Genetic variation in a population of tetraploid potatoes: Response to the potato leafhopper and the potato flea beetle

Progenies from a group of tetraploid parental clones from the USDA potato breeding program were used to investigate variation in resistance to the potato leafhopper,Empoasca fabae (Harris), and the potato flea beetle,Epitrix cucumeris (Harris). The study utilized two mating designs: i) selfing and testing both the parents and the S₁ progeny; and ii) nine clones, used as males, were each crossed to three different clones, and progenies from the resulting families were tested. Statistically significant differences between families were measured in each test for both insects. Non-additive genetic variance was larger than additive genetic variance in progeny reaction to leafhopper infestation and hopperburin, but was smaller in progeny reaction to flea beetles. Environmental variation contributed heavily to the total variation of plant reaction to both insect species. Selecting individuals was indicated to be slightly more effective than selecting males on half-sib progeny performance but not as effective as selecting clones on S₁ progeny performance. Because of the large environmental variance and small additive variance for both the leafhopper and flea beetle, slow progress in increasing the level of resistance to these two species in this sample population was predicted. Resistance to leafhopper infestation was genetically quite highly correlated (positive) with resistance to hopperburn, but phenotypically the correlation was considerably smaller. Negative genotypic, phenotypic, and environmental correlations between leafhopper infestation and flea beetle infestation suggest that selecting for resistance to one of these species, in the population sampled for these tests, would tend to increase susceptibility to the other.     

Control of the potato flea beetle with applications of insecticides to the soil

American Journal of Potato Research -     

The flowering tobacco as a new alternative host for the Colorado potato beetle

The potential of the flowering tobacco,Nicotiana alata, to sustain the survival and the development of the Colorado potato beetle (CPB) was assessed. We made food preference, larval development and rearing tests in relation with other plant species, specially with potato. In spite of a clear preference of the CPB for potato, the insects could complete a full life cycle on the flowering tobacco. In comparison with CPBs on potato, those on the flowering tobacco had a slight delay of two days in their development, beginning when larvae reached their tenth day. CPBs on the flowering tobacco had a much lower survival rate (14.0% against 66.7%) and adults were smaller (100.9 mg against 133.0 mg). Nevertheless, the flowering tobacco is the firstNicotiana species which is an acceptable alternative host for the CPB, and could facilitate the survival and the distribution of the insect.     

Evaluation of a vacuum collector for insect pest control in potato

A field scale vacuum insect collector designed for the control of the Colorado Potato Beetle,Leptinotarsa decemlineata (Say) was tested on potatoes in 1990. The vacuum collector was more effective against adults and small larvae than against large larvae. Results suggested that a large proportion of potato aphids can also be removed from plants. The spread of plant diseases PSTVd and PVX, readily transmitted by contact, was not increased by the repeated use of the vacuum collector.     

Bacillus thuringiensis a potential control agent for the Colorado potato beetle

In laboratory tests conducted to determine the effectiveness of the exotoxin ofBacillus thuringiensis against the Colorado potato beetle,Leptinotarsa decemlineata (Say), applications sprayed on tomato foliage at dilutions ranging from 10^?1 through 10^?4 killed 90% of the 1st and 2nd stage beetle larvae. As the dosage decreased, the time to achieve this level of mortality increased from 4 to 9 days. Adult beetles were not killed by these treatments; however they did cease feeding. In field tests, the highest dosages ofB. t. sprayed on either tomato or potato plants provided adequate or nearly complete protection when applied weekly. Young larvae that ingested sub-lethal doses developed into adults with atrophied mouthparts and antennae, transformations of the paired parts of the labial palps into an unpaired part, the appearance of a tarsal-like claw on a palp, and malformation of the cranial sclerities.     

Control of the Colorado potato beetle by treatment of potato seed pieces

Dusting or soaking freshly cut potato seed pieces in systemic insecticides controlled the first generation larvae of the Colorado potato beetle at Yakima, Washington in 1970. The most promising materials were tested again in a larger experiment in 1971. Fifty days after treatment, Bay 37344 (4-(methylthio)-3,5,xylyl methylcarbamate), Dasanit^® (O,O-diethyl-O-[p-(methylsulfinyl) phenyl] phosphorothioate), Shell SD 17250 (N-(methylcarbamoyl)oxy]thioacetimidic acid ester with 3-mercaptopropionitrile) and Plant Protection PP062 (dimethylamino)-4,5,6-dimethyl pyrimidinyl dimethylcarbamate) all gave significantly better control of the larvae than methomyl, azinphosmethyl and menazon.     

