Incidence Of Stem-end 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.

The Potential of Gaseous Chlorine Dioxide for the Control of Citrus Postharvest Stem-End Rot Caused by Lasiodiplodia theobromae.

The focus of this study was to develop technologies using chlorine dioxide (ClO2) gas to control postharvest stem-end rot of citrus caused by Lasiodiplodia theobromae. Mycelial growth of L. theobromae on potato dextrose agar (PDA) plugs was completely inhibited by a 24-h ClO2 exposure provided by 0.5 g of solid ClO2 generating granular mixture in a 7.7-liter sealed container. In vivo experiments were conducted on artificially inoculated Tango and naturally infected U.S. Early Pride mandarins. When ClO2 treatments were initiated 0 to 6 h after inoculation, decay development was significantly reduced as compared with the control, and higher ClO2 doses were more effective. A ClO2 treatment (using 3 g of generating mixture per 7.7-liter sealed container) administered 0 h after inoculation resulted in 17.6% Diplodia stem-end rot incidence compared with 95.6% in the control, whereas the same treatment administered 24 h after inoculation was much less effective, resulting in 63.0% incidence compared with 85.4% in the control. Diplodia stem-end rot incidence of naturally infected fruit after using 6 or 9 g of generating mixture per 24-liter sealed box was 23.8 or 25.7%, respectively, compared with 47.9% for control fruit. The ClO2 treatments had no negative effects on fruit quality characteristics including weight loss, firmness, puncture resistance, titratable acids (TAs), total soluble solids (TSSs), and rind color. Albedo pH at wounds was significantly reduced from 6.0 to 4.8 by the ClO2 treatments, whereas undamaged albedo remained at 5.8. In addition, no visible physiologic defects, such as peel browning and bleaching, were observed on ClO2-treated fruit. These results indicate that ClO2 gas has the potential to be developed as a component of an integrated citrus postharvest decay control system to minimize fruit losses.

Distribution of stem-end rot on the canopy in ‘Hass’ avocado trees in two coastal areas in Peru

Stem-end rot (SER) of avocado is caused by several fungal species, and it is presented worldwide. This plant disease currently affects several avocado producer regions in Peru, causing fruit rot, impacting the industry negatively. Research about SER distribution in the canopy of avocado trees is limited. Thus, the present study aimed to compare which areas in the canopy are prone to have more SER in ‘Hass’ avocado harvested fruit in two different coastal areas in Peru. The experiment was conducted in the northern (Barranca) and southern (Cañete) of Lima. ‘Hass’Avocado fruits from both producer areas were collected to identify the causal agent; Lasiodiplodia theobromae was isolated from infected fruits. Identification was conducted based on morphological features and a partial DNA sequence of the translation elongation factor 1-α gene (tef1-α). The results showed that fruits inside the tree canopy were prone to have a higher disease incidence than the fruits located in the external site (P<0.001). Besides, internal-site fruits displayed a higher percentage of infected fruit for each grade disease (P<0.001) than external-site fruits, except for grade 0 (fruits without symptoms) and grade 1. Finally, the results suggested that the altitude where the fruit is positioned on the canopy could influence the incidence of SER, where fruits located in the high part revealed less incidence than the low section. The results are valuable for enhancing management strategies and avoiding postharvest loss of avocado fruits in our region.

Postharvest Incidence of Stem End Rot in 'Hayward' Kiwifruit Is Related to Preharvest Botrytis cinerea Colonization of Floral Parts and Latent Infection.

Stem end rot (SER) caused by Botrytis cinerea is the primary postharvest disease in the Chilean kiwifruit industry. Relationships between the postharvest occurrence of SER in 'Hayward' kiwifruit and the temporal dynamics of earlier B. cinerea colonization of the floral parts (petals, sepals, receptacles, styles) was studied in five orchards over two consecutive seasons in Chile. Weather conditions in the first season favored B. cinerea infection with roughly constant colonization of floral parts up to about 120 days after full bloom, but colonization then increased up until harvest. In the second season, colonization was roughly constant throughout. Latent infections of the fruit occurred in both seasons but were high in the first season and low in the second. Incidence of latent infections at harvest were the best predictors (r > 0.8) of postharvest SER. The number of preharvest infection periods calculated using temperature, leaf wetness, and relative humidity satisfactorily predicted SER incidence by an exponential model, R2 = 0.90, P < 0.001. Results indicated environmental variables play key roles in the temporal dynamics of B. cinerea colonization. Quantification of latent B. cinerea infections in asymptomatic fruit close to harvest, is a practicable way to predict later incidence of SER during storage.

