THE ROLE OF SALICYLIC ACID IN REDUCING WATER REQUIREMENTS FOR HIBISCUS ROSA-SINENSIS L. PLANT

This investigation was conducted under full sun conditions at the nursery of Hort. Res. Inst., A.R.C., Giza, Egypt during 2020 and 2021 seasons to examine the effect of salicylic acid (SA) as a foliar spray at concentrations of 0, 50, 75 and 100 ppm on growth, flowering and chemical composition of Hibiscus rosa-sinensis L. transplants grown in 16-cm-diameter plastic pots filled with about 1.6 kg of clay and subjected to four water treatments: 100% field capacity (F.C.) as control, 75, 50 and 25% of F.C. as water stress treatments. The effect of interactions between SA and water treatments was also studied. The results indicated that mean values of various vegetative and root growth parameters were progressively increased with increasing either water amount or SA concentration compared to the means of low levels of both, with few exceptions. Thus, the highest means of the different growth traits were attained by the highest levels of both water treatments (75 and 100% of F.C.) and SA ones (75 and 100 ppm) as well as their interactions, with the superiority of a combination between 75% of F.C. water treatment and SA spray at 75 ppm, giving almost the highest records. A similar trend was also obtained regarding flowering parameters and chemical composition of the leaves with the exception of chlorophyll a concentration that was slightly affected by the different treatments used in this study, and the percentages of P and K which were fluctuated, as well as proline concentration that was descendingly decreased with increasing either SA concentration or water quantity and their interactions. Thus, it can be recommended to spray Hibiscus rosa-sinensis L. plants with salicylic acid at 75 ppm, 3 times at 3-weeks intervals and irrigate them with only 75% of F.C. to save as much water as 25% of F.C. with keeping growth, flowering and quality of the plants.