Red Gauntlet Research Articles

Study of a genetic collection of strawberry (Fragaria L.) for resistance to powdery mildew.

Powdery mildew (Sphaerotheca macularis Mag. (syn. Podosphaera aphanis Wallr.)) is a dangerous disease of strawberry (Fragaria L.). The resistance of strawberry to powdery mildew is controlled polygenically. Several genetic loci with a large contribution to disease resistance have been identified in various strawberry varieties. Diagnostic DNA markers have been developed for QTL 08 To-f. They showed a high level of reliable gene detection in mapping populations. The purpose of this study was assessment of a strawberry genetic collection for resistance to powdery mildew and identification of promising strawberry forms for breeding for resistance to S. macularis. The objects of the study were wild species of the genus Fragaria L., varieties and selected seedlings of strawberry (Fragaria × ananassa Duch.) created in the I.V. Michurin Federal Scientific Center, and strawberry varieties introduced from various ecological and geographical regions. To identify QTL 08 To-f, DNA markers IB535110 and IB533828 were used. Locus 08 To-f was detected in 23.2 % of the analyzed strawberry genotypes, including wild species F. moschata and F. orientalis, strawberry varieties of Russian breeding (Bylinnaya and Sudarushka) and foreign breeding (Florence, Korona, Malwina, Ostara, Polka and Red Gauntlet). The correlation between the presence of markers IB535110 and IB533828 and phenotypic resistance (powdery mildew effect on strawberry plants is absent) was 0.649. The determination coefficient (R2 ) showing the contribution of the studied locus to the manifestation of the trait was 0.421, that is, in 42.1 % of cases resistance was explained by the presence of QTL 08 To-f, and in 57.9 % of cases, by other genetic factors. All strawberry genotypes with locus 08 To-f were characterized by high field resistance to S. macularis in the conditions of Michurinsk, Tambov region. Thus, locus 08 To-f is promising for conferring resistance on local powdery mildew races, and markers IB535110 and IB533828 can be used in marker-assisted breeding programs to create powdery mildewresistant strawberry genotypes.

Evaluation of garden strawberry varieties against biochemical parameters and genetic aroma determinants

The paper presents the results of a long-term (2015-2020) study into a collection of domestic and foreign strawberry varieties cultivated in the Central Black Region, in terms of biochemical composition (content of soluble solids (SS), sugars, organic acids, ascorbic acid, anthocyanins) and genetic aroma determinants. The varieties with a high SS content (above 12.0%) herewith include Alena, Divnaya, Kupchikha, Olympic hope, Torpedo, Flora; sugars (above 9.0%) – Alena, Lastochka, Olimpiyskaya Nadezhda, Flora, Privlekatelnaya; ascorbic acid (above 80.0 mg/100 g) – Divnaya, Kupchikha, Sudarushka, Festival chamomile; anthocyanins (above 100.0 mg/100 g) – Alena, Fireworks. Among the varieties addressesd, the Kubata, Tsaritsa (domestic selection), Kimberly, Marshall, Red Gauntlet, Vima Tarda (foreign selection) varieties are characterized by a combination of functional alleles of FaOMT and FaFAD1 genes for a complex aroma profile. The selected promising varieties can be used as sources of valuable quality attributes and biochemical composition of fruits.

INFLUENCE OF PLANT GROWTH REGULATORS AND AGROCHEMICAL “SILAKTIV” ON CADMIUM ACCUMULATION BY STRAWBERRY (FRAGARIA X ANANASSA DUCH.) PLANTS

In a vegetation experiment, the effect of foliar treatments of strawberry varieties Honeoye, Troitskaya, Red Gauntlet with Epin-Extra, Emistim and Silaktiv on the accumulation of cadmium from HM-contaminated soil was studied. With the use of the studied drugs and agrochemical, the cadmium content decreased to the greatest extent in the roots of plants. The influence of the studied preparations and agrochemical on the accumulation of cadmium in the organs of strawberry plants and on their productivity significantly depended on the variety.