Effects of chitosan treatment on avocado postharvest diseases and expression of phenylalanine ammonia-lyase, chitinase and lipoxygenase genes

Stem-end rot (Lasiodiplodia theobromae) and anthracnose (Colletotrichum gloeosporioides) are major postharvest diseases in avocado that cause severe postharvest losses throughout the supply chain. One of the strategies to reduce development of such decay agents resides in the application of resistance inducers (e.g. chitosan), capable of reducing fungal growth and inducing resistance in fruit tissues.The influence of chitosan treatment (1% or 1.5% w/v) was investigated on decay incidence, gene expression of phenylalanine ammonia-lyase (PAL), chitinase (CHI) and lipoxygenase (LOX) and antioxidant enzyme activity [superoxide dismutase (SOD) and catalase (CAT)] in i) drop-inoculated (without wounding) or ii) artificially infected (with wounding) avocado (cv. ‘Hass’) with L. theobromae or C. gloeosporioides pathogens and also in iii) naturally infected (natural inoculum) avocado. Fruit were dipped in 1% or 1.5% w/v chitosan dissolved in water for 3 min, followed by storage for 14 d and 28 d respectively at 7.5 °C, and thereafter for 5 d at 18 °C to simulate market shelf conditions.Chitosan at 1.5% significantly reduced the incidence of stem-end rot and anthracnose in both inoculated and naturally infected avocados. The up-regulation of PAL and down-regulation of LOX genes moderately allowed higher epicatechin contents (90 mg kg−1 FW) in the exocarp, which could have contributed to improved anthracnose control. The up-regulation of CHI genes and higher SOD activity could have contributed to control of stem-end rot. Chitosan solution (1.5%) retained moderate levels of C7 sugars and firmness up to 5 d shelf life. The control of stem-end rot and anthracnose of avocados obtained with 1.5% chitosan can be ascribed to a combination of its antifungal and eliciting properties.

Differential response to combined prochloraz and thyme oil drench treatment in avocados against the control of anthracnose and stem-end rot

The ability to meet consumers demand for high-quality standard fruit entails the distribution of unblemished safe fruit free of chemical residues on its edible portion. Therefore, this study was focused on investigating the influence of the combined effect of aqueous plant volatiles with half strength prochloraz solution to control anthracnose and stem-end rot in the green-skinned avocado cultivar (Fuerte). This method was applied due to its practicability on bulk fruits in packhouses and the fruits were subjected to stand-alone and combined treatments to assess the development of the disease after cold storage and observe the elicitation of the residual effect of the treatments on the defence related enzymes in ‘Fuerte’. The incidence of stem-end rot was 10% by the combination of prochloraz® (500 μg mL−1; P50) with 0.1% v/v thyme oil compared to the 58.8% incidence exhibited by the untreated fruit during storage at 6.5 °C for 14 days followed by 3 days at retail shelf conditions (15 °C) (preventative application). Citral (0.1% v/v), P50 (500 μg mL−1) + 0.1% v/v citral and yucca extract alone reduced the stem-end rot incidence to about 25% during storage. More so, thyme oil (0.1% v/v) reduced both anthracnose and stem-end rot incidence to 35% after postharvest storage and P50 (500 μg mL−1) + 0.1% v/v thyme oil and 0.1% v/v thyme oil effectively induced the activity of phenylalanine ammonia lyase, chitinase and β-1, 3 glucanase in fruit inoculated with Lasiodiplodia theobromae and Colletotrichum gloeosporioides through the improvement of quality and firmness of the fruit after storage.

