Impact of Agronomic Strategies (Seed Tuber Pre-sprouting,Cultivar Choice) to Control Late Blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) on Tuber Growth and Yield in Organic Potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) Crops

In order to optimize potato crop management in organic farming systems, knowledge of crop growth processes in relation to limitations and reductions by nitrogen (N) and disease is necessary. This paper examines the effect of different prevention measures (seed tuber pre-sprouting, choice of cultivars: resistance to Phytophthora infestans; earliness of tuber initiation) against disease-related constraints on yields, depending on the N-mediated growing conditions of organic potato crops. Under conditions of a relatively high N supply, accelerating the early development and tuber initiation of potato crops by seed tuber pre-sprouting (yield increase of c. 18–23%) or the selective choice of cultivars with an earlier tuber initiation (yield increase of c. 0–21%) are the most effective strategies in combating late blight. They bring forward the crop development c. 7–10 days, escaping the negative impact of the fungus on tuber growth. Under conditions of a relatively low N supply, these strategies do not affect final tuber yield. The reason for the differences of the effect depending on N supply of the crops is, that the lower the N supply, the shorter the period of time over which tuber growth takes place, independent of whether P. infestans becomes severe or not. Tuber growth of organic crops low in N has mostly ceased by the time late blight becomes potentially important for limiting yield, with the consequence that preventative measures against P. infestans are meaningless. Surprisingly, the level of cultivar haulm resistance to late blight did not affect tuber yields in years with an early and strong late blight development. Probably, the positive effect of a longer resistance to the fungus (c. 1 week) was counterbalanced by a later tuber initiation (also c. 1 week). In years with a moderate late blight incidence, less susceptible cultivars were able to produce higher tuber yields on fields with a lower N availability (c. 17–20%), probably due to higher N use efficiency and a better match of N mineralization and N uptake. Under conditions of a relatively high N supply, the tested cultivars with a higher haulm resistance to late blight were not able to improve tuber yields.     

Challenges to Organic Potato Farming: Disease and Nutrient Management

For organic potato producers the two main challenges are disease and nutrient management. Both factors are limited by regulations that on the one hand prohibit the use of chemical fertilisers, especially nitrogen and, on the other hand, most synthetic pesticides. Late blight, caused by Phytophthora infestans is commonly thought to be the factor most limiting yield. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper the state of the art of organic potato management with respect to disease and nutrient management is summarised. In a second part, the interactive effects of N-availability in the soil, climatic conditions and late blight were studied in the presence and absence of copper fungicides from 2002–2004 for the mid-early main-crop potato cv. Nicola. From the experimental work it became clear that copper fungicides in most cases do slow down epidemics adding an average of 3 days to the growth duration. However, only 30% of the variation in yield could be attributed to disease reduction. A model including disease reduction, growth duration and temperature sum from planting until 60% disease severity was reached, and soil mineral N contents at 10 days after emergence could explain 75% of the observed variation in yield. However, the model failed when N-supply was extremely high. The implications of the results on the management of organic potatoes with respect to cultivar choice, nutrient and disease management are discussed. In conclusion, several points emerge from the results: In organic farming, yields are foremost limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deducted from results in conventional farming because of the strong interaction with nutrient status. Resistance clearly remains the most important strategy against late blight in organic potato production. However, as important or even more important than resistance is the early development and bulking behaviour and the ability of a cultivar to make use of organic nutrients efficiently. In the absence of efficient organic pesticides it is possible to reduce blight pressure to a certain extent by arranging the crop in small narrow fields perpendicular to the main wind direction neighboured either by non-hosts or completely resistant potatoes.     

A rapid screening technique for drought resistance in potato (Solanum tuberosum L.)

Summary The reduction in growth in the dark of leaf dises floated over polyethylene glycol 6000 solution of water potential −0.4 MPa, relative to the growth of similar leaf dises floated over water for the same period, varied in the range 10–87% in 28 genotypes. The growth reductions in the genotypes tested were in general agreement with what is known about their drought resistance. Publication No. 906, Central Potato Research Institute, Simla.     

