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.     

Vitamin C,B5, and B6 contents of segregating potato populations detected by GC‐MS: a method facilitating breeding potatoes with improved vitamin content

Vitamin C, B5, and B6 contents of potato tubers were measured by gas chromatography‐mass spectrometry (GC‐MS). Two diploid potato populations derived from two different crosses were analyzed. Plants were grown at two locations under different environmental conditions. Measurements of vitamin content of tubers showed high variation in both populations. A weak correlation was found between the vitamin concentrations of tubers harvested at the two locations. Correlations between the mean values of vitamins in field‐grown tubers and in different tissues derived from in vitro or greenhouse‐grown potato plants were also determined. A very high correlation between the vitamin content of field‐ and greenhouse‐grown tubers, and between field‐grown tubers and sink leaves of greenhouse‐grown plants was detected. This finding can facilitate breeding by preselection of individuals with improved vitamin content under greenhouse conditions at their early developmental stage.     

Studies on field resistance of strawberry varieties to Phytophthora fragariae

Summary Strawberry varieties were grown in a field infected with several races of Phytophthora fragariae and scored for resistance to red core disease caused by this fungus. Field resistance of a variety assessed in this way was not related to its pattern of immunity to specific races of the fungus. Possible mechanisms of field resistance were investigated by examining primary root regeneration and the amount of red steles developed in plants grown in infected soil. The least red steles were found in the roots of 53Q13, a highly field resistant Fragaria virginiana derivative. In the fairly field resistant varieties Crusader, Talisman and Templar, resistance was associated with a high capacity for root regeneration. No explanation was found for the field resistance of Cambridge Favourite.The design of a successful screening technique needs to take account of top growth because no single plant characteristic was universally linked with field resistance.     

The germination of freshly harvested seed of ripe and unripe barley and oats

Barley and oats were grown in a greenhouse and outside in the field to different stages of ripeness. After harvest the plants were threshed as soon as possible. The seeds were treated in different ways and sown immediately in a sand-bed. The kernels which germinated were counted.Seeds from plants which were grown in the greenhouse, on average germinated better than seeds from plants grown outside. Seeds from ripe plants germinated better than green seeds, but in some trials germination of green seeds was exceptionally good. The percentage of germination was increased by several treatments. Drying at 50°C was found to be the most efficient method.The result from such experiments may be different when the plants are grown in another environment. Under our conditions drying at a temperature of about 50°C was an efficient way to increase the germination of freshly cut seeds of barley and oats.     

Effect of mass selection for seed density in populations derived from Avena abyssinica x A. sativa amphidecaploids

Summary Seed of two heterogeneous amphidecaploid Avena populations (NY79143 and NY79148) were separated into three groups based on seed density using a commercial gravity table. Bulk populations were evaluated in a field trial to test the effect of selection for seed density on agronomic characteristics, while chromosome behavior was studied on similarly selected individual plants grown in a coldframe. Selection for seed density was associated with improved agronomic characteristics for individual plants grown in coldframes but the treatment effect was not significant in the field trial. Population and treatment effects were significant for chromosome number. Mean chromosome numbers were higher in NY79148 than in NY79143, and increased with selection for seed density. Populations did not differ for mean somatic instability but did show interactive population^*treatment effects. Several generations of selection for seed density is suggested.     

Grain dormancy in fixed lines of white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) grown under controlled environmental conditions

Pre-harvest sprouting (PHS) in wheat (Triticum aestivum L.) can be a significant problem, causing deleterious effects on grain quality. However, the adverse impacts of PHS can be reduced by introgressing genes controlling grain dormancy into white-grained bread wheat. Screening for grain dormancy typically involves germination testing of harvest-ripe grain grown in a glasshouse or field. However, the more uniform environmental conditions provided by temperature controlled glasshouses (i.e. controlled environmental conditions—CEC) may provide significant benefits for the assessment of grain dormancy. In this study, the dormancy phenotype of grain grown under CEC incorporating an extended photoperiod, was compared with 2 years of data from field grown material. Four dormant double haploid lines (derived from SW95-50213 and AUS1408) and two locally adapted non-dormant cultivars EGA Gregory and EGA Wills were compared in three replicated experiments grown under CEC (22 ± 3°C and 24 h photoperiod). The germination response of harvest-ripe grain was examined to assess the expression of grain dormancy. Two measures of germination, the predicted time to 50% germination (G ₅₀) and a weighted germination index, both clearly differentiated dormant and non-dormant lines grown under CEC. In addition, levels of grain dormancy were similar to field-grown plants. These results demonstrated that CEC with an extended photoperiod can be used for rapid and reliable characterisation of grain dormancy in fixed lines of bread wheat.     