Genetic variation in a population of tetraploid potatoes: Tuber resistance to the tobacco flea beetle

Variation in resistance to tuber damage by the tobacco flea beetle,Epitrix hirtipennis (Melsheimer) was investigated for progeny from a group of parental clones from the USDA potato breeding program. Each of nine clones, used as males, was crossed with three different clones, and the family responses were measured in field tests (Lubbock, Texas, 1967 and 1968) by counting tuber pits made by the flea beetle larvae. Statistically significant differences among families were found. The differences were due mainly to the male parents, since the male variance component, σ _M ² (0.470±0.235), was larger than the variance component of females mated to the same male, σ _F(M) ² (0.080±0.057). Theoretically, each of these components contains one-fourth of the genetic additive variance, and therefore, should be nearly equal if digenic, trigenic, and quadrigenic effects are small (and if no maternal effects are present). Apparently the male and female parents did not, in relation to the frequency of alleles controlling response to the flea beetle, represent the same genetic population. Heritability on an individual basis, calculated with 4 σ _M ² as numerator, equals 0.64±0.36; and at a 10% selection level the genetic advance value predicted for individual selection equals 1.896 SD units. If 100 males were crossed to one female each, and 20 progeny per family tested in 10 replicates, the genetic advance value predicted for selecting the best 10 males on the basis of their family performance equals 0.976 SD units. Thus individual or phenotypic selection appears to be more effective than selection based on half-sib progeny tests.     

ScreeningSolanum germplasm for resistance to Colorado potato beetle

TuberousSolanum accessions were screened for resistance to Colorado potato beetle (CPB),Leptinotarsa decemlineata (Say), in terms of CPB-caused defoliation in field trials with natural infestations of CPB. Cluster and multivariate discriminant analyses were used to distinguish among species and accessions. Several highly CPB-resistant and relatively homogeneous accessions were identified.     

Fine screeningSolanum (potato) germplasm accessions for resistance to Colorado potato beetle

This study was conducted to investigate the utility of systematic screening at the genotype level withinSolanum accessions highly resistant to the Colorado potato beetle. Evaluations of clonally replicated genotypes showed that most accessions reported to be uniform when screened as populations contained small but significant variation among genotypes for resistance to oviposition, larvae, and defoliation, differences for numbers of larvae being most common. Adult counts and percentage defoliation were not as useful in evaluating among-genotype variability in beetle resistance. Genotypes ofS. pinnatisectum WRF 343 andS. tarijense PI 473227 were the most uniformly and highly resistant to Colorado potato beetle. Genotypes of S.berthaultii PI 473331,S. chacoense PI 473405, andS. tarijense PI 473336 were moderately to highly resistant, and genotypes ofS. bukasovii PI 473494 andS. canasense PI 230511 were uniformly susceptible to Colorado potato beetle. Nonparametric correlation analyses indicated that number of egg masses, small larvae, large larvae, and defoliation scores were positively correlated, negatively correlated, or not correlated, depending on the species. One generation of selection attempting to segregate resistance and susceptibility in nearly uniform and highly resistantS. pinnatisectum WRF 343 resulted in “divergent” populations that could not be distinguished from each other or the base population. Thus, through genotype (“fine”) screening and selection, we showed that some existing populations are virtually pure for extreme resistance. Use of individuals from such families would make screening breeding populations more efficient, and reduce the risk of losing resistance genes that have non-dominant effects. Fine screening, recurrent selection, and maintenance of such elite populations is recommended as an extension of population-based evaluation usually done by genebanks.     

Colorado potato beetle resistance management strategies for transgenic potatoes

NewLeaf potatoes could provide substantial ecological and economic benefits to potato growers. A concern with NewLeaf potatoes, however, is that Colorado potato beetle may develop resistance to the Bt endotoxin because of the intense selection pressure imposed by its constant presence in the transgenic crop. Before these cultivars were released, however, entomologists throughout North America conducted biological research needed for a strategy to prevent or delay resistance in Colorado potato beetle. This paper describes the considerations and research behind the proposed strategy. Because NewLeaf potatoes express a relatively constant and high concentration of Bt endotoxin throughout the foliage of each plant, reducing selection for resistance must come from planting standard potatoes as a refuge for susceptible beetles. Avoiding resistance through random mixtures of NewLeaf and standard potatoes was evaluated in laboratory and field studies. The conclusion from this research was that the seed mixture would not provide an effective refuge. The most effective alternative refuge was judged to be a block of standard potatoes planted in the same field as the NewLeaf potatoes. By allowing susceptible beetles to survive in their fields, potato growers might sustain the benefits of very effective controls.     

