). Host plant resistance is a key component of an integrated pest-management program for potato tuberworm. Varying levels of resistance to insects occur naturally in crop plants and closely related species ( Stoner, 1996 ). Potatoes contain glycoalkaloids
Maria A. Estrada, Kelly Zarka, Susannah Cooper, Joseph Coombs, David S. Douches, and Edward J. Grafius
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.
Sara E. Smith and Durward Smith
Nightshades (Solanum spp.) are weeds that result in production losses of dry beans (Phaseolus vulgaris) due to interference and to staining of beans with nightshade berry juice at harvest. A method of cleaning beans stained with the juice of nightshade berries was developed. The method involved fluidizing the beans and gently abrading surface soil from the seedcoat. The beans were analyzed for total glycoalkaloid content, color, and suitability for processing. The total glycoalkaloid content was reduced from 26 mg/100 g to undetectable levels by cleaning. The cleaned beans had higher total light reflectance than unstained beans, but did not differ in Hunter Lab `a' or `b' values. Cleaned beans were not significantly different from unstained beans in quality when processed.
Abbas M. Lafta and James H. Lorenzen
Growth chamber and greenhouse experiments were conducted to investigate the effect of temperature and irradiance on foliar glycoalkaloids of three potato genotypes (Solanum tuberosum L.) that differ in glycoalkaloid content. Two genotypes (ND4382-17 and ND4382-19) produced the acetylated glycoalkaloids, leptine I and II, that contribute resistance to the Colorado potato beetle (CPB, Leptinotarsa decemlineata Say). The glycoalkaloids were separated and quantified by high performance liquid chromatography. Exposure of plants to high temperature (32/27 °C, 14-hour day/10-hour night) for 3 weeks under a 14-hour photoperiod with an irradiance of 475 μmol·m-2·s-1 significantly increased the levels of leptines I and II, solanine, and chaconine compared to that at low temperature (22/17 °C). Increases in foliar leptines and total glycoalkaloids at high temperature were 90% and 169%, respectively. Growing potato plants at low irradiance (75% reduction) for 2 or 4 weeks resulted in a significant reduction in the levels of leptine I and II (46%), solanine (43%), and chaconine (38%) compared to nonshaded plants. Transferring plants from high to low irradiance or from low to high irradiance for 2 weeks caused a decrease and an increase in glycoalkaloid concentration, respectively. Therefore, both temperature and irradiance influenced foliar levels of glycoalkaloids in potato plants without changing the leptines and solanine to chaconine ratios. Thus, irradiance and temperature influenced glycoalkaloid compounds that can effect resistance to CPB, especially leptine I and II.
Francine Dickie, Ron Voss*, Gyunghoon Hong, and Marita Cantwell
Red and white skin potatoes (`Cal Red', `Cal White', `Durango', VC1015, `Yukon Gold', `Latona', A94381, and `Satina') were harvested from plots in commercial fields in Kern and San Joaquin Counties and at the Univ. California Research Center at Tulelake. After washing and sorting, potatoes were held in plastic trays in the dark (black plastic bags) or exposed to light (90 cm below cool-white fluorescent GE Watt-Miser 34W bulbs, ≈1300 lux) at 20 °C. After 0, 3, 6 and 9 days, potatoes were scored for appearance of greening (1 to 5 scale), evaluated for external color (L*a*b* color values), skin chlorophyll concentration, and glycoalkaloid concentrations. For the latter, freeze-dried slices of tuber were extracted and analyzed by colorimetry and HPLC for alpha-solanine and alpha-chaconine. Initial glycoalkaloid concentrations varied among cultivars, with `Cal Red' consistently having the highest concentrations. Tubers stored in the dark had no or a slight increase in glycoalkaloid concentrations. Light exposure resulted in increased glycoalkaloid concentrations in all cultivars, but to varying degrees. Some varieties had negligible changes while others increased as much as eightfold. The average increase was 300%. Generally, `Cal White' had the largest light-induced increases in glycoalkaloids.
