Body Rot Research Articles

Postharvest diseases of mangoes in Fiji

ABSTRACT Despite considerable research globally on postharvest diseases of mango, virtually no work has been done to determine the occurrence of these diseases and their causal agents in Fiji. This study is the first major field and market survey of postharvest diseases of mango in Fiji. For the field survey, fruits from five local mango cultivars were harvested at each of five locations. Fruits from five imported cultivars were also harvested from one location in Nadi. For the market survey, vendors were selected at five municipal markets for fruit collection, along with ten roadside stalls. For field and market surveys, fruits were incubated at 23°C and assessed for postharvest disease (incidence and severity of body rots and stem end rots) when ripe. Isolations were made from disease lesions and fungal cultures were identified using multilocus sequence typing. High incidences of body and stem end rots were recorded across all surveys. In the field survey of local cultivars, ‘Salusalu’ fruits were found to have the lowest severity of body rot and stem end rot on average, while for imported cultivars, ‘Nam Doc Mai’ had the lowest average severity of these diseases. The market survey showed that ‘Salusalu’ had a lower incidence of anthracnose on the body of fruit compared to all other cultivars, although it did have a surprisingly high incidence of stem end rot at some localities. Fungal isolates from anthracnose lesions in the field and market surveys were identified as Colletotrichum asianum, C. simmondsii and C. fructicola. C. asianum was the predominant species associated with anthracnose symptoms, accounting for 97% of isolations. Lasiodiplodia theobromae and Neofusicoccum parvum were the predominant species found in association with mango stem end rot symptoms. Other species isolated from mango stem end rot in lesser numbers included L. brasiliensis, N. umdonicola and N. kwambonambiense. All of these fungi represent new reports for Fiji.

Avocado (Persea americana cv. ‘Hass’) Fruit Mineral Composition at Canopy Level towards Sustainable Quality

Sustaining avocado fruit quality is crucial to maintain customer satisfaction and confidence. Among fruit qualities, mineral nutrient composition is an important contributor to postharvest robustness. Towards better understanding and addressing variability within the plant canopy, ‘Hass’ fruit from across seven orchard blocks were individually characterised. From five representative trees in each block, five fruit were harvested (one from each of five positions: top (sun-exposed), bottom (shaded), middle (shaded), East (sun-exposed), and West (sun-exposed)). Fruit dry matter was significantly higher (p ≤ 0.001) in fruit from the top, East, and West sun-exposed positions. No significant (p > 0.05) effect of position was discerned for fruit weight at harvest or for either stem end rot (SER) or body rot (BR) incidence at eating soft. Shaded fruit had significantly higher (p ≤ 0.05) [N], [K], [Mg], N:Ca, K:Ca, and K + Mg:Ca in their flesh. Significant negative linear correlations (p ≤ 0.001) were obtained between fruit DM and flesh [N] (r = −0.75), [K] (r = −0.67), and N:Ca (r = −0.57). SER and BR incidence were significantly positively correlated (p ≤ 0.01) with flesh and skin mineral ratios of N:Ca, K:Ca, Mg:Ca, and K + Mg:Ca. Skin and flesh [Ca] were significantly negatively correlated with SER (r = −0.51, p ≤ 0.01) and BR (r = −0.74, p ≤ 0.001) incidences. Soil cation (Ca, Mg, K) availability (%base saturation of cation exchange capacity (CEC)) was not (p > 0.05) correlated with skin or flesh mineral concentrations or ratios. Considered collectively, results suggest that selective harvest of sun-exposed fruit with inherently lower mineral nutrient ratios yields relatively robust fruit. Such fruit lots should better tolerate the rigours of harvest and postharvest treatment and handling. In this context, they should better maintain quality upon passage through long, in terms of accumulated time-temperature increments, export supply chains. In contrast, shaded fruit could be directed into shorter domestic supply chains. As a harvest strategy, segregating fruit lots from harvest could underpin the quality offered to consumers at the end of ‘short’ and ‘long’ supply chains.