Delayed incidence of stem-end rot and enhanced defences in Aureobasidium pullulans-treated avocado (Persea americana Mill.) fruit

The stem-end rot of avocado, caused predominantly by Lasiodiplodia theobromae, can result in heavy postharvest losses. Application of a cell suspension of Aureobasidium pullulans at the stem-end of unripe fruit delayed (P 0.05) affect disease incidence. L. theobromae, when cultured together with A. pullulans, showed significantly (P < 0.05) reduced radial growth of colony towards A. pullulans at 48 and 72 h and shortened aerial mycelium compared to controls. Neither of the organisms overgrew on each other but their colony margins were in close proximity. Presence of A. pullulans significantly (P < 0.001) reduced germination of conidia in water, and the germ tubes were shorter and showed only emergence. Chitinase, β-1,3-glucanase and antifungal activity of the peel of control fruit declined during ripening. However, there was increased chitinase and β-1,3-glucanase activity in A. pullulans-treated fruits or fruits that were inoculated with L. theobromae after treatment with A. pullulans. β-1,3-glucanase activity increased only slightly in fruits that were inoculated with L. theobromae without treatment. Greater preformed antifungal activity was retained in A. pullulans-treated fruits during ripening. Enhanced activity of chitinase and β-1,3-glucanase and greater retention of preformed antifungal activity may have contributed to the delayed stem-end rot incidence in A. pullulans-treated avocados. Application of A. pullulans, 2 days prior to inoculation and retention of stalk at harvest, appears to have allowed better establishment of A. pullulans on the fruit surface.

First Report of Pestalotiopsis clavispora and Pestalotiopsis spp. Causing Postharvest Stem End Rot of Avocado in Chile.

Avocado (Persea americana) production in Chile has increased to more than 33,500 ha. Chilean avocadoes are sent to markets 15 to 45 days away by overseas transport to the United States, Europe, and Asia. Although apparently healthy avocadoes were harvested in 2009, a 10 to 14% incidence of stem end rot appeared after 15 days of cold storage. Symptoms appeared as small, irregular, brown lesions on the peel at the stem end. Lesions enlarged rapidly, became sunken and soft, eventually comprising the entire fruit as ripening progressed. A white mycelium often developed around the stem cavity. A dark brown necrosis of the pulp was observed that comprised a big part of the pulp as the fruits matured. Isolations were performed from 'Hass' avocadoes that developed stem end rot after fruits were kept in humid chambers for 15 days at 5°C plus 6 days at 20°C (n = 50) to simulate a transport period from Chile to U.S. markets or from diseased fruits (n = 50) kept for 15 days at 20°C. Fruits were surface disinfected for 60 s in 75% ethanol, and small pieces of tissue were excised from the margins of the pulp lesions and then plated onto potato dextrose agar (PDA) plus 1 ml/liter of Igepal CO-630 (Sigma-Aldrich, Atlanta, GA) (MPDA). Fungal colonies that developed on PDA were white and cottony, turning slightly yellow after 15 days. Black acervuli appeared after 15 days at 20°C. Conidia (n = 40) were fusiform, (22.2) 27.0 to 30.4 × (6.3) 7.0 to 9.8 μm with a length/width ratio of 3.4 ± 0.4. All isolates had five-celled conidia. Apical and basal cells were colorless, while the three median cells were dark brown. Conidia had one basal appendage (9.3 ± 3.3 μm) and two to four long apical appendages (34.5 ± 6.9 μm). On the basis of colony and conidia morphology, most of these isolates were initially identified as Pestalotiopsis clavispora (G.F. Atk) Steyaert, but other nonidentified species of Pestalotiopsis were also found (3). Identification was confirmed by amplifying and sequencing the internal transcribed spacer (ITS) region of rDNA using ITS1/ITS4 primers of P. clavispora isolate PALUC-12 (Accession No. HQ659767). A BLAST search of the NCBI database showed that isolate PALUC-12 had 100% homology with P. clavispora (No. EU342214.1). Pathogenicity tests were conducted on surface-disinfected (75% ethanol, 30 s) fruits by placing agar pieces (3 mm in diameter) from 7-day-old cultures and a 20-μl drop of 106 conidia/ml on wounded and unwounded stem cavities and equatorial area of five avocado fruits of 'Hass', per isolate tested, at the commercial maturity stage. Inoculated fruits were placed in moist chambers at 25°C for 10 days. Necrotic lesions resembling symptoms that occurred in storage fruits were observed on wounded fruits. No symptoms were observed on unwounded fruits inoculated in the equatorial zone. However, unwounded fruits inoculated in the stem cavity developed a slight necrosis probably because of undetectable wounds made at harvest. Koch's postulates were confirmed after the reisolation of P. clavispora and Pestalotiopsis spp. from diseased fruits. P. versicolor has been reported in South Africa (1), but to our knowledge, this is the first report of P. clavispora causing stem end rot of avocado. P. clavispora has been reported on blueberry in Chile (2).

