Weevil (Coleoptera: Curculionidae) and Storage Root Chemistry

The effects of root and foliage feeding on sweet potato resistance to sweet potato weevil, Cylas formicarius (F.), and on the levels of resin glycoside and caffeic acid in sweet potato storage root periderm tissues were studied. Genotypes (“Beauregard,” “Excel,” “W-244,” “W250,” and “Sumor”) with varying levels of sweet potato weevil resistance were evaluated. Adult banded cucumber beetle, Diabrotica balteata LeConte, and larval Spodoptera latifascia (Walker) were introduced onto caged sweet potato plants in the field to elicit root feeding and defoliation on plants. Storage roots were evaluated for sweet potato weevil resistance by quantifying sweet potato weevil adult feeding, oviposition, larval survival, and pupal weight. Both root and foliage injuries were associated with an increase in oviposition (significant in 1998 but not in 1997), but there was no association with adult feeding, larval survival and pupal weight. Genotype had a significant effect on adult feeding, oviposition, and larval survival but not on pupal weight. Root and foliage injuries did not have a significant effect on the levels of resin glycoside and caffeic acid in storage roots. The levels of these compounds differed significantly among genotypes, but there was no apparent relationship between sweet potato weevil resistance (antibiosis) and the levels of these compounds.

Host Reactions of Sweetpotato Genotypes to Root-knot Nematodes and Variation in Virulence of Meloidogyne incognita Populations

Sweetpotato [Ipomoea batatas (L.) Lam.] genotypes were evaluated for resistance to North Carolina root-knot nematode populations: Meloidogyne arenaria (Neal) Chitwood races 1 and 2; M. incognita (Kofoid &amp; White) Chitwood races 1, 2, 3, and 4; and M. javanica (Treub) Chitwood. Resistance screening was conducted using 150-cm3 Conetainers containing 3 sand: 1 soil mix. Nematode infection and reproduction were assessed as the number of egg masses produced by root-knot nematodes per root system. Host suitability for the root-knot nematode populations differed among the 27 sweetpotato genotypes studied. Five genotypes (`Beauregard', L86-33, PDM P6, `Porto Rico', and `Pelican Processor') were selected for further study based on their differential reaction to the different root-knot nematodes tested. Two African landraces (`Tanzania' and `Wagabolige') were also selected because they were resistant to all the nematode species tested. The host status was tested against the four original M. incognita races, and an additional eight populations belonging to four host races, but collected from different geographical regions. The virulence of root-knot nematode populations of the same host race varied among and within sweetpotato genotypes. `Beauregard', L86-33, and PDM P6 were hosts for all 12 M. incognita populations, but differences in the aggressiveness of the isolates were observed. `Porto Rico' and `Pelican Processor' had different reactions to the M. incognita populations, regardless of the host race. Several clones showed resistance to all M. incognita populations tested. These responses suggest that different genes could be involved in the resistance of sweetpotato to root-knot nematodes. The results also suggest that testing Meloidogyne populations against several different sweetpotato hosts may be useful in determining the pathotypes affecting sweetpotato.

Effect of nitrogen on resistance of sweet potato to sweetpotato weevil (Coleoptera: Curculionidae) and on storage root chemistry.

The effects of nitrogen fertilizer on sweet potato, Ipomoea batatas (L.) Poir., resistance to the sweetpotato weevil, Cylas formicarius elegantulus (Summers), was studied. Adult weevil feeding and oviposition preference, larval survival, and pupal weight were used as measures of sweet potato resistance. Sweet potato resin glycosides and caffeic acid concentrations in the periderm tissue of storage roots also were measured. Sweet potato genotypes (Beauregard, Excel, W-244, W-250, and Sumor) with varying levels of resistance to sweetpotato weevil were grown in the field under three nitrogen regimes (0, 45, and 135 kg N/ha). Harvested storage roots were evaluated in the laboratory for feeding and oviposition activity of sweetpotato weevil female adults under no-choice and choice test conditions. Larval survival rate and pupal weight were determined by rearing the insects individually on storage root sections. Nitrogen level had a significant effect on the number of eggs deposited, but not on the number of feeding punctures. Sweetpotato weevils laid fewer eggs on plants with the highest level of nitrogen. Nitrogen levels did not significantly affect larval survival and pupal weight. Genotype had a significant effect on feeding, oviposition, and larval survival. Beauregard had higher levels of feeding, oviposition, and larval survival compared with the other genotypes. No interaction effects between nitrogen and genotype were significant. Resin glycosides and caffeic acid concentrations were significantly different among genotypes and between years. Nitrogen levels significantly affected the concentrations of caffeic acid in 1997.