Automated detection of internal fruit rot in Hass avocado via deep learning-based semantic segmentation of X-ray images

Internal rot of avocado fruit (Persea americana), attributable to fungal infection, occurs at the end of the ripening process and causes only minor changes in the appearance and texture of the fruit surface. Manual inspection of rot by sight and touch commonly conducted in countries importing avocado fruit is time-consuming, labor-intensive, and subjective. In this context, X-ray line scanning has been proven as an advantageous method of fruit rot detection because of its speed of data acquisition and the indication of internal rot by bright regions in associated images. However, some fruit internal disorders exhibit only poor changes in contrast, resulting in low detectability by traditional image processing. This study aimed to test the effectiveness of a detection model using deep learning-based semantic segmentation in identifying two types of fruit rot, stem-end and body rot, in Hass avocados. Therefore, U-net+ + was trained and validated via 5-fold cross-validation to classify every pixel in an X-ray image as either infected or not. Then, each X-ray image was binarily classified based on either the presence or absence of internal fruit rots, achieving an accuracy of 0.98. Furthermore, the percentage of infected area was quantified with a root mean squared error (RMSE) of 3.15 %. Lastly, the proposed model detected both stem-end and body rot as well as rot along low-contrast fruit edges. The results of this study indicate that the proposed automatic inspection system using deep learning-based X-ray image analysis can effectively detect internal rot in Hass avocado fruit. This non-destructive, objective detection model can therefore increase efficiency and reduce misclassification in post-harvest avocado inspection. Furthermore, deep learning-based X-ray imaging has potential for applications in fruit inspection for internal cavities attributable to diseases or wounds.

β-Aminobutyric Acid Induced Resistance against Alternaria Fruit Rot in Apple Fruits.

Fruit body rot and calyx rot caused by Alternaria alternata f. sp. mali is an important disease of apple worldwide. The disease has recently become severe in cv. Pink Lady apple in Israel to an extent that has never been reported elsewhere in the world. No alternative control measures of the disease except fungicides are known. Here, we show for the first time that dl-β-aminobutyric acid (BABA) induces resistance against Alternaria fruit rot (AFR) in apple fruits in the laboratory and in the orchard. AFR was inhibited in fruits treated with BABA of 1000 μg/mL. BABA did not inhibit spore germination or mycelial growth of the pathogen in vitro (up to 2000 μg/mL). It was most inhibitory when applied 4 days prior to inoculation of detached fruits. BABA inhibited AFR also curatively when applied at 24 h post inoculation. Five other isomers of aminobutyric acid failed to protect the fruits from rot formation. Three field trials in commercial apple orchards proved that BABA was as protective against AFR as the commercial standard fungicidal mixture of azoxystrobin and difenoconazole. This research suggests that BABA may serve as a resistance inducer in apple against AFR. It can be used as an adequate alternative to the currently used fungicides or integrated in disease management programs to reduce fungicide load and buildup of fungicide resistance.

Aggregating ‘Hass’ avocado fruit before packing

ABSTRACT ‘Hass’ avocado fruit are usually packed the day after harvest and then immediately cooled and held no more than a few days before export. This procedure is considered to maximise the storage life and quality of the fruit. However, for packhouse logistics, there are times when it may be advantageous to aggregate fruit over a period of days before packing. It is hypothesised that the time at which fruit are cooled may be more significant to fruit quality than the time of packing. The impact of holding fruit at 7°C for up to 6 days before packing and cooling to storage temperature (5°C) has been investigated. In comparison with fruit held overnight at ambient conditions before packing and cooling, the holding of fruit at 7°C for up to 4 days before packing did not diminish the quality of the fruit markedly, either immediately out of storage (4 weeks after harvest) or after ripening at 20°C. Extending the holding period to 6 days may increase slightly the risk of fuzzy patches, stem end rots and body rots. However, there was as much variability in the incidence of disorders among orchards as there were differences among treatments.

‘Hass’ Avocado Internal Disorders under Simulated Export Conditions and Its Relationship with Flesh Mineral Content and Preharvest Variables

The most important issues that affect consumer fruit acceptance in the ‘Hass’ avocado international market are flesh disorders. These defects can be influenced by both pre- and postharvest factors. The aim of this work was to evaluate the effect of the harvest season, storage time, mineral content, and preharvest variables on internal fruit disorders. Here, fruit was sampled from four farms in Antioquia (Colombia) at 22%, 26%, and 30% dry matter (DM) content. Samples were stored and ripened under simulated export conditions. Then, flesh bruising, flesh discoloration, body rots, vascular browning, stem end rot, and mineral content were assessed. The results showed that flesh disorders differ among farms and by harvest index and storage time. The most frequent defects found were vascular browning and stem end rot. Boron, calcium, nitrogen, manganese, magnesium, and potassium have a strong relationship with flesh disorders. Therefore, high boron and calcium contents, as well as a harvest at 26% DM, can substantially reduce avocado flesh disorders and improve internal fruit quality. Farmers that had a high flesh and soil mineral content and low rainfall and temperature produced fruits with fewer internal disorders.

