Biological control of post-harvest anthracnose rot of loquat fruit by Pichia membranefaciens

Summary

The effect of Pichia membranefaciens on reducing post-harvest anthracnose rot caused by Colletotrichum acutatum in loquat fruit was investigated. Fruit were treated with different suspensions of P. membranefaciens before challenge with 1.0 10⁵ spores ml^–1 of C. acutatum, then incubated at 20°C for 6 d. The results showed that 1 10⁸ colony-forming units (CFU) ml^–1 of washed cell suspensions of the yeast provided better control of anthracnose rot than yeast in culture broth at the same concentration. Treatment with autoclaved cell cultures or culture filtrates did not prevent the incidence of disease. The concentration of a washed cell suspension of P. membranefaciens had a significant effect on the efficacy of controlling anthracnose rot in loquat fruit. At a concentration range from 1 10⁶ to 1 10⁹ CFU ml^–1, the higher the concentration of the antagonist, the lower the incidence of the disease and the smaller the diameter of the lesions. In inoculated wounds of loquat fruit, populations of P. membranefaciens increased approx. 34-fold after 6 d of incubation at 20°C.Washed cell suspensions of P. membranefaciens also significantly inhibited spore germination and germ-tube growth of C. acutatum, in vitro. These results suggest that P. membranefaciens has potential as a biocontrol agent to reduce post-harvest decay caused by C. acutatum in loquat fruit.     

Improving disease resistance in peach fruit during storage using benzo-(1,2,3)-thiodiazole-7-carbothioic acid S-methyl ester (BTH)

Summary

The compound benzo-(1, 2, 3)-thiodiazole-7-carbothioic acid S-methyl ester (BTH) effectively induces a systemic acquired resistance (SAR) response in plants and increases plant resistance to disease. To learn how BTH may affect post-harvest quality and disease resistance in peach, (Prunus persica L. cv. ‘Jiubao’) peach fruit were treated with 200 mg l^–1 BTH for 5 min immediately after harvest, then incubated for 60 h at 20°C, 85–95% RH. Sixty h after treatment, fruit were inoculated with spore suspensions of Penicillium expansum at 1.2 10⁴ CFU ml^–1. The incidence of disease and lesion areas on peach fruit were significantly reduced by BTH-treatment (P < 0.05). In addition, chitinase and -1,3-glucanase activities in peach fruit were significantly enhanced by BTH-treatment (P < 0.05). Moreover, the total levels of phenolic compounds and chlorogenic acid, and the lignin content of BTH-treated fruit were significant higher than in control fruit (P < 0.05). The effects of BTH on fruit quality were also analysed. Soluble solids content, soluble pectin, titratable acidity and ascorbic acid levels in peach fruit were not significantly affected by treatment with BTH. Our results suggest that the application of BTH may control post-harvest diseases in peach fruit during commercial production.     

梅奇酵母XY201菌株对采后冬枣黑斑病和青霉病的抑制效果

以采后冬枣(Zizyphus jujuba Mill.‘Dongzao’)为试材,研究了拮抗菌梅奇酵母XY201菌株(Metschnikowia zizyphicola strain XY201)在冬枣表面及伤口的定殖能力及对冬枣采后主要病害黑斑病(病原菌Alternaria alternate)和青霉病(病原菌Penicillium expansum)的抑制效果。结果表明,梅奇酵母菌XY201的悬浮液及与碳酸氢钠或施保克配合使用,均能在冬枣果面及伤口迅速生长。在25℃常温、0℃低温人工气调和0℃低温自发气调3种贮藏条件下,冬枣单果表面拮抗菌数分别达到2.2×106～2.6×106(接种XY201菌株4d后)、6.3×105～9.7×105(60d)和4.0×105～1.1×106CFU(75d),分别是接种时的34.3～57.0、15.2～25.5和4.8～20.3倍;冬枣果实每个伤口拮抗菌数分别为1.9×107～3.6×107(8d)、1.2×107～1.8×107(30d)和8.4×106～1.2×107CFU(60d),分别是接种时的34.2～364.3、16.9～144.3和11.2～90.0倍。XY201菌株(1×108CFU·mL-1)分别与2%碳酸氢钠和50μg·mL-1施保克组合,试验初期冬枣果面和伤口的定殖能力受到抑制,后期其抑制作用逐渐减弱。在人工气调(0℃,O2浓度为2%～8%,CO2浓度为0)条件下贮藏60d时,XY201菌株1×108CFU·mL-1的悬浮液可有效抑制采后冬枣黑斑病的发生,发病率降低了52.5%～59.2%,病斑直径减小了5.9%～10.7%;但对青霉病的抑制效果不明显,发病率仅减少了3.6%～6.1%,病斑直径减小了11.3%～19.0%。     

