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.     

A combination of gum arabic and chitosan can control anthracnose caused by Colletotrichum musae and enhance the shelf-life of banana fruit

Summary

Anthracnose, caused by Colletotrichum musae, is the major disease affecting the quality of banana fruit during storage. To control banana anthracnose, the combined effects of coatings with gum arabic [GA; at 5, 10, 15 or 20% (w/v)] and 0.75% (w/v) chitosan (CH) were investigated and compared to untreated controls. In vitro results showed significant (P < 0.05) inhibition of mycelial growth and conidial germination of C. musae in all combined treatments compared to the untreated controls after 7 d of incubation at room temperature (25°C). However, potato dextrose agar (PDA) plates amended with 10% (w/v) GA gave the most promising results among all test treatments in suppressing mycelial growth (86%) and inhibiting conidial germination (80%), while no effective inhibition of conidial germination was observed in the controls. In vivo results confirmed that 10% (w/v) GA was the optimum concentration to control fruit decay (70%), while showing efficacy on the reduction of growth of C. musae on artificially inoculated banana fruit. The combined coatings of GA + CH also significantly delayed ripening in terms of weight loss, fruit firmness, soluble solids content, and titratable acidity. These results support the possibility of using 10% (w/v) GA combined with 0.75% (w/v) CH as an alternative strategy to control post-harvest anthracnose disease in banana fruit.     

Control of black spot disease caused by Alternaria alternata on jujube (Ziziphus jujuba Mill. cv. Dongzao) using HarpinXoo protein

Summary

Currently, no adequate control measures exist for the fungal disease, black spot (Alternaria alternata (Fr.) Keissler) on ‘Dongzao’ jujube (Ziziphus jujuba Mill. cv. Dongzao). Black spot is an important factor limiting jujube fruit yield under certain conditions. In this study, three concentrations (10, 20, or 30 µg ml^–1) of the Harpin_Xoo protein, or water (negative control), were sprayed onto ‘Dongzao’ jujube trees to control black spot disease. Following Harpin_Xoo protein treatment, its effects on the control of black spot disease were determined, and the levels of a defence-related substance [i.e., salicylic acid (SA)], and the activities of peroxidase (POD), polyphenol oxidase (PPO), and phenylalanine ammonia lyase (PAL) were measured. The incidence of black spot disease was significantly decreased, compared with water-treated control, fruit by ≤ 88.4%. After 2 d, SA levels, and POD, PPO, and PAL activities in Harpin_Xoo-treated fruit were clearly higher than those in control fruit. After fruit had been stored for 45 d at 0ºC, SA levels, and POD and PPO activities showed no differences between the Harpin_Xoo treatments and the controls, but PAL activities in Harpin_Xoo-treated fruit were lower than those in the controls. The most appropriate concentration of Harpin_Xoo protein to control black spot disease was 20 µg a.i. ml^–1. These results suggest that the Harpin_Xoo protein induced systemic acquired resistance in ‘Dongzao’ jujube trees and may offer a worthwhile strategy for disease control.     

Pre-harvest application of 2, 6-dichloroisonicotinic acid, -aminobutyric acid or benzothiadiazole to control post-harvest storage diseases of melons by inducing systemic acquired resistance (SAR)

Summary

Field-grown rockmelon plants were treated with -aminobutyric acid (BABA), 2,6-dichloroisonicotinic acid (INA), benzothiadiazole (BTH) or water during fruit development and evaluated for increased resistance against plant diseases or post-harvest pathogens. One experiment was conducted at Camden, NSW, Australia (INA, BABA or water). Two experiments were at Griffith, NSW, Australia (INA, BTH or water). Growing plants and harvested fruits were assessed for disease symptoms from natural infections and assayed for the accumulation of chitinase and peroxidase, two major pathogenesis-related (PR) proteins induced as a result of systemic acquired resistance (SAR). Harvested fruit from both BTH- or INA-treated plants showed a significant (P < 0.05) reduction in the severity and incidence of post-harvest storage diseases mainly caused by Fusarium, Alternaria and Rhizopus. However, there were no differences in disease severity and the incidence of rots between using four fortnightly foliar sprays of INA or BTH during flowering and fruit development, or a single spray of BTH, 2 weeks before harvest. Each approach showed an equivalent reduction in storage diseases. Plants treated with BABA showed less resistance against powdery mildew in the field and storage rots from natural inoculum, and lower increases in chitinase and peroxidase activities than those treated with INA. In all trials, an additional post-harvest dip with guazatine [0.05% (w/v)] gave a substantial reduction in melon storage rots. Pre-harvest application of INA or BTH reduced the occurrence of powdery mildew and downy mildew on the leaves. Over the three field-experiments, INA had a small phytotoxic effect causing lesion-like symptoms on leaves and affected plant growth, but not yield, at Camden, when applied during flowering and 2 weeks after flowering. However, INA did not produce any phytotoxic effects in the two experiments at Griffith when applied serially, four times to plants after flowering.     