Genetic diversity of modern strawberry varieties of domestic breeding

The object of research was the pedigrees of strawberry varieties. An analysis of the genetic relationship of 129 varieties of domestic strawberry breeding, 6 parent forms, 2 of which are foreign varieties was carried out. Until the 1930s, strawberry culture in the USSR was based exclusively on Western European varieties: König Albert von Sachsen, Roschinskaya, Victoria, White Pine, Apricose, Konigin Luise, Noble Laxton, Siger, Spate von Leopoldshall, Kent’s Miracle, Sharpliss, Muto, etc. During the transition to the commercial production, these varieties were not insufficiently tolerant, which required the creation of a new assortment for various conditions of cultivation, and served as the beginning of the implementation of domestic strawberry breeding programs. At present, the State register of breeding achievements approved for use in 2020 includes 106 strawberry varieties, of which 82 are of domestic breeding. Existing domestic varieties have different geographical origins. The main Centers for strawberry breeding are: All-Russian Horticultural Institute for Breeding, Agrotechnology and Nursery, I.V. Michurin Federal Research Center, N. I. Vavilov All-Russian Institute of Plant Genetic Resources, North Caucasus Federal Research Center For Horticulture, Viticulture, and Winemaking, etc. Initially, the parent forms for creating a domestic assortment were European and American varieties: Culver, Deutsch Evern, Georg Soltwedel, Konigin Luise, Markee, König Albert von Sachsen Marshall, Macherauchs Marieva, Macherauchs Fruhernte, Muto, Premier, Red Coat, Red Gauntlet, Robinson, Senga Sengana, Sieger, Sparkle, Spate von Leopoldshall, Wander von Kothen. Analysis of pedigrees of 135 varieties from the 23 literature sources allowed to identify the most effective in the formation of domestic assortment genotypes of strawberry: Komsomolska (10 varieties in the first generation; 12 in the second; 14 in the third, 2 in the fourth), Mysovka (12 varieties in the first generation; 20 in the second; 21 – in the third; 2 in the fourth), Obilnaya (7 varieties in the first generation; 22 – the second; 20 for the third; 6 for the fourth), Festivalnaya (21 varieties in the first generation; 19 – in the second; 6 in the third), Culver (20 varieties in the first generation; 16 – in the second, 3 – in the third), Senga Sengana (13 varieties in the first generation; 7 – in the second; 4-in the third). The originator of 37.8% of domestic varieties included in the State register is the Obilnaya variety (Wander von Kothen × Deutsch Evern). On the basis of the Festivalnaya variety obtained with his participation (Obilnaya × Premier), an assortment was created that has not lost its relevance at the present time (26 varieties are included in the State register). The varieties Mysovka (Wander von Kothen × Deutsch Evern) and Zenga Zengana (Markee × Sieger) are included in the pedigree of 13 and 14 modern varieties, respectively. Based on the Komsomolka and Culver varieties, 7 and 9 varieties were created, respectively, which are currently included in the State register. Intraspecific hybridization has not exhausted the possibility of creating a genetically diverse breeding material. Taking into account the fact that domestic varieties often have closely related origin, it is desirable to involve introduced forms and varieties obtained with their participation in the breeding process more widely. The results of using various methods of breeding (inbreeding, saturating crosses) indicate that it is possible to further improve strawberry varieties creating donors of a high level of economically valuable traits. The current level of scientific knowledge and development of biotechnological research allows us to “model” varieties, including in the genotype of strawberry genes and gene blocks of valuable traits from closely related species, reducing the duration of the breeding process.

Effet du ni sur la productivité végétative et générative des plants de fraises de jardin (Fragaria × Ananassa Duch.)

