The potato amylase inhibitor gene SbAI regulates cold‐induced sweetening in potato tubers by modulating amylase activity

Potato cold‐induced sweetening (CIS) is critical for the postharvest quality of potato tubers. Starch degradation is considered to be one of the key pathways in the CIS process. However, the functions of the genes that encode enzymes related to starch degradation in CIS and the activity regulation of these enzymes have received less attention. A potato amylase inhibitor gene known as SbAI was cloned from the wild potato species Solanum berthaultii. This genetic transformation confirmed that in contrast to the SbAI suppression in CIS‐resistant potatoes, overexpressing SbAI in CIS‐sensitive potatoes resulted in less amylase activity and a lower rate of starch degradation accompanied by a lower reducing sugar (RS) content in cold‐stored tubers. This finding suggested that the SbAI gene may play crucial roles in potato CIS by modulating the amylase activity. Further investigations indicated that pairwise protein–protein interactions occurred between SbAI and α‐amylase StAmy23, β‐amylases StBAM1 and StBAM9. SbAI could inhibit the activities of both α‐amylase and β‐amylase in potato tubers primarily by repressing StAmy23 and StBAM1, respectively. These findings provide the first evidence that SbAI is a key regulator of the amylases that confer starch degradation and RS accumulation in cold‐stored potato tubers.     

Variations in resistance against Phthorimaea operculella in wild potato tubers

Tuber resistance can contribute to current management strategies against the potato tuber moth, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), in field and stored potatoes. Wild potatoes represent a potential source of novel resistance traits against the moth. We assessed resistance in three wild potato species, Solanum multiinterruptum Bitt., Solanum sparsipilum (Bitt.) Juz. & Buk., and Solanum wittmackii Bitt. against neonate and developing tuber moth larvae. All three species had high levels of resistance but accessions of S. sparsipilum and S. wittmackii were significantly more resistant. Resistance in S. multiinterruptum was generally concentrated in the tuber periderm, whereas in S. sparsipilum and S. wittmackii resistance was mainly cortex‐based. Unidentified cortex‐resistance factors in all three species reduced survival and increased larval and pupal development times, but had no apparent effects on the pupal weights of survivors. A high proportion of larvae abandoned or died within tubers of S. wittmackii, which has particularly high levels of unidentified cortex‐based defenses. Resistance decreased in S. multiinterruptum and S. sparsipilum as tubers sprouted but was more stable in S. wittmackii. Periderm‐based resistance was more stable than cortex‐based resistance in S. multiinterruptum during sprouting. In contrast, cortex‐based resistance was stable in tubers of S. wittmackii as these sprouted, and resistance may have increased on some older sprouting tubers. Solanum multiinterruptum and S. sparsipilum are proposed as potential sources of resistance against the potato tuber moth.     

Zur Rolle des Pektins bei der Ausprägung sorten- und jahresbedingter Unterschiede der Naßfäuleanfälligkeit von Kartoffelknollen

The influence of soil moisture and mean day temperature of July to September on pectin structure and soft rot resistance of potato tubers was investigated. Tuber samples of middle early and middle late potato cultivars respectively were tested from 1976 to 1979. Cultivar characteristics as well as growth conditions effect the pectin structure. The tuber tissue of soft rot resistant cultivars contains relative high amounts of esterified pectin. The pectin esterification was promoted by drought during vegetation periods (1976, 1978). A late rise of metabolic activity caused by rainfall at the end of the vegetation period (1978) increased the amount of soluble pectin in the cell wall. This lack of pectin stabilization facilitates tissue maceration by soft rot bacteria. Increased pectin solubility was also caused by unfavorable storing conditions of potato tubers. A low degree of esterification and high solubility of the cell wall pectin affect the relative resistance of potato tubers against soft rot caused by Erwinia carotovora var. atro-septica (van Hall) Dye adversely.     

