Corky Tissue Research Articles

Epigenetic Modifications Related to Potato Skin Russeting.

Potato tuber skin is a protective corky tissue consisting of suberized phellem cells. Smooth-skinned varieties are characterized by a clean, shiny appearance compared to the darker hue of russeted potatoes. The rough skin of russeted cultivars is a desired, genetically inherited characteristic; however, unwanted russeting of smooth-skinned cultivars often occurs under suboptimal growth conditions. The involvement of epigenetic modifiers in regulating the smooth skin russeting disorder was tested. We used smooth-skin commercial cultivars with and without the russeting disorder and three lines from a breeding population segregating for russeting. Anatomically, the russet skin showed similar characteristics, whether the cause was environmentally triggered or genetically determined. The old outer layers of the corky phellem remain attached to the newly formed phellem layers instead of being sloughed off. Global DNA methylation analysis indicated a significant reduction in the percentage of 5-methylcytosine in mature vs. immature skin and russet vs. smooth skin. This was true for both the smooth-skin commercial cultivars and the russeted lines. The expression level of selected DNA methyltransferases was reduced in accordance. DNA demethylase expression did not change between the skin types and age. Hence, the reduced DNA methylation in mature and russet skin is more likely to be achieved through passive DNA demethylation and loss of methyltransferase activity.

Potato Periderm Development and Tuber Skin Quality.

The periderm is a corky tissue that replaces the epidermis when the latter is damaged, and is critical for preventing pathogen invasion and water loss. The periderm is formed through the meristematic activity of phellogen cells (cork cambium). The potato skin (phellem cells) composes the outer layers of the tuber periderm and is a model for studying cork development. Early in tuber development and following tuber expansion, the phellogen becomes active and produces the skin. New skin layers are continuously added by division of the phellogen cells until tuber maturation. Some physiological disorders of the potato tuber are related to abnormal development of the skin, including skinning injuries and russeting of smooth-skinned potatoes. Thus, characterizing the potato periderm contributes to modeling cork development in plants and helps to resolve critical agricultural problems. Here, we summarize the data available on potato periderm formation, highlighting tissue characteristics rather than the suberization processes.

Population Dynamics and Control Potential of the Soil-Dwelling Stages of the South African Citrus Thrips, Scirtothrips aurantii (Thysanoptera: Thripidae), on Avocado

Scirtothrips aurantii (Thysanoptera: Thripidae) is a recently confirmed economic pest of avocado (Persea americana). Damage by S. aurantii, through their feeding on avocado fruit results in corky tissue development (scarring), making the fruit unsuitable for export. The study aimed to monitor S. aurantii population dynamics during the critical early fruiting period by means of dispersal/emergence (D/E) traps and fruit infestation indices. The field efficacy of biologicals (Beauveria bassiana, Steinernema feltiae), the pyrethroid beta-cyfluthrin, and the semi-synthetic spinosyn, spinetoram, against soil-dwelling stages of S. aurantii during early fruit development were determined. Finally, the study aimed to establish the pupation sites of S. aurantii in avocado. Above ground, population dynamics fluctuated directly in response to the host plant's phenological changes and were modified by rainfall. Control of soil-dwelling stages by the insecticides and the effectiveness of D/E traps in monitoring S. aurantii populations were not demonstrated, probably because the populations trapped using the D/E traps were not representative of the above-ground populations, as evidenced by fruit infestation indices. Under laboratory conditions, 81.60 % of mature larvae pupated away from the soil, demonstrating that S. aurantii does not passively drop to the ground in an avocado orchard, but actively seeks out dark, sheltered areas to pupate.

Application of Absorption and Scattering Properties Obtained through Image Pre-Classification Method Using a Laser Backscattering Imaging System to Detect Kiwifruit Chilling Injury.

Kiwifruit chilling injury (CI) damage occurs after long-term exposure to low temperature. A non-destructive approach to detect CI injury was tested in the present study, using a laser backscattering image (LBI) technique calibrated with 56 liquid phantoms for providing absorption coefficient (µa) and reduced scattering coefficient (µs’). Calibration of LBI resulted in a true-positive (TP) classification of 91.5% and 65.6% of predicted µs’ and µa, respectively. The optical properties of ‘SunGold™’and ‘Hayward’ kiwifruit were analysed at 520 nm with a two-step protocol capturing pre-classification according to the LBI parameters used in the calibration and estimation with the Farrell equation. Severely injured kiwifruit showed white corky tissue and water soaking, reduced soluble solids content and firmness measured destructively. Non-destructive classification results for ‘SunGold™’ showed a high percentage of TP for severe CI of 92% and 75% using LBI parameters directly and predicted µa and µs’ after pre-classification, respectively. The classification accuracy for severe CI ‘Hayward’ kiwifruit with LBI parameter was low (58%) and with µa and µs’ decreased further (35%), which was assumed to be due to interference caused by the long trichomes on the fruit surface.

