عنوان مقاله [English]
Introduction: Distribution of photosynthetic substances between vegetative and reproductive parts is influenced by the environmental factors as well as plant nutrition status. Therefore, application of nutrient substances (such as chelated magnesium sulfate and salicylic acid combination) can influence the distribution of photosynthetic substances which in turn result in changes in allocation of photo-assimilates between vegetative and reproductive parts. Since the investigation of partitioning of photo- assimilates is complex and the interpretation of treatments effects on partitioning of substances is difficult in garden plants, this examination has been focused on external application of nutritional treatments on different organs growth by comparing the effects of salicylic acid and chelated magnesium sulfate on the allocation of photo- assimilates.
Materials and Methods: This experiment was performed in a commercial 10-year old orchard of Qazvin in 2013. Initially, 60 uniform pears (cv. Louise Bonne) which were infected to fire blight disease were selected. Before treatment imposing, agronomic practices such as removing and pruning infected shoots were applied. Treatments were combination of salicylic acid and chelated magnesium sulfate at different levels, which were applied on foliage under the conditions of neutral pollution to fire blight. In the present research, vegetative parameters (current shoot growth, leaf weight, leaf area, relative water content and so on) and reproductive parameters (length: diameter ratio and density of fruit and so on) were measured.
The fully expanded leaves were collected randomly from each replicate. After washing the samples were weighed and these values referred to as initial readings (fresh weight). Then, the leaf samples were placed in distilled water for 24 h in the dark at room temperature. The turgid leaves were blotted dry and weighed (saturation weight). After weighing, the material was oven-dried at 70 °C for 24 h. Relative water content (RWC) of the leaves was appraised as described by Ritchie and Nguyen (19) using the following formula:
RWC (%) = [(f. wt. – d. wt.) / (t. wt. – d. wt.)] × 100
Where f. wt, d. wt and t. wt are fresh weight, dry weight and turgid weight, respectively.
Diameter and length of fruit were measured by nondestructive method (on the tree) and by using digital caliper in the places of maximum length and maximum width diameters, and length: diameter ratio from the division of these two parameters. Fruit weight was estimated by digital scale (0.01 g) and its volume by the difference of the water level of scaled column, and then fruit density was calculated by using formula d=M/V.
In order to estimate the parameters of leaf area, specific leaf area and specific leaf weight, leaf area meter and oven were used. To evaluate the effect of the treatments on decrease or increase current shoot growth, measuring shoot length was reported by tape measure according to centimeter.
Results and Discussion: The results indicated that the most amount of specific leaf weight was allocated in chelated magnesium sulfate (0.5 and 0.7 g: 1000 ml) treatments and the least amount was belonged to the control group. The extent of changes in leaf area was between 28.17 to 44.33 cm2, were recorded to control group (without water) and salicylic acid (0.1 g: 1000 ml) plus chelated magnesium sulfate (0.7 g: 1000 ml), respectively. The minimum and maximum of specific leaf area were ranged between 44.14 to 59.40 cm2 and belonged to control group (without water) and salicylic acid (0.1 g: 1000 ml), respectively. The most current shoot growth was observed in control group (without water) and the least quantity was in chelated magnesium sulfate (0.5 g: 1000 ml). The minimum and maximum of fresh weight of leaf was changeable between 1.513 to 1.94 g were recorded to control group and salicylic acid (0.1 g: 1000 ml) plus chelated magnesium sulfate (0.7 g: 1000 ml), respectively. The most and the least content of leaf relative water were observed to salicylic acid (0.5 g: 1000 ml) plus chelated magnesium sulfate (0.5 g: 1000 ml) and salicylic acid (0.5 g: 1000 ml) plus chelated magnesium sulfate (0.7 g: 1000 ml), respectively. The extent of changes in fruit specific gravity was changeable between 0.72 to 0.97 g to cm3. The maximum amount of fruit specific gravity was seen in salicylic acid (0.5 g: 1000 ml) plus chelated magnesium sulfate (0.7 g: 1000 ml) and the minimum amount was in salicylic acid (0.5 g: 1000 ml) treatment. The conformity of the maximum current shoot growth and leaf fresh weight with the minimum leaf dry weight, leaf area, specific leaf area and specific leaf weight to control group and control group (without water) can declare the effect of treatment substances on the allocating manner of substances in different organs in plants and its stimulating effect on vegetative indexes that is not observable in the lack of treatment substances. The allocation of the most fruit specific gravity and also the least leaf relative water content and the least fruit length: diameter ratio to salicylic acid (0.5 g: 1000 ml) and chelated magnesium sulfate (0.7 g: 1000 ml) can confirm the opposit relation among these parameters in the way of substances allocation and the effect of above treatment on this opposit relation. Denser fruits have fewer growth rather than types with the more blank space and receive a more carbohydrate from the tree rather than their weight. The decrease of relative water content of leaf can also be explained in the direction of the more absorption of carbohydrate by fruit as a strong sink. In other words, the existence of fruit as a strong sink in favorable conditions for photosynthesis (with paying attention to the high vegetative indexes) can prevent gathering water in chloroplast and cause an increase of fruit specific gravity.
Also, the allocation of the most specific leaf weight and the least fruit length: diameter ratio and the least current shoot growth to chelated magnesium sulfate (0.5 g: 1000 ml) express the positive role of sulfur in aforesaid concentration on stimulating leaf growth and its negative role in stimulating growth of shoot and fruit that somehow points on the effect of treatment substances on the allocation of substances (elaborate sap) to different organs. The sulfur compounds can cause preventing gibberellin synthesis and the decrease of internode length, like other growth retardants.
The maximum fruit length: diameter ratio was belonged to salicylic acid (0.1 g: 1000 ml) and chelated magnesium sulfate (0.7 g: 1000 ml). Salicylic acid (0.1 g: 1000 ml) treatment induced maximum amounts of fruit length and diameter to itself that confirms the positive role of salicylic acid in stimulating growth in stress conditions (biotic stress derived from Erwinia amylovora). The significant negative correlation (p