Impact Injury at Harvest Promotes Body Rots in ‘Hass’ Avocado Fruit upon Ripening

Global demand for avocados has risen rapidly in recent years, yet supplying fruit that consistently meets consumer expectations for quality remains a challenge in the industry. Body rots in avocado fruit are a leading cause of consumer dissatisfaction. Anecdotal evidence suggests that body rot development may be promoted by mechanical injury at harvest and packing, despite the fruit being hard, green and mature (i.e., unripe) at these stages. Here, ‘Hass’ avocado fruit, harvested across multiple fruiting seasons from commercial orchards, were subjected to controlled impact from drop heights of 15–60 cm at the time of harvest or packing. With increasing drop height, body rot development at eating ripe stage generally occurred more frequently and produced larger lesions at the impact site and, in some experiments, elsewhere on the fruit. These findings refute a general belief that green mature avocado fruit can tolerate a degree of rough physical handling without ripe fruit quality being compromised. Ideally, best avocado harvesting and packing practice should recognize that unripe fruit must not experience drop heights of 30 cm or higher.

Bacterial extracts and bioformulates as a promising control of fruit body rot and root rot in avocado cv. Hass

At least 20–40% of annual losses of avocado crops are caused by pathogenic fungi. The chemical treatments of these diseases are inefficient, cause environmental pollution and are increasingly restricted by international laws. This work aimed to assess the biocontrol capacity of a bacterial extract to protect avocado fruits and plants from pathogen infections. Extracts from the bacterial isolate Serratia sp. ARP5.1 were obtained from liquid fermentations in a biorreactor. A body rot postharvest infection model with Colletotrichum gloeosporioides on fruits was developed. Moreover, packaging conditions were simulated using the bacterial extract and the commercial fungicide prochloraz as a positive control. Additionally, seedlings infections with Phytophthora cinnamomi were performed on two types of avocado (West Indian race and cv. Hass). The Area Under Disease Progress Curve (AUDPC) was recorded using the bacterial extract and a commercial product with fosetyl-aluminium as treatments. The bacterial extract significantly reduced infections by C. gloeosporioides on injured avocado fruits at 31.1 μg mL−1. Intact fruits were also protected against body rot infections at the same concentration and showed no significant differences with the commercial fungicide. On the other hand, AUDPC in the seedlings was significantly reduced with the extract treatment at 3 μg mL−1 compared to the control. However, a possible phytotoxicity effect of the extract was evidenced in the seedlings and confirmed by pathogen recovery and tests on Raphanus sativus seedlings. Finally, formulations of the extracts (emulsion and emulsifiable concentrate) were prepared, and bioactive stability was assessed for 8 wk. The emulsion formulates demonstrated very stable bioactivity against P. cinnamomi. The extract and the emulsion formulate showed promising results for the control of avocado pathogens. New bioproducts based on this type of active principles could be developed for the benefit of avocado industry.

Control of Alternaria fruit rot in 'Pink Lady' apples by fungicidal mixtures

Fruit body rot and calyx rot caused by Alternaria alternata f.sp. mali recently appeared in Israel as a severe disease of apple, cv. Pink Lady. No such heavy rots of fruits were reported elsewhere, nor are there any known control measures against the disease. We found that the disease may be successfully controlled by application of fungicidal mixtures to the fruit at the proper phenological development stage. Ortiva-Top (azoxystrobin+difenoconazole) and Azimut (azoxystrobin+tebuconazole) effectively inhibited spore germination, mycelial growth, and rot development in detached fruits. Mixtures of Azimut or Ortiva-Top with Captan were synergistically effective in controlling the disease in detached fruits. In seven field trials Ortiva-Top and Orpan (tebuconazole+captan) were the most effective, and reduced calyx and fruit body rot by 60–88 and 58–92%, respectively, compared with untreated trees. Based on these findings a new spray program was adopted, in which only four to six sprays of Ortiva-Top, Orpan or Azimut were employed, starting at about 115 days after petal fall; it effectively controlled Alternaria fruit rot in 'Pink Lady' apples in Israel.