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.     

鲜枣采后生理及贮藏研究进展

枣（ZizyphusjujubaMill．）原产中国。鲜枣富含维生素C,营养价值高,果实一经变软,维生素C几乎全部被氧化。鲜枣果实具有独特的采后生理特点,贮藏保鲜难度较大。综述了80年代以来国内外在鲜枣采后生理包括果实形态、呼吸类型、内源激素、软化机理及营养成分变化等方面的研究进展,介绍了影响鲜枣贮藏寿命的外界因子及内在因素。     

Influence of a pre-harvest reflective orchard mulching film on lipid peroxidation and anti-oxidant activity in apple fruit during post-harvest storage

Summary

Studies have shown that applying a reflective film to the floor of an orchard enhances fruit colouration. Here we assessed whether this practice also prolonged the post-harvest storage life of apple (Malus domestica Borkh cv. Fuji and Malus prunifolia [Willd.]) fruit. Strips of reflective mulching film (RMF) were placed beneath the apple trees and RMF-treated fruit were compared with those from untreated control (CK) trees. Enzymes involved in reducing lipid peroxidation such as superoxide dismutase (SOD) and catalase (CAT) are associated with delaying fruit senescence. Their activities, as well as malondialdehyde (MDA) concentrations, were quantified as indicators of physiological changes related to lipid peroxidation and membrane damage in the peel and flesh of RMF-treated or control apple fruit during 50 d of post-harvest storage at 4ºC. SOD activities increased in the peel and flesh from RMF-treated fruit during the first 40 d post-harvest, but declined significantly during the final 10 d of storage. RMF treatment resulted in increases in CAT activities of 5 – 14% and 16 – 29% in the peel and flesh of RMF-treated apples, respectively, compared with untreated CK fruit. Conversely, MDA concentrations were 7 – 23% and 14 – 30% lower in the peel and flesh, respectively, of RMF-treated fruit than in CK fruit over the 50 d storage period. Similarly, RMF treatment resulted in reductions of 7 – 20% and 3 – 10% in saturated fatty acid (SFA) concentrations in the peel and flesh, respectively, compared to CK fruit, while the corresponding polyunsaturated fatty acid (PUFA) concentrations increased by 2 – 10% and 3 – 7%. In conclusion, the use of RMF in apple orchards appears to be an effective technique to delay post-harvest senescence in apple fruit.     

不同气体组分对冬枣采后生理及贮藏效果的影响

采用冬枣作试材,对在(-1.5±0.5)℃,相对湿度为90%～95%下采用普通冷藏和(1)2%～3%O2,0～0.5%CO2;(2)5%～6%O2,0～0.5%CO2;(3)8%～9%O2,0～0.5%CO2条件下贮藏的冬枣进行了比较研究。结果表明,从贮藏的45d始,普通冷藏的枣果呼吸强度显著高于气调贮藏的,但3种气体组分之间的呼吸强度均未达到显著差异水平。贮藏时间在30d前,各处理枣果果肉乙醇含量无显著差异,但普通冷藏冬枣的乙醛含量显著高于3种不同气体成分贮藏的冬枣。贮藏至60d时的乙醛含量和贮藏90d时的乙醇含量,均以2%～3%O2,0～0.5%CO2条件下最高,显著高于其它3个处理,在该气体成分下,冬枣表皮转红速度最慢,但是好果率却最低,而在5%～6%O2﹢0～5%CO2的气调指标下贮藏90d时,好果率达87%。     

Slowing the deterioration of mango fruit during cold storage by pre-storage application of oxalic acid

