Nutritional and mineral content of prickly pear cactus: A highly water‐use efficient forage,fodder and food species

Increased demand for food requires us to investigate livestock forage and fodder crops that can be grown over a wide range of locations where their cultivation will not compete with that of the food supply. A large portion of the southwestern United States consists of underutilized semi‐arid land. Crops typically used for livestock fodder or forage have high‐water demands that make them uneconomical or unsustainable for semi‐arid and arid regions. The growth rate and low‐input requirements of prickly pear cactus (Opuntia ficus‐indica) make it an excellent candidate for forage or fodder supplementation or replacement in these regions. Previous reports about forage quality data on Opuntia have been scattered across multiple locations, growing conditions and cultivars. Here, we report on the forage quality and mineral content of Opuntia ficus‐indica grown under both field and greenhouse conditions. Crude protein was 71 and 264 g/kg of dry mass for field and greenhouse conditions, respectively. Field‐grown plants showed higher acid and neutral detergent fibre content than greenhouse‐grown plants reflecting higher cellulose, hemicellulose and lignin accumulation. Nutritional values were also compared to requirements of cattle to determine what deficiencies might need to be addressed through supplementation. These data suggest that Opuntia can be used in combination with other feed sources to reduce the demand of resource‐intensive forage crops for raising livestock in dryland areas.     

Genetic gain from early generation selection for cold chipping genotypes in potato

Early generation selection for chip colour may accelerate potato chipping cultivar development. The research objective was to measure the response from early generation selection for light potato chip colour. Progeny from 175 4×× 4× families were propagated to the field using greenhouse grown tubers or seedling transplants. Tubers from progeny were made into potato chips after 3 and 6 months’ storage at 4° C. Chip colour was rated as 1 = light to 10 = dark. Genotypes were categorized as retained (≥ 4) or discarded (> 4) based on the 6‐month chip colour, then field grown a second year at two locations and re‐evaluated for chip colour. Positive selection responses resulted, but were lower in the seedling transplants. Interaction between genotype and environment, and genotype and storage duration reduced responses. Selected genotypes should be evaluated over multiple environments and storage conditions to insure reliable performance. Expanding variation by introgressing favourable alleles from wild species may further enhance breeding success.     

Field evaluation of antisense RNA mediated inhibition of GBSS gene expression in potato

Summary Granule-bound starch synthase (GBSS) catalyses the synthesis of amylose in starch granules. Analysis of antisense RNA mediated inhibition of GBSS gene expression in large numbers of tubers from in vitro grown, greenhouse grown and field grown transgenic potato plants revealed stable and total inhibition of GBSS gene expression in one clone. In three other transgenic genotypes partial and unstable inhibition was found. In these genotypes both GBSS activity and amylose content were remarkably reduced compared with the non-transformed control genotype. No relationship was found between the level of inhibition of GBSS gene expression and yield and dry matter content.     

Relationship of Carbon Isotope Discrimination to Water Use Efficiency and Productivity of Barley Under Field and Greenhouse Conditions

This study was conducted to evaluate the application of carbon isotope discrimination (CID) as a selection criterion for improving water use efficiency (WUE) and productivity of barley (Hordeum vulgare L.) under field and drought‐stress conditions in a greenhouse. A total of 54 genotypes were screened for variability in CID under field conditions, while 23 genotypes were evaluated under water‐deficit conditions in the greenhouse. A survey of leaf CID of 54 genotypes at two field locations showed more than 2.14‰ difference between extreme genotypes. Significant (P ≤ 0.05) genotypic variation was found in WUE and CID that had a negative strong correlation. There was a negative correlation between leaf CID and aerial biomass in the greenhouse and among six‐row genotypes in the field. Correlations between leaf CID across field locations and across irrigation regimes in the greenhouse were significant (experiment 1, r = 0.79 and 0.94 for six‐ and two‐row genotypes), suggesting stability of the CID trait across different environments. Overall, these results indicate the potential of leaf CID as a reliable method for selecting for high WUE and productivity in barley breeding programmes in the Canadian prairies. Further work is currently underway to determine heritability/genetics of leaf CID and application of molecular marker‐assisted selection for the traits in barley breeding programmes.     