In a vegetative experiment, the effect of two concentrations of Ni in the soil of 80 and 240 mg Ni / kg on the vegetative and generative productivity of plants of three varieties of strawberries Honeoye, Troitskaya, Red Gontlet was studied. Ni soil contamination had a significant impact on the vegetative and generative productivity of strawberry plants. The degree and direction of this effect was largely dependent on the variety. When the Ni content in the soil was 80 mg / kg in plants of strawberry varieties Honeoye and Red Gauntlet, there was a tendency to an increase in leaf mass, most of all in the Honeoye variety – by 16.6 % compared to an uncontaminated fertilized background. When the Ni concentration in the soil was 240 mg / kg in Honeoye plants, the leaf mass decreased by 19.0 % relative to the uncontaminated background, while in the Troitskaya and Red Gauntlet plants, the leaf mass increased, to a maximum, in Red Gontlet plants by 57.9 %. In plants of the strawberries varieties Honeoye mass of strawberries runners when soil is polluted, Ni was decreased to the greatest extent when the content of Ni in soil is 80 mg/kg – 23.3 % relative to the background values, the varieties Troitskaya and Red Gauntlet mass of strawberries runners, it became higher, especially when the content of Ni in soil is 240 mg/kg – 24.5 % and 42.5 % of the relatively polluted background, respectively. In plants of the Honeoye variety, the number of rosettes with Ni soil contamination tended to decrease relative to the background value (maximum, by 27.0 % when the Ni content in the soil is 80 mg / kg), in the Troitskaya variety – to increase (to the greatest extent, when the Ni content in the soil is 240 mg/kg – by 220 %). In plants of the Red Gauntlet variety, the number of rosettes per plant at each of the studied levels of soil contamination with Nickel tended to decrease (by a maximum of 11.8 % with a Ni content of 80 mg/kg in the soil). The number of peduncle in plants of strawberry varieties Honeoye and Troitskaya on polluted soil tended to decrease in comparison with the background. In plants, varieties of Red Gauntlet for this parameter was an opposite trend in the contamination of soil Ni number of peduncle per plant increased relatively polluted background (maximum 60.0 % when the contamination level of 240 mg/kg). The mass of berries on one plant of Red Gauntlet strawberry with Ni soil contamination at the level of 240 mg / kg statistically significantly increased by 38.3 % relative to the non-polluted background. In plants of the Honey and Troitsky varieties, the berries mass on one plant naturally decreased compared to the non-polluted background (by 10.2 % at a Ni content of 240 mg/kg and by 44.0 % at a Ni content of 80 mg/kg, respectively). When the soil was contaminated with Ni 240 mg / kg of Red Gauntlet strawberry plants, the number of berries per plant increased by 45.3 % relative to the non-polluted background. In plants of the Honeoye and Troitskaya varieties, the number of berries per plant decreased in comparison with the non-polluted background, to the greatest extent, by 30.9 % at a content of Ni 240 mg/kg and by 29.9 % at a content of Ni 80 mg/kg, respectively.

Polymorphism of the FaOMT and FaFAD1 genes for fruit flavor volatiles in strawberry varieties and wild species from the genetic collection of the Michurin Federal Research Center.

Fruit aroma is an important consumer attribute of strawberry varieties. The key volatile compounds of the aromatic complex of strawberry fruit are mesifurane (fruity and caramel aromas) and γ-decalactone (fruity, sweet, or peachy aroma). The mesifurane content in strawberry fruit is controlled by the FaOMT gene, which is mapped to the distal region of the long arm of chromosome VII-F.1. The γ-decalactone content in strawberry fruit is controlled by the FaFAD1 gene, mapped to the distal region of the long arm of chromosome III-2. Identification of forms carrying genes for fruit flavor volatiles is an important step in breeding varieties with fragrant fruit. The use of molecular markers allows highly reliable detection of target gene alleles in a genome at early developmental stages. This study involves molecular genotyping of Fragaria L. varieties for the FaOMT and FaFAD1 genes, analysis of polymorphism of the loci in question, and identification of genotypes valuable for breeding. The objects of our study were wild species of the genus Fragaria L. and strawberry varieties (Fragaria × ananassa Duch.) of different ecological and geographic origins. To assess the allelic states of the FaOMT gene, the codominant marker FaOMT-SI/NO was used, and for the FaFAD1 gene, the dominant marker FaFAD1. The functional allele of the FaOMT gene (FaOMT+) in the heterozygous state (FaOMT+FaOMT– genotype) was detected in 34.9 % of the accessions tested. The functional allele of the FaOMT gene in the homozygous state (FaOMT+FaOMT+ genotype) was detected in 51.2 % of the accessions. The homozygous state of the inactive allele (FaOMT–FaOMT– genotype) was detected in 13.9 % of the studied strawberry accessions. The FaFAD1 gene was identified in 25.6 % of the analyzed collection of strawberry genotypes, including the wild species F. orientalis Los., F. moschata Duch., F. ovalis Rydb. The combination of functional alleles of the FaOMT and FaFAD1 genes was detected in 16.3 % of the analyzed forms. The wild species F. orientalis Los. and F. moschata Duch. and strawberry variety Red Gauntlet combine the functional allele of the FaFAD1 gene with the homozygous state of the active allele of the FaOMT gene; therefore, we recommend them as promising sources of high contents of mesifurane and γ-decactone in fruit in breeding programs for fruit aroma.

