Potato Crop Response to Genotype and Environment in a Subtropical Highland Agro-ecology

Potato response to environment, planting date and genotype was studied for different agro-ecological zones in Lesotho. Field experiments were conducted at four different sites with altitudes ranging from 1,655 to 2,250 m above sea level during the 2010/2011 and 2011/2012 summer growing seasons. Treatments consisted of three cultivars that varied in maturity type, two planting dates and four sites differing in altitude and weather patterns. Various plant parts were measured periodically. To understand and quantify the influence of abiotic factors that determine and limit yields, the LINTUL crop growth model was employed which simulated potential yields for the different agro-ecological zones using weather data collected per site during the study period. Observed actual crop yields were compared with model simulations to determine the yield gap. Model simulations helped to improve our understanding of yield limitations to further expand potato production in subtropical highlands, with emphasis on increasing production through increased yields rather than increased area. Substantial variation in yield between planting date, cultivar and site were observed. Average tuber dry matter (DM) yields for the highest yielding season were above 7.5 t DM ha^?1 or over 37.5 t ha^?1 fresh tuber yield. The lowest yield obtained was 2.39 t DM ha^?1 or 12 t ha^?1 fresh tuber yield for cultivar Vanderplank in the 2011/2012 growing season at the site with the lowest altitude. Modelled potential tuber yields were 9–14 t DM ha^?1 or 45–70 t ha^?1 fresh yield. Drought stress frequently resulted in lower radiation use efficiencies and to a lesser degree harvest indices, which reduced tuber yield. The site with the lowest altitude and highest temperatures had the lowest yields, while the site with the highest altitude had the highest yields. Later maturing cultivars yielded more than earlier maturing ones at all sites. It is concluded that the risk of low yields in rain-fed subtropical highlands can be minimised by planting late cultivars at the highest areas possible as early as the risks of late frosts permit.     

Effect of Different Defoliation Systems of Ryegrass–Clover on Yield and Selected Quality Parameters of Organic Potatoes (Solanum tuberosum L.) for Industrial Processing at Harvest and After Storage

The nitrogen supply plays an important role in achieving quality characteristics in organic potato farming. Different defoliation systems of ryegrass–clover may influence the amount of fixed nitrogen available to the tubers. In a field experiment, the effect of different defoliation systems (cutting, mulching and a combination of them) of the pre-crop ryegrass–clover on selected quality attributes of organically grown potatoes, destined for processing into French fries (cv. Agria) or crisps (cv. Marlen), were conducted in two consecutive years (2003 and 2004). Parameters studied included compounds related to the sensory properties of potato food (tuber dry matter, starch, reducing sugars) as well as nutritional quality (nitrogen, minerals). Selected agronomic parameters such as total tuber yields and tuber size distribution were also compared. Furthermore, the influence of additional slurry fertilisation and 4 months of storage on these parameters were investigated. Total yields and portion of tuber yield 50–60 mm were significantly affected by the pure mulching variant in 2003. In 2003, the starch concentration at harvest, as well as after storage, was above the required minimum of 22% (cv. Marlen) and 19% (cv. Agria), while in 2004, this was slightly beneath these values. In 2004, a significant increase of starch concentration by the pure cutting variant was observed. In both years, mulched ryegrass–clover caused a decrease in tuber DM contents of 2.10 and 3.54%, respectively, compared to the cutting systems. Fertilisation significantly decreased DM and starch concentration. In 2004, the reducing sugar concentration of tubers of cv. Marlen from the pure cutting system was with 2.1 g kg^?1 FM above the required maximum of 1.5 g kg^?1 for crisps. In addition, storage led to a three to fivefold increase of reducing sugars concentrations in the tubers in this year. After slurry fertilisation, 8.8% higher N contents and up to 36% higher K concentrations were measured. Mulching of the pre-crop combined with slurry application led to an up to 61% higher tuber K concentration compared to the cutting system. The results indicate that different defoliation systems of the pre-crop ryegrass–clover and slurry fertilisation had only minor effects on internal tuber quality attributes. Quality parameters were more affected by the prevailing weather conditions in combination with the genotype of different potato cultivars.     

