Biography

My main research topic is plant pathology related to fruit growing. My researcher carrier started with a PhD about fungal fruit decay in sweet cherries. Later on it has been a wider focus with fruit rot on apple, plum and sweet cherry fruits in addition to important diseases on the trees such as European canker and bacterial canker. The research is done in cooperation with the fruit industry and related industries such as packinghouses and nurseries.

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Abstract

Infections of Neonectria ditissima, the cause of European fruit tree canker, may be initiated during propagation. In a survey of 19 commercial apple orchards in southern Norway in the year of planting or the following year, the graft-union area of 15,270 trees was examined. The disease was found in 53% of the orchards, at a low incidence (<10%) with two exceptions (13 and 42%). Scion wood from mother trees with no, a few or several cankers were used to propagate trees that were surveyed for up to 38 months. In total 20 out of 1116 (1.8%) trees developed canker. The higher the number of cankers was on the mother trees, the higher was the number of trees developing canker after grafting. Infections developed on both cultivars (Discovery, Summerred) and all three rootstocks (Antonovka, B9, M9), but more so on grafted than T-budded trees, and more in 2015 than in 2014. When the scion wood was inoculated at the time of T-budding or grafting, disease development went faster and to a higher incidence on T-budded (94%) than on grafted trees (50%). Dipping the scion wood end in a spore suspension prior to grafting resulted in more infections than when a suspension droplet was placed on the bud and bark surface of the scion wood after grafting. The present investigation documents that scion wood may harbour inoculum of N. ditissima. Furthermore, infections may be initiated at time of propagation, and management practices of both scion wood production and nurseries should encounter that fact.

Abstract

Sweet cherry fruit delivered at three packinghouses over two years in southern Norway was assessed for postharvest fungal decay after being graded in a line with water containing 2 ppm chlorine, in comparison with non-graded fruit. Assessment of decay was carried out after cold storage of the fruit for ten days at 2°C, followed by two days at 20°C. In mean of all assessments, there was no difference in total decay after storage between fruit graded in a water line or non-graded fruit, however, the first year there was a higher total incidence of fruit decay on water-graded fruit after storage. The grading-water was not changed during the day, but time of grading during the day did not seem to influence the amount of decay. Mucor rot and grey mould accounted for 80 and 19%, respectively, of the decay averaged for all assessments, and there was no significant difference in decay of the two diseases if graded in water or not. For blue mould and brown rot, the incidence was lower in water graded fruit, while it was the opposite for Cladosporium rot. On average, fruit decaying fungi developed on PDA from 57 and 17% of water samples from grading lines in the two years, respectively. On pieces with filter paper wetted in different locations of the grading line, 87% contained fruit decaying fungi when placed on PDA, and Mucor sp. was the most prevalent pathogen. Fruit cooled in a hydro-cooler containing either 2, 10 or 50 ppm chlorine, all reduced decay with about 75% compared to non-chlorinated water. Although the grading water may contain spores of pathogenic fungi, the present results indicated that water containing 2 ppm chlorine does not significantly increase fruit decay. Thus, only a slight chlorination of grading water may be sufficient to reduce postharvest contamination.

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Abstract

Modified atmosphere packaging (MAP) may inhibit undesirable quality changes of fruit and vegetables. The aim of this experiment was to evaluate the effect of MAP on selected quality parameters for sweet cherries (Prunus avium L.) stored at simulated distribution chain temperatures. ‘Lapins’ sweet cherries with maturity grade 4-5 and 6-7 were packaged in macroperforated polyethylene “carry bags” (control) and in trays wrapped in a laser perforated film giving passive modified atmosphere (MAP). After packaging, the cherries were stored at 4°C for 5 days and thereafter for 3 days at 4°C (chill) or 20°C (retail) simulating storage at chill or room temperature in the grocery stores. Headspace gas atmosphere in the MA packages, fruit quality, weight loss and amount of fungal fruit decay and other decays were recorded after 1, 5 and 8 days of storage. The gas atmosphere in MA packages was approximately 18% O2 and 4% CO2 at 4°C and between 6-9% O2 and 12-14% CO2 at 20°C. The weight loss was negligible in the MA packages at both storage conditions, whereas the cherries in carry bags showed a weight loss from 1 to 4%. The stem colour was significantly browner in the carry bags compared to the MA packages after 8 days of retail storage. Fungal decay was below 0.5% for both maturity grades stored at chill conditions for 8 days. At retail conditions, 4 and 6% decay was detected for maturity grade 4-5 in MA-packages and carry bags, respectively. For maturity grade 6- 7, the MA-packages had 9% decay and the carry bags 7%. The overall picture was that MA packaging for sweet cherries better maintained the fruit quality than the carry bags during the storage period of 8 days at two simulated retail conditions.

