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Sandra E. Vega-Semorile, John B. Bamberg, and Jiwan P. Palta

Frost damage to the foliage is a common problem where potatoes are grown, and results in significant reductions in tuber yield. Frost injury also limits the cultivation of high-yielding S. tuberosum cultivars in the mountain regions of Central and South America, where potato is a staple crop. Recent studies have shown that some wild potato species possess a high degree of non-acclimated frost tolerance (growing in normal conditions) as well as high cold acclimation capacity (able to increase frost tolerance upon exposure to cold). Natural frosts affecting potatoes are of two types: a) late spring or early fall frost, where the minimum temperature during the frost episode can be very low; b) frost during the growing season, where the minimum temperature during the frost episode is not as low. It is expected that potato species able to acclimate rapidly would survive better from the latter type of frosts, whereas species having higher acclimation capacity might have a great chance to survive better from the former type of frosts. The objective of this study was to find out if there is genetic variability for the speed of acclimation among different tuber-bearing wild potato species. The species used were: S. acaule, S. commersonii, S. megistacrolobum, S. multidissectum, S. polytrichon, S. sanctae-rosae, and S. toralapanum. Relative freezing tolerance of these species was measured during cold acclimation. Preliminary results suggest that there are differences in the speed of acclimation among these species. We found that these species can be divided into four groups: i) non-acclimators; ii) rapid acclimators, with low to medium acclimation capacity; iii) slow acclimators, with low to medium acclimation capacity; iv) slow acclimators, with high acclimation capacity. We plan to use this information in our breeding program aimed at improving the freezing tolerance of potatoes.

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Sandra E Vega, Jiwan P. Palta, and John B. Bamberg

Frost injury limits the cultivation of potatoes in many regions around the world. We are currently studying the factors that contribute to frost survival in potato in an attempt to improve its frost tolerance. Wild potato species have been distinguished for their high degree of non-acclimated frost tolerance (growing under normal conditions) and their high cold acclimation capacity (able to increase frost tolerance upon exposure to cold). Cold acclimation can be reversed upon exposure to warm temperatures (deacclimation). The ability to gain freezing tolerance rapidly in response to low temperatures as well as not being able to deacclimate rapidly in response to warm daytime temperatures would be advantageous for a plant against spring or fall freezes. Last year we presented evidence for the variability in the speed of cold acclimation among 7 wild tuber-bearing potato species (S. acaule, S. commersonii, S. megistacrolobum, S. multidissectum, S. polytrichon, S. sanctae-rosae and S. toralapanum). The same set of species was used for the present study to find out if there is also variability for the speed of deacclimation. Relative freezing tolerance of these species was measured before and after cold acclimation as well as after one day of deacclimation (exposure to warm temperatures). Our results suggest that there are differences in the speed of deacclimation among these species. We found that while some species lost near a half of their hardiness, others lost only a third or less of their hardiness after one day of deacclimation.

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Anusuya Rangarajan, A. Raymond Miller, and Richard Veilleux

Leptine (LP) glycoalkaloids have been demonstrated to confer natural resistance to the Colorado potato beetle (CPB) in Solanum chacoense (chc). Development of cultivated potatoes with natural resistance to CPB has the potential to reduce both costs and environmental impacts of production by reducing pesticide use. To introgress the genes conferring leptine production from chc into S. tuberosum (tbr), clones of chc have been crossed with clones of S. phureja. Leaf disks from eight hybrids were subjected to a CPB second instar feeding bioassay to determine if extent of feeding was related to LP levels. Most hybrids contained leptinidine (LD, the aglycone of LP) levels intermediate to chc and tbr, and insect feeding was suppressed 30% to 50% in hybrids containing >10 mg·g–1 DW LD. One hybrid displaying feeding suppression contained a very low level of LD, whereas another hybrid that contained higher levels of LD had higher feeding rates. The presence of LD at “threshold” levels in these hybrids will suppress feeding of CPB, but other factors affecting resistance are also present and need to be explored.