Effect of chitosan and a biocontrol streptomycete on field and potato tuber bacterial communities

Four treatments applied on potato seed tubers i.e. talc only, chitosan only, Streptomyces melanosporofaciens strain EF-76 in talc and S. melanosporofaciens strain EF-76 in chitosan were compared for their efficiency to reduce common scab incidence. As previously reported the joint application of the geldanamycin-producing S. melanosporofaciens strain EF-76 and chitosan was effective to control common scab of potato. Nevertheless, field application of S. melanosporofaciens EF-76 did not allow the selection of geldanamycin-resistant actinomycetes (GRA) in the bulk soil during the potato growing season. The number of GRA on harvested potato tubers was, however, significantly higher in treatments that contained chitosan than in other treatments suggesting that chitosan might promote the establishment of the antagonistic actinomycete on progeny tubers. Biolog EcoPlates were used to determine the metabolic profiles of the bacterial soil communities. A permutation MANOVA analysis detected significant differences within the metabolic profiles of the bacterial communities at the potato flowering period but not at the beginning of the season or a week before harvest. A combination of S. melanosporofaciens EF-76 and chitosan thus represents a promising tool against common scab, with low short-term impact on soil bacterial communities.     

Detoxification of sesquiterpene phytoalexins byGibberella pulicaris (Fusarium sambucinum) and its importance for virulence on potato tubers

Summary Gibberella pulicaris (Fusarium sambucinum) is a major cause of dry-rot of stored potatoes (Solanum tuberosum) worldwide. The ability of field strains ofG. pulicaris to cause dry-rot is correlated with their ability to detoxify sesquiterpene phytoalexins produced by potato. All highly virulent field strains can detoxify the sesquiterpenes rishitin and lubimin. Meiotic recombinational analysis indicates that rishitin detoxification can be controlled at two or more loci. High virulence has been associated with one of these loci, designatedRiml. Detoxification of rishitin and lubimin comprises a complex pattern of reactions involving epoxidation, dehydrogenation, and cyclization. To date, seven lubimin metabolites and one rishitin metabolite have been characterized. Genes for rishitin and lubimin detoxification are being cloned fromG. pulicaris in order to more rigorously analyze the role and regulation of sesquiterpene metabolism in potato dry-rot. Our results indirectly support a role for sesquiterpene phytoalexins in resistance of potato tubers to dry-rot and may enhance research on alternative control strategies for this economically important potato disease.     

Increased fatty acid production in potato by engineering of acetyl-CoA carboxylase

In contrast to oil seeds, potato (Solanum tuberosum L.) is characterized by a high amount of starch stored in the tubers. To assess the capacity for oil synthesis in potato tubers, the changes in lipid content and flux into lipid synthesis were explored in transgenic potatoes altered in carbohydrate or lipid metabolism. A strong decrease in the amount of starch observed in antisense lines for ADP-glucose pyrophosphorylase or plastidic phosphoglucomutase had no effect on storage-lipid content. Similarly, potato lines over-expressing the Arabidopsis thaliana (L.) Heynh. plastidic ATP/ADP transporter that contained an increased amount of starch were not altered in oil content, indicating that the plastidic ATP level is not limiting fatty acid synthesis in potato tubers. However, over-expression of the acetyl-CoA carboxylase from Arabidopsis in the amyloplasts of potato tubers led to an increase in fatty acid synthesis and a more than 5-fold increase in the amount of triacylglycerol. Taken together, these data demonstrate that potato tubers have the capacity for storage-lipid synthesis and that malonyl-CoA, the substrate for elongation during fatty acid synthesis, represents one of the limiting factors for oil accumulation.Abbreviations AATP Plastidic ADP/ATP transporter - ACCase Acetyl-CoA:carboxylase - DGAT Acyl-CoA:diacylglycerol acyltransferase - FW Fresh weight - TLC Thin-layer chromatography - WT Wild typeSource for transgenic plant material. Upon request, transgenic potato lines altered in ACCase activity can be obtained from Peter Dörmann. For potato lines with alterations in AATP transporter activity, please refer to H. Ekkehard Neuhaus. Transgenic AGP and PGM lines are available from A. Fernie (Max-Planck-Institute of Molecular Plant Physiology, Golm, Germany).     

