Foliar solanidine glycoside levels inSolanum tuberosum populations selected for potato leafhopper resistance

Solanum tuberosum L. Gp. Tuberosum populations that had been recurrently selected for resistance to potato leafhopper,Empoascafabae (Harris), were tested for levels of foliar solanidine glycosides. Leafhopper infestation level was 57% lower than for the unselected population after seven generations of selection. The mean concentrations of foliar solanidine glycosides significantly (P<05) increased from 40 mg/100 g fresh weight (fw) in the unselected population to 65 mg/100 g fw in the population developed from seven generations of selection for leafhopper resistance. The linear relationship between the level of leafhopper infestation and the concentration of foliar solanidine glycosides among population means was significant (P<01) and negative (r=?0.85).     

Glycoalkaloid contents in tubers fromSolanum tuberosum populations selected for potato leafhopper resistance

Solanum tuberosum L. Gp. Tuberosum populations that had been improved for resistance to potato leafhopper,Empoasca fabae (Harris), by recurrent selection, were analyzed for tuber contents of the glycoalkaloids α-solanine and α-chaconine. The mean content of both glycoalkaloids was significantly higher in the more resistant populations compared with the unselected population. In a population generated from seven cycles of selection for resistance, the mean content of solanine + chaconine was 9.5 mg/100 g fresh weight compared with 4.0 mg/100 g in the original, unselected population; a 137% increase. Kennebec, in the same experiment, averaged 10.9 mg/100 g; Katahdin averaged 4.6 mg/100 g.     

Tolerance to potato leafhopper inSolanum tuberosum L. gp. Tuberosum clones

We identified clones inSolanum tuberosum L. gp. Tuberosum breeding populations that, although susceptible to infestation by potato leafhopper,Empoasca fabae (Harris), exhibited a tolerance which was manifested by the ability to produce higher than expected tuber yields when heavily infested with leafhoppers. Such tolerance was noted in a number of clones in varying degrees, but one, B6930-1, was exceptional. It sustained only a 19% loss in tuber yield compared to ‘Katahdin,’ a susceptible cultivar, that averaged 33% lower tuber yields under similar infestation levels. We studied the seasonal growth patterns of this clone and compared them to those of Katahdin, and B6705-10, a breeding clone with known resistance to leafhopper infestation. We found that much of B6930-l’s tolerance results from its early, vigorous vine growth and its early and rapid rate of tuber bulking, enabling this clone to escape some of the effects of leafhopper feeding, whereas Katahdin was usually just beginning to tuberize at the height of leafhopper infestation.     

Progress report: Resistance to the Colorado potato beetle and potato leafhopper inSolanum tuberosum subsp.andigena

An extensive collection of 1527 clones ofS. tuberosum subsp.andigena was screened in 1973 in unreplicated plots to test for resistance to the Colorado potato beetle and potato leafhopper. All clones were susceptible to the beetle. Of 17 clones selected in the 1973 tests for resistance to the potato leafhopper, 7 selections were significantly more resistant than the control (Katahdin) in a replicated experiment in 1974.     

Resistance to potato virus Y inSolanum tuberosum spp.andigena

Tests were made on lines ofSolanum tuberosum spp.andigena to determine 1) whether resistance to potato virus Y exists in the Andigena germplasm, 2) the nature of its inheritance, and 3) the type of resistance. Results of the isolation and identification studies indicated that the pathogen involved was a common strain of potato virus Y. Under field conditions susceptible plants frequently escaped infection. However, field exposures over two seasons resulted in the same ratios as tests in which the same progenies were mechanically inoculated. Mechanical inoculation at the seedling stage proved to be a reliable means of transmission and resulted in accurate screening for resistance. Of 641 tub × tub clones tested, all were susceptible to the virus. Of 366 tub × adg clones tested, 170 were resistant and 196 were susceptible. This fits a 13:15 ratio, assuming random chromatid segregation and a single dominant gene conferring resistance. Plants that were resistant following mechanical transmission were also resistant when inoculated by aphids, indicating the reliability of mechanical transmission as a means of screening for resistance. To determine the type of resistance, top-graft and approach-graft tests were made. Failure to recover the virus from resistant plants inoculated by either grafting method suggests that immunity is the type of resistance involved.     