High temperature storage of potato (Solanum tuberosum L.) for processing — a feasibility study

Tubers of three potato cultivars were stored at room temperature (20–39°C, 30–75% RH), under an insulated storage run on passive evaporative cooling (16–30°C, 70–90% RH) and a refrigerated storage (2–4°C, 90–95% RH) for 14 weeks and studied periodically for storage losses, reducing sugar content and dry matter percent of tubers, in order to explore the possibility of storing potatoes for processing at higher temperatures. Physiological losses in tubers remained less than 10% until 12 weeks of storage under evaporatively cooled storage. Reducing sugar contents increased by only 52.4–242.1% in tubers stored in evaporatively cooled storage as compared to 90.5–484.2% increase in tubers stored in refrigerated storage until 14 weeks. Potatoes stored in evaporatively cooled store were more suitable for processing into chips and french fries due to lower physiological losses and lower reducing sugar content of tubers.     

Effects of Mulch and Potato Hilling on Development of Foliar Blight (<Emphasis Type="Italic">Phytophthora infestans</Emphasis>) and the Control of Tuber Blight Infection

Foliar and tuber blight caused by Phytophthora infestans accounts for significant losses in potatoes in field and storage. Nevertheless, limited research has been published on the effects of cultural practices on late blight control. Field experiments were conducted in two years on Howard gravely loam soil in New York State to evaluate the effectiveness of mulching using oat straw and hilling in preventing tuber blight infection for cvs Allegany and Katahdin. Potato hilling and mulching had little effect on foliar blight development. The cultivar affected the disease development in the foliage, with cv. Allegany showing lower foliar late blight than cv. Katahdin. Tuber blight incidence averaged 25% for cv. Allegany and 3% for cv. Katahdin in hilled plots, while in the mulched plots the incidence of tuber blight averaged 33% for cv. Allegany and 10% for cv. Katahdin. The straw hay mulch was ineffective in tuber blight control. Tubers set at a soil depth of more than 7 cm had lower tuber blight incidence than shallow tubers set at a depth of less than 7 cm. In both years, hilling provided partial protection of tubers but its effectiveness was limited in the presence of favourable conditions for late blight development. Even though large hills had proportionally a lower tuber blight incidence than medium-sized hills, the difference between the different hill sizes was not significant. These studies suggest that the use of cultivars with foliage resistance to late blight in combination with cultural practices may partially reduce the incidence of tuber blight. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation for endorsement by Cornell University or the US Department of Agriculture.     

氮素形态与马铃薯品质的关系

在田间条件下研究了不同形态氮素对马铃薯块茎硝酸盐含量、淀粉、蛋白质及还原糖含量的影响。结果表明,马铃薯块茎内硝酸盐含量从块茎形成期到成熟收获期是逐渐降低的。使用铵态氮肥并加硝化抑制剂双氰胺可以显著地抑制马铃薯块茎硝酸盐的积累;与硝酸盐含量变化相似,从块茎形成期到收获期蛋白质含量也逐渐降低,不同氮素形态处理对马铃薯块茎内蛋白质含量的影响无显著差异;铵态氮添加双氰胺处理可降低块茎还原糖含量。虽然马铃薯被认为是喜硝作物,但本研究表明,不同氮素形态处理不仅没有造成马铃薯产量的显著差异,而且块茎内淀粉含量也无显著差异。     

Pre-sprouting as a Tool for Early Harvest in Organic Potato (Solanum tuberosum L.) Cultivation

Earlier harvest of potatoes (Solanum tuberosum L.) can be achieved by different pretreatments of the seed tubers. In factorial field trials in 2008–2010, two different pre-sprouting methods were evaluated: conventional pre-sprouting of tubers and pre-sprouting of tubers with stimulation of adventitious root formation (PR). The results were compared with those for untreated seed tubers stored at 4 °C until planting (control). One variety was included in three trials, and two varieties were included in one trial. The new PR method was intended to give faster development and tuber initiation than conventional pre-sprouting, which can be of value when the growing season is restricted or when early harvest is important. Plant emergence, leaf necrosis (as a measure of maturity) and incidence of late blight were assessed during the growing season. After harvest, tuber fresh weight, size and density were assessed. It was found that pre-sprouting treatments gave on average 7 days earlier emergence compared with the control. Necrosis began earlier in pre-sprouted treatments in all cases except for the late variety Sarpo Mira. In 2008 and 2009 potato late blight struck late, after onset of senescence, but in 2010 it struck earlier and the pre-sprouted treatments proved more susceptible than the control. Total tuber yield was 7–24% higher on average in all pre-sprouted treatments in the different field trials. Tests on time of harvest showed that the advantage for the pre-sprouting treatments was maintained during the season, but the difference with the control decreased with time. When the different pre-sprouted treatments were compared, the new PR method proved to be not better than conventional pre-sprouting.     