The relationship between glycoalkaloids and resistance to the white potato cyst nematode, Globodera pallida in potato clones derived from Solanum vernei

No relationship was found between the degree of resistance to Globodera pallida and total glycoalkaloid content of the roots or tubers of a number of potato clones derived from Solanum vernei × S. tuberosum. Nematode infestation of the roots did not lead to increases in the glycoalkaloid content of susceptible or resistant potatoes.     

The effect of size and acetylation degree of chitosan derivatives on tobacco plant protection against Phytophthora parasitica nicotianae

Enzymatic degradation of chitosan polymer with Pectinex Ultra SPL was used to obtain derivatives with biological potential as protective agents against Phytophthora parasitica nicotianae (Ppn) in tobacco plants. The 24 h hydrolysate showed the highest Ppn antipathogenic activity and the chitosan native polymer the lowest. The in vitro growth inhibition of several Phytophthora parasitica strains by two chitosans of different DA was compared. While less acetylated chitosan (DA 1%) fully inhibited three P. parasitica strains at the doses 500 and 1000 mg/l the second polymer (DA 36.5%) never completely inhibited such strains. When comparing two polymers of similar molecular weight and different DA, again the highest antipathogenic activity was for the less acetylated polymer. However, degraded chitosan always showed the highest pathogen growth inhibition. Additionally, a bioassay in tobacco seedlings to test plant protection against Ppn by foliar application demonstrated that partially acetylated chitosan and its hydrolysate induced systemic resistance and higher levels of glucanase activity than less acetylated chitosan. Similarly, when treatments were applied as seeds coating before planting, about 46% of plant protection was obtained using chitosan hydrolysate. It was concluded that, while less acetylated and degraded chitosan are better for direct inhibition of pathogen growth, partially acetylated and degraded chitosan are suitable to protect tobacco against P. parasitica by systemic induction of plant resistance.     

Biochemical Studies on “Bakanae” Fungus. Part 54

Phosphate compounds in potato tubers were fractionated by ion-exchange chromatography. By the use of radio-phosphorus, the following compounds were tentatively identified to be present in potato tubers: G-1-P, G-6-P, F-6-P, FDP, PGA, AMP, UMP, ADP, UDPX, UDPG and ATP. When the tubers were stored at a low temperature, the contents of organic phosphate compounds showed a considerable increase over those of potatoes stored at a high temperature. However, the relative composition of each component was not much influenced by the storage temperature except ATP which showed a great increase at a lower temperature.     

The inhibition of potato sprout growth by light.

When potato seed tubers (Solanum tuberosum cv. Pentland Javelin) were stored in darkness or diffuse daylight at 9°C and transferred at intervals to conditions suitable for sprouting, their capacity for sprout growth was unaffected by the presence or absence of light during previous storage. When similar tubers were stored at 10°C, 18°C or 25°C, sprout growth commenced earliest at 25°C, but the date was unaffected by fluorescent light. It was concluded that light did not affect the length of the dormant period, but only the rate of sprout elongation after that period had ceased. When tubers with growing sprouts at 10°C or 18°C were transferred from darkness into fluorescent light, sprout growth virtually ceased. Transfer from light into darkness resulted in immediate sprout growth, at a rate comparable with tubers stored continuously in the dark. Tubers of three Peruvian cultivars, stored in farm-scale diffuse-daylight stores, grew progressively shorter sprouts with increasing daily exposure to light from 30 min to 12 h. Storage of cv. Wilja under 21 Wm^-2 (total) of white fluorescent light for 10 h per day maintained the sprouts at the same length as ten times this light intensity for 1 h per day. In a subsequent experiment with cv. Bintje the 10 h, low-intensity light regime gave slightly shorter sprouts. It appeared that the total light energy falling on the tubers was the dominant factor controlling sprout growth.     

