Microscopic study of fertilization and fruit set in apricot cultivars sprayed by zinc

Zinc (Zn) is an essential micronutrient in plants and has a vital role in cell division, nucleic acid metabolism, protein synthesis, photosynthesis, carbohydrate metabolism, and phytohormones regulation (Sharafi, 2019). Zn directly contributes in the biological synthesis of auxin (IAA) and gibberellin (GA3) which have utmost roles in the plant growth, pollination, fertilization and fruit set in fruit trees (Broadley et al. 2007). Also, Zinc plays a major role as a cofactor in the structure and function of more than 300 enzymes in plants, such as Cu/Zn superoxide (Cu/Zn-SOD), carbonic anhydrase (CA), and sorbitol dehydrogenase (SDH). Zinc toxicity in plants is far less widespread than Zn deficiency (Radunić., et al., 207). The most important goal for fruit growers is to achieve high yields in orchards. The amount of nutrients in the plant and its nutrition are the most important determinants of plant performance. Among micronutrients, zinc plays an important role in pollination, fruit set and function of fruit trees and is one of the influencing factors in germination and growth of pollen tube (Sharafi, 2019).

In this study, the effects of zinc foliar application at three concentrations of 0, 3000 and 5000 mg / l on flower buds of two cultivars of Beigi and Shahroodi apricots were investigated. After foliar application two weeks before flowering, the effect of foliar application on germination percentage, pollen tube growth, primary and final fruit set were evaluated.

The results were showed that 5000 mg / L zinc sulfate had the most effect on the rate of initial and final fruit set. The percentage of initial and final fruit set was 3,000 mg / l zinc sulfate. The results also showed that the effect of zinc on germination percentage at stigma level and penetration rate of pollen tubes at the beginning of pistil, middle style and ovarian inlet was significant at 1% probability level. The germination percentage with 3000 mg / L zinc sulfate with 63.91% germination and the lowest germination with 51.39% was related to control. Also, 3000 mg / l sulfate increased the penetration of pollen tubes into the beginning and middle parts of the styles and so ovary.

Overall foliar application of Zn increased the primary and final fruit set, and so increased germination and penetration of pollen tube to the ovary.