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The potato is one of the most important food and cash crops in Malawi, but current yields are low and the fertilizer recommendations rely on outdated soil fertility information. To understand the influence of soil factors in limiting current potato production, the mineralogical and physicochemical soil characteristics of 26 farms in the central highlands of Malawi were evaluated. Cluster analysis with clay, crystalline iron oxide, and total carbon content revealed three clusters with two corresponding to Ferralsols and one to Regosols, which are known to exist in the area. In the three clusters, the soil was generally acidic with low exchangeable acidity and aluminium (Al; < 0.7 cmolc kg-1); thus, Al toxicity was not a concern because the soil solution Al would be very low to negatively affect plant growth. Inorganic nitrogen was adequate, while available phosphate and exchangeable potassium (K) were variable within each cluster. However, a deficiency in exchangeable calcium (Ca; < 3.6 cmolc kg-1) and magnesium (Mg; < 1.2 cmolc kg-1) indicated that low base cation concentration was the problem and the potential yield-limiting factor. Soil management, not soil type, appeared to determine soil nutrient conditions based on the current soil Ca and Mg deficiencies and variable K nutrient status. There is a need for updating the current fertilizer recommendations by incorporating K, Ca, and Mg and promoting soil amendment interventions using locally available animal manure and plant ash. Key words: acid soil; fertilizer; Ferralsols, Regosols, Solanum tuberosum L., aluminium toxicity, calcium; magnesium.

Maize grain hardness influences storage pest resistance, a key characteristic valued by smallholder farmers. The structural changes in the endosperm determine grain hardness and are influenced by agronomic practices. The purpose of this study was to establish whether supply of calcium and magnesium based fertilizers can alter physicochemical properties of local and hybrid maize varieties and reduce the infestation by larger grain borer (Prostephanus truncatus (Coleoptera: Bostrichidae)) during storage. Two local and one hybrid maize varieties commonly grown by smallholder farmers in Malawi were cultivated under three fertilizer treatments (NPK (nitrogen, phosphorous, potassium), NPK plus gypsum, and NPK plus dolomite). After harvest, the grains were classified into flint and dent types, followed by P. truncatus infestation and determination of their physicochemical properties. The addition of gypsum and dolomite fertilizers led to higher levels of amylose, total zein and β-14 zein, traits associated with kernel hardness, compared to the application of NPK fertilizer. Moreover, local maize varieties showed higher resistance to P. truncatus infestation, hardness and biochemical properties associated with hardness (total zein, α-19 and β-14 zein, starch lysophosphatidylcholine, and non-starch free fatty acid) compared to hybrid variety. Our study suggests the potential for utilizing Ca and Mg nutrition in maize to improve kernel hardness, thus adoption of gypsum and dolomite by smallholder farmers may be beneficial against P. truncatus during storage.

The aim of this study was to establish the attributes of kernel type based on kernel hardness and its interrelationship with maize endosperm chemical components, which are essential during storage. Three local varieties and one hybrid variety commonly grown by smallholder farmers in central Malawi were used. For storage experiment, the maize samples were infested with Prostephanus truncatus, larger grain borer (LGB) for eight weeks. Due to the high propensity of maize to cross-pollinate, the kernels were classified into flint and dent kernels to establish the physicochemical properties of the kernel type and variety independently. Local variety (L-3) exhibited the lowest number and weight of damaged grains and the highest adult LGB cadavers. Local variety, L-1 and L-3 had significantly the highest proportion of flint kernels type. Moreover, flint kernels of local varieties showed significantly the highest hardness, and the highest content of protein, total zein, α-zein and zinc (p < 0.05). Furthermore, hardness was significantly and positively correlated with total zein and 14 kDa β-zein content (p < 0.05). Zein in the endosperm, particularly 19 and 22 kDa α-zein mainly contributed to distinct hardness of the local varieties hence may contribute to physical barrier of the kernels against storage pests. Key words: Maize, local variety, kernel type, hardness, chemical properties, larger grain borer.

Potato cultivars are propagated by tubers which are sensitive to damage by freezing. Potato has about 100 related wild Solanum species growing naturally in the Americas. When tubers of a spectrum of these species were slowly cooled, most were killed at a few degrees below 0 C. Only tubers of Solanum jamesii, native to the southwest USA, remained firm, sprouted and grew after one week exposure to freezing temperatures as cold as -15C. Differential Thermal Analysis was performed to detect low temperature exotherms (LTEs) in jamesii and similar-sized tubers of cultivars Russet Burbank and Snowden. LTEs, indicating supercooling, were detected only in the jamesii tubers. Survival of potato tubers at freezing temperatures could be useful in several ways. Even non-lethal cold exposure of potato tubers at harvest reduces quality for eating and for seed, but storage at freezing temperatures without damage could help preserve tuber dormancy and limit diseases.

Proper management of N, P, and K fertilizers is considered very important to maximize tuber yield and attain desirable processing quality. Generally, farmers apply NPK fertilizer rates based on the preplant soil tests. However, very limited information is available on the influence of available soil nutrients and in-season NPK application rates on yield and quality of tubers. In the present study, paired soil and tuber samples were evaluated from 170 commercial production sites to evaluate potential relationship between soil nutrients, tuber yield, and tuber quality. These paired samples gave us the opportunity to not only study yield response to fertilizer application rates but also study the relationship between soil nutrient availability and tuber nutrient concentrations. We found that about 50%, 80%, and 70% of farmers applied more NPK than recommended rates, respectively. Our results suggest that, in general available soil NPK increases tuber NPK concentrations and tuber N and K concentrations can reduce specific gravity. Interestingly, tuber P concentration had no effect on specific gravity. We also found some variations in these responses to nutrients (NPK) among cultivars suggesting some genetic control for the traits studied. Results also suggest that application of NPK fertilizers in excess of recommended rates on soils that are already rich in these nutrients does not increase tuber yields and may in fact increase potential environmental degradation associated with excessive fertilization and the cost of production.