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Laurie S. Weiss, John B. Bamberg, and Jiwan P. Palta

Solanum acaule (acl) and Solanum commersonii (cmm) represent the extremes of frost tolerance and cold acclimation ability among potato species. We have combined these species with cultivated S. tuberosum (tbr) to develop a potato with desired tuber traits and a high degree of frost tolerance. For this purpose diploid cmm was made 4x and crossed with naturally 4x acl. The F1 and F2 appear to exhibit hybrid vigor for vine growth for flowering, but none had frost tolerance greater than the parents. The F1 and F2 were crossed with S. tuberosum ssp. andigena and Katahdin via 2n eggs resulting in 6x 3-way hybrids. These hybrids were evaluated both in the field and laboratory for frost tolerance and acclimation ability. Results showed an increase of 1°C of frost tolerance and 2°C increase in cold acclimation capacity in the hybrids as compared to the sensitive tbr parents. Some of the 6x (3-way) hybrids produced significant tubers but yield and earliness needs much improvement. These results demonstrate that it should be possible to move both non acclimated freezing tolerance and cold acclimation ability from wild to cultivated species and offer exciting opportunities to enhance potato production in frost prone areas in the world.

Supported by USDA/NRI grant 91-3700-6636 to J.P.P. and J.B.B..

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C.M. Ronning, S.P. Kowalski, L.L. Sanford, and J.R. Stommel

The Colorado potato beetle is a serious pest of the cultivated potato. Natural resistance has been found in a few wild species, including Solanum chacoense Bitter, in which resistance is attributed to the presence of foliar specific leptine glycoalkaloids. Production and accumulation of these compounds within S. chacoense varies widely and appears to be inherited in a quantitative fashion, but high leptine producing clones occur rarely. In the present study, 15 different accessions from various locations and altitudes of origination were analyzed for foliar glycoalkaloid content in order to determine the frequency and distribution of genes for leptine production/accumulation, and to see if we could find a center, or core, of leptine production. Leptines were detected in eight of the 15 accessions, and the amounts within each accession varied widely, but none of the individuals produced high amounts of leptine (defined as greater than 62% of total glycoalkaloids). All of the leptine-containing accessions originated from western Argentina. There was no relationship between elevational level and leptine, but there was a negative trend with total glycoalkaloids and elevation; this was due to levels of solanine and chaconine decreasing with increasing elevation. In addition, nine unidentified glycoalkaloids were detected, in very high proportions in some individuals and accessions. AFLP marker frequency and diversity were used to compare subpopulations of these accessions. AFLP markers revealed substantial diversity among clones. The relationship of marker distribution to glycoalkaloid content is discussed. The results raise interesting questions about glycoalkaloid biosynthesis and inheritance, and point the direction for new avenues of leptine and glycoalkaloid research.

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Ram K. Birhman, Sylvain R. Rivard, and Mario Cappadocia

Using restriction fragment length polymorphism (RFLP) analysis, the genetic architecture of some anther-culture-derived S. chacoense Bitt. plants was studied, and their origins were elucidated. Our RFLP analyses showed that 1) several plants, even of different ploidy but otherwise genetically identical (clones), can be regenerated from callus originating from a single microspore and, conversely, that 2) some plants regenerated from single callus can have different genetic constitutions and, therefore, must have originated from two different microspore. These findings imply that previous anther culture efficiency estimates might have to be reconsidered.