QTL mapping of the domestication traits pre-harvest sprouting and dormancy in wheat (<Emphasis Type="BoldItalic">Triticum aestivum L.</Emphasis>)

A set of 75 recombinant inbred lines (RILs) of the ITMI mapping population was grown under field conditions in Gatersleben. The lines were evaluated for the domestication traits pre-harvest sprouting and dormancy (germinability). Main QTLs could be localized for pre-harvest sprouting on chromosome 4AL and dormancy on chromosome 3AL. In addition, 85 Triticum aestivum cv. “Chinese Spring”-Aegilops tauschii introgression lines grown under greenhouse conditions were researched. No QTL could be found for pre-harvest sprouting but a major QTL could be detected for dormancy on chromosome 6DL.     

Comparison of selection indices to screen lowland rice for drought resistance

Summary Although many selection indices have been used to screen rices (Oryza sativa L.) for drought resistance, there has been little comparison of the relative merits of these indices. Research was conducted to compare drought resistance as estimated from grain yields, canopy-temperature-based stress indices, visual scoring, and uprooting force for 30 rice genotypes grown in the field with a puddled Maahas clay (Typic Tropaquept) and to evaluate traits related to drought resistance from nonstressed plants grown in the field and in aeroponic culture. Water deficit was imposed in the field by withholding irrigation from 45 to 75 days after transplanting compared to a continuously flooded control. Grain yields in the stress treatment were most strongly correlated with visual assessment of drought stress symptoms according to a standard evaluation system (r = 0.66). Canopy-temperature-based indices were also significantly correlated with grain yields of the stress treatment (r from –0.55 to –0.63). No trait of aeroponically grown plants was correlated with traits of stressed plants in the field. We conclude that visual scoring of stressed plants was the best method of screening for drought resistance, but if controlled water deficit cannot be imposed, then drought resistance may be estimated by measuring both uprooting force and grain yield.     

Evaluation and verification of resistance to Meloidogyne hapla Chitwood in a Cannabis germplasm collection

A collection of Cannabis accessions was evaluated for resistance to the root-knot nematode Meloidogyne hapla Chitwood in a seedling test. After inoculation with a larval suspension, significant variation was found for the number of galls and egg masses on the seedling roots. These parameters were considered as estimates for nematode infection and larval multiplication, respectively. A subset of the tested accessions was grown on a naturally infested arable field to study the relation between the test results and host characteristics in the field. The ranking order of accessions for the number of galls in the seedling test agreed well with that for the number of root galls on juvenile plants in the field. Therefore the test provides a useful indication for nematode infection. The number of egg masses in the seedling test and the population density of Meloidogyne measured in post-treatment soil samples of the field trial, showed a comparable ranking of accessions. Differences between accessions in the field were however smaller and not statistically significant.     

Response of Growth and Yield of Rice (Oryza sativa) to Elevated Atmospheric Carbon Dioxide in the Subhumid Zone of Sri Lanka

Increasing atmospheric CO₂ is recognized as a major aspect of global climate change that would have a significant impact on the productivity of major agricultural crops. Two field experiments were done, with the objective of quantifying the response of a short‐duration rice (Oryza sativa) variety (BG‐300) to elevated atmospheric carbon dioxide, in the low elevation, subhumid zone of Sri Lanka. The experiment contained three treatments. In the elevated CO₂ treatment, rice was grown at a CO₂ concentration of 570 µmol/mol within open top chambers (OTC s). The ambient CO₂ treatment included crops grown within OTC s, but maintained at the ambient CO₂ concentration of 370 µmol/mol. The third treatment was a crop grown in the open field under ambient CO₂ concentration. Grain yields of rice crops grown under elevated CO₂ were 24 % and 39 % greater than the respective ambient treatments in the maha (January – March 2001) and yala (May – August, 2001) seasons. Significant increases in total biomass at harvest (23 % and 39 %, respectively, in maha and yala) were more responsible for the above yield increases than the slight increases in the harvest index (4 % and 2 %). Yields of the ambient and open field treatments did not differ significantly. Among the yield components, the number of panicles per hill was significantly higher in the elevated treatment and showed significant positive correlations with grain yield in both seasons. In addition, grain yield showed significant positive correlations with the percentage of filled grains in maha and the number of grains per panicle in yala. Significant increases in the number of tillers per hill under elevated CO₂ were responsible for its greater leaf area index and the greater numbers of panicles per hill. Crops under elevated CO₂ accumulated biomass faster than those grown under ambient CO₂ during the vegetative and grain‐filling stages. The results of this study demonstrate that elevated CO₂ causes significant yield increases in rice, even when it is grown in warm, subhumid tropical climates.     

