The potential of some ameliorative substances in improving growth, yield and quality of carrot under heat stress conditions

Abstract: A field experiment was carried out in two successive seasons of 2019 and 2020 on the late planting of carrot cv. Shantiny in El-Badrasheen, Giza, Egypt to study the effect of sowing dates and foliar spray applications by using some growth natural and chemical stimulants to increase the plants' ability to withstand heat stress. The experiment was established in a split-plot design with two sowing dates during 15 February and 15 March as the main factors and six treatments of exogenous foliar spray applications as submain factors as follows: untreated plants (control); potassium silicate K-Si at 2g/L; salicylic acid at 2mM; glycine betaine at 100 mM; moringa leaf extract (MLE) at 3.3% and date palm pollen grain extract (DPPGE) at 2g/L. Results revealed that sowing carrots in February significantly increased vegetative growth characteristics, i.e., plant height in both seasons and fresh and dry weight in the second season. Also, the fresh weight of roots in the second season and total marketable yield in both seasons were significantly increased with February sowing. All chemical parameters, either quality or heat indicators, were enhanced considerably with March sowing as a reaction to heat stress. Moreover, all foliar spray treatments gained the higher significant values of vegetative growth, yield, quality characteristics, and chemical parameters [N, P, K, Ca, Mg, proline, antioxidant activity DPPH, total carbohydrates, total carotenoids, total chlorophyll, and total phenols] as compared with untreated plants. In conclusion, foliar spray treatments with MLE and DPPGE are promising materials for heat stress-tolerant applications.