Ram Roshan Sharma

Catecholase and cresolase activities and phenolic content in mango (Mangifera indica L.) at panicle initiation

Abstract Catecholase and cresolase (PPO) enzyme activities and phenolic content were measured in different mango cultivars at panicle initiation. Enzyme activity and phenolic content varied widely amongst eight cultivars, the maximum being in Bhadauran and minimum in Tommy Atkins. Floral malformation incidence was maximum (53.75%) in ‘Tommy Atkins’ and minimum in ‘Bhadauran’ (1.10%). A strong negative correlation was found between both the enzyme activity, phenolic content at panicle initiation and the incidence of floral malformation. Thus, PPO activity and level of phenolic compounds at panicle initiation may give a possible estimate of malformation incidence in mango.

Relationships between storage disorders and fruit calcium contents, lipoxygenase activity, and rates of ethylene evolution and respiration in ‘Royal Delicious’ apple (Malus × domestica Borkh.)

Summary Experiments were conducted to determine the relationships between the occurrence of storage disorders in ‘Royal Delicious’ apple (Malus ×domestica Borkh.) and fruit Ca2+ ion contents, rates of ethylene evolution and respiration, and lipoxygenase (LOX) activity. Apples were stored at 0º ± 1ºC and 90 – 95% relative humidity and sampled each month, up to 6 months, for storage disorders, fruit Ca2+ ion contents, rates of ethylene evolution and respiration, and LOX activity. Storage disorders such as bitter pit, cork spot, and brown core appeared after 3 months and increased in frequency at subsequent samplings. Regardless of the presence or absence of storage disorders, fruit showed a decline in Ca2+ ion concentration during storage. Ca2+ ion concentrations (means of 3, 4, 5, and 6 month samples) were significantly higher in disorder-free fruit [0.419 mg g–1 dry weight (DW)] than in fruit showing bitter pit (0.329 mg g–1 DW) or cork spot (0.340 mg g–1 DW), but were not significantly higher than in fruit with brown core (0.393 mg g–1 DW). Conversely, LOX activity was significantly lower in disorder-free fruit [0.168 µmoles linolenic acid oxidised min–1 g–1 fresh weight (FW)] compared to symptomatic fruit. LOX activity increased with the duration of storage in all fruit samples. The rates of ethylene evolution (58.5 µl C2H4 kg–1 FW fruit h–1) and respiration (16.0 ml CO2 kg–1 FW fruit h–1) were significantly lower in disorder-free fruit than in symptomatic fruit. The rates of ethylene evolution and respiration increased between 3 – 5 months in storage. After 5 months in storage, they remained stable or declined in all fruit. The correlations (R2) between Ca2+ ion content vs. the presence of physiological disorders such as bitter pit (–0.77), cork spot (–0.75), and brown core (–0.64), and between Ca2+ ion contents vs. LOX activity were strongly negative (–0.94). In contrast; the correlation between LOX activity vs. physiological disorders was strongly positive. Our study concluded that an inverse relationship existed between fruit Ca2+ ion content and the occurrence of bitter pit, cork spot, and/or brown core, and between fruit Ca2+ ion content and LOX activity. Moreover, the relationship between LOX activity and the presence of storage disorders was strongly positive.

Paclobutrazol minimises the effects of salt stress in mango (Mangifera indica L.)

Summary We investigated the effects of paclobutrazol (PBZ) on 1-year-old plants of ‘Olour’ mango subjected to NaCl stress under polythene tunnel conditions. Plants were treated with two levels of salt [0.0 g NaCl kg−1 soil (control) or 1 g NaCl kg−1 soil] and three concentrations of paclobutrazol [PBZ; 0.0 mg l−1 (control), 750 mg l−1 or 1,500 mg l−1] after 30 d of establishment. Mortality in saline-treated mango plants was reduced significantly (LSD = 8.55; P ≤ 0.05) following the application of PBZ. NaCl-stress reduced the survival of plants without PBZ treatment by 89%, but only by 28.4% for 1,500 mg l−1 PBZ-treated plants. PBZ-treated plants also showed less defoliation, and fewer leaves per plant exhibited salt stress symptoms. It was also evident that treatment with PBZ increased the relative water and chlorophyll contents of mango seedlings, and reduced membrane injury, under salt stress. Furthermore, saline treatment without PBZ increased the Na+ and Cl− ion contents of leaves and roots; however, application of PBZ consistently and significantly lowered these ion contents (P ≤ 0.05). The Na+ content of leaves on saline-treated plants was reduced by 1.96- to 2.12-fold, whereas Cl− ion contents were reduced by 22 – 39% by PBZ treatment compared to salt-treated seedlings without PBZ. Our results suggest a role for PBZ in promoting the avoidance of salt stress in mango by increasing the levels of photosynthetic pigments, water content, K+ uptake and accumulation, and by reducing defoliation, the membrane injury index, and the uptake and accumulation of harmful Na+ and Cl− ions. These findings may be used to improve the yields and quality of mango trees grown in salt-affected areas.