Seed tuber production from true potato seed (TPS) in Egypt and the influence of environmental conditions in different growing periods

Summary The effect of environmental conditions on seed tuber production from true potato seed (TPS) in nurseries was evaluated in different growing periods during two seasons in Egypt. In the autumn season, high soil and air temperatures reduced emergence and initial foliage development of early-sown seedlings, and decreased tuber yields. In late-sown seedlings low night temperatures and short daylengths caused early tuberization, poor foliage development and low tuber yields. In the spring season, low temperatures and short daylengths resulted in a slow initial foliage development and early haulm-tuber competition for assimilates in early-sown seedlings. However, tuber yields were higher than for late-sown seedlings, presumably because net assimilation and assimilate partitioning to the tubers were impaired by above optimum air and soil temperatures in May and June. Slow development of true seed-sown plants caused a high sensitivity towards adverse environmental conditions and would limit yielding ability in Egypt.     

Yield and tuber characteristics of 4x progeny from 2x×2x crosses

Summary Unrelated, unselected 2x haploid-species hybrids that produce 2n eggs, by second division restitution and 2n pollen due to first division restitution were intercrossed to generate 4x progeny. The 19, 4x families were compared with seven cultivars for tuber yield, tuber appearance and tuber set. The mean yield of the 4x families was 30% higher than the mean yield of the cultivars. The best five 4x families outyielded the best five cultivars by 57% and 69% at two locations. Cultivars were superior for tuber appearance and tuber set. The high yields of the 4x families are due to genetic diversity of the 2x parents and their ability to transmit that diversity to the 4x progeny utilizing 2n gametes. The potential of the 2x×2x breeding method is dependent on developing 2x hybrid clones that form 2n eggs and possess desirable tuber types; clones producing 2n pollen and good tuber quality are available.     

Management of plant residue for cassava (Manihot esculenta) production on an acid Ultisol in Southeastern Nigeria

A study consisting of two experiments was conducted in southeastern Nigeria during 1983 and 1984 to determine whether cassava (Manihot esculenta Crantz) production on sandy, acid Ultisols could be improved by residue management techniques. One experiment studied the effect of location of Eupatorium odoratum mulch on soil properties and crop growth. A second experiment studied the effect of tillage system and Eupatorium odoratum mulch on soil properties and crop growth. In both experiments mulch was applied at an annual rate of 12 t¹ ha⁻¹ (25% moisture content) in a split application at planting and 150 days after planting (DAP). No fertilizer was applied during the experiment.Concentration of mulch in the plant row resulted in values of within-row bulk density in the surface 0.10 m which were lower by 15% and 13% in 1983 and 1984, respectively. Tillage in combination with mulch reduced bulk density in the surface 0.10 m by an average of 10% and 9% in 1983 and 1984, respectively. No significant differences were found among other treatments. Soil chemical properties were unaffected by treatments in both experiments. Cassava tuber yield was unaffected by location of Eupatorium odoratum mulch. Both plowing and no-tillage when combined with mulch improved tuber yields. Cassava tuber yields of untilled plots were 16.8 and 12.7 t ha⁻¹ during 1983–1984, and 13.1 and 8.3 t ha⁻¹ during 1984–1985 in mulched and unmulched treatments, respectively. Tuber yields of tilled plots were 14.5 and 13.1 t ha⁻¹ during 1983–1984, and 11.3 and 6.9 t ha⁻¹ during 1984–1985 in mulched and unmulched treatments, respectively.     