The demand for processing potatoes has been increasing in Japan since the 1970s due to changes in eating habits from fresh potatoes to processed products. However, domestic supply of potatoes has not changed for the past five decades and the country is not self-sufficient in potato production. Understanding potato crop and soil-environmental yield limiting factors at growers’ management level is important to guide formulation of better management practices to increase yields. This study was conducted in Hokkaido, Japan, to evaluate the performance of four popular processing potato cultivars under variable soil environment and grower management conditions. The study was conducted by obtaining soil and tuber samples from 90 and 80 fields in Tokachi and Kamikawa districts, respectively, in two growing seasons. These two districts represent very contrasting soil types. Kamikawa has pyroclastic flow deposit soils classified as Inceptisols whereas Tokachi has volcanic ash soils known as Andisols. Paired samples of soil and tubers were evaluated at each of these sites. The results indicated the following: (1) Significant cultivar effect on various measured parameters including tuber yield, tuber number, mean tuber weight and specific gravity. (2) Toyoshiro cultivar performed better than other cultivars in both Tokachi and Kamikawa districts. (3) Yields varied from 21.9 to 68.2 t ha−1 indicating that with good management, there is a considerable yield-improvement opportunity. (4) Interestingly, stem number was significantly affected by soil type. The stem numbers were generally greater in the Kamikawa District suggesting high available N and P and lower available Ca in this region, possibly in conjunction with other unmeasured factors, contributed to greater stem numbers.

Calcium (Ca) nutrition for potato (Solanum tuberosum L.) is important to increase tuber Ca concentration and improve potato tuber yield and quality. High tuber Ca content among other benefits mitig...

Many plants including potato, tobacco, tomato, and geraniums often develop intumescence (oedema) injury, which is observed exclusively on plants grown in controlled environments. Early studies have suggested a link between light quality and intumescence by showing UV and/or far-red light mitigation of injury. Here, we report that intumescence can be mitigated by calcium nutrition. Commercial cultivars of Solanum tuberosum L. cvs ‘Russet Burbank’ and ‘Atlantic’ were grown from in vitro shoot cultures in 20.4 L pots within a climate-controlled greenhouse. Plants were irrigated daily to excess with Peter’s Professional Peat Lite Special 20–10-20 fertilizer (0.52 g·L−1 tap water) supplemented with either 1 mM or 10 mM CaCl2·2H2O. We evaluated 13 replications from both potato cultivars and Ca2+ treatments. Intumescences were observed at about 32 days after calcium treatments began, exclusively on the upper and lower leaf surfaces of Russet Burbank. Upper canopy leaves of Russet Burbank showed approximately 65 and 5% intumescence injury for the 1 mM and 10 mM Ca2+ treatments, respectively. Average leaf calcium concentration was nearly double in the plants supplemented with 10 mM compared with 1 mM Ca2+. Tuber yield and foliage weight were higher in the plants supplemented with 10 mM Ca2+ as compared with 1 mM Ca2+ and suggests that intumescence injury reduced growth and partitioning. These data provide evidence that supplemental calcium can mitigate intumescence injury on susceptible cultivars of potato in controlled environments.

As one of the world’s most important food crops, the potato (Solanum tuberosum L.) has spurred innovation in autotetraploid genetics, including in the use of SNP arrays to determine allele dosage at thousands of markers. By combining genotype and pedigree information with phenotype data for economically important traits, the objectives of this study were to (1) partition the genetic variance into additive vs. nonadditive components, and (2) determine the accuracy of genome-wide prediction. Between 2012 and 2017, a training population of 571 clones was evaluated for total yield, specific gravity, and chip fry color. Genomic covariance matrices for additive (G), digenic dominant (D), and additive × additive epistatic (G#G) effects were calculated using 3895 markers, and the numerator relationship matrix (A) was calculated from a 13-generation pedigree. Based on model fit and prediction accuracy, mixed model analysis with G was superior to A for yield and fry color but not specific gravity. The amount of additive genetic variance captured by markers was 20% of the total genetic variance for specific gravity, compared to 45% for yield and fry color. Within the training population, including nonadditive effects improved accuracy and/or bias for all three traits when predicting total genotypic value. When six F1 populations were used for validation, prediction accuracy ranged from 0.06 to 0.63 and was consistently lower (0.13 on average) without allele dosage information. We conclude that genome-wide prediction is feasible in potato and that it will improve selection for breeding value given the substantial amount of nonadditive genetic variance in elite germplasm.

The formation of cross-links between pectin molecules via Ca2+ in the potato tuber cell wall is a determinant factor on processing properties of potato and the quality of its products such as French fries. Thus, in this study, potato tubers varying significantly in their calcium concentrations were analyzed to investigate whether an increased absorption of calcium by a potato tuber led to an increase in the calcium concentration in the cell wall and how the calcium concentration in the cell wall influenced on the formation of cross-links between pectin molecules via Ca2+. Correlation analysis revealed that calcium absorbed by a potato tuber was bound to the cell wall as a water insoluble form 99 days after planting or later. Furthermore, with an increase in the calcium concentration in the cell wall, the content of chelator soluble pectin increased throughout tuber bulking and maturation stages. However, the degree of methylation was not a limiting factor in the formation of cross-links between pectin chains via Ca2+. Atomic force microscopy images of parenchyma cell walls prepared from mature potato tubers indicated an increase in the amount of calcium cross-linked pectin molecules with an increase in the calcium concentration in the cell wall. The present study demonstrated that the calcium concentration of the cell wall of potato tubers significantly affected the formation of cross-linkages between pectin molecules and, consequently, contributed to an enhanced formation of pectin-calcium networks in the cell wall.