Susceptibility of Avocado Fruit to Scirtothrips aurantii Faure (Thysanoptera: Thripidae) and Wind Scarring Damage in Limpopo and KwaZulu-Natal Provinces of South Africa

In South Africa, the avocado (Persea americana) is an important fruit, grown primarily for export and contributing ZAR 1.75 billion to the gross domestic product of the country. As an export driven industry, optimising exportable avocado fruit volume is a primary concern. Wind induced abrasion and damage by thrips (Thysanoptera: Thripidae), through their feeding on avocado fruit results in corky tissue development (scarring) and making the fruit unsuitable for export. The study aimed to determine the economic losses caused by these agents as well as assess different cultivar responses to scarring damage. Across cultivars, the 1.49% revenue annually due to Scirtothrips aurantii downgrading (3.86% loss factor), translating to ZAR 34.90 million (US$2.39 million). Packhouse study results showed that both thrips and wind abrasion damage accounted for 30% scarring damage, a loss factor of 13.72% and a combined revenue loss of 5.57%. The cultivar ‘Pinkerton’ showed the greatest susceptibility to scarring damage by both wind and S. aurantii whilst the cultivar ‘Carmen®-Hass’ showed a natural predisposition to higher levels of thrips damage. The presence of macadamia trees near avocado trees predisposes avocado fruit to S. aurantii damage.

First Report of Tussock Moths (Bracharoa mixta (Lepidoptera: Erebidae)) Scarring Avocado Fruit in KwaZulu-Natal, South Africa

Avocado (Persea americana) is an important export crop for South Africa, contributing ZAR1.75 billion in export revenue to the gross domestic product. As an export-oriented industry, increasing the exportable percentage of avocado fruit is a major concern. A tussock moth, Bracharoa mixta (Snellen), is reported for the first time on avocado trees, scarring fruit and defoliating leaves. Feeding damage by the larva results in corky tissue development, making the fruit unsuitable for export. The study aimed to determine the identity of the larvae (morphologically and DNA barcoding) and ascertain levels of damage. Sequencing of the barcoding region of cytochrome oxidase subunit I (COI) gene was done. In-field fruit damage assessment of infested trees showed an 11 % scarring damage level resulting in 3.67 % downgrading of fruit. This represents a potential revenue loss of up to ZAR 1352.90/t (2.26 % revenue loss). The defoliating caterpillars also caused an 18.22 % reduction in leaf area. This study documents the potential of B. mixta to cause economic loss and sporadic, isolated outbreaks.

Attractiveness of Different Coloured Sticky Traps to the South African Citrus Thrips (Scirtothrips aurantii Faure) in Avocado, KwaZulu-Natal, South Africa

The South African citrus thrips, Scirtothrips aurantii, is a recently confirmed economic pest in South African avocado. Scarring damage by thrips results in corky tissue development, making the fruit unsuitable for export and potentially costing the country in lost export revenue. Thrips management is complicated by the multiple and protracted flowering patterns of susceptible cultivars. In addition, widespread pesticide resistance of thrips and the negative environmental effects along with minimum residue levels for export fruit limit the application of pesticides for thrips control. Monitoring an insect pest's presence and abundance is the first step in thrips management. This study aimed to investigate S. aurantii's colour preferences, establish the distribution of thrips in the orchard and population dynamics from flowering to fruit establishment. Attractiveness followed the order yellow > blue, white, clear > red, black, purple and orange. Thrips were evenly distributed throughout the orchard, with the highest populations occurring during flowering (August), declining sharply and picking up in the summer months starting December. Yellow sticky cards are recommended as a monitoring tool.