Abstract

Introduction and purpose: The ability of apple rootstocks to become infected by Neonectria ditissima, the cause of European canker, was studied over two years. Materials and methods: Rootstocks B9 and M9 with a size suitable for grafting (6-10 mm stem diameter, termed rootstocks), and smaller sized rootstocks (<5 mm stem diameter, termed transplants) of B9, M9, M26, MM106 and Antonovka were inoculated with N. ditissima at different times, either with contaminated map pins or with spore suspensions. In addition, the rootstocks were either defeathered (side shoots removed), topped (top shoot headed) or both, to create wounds that would normally occur during propagation, while wounds on transplants were made by removing leaves. Results and discussion: One month after inoculation, slightly sunken canker lesions had developed around the inoculation points of the map pins or wounds. No lesions developed on the non-inoculated controls. Map pin inoculation resulted in 30% to 89% infection and spore suspension sprayed on wounds from 5% to 45% infection. When the cankered areas were split open, brown lesions with necrotic tissue due to infection by N. ditissima appeared. The transplants of M9, M26 and MM106 inoculated with contaminated map pins in 2014 developed necrosis on 40% to 67% of the plants, but there were no differences in the incidence or severity among the different types. On the transplants of B9, Antonovka and M9 inoculated in 2015, there was more necrosis on B9 (42%) than on Antonovka (11%) and more sporulating lesions on B9 (29%) than on M9 (9%) or on Antonovka (4%). Conclusion: It can be concluded that rootstocks used for apple trees may become infected by N. ditissima, and wounds should thus be protected during propagation.

Abstract

Production of inoculum of Colletotrichum acutatum from both previously infected and overwintered tissue, as well as newly developed plant tissue of sour cherry (Prunus cerasus), was studied in southern Norway. Plant parts were sampled from commercial, private, or research orchards, and incubated for 2 to 14 days (time depended on tissue type) in saturated air at 20°C. In early spring, abundant sporulation was found on scales of overwintered buds and shoots. A mean of 35% infected buds in four cultivars was observed, with a maximum of 72% of the buds infected in one of the samples. Over 3 years, the seasonal production of overwintered fruit and peduncles of cv. Fanal infected the previous year was investigated. In all three years, the infected plant material was placed in the trees throughout the winter and the following growing season; in two of the years, fruit and peduncles were also placed on the ground in the autumn or the following spring. Old fruit and peduncles formed conidia throughout the season, with a peak in May and June. Spore numbers declined over the season, but the decline was more rapid for plant material on the ground than in the trees. On average over 2 years, 68.7, 24.0, or 7.3% of the inoculum came from fruit placed in the trees, placed on the ground in spring, or placed on the ground the preceding autumn, respectively. The number of fruit and peduncles attached to the trees in a planting of cv. Hardangerkirsebær was followed from February to July one year, and although there was a decline over time, fruit and/or their peduncles were still attached in substantial numbers in July, thus illustrating their potential as sources of inoculum. In observations over 2 years in a heavily infected orchard of cv. Stevnsbær, 75 and 47% of flowers and newly emerged fruit, respectively, were infected. Artificially inoculated flowers and fruit produced conidia until harvest, with a peak in mid-July. It may be concluded that previously infected and overwintered, as well as newly emerged tissue of sour cherry, may serve as sources of inoculum of C. acutatum throughout the growing season.

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Abstract

Aroma is an important quality factor in fruit, and it is important to know the effect of new orchard management practices on fruit aroma. Fruit growers are using more foliar fertilizers to achieve the optimum mineral status in fruit. In this work the effects of adding extra nitrogen, calcium and both nitrogen and calcium to apple trees in the fruit cell division phase were studied. Even though the given nitrogen and calcium did not give significantly higher content of N and Ca in the treated fruits, differences in the contents of some aroma compounds were found. Nitrogen treated trees gave apples with more hexanal, a compound known in unripe ("green, grassy") apples. When both calcium and nitrogen were applied, the negative effect of nitrogen on aroma compounds was less pronounced. The aroma of these fruits was more similar to the controls. Using multivariate statistical analyses, the grouping of the different treatments during storage was confirmed. Foliar fertilization with nitrogen and calcium during the cell division phase had a significant effect on the amount of aroma compounds in apples at harvest and during storage.