‘Hass’ avocado quality as influenced by temperature and ethylene prior to and during final ripening

Avocados (Persea americana Mill.) are often held for short periods after harvest at relatively high temperatures both in the field, in storage during preconditioning (ethylene ripening), or prior to ripening with unknown effects on subsequent quality. To better understand the quality effects of short-term high temperature exposure, avocados were harvested at five different times during the first commercial season and held at 20, 25, 30 or 35 °C for 24 h or 48 h, with and without ethylene. During the subsequent season (2) the experiment was repeated, but without the 30 and 35 °C treatments. In both seasons, following the short-term temperature treatment, fruit were either immediately ripened at 20 °C or stored for 14 d at 5 °C and then ripened to determine the influence of storage. After final ripening to eating firmness (4.4–6.7 N) the fruit were evaluated for quality parameters. Results from the first two seasons showed that even a 24 h exposure to 25 °C and above was sufficient to inhibit subsequent ripening and enhance the occurrence of postharvest disorders such as stem end rot and body rot. Application of ethylene during the short-term temperature exposure was ineffective in preventing the disorders. In the third season of the study the effect of prolonged temperature exposure on final ripening was examined. Although there had been research done in the past on this subject, prior work had not examined the effect of different ripening temperatures on flavor. Avocados were harvested at seven harvest dates, stored for either 4 d or 14 d at 5 °C and then ripened to eating firmness at temperatures ranging from 15 to 25 °C. Increasing temperatures up to 20 °C decreased ripening time, beyond which there was no further change. Avocados ripened at temperatures above 20 °C had an increased incidence of the development of pink discoloration in the mesocarp. Ripening temperature had no effect on overall likeability, or ratings of grassy or rich flavor. This correlated with a lack of clear effect of ripening temperature on aroma volatile content of the fruit. Panelists found fruit ripened at 15 °C to have a different texture that those ripened at 20 °C but this had no influence on likeability. This study strongly indicated the importance of maintaining the ripening temperature of avocados at or near 20 °C both when the fruit is ripened soon after harvest or after storage to optimize postharvest quality.

Phenology-Based Management of Alternaria Fruit Rot in Pink Lady Apples.

Fruit body rot and calyx rot caused by Alternaria alternata f. sp. mali has recently become a severe disease of Pink Lady apple in Israel. Severe fruit rot caused by A. alternata f. sp. mali has not been reported elsewhere in the world, and control measures are not currently known. Our objective was to determine the peak periods of susceptibility and develop methods to manage the disease by timing fungicide applications according to fruit phenological stage. We determined the relationship between fruit phenological stage and rot susceptibility by (i) monitoring the appearance of first fruit symptoms in the orchard; (ii) inoculating detached and attached fruit in the laboratory and orchard, respectively, at various time intervals after petal fall; and (iii) starting fungicide applications at various time intervals after petal fall. Fruit of Pink Lady acquired susceptibility to the disease at about 115 days after petal fall (DAPF) when reaching a diameter of ≥55 mm. Based on these findings, a new spray strategy was adopted involving a limited number of 4 to 6 foliar sprays of azoxystrobin + difenoconazole or tebuconazole + captan, or their alternation, starting at 115 DAPF. This strategy provided excellent control of both body rot and calyx rot in Pink Lady apple fruit in Israel.