Recurrent selection for potato leafhopper resistance in potato,Solanum tuberosum L. Gp. Tuberosum

ASolanum tuberosum L. Gp. Tuberosum population was recurrently selected for resistance to potato leafhopper (PLH) (Empoasca fabae, Harris). Primary selection was for low levels of nymphal infestation under natural infestation in field tests. The selection procedures allowed completion of a selection generation per year. The original population and seven selection-generation populations were tested for PLH resistance for three years at two locations. Averaged over six tests, seven generations of selection reduced the level of nymphal infestation by 71% and severity of plant damage (hopperburn) by 45%. The rate of reduction slowed in later generations.     

Glandular pubescence,glycoalkaloid composition,and resistance to the green peach aphid,potato leafhopper,and potato fleabeetle inSolanum berthaultii

Fifteen accessions ofSolarium berthaultii Hawkes andS. berthaultii xS. tarijense Hawkes were assessed for resistance to field infestations of the green peach aphid,Myzus persicae (Sulzer), potato leafhopper,Empoasca fabae (Harris), and potato fleabeetle,Epitrix cucumeris (Harris). Accessions bearing both Type A and Type B glandular trichomes were much more resistant to the green peach aphid and potato leafhopper than accessions bearing Type A hairs alone. All accessions had significantly smaller populations of these 3 pests than S.tuberosum cultivars. Total glycoalkaloid (TGA) content of foliage and tubers was not correlated with insect populations. Foliar TGA levels of field-grown plants varied among accessions, ranging from < 2–240 mg/100 g fresh wt. Solasonine and solamargine were the major foliar glycoalkaloids while solamarines predominated in tubers.     

Glycoalkaloids and resistance to the Colorado potato beetle inSolanum chacoense Bitter

Resistance of 20 F₂ Solarium chacoense Bitter clones to the Colorado potato beetle,Leptinotarsa decemlineata (Say), was measured in a field test. Levels of total glycoalkaloids (TGA) and composición of the glycoalkaloid mixtures in foliage of the clones were also determined. Clones with either commersonine or dehydrocommersonine as the major foliar glycoalkaloid were significantly more resistant (lower damage ratings, fewer larvae and adult insects) than clones with solanine and chaconine. Damage ratings were negatively correlated (r = -0.67, p = 0.01) with foliar TGA levels. The results indicate that the types of glycoalkaloids present in the foliage ofS. chacoense may be as important as the level of TGA in limiting damage and numbers of insects.     

Selection for resistance to potato leafhopper in potatoes I.selection methods

A randomly mated potato (Solarium tuberosum L.) population (3 generations, without selection) derived from clones from several breeding programs, displayed considerable resistance in the field to potato leafhopper,Empoasca fabae (Harris). Leafhopper population levels on 161 clones ranged from 2 to 28 nymphs per 45-sec count (mean = 12), whereas a susceptible check averaged 20 nymphs per count. Clones selected for low leafhopper counts in 1971 were compared with the population in 1972 to evaluate the effectiveness of selecting from small plots (three-hill) with minimum replication. The selected clones averaged 30% fewer leafhoppers than the population average in 1971 and 10% fewer in 1972. The average heritability (broad sense) for one plot per clone per location, two locations, and two 45-sec nymph counts per plot equaled 36%.     

Mechanisms of resistance to potato leafhopper,Empoasca fabae (Harris), in potato

Potato genotypes were evaluated for resistance to natural infestations of the potato leafhopper,Empoasca fabae (Harris), in the field. Characterization of Type A and B glandular trichomes, phenolic properties of Type A trichomes, glycoalkaloid content and composition,E. fabae adult and nymph infestation, leaf damage (hopperburn), yield, and yield reduction were determined on genotypes PI 473331 and PI 473334 (accessions ofSolatium berthaultii (Hawkes)), NY123 and Q174-2 (advanced hybrids), and Elba and Allegany (commercial cultivars). Regarding the Type A trichome, PI 473334 was most pubescent, followed by PI 473331, both had high levels of enzymatic browning; on PI 473334 no glycoalkaloids were detected, while on PI 473331 solamargine and solasonine were present. Those genotypes were the least infested by adults; moreover, nymphs were never found on their leaves. PI 473331 and Q174-2 possess Type B trichomes, the latter had levels of Type A trichome comparable to the first and to NY123, while displaying high levels of phenolic oxidation of Type A and very low levels of glycoalkaloids. Although Q174-2 had intermediate infestation ofE. fabae, it suffered a yield reduction comparable to the control cultivar Allegany. The density of Type A trichomes of NY123 was relatively low, even though the browning assay results were significantly elevated. Foliage of this genotype was found to contain the four types of glycoalkaloids studied at high levels.Empoasca fabae infestation on NY123 was intermediate, and it yielded well on infested plots, but suffered an intermediate yield reduction. Elba presented densities of Type A similar to NY123. It suffered the lowest yield reduction despite its high levels of leafhopper infestation and hopperburn. Its tolerance might be associated with its phenology, since it is a late-maturing cultivar. High scores of the modified enzymatic browning assay were correlated with high infestation and high leaf damage. Results indicated a significant correlation between leafhopper infestation and hopperburn.     