Preharvest Fruit Bagging for Better Protection and Postharvest Quality of Horticultural Produce

Abstract Among several good agricultural practices (GAPs), preharvest fruit bagging is becoming very popular in several countries of the world. It is a physical protection technique, which improves fruit appearance by promoting fruit coloration and reducing blemishes. It brings multiple effects to internal fruit quality. Fruit bagging also reduces disease and insect-pest incidence, mechanical damage, sunburn, fruit cracking, agrochemical residues, and damage by birds. Due to such beneficial effects, this GAP has become an integral part of peach, apple, pear, grape, and loquat production in countries like Japan, Australia, China, and the USA, and certain countries, viz., Mexico, Chile, and Argentina, do not import apples if they are not bagged. A number of studies have been conducted the world over to harness the effects of fruit bagging on color and quality of the produce, and different authors have reported contradictory results, which may be due to differences in the type of bag used, the stage of development when the fruit is bagged, the period of exposure to natural light after bag removal (before harvesting), and/or fruit- and cultivar-specific responses.

Low light and low leaf calcium and boron concentrations are associated with fruit pitting, a new disorder in mango (Mangifera indica L.) in India.

Summary A study was conducted to investigate factors associated with fruit pitting, a new physiological disorder in mango (Mangifera indica L.). The incidence of pitting, along with intercepted light (photosynthetic photon flux density; PPFD) and net CO2 assimilation (A) were measured over 2 years at the top of the tree, and 1.0 m and 0.5 m above the crotch (i.e., the main branch-point) in the SE, NE, NW, and SW directions of the tree canopy in the mango cultivars ‘Alphonso’, ‘Amrapali’, ‘Bangalora’, ‘Bombay Green’, ‘Chausa’, ‘Dashehari’, ‘Langra’, ‘Neelum’, ‘Sensation’ and ‘Tommy Atkins’. Leaf nutrient concentrations were also determined in branches bearing normal and pitted fruit. The incidence of pitting was lowest (6.3%) in fruit at the top of the tree, followed by fruit 1.0 m (13.6%) or 0.5 m (20.0%) above the crotch. Similarly, the incidence of pitting was lowest (4.9%) in fruit from the SE of the canopy, followed by those from the NE (8.3%), SW(13.6%), and NW (20.0%). The incidence of pitting in different parts of the canopy reflected the PPFD and A values (A = 0.03 PPFD – 5.736; R2 = 0.91; Pitting (%) = 0.002 – 0.05 PPFD2 – 0.56 PPFD + 37.79; R2 = 0.894). ‘Dashehari’ mango had the highest incidence of fruit pitting (21.8%), and ‘Tommy Atkins’ had the lowest incidence (9.1%). The concentrations of leaf calcium (Ca) [1.17% (w/v) vs. 2.08% (w/v)], and boron (B) (28 µg g–1 vs. 45 µg g–1) were lower in branches bearing pitted fruit than in those bearing normal fruit, respectively. There were inverse quadratic relationships between the mean incidence of pitting and mean leaf Ca levels (Pitting (%) = 11.40 Ca2 – 48.84 Ca + 61.95; R2 = 0.48), and mean leaf B levels (Pitting (%) = 0.040 B2 – 3.67 B + 90.26; R2 = 0.97), and a linear relationship between leaf B and Ca concentrations (B = 20.93 Ca + 0.156; R2 = 0.76). These results suggest that pitting is related to low light levels, and to low concentrations of Ca and B. Experiments are in progress to resolve this problem using foliar or soil applications of Ca and B, and pruning of trees.