Influence of Colorado potato beetle sample counts and plant defoliation on potato tuber production

Field experiments were designed to subject Superior potato plants to various levels of defoliation by the Colorado potato beetle (CPB)Leptinotarsa decemlineata (Say), Coleoptera: Chrysomelidae. Defoliation occurred during each of five consecutive plant growth periods and CPB population, plant leaf area, and tuber weight data were recorded for each period. A visual defoliation rating scheme provided an accurate estimate of actual potato plant leaf area of defoliated plants. Data generated from regression analysis demonstrated a significant dependence of leaf area on CPB numbers per plant during some plant growth periods, but numbers of CPB accounted for very little of the total variation in tuber weight. Plant leaf area was the most important independent variable in the tuber weight regression model.     

Control of the Colorado potato beetle withBacillus thuringiensis varietyThuringiensis

Field tests were conducted to determine the effectiveness of an experimental preparation ofBacillus thuringiensis var.thuringiensis against Colorado potato beetle infestations on potatoes and tomatoes. Applications were made weekly with a tractor-towed commercial sprayer at the rates of either 473, 946, or 2,838 ml. ofB.t.t. in 378.41 of water per 0.4 hectare. Significant reductions were observed in treated plots of all stages of the beetle. All untreated plants were completely defoliated by the end of the test due to beetle feeding. No significant differences were observed among the different treatment levels.     

Survey of Colorado potato beetle insecticide resistance in Idaho

Colorado potato beetle populations from Idaho were surveyed for resistance to carbofuran, endosulfan, esfenvalerate, and phosmet in a discriminating concentation bioassay of spring emergent and first generation adults. No carbofuran or endosulfan resistance was detected in 29 populations surveyed. Esfenvalerate and phosmet resistance was detected in all potato growing areas of the state. For the same populations, spring adults were more sensitive to phosmet than were first generation adults. Susceptible populations were found in the same regions as resistant populations.     

Tracking the global dispersal of a cosmopolitan insect pest, the peach potato aphid

Background  

Global commerce and human transportation are responsible for the range expansion of various insect pests such as the plant sucking aphids. High resolution DNA markers provide the opportunity to examine the genetic structure of aphid populations, identify aphid genotypes and infer their evolutionary history and routes of expansion which is of value in developing management strategies. One of the most widespread aphid species is the peach-potato aphid Myzus persicae, which is considered as a serious pest on various crops in many parts of the world. The present study examined the genetic variation of this aphid at a world scale and then related this to distribution patterns. In particular, 197 aphid parthenogenetic lineages from around the world were analysed with six microsatellite loci.     

Effects of pest and soil management systems on potato diseases

Long-term cropping systems research is important in order to reduce production costs, to control crop pests, and to optimize the sustainability of agro-ecosystems. Soil amendment use, improved disease management practices, and careful cultivar choice are some of the potential components for improving potato production systems. This research was conducted in long-term cropping systems plots in order to evaluate the impact of soil amendments, pest management practices, and cultivar on foliar and soil-borne potato diseases and to assess the relationships of soil and pest management practices to disease levels and soil microbial activity. Fungicide applications for management of foliar diseases varied between the pest management systems (e.g., biological, reduced input, and conventional). Incidence of potato foliar diseases was quantified five times during the cropping season. The impact of soil amendment and pest management practices on soil microbial activity and tuber-borne diseases was also investigated. Low incidences of foliar and selected soil-borne diseases were recorded. Disease levels varied between years, cultivars, pest management, and soil amendments. Significant differences between cultivars were detected for early blight, white mold, and black dot. The cultivar Superior had higher incidence of white mold and black dot, while cv Atlantic had higher early blight incidence. Pest management system significantly affected foliar early blight incidence in 1998, but not in 1997. Pest management system did not affect late blight, white mold, or black dot incidence, or tuber disease incidence in either year. The addition of soil amendments significantly impacted tuber black dot incidences. Microbial activity responded to increasing temperature as the season progressed and was significantly enhanced by the addition of manure and compost soil amendments; however, lower disease incidence was not associated with increased microbial activity. While pest management practices were not major determinants of disease levels in these experiments, the results show that soil amendments can increase incidence of selected tuber diseases and microbial activity in soils.     

The germplasm release of NYL 235–4, a clone with resistance to the Colorado potato beetle

Clones selected from the wild diploid species,Solanum berthaultii, have been shown to possess valuable levels of resistance to the Colorado potato beetle (Leptinotarsa decemlineata), as well as to insects such as aphids, flea beetles, leafhoppers and the potato tuber moth. Resistance is associated with the presence of glandular trichomes on the foliage ofS. berthaultii (2). Six generations after producing a hybrid between the diploid species and a tetraploid variety, a clone with good beetle and leafhopper resistance, as well as reasonable agronomic characteristics has been produced.