Effect of plant age on potato leafhopper infestation of resistant and susceptible potato clones

The effect of age of resistant potato clones,Solarium tuberosum gp.tuberosum, on infestation by potato leafhopper,Empoasca fabae (Harris), was investigated by varying the date of planting in a naturally infested fieldtest Significant differences (P < .05) in infestation levels were found among clones and among dates of planting. The responses of resistant and susceptible clones to infestation differed with date of planting. But lower levels of infestation occurred on all clones in the first 2–3 weeks of leafhopper migration on the early plantings, indicating that plant age in potatoes is a factor in host preference of potato leafhopper     

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.     

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%.     

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.     

Evaluation of potato clones for severity of Verticillium wilt, yield and specific gravity in Maine

In 1994 and 1995, the effect of Verticillium wilt, caused byVerticillium dahliae andV. albo-atrum, on tuber yields, number and weight of U.S. No. 1 and B size tubers, and specific gravity was studied in northern Maine, an area with a short growing season. Seven clones (four resistant and three susceptible) were evaluated in a split-plot design with three replications. Clones were the whole-plot factor, and seed pieces in sub-plots were either uninoculated or inoculated with 50 ml of 4 × 10⁴ cfu/mlVerticillium spp. at planting. Individual plants were scored for Verticillium wilt symptoms before harvest on a 1= <3% wilt to 10= >97% wilt. Differences among clones for wilting and specific gravity were significant. The inoculation treatment had no effect on any of the tuber traits measured. However, there were significant clone x inoculation interactions for most tuber traits. Reductions in yield, weight and number of U.S. No. 1 potatoes, and specific gravity were greater in the Verticillium wilt susceptible clones than in the resistant clones. These results suggest that breeding clones with resistance toVerticillium spp. will reduce yield losses, while maintaining tuber size and specific gravity under disease pressure.     

Tuber yield,soft rot resistance,bruising resistance and processing quality in a population of potato (cv. crystal) somaclones

Several important postharvest characteristics were evaluated in protoplast-derived somaclones after two consecutive growing seasons (1987, 1988). None of the somaclones had tuber yields significantly greater than the protoplast donor Crystal mother clone (MC), however, 8 of 37 clones had significantly lower yields. Of the 25 somaclones selected forErwinia soft rot resistance testing, 1 clone demonstrated significantly elevated resistance to soft rot while 12 clones were found to be significantly more susceptible relative to MC. Over half (20) of the 33 somaclones tested showed significant improvement in resistance to tuber bruising while only a single clone was more susceptible than MC. Based upon Agtron color analysis, 5 somaclones showed significantly enhanced chip color when processed directly out of cold storage (6 C). Six clones had significantly improved chip color after a reconditioning period (20 C). Four of the clones with significantly better cold processing characteristics were also among the 6 with significantly enhanced processing quality after reconditioning. Some clones showed improvement in two or more characteristics. Clone 72–93 had significantly elevated resistance to both bacterial soft rot and tuber bruising while the bruise resistant clones 74-14, 71-41, 71-18 and 71-2 demonstrated significant improvement in both cold and reconditioned processing characteristics.     

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.     

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.     

Hampton: A main season golden nematode resistant variety

Hampton is a golden nematode resistant variety suited for main season tablestock production. It is resistant toVerticillium wilt, but susceptible to scab and late blight. Hampton yields as well as Katahdin and produces essentially the same distribution of tuber sizes. Its shape is distinctively spherical with shallow eyes. Its specific gravity is like Katahdin and it will not produce acceptably light colored potato chips.     

Influence of slitted polyethylene mulch,nitrogen rates,and trickle irrigation on potatoes

In 1974, potatoes(Solanum tuberosum L.) were grown on unmulched, clear, and black slitted polyethylene. Production and tuber specific gravity of the potatoes were determined at four nitrogen rates (0, 75, 150 and 225 lb/A) and with two varieties (Superior and Katahdin). In 1975, potatoes were grown on unmulched and clear slitted polyethylene with and without trickle irrigation. Nitrogen increased marketable yields up to 150 lb/A on the unmulched potatoes. Irrigation increased the marketable yields of potatoes on both unmulched and mulched plots. However, no advantage was found in marketable yields, specific gravities or tuber sizes of the potatoes grown on either clear or black slitted polyethylene mulch over conventional unmulched soil for the ‘Superior’ or ‘Katahdin’ varieties.     

