Effect ofErwinia carotovora subsp.atroseptica on yield of potatoes from cut and uncut seed tubers in Valencia

Summary The effect on the development of blackleg symptoms and on yield of inoculating seed tubers of 15 cultivars withErwinia carotovora subsp.atroseptica (Eca) was investigated. Tubers were planted either whole or as pieces. Eca inoculation reduced the mean yield per plant by 8% for whole tubers and by 12% for cut tubers. There was no correlation between blackleg symptoms and yield loss.     

The effect of oxygen and carbon dioxide concentrations on bacterial soft rot of potatoes. I. King Edward potatoes inoculated withErwinia carotovora var.atroseptica

Summary MatureKing Edward potatoes were wounded, inoculated withErwinia carotovora var.atroseptica and stored at +10°C and 100% r.h. in controlled concentrations of oxygen and carbon dioxide for up to 18 days. After incubation in air or in 5% O₂ in N₂ rots were brown, dry and restricted; more extensive, soft spreading rots were produced in potatoes stored in 5% O₂+16% CO₂, in 1% O₂+20% CO₂, in 1% O₂ and in N₂, the most extensive rots occurring in the anaerobic conditions. In addition toE. carotovora var.atroseptica, pectolytic clostridia could also be recovered from the spreading rots. The experiments demonstrate the extent to which the concentration of oxygen and carbon dioxide in the environment may effect the sensitivity of tubers to bacterial attack.     

Effect ofErwinia carotovora subsp.atroseptica alone and withAlternaria solani orVerticillium dahliae on disease development and yield of potatoes in Israel

Summary Tubers of 17 cultivars were inoculated withErwinia carotovora subsp.atroseptica (ECA) and planted in 1986 and 1987 in the Negev in randomised plots in three blocks where eitherVerticillium dahliae orAlternaria solani were present or where both were absent. ECA reduced the yield in the control block and exacerbated the yield losses in the disease blocks, but the intensity of symptom expression did not always accord with the extent of yield loss. ECA had a greater effect on plants infected withA. solani than on those withV. dahliae. It was possible to categorise the cultivars as resistant, intermediate or susceptible with respect to ECA and early blight, but resistance toV. dahliae could not be differentiated from foliage maturity.     

Some effects ofRhizoctonia solani on growth and yield of potatoes

Summary Below ground infection byRhizoctonia solani had little effect on the development of potato haulm. Severe infection caused an increase in the number of tubers initiated, but a reduction in the total weight of tubers. Tubers often formed in leaf axils of severely infected plants. It is suggested that these effects occur because assimilate production is not markedly affected by infection, but the compounds need to be redistributed when lesion development on the stolons blocks transport to the usual sinks.     

Effect of temperature on differential persistence and insect transmission ofErwinia carotovora var.atroseptica andErwinia carotovora var.carotovora

Adult fruit flies (Drosophila melanogaster Meig.) transmittedErwinia carotovora var.carotovora (Jones) Dye (ECC) andErwinia carotovora var.atroseptica (van Hall) Dye (Eca) from vegetative material inoculated with equal proportions ofEcc andEca to uninoculated potato plants and from inoculated potato plants to sterile vegetative material at 15° and 27°C. The insects transmittedEcc andEca with approximately equal frequencies over an 18 hr period at 15°C. At 27°C the proportion ofEcc transmitted was significantly greater thanEca. At 27°C moreEcc thanEca was present in the inoculated vegetative material and potato stems, on fruit flies visiting these sites, and in injured potato tissues to which flies transmitted the bacteria. Results indicate that temperature is important in determining success ofEcc andEca transmission by insects and the relative persistence of the two organisms in plant tissues after transmission.     

Application of calcium and nitrogen for mitigating heat stress effects on potatoes

This study was designed to investigate the effect of calcium and nitrogen application during heat stress on leaf calcium concentration, transpiration rate, membrane thermostability, and biomass accumulation and partitioning. Micropropagated Russet Burbank potato (Solanum tuberosum L). plants were transplanted into 20 L pots containing 1:1 (v/v) soil: perlite and exposed to 30/20C (D/N) temperatures for four weeks (weeks 9–12 after transplanting) in a controlled-environment growth room. The maximum temperature was maintained for 6 hr during the middle of the 14 hr photoperiod. The nutrition treatments were N before stress (NBS), N during stress (NDS) and Ca and N during stress (Ca+NDS). Calcium was supplied as Ca(NO₃)₂. All treatments received the same total amount of nitrogen. Native soil Ca level without amendment (550 mg Ca/kg soil) was sufficient for potato plant growth under normal temperatures. Plants given Ca and N during heat stress had the highest leaf Ca concentration and transpiration rate during and 2 weeks after conclusion of the heat stress period. When measured after 4 weeks of heat stress, area and fresh and dry weight of the most recently mature leaf was significantly greater in NDS and Ca+NDS plants compared to NBS plants. Cellular membrane thermostability (measured as ion leakage from heat-treated leaf disks) was not affected by any treatment prior to heat stress. However, leaf tissue from Ca+NDS plants exhibited significantly higher membrane thermostability compared to NBS plants after 2 and 4 weeks of heat stress. At harvest, NDS and Ca+NDS plants had significantly higher leaf/stem (fresh weight ratio) values compared to NBS plants. Also, Ca+NDS plants had significantly greater total tuber and biomass values than NBS and NDS plants. Results of this study suggest that some detrimental effects of heat stress on plant growth and stomatal function may be alleviated by Ca and N application during heat stress. The data also suggest that mitigation of heat stress by Ca and N application during heat stress may maintain plant productivity when optimum growing temperatures are restored.     

Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes

The soil fumigant 1,3-dichloropropene (1,3-D) has been used in the UK for the control of potato cyst nematodes (PCN), Globodera pallida (Stone) and Globodera rostochiensis (Wollenweber), but its potential herbicidal activity has not been extensively investigated in this country. Field and glasshouse studies were therefore conducted to evaluate the potential of 1,3-D for the control of weeds in potatoes, and observations were made on the severity of potato stem canker, caused by the fungus Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk]. Autumn application of 1,3-D at 211.5 L active substance (a.s.) ha⁻¹ significantly suppressed the number of germinating weeds and the percentage of weed ground cover by 83% and 79%, respectively, relative to controls. There were also species-specific significant decreases (field pansy, Viola arvensis, in particular) in the number of weed seeds germinating in field soil in the glasshouse post-1,3-D treatment. The effect of 1,3-D declined in time and single (autumn or spring) or combined application produced a slight, but not significant, reduction in the number of weeds germinated on potato ridges relative to those recorded in untreated soil. The severity of stem canker on potato plants was not significantly reduced by 1,3-D but both mean number and weight of stems per plant were significantly increased compared with plants from untreated plots. These studies demonstrated that 1,3-D, in addition to giving PCN control, has efficacy against weeds; implications are the potential for reduced herbicide input in the crop rotation with accompanying economic and environmental benefits.     

The effect of storage factors on membrane permeability and sugar content of potatoes and decay byErwinia carotovora var.atroseptica andFusarium roseum var.Sambucinum

Russet Burbank and WC230-14 potato tubers were stored at 0 C (32 F) and 5 C (41 F) in air, air plus 4% CO₂ and air plus 8% CO₂ for a 175 day storage period. Four times during this period, tubers were removed and inoculated withErwinia carotovora var.atroseptica (van Hall) Dye orFusarium roseum var.sambucinum (L. K.) Sn. and H. and stored at 17 C (62.6 F). Tuber samples were also reconditioned for two weeks at 17C(62.6 F) and then inoculated. Tubers were evaluated for rate of membrane permeability, free glucose, free fructose, and sucrose content and the rate of tuber decay by the two pathogens. Relative to 5 C (41 F), 0 C (32 F) storage increased sugar content, membrane permeability and the rate of tuber breakdown. Increasing CO₂ during storage at 0 C (32 F) and 5 C (41 F) increased each of the above parameters. Reconditioning tended to alleviate the adverse effects of 0 C (32 F) storage and increasing CO₂ levels, but varietal differences existed. A significant and high correlation was obtained between the rate ofErwinia decay, membrane permeability, and sucrose content of the tubers.     

The effects of dihydroquercetin on the cut surface of seed potatoes

The purpose of this study was to determine the effects which dihydroquercetin (DHQ) has on the natural healing process of suberization and wound periderm initiation in cut seed potatoes. Dihydroquercetin is a phenolic compound extracted from the bark of Douglas Fir,Pseudotsuga menziesii (Mirb.) Franco. Anatomical studies of treated seed potato tissue showed that treatment with bark-383, the cork-rich fraction of the whole bark containing approximately 2% pure DHQ, increases the thickness of the suberized layer formed below the cut surface. Treatment with 4% bark fraction I, which is blended to that concentration with the inert carrier dust Pyrax and contains approximately the same amount of DHQ as does the bark-383, also promoted the formation of a thicker layer of suberized cells. The thickness of the wound periderm did not significantly vary as a result of the use of any treatments containing DHQ. The use of Captan (Orthocide 50W) as a cut seed treatment in these studies was found to inhibit the formation of a suberized layer and subsequently the initiation of a wound periderm. The combination of bark-383 and Orthocide 50W in a treatment mixture reversed the inhibitory affect of the Orthocide 50W alone and therefore allowed for the formation of a well suberized layer and a wound periderm. It was found that wound healing on the cut surface of seed potatoes is largely dependent on the type of tissue present at any given point on that cut surface. Therefore, the response to treatment of the stolon end, center, and blossom end tissues was related to the type of tissue which was present in each of those tuber regions. The fungal mold growth on treated seed pieces incubated in a controlled environment was adequately retarded when Orthocide 50W was combined with bark-383 in a mixture ratio of 1:9 respectively. The longer the treatment material was allowed to remain on the seed piece, the greater was the protection against mold growth afforded by the mixture.