Decapitation and genetic markers as related to haploidy inSolanum tuberosum

Summary Numerous haploids ofS. tuberosum are required if their value for breeding and genetic studies is to be adequately explored. Genetic markers, particularly pigmentation of the pre-transplant seedling, allows for early elimination of hybrids and consequently the ready detection of potential haploids among the F₁ from interspecific matings. Decapitation is an effective means of markedly increasing the number of seeds per pollination following such interspecificSolanum matings. The combined use of suitable genetic markers and decapitation substantially increases the efficiency of detecting haploids. Crops Research Division, Agricultural Research Service, USDA Cooperation of the Inter-Regional Potato Introduction Project (IR-1) in providingSolanum materials is hereby acknowledged.     

Performance of populations derived by selecting for resistance to potato leafhopper in A 4XSolanum Tuberosum X 2XSolanum Chacoense cross

Intercross and backcross populations derived from aSolanum tuberosum L. (2n = 2x = 48) ×Solanum chacoense Bitt. (2n = 2x = 48) cross by selecting for resistance to potato leafhopper (PLH) (Empoasca fabae Harris), were tested in the field. In F2 and F4 populations, the levels of nymphal infestation and leaf necrosis from PLH feeding were considerably lower and tuber yields were much lower compared with those measured on the susceptible cultivar Kennebec. No differences were found between the two populations. Backcrosses of the F2 and F4 populations toS. tuberosum decreased resistance to PLH. Resistance to infestation was still greater than that of Kennebec; severity of leaf necrosis equaled that of Kennebec. Tuber yields increased, but were less than Kennebec’s yield. Foliage types shifted closer to those ofS. tuberosum. Three generations of selection and intercrossing within the backcross populations did not change the level of resistance to PLH but did tend to lower tuber yields. Foliage types remained primarilyS. tuberosum in appearance although distinctive types segregated with increased frequency. A second backcross toS. tuberosum did not change the level of resistance to PLH or the level of tuber yield relative to those of the first backcross or Kennebec.     

Tuber yields of families from open pollinated and hybrid true potato seed

This work was undertaken to compare the tuber yields, vegetative vigor and uniformity of seedling transplants obtained from different breeding methods. Twenty hybrid families from different groups of crosses involving 4x clones and 2x Phureja-haploid Tuberosum hybrids; 4x × 4x, 4x × 2x (FDR), 4x × (4x × 2x), and (4x × 2x) × (4x × 2x) and eleven open pollinated families from 4x clones, and 4x hybrids from 4x × 2x crosses were compared in a replicated yield trial. Families from 4x × 2x (FDR) crosses were the highest yielding among the hybrid groups having approximately twice the yield of the open pollinated 4x clones. They also were the best group in relation to plant vigor and uniformity. Based on these results, it appears that a good breeding scheme for high-yielding and uniform progeny from true potato seeds is the 4x × 2x hybridization method where the male parent is capable of producing 2n pollen via a first division restitution mechanism.     

Disease resistance inSolanum phureja and diploid and tetraploidS. tuberosum × S. phureja hybrids

Summary DiploidSolanum phureja, diploid and tetraploidS. tuberosum × S. phureja hybrid, and tetraploidS. tuberosum backcross clones were assessed for resistance to commercially important diseases. There was a reduction in the expression ofS. phureja characteristics with increasing dosage ofS. tuberosum genetic material. The generally high resistance of theS. phureja group to common scab, potato leafroll virus and potato virus Y decreased, while resistance to gangrene, foliage and tuber blight tended to increase. Resistance genes were probably well dispersed throughout theS. phureja genotype so that many were lost on hybridisation, butS. phureja could be a useful source of scab and virus resistance in the production ofS. tuberosum cultivars.     