There is growing evidence of excessive use of phosphate fertilizer and high residual soil phosphate levels in arable cropping systems in Japan. However, there is a lack of regional-scale informatio...

Consistent with reports on other plants we recently reported that a potato transgenic line (AT010901) overexpressing sCAX1 show classic symptoms of calcium deficiency shoot tip injury, leaf curling, leaf margin necrosis and tuber internal defects such as hollow heart and brown spots. The present study was undertaken to quantify calcium in various fraction of leaf and tuber tissues of this transgenic and wild type potato clones to understand the development of these deficiency symptoms at normal calcium nutrition (1mM) and its mitigation at higher calcium nutrition (10mM). Plants were grown in controlled environment growth chamber and watered with balanced nutrient solution containing either 1 or 10 mM calcium. The plants overexpressing sCAX1 showed calcium deficiency symptoms while sequestering calcium in the vacuole as calcium oxalate crystals. Various fractions of calcium were qualified in the young and mature leaves as well as tuber tissue. A reduced concentration of water soluble fraction of calcium was most important factor related to the development of calcium deficiency symptoms in the line overexpressing sCAX1. Furthermore, an increase in this fraction appear to explain the alleviation of the deficiency symptoms in these transgenic plants.Ours is the first study to document the significance of water-soluble calcium in the development of calcium-deficiency symptoms in the potato transgenic lines overexpressing sCAX1. Furthermore, our result demonstrates that an increase in this fraction plays a significant role in the alleviation of calcium deficiency symptoms when calcium concentration in the nutrient media is increased. These results provide important insight on the role of sCAX1 in the calcium homeostasis.

Reliable pedigree information facilitates a scientific approach to breeding, but errors can be introduced in many stages of a breeding program. Our objective was to use single nucleotide polymorphisms (SNPs) to check the pedigree records of elite North American potato germplasm. A population of 719 tetraploids was genotyped with an Infinium SNP array, yielding 5063 high-quality markers. Based on pedigree records, the dataset contained 198 parent-offspring trios, of which 182 were consistent with the marker data. For 13 of the 16 trios with a pedigree error, the true parent was identified in the population. By comparing the additive relationship matrix calculated from pedigree with the genetic distance calculated from markers, an additional 24 pedigree modifications were proposed, including the paternity of several varieties developed with bulk pollen. To ensure accurate pedigree records are published in the future, we recommend that new varieties be SNP genotyped and checked against this dataset.

Lysophosphatidylethanolamine (LPE), a natural phospholipid, has been investigated for retarding senescence and promoting the shelf life of fruit and other plant tissues. LPE is a water insoluble phospholipid. For most experimental purposes, LPE is dispersed in water prior to treatment of fruit using sonication. In this study, the water solubility of LPE was improved by mixing it with soy lecithin prior to mixing with water. A combination of LPE and lecithin was used for a dip treatment of banana fruit. Banana fruit at ripening stage 2 (3/4 green) were dipped in this solution for 30 min and then stored at room temperature for 10 d. A combination of 200 mg L −1 LPE and lecithin gave the best shelf life. In this treatment over 75% of the fruit were marketable 7 d after treatment. While only about 20% and 28% of the fruit were marketable in the water (control) and lecithin treated-fruit respectively. Fruit treated with lecithin alone had better shelf life as compared to the control. Furthermore, the LPE + lecithin treatment gave better shelf life as compared to the LPE alone treatment. At 7 d after dip, fruit treated with LPE + lecithin had lower ion leakage from peel tissue, higher pulp firmness, and thicker peel as compare to the control and lecithin treatments. A dip treatment with NAA (1-naphthalene acetic acid) was compared with LPE + lecithin for fruit marketability and changes in various fruit properties during ripening. Although NAA improved shelf life and retarded fruit softening as compared to the control, this treatment resulted in abnormal de-greening of fruit peel tissue. Fruit treated with LPE + lecithin had normal yellow color development and had lower ethylene production as compared to NAA and control treatments. The results of this study suggest that a dip treatment with a combination of LPE and lecithin may have potential for improving shelf life of banana fruit.

Banana is one of the most consumed tropical fruits around the world. It is marketed nearly all year-around and has a relatively short shelf life. Fruits are harvested mature green and treated with ethylene to stimulate ripening before distribution and sale. The fruits generally ripen within 4–5 days after ethylene treatment and sold primarily at yellow stage of ripening. After turning yellow the fruit becomes unsuitable for marketing in 1–3 days. Thus 1–2 days of improvement in the fruit shelf life could enhance the market value of banana. Previous studies conducted in our laboratory have demonstrated that both pre- and postharvest application of lysophosphatidylethanolamine (LPE) can retard aging and improve shelf life of various fruits. The objective of this study was to investigate the possibility of improving shelf life of banana fruit by a postharvest dip in LPE. For this purpose, whole fruits obtained from the market at ripeness stage of 2.5 (about 75% green) were dipped in solution of 500 ppm LPE for 30 minutes and observed for a period of five days at room temperature. Each treatment was applied to 50 uniform fruits. From each hand bought, an equal number of fruits were separated for LPE and control treatments to reduce the variability. Five days after dip treatment, the fruit treated with LPE were firmer and thicker as compared with the control. Starch breakdown was also delayed in the LPE-treated fruits. LPE treatment slowed the development of brown spots on the peel tissue. Both peel and pulp tissue of LPE-treated fruits had lower ion leakage compared with the control. Fruit peel slices treated with LPE for 3 hours also showed a decrease in ion leakage and respiration rate at 24 hours after treatment. Results of the present study indicate that a postharvest dip treatment with LPE may improve shelf life of banana fruit by 1–2 days. These results suggest that LPE may improve shelf life by maintaining membrane integrity, reducing respiration, and slowing the breakdown of starch and cell walls during ripening and senescence of banana fruit tissue.