The effect of potato virus X on susceptibility of potato tubers toFusarium roseum ‘Avenaceum’

Potato virus X (PVX)-free and mild PVX-infected tuber lines originating from the same Katahdin clone were compared for susceptibility to tuber rot incited byFusarium roseum (Lk.) Synd. and Hans. ‘Avenaceum’. The effect of interval between top-kill and harvest on development ofFusarium tuber rot was also determined. A series of tubers from both PVX-free and PVX-infected tuber lines was either (i) mechanically bruised and inoculated by immersion in a spore suspension ofF. roseum ‘Avenaceum’, (ii) mechanically bruised but not inoculated, (iii) inoculated only or (iv) neither bruised nor inoculated. Tubers from all treatments were then stored at temperatures of 18–21 C (65–70 F) for a 3-week period prior to being placed at 4 C (39 F) for the remainder of the storage period. The amount of rot was determined after a 5–6 month storage period at the latter temperature. In a 4-year study PVX-free tubers were significantly (1% level) more susceptible to infection byF. roseum ‘Avenaceum’ than tubers infected with mild PVX. PVX-free tubers left in the ground for 2 or 3 weeks after top-kill were significantly (1% level) more susceptible toFusarium dry rot than those infected with the virus; however, there was no significant difference in disease incidence between PVX-free and PVX-infected tubers when harvested 4–5 weeks after top-kill. Tubers, both PVX-free and PVX-infected, remaining in the ground for a 2 week period following top-kill were significantly (1% level) more susceptible toFusarium tuber rot than those harvested 3 weeks after top-kill; similarly, both PVX-free and PVX-infected tubers harvested 3 weeks after top-kill were significantly (1% level) more susceptible than those left in the ground for a 4–5 week interval.     

Resistance toPseudomonas solanacearum in potato: Infectivity titrations in relation to multiplication and spread of the pathogen

When several wilt-resistant potato clones were tested against a highly virulent strain from Mexico (No. 276) by standard stem inoculation methods, only one clone ofSolanum phureja was resistant. When different inoculum concentrations were introduced quantitatively for infectivity titrations, however, different levels of resistance were clearly defined among clones previously rated as susceptible. Linear regression was used to estimate the ED₅₀ values (dosage required to wilt 50% of the population) for each of seven clones. These values ranged from 3 and 100 colony-forming units (CFU) for Katahdin and Russet Burbank, respectively, to 2.1 x 10⁶ CFU for S.phureja clone 1386.15. The distribution of bacteria in stems of Russet Burbank plants inoculated with the compatible strains 276 and K-60 and the incompatible strains B1 and S-210 was very different. In all cases, incompatible bacteria were not detected 10 cm above the inoculation point in the stem, even by 12 days after inoculation, whereas compatible strains multiplied rapidly at this site by 6 days. At the inoculation site and at sites immediately adjacent to it, however, incompatible bacteria attained populations that only differed by one order of magnitude from those of compatible bacteria. Similar results were obtained when a resistant clone (MS 118.24) was inoculated with the virulent strain K-60. Thus, resistance was characterized both by reduced acropetal spread and by tolerance to large numbers of the bacterium.     

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.     

General combining ability of Neo-Tuberosum for potato production from true seed

Neo-Tuberosum clones from the Cornell breeding population were evaluated as female parents in combination with Tuberosum for production from true seed. Field trials of hybrid seedling families were carried out in 1982 and 1983. Families were also grown in a hot greenhouse to measure combining abilities for tolerance to heat stress. General combining ability was highly significant for yield, vine and tuber characteristics, and heat tolerance. Several clones were identified which produced outstanding seedling families for yield, uniformity, and tuber appearance. Some individual crosses were equal to cultivars in yields, uniformity, and tuber appearance. Hybrids of Neo-Tuberosum and Tuberosum appear to be an excellent choice for potato production from true seed.     

Evaluation of six insect pests for transmission of potato spindle tuber viroid

Six insect pests of potato, green peach aphid,Myzus persicae (Sulzer); potato leafhopper,Empoasca fabae (Harris); Colorado potato beetle,Leptinotarsa decemlineata (Say); tarnished plant bug,Lygus lineolaris (Palisot de Beauvois); red-legged grasshopper,Melanoplus femurrubrum (DeGeer); and southern army worm,Prodenia eridania (Cramer), were tested for their ability to transmit potato spindle tuber viroid (PSTV). PSTV infection was determined by a gel electrophoretic assay made 6 weeks after transfer of insects from infected to non-infected plants of the cultivar, ‘Katahdin.’ Plants grown from tubers of the original non-infected hosts were also assayed. PSTV was detected in only 2 of 183 test plants; these 2 plants had been infested with the tarnished plant bug. These results suggest that the insect species studied are relatively insignificant as vectors of PSTV.     