Abstract

Fungi within the Colletotrichum acutatum species complex occur asymptomatically on plant parts of many different plant species. Leaves from apple orchards in southern Norway were sampled, frozen for five hours and incubated for six days to reveal presence of asymptomatic infections of C. acutatum. Number of leaves (incidence) and leaf area covered (severity) with conidial masses of C. acutatum were assessed biweekly on cv. Aroma from late May to late September during three growing seasons. The first finding of conidial masses occurred in the second half of July, and there was a higher incidence occurring in August and September. Sampling of leaves from fruit spurs and vegetative shoots of cvs. Aroma and Elstar showed that conidial masses of C. acutatum developed on leaves on both shoot types, and there was no difference in incidence between these two types. The fungus was detected on leaves from six of eight commercial orchards of cv. Aroma over three years, with a mean incidence of 5.5 %. After storage, bitter rot was found on apple fruit from all eight orchards. There was no correlation between incidence of conidial masses of C. acutatum on leaves and on fruit. In all orchards and seasons investigated, incidence and severity on leaves varied from 0 to 67%and 0 to 85 %, respectively. The discovery of apple leaves containing conidial masses of C. acutatum clearly indicate for leaves as a potential source of inoculum for fruit infections.

Abstract

Effects of controlled atmosphere (CA) conditions on physiological disorders and fungal fruit decay on apple ‘Aroma’ were investigated. Fruit from three growing seasons were stored at 1% or 2% O2 (both at 2% CO2) at either 1°C or 3°C in small research units; controls were kept in the same ventilated rooms at the two temperatures (ambient air). The fruit were removed from storage after four or six months and assessed for fruit decay immediately afterwards and after two weeks at 20°C. Fruit quality parameters were recorded at the end of storage. On a three-year average, fruit stored in CA was less ripe at the end of storage. After both four and six months storage, CA reduced total decay (physiological disorders and fungal decay) by on average 70% and 45%, respectively, compared to storage in ambient air. Senescent breakdown was lower after CA storage for four months, but not after six months and not after simulated shelf life. Soft scald was lower when stored in CA both after cold storage at 1°C and simulated shelf life. After storage at 3°C there was lower incidence of soft scald when stored in CA after four months, but not after six months. For fungal fruit decay in general, there was no effect of low oxygen, however, 2% O2 gave slightly less bitter rot (Colletotrichum acutatum) than 1% O2 and significantly less than ambient air after simulated shelf life. Averaged over all oxygen levels, 1°C gave significantly less bitter rot than 3°C. It may be concluded that use of CA for storage of ‘Aroma’ is a good way of reducing development of physiological disorders. However, development of bitter rot seemed to be more influenced by temperature and storage time than by low O2.

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Abstract

Shelf life of plum is limited by several factors, including development of fungal decay. In either one or two seasons, European plum cultivars were exposed to different applications of calcium or fungicide before harvest or left unsprayed. On the experimental trees, the yield was harvested as commercial practice, giving a sample of fruit with a range in maturity acceptable for sale. The yield was divided into two groups, less and more ripened fruit. Fruit samples from each group were stored for 10-14 days at 4°C followed by a simulated shelf life period of 2-3 days at 20°C. Fruit quality was assessed at harvest and after storage. Number of fruit with fungal decay was counted at the end of storage and after simulated shelf life. At harvest, the more ripened fruit had higher weight, soluble solids content, background and cover colour, and lower firmness in most of the experiments. Fruit from trees sprayed six times with calcium had higher weight in first year, but not in second, was less ripen as measured by colour and firmness on some cultivars, but not on others. Time of fungicide application had no effect on fruit quality at harvest. Differences in fruit quality at harvest were most often similar after storage. Fruit grouped as more mature at harvest developed more fungal decay after simulated shelf life than less mature fruit in five of eight experiments. In one out of six experiments calcium applications reduced development of postharvest fungal decay. Fungicide applications had no effect on postharvest fungal decay in either of four experiments. The present results indicate that the ripening degree of plum fruit is more important for development of fungal decay than preharvest applications of calcium or fungicides

