Comparative genetic analysis of field resistance to downy mildew in the lettuce cultivars ‘Grand Rapids’ and ‘Iceberg’

Downy mildew on lettuce is currently controlled using host resistance genes (Dm genes) that confer race-specific resistance in seedlings. Field resistance (FR) that is active in adult plants but not seedlings was identified in the cvs. Grand Rapids and Iceberg. The goal of our study was to evaluate the utility of Grand Rapids as a source of novel Bremia resistance alleles, particularly in comparison with Iceberg. To measure FR, downy mildew symptoms were evaluated following natural infection in field experiments. The responses of Grand Rapids and Iceberg were similar in many respects. Although both cultivars had a small percentage of plants exhibiting disease symptoms, the average disease ratings were as low as for cultivars with effective Dm genes. We observed no evidence for race specificity. FR was effective over 3 years of our study, despite documented variation within pathogen populations. Both cultivars lacked all known seedling resistance genes except Dm13, which was not responsible for the resistance observed in field experiments. Similar segregation of FR was observed in F₂ populations for both Grand Rapids and Iceberg. The presence of highly susceptible families within Grand Rapids × Iceberg populations suggested the presence of at least one unique resistance allele in each cultivar. Preliminary genetic analysis of FR from Grand Rapids revealed a high estimate of narrow-sense heritability that suggested simple inheritance, but single gene models did not fit the observed data. Our results suggest that Grand Rapids may represent an underutilized resource for controlling downy mildew in lettuce.     

Comparative studies within and between seed and seedling populations of leafed, ‘leafless’ and ‘semi-leafles’ genotypes of Pisum sativum L.

In an attempt to explain previously observed differences between the growth rates of leafless and conventional plants, we have compared representatives of three pea phenotypes; conventional (AfAfStSt), semileafless (afafStSt) and leafless (afafstst) with regard to their embryonic axis/embryo weight ratio and their patterns of pre-emergent growth. Within each phenotype, comparisons were made between genotypes which differed for mean weight per seed and between seed weight classes within each genotype. Although significant differences were found between genotypes for embryonic axis/embryo weight ratios, these could not be attributed to differences between phenotypes. Within each seed population there was a consistent decrease in this weight ratio with increasing seed size irrespective of phenotype.Relative growth rate (RGR) of the seedlings prior to emergence was similar for all genotypes within and between phenotypes and also for seed size classes from individual populations. There was however a positive relationship betweed seed size and absolute growth rate within and between seed populations.The results suggest that differences between the phenotypes do not become manifest until after emergence of the seedling from the soil and the possibility of a post-emergent lag phase in the leafless type is therefore suggested.     

Morphological and physiological behaviour of sweet cherry ‘somaclone’ HS plants in field

We reported earlier that somaclonal variant HS (HS), regenerated from Prunus avium `Hedelfinger’ (H) leaf explants, showed reduced apical dominance both in vitro and in vivo. In this report we found that the somaclone HS, showed reduced vegetative vigour as determined by trunk circumference and tree height nevertheless natural architecture of the tree was preserved. HS canopy was less crowded as to compare to H and leaves were shorter with a shorter petiole, they were better spaced out as indicated by internodes length. HS had a significantly thinner cuticle and wax layer compared to H leaves surface. Histological analysis of leaves also showed that HS had thicker mesophyll and palisade the latter composed of more than one layer which, together with increased stomatal density, are distinguishing signs of extensive exposure of leaves to sun. Chlorophyll a and chlorophyll b content did not differ between H and HS, β-carotene content was slightly lower in HS leaves. However no significant differences were found between the two genotypes in terms of net photosynthesis, intercellular CO₂ concentration, leaf transpiration and water use efficiency. HS flowered 1-year later than H and number of flowers was reduced. Fruit size, shape, skin colour change during the ripening process and the main parameters of fruit quality as assessed in the wild type and the somaclone were basically the same.     

