Delaying establishment of controlled atmosphere or CO2 exposure reduces ‘Fuji’ apple CO2 injury without excessive fruit quality loss

Storage of ‘Fuji’ apple fruit in a high CO₂ (3 kPa) and low O₂ (1.5 kPa) controlled atmosphere (CA) reduced firmness and titratable acidity (TA) loss during long term storage. This CA environment also induced development of internal CO₂-injury (brown-heart) and slowed the disappearance of watercore. The symptoms of internal CO₂-injury were first detected 15 days after CA establishment and the severity increased during the first 4 months of CA-storage. Delaying establishment of CA conditions for 2–12 weeks significantly reduced the severity of CO₂-injury. Delaying CO₂ accumulation to 3 kPa for 1–4 months during CA (1.5 kPa O₂+0.05 kPa CO₂) storage also reduced development of CO₂-injury symptoms. Delaying CA or CO₂ accumulation resulted in lower firmness and TA compared to establishment of CA within 72 h of harvest. However, the delay treatments did result in firmness and TA that were significantly higher compared to values for fruit stored in air. The incidence and severity of senescent injuries (flesh browning and core flush) detected during the late period of storage were greater in air- than CA-stored fruit. The results indicate the susceptibility of ‘Fuji’ apples to CO₂-injury is highest during the first weeks of storage after harvest. Delaying establishment of CA or exposure to elevated CO₂ after harvest may be a practical strategy to reduce CO₂-injury while maintaining other important quality attributes at acceptable levels.     

Predicting the spread of postharvest disease in stored fruit,with application to apples

Postharvest diseases can cause considerable damage to harvested fruit in controlled atmosphere storage. Since there is a large cost associated with opening the storage rooms, regular assessment of damage levels is not feasible, and many experts agree on the need for a reliable predictive model. Presented here is a simulation model that predicts the overall incidence of disease in a bin of stored fruit as a function of initial infection levels and the fruit's susceptibility to fungal attack. Uninfected fruit tissue, infected fruit tissue, and fungal growth are modelled by a system of three ordinary differential equations. Simulations of the growth and spread of the pathogen in storage were conducted, with disease incidence measured monthly. The model provides insight into the dynamics of postharvest fungal disease, and forms the basis of a predictive model that could be used by packinghouses to determine how long a given crop of fruit can be stored before the infection risk rises above a predetermined tolerable level.     

Impact of harvesting time and fruit firmness on the tolerance to fungal storage diseases in an apple germplasm collection

Blue mold and bitter rot, caused by Penicillium expansum and Colletotrichum gloeosporioides, respectively, are two of the most devastating diseases during and after storage of apple. The present project was conducted to evaluate the level of tolerance to these diseases in apple germplasm, and investigate possible associations with other fruit characteristics such as harvest date, firmness at harvest, softening (loss of firmness during storage) and sun-exposure. Apples were harvested at a maturation stage suitable for storage, inoculated with spore suspensions of P. expansum (127 cultivars) or C. gloeosporioides (70 cultivars), and stored for 6 or 12 weeks for early- and late-maturing cultivars, respectively. Fruit firmness was measured after harvest and after storage, and the difference was used as a measure of fruit softening. Average lesion diameter varied significantly among both early- and late-maturing cultivars. The amount of damage caused by the two diseases was significantly correlated across cultivars. Regression analyses indicated that lesion diameter was positively affected by fruit softening and negatively affected by harvest date and firmness at harvest. Impact of the independent variables was quantified with partial least squares discriminant analysis; approximately 40% of the genetic variation could be explained by these variables with harvest date being the most important. The effect of sun-exposure was analyzed on six bi-colored cultivars but the results were not conclusive. Cultivars that showed relatively small symptoms in spite of being early-maturing and/or only medium firm, may have other traits that are beneficial for storage and could therefore be especially useful in breeding programs.     

Allozyme variation in cultivars of Cucurbita pepo L.

Summary Cultivars of Cucurbita pepo were analyzed for their isozyme phenotypes by horizontal starch gel electrophoresis. Considerable allozymic variation was observed between cultivars, especially in the aspartate aminotransferase and malate dehydrogenase isozyme systems. Each of the five fruit types represented in the 21 cultivars tested (zucchini, pumpkin, spaghetti, acorn, scallop and yellow straightneck) could be distinguished by specific allozymes or combination of allozymes. Cultivars within a fruit type gave very similar allozyme phenotypes and often could not be distinguished on the basis of the 6 assays used. Despite the outcrossing nature of the species, allozyme polymorphism within most cultivars was low and did not seriously interfere with the analysis. Approximately half of the hybrid lines tested gave heterozygous phenotypes at one or more loci, indicating that such loci could be used to screen for the percentage of hybrid seed obtained from crosses.     