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Abstract

At main commercial harvest four pallet sized boxes of apple (Malus ×domestica) cultivar ‘Aroma’ from one grower were assessed for maturity by using a portable spectrometer giving an IAD index (index of the absorption difference between 670 and 720 nm) indicating chlorophyll content. The apples were sorted into three groups; IAD index <0.65, 0.66 - 0.80 and >0.81. Apples of all groups were assessed for quality parameters at harvest and after storage in CA-bags at 2°C (about 100% RH) or natural atmosphere (NA) at 1°C (about 90% RH) for three months and after simulated shelf life at 20°C for 14 days. At the same times the apples were assessed for decay, both physiological disorders and fungal attacks. The CA-bags were gas-tight plastic bags for one pallet and were connected to an external gas control unit. The atmosphere inside the CA-bags consisted of 2% O2 and 2% CO2 during the cold period. At the start of the experiment apples from the different IAD index groups were not similar in subjectively judged ground colour and cover colour but similar in firmness and starch content. After three months of cold storage both apples stored at natural atmosphere and in CA-bags were still different in ground and cover colour and IAD index. In apples from CA-bags the titratable acidity content was higher in >0.81 group than on those with an IAD index <0.65. After 14 days at 20°C apples with IAD index >0.81 were different from <0.65 group in ground-colour and IAD index, but other parameters assessed were similar. After three months CA-bag stored apples had 2% visible decay but apples stored in NA had up to 27% decay. The apples with IAD index <0.65 had highest incidence of decay. After 14 days at 20°C apples with IAD index <0.65 stored in CA-bags had developed 5% decay while there was no decay in the other IAD index groups. Apples with IAD index <0.65 stored in NA had developed 45% decay after 14 days at 20°C while apples from the other groups had developed about 20% decay. Senescent decay and breakdown accounted for 90% of the physiological disorder while bitter rot was the major reason of fungal decay. CA-bags were found to be an efficient tool to prolong storage period and IAD index values might be useful in determining the potential storage life.

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Abstract

The shelf life of plum fruit (Prunus domestica) is limited due to among other factors fungal fruit decay. Absorbent pads (“fruit pads”) are commercially used today in order to absorb juice from the berries and condense water and hence reduce fungal growth. The aim of this experiment was to evaluate the effect of different types of absorbent pads on weight loss, decay and quality for plum fruit under realistic storage conditions. Plum fruit (‘Reeves’ and ‘Jubileum’) were delivered at a commercial packing house, packed in trays on a flow packaging machine with three different types of absorbent pads placed at the bottom of the trays (standard fruit pad and two humidity control pads with different active compounds; denoted active pad 1 and 2). Trays without pads were controls. After packaging, plums were stored at 3 or 6°C for 7 days and thereafter 2 days at 20°C. Fruit quality, weight loss and amount of fungal decay were recorded at the end of the storage period. The different pads had no significant effects on ripeness state measured by DA-meter and fruit firmness measured at end of storage. The pads had significantly different effect on weight loss, and for ‘Jubileum’ the weight loss was 1.5% for the active pad 1, 2.5% for the active pad 2 and below 1% for the standard pad and the control. Significant effects were found for cultivar and absorbent pads on the total amount of decayed fruit. ‘Jubileum’ was more vulnerable to decay than ‘Reeves’, and the active pad 2 had the lowest number of decayed ‘Jubileum’ fruit stored at 3°C. More work and a cost-benefit analysis should be performed before absorbent pads are recommended for plum fruit.

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Abstract

The shelf life of plum fruit (Prunus domestica) is limited due to among other factors fungal fruit decay. Absorbent pads (“fruit pads”) are commercially used today in order to absorb juice from the berries and condense water and hence reduce fungal growth. The aim of this experiment was to evaluate the effect of different types of absorbent pads on weight loss, decay and quality for plum fruit under realistic storage conditions. Plum fruit (‘Reeves’ and ‘Jubileum’) were delivered at a commercial packing house, packed in trays on a flow packaging machine with three different types of absorbent pads placed at the bottom of the trays (standard fruit pad and two humidity control pads with different active compounds; denoted active pad 1 and 2). Trays without pads were controls. After packaging, plums were stored at 3 or 6°C for 7 days and thereafter 2 days at 20°C. Fruit quality, weight loss and amount of fungal decay were recorded at the end of the storage period. The different pads had no significant effects on ripeness state measured by DA-meter and fruit firmness measured at end of storage. The pads had significantly different effect on weight loss, and for ‘Jubileum’ the weight loss was 1.5% for the active pad 1, 2.5% for the active pad 2 and below 1% for the standard pad and the control. Significant effects were found for cultivar and absorbent pads on the total amount of decayed fruit. ‘Jubileum’ was more vulnerable to decay than ‘Reeves’, and the active pad 2 had the lowest number of decayed ‘Jubileum’ fruit stored at 3°C. More work and a cost-benefit analysis should be performed before absorbent pads are recommended for plum fruit.