Changes in Ripening Behaviors of 1-MCP-Treated ‘d’Anjou' Pears After Storage

Abstract

1-Methylcyclopropene (1-MCP), an ethylene action inhibitor, was applied to ‘d’Anjou' pears (Pyrus communis L.) at 20°C between 2 and 5 days after harvest. Scald of ‘d’Anjou' pears was completely controlled by 1-MCP at a concentration between 0.05 and 0.3 µl l1 after a prolonged cold storage plus 7 days of exposure to an environment with or without 500 µl l1 ethylene at a temperature of 20°C or 25°C. 1-MCP inhibited the biosyntheses of α-farnesene and its oxidative products (conjugated trienes) and thus controlled scald. However, fruit treated with the above concentrations of 1-MCP did not ripen normally in an environment with or without ethylene. Ethylene production and fruit softening of 1-MCP-treated ‘d’Anjou' pears were inhibited during 7 and 15 days at 20°C. ‘d’Anjou' fruit treated with 0.01 and 0.02 µl l¹ 1-MCP ripened normally on day 7 at 20°C after 3 months of cold storage at ? 1°C, and ripened fruit did not develop any incidence of scald. Untreated fruit developed substantial scald. After 4 months of storage or longer, both untreated fruit and fruit treated with 0.01 and 0.02 µl l 1 1-MCP developed an unacceptable incidence of scald upon ripening. Thus, use of other scald control methods may be necessary in addition to treatment with a low dosage of 1-MCP to insure both normal ripening and scald control for d'Anjou pear fruit from the Mid-Columbia district.     

Differential propylene induced ethylene production in ‘Anjou’ pears during storage at chilling and non-chilling temperatures

Summary

‘Anjou’ pears were harvested from the Mid-Columbia Experiment Station, Hood River, Oregon, at 67 N firmness, stored at –1° or 20°C for 85 d and periodically tested for sensitivity to 0 or 500 µl l^?1 propylene for at least 14 d at 20°C. Climacteric ethylene of pears stored at 20°C remained at low levels and started rising on the 90th day. Pears chilled at –1°C required 70 d to ripen and produced climacteric ethylene immediately upon transfer to 20°C. The sensitivity of the fruit to exogenous propylene increased progressively with storage time at –1°C. However, the non-chilled fruit responded to propylene similarly to freshly harvested fruit during the first 55 d of storage, then similarly to –1°C-stored fruit up to 85 d. Anjou pear ripening events and the sensitivity of the fruit to exogenous propylene developed differently in storage at non-chilling temperature compared with chilling temperature.     

Induction of resistance to Penicillium digitatum and chilling injury in ‘Star Ruby’ grapefruit by a short hot-water rinse and brushing treatment

Summary

Postharvest heat treatments have been used for many years as alternatives to chemical control of fungal diseases and insect infestation of fruits and vegetables. In this study, the effects of a new hot-water brushing (HWB) treatment on the resistance of red grapefruit (C. paradisi cv. Star Ruby) to green mould decay caused by Penicillium digitatum (Pers.: Fr.) Sacc. and on the development of chilling injury (CI) symptoms during cold storage were examined. The HWB treatment comprises rinsing hot water on the fruits as they move along a belt of brush rollers. A twenty second HWB treatment at 59 or 62° reduced decay, after arti®cial inoculation of wounded fruit, by 52 or 70%, respectively, compared with control unwashed fruit, whereas rinsing and brushing the fruit with tap water (~20°) or with hot water at 53 or 56°, were ineffective. HWB treatments applied 1–3 d prior to inoculation were most effective in enhancing the disease resistance of fruit, but were much less effective when the fruit were inoculated on the same day or 7.d later. HWB treatments at 59 or 62° for 20.s also significantly reduced the CI index and the percentage of fruit displaying CI symptoms by 42 and 58%, respectively, after six weeks’ storage at 2° and an additional week at 20°. Furthermore, HWB treatments cleaned the fruit and improved its general appearance without causing any surface damage, and did not influence fruit weight loss, percentage of total soluble solids (TSS) in the juice, juice acidity or fruit colour.     

