Gum oozing from the trunk and bark splitting on my citrus tree (santra)

Gum oozing from the lower trunk and collar, with bark cracking, darkening and dying, is most likely gummosis caused by Phytophthora, a soil and water-borne fungus-like organism that attacks the collar and roots. It is worse where soil stays wet around the trunk, in low-lying spots, and where the budding union is buried too deep. Confirm with your KVK, since borer damage can also cause gumming. Management is mainly about keeping the collar dry and healthy. Make sure water does not pond around the trunk, keep irrigation away from the stem by watering at the drip line, and never heap soil or mulch against the trunk. Plant on a slight ridge with the bud union well above ground, and use rootstocks tolerant to Phytophthora when establishing a new orchard. For affected trees, your KVK may advise scraping out the dead bark, exposing the lesion to air, and applying a recommended treatment such as a copper paste or a metalaxyl-based product to the collar, but follow the label and local advice. Improve drainage above all, since wet feet drives this disease. Get it diagnosed before treating so you do not confuse it with borer.