Beneficial Effects of Mycorrhizae in the Sustenance of Dry Zone Agriculture in Sri Lanka.

Mycorrhizal fungi lives in symbiotic relationship with roots of living plants and helps in enhancing the nutrient and water uptake. An experiment was conducted to study the beneficial association of Vesicular Arbuscular Mycorrhizae (VAM) in dry zone agriculture in Sri Lanka (represents two thirds of the country with low annual rainfall and pronounced dry seasons) with selected crops and under natural field conditions. Three locations (Madavachiya-MAD; Kiralogama-KIR; Puliyankulama–PUL) were selected to study the association of VAM under natural field conditions and rainfall. Soil collected from PUL site was  used in conducting a pot experiment to study the mycorrhizal interactions with three varieties each of selected five commonly grown dry zone crops; Vigna unguiculata (Cowpea), Sesamum indicum (Sesame), Momordica charantia, (Bitter gourd) Capsicum annuum (Chili) and Solanum lycopersicum (Tomatoes). Crop plants grown were subjected to destructive sampling; short term crops at 100%, and long term crops at 50% of flowering. Soils collected at the beginning and end of experiment were analyzed for spore counts, available phosphorous (P), zinc (Zn), pH and microbial biomass carbon. The rhizosphere soils from a well-managed site at MAD, recorded the highest live (1340) and dead (3520) spores, compared to least managed site in KIR had lowest live (213) and dead (2507) spores. In KIR and PUL, spore counts increased with time and rainfall. In the pot experiment, sesame had the highest root colonization (70.5%) and spore counts (832 spores/100 g of soil) whereas chili and tomatoes had the lowest colonization (11.8%, 7.1%), and spore counts (554, 381). Soil available P had a weak correlation with root colonization (R2= 0.49), while Zn showed a strong correlation (R2=0.79). Plant P and Zn showed strong correlations with VAM colonization of roots (R2=0.75; 0.79 respectively). Additional studies are warranted to study the effects of VAM on crop yields.