Monosomic analysis of fertility restoration in common wheat ‘Prof. Marchal’

Summary In common wheat (Triticum aestivum L.) a monosomic set of Chinese Spring and male-sterile Janus (with cytoplasm of T. timopheevi Zhuk.) were used to determine the chromosomal location of Rf-genes in Professeur Marchal. As revealed by test cross data, a major gene cofeerring fertility restoration was present in Prof. Marchal on chromosome 1B. A significant deviation towards sterility was observed in some fest cross progenies. Chromosome 1B of Chinese Spring appeared to carry a dominant restoring gene, which caused partial restoration of fertility.     

Regularity of the saturation lines’ change and stability analysis oftailings dam in the condition of flood

Yangtianqing tailings dam is a new dam planned for a copper mine. At the design period, test in laboratory is carried out to simulate the process of dam pile based on the design information of Yangtianqing tailings dam. And the regularity of the saturation lines’ change at the condition of flood and normal is studied, when the dam have been heaped to the about 2/3 of the total height (120 m). Based on the test data, the stability coefficients of the dam at this height in different conditions are obtained with the Slide software, and they could be served for the following test and the mine’s future safety production. It is shown that the dam is safe in the normal condition, while in the condition of flood, the stability coefficient is less than the benchmark in national standard. Thus, it is necessary to rectify the preliminary design or to take other measures to ensure the safety of the tailings dam.     

Identification of ‘Sib’ plants in hybrid cauliflowers using microsatellite markers

Hybrid cauliflowers have been developed to exploit heterosis and to improve uniformity of production. Two breeding systems are commonly employed, self-incompatibility (SI) and cytoplasmic male sterility (CMS). Sibs, assumed to be self-inbred, often contaminate hybrid seed lots in the SI system and whilst self-inbreeding is not possible in the CMS system, plants that look like sibs occur. The objective of this study was to develop microsatellite markers for male and female cauliflower parent lines of both SI and CMS systems and to use them to screen sibs and aberrant plants in F₁ hybrids. Fifty six pairs of microsatellite primers were screened and 8 primer pairs produced co-dominant markers in parent plants and two pairs of markers were chosen for purity testing of F₁ hybrid seeds. Controlled pollinations were conducted in the glasshouse to produce hybrid and selfed-seeds. These seeds were grown in a field trial to identify morphologically normal and sib plants and to assess the reliability of microsatellite markers in detecting sib plants. Microsatellite analysis of morphological sib plants from the SI system revealed that these were not always self-inbred, in contrast, most self-inbred plants showed normal growth. Similarly, all morphological sibs from the CMS system showed hybrid bands. This suggests that morphological sibs were not always due to selfing but possibly to an interaction between genetic and environmental factors and this requires further investigation.     

Pollen and pollination experiments. IV. ‘Mentor pollen’ and ‘pioneer pollen’ techniques regarding incompatibility and incongruity in apple and pear

Summary It was attempted to overcome self-incompatibility in apple and pear and incongruity between these species with the aid of compatible mentor or pioneer pollen. The mentor pollen was applied in a mixture (1:1) with the incompatible/incongruous pollen and the pioneer pollen was applied one day in advance of the other pollination. Two trials in 1976 with dead methanol-treated mentor pollen on apple were moderately successful, probably because of the hot spring weather. In the apple and pear trials of 1979 neither the methanol-treated nor the viable irradiated (100 krad) mentor or pioneer pollen significantly improved the seed set by self pollen or that after intercrossing. Competition and early embryo abortion after selfing or intercrossing probably contributed to the lack of success of these methods. The viable irradiated pollen induced a rather high parthenocarpic fruit set, whether applied on its own or mixed with or in advance of the incompatible pollen; the inviable methanol-treated pollen had no such stimulating influence.     