Infection of 'd'Anjou' Pear Fruit by Potebniamyces pyri in the Orchard in Relation to Phacidiopycnis Rot during Storage.

Phacidiopycnis rot, caused by Potebniamyces pyri, is a recently recognized postharvest fruit rot disease of 'd'Anjou' pear (Pyrus communis) in the United States. To determine the timing of fruit infection in the orchard in relation to incidence of Phacidiopycnis rot during storage, fruit were inoculated in the orchard at different times during the growing season, harvested, and monitored for decay development during storage at 0°C. Fruit inoculated in the field and laboratory were also used to determine the infection courts and the importance of necrotic tissues to infection of sepals that may lead to calyx-end Phacidiopycnis rot. Phacidiopycnis rot was observed during cold storage on the fruit inoculated any time after bloom till near harvest but not on the fruit inoculated during bloom. Phacidiopycnis rot symptoms only developed at the stem and calyx end of the fruit during storage. Relatively more calyx-end rot was observed than stem-end rot on the fruit inoculated before August. Incidence of stem-end rot increased significantly on the fruit inoculated near harvest. Incidence of total Phacidiopycnis rot increased as the timing of fruit infection in the orchard approached harvest. Potebniamyces pyri was recovered more frequently from sepals than from styles and stamens of the fruit. Most infections on sepals were associated with the necrotic tissues. Naturally occurring necrotic tissues occurred on more than 85% and all sepals in the early fruit-growing and late growing seasons, respectively. Such necrotic tissues on sepals could serve as potential infection sites for P. pyri. The results may suggest that chemical control of Phacidiopycnis rot should focus on protecting the pedicel (stem) and floral parts of fruit and that fungicides applied near harvest are likely most important in controlling latent infections of pear fruit by P. pyri leading to Phacidiopycnis rot during storage.

The potential of a new fungicide fludioxonil for stem-end rot and green mold control on Florida citrus fruit

Fludioxonil is a newly registered and classified as reduced-risk fungicide by the US EPA for citrus fruit postharvest treatments. The efficacy of fludioxonil for the control of diplodia stem-end rot caused by Lasiodiplodia theobromae and green mold ( Penicillium digitatum) on Florida citrus fruit was evaluated. The ED 50 values of fludioxonil against L. theobromae and P. digitatum in potato dextrose agar were 0.012 and 0.020 mg/L, respectively. Application of fludioxonil at 250–1200 mg/L on oranges using a simulated commercial drench system before fruit ethylene degreening reduced diploda stem-end rot incidence by 75.7–88.6%, and fludioxonil at 500–1200 mg/L performed similarly to the commercial postharvest fungicide imazalil or thiabendazole (TBZ) at 1000 mg/L. Fludioxonil was compatible with chlorine in drench suspension as measured by the efficacy of fludioxonil for diplodia stem-end rot control. Fludioxonil also effectively reduced both diplodia stem-end rot and green mold when applied through a simulated commercial packingline system. Fludioxonil was more effective for diplodia stem-end rot control on non-ethylene-treated oranges than on ethylene-treated fruit. Fludioxonil was also effective for the control of TBZ-resistant P. digitatum isolates on oranges. An active suppression of P. digitatum sporulation by fludioxonil on citrus fruit was observed. However, fludioxonil showed a much less activity for P. digitatum sporulation control compared to postharvest fungicide imazalil. The registration of fludioxonil has provided a new alternative, reduced-risk compound for citrus postharvest disease control and fungicide resistance management in Florida.