Two Serotypes ofSweetpotato feathery mottle virusin Uganda and Their Interaction with Resistant Sweetpotato Cultivars

ABSTRACT Isolates of Sweetpotato feathery mottle virus (SPFMV, genus Potyvirus, family Potyviridae) were obtained in several districts of Uganda from sweetpotato plants infected with the sweetpotato virus disease (SPVD), the most important disease of this crop in Africa. A monoclonal antibody (MAb 7H8) raised against the coat proteins (CP) of a mixture of the SPFMV strain C (United States) and the isolate SPV-I (West Africa) distinguished Ugandan SPFMV isolates into those detectable and not detectable by the MAb. These two serotypes differed in prevalence in different districts of Uganda and in two common sweetpotato cultivars. Both serotypes could be transmitted simultaneously by single aphids. The serotypes differed in their ability to systemically coinfect sweetpotatoes that were infected with Sweetpotato chlorotic stunt virus (SPCSV, genus Crinivirus), the virus required to induce SPVD in SPFMV-infected plants. One sweetpotato breeding line, resistant to SPFMV from the New World, was infected by graft-inoculation with all SPFMV isolates from Uganda. Another SPFMV-resistant sweetpotato line became infected with SPFMV and developed SPVD only following coinoculation with SPCSV.

Effect of local inoculum on the spread of sweet potato virus disease: limited infection of susceptible cultivars following widespread cultivation of a resistant sweet potato cultivar

A study compared the spread of sweet potato virus disease (SPVD) into crops of two moderately resistant and initially SPVD‐free sweet potato cultivars in northern and southern Mpigi, Uganda. Whiteflies, the vector of sweet potato chlorotic stunt crini virus (SPCSV), a component cause of SPVD, were similarly abundant in farmers' sweet potato fields around Namulonge in northern Mpigi, and Kanoni in southern Mpigi. However, mean incidence of SPVD in farmers' crops neighbouring the trials was higher at Kanoni (13.3%) than at Namulonge (2.8%). Furthermore, spread of SPVD into initially SPVD‐free sweet potato plots of two only moderately resistant cultivars was greater in plots at Kanoni than in plots at Namulonge. The SPVD‐resistant New Kawogo was the most common cultivar grown in farmers' fields at Namulonge and had few diseased plants, whereas susceptible cultivars with relatively high incidences of disease predominated at Kanoni. Final SPVD incidence in each trial was positively correlated with a measure combining the proximity and level of inoculum in surrounding fields. The study demonstrates the importance of local SPVD inoculum in determining the rate of spread of the disease into fields and implies that the widespread cultivation of a resistant variety limits infection of susceptible cultivars grown nearby.

Induced resistance of sweetpotato to Fusarium root rot by UV-C hormesis

`Jewel’ sweetpotato storage roots previously treated with a low hormetic dose of ultraviolet light-C (UV-C) were stored for 30 days before inoculated artificially with Fusarium solani. Storage roots showed an increase in resistance to Fusarium root rot, as indicated by a reduction in lesion diameter, depth and weight of rotted tissue following UV-C treatment. The rate of decay development around F. solani inoculum plugs on UV-C treated sweetpotato storage roots progressed slowly, and about 55% failed to develop lesions on wounded UV-C treated, compared to 11% of untreated sweetpotato storage roots, 10 days after inoculation. There was a polynomial curvilinear regression relationship between percent incidence of Fusarium root rot and hormetic UV-C doses. The hormetic dose of UV-C which suppressed decay to the greatest degree was 3.6 kJ m −2. Exposure of sweetpotato storage roots to doses of UV-C promoted phenylalanine ammonia-lyase (PAL) production with the maximum PAL activity occurred to the greatest degree at a UV-C dose of 3.6 kJ m −2. Similarly, a relationship between PAL activity and the incidence of Fusarium root rot was established. Crude extracts from UV-C treated sweetpotato storage roots reduced germination, germ tube elongation, and growth of F. solani compared to extracts obtained from untreated storage roots.