Efficacy of Seed Aging and Gibberellin Treatments for Manipulating Apical Dominance,Tuber Set and Size Distribution of cv. Shepody

The cultivar Shepody has excellent early processing qualities and produces above average tuber yields but sets relatively few tubers that often become excessively large relative to market demand. Optimizing tuber set and size of Shepody for seed and frozen processing markets currently entails adjusting in-row spacing and vine kill date. However, arresting tuber growth by vine killing for size control sacrifices yield potential. Aging seed by storing at 12, 22, and 32°C for 80-, 450-, and 900-degree days, or gibberellin (GA) treatments, were evaluated as more direct approaches for modulating stem number (apical dominance), tuber set, and size distribution relationships. Shepody proved to be inherently resistant to high temperature-induced age-priming treatments. In contrast to other cultivars studied previously, age-priming Shepody seed during storage had no effect on plant emergence and the resulting increases in stem number, tuber set, and associated decreases in average tuber weight were marginal. By contrast, GA applied as seed dip or spray effectively hastened plant emergence, reduced apical dominance, increased tuber set, and decreased average tuber size. The magnitude of these GA-induced effects depended on concentration and application technique (seed dip versus spray). For frozen processing, GA applied as a seed dip at 1 mg L^-1 added an additional tuber per plant and decreased average tuber size by 15% without affecting U.S. No. 1 tuber yields and gross returns; however, 2 and 3 mg L^-1 GA decreased U.S. No. 1 tuber yields and crop value by an average of 16 and 14%, respectively. Spray applications of 2–6 mg L^-1 GA also reduced U.S. No. 1 tuber yield and frozen processing value. Conversely, the increase in tuber set (1.5 tubers plant^-1) and associated 25% reduction in average tuber weight induced by 2 mg L^-1 GA applied as either dip or spray increased gross crop values on a seed contract by 25 and 38%, respectively. The differential efficacies of dip versus spray applications of GA on tuber set and size distribution were likely attributable to differences in GA deposition on the seed. Applying low concentrations of GA to cut seed of Shepody as either a dip (1–2 mg L^-1) or spray (2 mg L^-1) effectively modulated tuber set and size to significantly increase gross returns for seed, and to better satisfy the needs of processors for more moderate size tubers.     

The response of potatoes to a single transient heat or drought stress imposed at different stages of tuber growth

Summary The effects of a single treatment of heat or drought stress imposed at different stages of tuber growth, were investigated in two potato cultivars, Désirée and Cara. Both stresses impaired dry matter accumulation in tubers, and tuber yields. Stress imposed at early stages of tuber growth, when tubers were less than 20 mm in diameter, had little effect on dry matter accumulation, whereas stress imposed later resulted ingnificant losses of dry matter in tubers. Stress imposed during later tuber growth increased the percentage of tubers sprouting in the soil. Tuber malformation was less affected. The adverse effects of heat on tuber yield and quality seemed to be greater than those of drought. Drought increased the content of total soluble solids (TSS) and lowered the osmotic potential in the tuber tissue of both cultivars. These effects were detectable even 55 days after stress relief. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No 984-E, 1984 Series. This investigation was sponsored by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

Effect of Nitrogen Rate on Growth,Yield, Economics and Crisps Quality of Indian Potato Processing Cultivars

A field study was conducted during 2000–2001 and 2001–2002 at the Central Potato Research Institute Campus, Modipuram, India, in order to increasing the processing-grade tuber yield of India’s first ever developed processing potato cultivars, Kufri Chipsona-1 and Kufri Chipsona-2. Tuber yield and post-harvest quality characteristics were evaluated in response to five N levels (0, 90, 180, 270 and 360 kg N ha^-1). The crop growth traits (stem number, plant height and compound leaf number) responded positively to N application, whereas the effect of N fertilization on processing-grade tuber number, total tuber number per ha and tuber number per plant was quadratic. There was a steady increase in tuber weight per plant, processing-grade tuber yield, total tuber yield and biomass yield in response to N application. Kufri Chipsona-1 produced a 23.6% higher tuber yield per plant than Kufri Chipsona-2. Agronomic N use efficiency decreased linearly with increased N doses. Specific gravity and tuber dry matter percentage responded positively to N application, while crisps colour (at harvest and after storage) and reducing sugars remained unaffected. Cultivar was the major factor that influenced the tuber quality parameters (specific gravity, crisps colour). Higher values of these quality traits were observed in Kufri Chipsona-2 as compared to Kufri Chipsona-1. Net income and benefit cost ratio (B:C) indicated that Chipsona cultivars should be fertilized with 270 kg N ha^-1 for realizing higher processing-grade yields and desirable quality tubers.     