Cisgenesis Does Not Solve the Late Blight Problem of Organic Potato Production: Alternative Breeding Strategies

Average potato yields in Dutch organic farming systems vary from 15 to 29 Mg/ha and are limited by low input of nitrogen and severe late blight attacks caused by the oomycete Phytophthora infestans. Under Dutch late blight regulations it is mandatory to kill the haulm at 7% infestation. The late blight attacks have been so early in the organic potato production of the past few years that its acreage is now gradually decreasing whereas consumer demand is increasing. Agronomic control strategies have limited success. First priority lies in breeding for highly resistant varieties to safeguard organic potato production in the Netherlands. Cisgenesis, however, is not an option for the organic sector. Although the product of cisgenesis does not contain genes from non-crossable species it is a result of a genetic engineering process which is excluded from use in organic agriculture. As the principles and standards of organic agriculture are process-based, cisgenesis does not comply with the norms and standards of organic agriculture. The arguments of the organic sector go well beyond the alleged risks of the gene technology and relate to the technology itself. Breeding at DNA-level, instead of at whole-plant level, violates the integrity of life as described in the concept of naturalness. The Dutch organic sector is now aiming at increasing the traditional breeding activities including the participation of farmer-breeders in close cooperation with the formal breeding companies. Additional selection methods need to be developed to include required traits other than late blight resistance, such as nutrient efficiency. Recently two varieties have been released with high resistance against late blight based on introgressing genes from Solanum bulbocastanum. Organic agriculture can benefit from marker assisted breeding to achieve adequate pyramiding of different, new sources of resistance.     

Assessing the resistance to gangrene of progenies of potato (Solanum tuberosum L.) from parents differing in susceptibility

Summary The resistance to gangrene (caused byPhoma exigua var.foveata) of progenies from two hybridisation schedules involving cultivars resistant, susceptible, or of intermediate reaction to gangrene was assessed. Two methods of sampling tubers from field-grown single-plant plots of 18 clones representing each progeny were used: one tuber was taken from each plant, and a bulk sample of 18 tubers was selected at random from the whole progeny. Gangrene resistance was assessed after incubating tubers which had been rolled in cornmeal-sand inoculum ofP. exigua var.foveata, and was expressed as a percentage of tubers infected. Results from the two methods of sampling correlated closely, and agreed well with tests in a subsequent year on 10-tuber samples of each individual clone. It is concluded that an 18-clone sample adequately represented each progeny, and that the mid-parent gangrene score satisfactorily predicted the resistance of the resulting progeny. There are indications that susceptibility tended to be dominant. The implication of these findings to breeding for resistance to gangrene is discussed.     

Genetic Diversity and Yield Stability of Potato(Solanum tuberosum L.)

The present study was under taken to investigate the genetic distance and the performance of thirty one potato genotypes in diverse environments.Multivariate and canonical analysis were used to study genetic diversity among the genotypes and stability parameters were estimated according to Eberhart and Russell,Parkinge and Jinks and Freeman and Perkins models for plant height,branch number per plant,tuber number and tuber weight.Thirty one genotypes were grouped in to six clusters with the help of Mahalonobis distance and canonical analysis.The stability analysis revealed that yield was greatly influenced by the environments.Most of the studied genotypes were sensitive for yield with the environment.For over-all performance 'Hera','Chamak','Patnai','Lala pakri','TPS-7','TPS-364','Somerset' and 'Superior' were the best genotypes for tuber yield and breeding material for potato breeding.     

The History of Potato (Solanum tuberosum L.) Research in Spain

Principal activities of the NEIKER-Basque Institute of Agricultural Research contributing to potato research in Spain are described from its origin in 1933 to 2004. In the first period, the genetic crosses begun and the first Spanish variety called “Eminencia” was obtained. From the 1950s (second period) the Station was divided into four sections: virology, ecology, pre-basic potato production and genetics. In 1979 (third period) a new generation of scientists was brought in to reinvigorate activities like genetic breeding and to start new ones, such as tissue culture, nematology, pathology and serology. Since the 1980s, a total of 23 varieties have been registered, which have good industrial attributes or fresh consumption characteristics.     

Varietal and environmental effect on the glycoalkaloid content of potato (Solanum tuberosum L.)

