Impact of PEG Induced Drought Stress on Three Citrus Rootstocks

Citrus is one of the most popular fruit crops worldwide. However, citrus growth and productivity are widely influenced by unlimited biotic and abiotic stresses. Among stresses, drought is one of the most critical factors that affect citrus development and sustainability in many regions around the world. Therefore, screening for drought-tolerant rootstocks among citrus genotypes is an important step in breeding programs. In this investigation, in vitro evaluation of drought stress on three important rootstocks, i.e., volcameriana, sour orange, and lime by using polyethylene glycol (PEG-6000) at 5% was conducted based on morphological and chlorophyll analysis. Morphological characteristics involving proliferation rate, shoot/root length ratio, shoot/root biomass ratio, number of leaves per explant, rooting percentage, and number of roots per explant were considerably reduced under PEG stress compared to the control treatment. Volcameriana rootstock showed the greatest stability under drought stress compared to sour orange and lime rootstocks. Furthermore, total chlorophyll was highly declined under drought stress in the three rootstocks over their control. Data revealed also that volcameriana rootstock reflected the maximum chlorophyll (Chla/Chlb) ratio followed by sour orange rootstock, then lime rootstock. The results suggest that volcameriana was the most tolerant rootstock to drought stress, while sour orange rootstock was moderate to drought and lime rootstock was the most sensitive rootstock. This work offers an efficient protocol for drought screening in citrus that could help in enhancing breeding programs.