Nitrogen fertilizer efficiencies on potatoes

Nitrogen fertilizer efficiencies must be known to successfully apply N fertilizer according to crop growth needs. The objective of this study was to determine the recovery, partitioning, and translocation of N fertilizer applied at different times for potato production. Russet Burbank potatoes were fertilized preplant with¹⁵N-depleted ammonium sulfate, and during early and late tuber growth with urea containing K¹⁵NO₃ in 1978 or (¹⁵NH₂)₂CO in 1980. All N applications increased tuber yields above the control treatments. The N recovery efficiency was 60% for the preplant N application, and over 80% and near 60% for the N applications during tuber growth in 1978 and 1980, respectively. Good agreement was found between the isotope and difference methods of determining N recovery efficiencies. Labeled N was initially concentrated in the stems and leaves, particularly if applied during tuber growth. Over 80% of the assimilated, labeled nitrogen was found in the tubers at the start of plant maturation. These data indicate that a significant improvement in N fertilizer efficiency would result from split N fertilizer applications made according to crop growth needs.     

Relationships between weather,plant spacing and the incidence of hollow heart in Norgold Russet potatoes

Partial regression analysis of ten years’ data showed the percent of hollow heart (HH) tubers by weight in Norgold Russet potatoes increased with an increase in number of days and rainfall between tuber initiation and plant killing, and decreased with an increase in plant population and degree day accumulation during the same period. Highly significant third order partial correlation coefficients for these variables with percent HH were: days between tuber initiation and plant killing 0.699, rainfall between tuber initiation and plant killing 0.320, plant population -0.530 and degree day accumulation between tuber initiation and plant killing -0.753. When these variables were used in a multiple linear regression model with% HH as the dependent variable the coefficient of determination (R²) was 0.72. The model was not significantly improved by including solar radiation, yield of tubers, number of tubers, or soil moisture at tuber initiation as other independent variables.     

A framework for determining the efficient combination of organic materials and mineral fertilizer applied in maize cropping

Application of organic manures and composts in crop production has been strongly encouraged in many places but often without due consideration to their quality and price. Since organic amendments can vary greatly in composition and mineralization rate, a framework is needed to make rational choices on their use as replacements of inorganic fertilizer, especially when considering poor quality organic materials. A field experiment was carried out with maize grown annually for 5 years on a Rhodic Kandiustox in Thailand to test response to mineral fertilizer (at 0-0 to 125-55 kg N-P ha⁻¹ yr⁻¹), compost (0.59% N, 0.31% P and 0.55% K at 0-7500 kg ha⁻¹ yr⁻¹) and stubble removal. The DSSAT model was calibrated to predict yields using the first year's trial data and then used to predict treatment yields for the following 4 years. The Seasonal Analysis module of DSSAT using Dominance Analysis showed that mineral fertilizer (125-55 kg N-P ha⁻¹ yr⁻¹) with stubble return gave the highest net profit whereas the highest rate of compost without mineral fertilizer gave the biggest loss. The yield response was attributed primarily to N supply rather than P. Effects of compost, mineral fertilizer, stubble management, and their interactions on yield and profit were not related to bulk density or soil available water capacity even though soil organic matter (SOM) levels increased. With stubble return, the highest rate of mineral fertilizer increased SOM whereas with compost application or stubble removal it did not. The DSSAT simulation of yield indicated that the low quality compost would only be as profitable as mineral fertilizer if the N concentrations are 3-4 times higher than the present compost (1.8-2.4% N) or if the compost price is greatly reduced. The DSSAT yield simulation and Seasonal Analysis provided a framework whereby the suitability of compost as a N fertilizer replacement for maize could be determined based on its composition, rate of application and price. Further validation of this approach is needed where the organic amendments have significant effects on soil physical properties and where other nutrients besides N are a significant factor in the crop yield response.     