The transcriptome of potato tuber phellogen reveals cellular functions of cork cambium and genes involved in periderm formation and maturation

The periderm is a protective corky tissue that is formed through the cambial activity of phellogen cells, when the outer epidermis is damaged. Timely periderm formation is critical to prevent pathogen invasion and water loss. The outer layers of the potato periderm, the tuber skin, serves as a model to study cork development. Early in tuber development the phellogen becomes active and produces the skin. During tuber maturation it becomes inactive and the skin adheres to the tuber flesh. The characterization of potato phellogen may contribute to the management of costly agricultural problems related to incomplete skin-set and the resulting skinning injuries, and provide us with new knowledge regarding cork development in planta. A transcriptome of potato tuber phellogen isolated by laser capture microdissection indicated similarity to vascular cambium and the cork from trees. Highly expressed genes and transcription factors indicated that phellogen activation involves cytokinesis and gene reprograming for the establishment of a dedifferentiation state; whereas inactivation is characterized by activity of genes that direct organ identity in meristem and cell-wall modifications. The expression of selected genes was analyzed using qPCR in native and wound periderm at distinct developmental stages. This allowed the identification of genes involved in periderm formation and maturation.

Prevention of Incidence of Corky Tissue Disorder in Sapota cv. Cricket Ball Fruits by Preharvest Spray Treatment

Prevention of Incidence of Corky Tissue Disorder in Sapota cv. Cricket Ball Fruits by Preharvest Spray Treatment

Determination of the Natural Host Status of Avocado Fruit to Pestiferous Thrips (Thysanoptera: Thripidae) in KwaZulu-Natal, South Africa

The South African avocado industry is export-oriented, with approximately 3.0 % of international market share and with a five-year mean annual production of 118 000 t from 17 500 ha. Feeding by thrips results in fruit scarring and corky tissue development, making the fruit unsuitable for export. The study aimed to identify the spectrum of thrips in avocado flowers and more importantly, to confirm the identity of the thrips species responsible for damaging fruit. Thrips were collected from flowering panicles and identified using taxonomic keys. Frankliniella occidentalis (Pergande), Scirtothrips aurantii (Faure), Thrips gowdeyi (Bagnall), Thrips pusillus (Bagnall), Thrips tenellus (Trybom), Haplothrips gowdeyi (Franklin), Haplothrips bedfordi (Jacot-Guillarmod) and Megalurothrips sjostedti (Trybom) were consistently collected from May to September 2018. The minute size of thrips warranted a pre-season trial to determine the best netting material to contain thrips. Insect screen (149 µm), nylon netting (250 µm), chiffon (210 µm), voile (250 µm), organza (500 µm), tea filter paper (74 µm) and coffee filter paper (53 µm) were evaluated. The experiment was laid out as a randomised complete block design with six replications and the trials repeated twice. Only coffee filter paper and tea filter paper contained at least 85 % of the thrips and were therefore chosen for thrips exclusion trials. Surveillance by fruit sampling was undertaken to determine the natural host status of avocado to thrips. Avocado fruitlets were randomly sampled and incubated under laboratory conditions. Scirtothrips aurantii (Faure) (the South African citrus thrips) emerged from fruitlets and was sustained on that fruit to adulthood. This is the first study to demonstrate that avocado is a natural host to this pest in South Africa.

PM 7/109 (2) Epitrix cucumeris, Epitrix papa, Epitrix subcrinita, Epitrix tuberis

Specific scopeThis Standard describes a diagnostic protocol for adults of Epitrix cucumeris, Epitrix papa, Epitrix subcrinita and Epitrix tuberis.Specific approval and amendmentFirst approved in 2011‐09.Revision approved in 2016‐01.

Segregation of corky tissue affected fruits of sapota by specific gravity method

Sapota cv. Cricket Ball is a popular commercial variety in India which is plagued by the physiological disorder known as Corky Tissue (CT). This disorder adversely affects the eating quality of the fruit, making it unfit for consumption. This paper describes a technique of dipping sapota fruits in 12.5% salt solutions to segregate the CT affected fruits from healthy fruits based on differences in fruit specific gravity. The healthy fruits with a specific gravity of >1.0895 sank to the bottom, while the fruits affected by CT having a specific gravity of <1.0895 floated on the solution, thus ensuring complete separation of healthy and CT fruits in a single step process. The method is simple, rapid and cost effective and could be applied for culling out CT affected fruits at the field level by the growers and traders.

Antibiotic sensitivity against Xanthomonas axonopodis pv. citri by using Hi media disc

Citrus canker disease is of regular occurrence on several citrus cultivars in varying degrees of incidence depending on the climatic conditions. The bacterium, Xanthomonas causes different symptoms ranging from pustules to necrotic lesions consisting of erumpent corky tissue surrounded by water soaked tissues and yellow halo on leaves, stems and fruits. Sensitivity of different antibiotics were tested against Xanthomonas axonopodis pv. citri isolates ( Xac ). using eight different Hi-media disc viz. , HX006, HX007, HX010, HX032, HX038, HX060, HX067, HX069. Each Hi-media disc having six different antibiotics of different concentration have been tested against Xac isolates. The causal pathogen Xanthomonas axonopodis pv. citri showed sensitivity to most of the antibiotic tested. Hi-media disc HX060 having antibiotic Imepenem (10mg) and Ticarcillin (70mg) showed maximum zone of inhibition (42mm). However, no effect of antibiotics i.e. Co-Trimoxazole, Nofloxacin, Cefoxitin, Erythromycin observed against Xac.