Changes in race structure of Canadian populations ofPhytophthora infestans based on specific virulence to selected potato clones

Summary A collection of 80 isolates ofPhytophthora infestans, representing multilocus genotypes of the pathogen found in Canada from 1994 to 1996, was screened on a series of nine differential potato host cultivars to determine the physiological race of the isolates. A total of 28 pathotypes were found among the 11 genotypes present in the collection. There was a significant increase in the complexity of pathotypes from 1994 to 1996 which reflected the displacement of the US-1 genotype (mean of 2.2 host differentials infected) by the US-8 genotype (mean of 8.1 host differentials infected). Eighteen of the US-8 isolates could overcome all nine of the resistance genes tested. Virulence genes which overcame host resistance conferred by R8 were the rarest in the populations studied. The predominance of complex populations ofP. infestans in Canada implies that the introduction of cultivars with specific R genes for resistance would be an ineffective control measure. AAFC Contribution No. 901     

Selection for resistance to potato leafhopper in potatoes: III. Comparison of two selection procedures

A comparison was made of two breeding procedures for recurrently selecting potato,Solanum tuberosum L., for resistance to infestation by potato leafhopper,Empoasca fabae (Harris). On the basis of selection advance per year, the more efficient procedure involved randomly intermating a group of clones, planting seedling tubers in a field test to measure resistance to infestation, and then bulking the seed from the most resistant clones to complete the selection cycle in one year. A population developed by five cycles of selection (five years) for resistance to infestation using this procedure resulted in a decrease of 57% in the level of infestation from the original population.     

Agronomic performance of potato germplasm selected for high resistance to verticillium wilt

A three-year study was conducted from 1991 through 1993 to evaluate the field performance of potato clones that had been selected for resistance to wilt symptom development and stem colonization byVerticillium dahliae. The total yield, size distribution, and specific-gravity of these highly resistant clones were compared with standard cultivars and two parent clones with high Verticillium resistance and high yield, A66107-51 and A68113-4. Two groups of Verticillium resistant germplasm were selected in 1991. One group was the highly resistant progeny from a cross between A66107-51 and A68113-4. The second group consisted of hybrids between wild species accessions with high Verticillium resistance and cultivated diploid and tetraploid germplasm. Twenty-one out of 125 progeny clones from the A66107-51 × A68113-4 cross were highly resistant to Verticillium infection and were tested in yield trials for two years. Another eight selections had high Verticillium resistance but such low yield of seed tubers that they were tested only one year for yield. Eleven of the original 29 highly resistant selections were significantly lower in total yield than Russet Burbank. Only one clone was significantly higher in yield than RB, and none outyielded either of the resistant parents. Reddale and Century Russet had moderate to high Verticillium resistance, respectively. Both outyielded Russet Burbank and were comparable with the high yielding resistant parents. Of 15 interspecific hybrids tested in 1991, only four had sufficient yield to produce seed for yield trials and good wilt resistance after three successive seasons of evaluation. We concluded from this study that selecting at early stages of variety development strictly for Verticillium resistance is likely to be inefficient. Rather, selection should be for yield and other agronomic criteria in Verticillium infested fields.     

Research inSolanum spp. of sources of resistance to the potato tuber mothPhthorimaea operculella (Zeller)

Summary The potato tuber moth (PTM) represents a dangerous pest on potato crop in Italy, spreading out from southern areas to central and northern areas. Introductions ofSolanum berthaultii, S. commersonii, S. pinnatisectum, S. sparsipilum, S. spegazzini, S. sucurense, S. tarijense wild species andS. tuberosum × S. berthaultii hybrids were evaluated for resistance to a PTM population isolated from a field in central Italy, by means of an antibiosis test on tubers in the laboratory and of an antixenosis trial in the field. SeveralS. sparsipilum andS. pinnatisectum clones showed an antibiosis effect on larval survival and antixenosis of the aerial and the hypogeal parts of the plant. In the field, the genotypes with leaf glandular trichomes did not revcal the expected antixenosis effect of the acrial part of the plant.