Effectiveness of selection for quality traits during the early stage in the potato breeding population

Potato cultivars resistant to cold‐temperature sweetening are of major importance to the processing industry producing both chips (crisps) and French fries. When most modern potato cultivars are maintained in cold storage to retard sprouting, the tubers accumulate reducing sugars, and the products become an unacceptable brown colour when fried. Selection for better processing quality during the early generations of a breeding programme could be of considerable advantage. Using a portable ‘sugarmeter’, which requires only a drop of sap from the tuber on a test strip, many samples can be efficiently surveyed for low sugar as early as the F₁ generation. Using seedlings of three test crosses, glucose and specific gravity of field‐grown tubers, minitubers from greenhouses and microtubers from in vitro culture were compared after cold treatment. Although the mean glucose levels of minitubers and microtubers were higher than field‐grown tubers, the correlation between the glucose contents of the three types of tubers was fairly high. A considerable genetic improvement was noted when progenies were grown as minitubers or microtubers, even though the response to selection for low glucose levels in minitubers and microtubers was lower than from direct selection from field‐grown tubers. The specific gravity of field‐grown tubers showed a significant association with freshly harvested minitubers and microtubers. Selection for low glucose content in minitubers can therefore save considerable resources in a breeding programme.     

Is Discrimination of 13C in Potato Leaflets and Tubers an Appropriate Trait to Describe Genotype Responses to Restrictive and Well‐Watered Conditions?

Selection for drought tolerance entails prioritizing plant traits that integrate critical physiological processes occurring during crop growth. Discrimination against ¹³C (?) in leaflets (?_leaflet) and tubers (?_tuber) was compared under two water regimes in two potato‐improved varieties selected to maintain yield under drought conditions (Unica and Sarnav) and one drought susceptible European cultivar (Désirée). In the control treatment, soil water content was kept at field capacity over the whole growth cycle, while in the drought treatment water supply was restricted after tuber initiation (50 % of field capacity). Gas exchange and N content per unit leaf area (N_area) as well as ? were assessed at different stages. Sarnav showed the highest tuber yield in both water conditions, suggesting that yield in the water restriction treatment was largely driven by yield potential in this genotype. Higher stomatal conductance (g_s) and N_area and lower ?_leaflet in well‐watered Sarnav suggested higher photosynthetic capacity. Under water restriction, Sarnav maintained higher g_s indicating that carbon diffusion was a key factor for biomass accumulation under water restriction. Our results suggest the use of ? determined after tuber initiation as an indirect selection indicator for tuber yield under both well‐watered and restricted soil water availability conditions.     

Divergent strategies displayed by potato (Solanum tuberosum L.) cultivars to cope with soil drought

The physiological responses of potato (Solanum tuberosum L) cultivars to soil drought at the tuberization phase and their impact on agronomically important traits were investigated in potted plants under semi‐controlled conditions. Genotype‐dependent responses of potato to water deficiency were evaluated on two pairs (tolerant/sensitive) of Polish cultivars. Each pair of cultivars had a similar genetic background but was extremely different in terms of drought tolerance evaluated on the basis of loss of tuber yield under field conditions. The results clearly indicate different mechanisms of tolerance to water deficiency and the ability to recover from soil drought in two tolerant but genetically unrelated cultivars. When subjected to soil drought, the cultivar Gwiazda had low rates of transpiration and photosynthesis and low levels of stomatal conductance due to hypersensitivity to ABA, but its maximal photochemistry efficiency and PSII performance index were unchanged. Another strategy was displayed by the dehydration‐avoidant cultivar Tajfun, which kept the stomata partially open. Thus, the plants were able to retain a relatively high rate of photosynthesis over transpiration. The parameters measured for cultivar Tajfun for photosynthesis and transpiration were the same after plant rewatering, similar to the control plants. This was not the case for the cultivar Gwiazda. The ability of plants to regenerate after soil drought relief appears to be a good indicator of potato susceptibility to soil drought and allows the yield of potato tubers to be predicted. The physiological traits identified in closely related potato cultivars but differed in their drought tolerance seem to be useful for genetic engineering and breeding programmes.     