Nutrient value of fruit in promising strawberry varieties

One of the current areas in research of fruit and berry crops is the study of their nutritional value and micronutrient composition. Valuable chemical composition of the strawberry determines a wide spectrum of its utilization not only as fresh fruit, but also as a raw material for food industry. Breeding requirements for contemporary strawberry varieties together with yield, large-fruit, important taste and dietary qualities of fruit provide for higher content of biologic active substances. The aim of the research was an integrated assessment of strawberry fruit for content of nutrients and bioactive compounds, as well as mineral elements, and its antioxidant activity. Material and methods. The objects of investigation were berries of 5 strawberry varieties bred in the I.V. Michurin Scientific Centre (Lakomaya, Prazdnichnaya, Privlekatelnaya, Urozhaynaya CGL, Feyerverk) and 9 foreign varieties (Vima Zanta, Dukat, Zefir, Kama, Maryshka, Red Gauntlet, Festivalnaya romashka, Honey, Elsanta) which are promising for cultivation in the Black Soil Region of Russia. The content of soluble solids was determined by the refractometric method, sugars - by Bertrand's method, pectins - by the volumetric method, anthocyanins - by pH-differential spectrophotometry. Total content of antioxidants was defined by amperometric method with recalculation per quercetin. Determination of vitamin B1 was carried out using the fluorometric thiochrome method, vitamin B2 - by fluorometric titration with riboflavin-binding apoprotein after acid-enzymatic hydrolysis, ascorbic acid, vitamin E (tocopherols), niacin, organic and hydroxycinnamic acids - by HPLC, flavonols - spectrophotometrically, minerals and trace elements - by atomic absorption method. Results and discussion. A significant variation in the chemical composition indices depending on the varietal characteristics was found. Strawberry fruit accumulated 8.5-12.0% soluble solids, 5.9-8.7% sugars, 1.5-2.1% of fibre, 0.78-1.12% pectin substances, 0.89-1.45% organic acid; 100 g contain 33.5-48.2 mg vitamin C, 18.3-108.5 mg anthocyanins, 0.024-0.041 mg vitamin B1, 0.012-0.029 mg vitamin B2, 0.10-0.26 mg niacin, 0.26-0.60 mg TE vitamin E, 102-270 mg potassium, 0.15-0.95 mg iron; total antioxidant activity ranged within 180.8-350.0 mg/100 g. High level of anthocyan accumulation (over 80.0 mg/100 g) was observed in Privlekatelnaya, Lakomaya and Feyerverk strawberry varieties. Urozhaynaya CGL, Privlekatelnaya and Lakomaya varieties were characterized by dessert taste. According to the results of the studies Privlekatelnaya variety stood out because of the high complex accumulation of vitamin C, anthocyanins, and high total antioxidant activity. These varieties are recommended for both fresh use and for freezing, as well as for production of functional foods. Conclusion. The obtained data are of interest for further inclusion in the Tables of the chemical composition of Russian food products.