Maintenance of fresh boysenberry fruit quality with UV-C light and heat treatments combined with low storage temperature

Summary

Mature boysenberries (Rubus hybrid) were harvested, heat-treated (45°C for 1 or 3 h or 47°C for 1 h) or exposed to UV-C light (2.3, 4.6 or 9.2 kJ m^–2), and stored at 20°C for 2 d. Fruit treated with 9.2 kJ m^–2 or 45°C for 1 h showed less damaged drupelets per fruit and/or remained firmer than untreated fruit after 2 d. Those treatments were selected for further analyses. In another experiment, boysenberries were either UV-C (9.2 kJ m^–2) or heat-treated (45°C for 1 h) and stored either at 20°C for 1 d or at 0°C for 4 d before transfer to 20°C for 1 d. Both UV-C and heat treatments reduced softening and/or fruit damage. Treated fruit had lower respiration rates and anthocyanin leakage than control fruit suggesting greater tissue integrity. Titratable acidity, pH, total sugar content and antioxidant activity in treated fruit showed fewer changes than in control fruit when stored at 20°C for 1 d. Results suggest that heat or UV-C treatment, alone or in combination with refrigerated storage, may be a useful non-chemical mean of maintaining boysenberry fruit quality and extending postharvest life.     

苹果采后热空气处理对表面伤口愈合的影响

 以‘嘎拉’和‘红富士’苹果为对象，研究热空气处理（38°C 4d）对苹果伤口愈合的影响。扫描电镜观察发现，38°C 4d热空气处理能使苹果表面的果蜡融化，从而封堵微小伤口，并使真菌菌丝体胶囊化而失活，阻止病原菌的入侵。与人工刺伤后立即接种病原菌相比较，苹果伤口在38°C或者20°C下处理 4d后再接种病原菌能显著提高伤口的抵抗能力，降低伤口处病害的发生和发展。与20°C处理相比，38°C热处理有利于‘红富士’苹果人工刺伤伤口的愈合，但是不利于‘嘎拉’的伤口愈合。     

Effects of nitric oxide fumigation on post-harvest core browning in ‘Yali’ pear (Pyrus bretschneideri Rehd.) during cold storage

Summary

Core browning often occurs as a physiological disorder in ‘Yali’ pear (Pyrus bretschneideri Rehd.) and results in a high losses during storage. In this study, the effects of fumigation with nitric oxide (NO) gas on the incidence of core browning in ‘Yali’ pears during cold storage were investigated. ‘Yali’ pear fruit were treated with 0, 10, 20, or 30 µl l^–1 NO at 25º ± 2ºC for 3 h under anaerobic conditions, then stored at 0º ± 1ºC under normal air for up to 120 d. The data showed that fumigation with 20 µl l^–1 NO was most effective at suppressing core browning. Thereafter, treatment with 20 µl l^–1 NO was used for comparisons with untreated control fruit in experiments to measure changes in total phenolics contents, polyphenol oxidase (PPO) activities, and the contents of glutathione (GSH), ascorbic acid (AsA), and NO in fruit core tissue during storage. The results showed that NO-fumigated fruit had lower PPO activity, but higher GSH and AsA contents in their core tissue compared with untreated control fruit. NO fumigation also maintained higher endogenous NO levels in core tissue after 60 d in storage, while the total phenolics contents of fruit remained at lower levels until day-100 of storage. These results indicate that the inhibitory effect of fumigation with

20 µl l^–1 NO on core browning was associated with its effects on reducing PPO activity and total phenolics contents, while maintaining the contents of GSH and AsA in core tissue of ‘Yali’ pear during cold storage.     