The incidence of sweet potato virus disease and virus resistance of sweet potato grown in Uganda

SummarySweet potato virus disease (SPVD) was common (25–30% average incidences), and farmers recognised it as an important disease, in sweet potato crops in southern Mpigi, Masaka and Rakai Districts in Uganda, but SPVD was rare in Soroti and Tororo Districts. Whiteflies, which are the vector of sweet potato chlorotic stunt crinivirus (SPCSV) a component cause of SPVD, were correspondingly common on sweet potato crops in Mpigi and rare on crops in Tororo. However, aphids, which are the vectors of sweet potato feathery mottle potyvirus (SPFMV), the other component cause of SPVD, were not found colonising sweet potato crops, and itinerant alate aphids may be the means of transmission. Different sweet potato cultivars were predominant in the different districts surveyed and four local cultivars obtained from Kanoni in S. Mpigi, where whiteflies and SPVD were common, were more resistant to SPVD than four cultivars from Busia in Tororo District, where whiteflies and SPVD were rare. However, nationally released cultivars were even more resistant than the local cultivars from Kanoni. Yield results and interviews with farmers indicated that farmers in S. Mpigi were making compromises in their choice of cultivars to grow, some key factors being SPVD susceptibility, and the yield, taste, and marketability, duration of harvest and in‐ground storability of the storage roots. These compromises need to be included in an assessment of yield losses attributable to SPVD.

Identifying a Randomly Amplified Polymorphic DNA (RAPD) Marker Linked to a Gene for Root-knot Nematode Resistance in Sweetpotato

The inheritance of resistance to root-knot nematode race 3 [Meloidogyne incognita (Kofoid &amp; White) Chitwood] in sweetpotato [Ipomoea batatas (L.) Lam.] was studied in 71 progenies of the F1 single-cross population produced from the cross of resistant parent `Regal' and susceptible parent `Vardaman'. The distribution frequency of the progenies based on log total nematode number (egg + juvenile counts) was a bimodal distribution with a ratio of ≈4 resistant : 1 susceptible. Based on this phenotypic ratio, the proposed genetic model was duplex polysomic inheritance (RRrrrr = resistant parent and rrrrrr = susceptible parent). Bulk segregant analysis in conjunction with the RAPD technique was used to identify a RAPD marker linked to a root-knot-nematode-resistance gene. Of 760 random decamer primers screened, 9 showed polymorphic bands between the two bulk DNA samples. Primer OPI51500 produced a band in the resistant bulk but not in the susceptible bulk, suggesting a linkage in coupling phase. An estimated recombination fraction of 0.2421 ± 0.057 between the marker and the root-knot-nematode-resistance gene indicated linkage.

SWEETPOTATO WEEVIL RESISTANCE IN U.S. PLANT INTRODUCTIONS

One hundred plant introductions (PIs) were evaluated for sweetpotato-weevil resistance in experiment station field trials for 2 years in Beaumont, Miss. Weevil infestation was accomplished by applying adult weevils in year 1 and weevil infested roots in year 2. The percentage of uninjured roots ranged from 38% in `Centennial', the susceptible control, to 93% in PI538288. Severity of root and stem injury were measured in year 2. Stem injury ratings on a scale of 0, for no injury, to 4, for severe injury, ranged from 1.2 in PI564113 to 3.7 in `Beauregard'. Root injury ratings on a scale of 0 to 5 ranged from 0.1 in PI538288 to 4.2 in `Beauregard' (susceptible control). Thirty-five PIs had lower root injury values than `Regal' (resistant control), and the percentage of uninjured roots was higher in 45 PIs than in `Regal'. These results suggest that genes are available in PIs for increased levels of weevil resistance in sweetpotato.

