Mathieu Lechaudel

Chlorophyll fluorescence, a nondestructive method to assess maturity of mango fruits (Cv. 'Cogshall') without growth conditions bias.

The quality of ripe mango fruits depends on maturity stage at harvest, which is usually assessed by visible criteria or from estimates of the age of fruit. The present study deals with the potential of chlorophyll fluorescence as a nondestructive method to assess the degree of fruit maturity regardless of fruit growing conditions. Chlorophyll fluorescence parameters were measured along with respiration rates of fruits still attached to the tree. At the same harvest stage, based on the fruit age or the thermal time sum (degree-days) method, physical and biochemical measurements related to fruit maturity and quality were made. Shaded fruits had a significantly greener flesh color, as well as a lower fruit density and flesh dry matter content, than well-exposed fruits, showing that fruits at the top of the canopy were more mature than fruits within the canopy, which were still in a growth phase. Additionally, chlorophyll fluorescence parameters, F(o), F(m), and F(v), were significantly lower for fruits taken from the top of the canopy than for those from within the canopy. The unique relationship observed between chlorophyll fluorescence parameters and fruit maturity, estimated by internal carbon dioxide content, on fruit still attached to trees is independent of growing conditions, such as the position of the fruit in the canopy and carbohydrate supply. The chlorophyll fluorescence method evaluates maturity much more accurately than the degree-day method and, moreover, nondestructively provides values for individual fruits before harvest.

Leaf-to-fruit ratio affects water and dry-matter content of mango fruit

Summary Changes in water and dry-matter content of developing mango fruit (Mangifera indica L. ‘Lirfa’) were investigated over a single season in Réunion Island, along with the effects of leaf:fruit ratio (10, 25, 50, 100 and 150 leaves per fruit on girdled branches). As the fruit developed, about 8–13% of fruit water weight was in the peel compared with 78–86% in the pulp and 6–9% in the stone. When the data were expressed on a dry-weight basis, 12–20% was in the peel, 60–70% was in the pulp and 18–20% in the stone. At harvest, larger fruit, on treatment 100, had a higher proportion of weight in the pulp. Good relationships between water and dry weight of each fruit component were found, regardless of the treatment. They showed that the rate of water accumulation decreased when the dry weight increased and that the dry-matter content increased as the fruit developed as well. Increasing leaf:fruit ratio to 100 leaves per fruit improved fruit yield by 300 g and pulp dry-matter content by 6%, for a total of 550 g and 20% at harvest. Fruit quality as estimated by pulp dry-matter content could be calculated easily during the changes in fruit weight over the season. Moreover, this indicator could be useful to assess the maturity of mango fruit.

Quality and maturation of mango fruits of cv. Cogshall in relation to harvest date and carbon supply

The effects of harvest date (5 dates, between 100 and 140 days after full bloom) and carbon supply (2 leaf-to-fruit ratios, 10 and 100) on mango fruit (cv. Cogshall) quality and maturity were studied to find reliable indicators that take fruit physiological maturity into account and to establish a compromised harvest date according to the market. Fruit size and density varied with regard to the harvest date and assimilate supply. Changes in total soluble solids and titratable acidity were well correlated with concentrations of major soluble sugars and organic acids. Potassium concentration was increased according to harvest date. Metabolic changes occurred at 126–133 and 133–140 days after full bloom in fruit subjected to non-limited and stress conditions of assimilate supply, respectively. During this stage, sucrose and malic acid concentrations strongly increased, whereas those of starch and citric acid decreased according to the leaf-to-fruit ratio treatment. Synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl ACC, and a rapid increase in the respiration rate were observed during this period. The shortage of assimilate supply delayed the onset of maturation and reduced its intensity. Storage quality of mango cv. Cogshall may be influenced by assimilate supply since the K+ to Ca2+ ratio and the pulp dry matter content, in particular, were enhanced in fruit from the 100 leaf-to-fruit ratio treatment. Results for mango cv. Cogshall suggested that total soluble solids, sucrose, and malic/citric acid ratio can be used as physiological indices for mango fruit, whereas fruit fresh mass, density, and pulp dry matter content can be useful indicators for when to harvest fruit. It appeared that 133 days after full bloom was an optimal harvest date for fruit grown under non-limited conditions of assimilate supply, for a market where the time between harvest and consumption of fruit is short.