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.     

Potato production from true potato seed (TPS) in Egypt: Effect of the growing season on seedling development,recovery from transplanting and yield

Summary Ware potatoes were produced from true potato seed by transplanting seedlings to the field in different growing periods to evaluate environmental constraints of this production method in the Nile delta. In the autumn season, with high temperatures and long-day conditions during seedling culture in the nursery and transplant establishment in the field, seedling development was fast, and transplants resumed growth within 5 days of transplanting in the field. Tuber yields ranged between 120 and 160 dt ha⁻¹. In the spring season, with low temperatures and short-day conditions during the initial growing phase, seedling development in the nursery was slow and biomass partitioning between above ground organs (stems, leaves) and tubers was shifted towards the tubers. This partitioning was further enhanced by transplanting the seedlings in the field. Seedlings recovered only slowly from transplanting or died. It is concluded that potato production via transplants is poor in the spring season when premature tuberization of seedlings in the nursery leads to slow field establishment and low tuber yield.     

Response of Russet Burbank and Shepody potatoes to nitrogen fertilizer in two cropping systems

Russet Burbank and Shepody potatoes were grown with at-planting N fertilizer rates ranging from 0 to 270 kg ha^?1 during 1986 through 1989. Experiments were conducted each year following small grains and red clover. Total yields and tuber size were strongly increased by N on most sites where potatoes followed small grains. Specific gravities declined with increasing N rate. Total yields of Russet Burbank and Shepody were optimized at an average of 196 and 211 kg ha^?1 of N, respectively, following small grains. The effect of N fertilizer on yields was much less dramatic following red clover. Total yields averaged 88% of maximum with only 45 kg ha^?1 of N applied, compared to 77% of maximum for this N rate following small grains. Total yields for the two varieties were optimized at 126 and 136 kg ha^?1, respectively. U.S. #1 yields were generally not increased at N rates above 45 to 90 kg ha^?1 following red clover and tuber size was not increased at rates above 90 to 135 kg ha^?1. Based on these studies, the N fertilizer credit for red clover grown prior to potatoes can be up to 75 kg ha^?1. Maintenance of tuber quality necessitates conservative use of N fertilizer when potatoes are grown following legumes. The highest N rates tested suppressed total yields of Russet Burbank, a late-season, indeterminate variety, by approximately 9% averaged over cropping systems.     

Economic Optimum Nitrogen Fertilization Rates and Nitrogen Fertilization Rate Effects on Tuber Characteristics of Potato Cultivars

The objective of the research was to determine the economic optimum nitrogen (N) fertilization rates and to determine the effects of N fertilization rates on tuber characteristics and fresh mass loss after storage under cold and ambient conditions of four potato cultivars, Ágata, Asterix, Atlantic, and Monalisa. The experiments were, simultaneously, conducted in the same area and similar experimental conditions during the fall/winter period in Viçosa, Minas Gerais State, Brazil. In each experiment, five N fertilization rates (0, 50, 100, 200, 300 kg ha^?1) were evaluated in a randomized complete block design. For all cultivars, increasing N fertilization rate increased total and marketable yields and tuber dry matter yield up to a maximum following a quadratic model. Increasing N fertilization rate linearly increased the tuber protein concentration of Atlantic and Monalisa and had no effect on tuber pH. N fertilization rate effects on tuber mass, tuber titratable acidity, and fresh mass loss during storage were cultivar-dependent. N use efficiency (tuber yield divided by N fertilization rate) decreased with increase in N fertilization rate. The economic optimum N fertilization rates ranged from 147 to 201 kg ha^?1 depending upon cultivar and relative prices of N and potato tubers. Depending on the cultivar, under favorable price conditions (low N price and high tuber price), the economic optimum N fertilization rates to be applied by potato growers were 92–95% of the estimated N fertilization rate for obtaining the maximum potato yield, whereas under unfavorable conditions (high N price and low potato tuber price) the economic optimum N fertilization rates to be applied should be decreased to 86–92% of the rates for maximum yield.     