Improved seed yield in perennial ryegrass (Lolium perenne L.) from two generations of phenotypic selection

Two generations of recurrent phenotypic selection for seed yield per plant under controlled pollination were carried out to combine improved seed yield with improved forage grass performance in perennial ryegrass (Lolium perenne L.). Selected and unselected varieties (AberDartand AberElan respectively) and control varieties were grown for seed in pots in a glasshouse experiment and in two field plot experiments over 5 harvest years. Seed yield components and seed yield were measured. Significant improvements in seed yield of the selected AberDart over the unselected AberElan were observed both in individual plants grown in the glasshouse and in field plots. Detailed observations of the individual components of seed yield showed that the increased seed yield of AberDart can be attributed to a higher proportion of ovules forming seeds (% seedset), greater seed number per tiller and more reproductive tillers per plant. This improvement in seed yield of AberDart was also observed when it was grown in field plots with AberElan, experimental selection lines and commercial varieties. AberDart produced more seeds per tiller than the other commercial varieties and selection lines studied. The implication of this approach for the breeding of perennial ryegrass varieties that combine good agronomic performance and acceptable seed yields is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

Yield components,harvest index and plant type in relation to yield differences in field pea genotypes

Summary The effectiveness of yield components, harvest index and morphological characteristics as selection criteria among four field pea (Pisum sativum L.) genotypes was examined. Genotypes were grown at a wide range of plant populations (9 to 400 plants m^-2) to maximise environmental diversity.Both biological and seed yields approximately doubled from 9 to 100 plants m^-2. This response flattened from 100 to 400 plants m^-2. Differences among the genotypes were found only at 225 and 400 plants m^-2. Analysis of the yield components highlighted the plasticity and large genotype by environment interactions of field peas. The numbers of pods per plant and peas per pod were maximised when each genotype was grown as spaced plants, but the low plant numbers meant seed yields per unit area were at their lowest.Genotypic differences for plant harvest index (PHI) were also only found at 225 and 400 plants m^-2. Broad sense heritability estimates indicated that direct selection for PHI was not feasible. The inference from the yield component and PHI results was that alternative selection criteria such as physiological or morphological characteristics may be necessary for improved yield potential. Classification of each genotype indicated that low seedling vigour may be a positive attribute for crop plants of semi-leafless and conventionally leafed field peas. Selection based on any single plant attribute is unlikely to lead to dramatic improvements in the yield potential of field peas. Selection should be based on plant characteristics rather than on differences in yield components.     

Physiological responses of chickpea genotypes to terminal drought in a Mediterranean-type environment

Two field experiments were carried out to investigate the effects of terminal drought on chickpea grown under water-limited conditions in the Mediterranean-climatic region of Western Australia. In the first experiment, five desi (small angular seeds) chickpeas and one kabuli (large round seeds) chickpea were grown in the field with and without irrigation after flowering. In the second experiment, two desi and two kabuli cultivars were grown in the field with either irrigation or under a rainout shelter during pod filling. Leaf water potential (Ψ_l), dry matter partitioning after pod set and yield components were measured in both experiments while growth before pod set, photosynthesis, pod water potential and leaf osmotic adjustment were measured in the first experiment only.

In the first experiment, total dry matter accumulation, water use, both in the pre- and post-podding phases, Ψ_l and photosynthesis did not vary among genotypes. In the rainfed plants, Ψ_l decreased below −3 MPa while photosynthesis decreased to about a tenth of its maximum at the start of seed filling. Osmotic adjustment varied significantly among genotypes. Although flowering commenced from about 100 days after sowing (DAS) in both experiments, pod set was delayed until 130–135 DAS in the first experiment, but started at 107 DAS in the second experiment. Water shortage reduced seed yield by 50 to 80%, due to a reduction in seed number and seed size. Apparent redistribution of stem and leaf dry matter during pod filling varied from 0 to 60% among genotypes, and suggests that this characteristic may be important for a high harvest index and seed yield in chickpea.     

Genetic analysis of male sterility in rice mutants with environmentally influenced levels of fertility

Summary Twenty-six male sterile plants grown in the field were recovered in the M7 generation from ethyl methane sulfonate-treated material of the rice cultivar M-201. Fertility increased five-fold when ratooned plants from the field were grown in a growth chamber with a 12 hour daylength. Crosses between mutant and normal fertile cultivars produced fertile F₁ plants. Female fertility was normal as judged by percent seed set from unbagged panicles of parental and recombinant lines. Transgressive segregation for fertility was observed for all crosses in the F₂ and F₃ generations. Five of 37 F₃ male sterile plants showed moderate levels of seed fertility under winter greenhouse conditions and reduced seed set when transplanted to summer field plots. Fertility data from reciprocal crosses suggested cytoplasmic factors had little or no effect on levels of male sterility in the mutant lines. Chi-squared analyses of F₂ and F₃ generation results indicated male sterility of the mutants is conditioned by two nuclear genes with epistatic effects.     

