The Physiology of Root-parasitism in Sandal (<I>Santalum album</I> Linn.)

Abstract

The first evidence of root parasitism in sandal was presented by Scott in 1871. Its significance came to be realised only 30 years later, when the ravages of spike on sandal were very heavy. The earlier researches were directed to detecting haustorial connections made by it on several species growing in the forests. The number had gone beyond 320 today. To some, parasitism in sandal was secondary in character, whereas to many, it was the main channel of nutrient supply for the sandal. The absence of root hairs combined with the fact that the root of this plant haustorises anything from a pebble to its own roots, was sufficient evidence of its obligate parasitic nature. It was understood thereby that the host roots furnish all the mineral nutrients to the growing sandal. The absorption was through haustoria formed by the parasite on the host roots, for this specific purpose. Experiments conducted to verify this concept have been classified here. The observations and results have been discussed in an appropriate manner. In studying the physiology of root parasitism in sandal, the relation between its roots and the soils below such sandal with and without haustorial function had been examined, based on the analyses for the mineral constituents in such plants and the soils below them. It is now shown that sandal depends upon the soil below it for two major essential nutrients, viz., lime and potash, being directly absorbed therefrom through rootends. The dependence of sandal on its host associates, for its nutrient supply is only partial, being confined to two other major entities, nitrogen and phosphorus. This selective activity of haustoria would at once negative the earlier view that sandal is an obligate parasite. Since the absorption of tbe mineral nutrients by sandal roots takes place in 2 ways from 2 different sources, by 2 different methods of extraction by its roots, a balanced activity of the two active centres, viz., rootends and haustoria is indicated by the ratio Ca/N (Calcium to Nitrogen). Preliminary attempts have been reported here to assess the influence of the host plants on the foliar characteristics of sandal to correlate in the field the possible associates through measurements made on sandal leaves, chemically and biometrically. Whatever is known about the parasitism of sandal today, had been the outcome of researches on spike disease of sandal, and not directly on the physiology of its root activity. Based on its primary feature of haustorising the vegetation growing around it, the incidence of spike in sandal was also traced to many host species. This is found to be entirely incorrect. An appendix is included herein, indicating the host plants of sandal so far recorded.