Identification of stem soft rot (Erwinia carotovora subspeciesatroseptica) resistance in potato

Development of potato cultivars resistant to Erwinia species (Erwinia carotovora subspeciesatroseptica, E. carotovora subspeciescarotovora, andErwinia chrysanthemi) causing soft rot of stems and tubers involves identification and transfer of the resistance to breeding lines possessing desirable agronomic traits. In total, 363 accessions of six wildSolanum species, three somatic hybrids and nine sexual progeny of somatic hybrids were screened for stem soft rot resistance. Thirty-one, 50, and 67 percent of accessions ofSolanum boliviense, Solanum chacoense, and Solanumsanctarosae, respectively, were resistant or highly resistant, whereas, 100, 97, and 95 percent of accessions ofSolanum canasense, Solanum tarijense, andSolanum spegazzinii were susceptible or highly susceptible, respectively. Two tuber soft-rot resistant somatic hybrids, A937 and T355-11 produced earlier by the fusion ofSolanum brevidens (PI 218228) andSolanum tuberosum (PI203900) orS. tuberosum cv. Russet Burbank, respectively, and the sexual progeny of A937 andS. tuberosum cv. Katahdin were also highly resistant. Transfer of resistance fromS. brevidens to somatic hybrid (A937) and subsequently to the progeny suggests that the resistance is simply inherited. In addition to the identification of 65 resistant or highly resistant clones of wildSolanum species, this study has identified three tuber soft rot-resistant clones that are also resistant to stem soft rot. Potato cultivars showed a range of responses to the pathogen.     

Can germplasm resources be used to increase the ascorbic acid content of stored potatoes?

Freshly harvested potato tubers contain up to 50 mg/100g ascorbic acid (AA), but levels decline rapidly during cold storage. Genetic alterations to boost the AA content of stored tubers would contribute to human nutrition and might improve tuber resistance to oxidative damage during chilling. While studying the breeding potential ofSolanum phureja germplasm, we identified a 24-chromosome Phureja-haploid Tuberosum hybrid (clone I, USW5295.7) that retained a twofold higher content of tuber AA than neighboring clones after storage at 5 C. Clone I produces 2n-pollen through a mechanism genetically equivalent to first-division restitution (FDR), which transmits much of the nonadditive genetic variance for tuber yield. We now report a survey of clone I progeny showing significant family and ploidy effects on tuber AA levels during cold storage, consistent with the transmission of information for higher AA by FDR 2n-pollen. These results encourage further study of 2n-gametes and wild species germplasm to breed for increased tuber AA.     

Tuber yields and specific gravities inSolanum tuberosum populations recurrently selected for resistance to potato leafhopper

Solanum tuberosum genotypes from the 3rd, 5th, and 7th generations of recurrent selection for resistance to potato leafhopper were compared with genotypes from the base, unselected population for tuber yield and specific gravity over a five year period. Mean tuber yields of the genotypes in the 3rd and 5th generations were equal to the yield of those in the base population. The mean tuber yield in the 7th generation was significantly lower than the mean in the base population and the means in the other selection generations. However, the mean tuber specific gravities of the 5th and 7th generation genotypes were slightly higher than the mean in the base population. The variability of tuber yield among genotypes in the 7th selection generation was lower than the variability in the base population and in the 3rd and 5th selection generations. It was concluded that there was moderate genetic potential for selecting genotypes with resistance to potato leafhopper that had acceptable tuber yields in the 3rd and 5th selection generations, but by the 7th generation the potential was considerably lower. The genetic potential for selecting resistant genotypes with acceptable tuber specific gravities remained about the same in each of the selection generations.     

Investigations into the mode of resistance of potato tubers toFusarium roseum ‘Sambucinum’

In a histological study comparing tuber resistance of potato clone B7200-33 and susceptible variety “Russet Burbank” toFusarium roseum ‘Sambucinum’, the formation of suberin and wound periderm was found to be an important resistance mechanism. In B7200-33 tubers a continuous suberin layer was formed whereas in ‘Russet Burbank’ tubers the suberin was formed in clumps so that the pathogen easily could invade the tissue between the clumps but not through a continuous layer. Wound periderm also was formed at a more rapid rate in B7200-33 than in ‘Russet Burbank’ tubers thereby “walling off” the pathogen and reducing decay.     

Growth response of potato tuber eyes to irradiation with X-rays and fast neutrons

Only slight reductions were observed in sprouting and growth from irradiated tuber eyes of ‘Katahdin” and B5141-6 potatoes at irradiation doses below 4500 rads X-rays or 1200 rads fast neutrons. Survival was reduced about 50% by 1400 rads fast neutrons and 97% by 5500 rads X-rays. Visible mutants and pollen steriles were rare at all doses used. A small number of subclones of irradiated ‘Katahdin’ having greater than normal pollen abortion were selected in an effort to locate irradiationinduced chromosome mutations.