Identification of Resistance in Sweetpotato to Rhizopus Soft Rot Using Two Inoculation Methods

Two inoculation methods were developed and compared to evaluate cured sweetpotato (Ipomoea batatas) storage roots for resistance to Rhizopus soft rot caused by Rhizopus stolonifer and R. arrhizus. Roots that had been cured and stored for at least 3 wk were first washed in a commercial washer. In the impact/dip method, roots were wounded by allowing them to drop approximately 1 m from the end of the washer into crates, after which they were dipped in a suspension of sporangiospores. In the puncture inoculation method, deep-threaded wood screws were dipped in a spore suspension and then hammered about 5-10 mm deep into the median of the root. Most genotypes were more susceptible to R. stolonifer than to R. arrhizus; thus, subsequent evaluations were made using only R. stolonifer

Resistance of Sweet Potato to Bacterial Root and Stem Rot Caused by Erwinia chrysanthemi

Greatest differences in resistance of sweet potato (impomoea batatas) storage roots to bacterial root rot were observed 6 or more days after a micropipette tip containing 50 μl of a 10 9 cfu/ml suspension of Erwinia chrysanthemi had been inserted 1 cm into the root. The frequency of disease was variable when the suspension contained less than 10 6 cfu/ml, but lesion size was consistent for each genotype at 10 7 -10 9 cfu/ml

Resistance in sweetpotato to sweetpotato weevil

Sweetpotato weevil, Cylas formicarius formicarius F is the most destructive pest of sweetpotato, Ipomoea batatas in tropical and subtropical regions. The larvae and adults feed on sweetpotato roots and crowns. For the past 12 years we have been screening sweetpotato germplasm for resistance to this pest in order to breed an agronomic cultivar with weevil resistance. Resistance screening is conducted at AVRDC and Penghu island in autumn and summer, respectively. Germplasm is planted between heavily infested source rows maintained in a weevil nursery. Roots are harvested, sliced into thin pieces, and the number of insects (larvae + pupae + adults) per unit weight, as well as the weight of damaged and healthy root slices, are recorded. The resistance rating is based mainly on the number of insects found in the root. Considerable differences in resistance rating are observed from location to location and season to season. Even at one location, tremendous differences are observed in weevil infestation of a particular entry among the replicates. Although over 1000 sweetpotato accessions have been screened, we have not found any that is consistently less damaged over several seasons at either location. Our recent screening of a population of I. trifida x I. batatas crosses show certain hybrids with high yield and low weevil infestation. These hybrids need to be evaluated further to confirm their resistance.

Control of Soil Insect Injury by Resistance in Sweet Potato

Abstract Soil insect root injury to resistant sweet potato [Ipomoea batatas (L.) Lam.] cultivars ‘Regal’ and ‘Southern Delite’ was compared to injury to ‘Jewel’ and ‘Centennial’ in trials with the resistant-standard W-13 and the susceptible-standard SC 1149-19. Injury by three groups of insects was evaluated: the wirewoom-Diabrotica-Systena complex (WDS), which includes the southern potato wireworm (Conoderus falli Lane), the tobacco wireworm (C. vespertinus Fabricius), the banded cucumber beetle (Diabrotica balteata LeConte), the spotted cucumber beetle (D. undecimpunctata howardi Barber), the elongate flea beetle (Systena elongata Fabricius), the pale-striped flea beetle (S. blanda Melsheimer), and S. frontalis Fabricius (a flea beetle); the sweet potato flea beetle (Chaetocnema confinis Crotch.); and a white grub (Plectris aliena Chapin). Relative control estimates were obtained by comparison to the susceptible standard. ‘Regal’ and ‘Southern Delite’ provided good control of all three insect groups with control of all insect injuries of 79.2% and 81.0%, respectively. ‘Jewel’ and ‘Centennial’ were resistant to the sweet potato flea beetle and sustained less damage by WDS than the susceptible standard, but would still be classed as susceptible to WDS. ‘Centennial’ was as susceptible to the white grub as SC 1149-19. The levels of resistance demonstrated for ‘Regal’ and ‘Southern Delite’ would provide growers an alternative to insecticides for the control of these insects.