The impact of mating structure on progeny performance is not routinely analyzed in potato breeding programs, despite the importance of choosing parental lines. Varying degrees of assortative and disassortative mating can have a significant effect on the agronomic performance and cold chipping ability of potato breeding clones. A disassortative mating strategy of crossing parents from different market types can incorporate commercially relevant traits into a market class which lacked that trait. Here we report the effect of mating structure in three breeding families created from parental lines from different market classes, within the same market class, and from self-pollination. Disassortative mating structure produced clones with increased yield and tuber size while assortative mating produced clones with improved cold-storage chipping ability. Inbreeding depression was observed for yield, tuber traits, and chip color in the selfed progeny. Chip color in a russet type clone was improved through crossing with an elite chipping parent, demonstrating a viable method for improving russet processing quality. Mating structure explained a significant proportion of phenotypic variance for yield, tuber, and chipping traits across the three families. Discriminant analysis of principal components and genetic distance based on SNP markers from the SolCAP project were able to discriminate among family types and were informative about the relative diversity generated from each particular cross. A number of promising genotypes from both the russet × chipper family and the chipper × chipper families were identified which outperformed parental varieties for chip color and tuber size.

Common scab (CS) of potato, caused by Streptomyces scabies, is an important disease in the US. CS problems can be avoided using resistant varieties. However, evaluating breeding clones can be complicated by high location and season-based soil and environmental variation. In this study we evaluated the efficacy of screening for CS resistance within the Wisconsin breeding program across multiple environments from 2006 to 2013. In each trial, 60–160 clones were evaluated. We compared the ability to select for CS resistance in a set of 18 dedicated CS screening trials (DST) versus 18 similar parallel standard breeding trials (SBT). Heritability for CS rating across DST was 0.83 vs. 0.53 in SBT. Data analysis from DST was able to separate CS susceptible cultivars (Atlantic, Snowden) from resistant cultivars (Pike, Snowden). However, same data analysis from SBT was not able to separate susceptible from resistant cultivars. Using DST datasets, we estimated the genotypic stability of scab performance across years and locations. We also calculated the probability distributions for the better or worse performance of a given clone vs. a standard variety. Using results from six or more DST we identified five round white clones that outperformed or matched CS tolerant Pike, eleven russet clones that outperformed or matched CS tolerant Russet Burbank and five red or yellow skin clones that outperformed or matched CS resistance level of Dark Red Norland. The approaches utilized here offer useful additional information for breeding programs which aim to improve selection efficiency for scab resistance.

Potato virus Y (PVY) is responsible for the majority of seed potato lot rejections in North America. Some commercial cultivars and breeding lines have major genes for PVY resistance, but their use in North American breeding programs has been limited. Marker assisted selection of PVY resistance can increase the efficiency of identifying resistant plants and integrating resistance into new cultivars. We used markers RYSC3 and YES3-3B, linked to genes Ryadg and Rysto, respectively, to screen 46 breeding clones and cultivars, and identified 19 resistant clones. Resistant parents were crossed with susceptible parents with good market and agronomic traits and molecular marker analysis of each family showed a 1:1 segregation ratio. The persistence of this segregation ratio over 2 years of selection and the lack of major linkage drag as assessed by a breeder rating indicated that there was no evidence of an association of PVY resistance with undesirable traits.

Developing chipping cultivars with improved tuber quality and disease resistance is a major interest for breeders and the potato industry. A popular chipping cultivar ‘Atlantic’, is desired for its high yield and gravity. However, this cultivar suffers from poor internal tuber quality and high scab susceptibility. On the contrary, cultivar ‘Superior’ is known to have excellent tuber internal quality and moderately scab resistance. In addition, this cultivar is known to have high tuber calcium as compared to ‘Atlantic’. The present study intended to generate populations that can be suitable for the genetic study of tuber calcium, internal quality, common scab, and other commercially important traits such as yield, specific gravity and chip quality at the tetraploid level. Two populations obtained by reciprocally crossing the cultivars ‘Atlantic’ and ‘Superior’ were evaluated during 2009 to 2012 at Hancock, Wisconsin. Significant genotype effects and moderately low to high broad-sense heritabilities were identified for all traits evaluated indicating that the observed phenotypic variation has an important genetic component. In addition, the parents differed significantly for all traits across trials, and most genotypes performed in between the two parents but some genotypes were more extreme than the parents. Furthermore, evidence of reciprocal effects was found for some traits. In addition to learning about the genetics of these important traits we were able to identify some genotypes that combined the commercially desired traits of the two cultivars.