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Ruth S. Kobayashi, Stephen L. Sinden, and Lind L. Sanford

Leptine glycoalkaloids found in certain genotypes of Solanum chacoense, a wild potato relative, are resistance factors against the Colorado potato beetle (CPB). To efficiently introgress CPB resistance through leptine production into the cultivated potato, an understanding of leptine inheritance is important. Analysis of sibs within PI lines revealed a wide segregation for level of leptines. Leptine levels ranged from not detectable to 120 mg/100 g fresh weight among six sibs in a PI line, suggesting leptine production may be controlled by a few major genes. TLC analysis of F2 and backcross progeny, however, indicated that several genes probably control leptine level. This apparent multigene control of leptine level may make it difficult to incorporate leptine synthesis into the cultivated potato. Therefore, we are presently identifying microsatellite and RAPD markers associated with leptine synthesis to enable marker-assisted selection and facilitate the incorporation of leptine synthesis into the cultivated potato.

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Jim Mooney and Shelley H. Jansky

Resistance to the Colorado potato beetle (CPB) and green peach aphid (GPA) would be valuable if it could be effectively transferred from wild potato species to the cultivated potato. Eighteen diploid interspecific hybrids have been developed using Solanum tuberosum Gp. Tuberosum haploids (2n = 2x = 24) and the diploid wild species S. berthaultii (ber), S. chacoense (CHC), S. jamesii (jam), and S. tarijense (tar). Twenty-five genotypes per family were screened for resistance to CPB and GPA. Feeding trials were carried out on intact leaves. The degree of resistance to CPB was determined by the stage of instar development and weight of larvae after a four day feeding period; resistance to GPA was evaluated by aphid reproduction and survival after a fifteen day feeding period. Highly CPB or GPA resistant clones, compared to `Norgold Russet',, have been identified thus far. Some clones express high levels of resistance to both CPB and GPA. Crosses between resistant clones and S. tuberosum will be carried out at the diploid level in an attempt to combine resistance with good tuberization qualities.

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Jim Mooney and Shelley H. Jansky

Resistance to the Colorado potato beetle (CPB) and green peach aphid (GPA) would be valuable if it could be effectively transferred from wild potato species to the cultivated potato. Eighteen diploid interspecific hybrids have been developed using Solanum tuberosum Gp. Tuberosum haploids (2n = 2x = 24) and the diploid wild species S. berthaultii (ber), S. chacoense (CHC), S. jamesii (jam), and S. tarijense (tar). Twenty-five genotypes per family were screened for resistance to CPB and GPA. Feeding trials were carried out on intact leaves. The degree of resistance to CPB was determined by the stage of instar development and weight of larvae after a four day feeding period; resistance to GPA was evaluated by aphid reproduction and survival after a fifteen day feeding period. Highly CPB or GPA resistant clones, compared to `Norgold Russet',, have been identified thus far. Some clones express high levels of resistance to both CPB and GPA. Crosses between resistant clones and S. tuberosum will be carried out at the diploid level in an attempt to combine resistance with good tuberization qualities.

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A. del Rio, J.B. Bamberg, Z. Huaman, R. Hoekstra, A. Salas, and S.E. Vega

Effects of genebank seed increases on the genetic integrity and whether germplasm in the genebank still represents the in situ populations from which it was collected are major concerns of the recently formed Association of Potato Intergenebank Collaborators (APIC), a consortium of world potato genebank leaders. This cooperative APIC research used RAPDs and morphological markers 1) to establish genetic relationships between seed increased populations within accessions and (2) to measure genetic differentiation between diploid and tetraploid potato germplasm maintained for many years and current in situ populations from the same collection sites in the wild. Solanum jamesii Torrey (2n = 2x = 24) and S. fendleri A. Gray (2n = 4x = 48), two wild potato species native to North America, were used as plant material. These species represented two major breeding systems found among Solanum species: outcrossing diploids and inbreeding disomic tetraploids, respectively. Comparisons made between populations one generation apart and between sister populations generated from a common source indicated that there has been minimal loss of genetic diversity in captive germplasm using the genebank techniques standard at NRSP-6 and other world potato genebanks. RAPD markers also revealed that significant genetic differences were found between genebank-conserved and re-collected in situ populations for all diploid potato comparisons and for about half of the comparisons within tetraploid potato populations.