Diversity of arbuscular mycorrhizal fungi and P-solubilising bacteria in rubber tree rhizospheres in Thailand

Rubber tree (Hevea brasiliensis) is a crop of major importance for smallholders in Southern Asia because it produces latex, a substantial source of income for farmers. Rubber tree can grow on very poor soils (sandy soils, low fertility, subject to erosion and leaching of applied fertilizers), which are unsuitable for other commonly cultivated cash crops. It covers 2.7 million ha across Thailand, but its establishment in areas with very poor soils, especially in Northeast Thailand, represents a major potential for increased production. The important roles of rhizosphere microbial communities in supporting soil fertility and plant nutrition has been widely recognized. In particular, root -interacting P-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) contribute to plant P nutrition by increasing mineral nutrient availability and by enhancing plant nutrient uptake. The diversity of AMF in roots and of PSB in rhizosphere soil was assessed along a chronosequence of rubber tree plantations (3, 6 and 16 year-old) and compared to cassava fields. AMF diversity was assessed by 454 sequencing of SSU 18S rDNA. PSB strains were characterized after culturing on selective media. AMF communities in cassava roots were twice as rich as in rubber tree samples. AMF diversity was not affected by the age of rubber trees, but was related to the soil P content. The improved understanding of the diversity of root-or rhizosphere-associated microbes will contribute to the development of alternative sustainable practices to improve and sustain soil fertility. (Texte intégral