Progresso de doenças fúngicas e correlação com variáveis climáticas em mamoeiro

Avaliou-se o progresso de doenças fúngicas do mamoeiro e os efeitos dos fatores climáticos em três áreas experimentais: 1- área de produção de mamão conduzida no sistema convencional, que recebeu irrigação por gotejamento; 2- área de produção de mamão conduzida no sistema convencional, que recebeu irrigação por aspersão; 3- área de produção de mamão cultivada no sistema orgânico, com irrigação por microaspersão. Na área 1 foram avaliados três sistemas diferentes de condução: 1) sem a aplicação de fungicidas e sem sanitização das plantas (testemunha sem sanitização); 2) sem a aplicação de fungicidas e com sanitização das plantas (testemunha com sanitização); e 3) com a aplicação de fungicidas para o controle de doenças foliares e sem sanitização (padrão do produtor). Em cada sistema de condução foram demarcadas quatro parcelas (repetições) com 20 plantas, sendo 10 plantas consideradas úteis. Foram avaliadas a incidência e a severidade da mancha-de-ascoquita, pinta-preta e do oídio como doenças foliares. Nos frutos, após a colheita foram avaliadas as incidências da antracnose, mancha-chocolate e podridão-peduncular. As epidemias da mancha-de-ascoquita ocorrem em temperaturas variando de 15 ºC a 20 ºC; para a pinta-preta as condições favoráveis ao desenvolvimento de epidemias foi temperatura variando de 25 ºC a 30 ºC e umidade relativa variando de 80 % a 100 %, sendo o pico da intensidade da doença ocorre entre os meses de novembro a março. Para o oídio, a faixa de temperatura que favoreceu a doença foi 15 ºC a 20 ºC e umidade relativa de 60 a 70 %. Em relação às podridões que incidiram nos frutos, observou-se que não houve relação entre a incidência da podridão-peduncular e a precipitação pluvial acumulada, 15 dias antes da avaliação ou no período de desenvolvimento do fruto (r &lt;0,21). A incidência da antracnose e da mancha-chocolate não se correlacionaram com as condições climáticas. Na área Santa Terezinha 10, a mancha-de-ascochyta foi constatada em todas as épocas de avaliação, tendo severidade máxima na data juliana 155 aos 250 dias e mínima dos 20 aos 80 dias; a pinta-preta progrediu na data 326 aos 70 dias com severidade máxima na data 336 dias, e o oidio progrediu em duas épocas distintas sendo uma na data 330 aos 80 dias e a outra na data 240 aos 320 dias com o máximo na data 240 a 250 dias. A incidência da podridão dos frutos em pós-colheita foi detectada no armazenamento, quando os frutos foram colhidos nas datas de 140 aos 320 dias, sendo alta até a data 220; a partir daí decresceu até a data 320. O tratamento padrão praticado pelo produtor diferiu significativamente dos tratamentos envolvendo práticas culturais com e sem sanitização, excetuando a podridão peduncular onde o tratamento padrão igualou-se ao tratamento com sanitização. Os tratamentos culturais com e sem sanitização não diferiram entre si. Comparando-se os tratamentos com sanitização e sem sanitização para podridão peduncular houve ganhos de 24 % e 9 %, para as datas julianas 170 e 210, respectivamente; para a antracnose houve ganhos de 13 % e 55 %, para as datas julianas 160 e 230, respectivamente e para a mancha-chocolate 30 % e 9 %, para as datas julianas 170 e 210, respectivamente. O progresso das doenças nas áreas de plantio do curral e Bitchisner foram quase idênticos com relação à incidência de folhas doentes total; a severidade máxima da mancha-de-ascoquita atingiu 20 % na área do curral e 10 % na área Bitchisner, entre as datas 110 e 320. A pinta-preta foi muito severa na lavoura do curral e de baixa severidade na lavoura Bitchisner. O oidio foi detectado nas duas lavouras nas datas 230 aos 320, com maior severidade na lavoura do curral onde predomina a irrigação por aspersão. Obtêve-se severidade do Oidio máxima de 45 e 65 % nas lavouras do curral e Bitchisner, respectivamente. Em se tratando da podridão dos frutos do mamoeiro, a incidência foi maior nas plantas da localidade do curral do que Bitchisner devido ao método de irrigação por aspersão.