Summary

The effects of pre-storage application of oxalic acid (OA) on the incidence of decay and ripening in mango fruit, and its physiological effects on the peel and flesh of mango were investigated after mango fruit (Mangifera indica L. cv. Zill) were dipped in 5 mM OA for 10 min at 25ºC then stored at 14º ± 1ºC for 5 weeks. In addition, spore germination and mycelium growth of Colletotrichum gloeosporioides Penz. on potato dextrose agar (PDA) media containing different concentrations of OA were measured. Application of OA decreased the incidence of decay and delayed the ripening process in mango fruit during cold storage. However, there was no reduction in fruit quality, as judged by the soluble solids content (SSC) and titratable acidity (TA) of fruit ripened at 25ºC for 3 d, following 3 weeks of cold storage. Oxalic acid-treatment resulted in decreased lipoxygenase (LOX) activity and increased superoxide dismutase (SOD) activity in the peel, and increased ascorbate peroxidase (APX) activity in both the peel and the flesh, coincident with a decrease in reactive oxygen species (ROS).At or above 5 mM, OA with unaltered (natural) pH or after neutralisation, also inhibited C. gloeosporioides development in vitro. It is suggested that the physiological effects of OA, in decreasing LOX activity and enhancing defense against oxidation damage, contributed to delaying the ripening process in mango fruit during cold storage. Thus, pre-storage application of OA could be a promising method to suppress post-harvest deterioration and extend the shelf-life of refrigerated mango fruit, possibly due to a combination of its physiological effect in delaying the ripening process, coupled with an inhibition of the development of pathogens such as C. gloeosporioides.     

Oxylipin affects ethylene metabolism and ethylene receptor gene expression levels in peach fruit (Prunus persica L. Batsch)

The effects of two oxylipins – jasmonic acid (JA) and 9, 10-ketol-octadecadienoic acid (KODA) – on ethylene metabolism and ethylene receptor genes were examined in peach fruit (Prunus persica L.) harvested at 88 days after full bloom (DAFB), in the pre-climacteric stage, and at 102 DAFB, at the beginning of the climacteric stage. Immediate post-harvest applications of either n-propyl dihydrojasmonate (PDJ) (a JA analog) or KODA stimulated ethylene production and 1-aminocyclopropane-1-carboxylate (ACC) concentrations in fruit that were harvested at 88 and 102 DAFB. KODA application significantly increased levels of ACC oxidase (PpACO1) expression at 5 and 8 days after treatment (DAT) in 88-DAFB-harvested fruit, and at 1 DAT in 102-DAFB-harvested fruit. Expression levels of ethylene response factors (PpERS1) were not influenced by either PDJ or KODA applications at 88 or 102 DAFB. In contrast, levels of ethylene-receptor-coding genes (PpETR1) expression in 88-DAFB KODA-treated fruit increased at 8 and 14 DAT. Expression levels of constitutive triple response (PpCTR1) in the untreated control fruit decreased with DAT in both 88- and 102-DAFB-harvested fruit.

These results suggest that certain oxylipins may promote ethylene production in peach fruit, and that PpETR1 and PpCTR1 may be associated with the autocatalytic system of ethylene production.     

Effects of Artificial Pollination Using Pollen Suspension Spray on Nut and Kernel Quality of Pistachio Cultivar Owhadi

Yield and nut quality in pistachio are highly dependent on cultural practices especially pollination. This study was conducted to investigate the effects of pollen suspension spray containing 0.01% and 0.02% boric acid combined with 1% (w/v) pollen on nut and kernel quality of pistachio (Pistacia vera L. cv. Owhadi). The experiment was carried out as RCBD with three replications over 2011–12 period. The results showed that application of medium containing agar (A) and 0.01% boric acid (B1) combined with 1% (w/v) pollen decreased fruit set in both years compared to control whereas nut splitting was increased during 2012. Pollen suspension sprays unaffected nut and kernel dimensions in both years but increased kernel proteins and decreased oil during 2011. According to this study, it could be postulated that artificial pollination in pistachio using pollen suspension spray is possible.     

Response of kiwifruit (Actinidia deliciosa cv. Allison) to post-harvest treatment with 1-methylcyclopropene