Abstract

Sweet cherry fruit in Norway are graded and packed with chlorinated water according to drinking water standards (max. 2 ppm free chlorine after fruit contact) as a transport medium in parts of the grading lines. A possibility of fruit contamination from fungal pathogens exists in such water. ‘Lapins’ fruit from 10 commercial orchards at each of three packinghouses were put through a simulated sale period (10 days at 2°C and 2-3 days at 20°C) either directly or after being transported on a grading line in 2007. In 2008, fruit were sampled at different times of the day (early, mid and late) and compared with the control. Fruit samples containing 5 x 100 fruits were weighed at time of sampling, after 10 days at 2°C (in a Lifespan bag) and after 2-3 days at 20°C. The number of fruit decayed with fungal pathogens were counted and diagnosed. Total fruit decay in a mean of 3 packing houses x 10 orchards was 14% before packing and 28% after packing in 2007. Brown rot (caused by Monilinia laxa) incidence decreased from 1.1% to 0.3% and Mucor rot (caused primarily by Mucor piriformis) incidence increased from 11% to 26%. In 2008, there were no significant differences between unpacked and packed fruits, or between the different packing hours, on the different fungal diseases or incidence of total fruit decay. These preliminary results indicate that there might be a risk of contamination in seasons with high levels of fruit decay (such as 2007), but in normal seasons a slight chlorination of water is satisfactory to minimize the risk to an acceptable level.

Abstract

Combinations of covering and fungicide applications were tested on two sweet cherry cultivars; Van during two years (2001 and 2002) and Lapins three years (2001"2003). The following treatments were tested in 2001 and 2002: (i) covering during flowering and from 5 to 6 weeks prior to harvest and throughout harvest, no fungicides applied, (ii) as (i) but fungicides were applied once or twice between the two covering periods, (iii) covered 5 to 6 weeks prior to harvest and throughout harvest, fungicides applied two or three times prior to covering, and (iv) uncovered throughout the season, fungicides applied two or three times in the period from flowering towards harvest. In 2003, the trees were covered only from 5 to 6 weeks prior to harvest and throughout harvest. Both treatments that year received fungicide applications during flowering, but one of the treatments was left unsprayed during the green fruit period prior to covering. Every combination of covering and fungicide applications reduced total fruit decay at harvest significantly compared to a full fungicide programme and no covering. In three of four trials when the trees were covered during flowering and prior to harvest, and fungicide applications were omitted in the green fruit phase between the covering periods, no significant increase in fruit rot occurred compared to treatments where fungicides were applied. However, in one trial there was a significant increase in fruit rot by leaving out one fungicide spray during that intermittent period. Furthermore, if fungicides were only applied during flowering and not on green fruit before covering in 2003, a significant increase in fruit rot occurred. Thus, leaving out fungicide applications during that supposedly less susceptible green fruit period, increased the risk of acquiring fruit rot. Applying fungicides during the green fruit stage significantly reduced the amount of brown rot in four of five trials and anthracnose in one of five trials. No negative effect on fruit quality was found from the extended covering periods. It can be concluded that covering effectively replaced fungicide applications during flowering and prior to harvest.

Abstract

Resultat frå forsøk med ulike dekkesystem for søtkirsebær sin effekt på mikroklima og fruktkvalitet er skildra i ein vitskapleg artikkel på engelsk. Resultata er delvis publisert på norsk i følgjande artikkel: Børve, J., A. Stensvand & M. Meland, 1997. Verknad av plastdekking på rotning hjå søtkirsebær. Informasjonsmøte i plantevern 1997 Grønn forskning 2/97. 252-255.