A Comparison of Screening Criteria for Salt Tolerance in Wheat under Field and Controlled Environmental Conditions

Although many screening criteria have been suggested to distinguish between genotypes for their salt tolerance under controlled environmental conditions, there is a need to test these criteria in the field. Saline soils are often complex and, therefore, unlikely to show a simple relationship to controlled conditions. To address this deficit, different agronomic and physiological screening criteria for salt tolerance in wheat at different stages were examined under both field and controlled conditions. Four wheat genotypes differing in their salt‐tolerance levels were grown in salt‐affected soil at two different locations and also under greenhouse conditions. Dry weight and leaf area of the upper and lower two leaves of the main stem and total dry weight at Zadoks scale 47 were measured in plants grown under field conditions. The concentrations of Cl^?, Na⁺, K⁺ and Ca²⁺ in the upper and lower two leaves of the main stem at Zadoks scale 47 and different yield components were measured in plants grown under both conditions. Our results indicate that measurements derived from the upper two leaves of the main stem were generally more effective as screening criteria than those from the lower two leaves. Correlation coefficients between grain yield and either dry weight or leaf area of the upper two leaves of the main stem indicated that dry weight is inferior to leaf area as a screening criterion under field conditions. Number of sterile spikelets per plant performed well under both conditions, whereas the number of spikelets per plant and 1000‐grain weight failed to distinguish the differences of salt‐tolerance levels among genotypes accurately. Weight and number of grains per plant and number of fertile spikes per plant were poor criteria under controlled conditions, but effective under field conditions. The maintenance of low Cl^? and Na⁺ concentrations in the upper two leaves offered the best guide to salt tolerance under both conditions. Potassium concentration was a poor criterion compared with the selectivity of K⁺ over Na⁺, which was useful under both field and controlled conditions. Calcium concentration and Ca²⁺ over Na⁺ selectivity in the upper and/or lower two leaves of the main stem were also effective in ranking genotypes according to their salt tolerance under both field and controlled conditions. Therefore, we conclude that simple measurements of the upper two leaves of the main stem including a straightforward measurement of leaf area, visually estimating the number of sterile spikelets, and a quick, practical determination of Na⁺ and Ca²⁺ concentration constitute effective criteria to screen wheat genotypes for salt tolerance under both field and controlled conditions.     

Influence of the Indoleacetic Acid-Lysine Synthetase Gene (iaaL) of Pseudomonas syringae subsp. savastanoi on Yield Attributes of Potatoes

The iaaL gene of Pseudomonas syringae subsp. savastanoi encodes an indoleacetic acid-lysine synthetase which conjugates free indoleacetic acid (IAA) with lysine. lAA-lys is biologically less active than free IAA. The iaaL coding region was expressed under the control of the cauliflower mosaic virus 35S promoter and transgenic potato plants were produced (Spena et al. 1991). 35S iaaL potato plants are characterized by increased internodal length and epinastic bending of older leaves. In three greenhouse experiments with plants grown in pots of different size and in two growth chamber experiments tuber number increased in iaaL transgenic plants compared to untransformed and vector-transformed controls of the same genotype. The increase in tuber numbers observed under controlled conditions was reflected in tuber yield which increased in the pot grown transgenics.     

Production and performance of potato mini-tubers

Summary Production of mini-tubers as a source for seed potato was investigated by growing in soil micropropagated plants and micro-tubers produced from micropropagated plants. Cultures of several cultivars were initiated from indexed tubers and multiplied on modified MS medium. Cultures were micropropagated by using a modular system which allowed batch handling. Micropropagated plants produced mini-tubers in glasshouse after 70–115 days of growth in soil. A large proportion of the mini-tubers produced were between 9 and 15 mm diameter. Several factors, e.g., explant number, duration of in vitro culture and genotype influenced mini-tubers production. Micropropagated plants after culture of 86 days or longer produced micro-tubers ca. 2 to 10 mm diameter. Plants, which formed micro-tubers in vitro, produced less number of mini-tubers in soil. Micro-tubers produced 1 to 3 mini-tubers when grown in soil in chain-type paper pots, but produced conventional sized tubers when grown in soil under plastic polytunnel. Mini-tuber number varied widely between potato cultivars; cvs. Bintje and British Queen produced more mini-tubers than the other cultivars. Mini-tubers developed green hard skins when kept in light for 3 weeks, and could be stored in dark at 4° C upto 6 months. In a field trial, small mini-tubers ca. 5–10 mm diameter produced more but smaller tubers than mini-tubers ca. 15–20 mm diameter. The micropropagated plants and the plants grown from mini-tubers were genetically stable, and did not show any morphological aberrations except for one variegated plant among the several thousand produced. It is concluded that the production of mini-tubers by soil planting of micropropagated plants is a rapid and efficient method for producing seed potato tubers.The use of any trade mark and other commercial products mentioned in this paper does not constitute any recommendation or advertisement for such products on behalf of the Agriculture and Food Development Authority, Dublin, Ireland     