Towards development of Al-toxicity tolerant lines in indica rice by exploiting somaclonal variation

Somaclonal variations, induced in vitro, were used to enhance tolerance to aluminium (Al) toxicity in rice. Tolerant plants were developed through in vitro screening of embryogenic calli. The calli were derived from mature seed embryos and cultured on medium stressed with different concentrations of Al₂(SO₄)₃⋅18H₂O. Seed germination, callus induction, plantlet regeneration and callus health declined with increased concentration of Al. At higher Al concentrations, callus health deteriorated drastically with partial to total necrosis. Plantlet regeneration varied largely among varieties and treatments. The variety IR72 produced maximum plantlets among all genotypes tested. An amount of 60 ppm or more Al was highly toxic, which greatly reduced plantlet regeneration from callus. R₀ plantlets were grown under glasshouse. Based on the appearance of bronzing symptoms on leaves, the tolerant R₁ plants were selected. R₁ and R₂ lines derived from putative tolerant somaclones, were evaluated in fiberglass tanks filled with Al-toxic soil. R₃ population was evaluated in the field. A few lines derived from IR72 showed high yield and good plant type. The progenies at R₃ showed normal root growth under stressed environment in sand culture. The study revealed that in vitro screening would be an appropriate alternative to conventional breeding in evolving Al-tolerant lines as observed in case of other abiotic stresses. The technique was useful in creating de novo synthesized Al-tolerance character in rice.     

Phenotypic variation in local populations and cultivars of meadow fescue – potential for improving cultivars by utilizing wild germplasm

The utilization of gene bank accessions for breeding purposes is generally hampered by a lack of sufficient genetic and phenotypic characterization. Results are given here of a phenotypic analysis of 30 Norwegian local populations and 10 Nordic cultivars of meadow fescue, and a combined analysis of phenotypic data with previously published molecular data based on 95 amplified fragment length polymorphic markers. Seventeen phenological and morphological, and two derived characters, were assessed on 2264 individual plants. Previous molecular diversity analyses have shown that the Norwegian local populations can be divided into three groups based on a likely history of the introduction of the species into Norway. A similar pattern was evident from relationships between the mean phenotypic values of populations and cultivars. Such a combined phenotypic and genetic characterization of germplasm can facilitate the use of gene bank material in breeding, as breeders can use these data to select populations with extreme values of a field trait, along with markers which represent potential predictors of phenotypic value.     

Genetic variation in seed production and its components in four cultivars of the pasture grass Setaria sphacelata

Variation in seed production and its components was investigated between and within four cultivars of the pasture grass Setaria sphacelata, in two experiments over two years, as a basis for future cultivar improvement. The study sought to determine the basis for the considerable differences in seed production of the four cultivars Nandi, Narok, Solander and Kazungula, to determine the extent of genetic variation in the four cultivars in attributes which contribute to seed yield, and to investigate genotypic consistency in seed production over years and seasons. Each experiment comprised 50 genotypes of each cultivar. In the first experiment, plants were harvested a set number of days after median flowering date whereas in the second experiment, which was unreplicated, each genotype was harvested a set number of days after it had flowered. In the first experiment, seed yields were generally highest for Kazungula, lowest for Narok and intermediate for Nandi and Solander. All measured attributes contributing to seed yield exhibited a high order of variation between and within cultivars, but the basis for the large difference in seed yield per plant between cultivars was tiller fertility rather that total tiller number. Averaged over the four harvests, there was a six fold to > 100–fold intra-cultivar genetic range in seed production, associated with differences in tiller fertility, which were associated with differences in date of first flowering. Broad sense heritability for seed yield averaged 0.68 for the four cultivars and showed little change over the four harvests. Genotypes which produced high seed yields in summer were also more productive of seed in autumn and the 0ore productive genotypes in the first year were also more productive in the second year. Cultivars differed in the relative importance of factors which contributed to the high seed yield of high-yielding genotypes. In the second experiment, genotypes with a high seed yield also generally had the highest tiller fertility, even though all genotypes were harvested the same number of days after first flowering. Within-cultivar correlations in seed yield between the two experiments were generally significant and the elite 20% of genotypes from this experiment had 1.2–2.9 times the seed yield of the same genotypes with a very different harvesting regime in the first experiment. It is concluded that opportunities exist in all four cultivars for improvement in seed production and that the selection criterion offering the best opportunity for advance would be fertile tiller number. In Narok, Solander and Nandi, this would result in increased tiller fertility, whereas in Kazungula, it would result in an increase in total tiller number. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal variation in resistance of chrysanthemum cultivars to Frankliniella occidentalis (Thysanoptera: Thripidae)