Correlation and path-coefficient analyses of ripening attributes and storage disorders in ‘Ambrosia’ and ‘Empire’ apples

The objectives of this study were: (1) to determine correlation effects among the ripening attributes of ‘Empire’ and ‘Ambrosia’ apples during storage, and (2) to determine the direct and indirect contributions of these ripening attributes on the incidence of physiological disorders and storage rots using path-coefficient analysis. The analysis was applied to data obtained from a variety of harvest dates and storage regimes from apples. Pearson correlation analysis of the data indicated a strong positive correlation between internal ethylene concentration (IEC) and peel greasiness, a negative correlation between IEC and soluble solids concentration, and a negative correlation between firmness and peel greasiness in both cultivars, as well as a negative correlation between IEC and firmness in ‘Empire’. Results indicated that increased IEC in ‘Ambrosia’ apples during storage was related to higher incidences of core browning and lenticel damage and lower incidence of internal browning. Higher IEC in ‘Empire’ apples during storage was associated with less internal browning. Several significant correlations, representing different relationships among the ripening attributes and storage disorders were obtained.     

Changes in volatile production and sensory quality of kiwifruit during fruit maturation in Actinidia deliciosa ‘Hayward’ and A. chinensis ‘Hort16A’

Although volatiles have been previously studied in kiwifruit (Actinidia spp.), there has been no co-ordinated study of volatile release and softening through the full edible period. In this report, the two most important commercial cultivars A. deliciosa ‘Hayward’ and A. chinensis ‘Hort16A’ were evaluated for volatiles released at different ripening stages corresponding to their typical commercial shelf life, and compared to the sensory quality assessed by a trained taste panel. Gas chromatography–mass spectrometry data indicated that large amounts of straight-chain aldehydes and esters were the dominant volatiles in the two cultivars. In particular, butanoates, the main fruity esters in both fruit, significantly increased during ripening and an extremely high level of butanoates was found in the over-ripe fruit. Sensory results indicated that with fruit softening, some of the changes in volatile content could explain changes in fruit flavor detected by a trained panel, and differences in characteristic flavor of the two cultivars. The results have implications for fruit sample handling and volatile assessment.     

Integrated ethylene and temperature conditioning for induction of ripening capacity in ‘Anjou’ and ‘Comice’ pears

‘Anjou’ and ‘Comice’ pears from three harvest dates were conditioned to develop ripening capacity by exposure to 100 μL L⁻¹ ethylene at 20 °C for 0, 24, 48, or 72 h, followed by varying durations of temperature conditioning at −0.5 or 10 °C. Ripening capacity was tested by measuring fruit firmness after 7 d at 20 °C after completion of conditioning treatments. Fruit firmness was also measured after conditioning but before ripening, and was designated “shipping firmness”, indicative of the potential for the fruit to withstand transport conditions without physical injury. Ripening capacity in both cultivars developed more rapidly with later harvest date, increasing duration of ethylene conditioning, and increasing duration of temperature conditioning. Ripening capacity developed much more rapidly at 10 °C than at −0.5 °C. Useful durations of temperature conditioning at 10 °C were limited by fruit softening below acceptable values of shipping firmness. However, sequential combinations of ethylene and temperature conditioning at both −0.5 and 10 °C were identified wherein post-conditioning shipping firmness was acceptable.     

Induction of ripening capacity in ‘Packham's Triumph’ and ‘Gebhard Red D’Anjou’ Pears by temperature and ethylene conditioning