Effect of gibberellic acid and Vapor Gard on ripening,amylase and peroxidase activities and quality of mango fruits during storage

Post harvest application of gibberellic acid at 200 mg 1^?1, Vapor Gard (di-l-p-menthene) at 2.5% and their combination was studied on ‘Mallika’ mangoes (Mangifera indica L.) stored at ambient temperature (37 ± 2° maximum and 34 ± 2°C minimum) and at 15°C. Significant delay in the ripening of mango fruits was observed when gibberellic acid was applied with or without Vapor Gard. Gibberellic acid significantly retarded the degradation of ascorbic acid and chlorophyll in the peel, and reduced a-amylase and peroxidase activities during storage. Loss of weight decreased following treatment with Vapor Gard either alone or with gibberellic acid during storage at both ambient temperature and at 15°C. A pronounced retardation of ripening was observed when fruits were treated with gibberellic acid and Vapor Gard and stored at 15°C. The study thus suggests that mango fruits can be successfully stored for 20 d by application of gibberellic acid (200 mg 1^?1) in combination with Vapor Gard (2.5%) and stored at 15°C.     

Re-initiating softening ability of 1-methylcyclopropene-treated ‘Bartlett’ and ‘d’Anjou’ pears after regular air or controlled atmosphere storage

Summary

‘Bartlett’ and ‘d’Anjou’ pears treated with 300 nl l^–1 1-methylcyclopropene (1-MCP) did not soften to eating quality within 7 d, a desirable ripening period. A pre-conditioning method was evaluated as a means to re-initiate the softening ability of pears prior to marketing. Fruit were treated with 1-MCP and stored at –1°C in regular air, or in a controlled atmosphere for 2 – 9 months. After storage, fruit were pre-conditioned with nine temperature (10°, 15° or 20°C) and time (5, 10 or 20 d) combinations. Pre-conditioned fruit were then assessed for ripening ability following storage for 14 d at 20°C. The ripening ability of 1-MCP-treated ‘Bartlett’ fruit recovered in response to many pre-conditioning combinations of 10° – 20°C for 10 – 20 d, as indicated by a decrease in flesh firmness to 27 N or lower. The requirements for pre-conditioning regimes are storage atmosphere- and time-dependent. For ‘d’Anjou’ pears, no pre-conditioning combination resulted in re-initiating the ripening of fruit treated with 300 nl l^–1 1-MCP. However, when the 1-MCP dose was 50 nl l^–1, ‘d’Anjou’ pears ripened over an extended shelf-period with a substantial decrease in superficial scald. The results indicate that treatment with 1-MCP at approx. 50 nl l^–1, combined with a pre-conditioning prior to marketing, is a potential means to control scald in ‘d’Anjou’ fruit. Re-initiation of ripening occurred concomitantly with a substantial increase in ethylene production. The control of superficial scald by 1-MCP in ‘d’Anjou’ pears was due to the inhibition of the biosynthesis of -farnesene and conjugated trienes.     

Antioxidant Bioactive Compounds and Spoilage Microorganisms of Wax Apple (Syzygium samarangense) during Room Temperature Storage

Postharvest deterioration of wax apple leads to unacceptable appearances, physical and quality losses that raise serious concerns commercially. Bioactive compounds of wax apple and spoilage microorganisms were studied at room temperature storage (23 ± 1 °C). Antioxidant activity and total phenolic content increased up to a maximum of 1.56 mg AAE/100 g and 88.37 mg GAE/100 g, while prolonged storage resulted in 70.0% and 33.6% loss, respectively. Further, 80% loss in vitamin C content was observed from an initial value of 21.63 mg AAE/100 g during storage. Bacterial isolates of Enterobacter sakazakii, Klebsiella pneumoniae, Klebsiella planticola, Pantoea agglomerans, Chromobacterium violaceum, and Streptomyces roseochromogenus with microbial load of 1.19 * 10⁸ CFU/g fresh weight, and fungal isolates of Penicillium purpurogenum, Mucor hiemalis, Aspergillus niger, Aspergillus fumigatus, and Candida tropicalis with a total load of 5.64 * 10⁷ CFU/g fresh weight were identified as spoilage organisms. Bacterial isolates of Klebsiella pneumoniae was the most prevalent at 47.78%, occurring 21 times, while Penicillium purpurogenum was the most prevalent fungi, occurring 5 times at 38.46%. Results have significant implications on measures to preserve quality of wax apples during storage by adoption of advanced postharvest handling and processing approaches.     