Phenotyping early blight resistance in potato cultivars and breeding clones

Thirty-two potato cultivars/clones were evaluated for resistance to early blight using different methods. The evaluations were performed under field and greenhouse conditions. In the field experiments, plants were evaluated for disease symptoms, and the relative area under the disease progress curve and percent defoliation were determined. In the greenhouse experiments, leaf lesion sizes were determined on either intact plants or detached leaves after drop inoculation with Alternaria solani. The effect of leaf position (lower, middle or upper part of the plant) on lesion size was investigated. There was no correlation between lesion sizes on lower leaves and upper leaves after inoculation. However, significant correlations between lesion sizes on lower and middle leaves and also between middle and upper leaves were found. Furthermore, we found significant correlation between the results of resistance studies in the field and in intact plant inoculation experiments in the greenhouse. In contrast, results from the detached-leaf experiment were not correlated with either greenhouse intact plant tests or field results. The results indicate that using detached-leaf assays for screening potato for early blight resistance is not accurate. We found significant differences in resistance to A. solani among cultivars/clones in both the field and in greenhouse experiments.     

Potato germplasm development for warm climates: genetic enhancement of tolerance to heat stress

Complex potato hybrids were derived through unilateral sexual polyploidization between Solanum tuberosum cv. Atlantic and 11 diploid hybrids that produced 2n pollen through co-orientation of second division spindles. The hybrids represented the following genomic compositions: TAPB, TAPC, and TAPM where T = S. tuberosum, A = S. andigena, P = S. phureja, B = S. berthaultii, C = S. chacoense, and M = S. microdontum. The B, C, and M components of the hybrids had been selected from heat tolerant accessions. The heat tolerance and agronomic performance of the hybrids were assessed under both controlled environments and field tests. The hybrids exhibited good tuberization potential (tuber number, tuber weight and percent plants producing tubers) under heat stress conditions in controlled environments. Under severe heat stress conditions in the field in Israel, many of the hybrids tuberized when Atlantic failed to produce any tubers at all. Under more moderate heat stress in Virginia, the complex hybrids exhibited total tuber yield not significantly different from Atlantic, although the tuber set per plant was greater. However, the complex hybrids were more tolerant to heat necrosis and hollow heart than Atlantic. Total glycoalkaloids in field-grown tubers did not exceed the acceptable limit for 13 of 26 selections examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic and environmental effects on the occurrence of speltoids in winter wheat cultivars

The occurrence of speltoid off‐types during seed multiplication is one of the major causes for rejection of a wheat cultivar candidate due to phenotypic inhomogeneity. These aberrant plants express an atypical spear‐shaped spike with tenacious glumes. To analyse the frequency of speltoids under field conditions, field trials were conducted at three locations and two sowing times over 2 years based on speltoid off‐type spikes derived from 14 different wheat genotypes. One hundred single ear progeny were developed from the normal and speltoid progeny plants in 2007. A mean frequency of 21.1% and 36.6% speltoid off‐types in plots from normal and speltoid lines was observed, respectively. Plots sown late in the season displayed on average 5.3% less speltoid off‐types, in particular when both sowing times were far apart. Field trials from 2010 revealed 7.9% more aberrant plants compared with 2011. The percentage of speltoids within the field plots ranged from 0.2% to 83.7%, which indicates a large effect of the respective genotype. Finally, strategies to reduce the number of speltoid off‐types are discussed.     