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.

Preharvest application of fungicides for postharvest disease control on early season tangerine hybrids in Florida

Postharvest anthracnose and stem-end rot, caused by Colletotrichum gloeosporioides and Lasiodiplodia theobromae, respectively, can be severe problems to certain ethylene-degreened early season citrus cultivars in Florida. Preharvest application of fungicides can be an effective approach for control of these diseases. The potential of five fungicides, benomyl, thiophanate methyl, azoxystrobin, fludioxonil and pyraclostrobin applied 2, 14, 21, and 28 d before harvest for control of postharvest anthracnose, stem-end rot, and green mould ( Penicillium digitatum) was evaluated on early season Florida Fallglo and Sunburst tangerine hybrids in 2003 and 2004. Most fungicides significantly reduced anthracnose incidence on Fallglo when applied 2 d before harvest in both years and at 14 and 21 d before harvest in 2003. At other application dates, none of the fungicides was effective. On Fallglo fruit in 2004, the five tested fungicides reduced postharvest anthracnose by 37.4–62.6% when sprayed 2 d before harvest. Little anthracnose was observed on Sunburst fruit in either year. On both cultivars and in both years, benomyl and thiophanate methyl consistently and significantly reduced stem-end rot incidence. Other fungicides were less effective or ineffective in controlling stem-end rot. Benomyl and thiophanate methyl also reduced green mould incidence by 58.9–100% on Sunburst tangerines in 2004, but were ineffective in 2003 due to the presence of resistant strains. Thiophanate methyl appears to be an excellent alternative to benomyl for citrus postharvest disease control since benomyl, the only registered fungicide for preharvest application for postharvest decay control, is no longer being produced in the USA.

Effects of rootstock and nitrogen fertiliser on postharvest anthracnose development in Hass avocado

These rootstock and nitrogen fertiliser studies confirmed that rootstock race can significantly affect the development of postharvest disease and mineral nutrient accumulation in Hass avocado fruit. When Hass (Guatemalan race) was grafted to seedling Velvick (West Indian race) rootstock, the severity and incidence of anthracnose in fruit were significantly reduced by up to 64 and 37%, respectively, compared with seedling Duke 6 (Mexican race) rootstock. Stem-end rot was also influenced by rootstock in some seasons, and significant reductions (up to 87%) in the severity and incidence of stem-end rot were recorded in Hass fruit from Velvick compared with Duke 6 rootstock trees. These improvements in postharvest diseases were associated with significantly lower concentrations of nitrogen and potassium, higher concentrations of calcium and magnesium, lower ratios of nitrogen: calcium and higher ratios of calcium+magnesium: potassium in Hass leaves and fruit from Velvick compared with Duke 6 rootstock trees. Altering the rate of nitrogen fertiliser had minimal impact on postharvest disease development. However, in one season, reducing the rate of nitrogen fertiliser to nil significantly reduced the concentration of nitrogen in the fruit skin, decreased the nitrogen: calcium ratio and significantly reduced the severity and incidence of anthracnose in Hass fruit from both Velvick and Duke 6 rootstock trees. The form of nitrogen fertiliser (ammonium compared with nitrate) applied to the trees did not significantly affect the postharvest disease susceptibility of Hass avocado fruit on either Velvick or Duke 6 rootstock. The Guatemalan race rootstocks, Anderson 8 and Anderson 10, were also found to be superior to the Mexican race rootstock, Parida 1, for reducing anthracnose severity. This again, was associated with a better balance of mineral nutrients (significantly lower nitrogen: calcium and higher calcium+magnesium: potassium ratios) in the fruit. This rootstock effect, however, was only observed in the first season of a 3-year experiment, possibly because of a better balance between vegetative growth and fruit production in Parida 1 in the latter two seasons. Significant positive correlations between anthracnose severity and fruit skin nitrogen: calcium ratios were evident across all experiments.