Effects of post-harvest storage conditions on the levels of glucosinolates in broccoli sprouts (Brassica oleracea var. italica) grown under different temperature regimes

Summary

Broccoli sprouts have been recognised as a rich source of glucosinolates, particularly 4-methylsulphinylbutyl glucosinolate, the precursor of the potent anti-cancer compound, sulphoraphane. Previous results have shown that temperature can significantly affect the levels of glucosinolates. In this study, we showed how sprout age and storage temperature affected glucosinolate levels in broccoli sprouts grown under different temperature regimes. Experiments were conducted in growth cabinets with day/night temperature regimes of 30°/15°C, 22°/15°C and 18°/12°C. At 9, 10 and 11 d after sowing in the first temperature regime, 10, 11 and 12 d in the second, and 12, 13 and 14 in the third, sprouts were submitted to 4°C or 20°C to simulate refrigerated and room temperature storage. Sampling was done after 1 d or 2 d of exposure to these conditions. The results showed that total glucosinolate levels and the potential health effects of broccoli sprouts depended on the growth temperature regime (P < 0.05), the age of the sprouts (P < 0.001), and the storage conditions (P < 0.01). The highest total glucosinolate levels (65.7 µmoles g^–1 dry weight) were obtained under the 30º/15°C temperature regime for the youngest sprouts (harvested 9 d after emergence), after being submitted to a storage temperature of 4°C for 24 h. However, these levels were much lower than in 3-d-old sprouts. Consuming old sprouts provides less health-protective effects due to reduced levels of glucosinolates.     

Phenol induced browning and establishment of shoot-tip expiants of 'Fuji' apple and 'Jinhua' pear cultured in vitro

SUMMARY

Several factors influencing phenol induced browning and establishment of apple (Malus pumila Mill. cv. Fuji) and pear (Pyrus bretschneideri Rend., cv. Jinhua) were investigated by using shoot-tip expiants cultured in vitro. Expiants of 'Fuji' apple and 'Jinhua' pear collected from November to February produced low browning percentages. Browning percentages increased rapidly as the stock plants entered the growing season, reached a maximum during April and August and then decreased. Dark treatment of the stock plants reduced browning. Lowest incidence of browning and the highest surviving percentages of both 'Fuji' apple and 'Jinhua' pear were obtained after four weeks of dark treatment. However, bud-break percentage, fresh weight and the number of new leaves of the surviving expiants decreased with increase in the length of dark treatment. When the dark treatment was used during the first phase of culture initiation, 5°C was better than 24°C for reducing browning and improving establishment of the expiants. At 5°C, 6 d of dark treatment for 'Fuji' apple and 8 d for 'Jinhua' pear produced the least browning and the highest surviving percentages. However, bud break percentages, fresh weights and numbers of new leaves decreased as the length of the dark treatment increased. Addition of 2.5 g l"1 activated charcoal to the initiation medium favoured establishment of 'Jinhua' pear expiants and 100/150 mg 1"' ascorbic/citric acid were effective with 'Fuji' apple.     

Effects of culture conditions on in vitro bulblet induction in the medicinal plant Amana edulis (Miq.) Honda

Amana edulis (Miq.) Honda is an important medicinal plant with a variety of anti-cancer properties, and it is of great importance to improve its reproductive rate through micropropagation technology to meet increasing demand. In the present study, in order to establish a rapid in vitro bulblet propagation protocol for A. edulis, an L₁₆ (4⁵) orthogonal design was used to investigate the effects of sucrose, 6-benzyladenine (6-BA), α-naphthaleneacetic acid (NAA), and macro-elements on bulblet induction. The results show that the sucrose concentration was the crucial factor for A. edulis bulblet initiation, followed by 6-BA and macro-elements, while NAA had the weakest effect. The optimal medium for in vitro bulblet induction was Murashige and Skoog medium supplemented with 0.1 mg·L^?1 6-BA, 0.01 mg·L^?1 NAA, and 100 g·L^?1 or 80 g·L^?1 sucrose (pH 5.8), in which A. edulis shoot clusters (without roots) were cultured at 5(±2)°C for 35 d or 60 d and then incubated at 23(±2)°C for 90 d. The entire cultivation process occurred in the dark. The present study demonstrates that this protocol can be used for the propagation of A. edulis.     