Impedance Measuring Technique for Identifying Irradiated Potatoes

The magnitude, resistance, and reactance of impedance of potato tubers were significantly influenced by irradiation. Although different types ofelectrode resulted in different values of these impedance parameters, the ratios of the impedance parameters at 5 kHz to 50 kHz got rid of the influence of the type of electrodes. The ratio of impedance magnitude at 5kHz to 50kHz (Z_5k/Z_50k) resulted in a larger difference between unirradiated and irradiated potatoes than those of resistance and reactance. The degree of difference in Z_5k/Z_50k between unirradiated and irradiated potatoes was dependent upon the measuring temperature and the region of the tuber punctured with electrodes. The impedance ratio (Z_5k/Z_50k) measured at 22–25°C at an apical region of potato tuber with 1 mA of alternating current resulted in the best identification of irradiated potatoes and enabled differentiation of irradiated potatoes from unirradiated ones for up to 6 months.     

Role of Protease Inhibitors in Potato Protection

Mechanical wounding or infection of potatoes with Phytophthora infestans caused an accumulation of only serine protease inhibitors in exudates of potato tubers. Among them, proteins prevailed that are structurally similar to those present in healthy tubers: a 22-kDa trypsin inhibitor, a 21-kDa serine protease inhibitor consisting of two polypeptide chains, and a 8-kDa potato chymotrypsin I inhibitor produced de novo. The accumulated proteins inhibited the growth of hyphae and germination of zoospores of P. infestans. Treatment with elicitors, jasmonic and arachidonic acids, intensified the accumulation of these inhibitors in tubers in response to the wound stress, whereas salicylic acid blocked this process. These results suggest that lipoxygenase metabolism plays a substantial role in signal transduction of the protective system of resting potato tubers.     

Life Histories and Fitness of Two Tuber Moth Species Feeding on Native Andean Potatoes

In the inter-Andean valleys of central Perú, two species of tuber moth, Phthorimaea operculella (Zeller) and Symmetrischema tangolias (Gyen), often occur simultaneously in stored potatoes. Traditional farming communities in the region produce a variety of native potatoes for local consumption. These include Solanum tuberosum subsp. andigena, the presumed predecessor of commercial potatoes, S. tuberosum subsp. tuberosum. In this study, we examined resistance against P. operculella in ten native Peruvian potato varieties (Casa blanca, Chispiadita, Madre de vaca, Mamaco negro, Misha, Chorisa, Mamaco rosado, Occa papa, Vacapa jayllo, and Yana tornasol). We also compared resistance in the first five of these varieties against S. tangolias. Varieties with pigmented periderms showed moderate resistance (30?C40% against P. operculella in Mamaco negro, Mamaco rosado, and Yana tornasol and 55% against S. tangolias in Mamaco negro). All the other varieties were susceptible to both moth species. Small tubers tended to be the most resistant to the attack by both moths; however, this was not related to the availability of food for developing larvae, since pupal weight and development time were unaffected by the size of tubers. Similar responses by the two moths to native potatoes indicate that tuber resistance could be used to control the complex of tuber moths that damage potatoes in the Andes. We suggest that native potatoes, which are often easily introgressed with commercial potatoes, are a potential source of resistance against tuber moths.     

Modulation of gene expression in cold-induced sweetening resistant potato species <Emphasis Type="Italic">Solanum berthaultii</Emphasis> exposed to low temperature

Cold-induced sweetening (CIS) is a crucial factor influencing the processing quality of potato tubers. To better understand the molecular events of potato CIS and different CIS-sensitivity among various potato species, a suppression subtractive hybridization library and cDNA microarray gene filters were developed. A total of 188 genes were found to be differentially expressed (DE) in Solanum berthaultii (ber) upon cold stimulation. These functional genes were mostly related to cell rescue, defense and virulence, metabolism, energy and protein fate, included in various processes of plant defense against abiotic stresses. Four expression patterns of these DE genes were profiled by qRT-PCR using the cold-stored tubers of both CIS-resistant (ber) and CIS-sensitive (E-potato 3, a variety of S. tuberosum) potatoes. The expression pattern and abundance of many DE genes encoding proteins involved in metabolism were different in these two potato tubers, especially genes associated with amylolysis, sucrose decomposition and glycolysis pathways, indicating distinct regulatory mechanisms between ber and E3 in response to cold stress, which may be crucial for potato CIS. Further investigation of these cold-regulated genes will deepen our understanding of the regulatory mechanisms of potato CIS and direct approaches for the genetic improvement of potato processing quality.     