Differential Response of Southern US Rice (Oryza sativa L.) Cultivars to Ultraviolet‐B Radiation

Elevated ultraviolet‐B (UV‐B; between 290 and 320 nm) radiation, because of depletion of the stratospheric ozone layer, is one of the major environmental factors influencing plant metabolic processes and yield. The southern US rice cultivars contribute greatly towards US rice production, but the effects of elevated UV‐B radiation on these cultivars are not well known. The objective of this study was to determine the effects of elevated UV‐B radiation on leaf photosynthetic rate (P_n), membrane stability, pollen viability, phenolic concentration and yield of eight commercially popular southern US rice cultivars (five inbred cultivars and three hybrids). Plants were grown in a temperature‐controlled greenhouse in Beaumont, TX, USA, and were exposed to UV‐B radiation of 0, 8 or 16 kJ m^?2 day^?1 for 90 days. For most of the cultivars, plants grown under 8 or 16 kJ UV‐B radiation showed significant decreases in P_n, membrane stability, pollen viability, and yield compared with the plants grown under an UV‐B‐free environment, whereas there was a significant increase in leaf phenolic concentration under 16 kJ UV‐B radiation. The hybrid ‘Clearfield XL729’ performed best among the selected southern US rice cultivars under 16 kJ UV‐B radiation.     

Greenhouse and field techniques for testing sugar beet for resistance to Rhizoctonia root and crown rot

Rhizoctonia‐resistant sugar beet varieties are the key to an integrated control strategy for Rhizoctonia root rot. Because of the unpredictable occurrence of Rhizoctonia solani in the field testing of sugar beet for resistance to Rhizoctonia root rot is difficult. The aim of the study was to develop advanced greenhouse and field techniques which allow a reliable assessment of sugar beet for resistance to R. solani. A highly infectious liquid inoculum was used for the first time in this study. It can be produced in large quantities of a standardized quality, sterile, and exactly quantified according to its carbon content. In a greenhouse trial, sugar beet grown in the same way as field grown beet was inoculated by applying a suspension of Rhizoctonia mycelium (equivalent to 10 mg carbon per plant) to the beet crown. After 3 weeks, inoculation had led to uniform and severe root rot. Disease symptoms were similar to those found under natural conditions in the field. No ‘escapes’, i.e. susceptible plants apparently expressing resistance were observed in the test. A new nine‐class disease scale was established and a Rhizoctonia index (RI) was calculated. Reliability of disease assessment was demonstrated on progeny of plants, selected from segregating populations, showing Rhizoctonia resistance more closely related to the resistant parent lines than to the susceptible ones. Sugar beet varieties could be assessed in the greenhouse within only 11 weeks. All varieties were affected by the pathogen but partially resistant varieties could be clearly recognized by a significantly lower Rhizoctonia index. Significant differences in susceptibility were also found within the group of new resistant genotypes. Infection studies performed in the field showed the superiority of the new liquid inoculum compared with a solid form and revealed the influence of inoculation date and inoculum level on the development of Rhizoctonia root rot. In field tests performed at different sites under different environmental conditions, susceptible and partially resistant sugar beet varieties could be reproducibly rated according to their susceptibility to R. solani. On average, susceptible varieties showed a Rhizoctonia index of 8 while resistant genotypes ranged from 5 to 6. The newly developed techniques allow fast and reliable evaluation of sugar beet for resistance to R. solani.     

Somaclonal variation in explant-derived potato clones over three tuber generations

Summary Tuber characteristics of potato clones (Solanum tuberosum L.) regenerated from cultured leaf, rachis or stem pieces of cv. Desiree were assessed in field trails over three years. In the first two seasons, when the crop was grown for seed potato production, tuber numbers and the tuber yields were normally distributed and the population means of the clones were about the same as those of the controls. When 78 of the clones were grown as a ware crop in a replicated field trial there were statistically significant differences between most clones and the controls in total yield (generally lower) and ware yield (generally higher), brought about by alterations of the size distributions of tubers. In all years the population of clones had fewer scab (Streptomyces scabies) lesions than the controls. Clones with consistent differences in flesh colour and eye depth were also observed. Two out of 78 clones, in 1984, had significantly higher dry matter content. No stable decrease in susceptibility to the cyst nematode Globodera pallida was observed amongst 167 clones tested. These potato plants regenerated from explants clearly show that somaclonal variation can include agronomically relevant changes.     