Stephen L. Love, Timothy J. Herrman, and Asunta Thompson-Johns
Glycoalkaloids are a naturally occurring steroidal alkaloid of potatoes exhibiting human toxicity at levels > 30 mg/100 of tuber fresh weight. It has been documented that genotype and environment have a large impact on tuber levels within a potato crop. The impact on glycoalkaloid content was determined for four management variables including variety grown, N fertilizer rate, storage temperature, and length of storage period. In 1989 and 1990, three varieties (Russet Burbank, Norchip, and Gemchip) were planted in plots with three rates of applied N fertilizer (0, 168, and 336 kgh·m-1). Harvested tubers were stored at 4.4 or 10.0C. Tuber samples were obtained 1 month before harvest, at harvest, and then 3 and 9 months after harvest and analyzed for glycoalkaloid content. All four management variables had a significant (P = 0.05) effect on tuber glycoalkaloid content, but only length of storage period had a greater influence than the natural environmental effect as measured by the difference between years. There were significant year the trial was conducted × N fertilizer rate, year × variety, length of storage × variety, and N rate × variety interactions. The interactions were analyzed and explored.
Annette Wszelaki, Jeannine Delwiche, Sonia Walker, Rachel Liggett, Joseph Scheerens, and Matthew Kleinhenz
Sensory evaluations (triangle tests) were used to determine if panelists could distinguish, by tasting, cooked wedges of potatoes grown organically, either with or without compost, and conventionally. Mineral and glycoalkaloid analyses of tuber skin and flesh were also conducted. When the skin remained on the potatoes, panelists detected differences between conventional potatoes and organic potatoes, regardless of soil treatment. However, they did not distinguish between organic treatments (±compost) when samples contained skin or between any treatments if wedges were peeled prior to preparation. Glycoalkaloid levels tended to be higher in organic potatoes. In tuber skin and flesh, potassium, magnesium, phosphorus, sulfur, and copper concentrations were also significantly higher in the organic treatments, while iron and manganese concentrations were higher in the skin of conventionally grown potatoes.
Anusuya Rangarajan, A. Raymond Miller, and Richard E. Veilleux
Leptine glycoalkaloids in leaves of the weedy diploid potato, Solanum chacoense Bitt., have been shown to reduce feeding by Colorado potato beetle (CPB; Leptinotarsa decemlineata Say). Development of cultivated potatoes with natural resistance to CPB has the potential to reduce costs and environmental impacts of production by reducing pesticide use. Through efforts to move the genes controlling leptine biosynthesis into cultivated potato, a series of hybrids was generated between the high leptine producing S. chacoense and a cultivated type, S. phureja Juz. and Buk. These hybrids were evaluated for solanine (+chaconine), leptinins, leptines, and total steroidal glycoalkaloid content. All hybrids contained leptines, but at different levels (ranging from 117 to 802 mg·g-1 dry weight of leptine aglycon). Some hybrids appeared to convert solanine (+chaconine) to leptinine and leptine efficiently and had no detectable solanine in sampled leaves. To verify the biological significance of these glycoalkaloids, leaf tissue was subjected to feeding assays with second instar CPB. CPB feeding rate ranged from 38 to 87 mm2·d-1 and was most closely correlated with leptine concentration. A minimum leptine level of 300 mg/100 g fresh leaves suppressed feeding by 50%, and levels below this had no effect on CPB feeding.
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.
Richard E. Veilleux and A. Raymond Miller
F1 hybrids between high leptine-producing clones (8380-1, PI 458310 and 55-1) of Solanum chacoense Bitt. and anther culture competent or anther-derived clones of S. phureja Juz. & Buk. that did not produce leptines were generally weak plants that grew slowly and died before flowering. Exceptional hybrids could be found that were capable of completing a life cycle, especially during the hot summer months in the greenhouse. All F1 hybrids produced leptines in the leaves but not the tubers, albeit at lower levels than in the S. chacoense parent. Anther-derived monoploids from the F1 hybrids exhibited a range of leptine production from none to levels approaching the S. chacoense parent. Backcross populations of an F1 hybrid to the S. chacoense and S. phureja parents were examined for leptine production. Backcross hybrids were generally much more vigorous than the F1 hybrids. All of the S. chacoense backcrosses produced leptines ranging from intermediate to high levels; four of the twelve S. phureja backcrosses exhibited low leptine levels. A general dominance of leptine synthesis was therefore exhibited, although the nonleptine-producing parent affected the expression of leptines in the hybrids.