Influence of cold storage prior to and after ripening on quality factors and sensory attributes of ‘Hass’ avocados

Partially-ripened avocados are often held in cold storage in an attempt to enable the consistent delivery of ripe fruit to food service or retail outlets. It is also common to hold fruit without any prior ripening for a few days to several weeks prior to ethylene treatment and final ripening. The purpose of this study was to determine the impact of these practices on ripening time and subsequent fruit quality. ‘Hass’ avocados were harvested from three different orchards on six harvest dates and placed at either 5°C or 12°C immediately after harvest or after ripening to average firmness values of either 80N (partially ripe) or 19N (near ripe). After storage the fruit were then ripened to eating firmness (4.4–6.7N) and evaluated for quality parameters. A portion of the fruit at harvest firmness were stored for 0d, 7d, 14d or 28d and then treated with ethylene to ripen the fruit. Continual softening during storage resulted in fruit that had been ripened prior to storage being nearly at eating firmness at the end of 14d, especially those stored at 12°C. Stem end rot, body rot and pink staining of the vascular tissue occurred more frequently in the previously-ripened fruit after 14d, the severity being greatest at 12°C where the incidence exceeded 50% for both stem end rot and pink staining. Both harvest date and orchard influenced the amount of pink staining observed. Storage of firm fruit prior to ethylene treatment resulted in higher levels of both stem end rot and pink staining only when the storage time exceeded 14d. In an additional study to assess the impact of the storage of partially-ripened fruit on both quality and sensory characteristics, ‘Hass’ avocados were harvested six times at monthly intervals, ripened to approximately 16N firmness at 20°C and then placed at either 1°C or 5°C for 7d or 14d. Following storage the fruit were ripened to eating firmness and evaluated. The occurrence of fruit quality defects was not affected by the timing of ripening. Sensory panelists liked fruit ripened prior to or after cold storage equally well and there were no differences among the ripening treatments, within a storage time, in the level of rich, nutty or grassy attributes that composed the fruit flavor. There were statistically-significant differences in the degree of textural creaminess among the ripening treatments, although these differences were inconsistent and slight. Storing partially ripe ‘Hass’ avocados for up to 4d at either 1°C, 5°C or 12°C does not greatly alter avocado quality, while storage for longer periods, such as 14d, may be problematic due to enhanced development of decay and pink staining, especially at higher temperatures. Holding unripe avocados for longer than 14d prior to ethylene treatment may predispose the fruit to the development of pink staining.

Metabolites produced by antagonistic microbes inhibit the principal avocado pathogens in vitro

<p>The demand for Hass avocado in the global market exceeds the supply by over 50%. Colombia has a remarkable advantage as a producer in the region due to its high yields. However, the productivity of this crop can be seriously affected by diseases such as root rot, caused by <em>Phytophthora cinnamomi,</em> postharvest body rot and stem end rot, caused by <em>Colletotrichum</em> sp. and <em>Phomopsis</em> sp., respectively. The potential of 76 bacterial isolates obtained from avocado rhizosphere to produce inhibitory metabolites against avocado´s pathogens was evaluated. The antagonistic effect of the rhizobacteria against <em>P. cinnamomi</em>, <em>Colletotrichum </em>sp. and <em>Phomopsis</em> sp. was tested through dual cultures. Thirty-six percent of the tested isolates presented inhibition halos against <em>P. cinnamomi</em>, 36% against <em>Colletotrichum</em> sp. and 67% against <em>Phomopsis</em> sp. Additionally, three isolates were selected for fermentation tests using different broth cultures. The extracts obtained from fermentations in the minimal medium of isolates ARP5.1 and AED06 showed inhibitory activity against the evaluated pathogens, but this effect was not observed with the AED26 extract. The media supplemented with copper chloride did not enhance activity of the extracts. These results suggest that using microbial metabolic extracts is a viable alternative for controlling avocado pathogens<em> in vitro</em>.</p>

