Tyrosine synthesis in potato tuber tissue from blackspot-susceptible and resistant genotypes

Summary Radioactively-labeled shikimic acid (¹⁴C) was incubated with potato tuber tissue disks to determine the relative rate of tyrosine synthesis in blackspot-resistant and susceptible cultivars. Tyrosine synthesis was 55% higher in the susceptible cultivar, Lemhi Russet, than the resistant clone TXA 763-5. The susceptible clone also partitioned a lower percentage of¹⁴C tyrosine into soluble protein than did the resistant genotype. The percentage of labeled free tyrosine which would be available for oxidation by polyphenyloxidase was therefore much higher in the susceptible cultivar. Hort/LA Paper No. 90-27. Project No. 0766. Washington State University, College of Agriculture and Home Economics Research Center, Pullman, WA 99164     

Periderm and lenticel characterization in relation to potato cultivar, soil moisture and tuber maturity

Summary Using the fluorescent lipid stain fluorol yellow 088 to detect suberin in tubers, the numbers of layers and the thickness of the suberized cells in the periderm and within the lenticels showed changes after the early stage of tuber formation. These changes as tubers matured were affected by cultivar and soil moisture conditions. Penetration of the surface tissues of tubers by the water soluble stain safranin O was confined to the lenticles. Although the zone of suberized cells in lenticels acted to some extent as a barrier to penetration, there was not a clear relationship between permeability and suberization. Stored tubers showed thicker suberin berriers in lenticels than freshly harvested tubers. When lenticels of stored tubers proliferated the suberin barrier was disrupted but a further thick suberin barrier formed after exposure to air for two weeks. The findings are discussed in relation to biological control ofErwinia by antagonistic bacteria.     

Comparison of resistance toFusarium spp. of glasshouse-and field-grown tuber progenies of potato

Summary Field-grown tubers of 22 progenies ofSolanum tuberosum L. generated in a crossing programme involving seven parents differing in resistance toFusarium coeruleum Lib. ex Sacc. andF. sulphureum Schlect. (=F. sambucinum Fuckel, teleomorphGibberella pulicaris (Fr.) Sacc.) were wound-inoculated with a cornmeal + sand culture of each pathogen. Parental genotypes were also included. The mean lesion size of each progeny was compared in 2 years of tests, as well as with published data on glasshouse-grown tubers. ForF. coeruleum there was a high correlation between years as well as with the glasshouse data, but no such correlations were apparent withG. pulicaris. Furthermore, parental and GCA values, as well as progeny means and mid-parent scores, also correlated highly forF. coeruleum but not forG. pulicaris. Glasshouse-grown tubers of 11 wildSolanum spp. were also inoculated with both pathogens. Some resistance to one or other, or both, was apparent, particularly inS. chacoense.     

Effect of leaf age on photosynthesis,carbon transport and carbon allocation in potato plants

Summary Photosynthetic characteristics, carbon allocation and partitioning of newly-fixed¹⁴C among the various carbohydrate fractions were studied in leaves of potato plants (Solanum tuberosum L. cv. Désirée) of different ages. The higher photosynthetic rate of young leaves was associated with higher levels of starch and reducing sugars. After 24 hours, in young leaves the fixed¹⁴C had been partitioned mainly to the residue and starch fractions, while in older leaves there was an increase in partitioning to sucrose and reducing sugars. The activities of the various sink organs were found to be dependent upon their distance from the source leaf. Tuber activity, however, was affected similarly by all fully expanded leaves. Although young fully expanded leaves are thought to be the major source of assimilates for tuber growth, it seems that a vast potential for contributing to plant productivity and tuber yield lies also in the older leaves, which translocate most of their photoassimilates to the tubers.     

Variation in pathogenicity on potato tubers and sensitivity to thiabendazole of the dry rot fungusFusarium avenaceum

Summary The majority of isolates ofFusarium avenaceum caused dry rot on potato tubers; many were as pathogenic asF. coeruleum. Pathogenicity ofF. avenaceum was not related to the plant species from which the isolates originated. Tubers of potato cv. Cara were more susceptible than those of cvs Romano or Maris Piper. Temperature (5–15° C) had no effect on lesion depth but lesions tended to be slightly wider at the lowest temperature. Two isolates (of 61) from wheat and white lupin had a moderate level of resistance to thiabendazole. The results are discussed in relation to the control of dry rot in stored potato tubers.     

