Arbuscular mycorrhizal fungi modulate physiological and morphological adaptations in para rubber tree (Hevea brasiliensis) under water deficit stress

Abstract

Budding master stock of an elite clone- RRIT251 (a high latex yield clone) of para rubber (Hevea brasiliensis), and root stock of RRIM600 (a drought tolerant clone) were selected as initial plant materials. Arbuscular mycorrhizal fungi (AMF) were chosen for inoculation (+AMF). Both +AMF and non-inoculated (‒AMF) soils were kept for 30 d, and subsequently subjected to water deficit (WD) conditions through water withholding for 14 d (11.45% soil water content). Root colonization and frequency percentage of AMF were observed only in the AMF-inoculated plants. AMF colonization was reflected through increased total phosphorous content in the leaves (0.52 mg g−1 DW) and it correlated positively with number of roots (r = 0.95). Under drought stress, enrichment in free proline (45.14 µmol g−1 FW) and total soluble sugar content (211.7 mg g−1 DW) in AMF-inoculated plants functioned as major osmolytes for the maintenance of cellular osmotic potential. This led to retention of the photosynthetic pigments, chlorophyll a fluorescence (Fv/Fm and ΦPSII), net photosynthetic rate (Pn), and stomatal closure. In summary, physiological and biochemical changes in AMF inoculated plants under WD conditions act as an adaptive strategy for the maintenance of overall growth performances in terms of root fresh weight, root dry weight, shoot height, number of leaves, shoot fresh weight and shoot dry weight. The study concludes that AMF inoculation in para rubber improves its adaptation to the natural ecosystem, especially in the dry season. Thus, AMF inoculated master stocks of para rubber should further be tested in the multi-location field trials to validate the hypothesis of rapid adaptation to the natural ecosystem, especially in the rainfed regions.