Seasonal variation in the level of host plant resistance can have important consequences for the repeatability of tests to measure host plant resistance to insect pests. In the present study, the levels of resistance to Frankliniella occidentalis of a susceptible and a partially resistant cultivar of chrysanthemum, Dendranthema grandiflora, were determined throughout the year. Thrips damage, reproduction and adult female survival were determined on excised leaves in Petri dishes under uniform conditions. Strong seasonal fluctuations were observed in these three characteristics. On leaves from plants grown in winter, damage, reproduction, and survival were higher than on leaves from plants grown in summer. Clear differences in resistance were observed between the susceptible and the partially resistant cultivar on leaves from plants grown in winter, while differences disappeared in summer. Damage on both cultivars and survival on the susceptible cultivar were negatively correlated with mean daily solar radiation during plant growth, suggesting that the level of resistance depends on light intensity during plant growth. This was confirmed in an experiment carried out in summertime with shaded and unshaded plants. Leaves from control plants, grown under high light intensity had a higher level of resistance than leaves from shaded plants grown under reduced light intensity. There were clear differences in resistance between the cultivars under shaded conditions (low light intensity), but not under unshaded control conditions (high light intensity). This revised version was published online in July 2006 with corrections to the Cover Date.     

Increase of genetic variation in some lettuce cultivars by induction of mutations: A technical note

Summary Colchicine treatments of 13 lettuce cultivars for production of polyploid lettuce also resulted in rapid growing diploid mutants.     

Somaclonal variation in three Argentinean varieties of Triticum aestivum with different karyotypic instability*

Three cultivars of wheat showing different levels of spontaneous karyotypic instability were studied regarding their stability in vitro for a number of characters, i.e. chromosome structure, gliadin pattern, glume and grain colour, awn type, chlorophyll pigmentation and plant morphology. The progenies of somaclones derived from immature embryos of both aneuploid and euploid plants were used in this study along with foundation seeds and a large number of their sexual progeny in order to discriminate between pre-existent variability and any novel variation induced by the in vitro culture. Only one translocation not described before and a new gliadin pattern were detected which could be ascribed to the effects of tissue culture, suggesting that this technique is not effective for inducing novel variation for breeding purposes in wheat.     

Preharvest application of methyl jasmonate (MeJA) in two plum cultivars. 2. Improvement of fruit quality and antioxidant systems during postharvest storage

‘Black Splendor’ (BS) and ‘Royal Rosa’ (RR) plums were treated preharvest with methyl jasmonate (MeJA) at three concentrations (0.5, 1.0 and 2.0 mM) along the on-tree fruit development: 63, 77 and 98 days after full blossom (DAFB). Both control and treated fruit were harvested at the commercial ripening stage and stored in two temperature conditions: 9 days at 20 °C or at 2 °C + 1 day at 20 °C for 50 days. Preharvest MeJA at 2.0 mM significantly accelerated whereas 0.5 mM delayed the postharvest ripening process for both cultivars, since ethylene production, respiration rate and softening were reduced significantly at the two storage conditions for 0.5 mM. In these fruit, total phenolics, total antioxidant activity (hydrophilic fraction, HTAA) and the antioxidant enzymes peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were found at higher levels in treated than control plums during postharvest storage, which could account for the delay of the postharvest ripening process and the extension of shelf-life.     

A partial diallel study of powdery mildew resistance in six apple cultivars under three growing conditions with different disease pressures

Summary The suitability of large-fruited apple cultivars as alternative donors of powdery mildew resistance to the crabapples carrying major gene resistances was assessed. Five accessions with varying levels of mildew resistance (‘Dülmener Rosen', ‘Liberty', ‘Sciros', ‘Prima' and ‘Red Delicious') and one susceptible cultivar (‘Cox's Orange Pippin') were mated in a partial diallel design, and sub-sets of each seedling family were evaluated for three years at three New Zealand sites (Havelock North, Riwaka and Clyde) with different climatic conditions. There was a high correlation among the powdery mildew susceptibility scores of the individual seedlings over the three years, but disease levels varied among sites, with those at Clyde being the highest. All accessions with some resistance were found to confer additive resistance to their progenies to varying degrees depending on the climatic conditions of the sites, but findings suggest that progeny selection at Clyde will be sufficient for breeding purposes. The performance of the cultivar itself was not necessarily a good predictor of the level of resistance conferred to its progenies. The mostly negative genetic correlations between powdery mildew scores and fruit quality attributes suggest that selecting for powdery mildew resistance and desirable fruit quality traits may not be difficult. However, a larger number of families may be needed for more precise estimates of the genetic correlations to strengthen confidence in this conclusion.     