Summary

Experiments were conducted to observe the effect of different concentrations of 1-methylcyclopropene (1-MCP) on the post-harvest life and quality of ‘Allison’ kiwifruit (Actinidia deliciosa). Fruit were treated with 1-MCP at 0.5 µl l^–1, 1.0 µl l^–1, or 2.0 µl l^–1, un-treated fruit served as controls. Each 1-MCP treatment was applied for 24 h at 20°C. After treatment, fruit were transferred to ambient temperature storage (22º ± 4ºC; 65 – 70% relative humidity) for 18 d, during which time observations on various physical, physiological, and biochemical parameters were recorded at 3 d intervals. Our results indicated that 2.0 µl l^–1 1-MCP was the most effective treatment to delay softening and ripening in ‘Allison’ kiwifruit, as such fruit showed the lowest mean weight loss (9.8 ± 0.2%), the highest mean fruit firmness value (32.7 ± 0.2 N), and began to ripen only after 12 d in storage, whereas untreated fruit started ripening on day-6 of storage. The activities of fruit softening enzymes such as polygalacturonase (PG; 58.5 ± 0.3 µg galacturonic acid g^–1 FW h^–1), and lipoxygenase (LOX; 3.96 ± 1.3 µmoles linoleic acid oxidised min^–1 g^–1 FW h^–1) were lower, and total phenolics (TP) contents (24.3 ± 0.3 mg 100 g^–1) and anti-oxidant (AOX) activities (12.5 ± 0.03 µmol Trolox g^–1 FW h^–1) were higher in 1-MCP-treated fruit than in untreated fruit (PG, 98.3 ± 0.5 µg galacturonic acid g^–1 FW h^–1; LOX, 4.39 ± 1.0 µmoles min^–1 g^–1 FW h^–1; TP, 5.3 ± 0.6 mg 100 g^–1; AOX, 4.7 ± 0.02 µmol Trolox g^–1 FW h^–1, respectively). In addition, 1-MCP-treated fruit exhibited lower rates of respiration (48.3 ± 0.4 ml CO₂ kg^–1 h^–1) and ethylene production (30.2 ± 0.02 µl kg^–1 FW h^–1) than untreated fruit (58.9 ± 0.6 ml CO₂ kg^–1 h^–1; 38.7 ± 0.04 µl kg^–1 FW h^–1, respectively). Similarly, 1-MCP-treated fruit had higher titratable acidity (TA; 1.33 ± 0.3%) and ascorbic acid (AA) contents (115.9 ± 2.6 mg 100 g^–1 pulp) and lower soluble solids contents (SSC; 8.33º ± 0.2º Brix) than untreated kiwifruit (TA, 1.0 ± 0.2 %; AA, 105.3 ± 2.2 mg 100 g^–1 pulp; SSC, 13.7º ± 0.3º Brix, respectively). Thus, 2.0 µl l^–1 1-MCP can be used for the post-harvest treatment of ‘Allison’ kiwifruit to enhance its shelf-life and marketability by approx. 6 d.     

Morphology and anatomy of the burl disorder of mango (Mangifera indica L.) in India

Summary

Burl, typically manifest as a swelling of the trunk and lower branches, is a relatively unknown disorder of mango (Mangifera indica L.). We studied the incidence of the disorder in trees of each of three mango cultivars in India, and its effect on fruit yields over 2 years. Information was also collected on the relationship between the growth of the burl and the age of the trees, together with details of the anatomy of the affected tissues. ‘Langra’ had the highest incidence of the disorder (80.3% of 24 studied trees affected) and the largest burl (31.8 cm diameter), followed by ‘Chausa’ (17.5%; 16.4 cm), then ‘Gulab Jaman’(7.5%; 4.0 cm). Burl significantly reduced fruit yields in ‘Langra’ (121 kg tree^–1 in affected trees vs. 162 kg tree^–1 in normal trees), but not in ‘Chausa’ (110 vs. 129 kg tree^–1) or ‘Gulab Jaman’ (100 vs. 98 kg tree^–1). The sizes of the burls increased as the ages of the trees increased from 15 to 55 years, especially in ‘Langra’ and ‘Chausa’. No pathogens or insects were found to be associated with the affected tissues. The woody tissues in the burl lacked orientation and were not specifically aligned in a transverse, radial, or tangential direction. Further studies are warranted to determine the cause of this disorder and how it can affect fruit yields.     

Effect of growing medium water content on the biological control of root pathogens in a closed soilless system

Summary

The water content of the growing medium and its interaction with a biocontrol agent was studied in a closed soilless culture system in order to identify factors that could increase the efficiency and decrease the variability of biocontrol agents. Pumice was chosen as the growing medium because of its high water-holding capacity and in view of the high water content required for the growth of the root pathogen. The commercial biocontrol agent Binab T (active strains Trichoderma polysporum and T. harzianum) was evaluated at 50% and 70% water content. Studies were carried out in a controlled environment, in a climate chamber, using tomato as the model plant and Pythium ultimum as the model pathogen. Pathogen levels were affected by the water content of the medium and the biocontrol treatment, while the amount of biocontrol agent was not affected by the water content of the growing medium. The Trichoderma strains in Binab T were able to reduce the amount of pathogen and the incidence of disease at both water contents tested. The biocontrol activity of Binab T against P. ultimum, as indicated by the level of glucanase production, was affected by variations in the water content of the growing medium. The pathogen, the biocontrol agent, and the water content of the growing medium, all had an impact on the microbial communities resident in the system.     