Resistance of Sweet Potato to Virus Complex1

Abstract A core-graft transmission method has been used successfully for rapid screening of sweet potato (Ipomoea batatas (L.) Lam) for resistance to sweet potato virus complex (SPVD). Field test scores of resistance to SPVD were significantly correlated with core-graft test scores (r = 0.60). A high broad sense heritability estimate of 0.95 ± 0.02 for resistance to SPVD was computed based on the core-graft test for 24 cultivars tested in one year, while a lower broad sense heritability (h2 = 0.48 ± 0.02) was estimated based on the field test for the same cultivars (except one) conducted at four locations for three years. Broad sense heritability estimates from diallel crosses ranged from 0.82 ± 0.02 to 0.98 ± 0.19. ‘TIS 2498,’ ‘TIS 3228,’ ‘TIS 3053,’ ‘TIS 2544’ and ‘TIS 2534’ sweet potato were resistant to SPVD.

W-51 Root Knot Resistant Sweet Potato Germplasm1

Abstract Root knot caused by the southern root-knot nematode (Meloidogyne incognita (Kofoid &amp; White) Chitwood) is a serious disease of sweet potato (Ipomoea batatas (L.) Lam.) in most production areas of the U. S. and especially in the southern states (3). Considerable variation in pathogenicity of this obligate parasite on sweet potato was reported by Giamalva et al. (1) in 1963. In 1973, Martin and Birchfield (2) reported the discovery of a race of M. incognita that was highly virulent and reproduced abundantly on a sweet potato line, L4-73, that had been established as resistant to root-knot nematode populations commonly found in Louisiana. This strain of M. incognita, herein designated the “resistance breaking” (RB) race, was provided through the courtesy of Dr. W. J. Martin of the Department of Plant Pathology, Louisiana State Univ., Baton Rouge. These findings have caused considerable concern about the future of breeding for root knot resistance in sweet potato, since the existence of RB races makes the work much more difficult and complicated. A breeding line of sweet potato (W-51) was developed at the U. S. Vegetable Laboratory, in cooperation with Clemson University, that is resistant to both the common and the RB race of root-knot nematodes (M. incognita). It also carries resistance to fusarium wilt (Fusarium oxysporum f. sp. batatas (Wr.) Snyd. &amp; Hans.) and the sweet potato flea beetle (Chaetocnema confinis Crotch.). W-51 is being released for use as a root knot resistant parent in sweet potato breeding programs.

Resistance to Root-knot Nematodes (Meloidogynespp.) in Vegetable Crops

Abstract The development of root-knot nematode resistant vegetable varieties has provided an alternative control method to chemical and crop rotation. The term resistance is discussed. Work on 18 vegetables is reviewed. Thirty tomato strains resistant to one or more Meloidogyne sp. are listed, there was a marked absence of reports on varieties resistant to M. hapla. Several workers have observed resistance in some cultivated and wild Solanum spp. The resistance could be increased by further sib and backcrossing experiments. Eggplant varieties tested for resistance to Meloidogyne spp. showed varying degrees of resistance in about 14 varieties. Further backcrossing studies between Solanum melongena and S. sysimbrifolium could provide useful results. Tests on resistance to nematodes in pepper have revealed many resistant varieties. All the pepper varieties tested were susceptible to M. hapla. The nature of resistance in sweet potato has been studied. Some varieties of Cucumis spp. have been found to be resis...

Resistance in sweetpotato to the scurf and black rot pathogens

Abstract Over 600 sweetpotatoes (Ipomoea halalas (L.) Lam.) were evaluated for resistance to black rot (Ceratocystis fimbriata Ell. & Halst.) and 506 to scurf (Monilochaetes infuscans Eli. & Halst.). Vine cuttings from the varieties were inoculated to initially evaluate disease resistance to both fungi. From the3e tests approximately 8% of the varieties were selected for re:;istance to black rot and 7% for resistance to scurf. Enlarged roots of these varieties were inoculated with the respective pathogens, and lesion diameter after incubation was the criterion for measuring resistance. No variety was immune from eithcr pathogen. For both diseases, varieties selected from the vine cutting inoculations developed symptoms in their inoculated roots ranging from rcsistant to very susceptible; and there was no correlation between the disease reaction expressed by vine cuttings and that by roots of the varieties. Most varieties with superior resistance in their enlarged roots to either scurf or black rot came fr...