Incidence and Effect of Heart Rot in Marayur Sandalwood (Santalum album L.) Reserve, Kerala, and Its Natural Durability Against Fungi

Indian sandalwood (Santalum album L.) is a semi-parasitic tree, well known for its valuable sandalwood oil extracted from heartwood and roots. Extensive loss of heartwood as a result of its decay is observed in living trees and this has inspired the current study, to investigate the health of sandalwood in Marayur sandalwood forest reserves. Located in Kerala, India, the majority of the trees in Marayur are facing high mortality with the loss of heartwood. The current study evaluated the health status and heartwood-rot disease severity of each tree, which revealed that only 16.67 % of the total trees were healthy and 1.5 % of them were dead. Statistical analysis revealed increasing girth class of trees has a significant positive association with increased disease severity at a 0.05 level of significance. Laboratory analysis confirmed the presence of the major wood-rotters Allophoma tropica, Xylaria berteroi, Diaporthe sp., Fomes sp., Ganoderma appalanatum, and Trametes sp., and that they are collectively responsible for the heart rot. A durability assessment revealed sandalwood is highly resistant (durability class I) to white-rot fungi (viz., Trametes hirsutus and T. [Coriolus] versicolor) and moderately resistant (durability class II) to brown-rot fungi (Oligoporous placenta and Fomitopsis meliae). Study implications: This study highlights the health status and heart-rot disease severity of sandalwood trees in Marayur Forest Reserves. Of the total trees surveyed, about 1.5% mortality was observed and only 17% of the trees were devoid of any heart-rot symptoms. Allophoma tropica, Ganoderma applanatum, Xylaria berteroi isolate SR52, Diaporthe sp., Fomes sp., G. appalanatum, and Trametes sp. are typical species collectively responsible for the heart rot and this was found to be the case in our study. These findings will sensitize forest managers to the loss of valuable sandalwood and death of the trees due to the heart rot, thereby enabling them to take appropriate preventive measures. Also, the natural durability of sandalwood against brown- and white-rot fungi is reported for the first time, indicating that sandalwood falls in the resistance class I (highly resistant) against white-rot fungi (Trametes hirsutus and T. (Coriolus) versicolor) and resistance class II (resistant) against brown-rot fungi (Oligoporous placenta and Fomitopsis meliae).