Influence of Drought Stress on Corky Tissue Formation, a Physiological Disorder in Sapota Fruit cv. Cricket Ball

Corky tissue incidence in sapota fruit during the summer months increased in direct proportion to the intensity and duration of stress showing a possible link between drought stress and corky tissue development. Corky tissue incidence was enhanced when the growth of newly initiated shoot buds was promoted by the application of gibberellic acid and reduced when it was inhibited by paclobutrazol, indicating that newly initiated shoots were competing with developing fruits for water and assimilates. An enhanced reverse flow of water and nutrients from fruit to newly initiated shoot buds was found to be the principal contributing factor for the increased incidence of corky tissue in sapota under drought stress.

Drought-stress-induced corky tissue formation in sapota fruit cv. Cricket ball is linked to enhanced “reverse flow”

Corky tissue (CT) of sapota fruit cv. Cricket ball is a physiological disorder caused by reduced seed viability during the early phase of fruit growth on the tree. The reduction of seed viability was found associated with a loss of moisture from fruit leading to CT formation. However, the exact process by which moisture is lost from fruit has not been determined yet. The principal aim of this study, therefore, was to determine the mode of water loss from fruit and to delineate the mechanism by which moisture loss influences corky tissue formation in sapota fruits. Experiments with developing sapota fruits treated with radioactive tritiated water (1H3) established the movement of water away from fruit to the subtending shoot buds by the process of “reverse flow”. The reverse movement of water from fruit to developing shoots contributed to a fall in seed total dehydrogenase (TDH) activity and a consequent reduction in the hydrolysis of starch in the mesocarp. The concurrent loss of calcium from pulp along with the efflux of water gave rise to structural and compositional changes in the pulp resulting in the development of CT in sapota. The study has provided confirmatory evidence for the movement of water away from fruit and established the occurrence of enhanced reverse flow in sapota during CT development. The present study is the first report demonstrating the occurrence of the phenomenon of reverse flow in sapota and describing how it influences the process of CT development in sapota.

The role of seed viability in the development of corky tissue in sapota (Manilkara achras) fruit in India

SummaryCorky tissue (CT) is a major disorder affecting the fruit of sapota (Manilkara achras) ‘Cricket Ball’ in India. Affected fruit have a hard lump in the pulp and dry acidic flesh, but have no external symptoms. The main objective of the present study was to investigate the role of seed in the disorder. Treating fruit with 1.0 g l–1 gibberellic acid (GA3) at 50% maturity increased fruit fresh weight and presumably seed growth, and reduced the incidence of CT compared with that in untreated control fruit. In contrast, fruit treated with 3.0 g l–1 paclobutrazol (PBZ) showed the opposite response. Fruit treated at 70% or 90% maturity gave no response, suggesting that poor seed viability during the early stage of fruit development was associated with CT. Seed stored for 30 d under ambient conditions lost water and had lower viability. There were decreases in the moisture content and calcium concentration in seed and pulp as the severity of CT increased in fruit harvested in the field, indicating a “reverse flow” of water and nutrients from the fruit. It is proposed that the incidence of CT is related to reduced seed viability and the consequent losses of water and calcium from fruit due to competition for resources with the rest of the tree. Further studies are required to assess the potential of the application of GA3 to reduce the incidence of CT in commercial orchards.

Non-destructive measurement of bitter pit in apple fruit using NIR hyperspectral imaging

A hyperspectral NIR imaging system was developed to identify bitter pit lesions on apples. A discriminant PLS calibration model was constructed to discriminate between pixels of unaffected apple skin and bitter pit lesions. The calibration model was successfully validated on a different apple. The system was able to identify bitter pit lesions, even when not visible to the naked eye such as just after harvest, but could not discriminate between bitter pit lesions and corky tissue. The reduced luminosity at the boundary of the image caused in one image some misclassification errors.

