OCCURRENCE OF AN ENDOPHYTIC BACILLUS ANTAGONISTIC TO PHYTOPHTHORA PALMIVORA IN COCONUT SEEDLINGS
H MOOSA1, R AHMED2, R
IYER1 and SR PRABHU1
1Central Plantation Crops Research Institute, Kasaragod - 671 124, Kerala, India; 2Applied Botany, Mangalore University, Mangata Gangotri - 574 199, DK, India
Background and objectives
Coconut palm, Cocos nucifera, is one of the main perennial sources of edible and industrial oil in India and also is an essential ingredient of many Indian food items. Bud rot caused by Phytophthora paimivora is the most important killer disease of coconut palm at all stages of its growth, causing losses up to 10%. Spraying of 1% Bordeaux mixture to the crown as a prophylactic to check the disease was recommended . However, this technology has its drawbacks. It is labour-intensive and time of application of chemical is very critical. Treating large number of palms within a short period of time is highly impractical. In addition to this, some dwarf varieties are highly sensitive to copper. Therefore an alternative to the existing recommendation was necessary.
In recent years, endophytic bacteria with antagonistic properties have gained importance . The main objective of the present study was a survey of potential endophytic antagonists against P. palmivora in coconut palm tissues and development of a carrier-based inoculant based on such antagonists.
Materials and methods
Source material was unfurled spindle leaves from 1-year-old WCT seedlings. Bacteria were isolated by dilution plating on nutrient agar. Purified isolates were tested against P. palmivoraby dual culture method. Natural liquid media such as molasses, coconut water and jaggery solution were tested for their suitability to support the growth of proven antagonists. Culture filtrates were used for testing their inhibitory properties in vitro on carrot agar. In vivo tests were done on 5-month-old Chowghat Orange Dwarf nuts. The suitability of coconut cake, coir dust, cow dung, neem cake, lignite, rice bran and peat soil were tested as carriers for field applications.
Results and conclusions
In our pursuits, we came across a Bacillus spp. which was present as a benign endophyte in the leaves of 1-year-old West Coast Tall coconut seedlings raised in CPCRI nursery. The population of these endophyte was of the order of 102/g dry leaf weight. This could inhibit P. palmivora to an extent of 87% in vitro in direct plating. The culture filtrate of bacteria could totally inhibit the pathogen at a concentration of 15%. Similar results were obtained when the tests were conducted in vivo on 5-month-old COD nuts. From among the substrates tried for mass multiplication, coconut liquid endosperm proved to be the best with a population density of 7-9x106cfu/ml after 72 h. Peat soil proved to be a promising carrier material for this organism for field applications.
Thus this spore-forming Bacillus sp. offers itself as a highly promising biocontrol agent against P. palmivora infecting coconut palm.
1. Menon KPV, Pandai KM, 1958. The coconut palm. A monograph. Indian Central coconut committee, Emakutam.
2. Dickie GA, Bell CR, 1995. Can. J. Microbiol 41, 284-293.