There is ample evidence for global warming and resulting climate change. To sustain food production in view of climate change, we need to improve resistance to abiotic stresses in commercially desired cultivars. Using potato as an example, a strategy is illustrated for such improvement by merging physiological and genetic approaches. Potato (Solanum tuberosum L.) is a cool-season crop, cultivated in the temperate zone in North America, Europe, and the highlands of South America, Africa, and Asia. In these areas, frost is often a major factor limiting potato production. Climate change models predict erratic weather patterns including more severe and untimely frost episodes. Cultivated potatoes are highly frost sensitive and are often killed when tissue temperatures fall below −3°C. Several wild potato species are frost tolerant. These species carry two desired traits: 1) They can survive temperatures as low as −6°C while growing under normal conditions (NAFT), and 2) they are able to acclimate in response ...

Cultivated potato (Solanum tuberosum L.) is a highly heterozygous autotetraploid crop species, and this creates challenges for traditional line development and molecular breeding. Recent availability of a single-nucleotide polymorphism (SNP) array with 8303 features and software packages for linkage and association mapping in autotetraploid species present new opportunities for the identification of genomic regions that contribute to high-value traits in cultivated potato. A biparental tetraploid potato population was evaluated across three field seasons and storage trials in order to identify quantitative trait loci (QTL) for multiple tuber traits including fried chip color after 5.5–7.2 °C storage. Tetra-allelic dosage information was used to construct a genetic linkage map that covered 1041 cM and contained 2095 SNP markers with a median marker interval of 0.4 cM. A total of 41 QTL were identified for flower color, tuber yield, tuber number per plant, tuber weight, tuber size, and chip color after various storage regimes. Moderate effect QTL for chip color at 3 months were identified that co-localized with candidate genes vacuolar invertase (VInv), invertase inhibitor (INH2), and apoplastic invertase (Inv ap -b). A separate QTL for chip color after 6 months of storage was identified in the short arm of chromosome 2, and this locus may contribute to variation in senescent sweetening resistance. QTL for tuber weight, length, and width co-localized with a known QTL for plant maturity on chromosome 5. Genome-wide association mapping using a polyploid model detected the tuber size QTL and identified a number of candidate SNPs, but was unable to detect markers significantly associated with chip color.

The important roles of calcium on plant growth and development including cell division and cell elongation is well documented. The purpose of the present study was to determine the impact of root zone calcium on the growth and health of potato apical meristem and on the maintenance of apical dominance. For this purpose, single-node potato cuttings (Solanum tuberosum L. cv. Dark Red Norland) were grown in sterilized modified Murashige and Skoog (MS) media containing varying concentrations of calcium (1 to 3000 μM). After 13 to 30 d of growth, plantlets were harvested and data for height of the main shoot and for the number of axillary shoots produced were recorded. Plantlets were ashed and tissue calcium concentration was determined. Shoot height was retarded with decreasing concentration of calcium in the media. Calcium deficiency induced shoot tip injury and loss of apical dominance. Tip injury was followed by the development of axillary shoots. The number of axillary shoots increased from one to 21 as calcium concentration in the media decreased from 3000 to 1 μM. At calcium concentration of 1500 μM or higher, there was a single main shoot with no axillary shoots. Addition of ethylene glycol tetra acetic acid (EGTA), a calcium chelator, to the media with 2720 μM calcium (sufficient calcium) resulted in the development of shoot injury and in the formation of axillary shoots. Calcium deficiency injury symptoms were prevented by the addition of a calcium analog, strontium, to MS media deficient in calcium. Strontium has been reported to strongly bind to plant cell walls and the inclusion of strontium prevented injury in shoots of plants grown on calcium-deficient media. These results suggest that strontium is able to mimic the role of calcium in the maintenance of cell wall integrity and supports previous studies that showed that calcium deficiency results from cell wall collapse of the subapical cells.

Calcium plays a major role in plant growth and development and in the maintenance and modulation of various cell functions, especially related to membrane structure and function and to cell wall structure. Calcium stabilizes cell membranes by bridging polar head groups of phospholipids at the membrane surface. Calcium is also an integral part of the cell wall where it provides stable intra-molecular linkages between pectin molecules, resulting in cell wall rigidity. A change in the cytosolic calcium concentration is also known to provide a cellular signal that regulates metabolism and mediates plant responses to stresses. Calcium deficiency is pervasive among fruit and tuber crops because calcium moves with water in the xylem and very little water moves to fruit and tuber tissues as compared to leaves. The water potential gradient within the potato plant favors xylem transport to the foliage since tubers are surrounded by moist soil. As a result, the calcium concentration is much higher in foliage than in the tuber. In our early work, we demonstrated that water and calcium taken up by the main root system bypass the tubers and are delivered to the above-ground portion of the plant, and roots arising from the stolons and tubers supply calcium to the tubers. Tuber calcium concentration can therefore be increased by selectively feeding tubers with calcium nutrients during tuber bulking period. The discovery of tuber roots has led to the development of a new concept in potato nutrition. We have demonstrated that in-season fertilization with calcium increases tuber calcium and lowers incidence of physiological disorders such as internal brown spot, hollow heart, and bruising. Localized tissue calcium deficiencies are implicated as mechanisms initializing cell death and tissue necrosis leading to internal brown spot and hollow heart in potatoes. There is also strong evidence for reducing storage rot by increasing tuber calcium. Finally, tuber calcium is important for the health of the sprout and of the tuber skin.