甘蓝型油菜小孢子培养影响因素研究及再生苗早期倍性鉴定

对不同年份、不同地点种植的油菜育种材料进行小孢子产胚率鉴定,并以11种不同基因型的甘蓝型油菜品系为供体材料,在武汉田间,分别于初花期和盛花期分离培养小孢子,研究基因型、生态条件、开花时间对小孢子产胚率的影响及秋水仙碱处理的加倍效果,通过采用流式细胞仪测定小孢子再生苗的DNA含量鉴定其倍性,并种植验证.结果表明:相同基因...     

Contribution of White Clover Varieties in High-Productivity Systems under Grazing and Cutting

Two medium leaf size varieties of white clover (Trifolium repens L.) were grown in mixture with a range of grass species and varieties in a field experiment conducted over 4 years. The clovers were grown singly or as a blend in swards with a tetraploid perennial ryegrass (Lolium perenne L.), a diploid Italian ryegrass (Lolium multiflorum L.) or tetraploid hybrids between these two species (Lolium x boucheanum Kunth). These grasses were also grown in monoculture. Swards were managed in a regime involving two periods of sheep grazing, two periods of cattle grazing and a silage cut in the same year for 4 years. The objectives of this experiment were 3‐fold: (1) to examine the yield and persistency of white clover in highly productive systems with modern perennial, hybrid and Italian ryegrasses; (2) to compare the performance of white clover varieties grown singly in mixture with grasses with their performance together as a blend, and (3) to examine the persistency of new Italian ryegrass varieties, exemplified by AberComo. The clover content of the sward remained high throughout the experiment, with a mean of 31 % overall. Differences in clover yield between plots were largely attributable to the effects of companion grasses. Total yields were very similar in plots containing different clover varieties and in plots where these varieties had been grown singly or as a blend. Grass yields in mixture were greater than those in monoculture but showed similar relative rankings. The diploid Italian ryegrass variety AberComo showed an unexpectedly high yield in the 4th year of the experiment. The implications of these results for strategies for productive, sustainable agriculture using modern white clover and ryegrass varieties are discussed.     

Selection for cold chipping genotypes from three early generations in a potato breeding program

Chipping potatoes are an important market for the processing industry. Of the traits influencing chip quality,chip color is market limiting since other traits have diminished value without light chip color. Cold (4 ^°C) storage can reduce storage losses and cultivars producing light colored chips directly from cold storage are needed for this reason. Selection for cold chipping cultivars is traditionally practiced by visual evaluation of progeny the first few years in the field, followed by selection for cold chipping in years 4–5. Early generation selection for cold chipping may reduce cultivar development time by identifying good chipping progeny, families and parents earlier in the breeding cycle. Progeny from 175 4x × 4x families were evaluated from three early generations. They were greenhouse grown tubers (GGT) evaluated after6 mo. storage using randomly selected progeny, and field grown single hills propagated from either seedling transplants (FTR), or from greenhouse grown tubers (FGT). Progeny from field grown generations were selected first by visual evaluation, and then by random selection and chipped after6 mo. (visual selections) or 3 and 6 mo. storage (random selections). Cold chipping progenies were found in all three early generations. The earliest generations for selection are GGT or FTR, but may be less efficient than FGT. Correlations suggest that reliable parent and family selection is possible using GGT data. Visual selection eliminated 4/5 of the good chipping progeny, while identifying 8 of 11,714 genotypes combining visual merit and cold chipping potential. Increased genetic variation and sexual polyploidization are possible strategies for increasing the number of desirable genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.     

A method to select for reproductive frost tolerance in field pea (Pisum sativum L.)

This study describes an investigation to test whether genotypic differences for reproductive frost tolerance in field pea (Pisum sativum L.) can be measured in the field. The method involved individually tagging flowers or young pods at particular stages of development within 48 hr after a frost event and assessing pod survival and seed damage at maturity. Four field pea varieties were grown in 2011 in an experiment which measured the loss of pods following a specific frost event. This experiment also tested the impact of trellis and pathways sown with barley on the efficacy of the frost tolerance data. In 2012, an additional genotype was also tested and, in addition to pod loss, data were collected on seed damage in surviving pods. Results from both years showed significant genotypic differences. There was also a significant positive correlation between mean variety pod loss in 2011 and 2012 indicating reliability of this method across seasons.