Study on the Varieties Influnce of Strawberries Productivity Grown in South of Teleorman County

Abstract Strawberries, the single species in the orchards which appropriate in the same time at common culture in the field and in protected culture, is of great importance on the line of profitability.. We can expect that in the next years the requirements for strawberries fresh and preserved, fruit with an exceptional taste, will double or even triple. For this reason, I noticed the strawberry culture in the field, at three varieties (Surprise des Halles, Red Gauntlet, Senga Sengana), into an favorable ecosystem for studied species and in various crop systems advantageous from economically point of view. The objectives of the paper are to capitalize and promote the strawberry culture in the area where the observations were made, the south of Teleorman County.

THE USAGE OF NEW AMERICAN STRAWBERRY VARIETIES IN REPUBLIC OF MOLDOVA IN OPEN FIELD

The implement of varieties with a high potential productivity, in course of 30 years(1974-2004) leaded to increase gross production of strawberry from 224 thousands tones to 1 mln tones.These results was obtained on basis of renovating continuance the assortiment used in cultivation. The lead role in this activity become to University of California, wich varieties being implement only in this state assure 75% from gross production on this country.After view of scientists from this University, the usage of varieties will facilitate to increase gross production and in other states of USA. It is necesary to specify, the aproximatly 70% from expenses related to strawberry research are meant in special associated for creation a new varieties. In result was obtained varieties:Camarosa, Chandler, Oso Grande, Pajaro, Seascape, Selva, Sparcle etc. wich potential in plantation of production go beyond quoto 50 tones per ha of fruit. Each variety it is destined for the certain condition of cultivation in open field, and even in protected field. Respective varieties have a high level of capitalization a nutritive space and capacity to develop more undergroung stems in the first years of vegetation. These varieties are in a investigation stage for cultivation on open field in central area of R. Moldova. Researching objects serve strawberry plants of 1-3 years, varieties: Red Gauntlet, Camarosa, Seascape, Chandler, Selena, Elsanta. Investigations are effected at Fruit Growing chair of the State Agrarian University of Moldova, field-experience on the agricultural lands at SA ’’ORHEI-VIT’’ and Private Family Farm ’’VRABIE NICOLAE’’ district Hincesti, wich it is situated in central area of Republic. Investigations are effected after wide methods used in modern Fruit Growing.

The quantitative estimation of Phytophthora cactorum in infected strawberry tissue

A comminution, dilution plate, colony counting method is described for the quantitative measurement of colonisation of strawberry crowns by Phytophthora cactorum. The survival of mycelial fragments was greatly affected by homogenisation speeds and time. Comminution times in excess of 30 s at a speed of 15000 rev. min−1 led to a rapid decrease in viability. In recovery experiments using a suspension of hyphal fragments, the presence of host tissue significantly increased the numbers of colonies obtained over a range of comminution times. The recovery of fungal colonies was similar in the presence of healthy crown tissues from cvs Tamella and Red Gauntlet. Crown tissue from partially resistant Cambridge Favourite comminuted with Phytophthora mycelium led to a 20% reduction in colonies. The survival of hyphae was related to length over the range 400–800 μm, but more especially to the numbers of hyphal branches per fragment. Hyphae from tissue homogenates survived better submerged in selective agar than on the surface. Optimal recoveries were obtained in the pH range 5·5–6·5, they physiological pH of strawberry crown tissue. Polyethylene glycol (PEG 1500) and mannitol used as osmotic stabilizers between − 1·2 and − 7·6 bars had little or no effect on colony number. Most colonies derived from infected crown tissue developed from tissue fragments much greater in size than the minimal viable hyphal length. Colonisation of infected, highly susceptible cv. Tamella was approximately twice as great as that of cv. Cambridge Favourite based on recovered colonies.