Semi-commercial evaluation of Bacillus licheniformis to control mango postharvest diseases in South Africa

Efficacy of the biocontrol agent Bacillus licheniformis was evaluated under semi-commercial conditions on a mango packing line to control anthracnose and stem-end rot on the mango cultivar ‘Keitt’. Mango fruit were treated with either the biocontrol agent applied in hot water (45 °C) followed by a quarter strength prochloraz dip or with the biocontrol agent applied on its own in hot water. These treatments were compared to the untreated control and commercially used prochloraz hot water dip. Treated fruit were dried and waxed on the commercial packing line. Fruit subjected to the prochloraz-biocontrol hot water combination showed reduced anthracnose and stem-end rot incidence after market simulated conditions of low temperature storage at 10 °C with 90% RH and at room tempeature (20 °C at 75% RH for 7 days). This integrated treatment retained the fruit colour and firmness with high marketability most effectively, compared to the other treatments. The biocontrol agent was effectively recovered from treated fruit after 21 days storage at 10 °C, 90% RH (6 log units) and declined to 3 log units after an additional 7 days storage at 20 °C, 75% RH. Total recovered bacterial and yeast populations on the fruit surface were higher in fruit subjected to the integrated treatment and held under both storage conditions. In contrast, the total recovered fungal population was higher on untreated control fruit.

EFFICACY OF DIFFERENT HEAT TREATMENT PROCEDURES IN CONTROLLING DISEASES OF MANGO FRUITS

Different heat treatment procedures were evaluated to compare their efficacy in controlling diseases of mango fruits. Mature green 'Carabao' mangoes were subjected to the following heat treatments within 30 h after harvest: hot water treatment (HWT; 53°C, 10 min), hot water brush (HWB; 60°C, 20-35 sec) and a brief exposure to hot water dip (HWD; 60°C, 20-35 sec). Fruits were then subjected to vapor heat treatment (VHT) and ripened at 25°C. All heat treatment procedures resulted in a reduction in anthracnose and stem end rot incidence. The usual HWT and the brief exposure to HWD at 60°C for 35 sec controlled the development of anthracnose. Hot water brush for 35 sec also effected a considerable reduction in disease incidence. Variable degree of disease control was obtained when the different heat treatments were combined with VHT. Vapor heat treatment alone did not control anthracnose and stem end rot since incidence was comparable with the control. Hot water treatment in combination with VHT resulted in faster peel color change compared with the rest of the treatments. At the ripe stage, lenticel spotting was more prominent in fruits subjected to HWB compared with HWT and least in HWD. Physicochemical characteristics of the fruits were not influenced by any of the heat treatments employed.

NEW PROCEDURES FOR “CURING” AND CONTROLLED ATMOSPHERE (CA) STORAGE TO CONTROL BOTRYTIS CINEREA IN KIWIFRUIT

In kiwifruit (Actinidia x deliciosa var. deliciosa cv. Hayward (A. Chev.) C.F. Liang et A.R. Ferguson), “curing” is particularly laborious (and expensive) as it involves storing the fruits under cover for 2-5 days period, depending upon temperature. Storage management is thus particularly difficult. “Curing” performed directly in the cold storage rooms is complicate, but trials carried out at commercial level suggests that when possible, its use could become generalised. The advantages could be significant at financial level (as fruit handling is reduced) and considerable at biological level as they enable “curing” to be carried out at a controlled rather than a variable temperature as at present and the product to be protected naturally rather than through the use of chemicals. For kiwifruit, the use of CA is known to prolong storage time by about two months with respect to regular storage, but at the same time, stem end rot caused by Botrytis cinerea increases considerably. The aim of this study was to identify the best method for “curing” in a cold storage room and verify the optimum delay for the commencement starting of the CA regime (taken as far as 40-45 days after harvesting) without compromising maintenance of the flesh softening of the fruit. The study confirmed that the incidence of stem end rot caused by Botrytis cinerea can be reduced using natural systems involving neither higher costs nor the use of chemicals. “Curing” directly in cold storage rooms and delaying establishment of the CA regimes to 30-40 days after harvesting, reduces the incidence of stem end rot. At the same time, there are no major negative effects on the fruit flesh softening, to the point of compromising their marketable value.