ADDITIONAL INDEX WORDS. micropropagation, shoot tip, apical dominance, axillary shoot growth, tip necrosis, Solanum tuberosum, calcium deficiency ABSTRACT. Shoot tip necrosis has been attributed to calcium deficiency in in vitro cultures, resulting in death of the stem tip, the loss of apical dominance, and axillary branch development. Using an in vitro shoot culture system with Solanum tuberosum L. cv. Dark Red Norland, we studied the development of injury symptoms at the microscopic and tissue levels at a range of media calcium concentrations varying from 6.8 to 3000 mM. Light and electron microscopic studies revealed that the primary injury due to calcium deficiency was the death and collapse of expanding pith cells below the shoot apex. The structure and organization of the shoot apical meristem was the same when plants were cultured on sufficient or suboptimal media calcium concentrations. However, the apical meristem senesced following subapical shoot tissue collapse. Death of the shoot apical meristem was a secondary effect of calcium deficiency, resulting in loss of apical dominance. Studies with 45 Ca indicated that calcium was distributed in a gradient along the shoot, with highest concentration at the base and the lowest at the apex. Shoot tip necrosis developed after 20 days of culture on the suboptimal calcium concentration medium. The development of these symptoms and axillary shoot growth was associated with the lack of calcium accumulation in the shoots. Our results provide evidence that a primary injury of calcium deficiency is localized in the expanding pith cells below the shoot apical meristem and this injury results in the collapse of subapical cells. Death of the shootapical meristem is asecondary injury resulting from calcium deficiency.

‘MegaChip’ is a medium-late variety for chipping, with round-oval tubers of white tan skin and white flesh. MegaChip has consistently shown good to high yield potential. The tubers bulk early and produce a good size distribution for chipping. The specific gravity is consistently high and is close to the solid content of ‘Atlantic’. MegaChip has longer dormancy than ‘Snowden’ and Atlantic and stores well. It produces high quality chips that have an excellent color both from the field and after storage at 7.2 to 10 C. MegaChip showed a high level of resistance to common scab at most locations in North Central Regional trials and is moderately resistant to foliar early blight, powdery scab, pink rot, dry rot and soft rot. MegaChip is also fairly resistant to shatter bruise.

Gibberellins (GAs) are involved in internode elongation and other important processes such as seed germination, flowering, maturation, tuberization, and tuber dormancy. The discovery of GA-deficient mutants enabled further study of the role of these hormones in many plant processes. GA-deficient mutants lack the ability to produce adequate amounts of gibberellin for normal growth, resulting in a rosette type growth and short internodes. Thega 1 mutant allele was introduced into various genetic backgrounds including differentSolanum species and ploidies. Diploid GA-deficient genotypes were obtained by crossing haploidSolanum tuberosum ssp.andigena withSolanum chacoense. The progeny was then bulked and intermated to produce F2 individuals. Tetraploid GA-deficient genotypes were obtained by crossingS. tuberosum ssp.andigena withSolanum sucrense and withSolanum gourlayi. The two resulting progenies were then bulked and intermated. Diploid and tetraploid GA-deficient genotypes were grown on MS media containing different levels of gibberellin (GA3). Plant height and visual observations were made as a way to assess the response of these genotypes to GA3. Concentration of 0.1 µM GA3 and lower failed to restore normal plant height in both diploid and tetraploid genotypes. Normal plant height was restored in most of the GA-deficient genotypes when concentrations between 0.8 and 1.2 µM GA3 were used. We found some important differences between these genotypes: (1) the level of GA3 to restore normal plant height varies among the GA-deficient genotypes, some needed more GA3 than others to grow normally; (2) the time to respond to the presence of GA3 in the media differs between the GA-deficient genotypes, (3) tetraploid genotypes exhibited normal growth and internode length in response to GA3, while diploid genotypes tended to show a rosette-type growth at the apical end. These results suggest thatga 1 mutants can be affected by a series of modifier genes and/or iso-alleles. The importance of variable response to GA among dwarf individuals is two fold: (1) experiments measuring GA response should choose and clonally multiply one genotype to ensure uniform optimal response to GA application; and (2) variation betweenga 1 mutant phenotypes could be used to characterize GA-response modifier genes.

Our previous research has provided evidence that in-season calcium applications can increase tuber calcium and improve tuber quality with reduced internal defects. To determine if increasing the tuber calcium concentration also mitigates tuber bruise incidence, five commercially relevant potato (Solanum tuberosum L.) cultivars (`Russet Burbank', `Atlantic', `Snowden', `Superior', and `Dark Red Norland') were grown during three seasons, 1999–2001. Three split applications of a calcium/nitrogen water soluble blend totaling 168 kg·ha–1calcium were made starting at hilling. All plots, including controls, received an equal amount of total nitrogen in a season. Tubers were allowed to be bruised during normal machine harvest standard to commercial production in Wisconsin. Over 100 tubers from each replication (5–10 replications/treatment) were cut and examined for the incidences of bruise and internal brown spot. Paired samples of medullary tissue were taken for measuring calcium concentration. As expected, tuber tissue calcium concentration increased significantly, in all cultivars and in all years, with in-season calcium application. Bruise incidence varied among cultivars and seasons. Although tuber calcium concentration varied among seasons, `Atlantic' and 'Snowden' consistently had the lowest calcium concentration, whereas `Superior' and `Dark Red Norland' consistently had the highest calcium concentration. Meta-analysis of pooled data for three years showed that blackspot bruise incidence was significantly reduced with calcium application in `Atlantic', `Burbank', and `Snowden'. On the other hand, `Dark Red Norland' and `Superior' had low incidence of bruise and were unaffected by calcium applications. Regression analyses of pooled data from all cultivars for three years revealed a significant quadratic relationship between blackspot bruise and tuber tissue calcium as well as between blackspot bruise and internal brown spot. A linear to plateau plot of medullary calcium concentration versus blackspot bruise incidence revealed that bruise incidence is minimized between 200 and 250 μg/kg (dry wt)–1 tuber calcium concentration. To our knowledge, ours is the first study providing evidence for reducing bruise by improving tuber calcium. Variations in the bruise incidences among cultivars generally followed tuber calcium concentration suggesting a genetic control. Given the role of calcium in improved membrane health and enhanced wall structure, and as a modulator of physiological responses, it is not surprising that internal brown spot and bruise incidences are reduced by in-season application to calcium-deficient cultivars.