The effect of irrigation strategies during tuber initiation on marketable yield and development of common scab disease of potato in Russet Burbank in Tasmania

Summary Management of soil moisture deficit during tuber initiation and early development was important for the optimisation of net and marketable tuber yields of cv. Russet Burbank on the typical red ferrosol cropping soils of Northern Tasmania, Australia. An effect of reduced water input during the tuber initiation period on increasing incidence of common scab disease was noted in one trial. In subsequent trials disease inoculum levels were not sufficient to show differences between treatments despite a history of disease at the site. For optimisation of marketable yield and probable assistance in the management of common scab disease it is recommended that irrigation scheduling to known soil moisture deficits be adopted during this period of growth on this soil type.     

1,4-Dimethylnaphthalene treatment of seed potatoes affects tuber size distribution

1,4-DMN is a relatively new sprout inhibitor for use on maincrop and seed potatoes. Despite its registration as a “dormancy enhancer” for seed, relatively little is known about its effects on plant establishment and productivity. The main objective of this study was to evaluate the effects of 1,4-DMN on the productivity of seed potatoes. ‘Umatilla Russet’ (UR), ‘Ranger Russet’ (RR), and ‘Russet Burbank’ (RB) seed tubers were stored at 4, 7, and 9 C over three seasons to create 80-, 554- and 642-degree-day seed, and 1,4-DMN was applied to maintain dormancy several times during each season. 1,4-DMN residue levels at the end of storage were lower in seed aged at higher temperatures. Multiple applications of 1,4-DMN at higher-than-label rates were necessary to effectively inhibit sprouting of seed of all cultivars stored above 4 C. In field trials, depending on cultivar and year, 1,4-DMN either delayed plant emergence slightly or had no effect. 1,4-DMN increased stem numbers from RB and UR seed, but not from RR seed. 1,4-DMN reduced total tuber yields by 3.2 to 5.6 t ha^?1 (5% to 9%), and U.S. No. 1 tuber yields by 4.8 to 7.8 t ha^?1 (8% to 15%) in all cultivars, regardless of seed tuber age. 1,4-DMN also reduced the average tuber weight for all three cultivars and shifted the size distribution from larger (> 284 g) to smaller tubers. 1,4-DMN reduced the respective yields of > 397-g, 340-to 397-g, and 284-to 340-g tubers by 43%, 19%, and 18% for RR seed, 31%, 14%, and 11% for RB seed, and 40%, 47%, and 27% for UR seed. Conversely, depending on cultivar, yields of smaller tubers (≤170 g) were 11% to 38% higher from 1,4-DMN-treated seed. The shift in tuber size distribution for RR was accompanied by a 1,4-DMN-induced increase in tuber number per plant and per hectare. However, no such effects on tuber set occurred in RB and UR. Moreover, in most cases, the 1,4-DMN effects on yield and tuber size distribution were independent of seed age. Since the 1,4-DMN-induced shifts in tuber size distribution were greater than the reductions in total and U.S. No. 1 yields, 1,4-DMN may be a suitable treatment to reduce average tuber size and increase yield and uniformity of specific size classes of tubers to more closely match market requirements.     