Respiration and ripening patterns in the life cycle of the mango fruit

Alphonso mangoes picked at any stage of maturity (starting from fruit-set) and stored at room temperature show typical respiratory changes characteristic of a fully matured mango. Fruits picked during the earlier and later stages of development show respiration climacteric within 6–10 days. During the middle stages of development the preclimacteric trough continues to extend and the climacteric occurs after 10 days. Fully mature, tree-ripe mangoes do not show a respiratory climacteric during post-harvest storage.

Chemical constituents, such as titratable acids, apparent ascorbic acid, carbohydrates and carotenoids, estimated both at harvest and in ripe fruits from different pickings show changes similar to those characteristic of a fully matured ripening fruit.

Possibilities of reducing losses from pre-harvest fruit drop and post-harvest decay by resorting to early harvesting are discussed.     

Optimisation of a highly efficient shoot regeneration system using leaf explants of Chinese jujube (Ziziphus jujuba Mill.) by response surface methodology

Chinese jujube (Ziziphus jujuba Mill.) is a major fruit crop in Asia. In this study, response surface methodology (RSM) was successfully employed to establish a highly efficient in vitro propagation and regeneration system for the ‘Teapot’ jujube via shoot organogenesis. Among the tested factors, gibberellic acid (GA₃) concentration showed the most significant positive effect. The pre-culture darkness timing and medium were also important factors for highly efficient shoot regeneration of the ‘Teapot’ jujube. The highest regeneration (> 75%) was achieved by 1 week in darkness and culture on wood plant medium (WPM) containing 0.25 mg·L^?1 GA₃, 0.5 mg·L^?1 6-benzylaminopurine (BAP) and 0.1 mg·L^?1 3-indoleacetic acid (IAA). In vitro-derived shoots rooted very well in the modified ¹/₂ Murashige and Skoog (MS) medium containing 0.4 mg·L^?1 3-indolebutyric acid (IBA), resulting in a 100% rooting rate. These findings suggest that the RSM can be employed to optimise the protocols needed for successful in vitro plant regeneration of jujube cultivars, with potential applications in plant genetic transformation practices, polyploidy induction and germplasm preservation.     

Foliar application of calcium plus boron reduces the incidence of sunburn in ‘Golden Delicious’ apple

Summary

Losses of apple fruit due to sunburn damage under South African climatic conditions can reach up to 40% per annum for specific cultivars in certain years. Various approaches to reduce the incidence and severity of sunburn resulted in temporary effects but, at present, no single remedy is available to provide a significant and consistent reduction in sunburn damage on a commercial scale. ‘Golden Delicious’ apple trees that received both calcium (Ca) and boron (B) as foliar applications on a weekly basis, when applied from approx. 21 – 70 d after full bloom (DAFB), showed significantly less sunburn in two consecutive seasons (P = 0.0500 and P = 0.0247 respectively) than untreated control fruit, or treatments based on Ca alone. The minerals were applied as supplements of sugar-alcohol complexed with Ca and B, trading as Manni-Plex^® Ca [10% (w/w) Ca] and Manni-Plex^® B [3.3% (w/w) B], respectively. The mode of action by which the incidence of sunburn was reduced using combined sprays of Manni-Plex^® Ca plus Manni-Plex^® B remains to be elucidated.     

Effect of methyl jasmonate on reactive oxygen species,antioxidant systems,and microstructure of Chinese winter jujube at two major ripening stages during shelf life

The effect of post-harvest application of methyl jasmonate (MeJ) on reactive oxygen species, antioxidant systems, and cellular structure in Chinese winter jujube (Ziziphus Jujuba Mill.) at the major ripening stages of green maturity (GM) and half-red maturity (HM) were investigated. Jujube fruit at each ripening stage were treated with 0, 50, 100, and 200?μmol?l^?1 MeJ for 24 h, then stored at 20 ± 2°C for shelf-life testing. Thereafter, changes in firmness, color, respiration rate, superoxide anion (O₂^?), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), ascorbic acid (AsA), and glutathione (GSH) were measured at 4-d intervals for up to 8 d. Results showed that, in comparison with control fruit, MeJ treatment effectively suppressed the decrease of firmness, color, and respiration rate, inhibited the production of O₂^? and accumulation of H₂O₂ and MDA, maintained higher activities of SOD and CAT and contents of AsA and GSH, and preserved the integrity of cell membranes and organelles. The degree of maturity influenced the benefits of MeJ application. The 100?μmol?l^?1 MeJ treatment had a positive impact on antioxidant systems for GM fruit, whereas a MeJ concentration below 100 μmol l^?1 was found to extend the shelf life of HM fruit.     

Bioherbicide Research: Defining Success (A Tribute to RaghavanCharudattan)

Summary

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