Variations in hosting beneficial plant-associated microorganisms by root wilt-diseased and field-tolerant coconut palms of West Coast Tall variety.

摘要

Coconut (Cocos nucifera) in Kerala, India, are affected by root wilt, a debilitative disease caused by a phytoplasma, resulting in substantial yield loss. One of the strategies to combat this problem involves breeding for root wilt-resistant/tolerant palms by exploiting the genetics of disease escapees identified in the heavily diseased tracts. A preliminary study on the rhizosphere microflora of these disease escapees and diseased coconut palms revealed that the bacterial population ranged from 6.2 to 12.4x105 cfu [colony-forming units]/g dry soil in the rhizosphere of root wilt-infected palms, but was only 1.0 to 8.3x105 in field-tolerant palms. The population of actinomycetes was higher in field-tolerant palms, whereas the population of fungi was similar between infected and tolerant palms. Among the function-specific microbes, the number of cellulose degraders and phosphate solubilizers did not differ much in both diseased and field-tolerant palms. However, significantly higher counts of N2-fixers (maximum of 104x102 cfu/g dry soil) and silicate solubilizers (6x102 cfu/g dry soil) were recorded in field-tolerant palms compared to diseased palms (maximum of 34x102 and 1.0x102 cfu N2-fixers and silicate solubilizers/g dry soil, respectively). At a 25- to 50-cm depth, the overall microbial counts in both the diseased and field-tolerant root wilt palms were lower than at a 0- to 25-cm depth. Diseased palms had higher bacterial population, but these included only 0.21% of beneficial microbes, while the root wilt-tolerant palms generally had lower bacterial population, but had 3.6% of beneficial microorganisms. The occurrence of higher population of beneficial plant-associated microbes, particularly silicate solubilizers, in the rhizosphere of disease-tolerant palms, and the probable mechanisms they endow to such palms to evade the phytoplasmal infection are discussed..