No Ethics without Resistance

In the posthumously published Conversations of Goethe with Eckermann and Soret, Goethe expresses no small degree of perplexity concerning a short passage in the tragedy of Antigone: There is a passage in Antigone which I always look upon as a blemish, and I would give a great deal for an apt philologist to prove that it is interpolated and spurious.1 Goethe's open-ended request is hardly compatible with the popular picture that people form of Anti- gone's motivations, namely that she acted solely out of a sense of duty and love for her brother because he belonged to the inner circle of the family. What then is this passage that so perplexed Goethe? the heroine has, in the course of the piece, explained the noble motives for her action, and displayed the elevated purity of her soul, she at last, when she is led to death, brings forward a motive which is quite unworthy, and almost borders upon the comic. At this point Goethe then paraphrases the Greek text (lines 902-12) in the following way: [Antigone] says that, if she had been a mother, she would not have done, either for her dead children or for her dead husband, what she has done for her brother. For, says she, 'if my husband died I could have had another, and if my children died I could have had others by my new husband. But with my brother, the case is different. I cannot have another brother; for since my mother and father are dead, there is no one to beget one.' After rewording the text in this way, Goethe then reiterates how crudely bare Antigone's declaration is and reiterates his demand: is, at least, the bare sense of the passage, which in my opinion, when placed in the mouth of a heroine going to her death, disturbs the tragic tone, and appears to me very far fetched-to savor too much of calculation. As I said, I should like a philologist to show us that the passage is spurious. In Goethe's estimation, what is so shocking here is that Antigone makes a dialectical calculation in the face of her death. It is by no means a utilitarian calculus, but rather a rational justifica- tion meant to clarify, here and now, what it is that makes Polynices irreplaceable for her. For Goethe, the justification spoils her purity as a tragic character and unintentionally casts her action in a disturbingly comic light.Antigone explains that she would not have made the same sacrifice for a hus- band that she made for her brother. A husband is replaceable-if you lose one, you can always find another one somewhere else. In other words, Antigone's maternal role does not depend on one particular man, for a different husband could give her a child if she were childless in her first marriage, or he could give her a second child if she were to lose the first. Antigone thereby reduces her husband to a pure and simple procreative function-he is like a variable in an equation that could easily be filled in by any old replacement. According to Goethe, Antigone would not even have carried out the same sacrifice for her own child. This is because, just like a husband, a child is not irreplaceable in the same way as Polynices is. Antigone's reasoning here brings to mind the cruel popular wisdom that having a new child is the best remedy for losing a first. But what is it that makes Polynices so unique for her? The motive for her action is not that he is a member of the family with whom she shared a direct blood relationship. It cannot be due to his direct blood tie to Antigone, for she would not have done what she did for just any family member, nor even for any brother. If she had had another living brother, or if her parents had still been alive and were capable of producing another one, she would have let his body rot in the desert. Was Polynices perhaps her favourite brother? No, this couldn't possibly be the case, for her particular affection for him was not in the game: if personal bonds had been her motive, then her behaviour would not have been influenced by the existence of another brother. …

The effect of metabolic stress disinfection and disinfestation (MSDD) on ‘Hass’ avocado fruit physiology and mortality of longtailed mealybug ( Pseudococcus longispinus)

Metabolic stress disinfection and disinfestation (MSDD) is a potential quarantine treatment in which a combination of cycles of rapid decompression and compression are followed by exposure to ethanol vapour under decompression. The response of ‘Hass’ avocado ( Persea americana Mill., cv. Hass) to MSDD treatment for control of longtailed mealybug ( Pseudococcus longispinus) was investigated. The best treatment for the most resistant life stage (2nd/3rd instars) was 90-min MSDD treatment with 371 mg L −1 ethanol. Early and late season ‘Hass’ avocados were subjected to MSDD treatments (with 371 mg L −1 ethanol), or in air (control). Following the treatments, early season fruit were ripened at 20 °C and 25 °C. Half of the late season fruit were ripened at either 20 °C or 25 °C, and the remainder were stored at 5.5 °C for 6 weeks, then ripened at 20 °C. There were no significant difference in quality and rot incidence between non-treated controls and MSDD-treated fruit. The main disorders found were stem-end and body rots, vascular browning and flesh greying for the stored fruit. There were also no significant differences in fruit respiration rate or ethylene production. Thus, MSDD was shown to be a potentially ‘soft’ disinfestation treatment for surface pests of avocado.

The effect of delays in establishment of a static or dynamic controlled atmosphere on the quality of ‘Hass’ avocado fruit