Heritability estimates of spaced-plant traits in three perennial ryegrass (Lolium perenne L.) cultivars

Summary Seed yield in perennial ryegrass is low and unpredictable. Spaced-plant traits suitable for indirect selection for total seed yield in drilled plots would be very useful. The objectives of this investigation were to evaluate genetic variation for seed yield components and other traits among clones from three perennial ryegrass cultivars differing in seed yield and their open-pollinated progenies. Per cultivar, a random set of 50 genotypes was cloned and on each genotype seed was generated by open pollination. Clonal ramets of the parents were observed for 17 traits in 1986 at two locations. In 1987 and 1988, parents and progenies were observed as single plants in a randomized complete block design with two replications. There was little cultivar-environment interaction for most traits. The parents differed significantly for almost all traits. Half-sib (HS) families differed for only three to five traits. Broad-sense heritabilities (h² _b), based on variance components of the parents, were moderate to high; earliness had the highest h_b ². Narrow-sense heritabilities (h² _n), based on variance components among HS-families, were low to moderate and mostly not significant; for most traits h² _n estimates varied between years and cultivars. Flag leaf width and date of first anthesis showed the highest h² _n. Narrow-sense heritability estimates from parent-offspring regressions (h² _nPO) ranged from non-significant to high, depending on year and cultivar; they were generally higher than the corresponding h² _n estimates. Generally, h² _nPO was highest for earliness, flag leaf width, ear length and the number of spikelets per ear. Breeding methods that capitalize on additive genetic variance, such as mass selection, should result in improvement for these traits.     

The potential role of PR-8 gene of apple fruit in the mode of action of the yeast antagonist,Candida oleophila,in postharvest biocontrol of Botrytis cinerea

Several pathogenesis-related (PR) genes of apple have been cloned and their response to different pathogens has been studied. Different PR genes, however, may have a variable response depending on the specific organ or tissue as well as microbe. The objective of the current study was to characterize the expression of specific apple PR genes in fruit tissues in response to the antagonistic yeast, Candida oleophila (a common postharvest biocontrol agent), and the fungal pathogen, Botrytis cinerea (a major postharvest pathogen). Apple PR-5 and PR-8 gene expression was characterized in fruit in response to C. oleophila and B. cinerea. Results indicated that PR-8 expression was significantly elevated in response to both fungi. In contrast, neither C. oleophila nor B. cinerea treatment markedly affected PR-5 expression. The PR-8 gene was then synthesized and cloned into a Pichia pastoris expression system to study the antifungal activity of the PR-8 protein against B. cinerea both in vitro and in vivo. Collectively, the PR-8 gene of apple is associated with the response to B. cinerea infection, and may play a role in the mechanism by which C. oleophila effectively inhibits B. cinerea disease in apple fruit, namely by the induction of this specific host PR gene.     

Allelic variation of a clubroot resistance gene (Crr1a) in Japanese cultivars of Chinese cabbage (Brassica rapa L.)

Clubroot resistance (CR) is an important trait in Chinese cabbage breeding worldwide. Although Crr1a, the gene responsible for clubroot-resistance, has been cloned and shown to encode the NLR protein, its allelic variation and molecular function remain unknown. Here, we investigated the sequence variation and function of three Crr1a alleles cloned from six CR F₁ cultivars of Chinese cabbage. Gain-of-function analysis revealed that Crr1a^Kinami90_a isolated from the cv. ‘Kinami 90’ conferred clubroot resistance as observed for Crr1a^G004. Because two susceptible alleles commonly lacked 172 amino acids in the C-terminal region, we investigated clubroot resistance in transgenic Arabidopsis harboring the chimeric Crr1a, in which 172 amino acids of the functional alleles were fused to the susceptible alleles. The fusion of the C-terminal region to the susceptible alleles restored resistance, indicating that their susceptibility was caused by the lack of the C-terminus. We developed DNA markers to detect the two functional Crr1a alleles, and demonstrated that the functional Crr1a alleles were frequently found in European fodder turnips, whereas they were rarely introduced into Japanese CR cultivars of Chinese cabbage. These results would contribute to CR breeding via marker-assisted selection and help our understanding of the molecular mechanisms underlying clubroot resistance.     