Effect of 2,4-dichlorophenoxyacetic acid on the incidence of side and stem end rots in mango fruits

Abstract A treatment of hot water brushing and prochloraz followed by 2,4-dichlorophenoxyacetic acid (2,4-D) diluted in wax, reduced postharvest diseases by 50–70% and improved fruit quality during prolonged storage. Alternaria alternata, Phomopsis spp. and Lasiodiplodia spp. were the main causal organisms of stem end decay. The best control was obtained by concentrations of 2,4-D ranging from 75 to 175 μg ml−1, which could efficiently control side rots caused by A. alternata and the stem end rot-causing pathogens. The combination of hot water brushing, prochloraz application and 2,4-D treatment reduced the incidence of stem end rot after 4 weeks of storage at 14°C and 7 days of shelf life at 20°C from 86 to 10% in cv. Tommy Atkins and from 63 to 12% in cv. Keith. At 175 μg ml−1 2,4-D did not affect fruit firmness or colour development but ensured high quality and fewer rotten fruits.

Application of Candida saitoana and Glycolchitosan for the Control of Postharvest Diseases of Apple and Citrus Fruit Under Semi-Commercial Conditions.

The efficacy of the combination of Candida saitoana with 0.2% glycolchitosan (the bioactive coating) as a biocontrol treatment of postharvest diseases of apple and citrus fruit was evaluated in tests with natural inoculations that simulated commercial packinghouse conditions. The growth of C. saitoana in apple wounds and on fruit surfaces was not affected by glycolchitosan. The bioactive coating was more effective in controlling decay of several cultivars of apples (Red Delicious, Rome, Golden Delicious, and Empire) than either C. saitoana or 0.2% glycolchitosan alone. Depending on the apple cultivar used, the bioactive coating was comparable or superior to thiabendazole in reducing decay. The bioactive coating was also superior to C. saitoana in controlling decay of oranges (cvs. Washington navel, Valencia, Pineapple, and Hamlin) and cv. Eureka lemons, and the control level was equivalent to that with imazalil. The bioactive coating and imazalil treatments offered consistent control of decay on Washington navel oranges and Eureka lemons in early and late seasons, while C. saitoana or 0.2% glycolchitosan were most effective on early-season fruit. The combination of C. saitoana with 0.2% glycolchitosan also reduced the incidence of stem-end rot of cv. Valencia oranges, but control was less effective than treatment with imazalil.

Quality and Disease Incidence of `Waimanalo Solo' Papaya following Forced-air Heat Treatments

Papaya fruit (Carica papaya L. cv. Waimanalo Solo), at color break ripeness, were either not heated (controls) or forced-air heated to center temperatures of 47.5, 48.5, or 49.5 °C, and held at these temperatures for 20, 60, 120, or 180 minutes. Following heat treatment, fruit were hydrocooled until reaching a center temperature of 30 °C, treated or not treated with prochloraz, allowed to ripen at 26 °C and then assessed for quality. Treatment at 48.5 °C or 49.5 °C for ≥60 minutes was associated with skin scalding. No significant scald was observed in other treatments or in the controls. Both control and heat-treated fruit had relatively high levels of decay. Heat treatment increased the incidence of body rots but did not affect the incidence of stem-end rots. Prochloraz treatment significantly reduced the incidence of decay. With the inclusion of a prochloraz treatment to control postharvest decay, fruit tolerated treatments of 47.5 °C for up to 120 minutes, and 48.5 °C and 49.5 °C for 20 minutes with no significant damage. Chemical name used: 1-N-propyl-N-(2-(2,4,6-(trichlorophenoxy)ethyl)-1H-imidazole-1-carboxamide (prochloraz).