The tubers of 14 potato varieties were analysed for glycoalkaloids. The level of glycoalkaloids in tubers of all the varieties analysed are within the safe limits for human consumption. The peels of tuber contained about 60–70% of the total glycoalkaloids present in the whole tuber. The levels of glycoalkaloids in leaves and tubers were correlated (r=0.865). There was a significant increase in the content of glycoalkaloids in peels of tubers exposed to sunlight. Glycoalkaloid contents increased at the rate of 1.9mg/100g fresh weight per day in peels of Kufri Jyoti tubers exposed to diffused sunlight.     

Foliar and tuber assessment of late blight (Phytophthora infestans (Mont.) de Bary) reaction in cultivated potato (Solanum tuberosum L.)

Summary Host plant resistance is an important component to the management of potato late blight,Phytophthora infestans (Mont.) de Bary. Assessment of potato lines (Solanum tuberosum L.) with various levels of resistance toP. infestans (US8, A2 genotype) were evaluated in field trials, greenhouse controlled environment chambers and inoculated tuber reactions. Five lines (AWN86514-2, B0692-4, B0718-3, Jacqueline Lee, and B0288-17) with strong foliar resistance to late blight were identified in these inoculated field trials. Greenhouse controlled environment chamber studies allowed resistant and susceptible lines to be distinguished, but the 1998 greenhouse results did not correlate well with field data. Four lines (A084275-3, Bzura, MSG007-1, and MSG297-4RD) evaluated by a digital image analysis technique demonstrated tuber resistance based upon average reflective index values in the inoculated tuber studies. Tuber resistance did not correlate with field foliar resistance. Based upon these results, field assessment of foliar reaction toP. infestans provides the best measure for assessing late blight resistance in potato. Tuber resistance to late blight can be identified among lines with varying levels of foliar resistance.     

Screening for resistance to early blight (Alternaria solani) in potato (Solanum tuberosum L.) using toxic metabolites produced by the fungus

Summary The phytotoxic components of the culture filtrate of the fungusAlternaria solani Sor, which causes early blight in potato, were used in this study to differentiate between resistant and susceptible genotypes selected to represent a range of reactions when screened in the field. Detached leaflet assays, using spores and toxic metabolites from the culture filtrate, were compared with field ratings and a whole-plant glasshouse test. Rank correlations between several detached leaflet tests were highly significant (P<0.01) but the correlations between these tests and the glasshouse and field tests were poor. The disease ratings obtained in the various tests were clustered into four groups and assigned to resistance classes. For many of the genotypes there was a good correspondence between resistance classes for all test methods. Divergent results between tests were associated with foliage maturity characteristics of the genotypes. Contribution no. 3879050 of the Lethbridge Research Station.     

Unsaponifiable lipids from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary Fractions containing Δ⁵- and Δ⁷-sterols, 4-methyl-sterols, triterpenic alcohols, tocopherols and hydrocarbons were isolated by TLC from petroleum ether extracts of the haulm and tuber sprouts of cv Désirée. Sterol and triterpenic alcohol fractions of unsaponifiable lipids of the haulm and tuber sprouts were found to contain twelve sterols and four triterpenic alcohols, respectively. 24R-4-stigmasten-3-on, Δ⁷, Δ⁷, lanosterol, cycloeucalenol and obtisufoliol have not been identified previously in unsaponifiable lipids from haulm and sprouts. In the hydrocarbon fractions of the haulm extract, C₂₃-to C₃₃-n-parafins, C₁₉-and C₃₁-cyclohexyl hydrocarbons, C₂₂-to C₃₈-olefins and squalene were identified, and in the hydrocarbon fractions of the tuber sprouts C₁₂-to C₂₆-olefins and squalene were identified.     

Effect of crop rotation,cultivar and nematicide on growth and yield of potato (Solanum tuberosum L.) in short rotations on a marine clay soil

Summary The effects of cropping frequency on the yield of potato and on the development of soil-borne diseases was studied from 1979 to 1985 in a crop rotation experiment on a marine clay soil. Tuber yield decreased markedly with increasing cropping frequency. The yield of cv. Hertha was reduced by 27% in continuous cropping and by 15% in a wheat/potato or sugar beet/potato rotation, when compared with the rotation wheat/sugar beet/oats/potato. However, a pot experiment showed that yield depression in continuous cropping depended on the cultivar used. Crop growth declined in the second part of the growing season, and senescence accelerated as the cropping frequency increased.Verticillium dahliae was the most important yield-reducing factor. Root infection by this fungus was stimulated by the root-lesion nematodePratylenchus neglectus.     