Response of the physiological parameters of mango fruit (transpiration, water relations and antioxidant system) to its light and temperature environment

Depending on the position of the fruit in the tree, mango fruit may be exposed to high temperature and intense light conditions that may lead to metabolic and physiological disorders and affect yield and quality. The present study aimed to determine how mango fruit adapted its functioning in terms of fruit water relations, epicarp characteristics and the antioxidant defence system in peel, to environmental conditions. The effect of contrasted temperature and light conditions was evaluated under natural solar radiation and temperature by comparing well-exposed and shaded fruit at three stages of fruit development. The sun-exposed and shaded peels of the two sides of the well-exposed fruit were also compared. Depending on fruit position within the canopy and on the side of a well-exposed fruit, the temperature gradient over a day affected fruit characteristics such as transpiration, as revealed by the water potential gradient as a function of the treatments, and led to a significant decrease in water conductance for well-exposed fruits compared to fruits within the canopy. Changes in cuticle thickness according to fruit position were consistent with those of fruit water conductance. Osmotic potential was also affected by climatic environment and harvest stage. Environmental conditions that induced water stress and greater light exposure, like on the sunny side of well-exposed fruit, increased the hydrogen peroxide, malondialdehyde and total and reduced ascorbate contents, as well as SOD, APX and MDHAR activities, regardless of the maturity stage. The lowest values were measured in the peel of the shaded fruit, that of the shaded side of well-exposed fruit being intermediate. Mango fruits exposed to water-stress-induced conditions during growth adapt their functioning by reducing their transpiration. Moreover, oxidative stress was limited as a consequence of the increase in antioxidant content and enzyme activities. This adaptive response of mango fruit to its climatic environment during growth could affect postharvest behaviour and quality.

Physiological age at harvest regulates the variability in postharvest ripening, sensory and nutritional characteristics of mango (Mangifera indica L.) cv. Coghshall due to growing conditions

BACKGROUND Climacteric fruits are harvested at the green-mature stage and ripen during their marketing cycle. However, growing conditions induce variability into the maturity stage of mangoes at harvest, with an impact on their final quality. Assuming that the physiological age can be correctly evaluated by a criterion based on the variable chlorophyll fluorescence of the skin (F(v)) and that differences in physiological age depend on growing conditions, controlled stress experiments were carried out on mango fruit by manipulating either the leaf/fruit ratio or the light environment. RESULTS Delays from 9 to 30 days were observed, depending on stress level and harvest stage, to obtain the same F(v) value. For moderate stress, fruit composition after ripening was partially compensated for, with little or no difference in sugar, dry matter, carotenoid and aroma contents. For more pronounced stress, the major metabolites were not particularly affected, but the synthesis capacity of carotenoids and aromas was lower after maturity. CONCLUSION The ripening ability of a fruit is acquired on the tree and defines its postharvest changes. Control of the physiological age at harvest can minimise the variability observed under natural conditions and guarantee fruit batches whose postharvest changes will be relatively homogeneous.

Effect of leaf-to-fruit ratio on leaf nitrogen content and net photosynthesis in girdled branches of Mangifera indica L.

Variations in leaf nitrogen concentration (Nm), mass-to-area ratio (Ma), amount of leaf nitrogen per unit leaf area (Na), and non-structural carbohydrates were measured in well-lit girdled branches of 11-year-old mango trees that were experiencing similar conditions of irradiance and gap fraction. The influence of source–sink relationships was studied by testing three levels of leaf-to-fruit ratio: 40, 70 and 150, during the period of linear fruit growth. Na was negatively correlated to the leaf-to-fruit ratio. Differences in Na were reflected in differences in net photosynthetic assimilation, Anet, although they could not fully account for them. All differences in Na resulted exclusively from differences in Nm, not Ma. Starch and total non-structural carbohydrates accumulated in the leaves as the result of higher leaf-to-fruit ratio, which suggests that the leaf carbohydrate status may play a role in photosynthetic acclimation to fruit load in mango. These observations complement previous findings where photosynthetic acclimation to light was found to be driven by changes in Ma, while Nm remained almost constant over a large range of gap fractions. Observations about the effect of fruit load were also in contrast with previous observations, since no evidence was found that leaf carbohydrate status played any role in photosynthetic acclimation to light. This study demonstrates that acclimation to changing source–sink relationships does not follow the same pattern as acclimation to progressive shading; but these observations do suggest that there may be different mechanisms by which leaves acclimatise to changing conditions.

Model-assisted analysis of spatial and temporal variations in fruit temperature and transpiration highlighting the role of fruit development

Fruit physiology is strongly affected by both fruit temperature and water losses through transpiration. Fruit temperature and its transpiration vary with environmental factors and fruit characteristics. In line with previous studies, measurements of physical and thermal fruit properties were found to significantly vary between fruit tissues and maturity stages. To study the impact of these variations on fruit temperature and transpiration, a modelling approach was used. A physical model was developed to predict the spatial and temporal variations of fruit temperature and transpiration according to the spatial and temporal variations of environmental factors and thermal and physical fruit properties. Model predictions compared well to temperature measurements on mango fruits, making it possible to accurately simulate the daily temperature variations of the sunny and shaded sides of fruits. Model simulations indicated that fruit development induced an increase in both the temperature gradient within the fruit and fruit water losses, mainly due to fruit expansion. However, the evolution of fruit characteristics has only a very slight impact on the average temperature and the transpiration per surface unit. The importance of temperature and transpiration gradients highlighted in this study made it necessary to take spatial and temporal variations of environmental factors and fruit characteristics into account to model fruit physiology.

