M.Sc.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous, which promote the plant growth by assisting in nutrient uptake and also mitigate several biotic and abiotic stresses in plants. Soil temperature, soil moisture, soil pH and nutrient availability are the major factors that affect the diversity, distribution and activity of AMF. The arbscular mycorrhizal fungi are obligate symbiont and require a host plant to complete its life cycle. Solenostemon rotundifolius or Chinese potato is one of the important minor tuber crop of Kerala, which is rich in starch, proteins, vitamins and minerals, with 70- 90% mycorrhizal colonization.
The present study was undertaken to assess the effect of soil microclimatic parameters and microbial activities on the population and diversity of AMF and also evaluate the influence of AMF on the growth and yield of Solenostemon rotundifolius. The field experiment was conducted in a randomized complete block design (RCBD) with nine treatments and three replications at Agronomy farm, College of Horticulture, Vellanikkara during 2017 to 2019. The treatments consisted of five AMF species viz., Rhizophagus fasciculatus (T1), Funneliformis mosseae (T2), Glomus etunicatum (T3), Acaulospora sp. (T4), and Gigaspora sp. (T5), consortium of AMF (T6), POP recommendations of KAU, 2016 (T7), Organic POP of KAU, 2017 (T8) and absolute control (T9).
Per cent AMF root colonization was higher (93.33%) in Rhizophagus fasciculatus (T1), Funneliformis mosseae (T2), Acaulospora sp. (T4) and T6 (T1 +T2 +T3 +T4 +T5). Spore population varied between the months, but highest spore population were recorded at 30 DAP and 120 DAP, whereas lowest was at 60 DAP. However, AMF spore diversity was highest in T6 (T1 +T2 +T3 +T4 +T5) throughout the experiment.
AMF spore count and per cent root colonization increased with soil temperature but, not affected by soil moisture and soil pH. However, AMF spore diversity decreased with soil pH.
Funneliformis mosseae (T2) and consortium of AMF (T6) recorded highest dehydrogenase activity throughout the experiment. Carbon dioxide evolution was
highest at 120 DAP, in Gigaspora sp. (T5), which was on par with Acaulospora sp. (T4) and Funneliformis mosseae (T2). Acid phosphatase activity was highest in Funneliformis mosseae (T2) followed by Acaulospora sp. (T4).
Per cent root colonization by AMF was positively correlated with dehydrogenase activity, CO2 evolution and acid phosphatase activity. AMF spore population was positively correlated with dehydrogenase activity and CO2 evolution. AMF spore diversity was positively correlated with CO2 evolution and acid phosphatase activity.
Funneliformis mosseae (T2) showed better performance with respect to biometric characters (plant height, root biomass and dry weight) of the plant. AMF consortium (T6) treated plants recorded highest (16.98 t ha-1) tuber yield, which was also on par with T1 (Rhizophagus fasciculatus), T2 (Funneliformis mosseae), T4 (Acaulospora sp.) and T7 (POP recommendations of KAU, 2016). Phosphorus uptake by Chinese potato plants were highest (60.06 kg ha-1) in T2 (Funneliformis mosseae) and lowest in absolute control. Plant biometric characters, tuber yield and P uptake in Chinese potato were enhanced with AMF root colonization.
Consortium of AMF (T6), Rhizophagus fasciculatus (T1) and Acaulospora sp. (T4) treated plots were recorded with less nematode population (506.67 to 559 nematodes per 250 g soil).
The present study indicated that soil temperature affected AMF root colonization and spore count. Increase in soil microbial activities (dehydrogenase activity, CO2 evolution and acid phosphatase activity) showed increased root colonization, spore count and spore diversity. AMF root colonization enhanced growth, phosphorus uptake and yield of plant. Funneliformis mosseae (T2) was the most promising AMF for improving the growth, yield and phosphorus uptake in Solenostemon rotundifolius. However, extensive field studies are needed under different seasons and agro ecological zones, in order to develop an abiotic stress tolerant AMF for Chinese potato plant.