Drought Impacts Mineral Contents in Andean Potato Cultivars

Mineral micro‐ and macronutrients in tubers of 21 Andean potato cultivars were investigated in a field trial under control and drought conditions. Mineral concentrations in potato tubers were highly variable between genotypes; some were significantly and positively correlated with each other, the most noteworthy associations being Na–Ca, Mn–Mg and Zn–Fe, in both control and drought‐stressed plants. Overall, increasing yields are related to decreased concentrations of some nutrients, albeit some higher‐yielding cultivars also displayed important concentrations of nutrients in their tubers. The most striking result was the increase in the concentration of the majority of the analysed cations in a large number of cultivars in response to water depletion; some of them, such as K, may be related to water homeostasis and/or to sucrose loading and unloading in phloem sap. Tuber mineral concentrations were not related to drought tolerance in terms of tuber productivity. Interestingly, yield loss under drought was not correlated with yield potential under control conditions. Identification of cultivars such as 703264 and 701106 able to maintain good yield stability in association with high mineral contents under water deprivation is of particular interest, especially in view of the importance of potato as a staple crop and the expansion of its cultivation to non‐optimal cultivation areas in the context of changing climatic conditions.     

Inheritance of resistance to early blight disease in a diploid potato population

Early blight disease, caused by Alternaria solani Sorauer, is a serious disease of potato foliage and tubers that occurs in most potato‐growing regions world‐wide. Developing new potato cultivars with resistance to early blight may reduce losses in the field and in storage, and lessen the need for fungicide applications. A total of 280 clones, derived from 72 maternal half‐sib families from a diploid random‐mated hybrid population of Solarium phureja×Solarium stenotomum were examined for resistance to early blight. The clones that were evaluated in a replicated field trial for 2 years in Pennsylvania, USA, had similar early blight intensity both years. Significant differences were found among families, within families and for the interaction of years × within families. Broad‐sense heritability for resistance, measured as area under the disease progress curve (AUDPC), was estimated as 0.73, with a 95% confidence interval of 0.65‐0.78, and narrow‐sense heritability was estimated as 0.61 ± 0.29 (P = 0.05). The correlation of AUDPC for early blight between years was 0.57 (P < 0.0001). These results suggest that this diploid population is worthy of use in breeding for early blight resistance.     

Influence of suboptimal temperature on biomass production of potato populations of Andean and European origin

Summary Plants grown from seed derived by crossing conventional European S. tuberosum material were compared with plants grown from seed derived by crossing S. tuberosum with various, Andean frost resistant tuberbearing Solanum species. Biomass growth at optimal (20°/10°) and suboptimal (10°/4°) temperatures was studied.Differences in increase of fresh and dry matter were found between populations of Andean and European orgins at 10°/4°. At 20°/10° no such differences were found.At suboptimal temperature, Andean hybrids produced significantly more fresh and dry matter than European crosses in two harvests (64 and 178 days old plants). Statistically, Andean hybrids were found to produce the same amount of dry matter per day at both temperatures, over the complete growth period.Height increase and flower development were strongly depressed in European crosses under the suboptimal temperatures, but much less so in Andean crosses.The Andean material appears to be an under utilized resource in potato breeding for cool climates.     

烯效唑（S3307）和胺鲜酯（DTA-6）对马铃薯叶与块茎糖代谢及产量的影响

在大田栽培条件下,以马铃薯克新1号为试验材料,在苗期叶面喷施调节剂烯效唑（S₃₃₀₇）和胺鲜酯（DTA-6）进行处理,以清水作为对照（CK）,研究不同植物生长调节剂对马铃薯叶和块茎间光合产物变化和产量的影响。结果表明:S₃₃₀₇和DTA-6处理可以显著提高马铃薯产量,增加前期叶片内蔗糖和淀粉含量;喷施调节剂第34天（块茎膨大期）,S₃₃₀₇和DTA-6处理促进叶片中淀粉含量向块茎中转运降低叶片内淀粉含量,利于源器官的物质输出;S₃₃₀₇和DTA-6显著增加各取样时期马铃薯块茎中淀粉含量;S₃₃₀₇和DTA-6在喷施后第18和34天显著增加块茎可溶性糖含量;马铃薯块茎内淀粉含量的变化与叶片内蔗糖和淀粉含量均呈极显著正相关,与转化酶和淀粉酶活性呈极显著负相关。S₃₃₀₇和DTA-6处理均显著促进单薯重,同时DTA-6处理的单株薯数也显著高于CK。