Hypolipidemic effect of flavonoids from Solanum melongena

Flavonoids extracted from the fruits of Solanum melongena (Brinjal) orally administered at a dose of 1 mg/100 g BW/day showed significant hypolipidemic action in normal and cholesterol fed rats. HMG CoA reductase activity was found to be enhanced, while activities of glucose-6-phosphate dehydrogenase and malate dehydrogenase were significantly reduced. Activities of lipoprotein lipase and plasma LCAT showed significant enhancement. A significant increase in the concentrations of hepatic and fecal bile acids and fecal neutral sterols was also observed indicating a higher rate of degradation of cholesterol.     

The influence of tuber position on periderm calcium content and its relationship to soft rot susceptibility

Summary Calcium levels in the periderm of tubers (cv. Sebago) growing in irrigated sands were influenced by the stem position at which the tuber grew, but the effect was not consistent over two seasons. Calcium levels were increased at all tuber positions by addition of calcium to soil; combined treatments of gypsum (1400 kg Ca²⁺/ha) pre-plant and calcium nitrate (37 kg Ca²⁺/ha) side dressings gave the greatest response. Percentage incidence of soft rot lesions caused byErwinia chrysanthemi pv.zeae was not influenced by periderm calcium content. The severity of infection (weight of tissue macerated within 48 h at 30°C) was significantly reduced only by the pre-plant gypsum treatment, but there was no correlation with calcium content of the periderm. Calcium levels in periderm tissue (60–208 mg Ca²⁺/100g) are within the range of published data for other cultivars and results support previous reports that the correlation between tuber susceptibility toErwinia spp. and periderm calcium content is inconsistent.     

Fungicide treatment of seed tubers infected with thiabendazole-resistantHelminthosporium solani andPolyscytalum pustulans for controlling silver scurf and skin spot on stored progeny tubers

Summary Seed tubers, cv. Désirée, derived from stocks treated annually with thiabendazole were infected with thiabendazole-resistant strains ofHelminthosporium solani andPolyscytalum pustulans. Samples of seed tubers were either untreated or immersed for 5 min in fungicide suspensions of thiabendazole, imazalil or thiabendazole plus imazalil and planted on four farms in 1988 and 1989. After harvest, tuber samples from each treatment were treated with thiabendazole and stored for 6 months. Applying imazalil or thiabendazole plus imazalil to seed tubers decreased the severity of silver scurf and skin spot on stored progeny tubers. Thiabendazole applied to seed tubers or to progeny tubers after harvest did not affect the severity of either disease, but post-harvest treatment decreased the incidence of black scurf after storage.     

Nitrate estimates using the Nitrachek Test for precise N-fertilization during plant growth and,after harvest,for quality testing potato tubers

Summary The effect of various levels, timing, and form of inorganic and organic nitrogenous fertilizers on the variation in nitrate content of stem bases over time was measured by means of the Nitrachek test in experiments carried out on sandy soils in Bremerv?rde, Germany (1985–7) and Helsinki, Finland (1987). There were good correlations between fertilizer use and nitrate content in the stem sap, and it was shown to be feasible to derive standard nitrate values which varied with growth stage. Splitting the application of N gave higher yields than applying all the N in the seedbed. The nitrate contents of tubers at harvest were correlated with the intensity of fertilizer use and was influenced by season. Soil N balances showed that splitting the N dressings reduced the soil N content more than applying all the nitrogen at the time of planting.     

Transgenic potatoes expressing anErwinia pectate lyase gene — results of a 4-year field experiment

Summary Four potato lines of cv. Désirée that express the pectate lyase (PL) isoenzyme 3 ofErwinia carotovora subsp.atroseptica were examined in a 4-year field experiment with respect to plant development, tuber yield and resistance of tuber tissue toErwinia soft rot. The PL3 degrades plant cell wall pectin into unsaturated oligogalacturonates eliciting plant defence responses. In one line, enzyme expression was controlled by the CaMV 35S promoter (C) and in three lines it was driven by the potato patatin B33 promoter (D). Plant development of the D-lines in field plots was not distinguishable from that of the non-transgenic counterpart. Also tuber yield was not too different. By contrast, plants of the C-line were smaller than those of the nontransformed counterpart and also showed reduced tuber yield. There were no significant differences in dry mass, starch and protein content of tuber tissue between PL transgenic and non-transgenic potatoes. But compared with the latter, field-grown tubers expressing the PL displayed an enhanced resistance toErwinia soft rot. Thus, average rotting caused byEc-bacteria was diminished in tubers of PL-transgenic lines by 34.1%. The resistance of tubers toEc soft rot was significantly correlated with the PPO activity in tuber tissue.