Calcium is believed to be transported with water in the xylem. Consistent with this proposal, low-transpiring organs such as potato Solanum tuberosum tubers are known to suffer from calcium deficiency. Although roots on tubers and stolons have been shown to supply water to tubers, there is no direct evidence for the calcium transport pathway to tubers. Both a xylem and a phloem transport pathway have been suggested. We investigated in vivo calcium transport to developing potato, cv. Dark Red Norland and cv. Russet Burbank, tubers using 45Ca in a controlled environment facility. Whole plant split pot experiments allowed the placement of 45Ca either in the main (basal) root or the tuber and stolon areas of the pot. The results showed that 45Ca was transported to the shoot with the transpiration stream from both areas but was not re-translocated to tubers or the main (basal) root system even 57 days after 45Ca application. Radioactivity could only be detected in the tuber when 45Ca was fed to the stolon and tuber area. When 45Ca was fed to specific tubers, radioactivity was detected in the aerial shoot; however, no activity was detected in other tubers or the main (basal) roots. In another set of experiments, roots on a stolon near a tuber were precisely fed 45Ca and Safranin O. The radioactive signal exactly overlapped the water transport pathway in the tuber marked with Safranin O dye, suggesting that water and calcium can be simultaneously transported from stolon roots to the tuber. No transport of 45Ca across the tuber periderm was detected 8 days after 45Ca was applied to the tuber periderm. This indicated that no significant transport of calcium occurs from the soil across the periderm. Our results provide evidence that: (1) calcium is not re-translocated via the phloem from the aerial shoot tubers and main (basal) roots; (2) the main root system does not supply calcium to the tuber; (3) calcium is not transported across the periderm to the interior tuber tissue; (4) calcium is transported to the tuber via the xylem along with water, and the roots on the stolon associated with the tuber supply water and calcium to the developing tuber; and (5) transpirational demand is a significant determinant of calcium distribution within the plant.

It has previously been suggested that plasma membrane ATPase (PM H+-ATPase, EC 3.6.1.3.) is a site of incipient freezing injury because activity increases following cold acclimation and there are published data indicating that activity of PM H+-ATPase is modulated by changes in lipids associated with the enzyme. To test and extend these findings in a tree species, we analyzed PM H+-ATPase activity and the fatty acid (FA) composition of glycerolipids in purified plasma membranes (PMs) prepared by the two-phase partition method from current-year needles of adult red pine (Pinus resinosa Ait.) trees. Freezing tolerance of the needles decreased from -56 degrees C in March to -9 degrees C in May, and increased from -15 degrees C in September to -148 degrees C in January. Specific activity of vanadate-sensitive PM H+-ATPase increased more than two-fold following cold acclimation, despite a concurrent increase in protein concentration. During de-acclimation, decreases in PM H+-ATPase activity and freezing tolerance were accompanied by decreases in the proportions of oleic (18:1) and linoleic (18:2) acids and increases in the proportions of palmitic (16:0) and linolenic (18:3) acids in total glycerolipids extracted from the plasma membrane fraction. This pattern of changes in PM H+-ATPase activity and the 18:1, 18:2 and 18:3 fatty acids was reversed during cold acclimation. In the PM fractions, changes in FA unsaturation, expressed as the double bond index (1 x 18:1 + 2 x 18:2 + 3 x 18:3), were closely correlated with changes in H+-ATPase specific activity (r2 = 0.995). Changes in freezing tolerance were well correlated with DBI (r2 = 0.877) and ATPase specific activity (r2 = 0.833) in the PM fraction. Total ATPase activity in microsomal fractions also closely followed changes in freezing tolerance (r2 = 0.969). We conclude that, as in herbaceous plants, simultaneous seasonal changes in PM H+-ATPase activity and fatty acid composition occur during cold acclimation and de-acclimation in an extremely winter hardy tree species under natural conditions, lending support to the hypothesis that FA-regulated PM H+-ATPase activity is involved in the cellular response underlying cold acclimation and de-acclimation.

`Stevens' cranberry (Vaccinium macrocarpon Ait.) terminal bud freezing stress resistance was assessed by nonlinear regression utilizing relative scoring of the post-thaw bud growth and development based on defined bud stages 2 weeks following controlled freezing tests. Bud stages tested were chosen based on a phenology profile from each sampling date throughout the spring season. Previous year (overwintering) leaf freezing stress resistance was evaluated after both 2 days (injury) and 2 weeks (survival). The Gompertz function with a bootstrapping method was used to estimate the tissues' relative freezing stress resistance as the LT50. Bud injury levels (LT50) were expressed as the temperatures at which the mean potential regrowth capability was impaired by 50%, as compared with the unfrozen controls. In leaves, the LT50 is the temperature at which 50% injury (2-day evaluation) or survival (2-week evaluation) was modeled to occur. Dramatic changes in terminal bud relative freezing stress resistance occurred both within and between the tight and swollen bud stages. These results clearly show that seasonal changes in freezing stress resistance do not necessarily parallel changes in crop phenology and bud development. These results indicate that some physiological, biochemical, or fine anatomical changes may explain the seasonal loss in hardiness within a visual bud stage. Previous year leaves may possess the ability to recover from freeze-induced injury, as leaf survival was found to be the most reliable indicator of cranberry leaf hardiness. Major shifts in phenology and bud and leaf hardiness coincided with the rise of minimum canopy-level air temperatures to above freezing. The nonlinear regression technique utilized made it possible to estimate LT50 with data points comprising half or more of the sigmoidal dose response curve. Our study provides precise and quantitative estimates of the cold hardiness changes in cranberry terminal buds and leaves in spring. From precise estimates we were able to define critical temperatures for the impairment of cranberry bud growth. This is the first systematic study of cranberry terminal bud cold hardiness and spring bud development in relation to changes in the soil and air temperatures under natural conditions. Our study shows that regrowth assessment of the cranberry upright inherently describes the composite effects of freezing stress on plant health.