Yield variation of spring cereals in relation to selected soil physical properties on three clay soil fields

The crop growth is highly dependent on growth conditions which vary from year to year making precision farming challenging. In the present paper was first investigated whether varying soil physical properties reflect the within-field yield variation of small grain cereals and how do the variations in weather conditions between growing seasons affect the within-field yield variation. Secondly, the potential biomass accumulation of the crop in existing soil and weather conditions was simulated. The simulated and experimentally based site-specific total biomasses were compared in order to find out whether the soil data explains the observed variations in yield.Three experimental fields size of 3–4 ha were established to examine the spatio-temporal yield variation during three years. The clay content of soils was high (> 46%) and soils were classified as Stagni-Vertic Cambisols. Correlations between soil water retention properties and crop yield were studied. Top and subsoil saturated (SWC), field capacity (FC) and permanent wilting point (PWP) water content, and saturated hydraulic conductivity of soil (K_sat), were determined from 19 to 24 places on each field once during the three years experimental period. During growing seasons, soil moisture content and leaf area index (LAI) were determined at same places biweekly, and yield was harvested. Spring barley (Hordeum vulgare) was grown on two fields, and spring wheat (Triticum aestivum, 2 years) and spring oilseed rape (Brassica napus L., one year) were grown on the third field.The measured grain yields correlated with selected soil physical properties only in few cases. The observed spatial variation in the biomass was in most cases found to be higher than the simulated. Therefore, the above mentioned parameters were not enough to predict the yield correctly in case of high variations. There were other factors decreasing the observed yield e.g. lodging, cold summer, extremely high precipitation and slopes in field. According to our results it is evident that it is very difficult to predict site-specific biomass accumulation solely by soil properties in order, for instance, to fertilize in a site-specific manner. Therefore one needs to measure the crop during the growing season in order to simulate the biomass accumulation for precision farming purposes.     

Contributions of cultivars,management and climate change to winter wheat yield in the North China Plain in the past three decades

The detailed field experiment data from 1980 to 2009 at four stations in the North China Plain (NCP), together with a crop simulation model, were used to disentangle the relative contributions of cultivars renewal, fertilization management and climate change to winter wheat yield, as well as the relative impacts of different climate variables on winter wheat yield, in the past three decades. We found that during 1980–2009 cultivars renewal contributed to yield increase by 12.2–22.6%; fertilization management contributed to yield increase by 2.1–3.6%; and climate change contributed to yield generally by −3.0–3.0%, however by −15.0% for rainfed wheat in southern part of the NCP. Modern cultivars and agronomic management played dominant roles in yield increase in the past three decades, nevertheless the estimated impacts of climate change on yield accounted for as large as −23.8–25.0% of observed yield trends. During the study period, increase in temperature increased winter wheat yield by 3.0–6.0% in northern part of the NCP, however reduced rainfed winter wheat yield by 9.0–12.0% in southern part of the NCP. Decrease in solar radiation reduced wheat yield by 3.0–12.0% across the stations. The impact of precipitation change on winter wheat yield was slight because there were no pronounced trends in precipitation. Our findings highlight that modern cultivars and agronomic management contributed dominantly to yield increase in the past three decades, nevertheless the impacts of climate change were large enough in some areas to affect a significant portion of observed yield trends in the NCP.     

The use of allozymes at three life stages influences genetic variation analysis and clustering in Cicer arietinum germplasm collections

Levels of genetic variation using 6 enzyme systems for a total of 11 interpretable loci were examined in chickpea (Cicer arietinum) originating from 9locations in Bangladesh. The measurement of genetic variation at enzyme loci was carried out on the seed embryo, on the early leaves of seedlings and on the mature leaves at the vegetative stage. A total of 592individuals, including 240 seeds, 200 seedlings and152 mature leaves were investigated. Using electrophoretic data, chickpea was found to express higher percentages of polymorphic loci at the seed stage (36–64%) than at seedling (22–56%) or the vegetative stage (11–44%). The proportion of mean number of alleles and the average mean observed heterozygosity also were higher at the seed stage when compared to the seedling and vegetative stages. Unique alleles were absent, and only differences infrequencies could be noticed. Positive values of the fixation index were noted for pgm-1 and 6pg-1 for all stages and in both mnr loci for the seed embryo's. A trend towards lower genetic distances of all possible pairs of populations could be observed when comparing those of seed embryo's with seedlings or mature leaves. This trend was even more pronounced when pooling the data of 9 populations into their 3regions. Slight differences in genetic distances caused a separative clustering of population 3 at seed embryo, of population 2 at seedling and of population5 at vegetative stages. It is suggested that careful examination of enzyme polymorphisms at different developmental stages is a prerequisite before drawing conclusions on the genetic distance between germplasm collections from different origins since small differences in the data entry for clustering results in ties that may affect tree topologies. This revised version was published online in July 2006 with corrections to the Cover Date.