Antioxidant and enzymatic responses to oxidative stress induced by pre-harvest water supply reduction and ripening on mango (Mangifera indica L. cv. ‘Cogshall’) in relation to carotenoid content

The effects of a reduction in water supply during fruit development and postharvest fruit ripening on the oxidative status and the antioxidant defense system were studied in the mango fruit (Mangifera indica L.) cv. Cogshall. Changes in non-enzymatic (ascorbate) and enzymatic (SOD, CAT, APX, MDHAR, DHAR and GR) antioxidants, as well as oxidative parameters (H2O2 and MDA) and major carotenoids, were measured in unripe and ripe fruits from well-irrigated and non-irrigated trees. Under non-limiting water supply conditions, ripening induced oxidation as a result of the production of ROS and decreased ascorbate content. Antioxidant enzymatic systems were activated to protect fruit tissues and to regenerate the ascorbate pool. The carotenoid pool, mainly represented by β-carotene and esterified violaxanthine isomers, accumulated naturally during mango ripening. The suppression of irrigation decreased fruit size and induced accumulation of ABA and of its storage form, ABA-GE, in fruit pulp from the earliest harvest. It also increased oxidation, which was observable by the high levels of ascorbate measured at the early stages at harvest, and by the delay in the time it took to reach the pseudo constant carotene-to-xanthophyll ratio in ripe fruits. Nevertheless, differences between the irrigation treatments on the antioxidant system in ripe fruits were not significant, mainly because of the drastic changes in this system during ripening.

Spatial and temporal variations in mango colour, acidity, and sweetness in relation to temperature and ethylene gradients within the fruit

Managing fruit quality is complex because many different attributes have to be taken into account, which are themselves subjected to spatial and temporal variations. Heterogeneous fruit quality has been assumed to be partly related to temperature and maturity gradients within the fruit. To test this assumption, we measured the spatial variability of certain mango fruit quality traits: colour of the peel and of the flesh, and sourness and sweetness, at different stages of fruit maturity using destructive methods as well as vis-NIR reflectance. The spatial variability of mango quality traits was compared to internal variations in thermal time, simulated by a physical model, and to internal variations in maturity, using ethylene content as an indicator. All the fruit quality indicators analysed showed significant spatial and temporal variations, regardless of the measurement method used. The heterogeneity of internal fruit quality traits was not correlated with the marked internal temperature gradient we modelled. However, variations in ethylene content revealed a strong internal maturity gradient which was correlated with the spatial variations in measured mango quality traits. Nonetheless, alone, the internal maturity gradient did not explain the variability of fruit quality traits, suggesting that other factors, such as gas, abscisic acid and water gradients, are also involved.

Low-input pineapple crops with high quality fruit: Promising impacts of locally integrated and organic fertilisation compared to chemical fertilisers

Fruit and vegetable farming generally involves high levels of chemical inputs despite the fact that consumers are increasingly concerned about the sanitary and organoleptic aspects of fruit quality. Pineapple is largely subject to these issues since it is dominated by conventional monocropping with high levels of agrochemical inputs due to nitrogen (N) and potassium (K) fertilisation, weed management, crop protection and flowering induction. However, low-input pineapple cropping systems are both rare and little documented. Our study aimed at replacing all or part of the chemical fertilisers used with local organic fertilisers. It was conducted on the cultivar ‘Queen Victoria’, without pesticides or herbicides, in Reunion Island. We compared the impacts of three fertilisation treatments on pineapple growth and yield, fruit quality traits, symptoms of two major fungal diseases in fruit and production costs and labour times: (i) conventional: NPK fertiliser at recommended doses (265.5 kg ha −1 N–10.53 kg ha −1 P–445.71 kg ha −1 K); (ii) integrated: Mucuna pruriens green manure (240.03 kg ha −1 N, 18.62 kg ha −1 P, 136.11 kg ha −1 K) incorporated into the soil and a half-dose of NPK fertiliser and (iii) organic: M. pruriens green manure incorporated into the soil and foliar applications of sugarcane vinasse from a local distillery, rich in K (14.44 g L −1 ). Our results showed that NPK fertilisation could be replaced by organic fertilisers as well as by integrated fertilisation. ‘D’-leaf analysis showed that vinasse supplies a largely sufficient K level for growing pineapples. With organic fertilisation, pineapple growth was slower, 199 days after planting vs. 149 days for integrated or conventional fertilisations, and fruit yield was lower, 47.25 t ha −1 vs. 52.51 and 61.24 t ha −1 , probably because M. pruriens green manure provided an early increase in soil mineral N, whereas N requirements are much higher four months after planting. However, the fruit weight (709.94 ± 123.53 g) was still within the size range required for the export market (600–900 g). Interestingly, organic fertilisation significantly reduced Leathery Pocket disease and produced the best quality fruit with the highest total soluble solids contents (TSS) and the lowest titratable acidity (TTA). Fruit quality was also significantly improved with integrated fertilisation, with fruit weight similar to that of conventional fertilisation. To conclude, these findings have implications for the sustainability of pineapple production and could lead to low-input innovative cropping systems that reduce production costs and develop local organic inputs.