马铃薯防御酶系活性与其抗晚疫病的关系

应用比较生理学方法,以6个对晚疫病抗性不同的马铃薯品种为材料,研究无病原菌浸染及病原菌浸染后抗、感病品种的马铃薯叶片中防御酶系活性的变化与其抗晚疫病的关系。结果表明:无病原菌浸染及病原菌浸染后,抗病品种比感病品种有较高的PPO、POD和-β1,3-葡聚糖酶活性。因此认为PPO、POD和-β1,3-葡聚糖酶活性与马铃薯抗晚疫病有关。另外,接种后各指标测定结果均不同程度地高于无病原菌浸染时期,表明病原菌浸染后诱导马铃薯体内与抗晚疫病有关的防御酶活性升高。本研究从防御酶活性变化方面阐明马铃薯抗病的生理基础,为马铃薯抗病生理选种提供理论依据。     

Causes of differences in growth pattern,yield and quality of potatoes (Solanum tuberosum L.) in short rotations on sandy soil as affected by crop rotation,cultivar and application of granular nematicides

Summary A crop rotation experiment was carried out on a light sandy soil in 1979–1986 to study the effects of the frequency of potato cropping on yield, quality and on the occurrence of soil-borne pathogens other than potato cyst nematodes. Tuber yield decreased markedly with increasing cropping frequency, but also depended on what crops were grown in rotation with potato. Growth during the early part of the season, as well as the length of the growing period, were reduced in short rotations. The fungiVerticillium dahliae andRhizoctonia solani, and root-knot nematodes (Meloidogyne spp.) were the most important yield reducing pathogens. The effects of rotation depended on the cultivar used. The percentage of mis-shapen tubers increased with increasing cropping frequency and after application of granular nematicides, but the incidence of common scab (Streptomyces scabies) was not affected.     

Applied Biotechnology to Combat Late Blight in Potato Caused by <Emphasis Type="Italic">Phytophthora Infestans</Emphasis>

Potato is an important crop, grown worldwide. It suffers from many pests and diseases among which late blight, caused by the oomycete Phytophthora infestans, is the worst. The disease is still causing major damage in many potato production areas and control is only possible by applying fungicides frequently. The knowledge on the molecular biology and genetics of the interaction between the plant and the oomycete is developing rapidly. These are relevant fields of study, currently dominated by the discovery of many resistance genes and numerous effector proteins and the analysis of their specific mode of action. These studies may yield essential information needed for the development of durable resistance. The long-term and worldwide effort to breed for resistance so far has had little effect. A novel breeding approach may change this. It is based on cisgenic modification (CM) consisting of marker-free pyramiding of several resistance genes and their spatial and temporal deployment yielding dynamic varieties that contain potato genes only. It is envisioned that this CM approach with potato’s own genes will not only prove societally acceptable but may also result in simplifications in the legislation on use of the CM approach. Various parties in the potato research arena intend to cooperate in this novel approach in a number of developing countries where potato substantially contributes to food security. The use of resources such as land, water and energy improves when the effect of late blight is markedly reduced.     

Resistance of Potato Tubers to a Highly Aggressive Isolate of Phytophthora infestans in Relation to Tuber Age

The goal of these studies was to evaluate the influence of tuber age on the expression of resistance to Phytophthora infestans in five selected potato genotypes (three cultivars and two clones) varying in tuber resistance and maturity type, and also to select the best time for testing potato tubers for resistance to blight. Resistance was evaluated by inoculating whole tubers at 13 different times as they progressively aged during growth and storage. Tuber age was expressed as weeks after planting. Tubers were rated from week 13 (late July) until week 43 (late February) for tubers planted on 27–28 April, over three consecutive seasons (2001–2003). Analysis of variance performed on tuber resistance data showed significant effects of genotype, year and tuber age. Significant contributions of genotype × year, genotype × tuber age, year × tuber age and year × genotype × tuber age interactions were also detected. A slight increase in tuber resistance with tuber age was observed for cvs Bzura, Sokół and Irga, while the opposite trend was observed for the clones 97-A-63 and DG 92-227. Changes in tuber resistance with age of tested genotypes were not related to their maturity type. The period of most stable expression of tuber resistance was observed when tubers were tested between the 16th and 28th week after planting.