Analysis of Cross‐Reactive Antigens of Phytophthora fragariae and Strawberry and their Relation to Resistance and Susceptibility

AbstractThe presence of cross‐reactive antigens between five isolates of P, fragariae (Pf 1, Pf 2, Pf 3, Pf 10 and Pf 11) belonging to five physiological races of the fungus and five strawberry cultivars (Cambridge Favourite, Hapil, Red Gauntlet, Siletz and 52AC18) exhibiting different disease responses to the five isolates was demonstrated by Western blotting. Antiserum anti‐H, raised against extracts of healthy Cambridge Favourite roots, detected two antigens which were common to all isolates. Concentration of one of these antigens might be related to the pathogenicity of P. fragariae isolates. Antiserum anti‐PfM, raised against mycelial suspensions from the five isolates, detected a doublet of 64 and 61 kDa in the soluble extracts of healthy roots from the five cultivars tested. The corresponding root suspensions revealed numerous other antigens which reacted with anti‐PfM.In susceptible interactions, the doublet described above and two additional polypeptides of 38 and 31 kda were detected in large concentrations in both the soluble extracts and root suspensions. These four polypeptides were shown to be present in the healthy roots as well as in the mycelial extracts. In resistant interactions, a 116 kDa polypeptide, present in the root suspensions of the healthy host, was detected in the soluble extracts of the infected roots. It is suggested that these antigens might have a role in resistance and susceptibility.

Evaluation of antisera raised against Phytophthora fragariae for detecting the red core disease of strawberries by enzyme‐linked immunosorbent assay (ELISA)

Antiserum was raised against pooled mycelial suspensions from five isolates (designated Pf 1, Pf 2, Pf 3, Pf 10 and Pf 11) representing five physiologic races of Phytophthora fragariae. In enzyme‐linked immunosorbent assay (ELISA), this antiserum detected homologous soluble antigens at protein concentrations as low as 2 ng/ml.Fungal antigens could also be detected in extracts of strawberry plants infected with P. fragariae. Root extracts prepared from the alpine strawberry Fragaria vesca and F. ananassa cv. Cambridge Favourite infected with any of the five isolates studied produced strong reactions in ELISA. In F. vesca, ELISA‐positive material was detectable 6‐8 days after inoculation before macroscopic symptoms appeared. The cultivar Red Gauntlet, which is resistant to Pf 1, 2 and 3 but susceptible to Pf 10 and 11, reflected this differential response in ELISA; the absorbance produced by extracts of plants infected with virulent isolates was significantly higher than that obtained with the corresponding extracts of plants inoculated with a virulent isolates. The recently introduced cultivars Hapil, Ostara and Providence were found to be susceptible to all isolates in this study: the corresponding root extracts were also positive in ELISA.The antiserum also detected P cactorum infections. Nevertheless, the ELISA test described should prove valuable in screening certified strawberry stocks.

The production of strawberry plants from callus cultures

Shoots were regenerated from callus of the commercially important strawberry varieties Bogota, Brighton, Cambridge Favourite, Hapil, Ostara, Rapella, Red Gauntlet and JILA33 which is a promising selection from a current breeding programme.

Population dynamics of two-spotted spider mites in multiple year strawberry crops in Canterbury

Abstract The population dynamics and dispersion characteristics of two-spotted spider mite (Tetranychus urticae Koch) in strawberry plants (cv. Red Gauntlet) were examined. Several indices of dispersion were compared; Green’s coefficient of dispersion was simple to use and gave reproducible results over several seasons. Mite dispersion was strongly contagious at the start and end of the season, November and March, respectively, but only weakly contagious between these months. Most mites were found on the large mature leaflets located at the side of the plant; hence, leaflets in this category were suitable sample units. Fewer mites were found on strawberry plants more than one season old. Development of induced resistance by the plant in response to previous mite feeding may be responsible for this phenomenon rather than the influence of natural enemies.

The relationship between two-spotted spider mite and strawberry yield in Canterbury

Abstract Strawberry (cv. ‘Red Gauntlet’) yield was measured over two growing seasons, 1984 — 85 and 1985 — 86, in field experiments with a series of treatments involving two-spotted spider mite (TSSM) (Tetranychus urticae Koch), exclusion of predators and pesticide application. Two-spotted spider mite populations were much higher on first season plants than on older plants. Insecticides and miticides apparently play an important role in TSSM population regulation in first season plants but natural population regulation may be more important in populations on older plants. In their first season, plants yielded significantly less than second season plants, although mean berry weight was similar. The yield variation in plants of different ages cannot solely be attributable to seasonal affects. High, uncontrolled TSSM infestations in one season reduced yield in the following season but in the second season the yield variation between newly planted and established plants was still evident. Mite levels on established plants may not attain yield-reducing levels in Canterbury. Poor yields from new plantings may be due to treatment received by mother plants before runner lifting.