Methods were tested for rapid induction of ripening capacity in ‘Packham's Triumph’ and ‘Gebhard Red D’Anjou’ pears in order to facilitate early marketing. Fruit of each cultivar were harvested at the onset of maturity and conditioned to develop ripening capacity by exposure to 100 μL L⁻¹ ethylene at 20 °C for 0, 24, 48, or 72 h, followed by varying durations of temperature conditioning at −0.5 or 10 °C. Ripening capacity was tested by measuring fruit firmness after 7 d at 20 °C after completion of conditioning treatments. Fruit firmness was also measured after conditioning but before ripening, and was designated “shipping firmness,” indicative of the potential for the fruit to withstand transport conditions without physical injury. With temperature conditioning at −0.5 °C only, ‘Packham's Triumph’ pears needed 45 d to develop ripening capacity, while ‘Gebhard Red D’Anjou’ pears were not capable of fully ripening after 60 d, the longest duration tested. Using ethylene only, 72 h exposure was necessary to develop full ripening capacity in both cultivars, and adequate shipping firmness was maintained. Using temperature conditioning at 10 °C, ripening capacity in ‘Packham's Triumph’ and ‘Gebhard Red D’Anjou’ developed within 10 and 20 d, respectively, but shipping firmness in ‘Gebhard Red D’Anjou’ was compromised at 20 d. In both cultivars, 24 or 48 h in ethylene followed by 5 d at 10 °C induced ripening capacity while maintaining adequate shipping firmness.     

Origin of the ‘Weisse Schlesische Rübe’ (white Silesian beet) and resynthesis of sugar beet

Summary Sugar beet-besides fodder beet, red beet, and chard-belongs to Beta vulgaris L. After it had been confirmed that the sugar of Beta beet is chemically identical with cane sugar, ACHARD started experiments on the production of sugar from fodder beet. He noticed that conical white beets seemed to have the highest sugar content. This first sugar beet, the Weiße Schlesische Rübe, is considered the ancestor of all sugar beets of today. It has been, and continues to be supposed that it had originated from crossings between typical fodder beet and chard. Hints in the literature about possibilities to resynthesize sugar beet by crossing fodder beet with chard were confirmed in the author's own trials; the F₂ from the crossing fodder beet Rote Walze x chard Lukullus segregated forms and colour variants largely corresponding to sugar beet. Such new sugar beets are not only important from a theoretical point of view; breeders are interested in new types, too. The synthesis of sugar beet is interpreted from a genetic point of view.     

Low-temperature induction of ripening capacity in ‘Comice’ and ‘Bosc’ pears as influenced by fruit maturity

The relationship between fruit maturity at harvest and the duration of postharvest exposure to ?1 °C required to induce ripening capacity was studied in ‘Comice’ and ‘Bosc’ pears. As fruit of both cultivars were harvested progressively later, shorter durations of exposure to ?1 °C were required to induce ripening capacity. The relationship between the duration of conditioning at ?1 °C and the fruit flesh firmness after 7 d at 20 °C was well-described by second-order polynomial equations. These equations were used to determine the number of days at ?1 °C required to induce ripening capacity for each harvest date. A linear relationship was observed between the number of days after fruit in the orchard reached maturity that fruit were harvested and the number of days of low-temperature conditioning needed to induce ripening capacity. This relationship may be used to predictively estimate the duration of low-temperature conditioning required to induce ripening based on harvest date.     

Dynamics of ascorbic acid in ‘Braeburn’ and ‘Gala’ apples during on-tree development and storage in atmospheres conducive to internal browning development

The underlying causes as well as chemical and biochemical alleviation for CO₂-induced browning in apple fruit are poorly understood. Ascorbic acid (AsA) dynamics in ‘Braeburn,’ a susceptible cultivar, and ‘Gala’, a resistant cultivar, were evaluated during on-tree development and storage at 0.5 °C in air or controlled atmospheres (CA) containing 1 kPa O₂ and 1, 3 or 5 kPa CO₂. ‘Braeburn’ fruit treated with diphenylamine (DPA) was also stored for 1 month to determine effects on browning incidence and AsA concentration. ‘Braeburn’ apples had significantly higher (p ≤ 0.05) AsA levels than ‘Gala’ during on-tree development, and storage. No correlation between AsA and maturity/ripening indices for ‘Braeburn’ or ‘Gala’ was apparent. Histochemical localization of fruit AsA showed a staining intensity consistent with the quantity analytically determined, and showed that AsA is diffusely distributed throughout the cortex in both cultivars during on-tree development. During storage, AsA was localized to the periphery of brown tissue in ‘Braeburn’ and to the coreline and cortex proximal to the peel in ‘Braeburn’ and ‘Gala’ tissues. DPA decreased browning development during storage, however, no correlation between DPA treatment and AsA quantity in healthy or brown cortex tissue was observed. The results indicate AsA quantity alone is not an indicator of CO₂ sensitivity in these two cultivars.     