The effect on gangrene incidence of dusting seed potatoes with benomyl at time of planting

In 1 out of 2 years' field trials benomyl applied as a dust treatment at time of planting seed potatoes resulted in an increase in potato gangrene in the progeny of both gangrene-free tubers planted in land contaminated with Phoma exigua var. foveata and gangrene-diseased tubers planted in clean land. Gangrene-infected seed tubers treated with benomyl also produced more stems infected with var. foveata than untreated tubers. Two hypotheses are presented to account for this increase in gangrene which does not occur in seed potatoes treated shortly after lifting. In all cultivars tested an organo-mercury dip-treatment increased total numbers of tubers in the seed and chat-size grades without increasing total weight whereas benomyl dust increased the numbers in these grades in Majestic only. The treatment of gangrene-diseased seed with benomyl dust affected neither total weight nor total number of tubers.     

Clonostachys rosea,a potential biological control agent for Rhizoctonia solani AG-3 causing black scurf on potato

Rhizoctonia solani AG-3 forms sclerotia on potato tubers, reducing quality and marketability. Potato discs with sclerotia were exposed to saturated soil, and following toothpick baiting, hyphae of R. solani parasitised with mycelia that either coiled around or penetrated cell walls were observed. Similar parasitic behaviour was observed in dual cultures. Clonostachys rosea was identified as the mycoparasite by morphology and ITS sequencing. When co-inoculated onto stems grown from disease-free seed potatoes, tubers of the C. rosea?+?R. solani inoculated plants had significantly lower black scurf (P?0.0001) and higher yield (P?=?0.0002) than R. solani inoculated controls.     

Resistance of potatoes transgenic for a cry1Ac9 gene, to Phthorimaea operculella (Lepidoptera: Gelechiidae) over field seasons and between plant organs

Stable performance of insect‐resistant transgenic plants across field seasons and between plant organs damaged by the insect pest is critical for management of this resistance in the field. To evaluate this, potato (Solanum tuberosum) lines transgenic for a cry1Ac9 gene with resistance to potato tuber moth (Phthorimaea operculella) were established in the field during the southern hemisphere summers of 1997/98, 1998/99 and 1999/00 as small field plots, each of 10 plants. Replicate plots of the non‐transgenic parent cultivars (at least one for every three independently derived transgenic lines) were planted randomly throughout the trials. Field‐grown foliage was challenged with larvae in the laboratory and a growth index (GI) was calculated for recovered larvae from each transgenic and non‐transgenic potato line. Larval growth on young and mature leaves, and on newly harvested or stored tubers was also measured in the laboratory. Foliage from the transgenic lines inhibited larval growth in all seasons tested. For both control and transgenic lines, larvae had slightly lower GIs when reared on mature leaves compared with young leaves, although the correlation between mean GI for young and mature transgenic leaves was high (r = 0.97). The correlation between the mean GIs of larvae on newly harvested tubers and on those stored for 5 months was also high (r = 1.0). However, the GIs of larvae on newly harvested transgenic tubers were larger than on transgenic tubers stored for 5 months. The relative growth indices (RGI = mean GI/number days before final weighing) of larvae reared on newly harvested tubers from transgenic lines were generally higher than those from young transgenic foliage, while the RGIs of larvae reared on non‐transgenic tubers were slightly lower than those fed non‐transgenic foliage. The correlation between mean RGIs of larvae fed tubers or foliage was 0.62. The transgenic potato lines exhibited stable resistance to larvae across field seasons, between affected plant organs, and between plant organs of different ages.