Abstract
Sandal, S. album L., a hemi-root parasite is the source of highly priced and fragrant heartwood which on steam distillation yields 5-7 per cent oil of high perfumery and medicinal value. Low seed setting, seedling mortality caused by over exposure, fungal disease, lack of haustorial connection with host plant roots and loss of genetic diversity caused by over-exploitation and illicit felling are the major problems affecting sandal regeneration. IUCN categorised S. album as ‘vulnerable’ species; hence, it is of paramount importance to maintain genetic variability within and among populations through enhanced natural regeneration.
Conservation as well as mass propagation are the two strategies to be given due importance. For this purpose, precise knowledge of the factors influencing regeneration and survival of the species at seedling stage is essential. Hence, the present work was undertaken with the objective of investigating the autotrophic and parasitic phase of sandal seedling growth through studies on chlorophyll content and chlorophyll fluorescence, genetic diversity of sandal populations in seed stands using ISSR markers and diversity of Fusarium oxysporum isolates causing sandal seedling wilt using RAPD markers.
Seedling dependency on seed reserve (cotyledonary) showed that sandal seedlings need to be transferred to containers with potting mixture within 26 days after germination for proper growth and development. The impact of host plant root connection on seedling growth and survival showed that Vigna unguiculata was a better primary host among the eight annual host species tested for this purpose; among perennials, Pongamia pinnata was the appropriate long term host. Fifty to seventy five per cent shade was optimal for growth of sandal seedlings up to one year after germination. High light intensity affected normal photosynthetic activity through photoinhibition.
ISSR marker study showed identity of DNA profiles of nearby sandal trees indicating that such trees could be clones which might have arisen from root suckers. Low percentage of polymorphism and low genetic diversity showed very high chance of inbreeding in the seed stand which could be the major reason for poor seed production in the seed stands. The practise of root sucker induction as a method of improving regeneration in natural sandal forest has to be discontinued.
Genetic diversity of F. oxysporum isolates from wilt affected sandal seedlings of sandal nursery located in nurseries at Marayur in Idukki district and Peechi in Trichur district of Kerala state was evaluated using RAPD markers. A wide range of genetic variation was detected among the F. oxysporum genotypes indicating the ability of the pathogen to adapt to different eco-climatic conditions. The pathogen is highly successful in infecting sandal seedlings at different stages of development. Hence prophylactic treatment of sandal seeds, preferably with a systemic fungicide is suggested.