Effect of modified atmosphere packaging and storage temperature on volatile composition and postharvest life of minimally-processed pomegranate arils (cvs. ‘Acco’ and ‘Herskawitz’)

This study investigated the effects of passive modified atmosphere packaging (MAP), storage temperature (5, 10 and 15 °C) and duration of 14 days on the postharvest quality attributes, compositional change in flavour attributes and microbiological quality of minimally processed pomegranate arils (Punica granatum L.), cvs ‘Acco’ and ‘Herskawitz’. Volatile compounds were extracted via headspace solid phase micro-extraction (HS-SPME) and analyzed by gas chromatography–mass spectrometry (GC–MS). A total of 17 and 18 volatiles were detected and identified in the headspace of pomegranate juices of ‘Acco’ and ‘Herskawitz’, respectively. Based on the physicochemical attributes and microbial evaluation, the postharvest life of MA-packaged ‘Acco’ and ‘Herskawitz’ was limited to 10 days due to fungal growth ≥2 log CFU g⁻¹ at 5 °C. However, the concentration (%) and compositional changes in volatile compounds indicated that the flavour/aroma life (7 days) was shorter than the postharvest shelf-life based on appearance and other physicochemical (10 days) for both cultivars.     

Detection of downy and powdery mildew resistance QTL in a ‘Regent’ × ‘RedGlobe’ population

One hundred and eighty six F₁ plants from a ‘Regent’ × ‘RedGlobe’ cross were used to generate a partial linkage map with 139 microsatellite markers spanning all 19 chromosomes. Phenotypic scores for downy mildew, taken over two years, confirmed a major resistance QTL (Rpv3) against downy mildew in the interval VVIN16-cjvh to UDV108 on chromosome 18 of ‘Regent’. This locus explained up to 62 % of the phenotypic variance observed. Additionally a putative minor downy mildew resistance locus was observed on chromosome 1 in one season. A major resistance locus against powdery mildew (Ren3) was also identified on chromosome 15 of ‘Regent’ in the interval UDV116 to VChr15CenGen06. This study established the efficacy of and validated the ‘Regent’-derived downy and powdery mildew major resistance genes/QTL under South African conditions. Closely linked SSR markers for marker-assisted selection and gene pyramiding strategies were identified.     

Biochemical and proteomic analysis of ‘Kyoho’ grape (Vitis labruscana) berries during cold storage

Low temperature storage is widely used to maintain the quality of postharvest fruit and extend their shelf-life. In this study, changes in specific metabolites and protein expression profiles of grape berries under cold storage were investigated by liquid chromatography and proteomic studies, respectively. During cold storage, total soluble solids and reducing sugars accumulation was accompanied by a decline in organic acids and phenols contents. A comparative analysis of the proteomes of grape berries during cold storage was performed using a two-dimensional electrophoresis (2-DE) proteomic approach. Seventy-nine differentially regulated proteins during cold storage were successfully identified by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry, and classified into eight main categories based on their biological function. Down-regulation of proteins associated with glycolysis and the Krebs cycle, and up-regulation of cell wall polysaccharide degradation-related enzymes provided molecular evidence that soluble sugar and carbohydrate metabolism play a crucial role in postharvest regulation. In addition, cold storage increased the expression abundance of several stress related proteins such as heat shock proteins, proteasome and antioxidant enzymes, suggesting a physiological adaptation to low temperature was induced in grape berries. This study contributes to a better understanding of the cellular events in grape berries under cold storage and provides potentially useful information for maintaining fruit quality and minimizing postharvest losses.