Chilling-induced changes in the apoplastic solution of tomato pericarp

Summary

Low-temperature storage of chilling-sensitive commodities affects membrane function and is likely to induce changes in the apoplastic environment. Mature-green tomato (Solanum lycopersicum L.) fruit were stored at 5°C for 14 d, then transferred to 15°C for an additional 6 d. Low-temperature storage induced acidification and a slight increase in the osmolality of pressure-extracted tomato apoplastic fluid. The apoplastic levels of cations such as K⁺, Ca²⁺, and Mg²⁺ remained constant during low-temperature storage, but decreased upon transfer of fruit to 15°C following low-temperature storage. These changes in apoplastic cations paralleled the changes observed in electrolyte leakage. Apoplastic pH and mineral concentrations were altered in chill-injured fruit, but the small changes observed in osmolality provide evidence against severe membrane dysfunction in chill-injured fruit.     

Vascular blockage in cut roses in a suspension of Pseudomonas fluorescens

Summary

To analyse quantitatively the relationships between cut rose (Rosa hybrida L. ‘Pascha’) vase-life, the onset of cavitation, plant water potential, and bacterial concentrations in the vase water, rose stems were placed in water containing different concentrations of Pseudomonas fluorescens 2892 tet^r rif ^r. There was a significant correlation (P = 0.0009) between cut rose vase-life and the concentration of bacteria in the vase water. As the number of bacteria in the vase water increased, the rate of senescence also increased. The water potential for roses in the bacterial suspension (at 8.50 log₁₀ CFU ml^–1) proceeded to drop constantly after 5.17 h in the vase solution, with the water potential falling to as low as -2.35 MPa by the end of the experiment (at 117 h). In contrast, the water potential of roses in deionised water dropped from -0.419 MPa at 5.17 h, to only –0.663 MPa after 117 h. When roses were stood in a bacterial suspension (at 8.5 log₁₀ CFU ml^–1) for 30 h, 63.8% of the total cumulative cavitation events were seen, while roses stood in deionised water exhibited only 26.8% of the total cavitation events. Uptake of acid fuchsin and the movement of tagged P. fluorescens 2892 in the xylem indicated that bacteria did not travel beyond the open-ended xylem vessels and were generally restricted to the first 50 mm from the cut end of the stem.     

Sensitivity of Geraldton waxflower to ethylene-induced flower abscission is reduced at low temperature

Summary

Exposure to ethylene gas elicits flower abscission from cut stems of Geraldton waxflower (Chamelaucium uncinatum Schauer). Ethylene response rates in plants are mediated by temperature. At 20°C, flower abscission from waxflower ‘Purple Pride’ occurred upon 12 h exposure to 1 µ11^–1 ethylene. This ethylene treatment did not cause flower abscission at either 10 or 2°C. Moreover, flowers held at 2°C were insensitive to 48 h exposure to 1, 10 and 100 µ11^–1 ethylene. However, increasing the duration of treatment with 1 µ11^–1 ethylene at 10 and 2°C to 48 and 144 h, respectively, induced flower abscission. When flowers were held at 20°C in air without exogenous ethylene following continuous exposure to 1 µ11^–1 ethylene at 2°C, the duration required to elicit flower abscission was reduced from 144 to 72 h. Collectively, these responses show that maintaining harvested waxflower at low temperature (e.g. 2°C) is an effective means to minimise ethylene-mediated flower abscission.     

Effect of storage temperature on ripening and quality of custard apple (Annona squamosa L.) fruits

Summary

The effect of storage temperature on ripening, shelf life and chemical composition of custard apple (Annona squamosa L.) fruits stored at 10,15,20 and 25°C was studied. The safe range of storage temperature was found to be between 15 and 20°C, with maximum shelf life at 15°C. The ripening of fruits was observed on days 4, 6 and 9 of storage at 25,20, and 15°C respectively. The colour of the pulp, texture, taste and flavour of ripe fruits held at 25 and 20°C were superior followed by fruits stored at 15°C. At 10°C, the fruits became hard with surface blackening, messy pulp and less sweetness. The major changes during ripening were a continuous decrease in fruit firmness and starch content and a continuous increase in TSS and sugars, the changes being more rapid at 25 and 20°C than at 15 and 10°C. The acidity and ascorbic acid contents increased slightly during the initial stages of ripening followed by a decline, in the fruits stored at different temperatures. Custard apple fruits stored at 25 and 20^CC had a clear climacteric peak whereas those stored at 15 and 10°C did not show any distinct rise in respiration rate. Ethylene peak (2.40 µl kg^–1 h^–1) coincided with the respiratory climacteric at 25^CC storage, corresponding with the peaks in TSS, sugars, ascorbic acid and acidity.     