The effect of delays of 1, 5, 10 or 15 d after harvest in establishing a static controlled atmosphere (SCA) or dynamic controlled atmosphere (DCA) on the quality of ‘Hass’ avocados ( Persea americana Mill.) was investigated. Fruit were stored at 5 °C in SCA (5% O 2/5% CO 2) or DCA (<3% O 2/0.5% CO 2) for 6 weeks and compared with fruit stored in air. In addition, to determine whether increasing the CO 2 in the DCA would affect the fruit quality, DCA-stored fruit were compared with fruit held in a DCA with 5% CO 2 (DCA + CO 2) established 1 d after harvest. The quality of fruit was assessed at the end of storage and after ripening at 20 °C. DCA-stored fruit ripened in 4.6 d compared with 7.2 d for SCA-stored fruit, or 4.8 d for air-stored fruit. In addition, the incidences of stem end rot (SER), body rot (BR) and vascular browning (VB) were lower in DCA-stored fruit (35%, 29% and 29%, respectively) than in SCA-stored fruit (57%, 52% and 49%, respectively), or air-stored fruit (76%, 88% and 95%, respectively). Delaying the establishment of both SCA and DCA for 15 d resulted in significantly more advanced skin colour at the end of storage (average rating score 11.9) compared with other delay periods (4.6–5.1). There was no significant effect of delay on the time to ripen, skin colour when ripe or any ripe fruit disorder incidence. The incidence of diffuse flesh discolouration (DFD) was not only <1% when averaged over all delays but only occurred at >0.5% incidence in the 15 d delay treatment in DCA (4.8%) and not in SCA. The incidence of diffuse flesh discolouration was 62% in air-stored fruit. Inclusion of 5% CO 2 in DCA retarded fruit ripening from 4.7 to 6.9 d and increased the incidence of rots at the end of storage from 5% to 14%, and increased the incidence in ripe fruit of SER from 30% to 56% and of BR from 27% to 55%. It is concluded that fruit quality was better after CA storage than after air storage, and that DCA storage was better than SCA. The effect of DCA is to independently reduce the time to ripen after storage and the incidence of rots when ripe. Delaying the application of SCA or DCA did not affect the expression of rots, but may increase the incidence of DFD. Inclusion of CO 2 at 5% in CA retarded fruit ripening but stimulated rot expression and should not be used for CA storage of New Zealand grown ‘Hass’ avocados.

Calcium, fungicide sprays and canopy density influence postharvest rots of avocado

A study was carried out in eight orchards in 1999, 2000 and 2001 to examine the effect of preharvest factors on postharvest rots of ‘Hass’ avocados in New Zealand. A further 14 orchards were sampled in 1999 and, of these, 13 were sampled in 2000, depending on fruit availability. Orchards were selected following consultation with industry personnel to obtain a sample representative of fruit quality in New Zealand. Fruit were harvested in early January at a dry matter content of ≈33%, then stored and ripened at 20°C. Fruit were assessed for stem-end and body rots when ripe, and fungi from rots were isolated and identified. For the 3 years’ data collected from the same eight orchards, the incidence of stem-end rots was linearly related to the number of fungicide applications, mainly of copper and a few of benomyl. In 1999 and 2000, an index describing canopy density and the amount of dead branches in the canopy was significantly related to the incidence of body rots, but not to the incidence of stem-end rots. In 2000, a significant relationship was found between body rot incidence and severity and fruit calcium levels. Body rots were found to decrease with increasing temperature and rainfall in 2000 when these data were collected for seven orchards. In contrast, calcium content in fruit was positively related to these factors. The most common pathogen from isolations was Botryosphaeria parva, followed by Colletotrichum acutatum. To improve fruit quality of avocados in New Zealand, it is recommended that growers apply fungicides more than eight times and calcium to increase the (calcium+magnesium)/potassium ratio above 0.065 in fruit.

Between-tree variation in fruit quality and fruit mineral concentrations of Hass avocados

Inconsistent internal fruit quality in Hass avocados affects consumer confidence. To determine the influence of individual trees on fruit quality, Hass avocado fruit were harvested from adjacent trees of similar external appearance in 3 commercial orchards in 1998 and 1 orchard in 1999. The trees in each orchard were grown with similar commercial practices and in similar soil types. Within each location, there were significant (P&lt;0.05) differences in the mean ripe fruit quality between trees with respect to fruit body rot severity (mainly anthracnose) with and without cold storage, internal disorders severity due to diffuse discolouration and vascular browning (after cold storage), days to ripen, percentage dry matter, and the percentage of the skin area with purple-black colour when ripe. These effects were also noted in the same orchard in 1999. There were significant (P&lt;0.05) differences in fruit flesh calcium, magnesium, potassium, boron and zinc concentrations between trees. Significant (P&lt;0.05) correlations were observed between average fruit mineral concentrations in each tree (particularly calcium, magnesium and potassium) and body rot severity, percentage dry matter and fruit mass. There was little conclusive evidence that characteristics such as the growth of the non-suberised roots or the degree of scion under- or overgrowth was involved in these tree effects; however, differences between trees with respect to other rootstock characteristics may be involved. The inconsistency of the correlations across sites and years suggested that other factors apart from tree influences could also affect the relationship between fruit minerals and fruit quality.