Externally Induced Acceleration of Transpiration of Dark-stressed Strawberry Plants

Summary Transpiration of strawberry plants ( Fragaria grandiflora Duch. cv. Red gauntlet), was investigatedwith an infrared gas analyser. It has been found that long darkening of plants (100-500 h) causes considerable inhibition of transpiration recovery after illumination. This effect could be reversed by several hours of illumination or immediately by feeding the leaf with a solution of KCl, NaCl, ATP, HCl, sucrose, mannitol or fusicoccin. Some indirect evidence suggests, that acceleration of transpiration recovery after treatmentwith these substances is not due to decrease of turgor in epidermal cells but rather due to its increase in guard cells. Acceleration of stomatal opening by externally supplied substances can be observed only inthe light. This may suggest that plasmalemma of guard cells disorganized by long darkness is in some way modified by solutes in the apoplast, which in effect ensures intensification of transport of osmoticum into guard cells.

Abscisic acid induced decay of strawberry transpiration

The effect of 0–7.5 × 10−3μmol abscisic acid (ABA) on the transpiration of strawberry (Fragaria grandiflora Duch. ev. Red gauntlet), both under illumination and in darkness, was investigated with the use of an infrared gas analyser. Mathematical analysis of the results suggests that the decrease in transpiration after darkening can be described by a series of first‐order processes with continuous distribution of rate constants k. Application of ABA makes the rate constant distribution narrower, so that one single rate constant occurs at the highest doses. ABA accelerates the decrease of transpiration more in darkness than under illumination. This suggests that the process of efflux of osmotically active particles from guard cells is influenced more than influx. For ABA doses greater than 7.5 × 104μmol, the transpiration decreases in two stages, of which only the first one seems to be affected by ABA: but above this dose further acceleration of decay of transpiration after darkening is not observed. The observations may indicate that above this critical dose of ABA the rate determining step consists in guard cell wall relaxation rather than in efflux of osmotica.

Altering the sensitivity of strawberry plants to exogenous abscisic acid

Abscisic acid (ABA) causes the closure of stomata. By means of an infrared gas analyzer it was found that changes in the physiological status of Fragaria grandiflora Duch. cv. Red gauntlet, caused by pretreatment with exogenous ABA, decreased the sensitivity to the next dose of the hormone. A similar decrease of sensitivity to ABA may be obtained by shortening the light period. It is proposed that this decrease in sensitivity to ABA may be due to adaptation of guard cells to an excess of ABA.

Field Evaluation of Soil Fumigation and Fungicide Drenches for Control ofPhytophthora fragariaein Red Gauntlet Strawberries

Comparaison de la desinfection du sol et de l'aspersion avec des fongicides pour le controle de la maladie du fraisier induite par Phytophtora fragariae, dans le sud de l'Australie

Susceptibility of Strawberry Varieties to Post‐harvest Fungal Spoilage

The susceptibility of strawberry fruits from eleven varieties, Cambridge Favourite, Cambridge Vigour, Cambridge Prizewinner, Red Gauntlet, Chanil, Domanil, Grandee, Litessa, Tamella. Senga Gigana and Precosana, to post‐harvest spoilage fungi was investigated over the 1974 and 1975 seasons. Although the fruit from the different varieties from each of two sites at each harvest was contaminated with a similar level of fungi, the pattern of development of the spoilage fungi revealed marked differences between some varieties. Botrytis cinerea and Mucor mucedo were the predominant spoilage fungi on all varieties with Rhizopus sexualis and R. stolonifer being of minor importance. The relative importance of these fungi changed on all varieties as the season progressed, although to a different degree according to variety, site and season. Cambridge Vigour, Senga Gigana, and Chanil were the most susceptible varieties, while Red Gauntlet was the most resistant, especially to the Phycomycetes.