CLASSIFYING APPLES BY THE MEANS OF FLUORESCENCE IMAGING

Classification of harvested apples when predicting their storage potential is an important task. This paper describes how chlorophyll a fluorescence images taken in blue light through a red filter, can be used to classify apples. In such an image, fluorescence appears as a relatively homogenous area broken by a number of small nonfluorescing spots, corresponding to normal corky tissue patches, lenticells, and to damaged areas that lower the quality of the apple. The damaged regions appear more longish, curved or boat-shaped compared to the roundish, regular lenticells. We propose an apple classification method that employs a hierarchy of two neural networks. The first network classifies each spot according to geometrical criteria and the second network uses this information together with global attributes to classify the apple. The system reached 95% accuracy using a test material classified by an expert for "bad" and "good" apples.

567 Effects of Mancozeb, NOVA, GA, and Yeast-like Fungi on Stylar-end Russeting of Navel Orange

Stylar-end russetting (SER) is a cosmetic defect of Florida citrus fruit most frequently associated with navel orange. SER is evident as spots or streaks of corky tissue that often form a network of intersecting lines. Occurrence of SER is reported to vary widely from year to year, but some orchards have a history of severe SER, with fruit culled annually for this defect. Growers report that SER is typically first evident in August. The cause of SER has not been determined. Reports of yeast-like fungi inducing russet in pome fruit suggest that similar organisms may be implicated in SER. Yeast-like fungi were isolated on acid PDA from navel oranges in an orchard with frequent severe SER. Strains were selected with a wide range of colony morphology, but were not identified taxonomically. These strains, and strains of Aureobasidium pullulans and Rhodotorula glutinis that caused russetting in pome fruit, were grown in liquid suspension and sprayed on navel orange trees with three repeated applications during July and Aug. 1998. No increase in SER was observed on strain-inoculated trees compared to controls. Two broad-spectrum fungicides were sprayed on other navel orange trees to further explore the possibility that fungi may be involved in SER. GA (gibberellic acid) was also applied in this experiment because it can reduce russetting in apples. All applications were made five times at 3-week intervals in June through Sept 1998. SER was assessed in fruit harvested late Sept. 1998. The proportion of fruit with less than 10% of the surface exhibiting SER was 51% for controls, increased to 69% where myclobutanil was applied at 74 mg a.i./L and increased further to 93% where manganese ethylenebisdithiocarbamate was applied at 1775 mg a.i./L. GA did not significantly influence SER.

Fruit Cracking in Tomato

The environmental and physiological causes of cracking or splitting of soft fruits and citrus as they ripen are not well understood. This paper explores factors contributing to radial cracking in tomatoes, gives suggestions for prevention of cracking, and suggests directions for future research. Fruit cracking occurs when there is a rapid net influx of water and solutes into the fruit at the same time that ripening or other factors reduce the strength and elasticity of the tomato skin. In the field, high soil moisture tensions suddenly lowered by irrigation or rains are the most frequent cause of fruit cracking. Low soil moisture tensions reduce the tensile strength of the skin and increase root pressure. In addition, during rain or overhead irrigation, water penetrates into the fruit through minute cracks or through the corky tissue around the stem scar. Increases in fruit temperature raise gas and hydrostatic pressures of the pulp on the skin, resulting in immediate cracking in ripe fruit or delayed cracking in green fruit. The delayed cracking occurs later in the ripening process when minute cracks expand to become visible. High light intensity may have a role in increasing cracking apart from its association with high temperatures. Under high light conditions, fruit soluble solids and fruit growth rates are higher. Both of these factors are sometimes associated with increased cracking. Anatomical characteristics of crack-susceptible cultivars are: 1) large fruit size, 2) low skin tensile strength and/or low skin extensibility at the turning to the pink stage of ripeness, 3) thin skin, 4) thin pericarp, 5) shallow cutin penetration, 6) few fruits per plant, and 7) fruit not shaded by foliage. Following cultural practices that result in uniform and relatively slow fruit growth offers some protection against fruit cracking. These practices include maintenance of constant soil moisture and good Ca nutrition, along with keeping irrigation on the low side. Cultural practices that reduce diurnal fruit temperature changes also may reduce cracking. In the field, these practices include maintaining vegetative cover. Greenhouse growers should maintain minimal day/night temperature differences and increase temperatures gradually from nighttime to daytime levels. For both field and greenhouse tomato growers, harvesting before the pink stage of ripeness and selection of crack-resistant cultivars probably offers the best protection against cracking. Areas for future research include developing environmental models to predict cracking and exploring the use of Ca and gibberellic acid (GA) sprays to prevent cracking.