SEPARATING HIGH HARVEST TEMPERATURE EFFECTS ON POSTHARVEST AVOCADO QUALITY

The logistics of the current Australian and Californian recommendations to harvest avocado below 30 °C and remove field heat within 6 hours of harvest are increasingly being challenged as the Western Australian industry expands. Despite this, there has been little feedback of quality sacrifice in the market as a result. Through factorial experiments, we harvested both shaded and sun-exposed 'Hass' avocado over an ambient air temperature range of 27-34 °C, subjected to a 2, 6 or 24 h pre-cooling delay and a 14 or 28 day cool-storage, before ripening and quality assessment. We found significant temperature correlations to softening, vascular browning, body rots and, when a temperature-by-delay interaction was considered, skin colour. The relationships of temperature to softening and body rot were quadratic: softening increased significantly up to an ambient temperature of about 30 °C but did not change significantly thereafter; body rots did not change significantly up to 30 °C but declined significantly thereafter. The interaction effect of temperature-by-delay on colour was also quadratic when fruit were subjected to a 24 h pre-cooling delay. Fruit colour increased significantly up to about 30 °C but did not change significantly thereafter. The relationship of temperature to vascular browning was negatively linear; showing a significant decline over the range of 27-34 °C. There was no significant main effect of sun-exposure, although there were significant interactions; showing that postharvest behaviour varied between shaded and sun-exposed fruit. However, the average elevation of 6 °C above shaded fruit temperatures was not as large as reported by previous studies and was thus interpreted with caution. In light of the results, experiments have been designed to further explore the main effects and interactions of temperature, sunlight, and postharvest handling on avocado quality and physiology.

Manipulating avocado fruit ripening with 1-methylcyclopropene

Previous investigations with 1-methylcyclopropene (1-MCP) on avocado (Persea americana Mill.) fruit have focussed mainly on improving storage life by reducing the severity of disorders causing discolouration of the flesh. Development of 1-MCP and ethylene treatments, which also help control the time to reach the eating ripe stage, may confer additional practical benefits. In this context, the current study investigated the potential of 1-MCP to accurately manipulate ripening of non-stored 'Hass' avocado fruit by treatment before or after ethylene and at different times during ripening. To investigate this, 500 nL L-1 1-MCP was applied within 1 day after harvest, followed by ethylene 0-14 days after 1-MCP. In addition, fruit were treated with ethylene, then 1-MCP 0-8 days after ethylene. Treatment of fruit with 500 nL L-1 1-MCP for 18 h at 20 degreesC provided the maximum effect by increasing the days from harvest to ripe (DTR) from 8 (with no 1-MCP) to 20. Fruit treated with 500 nL L-1 1-MCP for 18 h at 20 degreesC remained insensitive to 100 muL L-1 ethylene applied between 0 and 14 days after 1-MCP for 24 h at 20 degreesC. Ripening of fruit exposed to 100 muL L-1 ethylene for 24 h at 20 degreesC could be delayed by up to 3.3 days by applying 500 nL L-1 1-MCP for 18 h at 20 degreesC up to 2 days after ethylene treatment. However, once the fruit started to soften (sprung) there was little effect of 1-MCP on DTR, compared with no 1-MCP. 1-MCP treatment was associated with increased severity of body rots (caused mainly by Colletotrichum spp.) and stem-end rots (caused mainly by Dothiorella spp.), which was likely due to the increased DTR in these treatments. Significant differences in disease severity were found between orchards (replications), with replicates with low disease severity being less affected by 1-MCP treatment. These results indicate that 1-MCP can delay ripening, but careful sourcing of fruit is required to reduce the risk of diseases in ripe fruit. There is some capacity to delay ripening using 1-MCP after ethylene. There is little potential to control ripening using ethylene after treatment with 500 nL L-1 1-1-MCP, but lower concentrations may be more effective. (C) 2004 Elsevier B.V. All rights reserved.