Potato tuber tissue is low in calcium as compared to leaves and stems. Several recent studies have provided evidence linking tuber quality with tuber tissue Ca concentration. The purpose of the present study was to determine the influence of supplemental Ca and N fertilization on tuber Ca concentration and internal brown spot of potato. Three soluble products (calcium nitrate, calcium chloride, and N-Plus; 9N:0K:0P:11Ca) were used as Ca sources with and without gypsum. In addition, a combination of calcium chloride, urea, and calcium nitrate (CUC) was also used without gypsum. Each treatment consisted of five replications, which received the same total amount of N (252 kg ha−1) supplied either alone or in various combinations of ammonium nitrate, urea, calcium nitrate, calcium chloride, and N-Plus. The soluble sources of Ca were added at 68.8 to 168.0 kg ha−1 while gypsum supplied Ca at 49 kg ha−1. The application of all N by hilling (non-split) was compared to split application of N and Ca at hilling and 2, 4, and 6 wk after hilling. Tubers were mechanically harvested and graded according to industry standards. About 100 U.S. No. 1 tubers from each replication were cut in half along the longitudinal axis and visually inspected for internal defects. From each replication, non-periderm tissue from 15 tubers was combined for Ca analysis. There was no treatment effect on tuber yield in both years. Application of gypsum, either alone or in combination with the soluble sources, was not effective in reducing incidence of internal brown spot (IBS). Furthermore, with one exception, application of gypsum either alone or in combination with soluble sources of Ca was not effective at increasing tuber tissue Ca concentration. Combined analyses of data from 2 years showed that the application of soluble sources of Ca without gypsum increased tuber Ca concentration and decreased the incidence of IBS. Furthermore, split application of N had similar beneficial effects as compared to non-split N. Data from 1997 (a year with high IBS) gave a significant inverse relationship between tuber Ca and IBS, suggesting that an increase in tuber Ca can reduce IBS incidence.

Solanum commersonii Dun. (cmm) is the most frost hardy wild potato species known, being able to tolerate an acute freezing episode to about -5 C and further acclimate to tolerate −10 C after being exposed to chilling temperatures for several days. Breeding with this species to incorporate its frost-hardiness traits can be accomplished by standard sexual hybridization or protoplast fusion. These methods can result in hybrids that vary in contribution of the cmm plastome. To test the effect of cmm cytoplasm, cytoplasmic substitution backcross hybrids were made with three very frost-sensitive species,S. brachistotrichum, S. cardiophyllum, andS. pinnatisectum, by usingS. commersonii as the female to make an F1, then performing repeated backcross (BC) using the sensitive species as males. Relative freezing tolerance (RFT) of all genotypes was assessed by measurement of ion leakage of excised terminal leaflets subjected to a controlled ice nucleation and simulated freeze-thaw stress. Even against the background of these very sensitive species’ genomes, the cmm cytoplasm of substitution hybrids promoted insignificant improvement in frost hardiness or ability to acclimate. We conclude that either (1) cmm cytoplasm does not contribute to frost hardiness, or (2) if cmm cytoplasmic frost hardiness genes do exist, they must be epistatic to (depend on the presence of) nuclear hardiness genes for expression.

Tuberization in potato is known to be under complex biochemical control involving hormones. A number of studies have provided evidence for a critical role of GA in tuberization. There is also evidence that GA in plants can be modulated by a Ca/calmodulin pathway. The purpose of the present study was to determine the influence of supplemental Ca fertilization on tuber size and tuber number. Plantlets of Solanum tuberosum `Russet Burbank' raised in tissue culture were planted in 20-L pots filled with sandy loam field soil with the pH of 6.9 and exchangeable soil Ca level of 350 ppm. All treatments received the same total amount of N (equivalent to the rate of 280 kg·ha-1). Four treatments were evaluated: nonsplit N (from ammonium nitrate), split N (from ammonium nitrate), split N+Ca (from calcium nitrate), split N+Ca (50% N from urea, 50% N from ammonium nitrate and Ca from calcium chloride). The total Ca was applied at the rate equivalent to 168 kg·ha-1 on a split schedule (equally split at four, six, eight and ten weeks after planting). Four months after planting tubers were harvested and evaluated. As expected tuber tissue Ca was increased by Ca application from 144 to 245 μg·g-1. In general, the two Ca treatments had significantly lower tuber number per plant as compared to the nonsplit and split N treatments. A plot of mean tuber Ca and tuber number for individual plants showed a significant negative relationship. Both Ca treatments produced tubers with higher mean tuber weight compared to nonsplit N. This increase in tuber size with Ca application was not apparent when compared with split N treatment. These results show that Ca application to soil can decrease tuber number suggesting that soil Ca may influence tuberization in potato.