Manipulating Stem Number, Tuber Set and Size Distribution in Specialty Potato Cultivars

Manipulating seed physiological age is an effective method to alter tuber set and size distribution for many cultivars. However, cultivars Cal White, Red La Soda, Chieftain, Yukon Gold, and Satina were largely insensitive to high temperature-induced age-priming treatments. Gibberellins (GA) also have potential for altering tuber set and size development. When applied to cut seed of the five cultivars, GA hastened plant emergence, increased stem and tuber numbers per plant, and decreased average tuber size. The optimum concentration of GA for shifting tuber size distribution to maximize crop value without decreasing total yield depended on cultivar. Total yields decreased substantially in all cultivars with 10 mg L^?1 GA but lower concentrations (0.5–4 mg L^?1) either increased yields of Red La Soda, Yukon Gold, Chieftain and Satina by 11, 13, 15, and 24 %, respectively, or had no effect (Cal White). GA-induced increases in tubers per hectare ranged from zero (Cal White, Satina) to 36 % (Chieftain) and associated increases in yields of premium priced creamer size potatoes (C size; 10–66 g, 28–51 mm diameter) ranged from 0 to 140 %, depending on cultivar and length of the growing season. Increases in total crop values ranged from 7 to 30 % (Chieftain) with the optimum concentrations of GA, which also varied by cultivar. Effective use of GA to alter tuber size distribution for increased value depends on cultivar, concentration, and harvest timing.     

Leaf Positions of Potato Suitable for Determination of Nitrogen Content with a SPAD Meter

Abstract

Hand-held SPAD meter can be used to evaluate the leaf nitrogen status of potato. For practical use, it is necessary to select a proper compound leaf, a proper leaflet within compound leaf and position of leaflet suitable for measurement. Therefore, field experiments were conducted in northern China in 2009 and 2010. The SPAD values, plant growth, N uptake of potato plants at tuber initiation and tuber bulking stages under different N supply levels, and final tuber yields were examined. The criteria for determining the most suitable leaf, leaflet and position within a leaflet are that the SPAD values show less variation at a given N supply level, and show a more sensitive response to different nitrogen levels. Our results showed that the coefficients of variance of SPAD values ranged from 8.7 to 25.9% with a leaf N concentration range of 2.1 to 3.8 gN 100 g-¹ at tuber initiation stage, and 7.2 to 21.6% with leaf N concentration range of 0.96 to 1.26gN 100 g-¹ at the tuber bulking stage. The SPAD values of the 4th compound leaf from apex were more stable and more sensitive to the nitrogen level than those of other leaves, suggesting that the 4th compound leaf is suitable for estimating the leaf N status using a SPAD meter. Within a compound leaf, the SPAD value of the top leaflet was more sensitivethan the other leaflets to nitrogen supply, whereas it was less stable, making it difficult to chose the leaflet for measurement. However, the top leaflet emerges and expands much earlier than the side leaflets, and should be better for SPAD value measurement. The SPAD measurements at the top point of the top leaflet of the 4th leaf demonstrated both less variation and higher sensitivity to nitrogen supply. Therefore, we conclude that the top point of the top leaflet of the 4th compound leaf is the best position for potato N status diagnosis using a SPAD meter.     

The potential for production of high quality seed potatoes in Tierra del Fuego Island, Argentina

Summary In Argentina, different areas are suitable for seed potato production: however, each has particular problems, mainly related to different pest and diseases. Tierra del Fuego Island is well isolated from traditional potato growing areas. Therefore, it was tested for its potential for seed production. The cultivars Achatt. Mailén INTA. Pampeana INTA and Spunta were grown in Río Grande, San Pablo and Ushuaia from 1991–1994. Nematode presence and aphid population dynamics were recorded. Average tuber yield ranged from 20.1–37.6 t ha⁻¹. After three years PVY and PLRV remained low (0–1% for different cultivars and locations). Moreover, seed tubers obtained were physiologically young. Long days, early frosts and strong winds may limit tuber yield in some years. The island can be considered as an ecological “safe haven” and is very suitable to obtain healthy and physiologically adequate seed potatoes.