Floral induction in tropical fruit trees: Effects of temperature and water supply

Summary

Floral induction in tropical trees generally follows a check in vegetative growth. However, it is not easy to identify the environmental factors involved in flowering, which normally occurs during the dry season when temperatures are also often lower. The separate and combined effects of temperature and water supply on floral induction were investigated in ‘Hass’ avocado (Persea americana), ‘Lisbon’ lemon (Citrus limon). ‘Wai Chee’ litchi (Litchi chinensis) and ‘Sensation’ mango (Mangifera indica). Low temperatures (15°/10°C or 15°/10°C and 20°/15°C compared with 30°/25°C and 25°/20°C) generally decreased vegetative growth and induced flowering in well-watered avocado, litchi and mango. A pre-dawn leaf water potential (ψ_L) of ?1.7 to ?3.5 MPa compared with ?0.4 to ?0.7 MPa in control avocado and litchi, and a pre-dawn relative water content (R.W.C.) of 90-93% compared with 97% or above in control mango plants also reduced or eliminated vegetative growth, but did not induce flowering. Low temperatures (15°/10°C compared with 20°/5°C, 25°/20°C or 30°/25°C) and water stress (pre-dawn ψ_L of ?2.0 to ?3.5 MPa compared with ?0.7 to ?0.8 MPa in controls) reduced or eliminated vegetative growth in lemon. In contrast to the response in avocado, litchi and mango, flowering in lemon was very weak in the absence of water stress at 15°/10°C or outdoors in Brisbane in subtropical Australia (Lat. 28°S), and was greatest after a period of water stress. The number of flowers increased with the severity and duration of water stress (two, four or eight weeks) and was generally greater after constant rather than with cyclic water stress. In lemon and litchi, net photosynthesis declined with increasing water stress reaching zero with a midday ψ_L of ?3.5 to ?4.0 MPa. This decline in carbon assimilation appeared to be almost entirely due to stomatal closure. Despite the reduction in midday CO₂ assimilation, starch concentration increased during water stress, especially in the branches, trunk and roots of lemon. Leaf starch was uniformly low. The number of flowers per tree in lemon was strongly correlated with starch in the branches (r²=77%, P<0.01) and roots (r²=74%, P<0.001). In litchi, starch was lower than in lemon roots and was not related to flowering.

In separate experiments to test the interaction between temperature and water supply, low day/night temperatures (23°/18° and 18°/15°C compared with 29°/25°C) reduced vegetative growth and induced flowering in avocado, litchi and mango. None of these species flowered at 29°/25°C or as a result of water stress (ψ_L of ?1.5 MPa compared with ?0.3 MPa for avocado and ?2.0 MPa compared with ?0.5 MPa for litchi, and R.W.C, of 90-93% compared with 95-96% in mango). In contrast, in lemon, flowering was very weak (<10 flowers per tree) in the absence of water stress (pre-dawn ψ_L of ?2.0 MPa compared with ?0.5 MPa) and was only heavy (>35 flowers per tree) after stressed trees were rewatered. There were slightly more flowers at 18°/15°C than at 23°/18° and 29°/25°C in control plants, but no effect of temperature in stressed plants. Starch concentration in the roots of avocado, lemon, litchi and mango was generally higher at 18°/15°C and 23°/18°C than at 29°/25°C. Water stress increased the starch concentration in the roots of lemon and litchi and decreased it in avocado. There was no effect in mango. There was a weak relation (r²=57%, P<0.05) between the number of flowers per tree in lemon and the concentration of starch in the roots. In contrast, there was no significant relationship between flowering and starch levels under the various temperature and water regimes in the other species. In another experiment, only vegetative growth in litchi and mango occurred at 30°/25°C and only flowering at 15°/10°C. Six weeks of water stress (pre-dawn ψ_L of ?2.5 MPa compared with ?1.0 MPa or higher in litchi, and R.W.C, of 90-93% compared with 95% or higher in mango) in a heated glasshouse (30°C days/20°C night minimum) before these temperature treatments did not induce flowering.

Temperatures below 25°C for avocado and below 20°C for litchi and mango are essential for flowering and cannot be replaced by water stress. The control of flowering in lemon over the range of day temperatures from 18°C to 30°C differed from that of the other species in being mainly determined by water stress. Flowering was generally weak in well-watered plants even with days at 18°C. Starch did not appear to control flowering.