Vesicular arbuscular mycorrhizal (VAM) spores showed great variation In their distribution in soil of wheat (Triticum aescivum L.) fields of 8 District of Sindh with higher VAM infection was greatly dispersed (R=1161) in soil of the Nawabshah district with higher VAM infection and lower foot and root rot disease of wheat. There was least dispersion of VAM spores(R =559) with lower VAM infection and higher foot and root rot disease of wheat in Jaccobabad district. A positive and significant correlation was found between the number of YAM spores in the rhizospheric regions and extent of YAM infection in roots of wheat vars.
Twenty two VAM species belonging to 5 genera were found present in the rhizospheric regions of wheat where Glomus was represented by 14 species, Acaulospora by 5 species and Gigspors, Selerocystis and Scutellispora were represented by one species each. Similarly 21 species of fungi belonging to 10 genera were isolated from foot and root infected tissues of 6 wheat vars. where Drechslera sorokiniana, Fusarium culmorum, Pythium aphanidermatum and Rhizoctonia solani produced root rot disease on inoculation in all the 6 wheat vars.
In the wheat fields of Sindh 20 weed species growing in and out of wheat season showed VAM infection in their roots where Avena sativa, Choloris barbata, Cynodon dactylon, Dichanthium annulatum, Lolium temulentum, Polypogon monspeliensis of the family Graminae showed higher VAM infection. of the 22 VAM species isolated from the soil of wheat fields, 10 VAM species were Common in the rhizospheric regions of wheat vars. and weeds.
VAM spores showed greater viability in soil with wheat crop and low in soil without wheat crop. Highest viability percentage was found during March / April in soil with wheat crop which gradually declined and become lowest during September/October in soil with no wheat crop. of the 8 districts, VAM spore8 inisoi1 of Nawabshah district showed greater viability whereas it lowest in the soil of Jaccobabad district. Spores of the 6 Glomus species was kept in soil in small plastic pots at 5 °C and 10°C (±1°C) showed a gradual loss in viability after 2 years. Loss in viability was greater when the Glomus spp. were kept in soil pots under field condition with temperature 10 °C to 25°C during winter and 22°C to 38°C during summer season. of the 6 Glomus species, G. macrocarpum retained highest viability and G. warcupii showed lowest viability after 2 years.
The total phosphorus content in soil samples of fallow fields was higher than in cultivated fields and the status of available phosphorus was lower in soil of fallow fields than cultivated wheat fields of Sindh. Available phosphorus in soil samples from cultivated wheat fields of Hyderabad, Mirpurkhas, Nawabshah and Thatta districts was 0.02, 0.04, 0.03, 0.04 % respectively I whereas in the remaining 4 districts available phosphorus was below the standard level (0.01 %).
On inoculation with a single spore of the six species of Glomus separately in roots of the 6 wheat vars. groom in pots, VAM infection took place slightly without producing any marked effect on plants growth over the control. On inoculation with axenic & mixed soil base inocula and axenic & mixed rhizo base inocula @ 10 g, 20 g and 40 g / 200 g soil, all the 6 wheat vars. showed better response in respect of growth and yield over the control. showed inocula of soil base or rhizo base produced better response than axenic Inocula of soil base and rhizo base. The mixed rhizo base inocula produced most significant response when inoculated @ 40 g / 200 g soil in all the wheat vars. especially in wheat var. Blue Silver. On inoculation with mixed rhizo base inocula in pots containing soil deficient in phosphorus (@ 0.0053 mg / kg soil-PO) adjusted at 4 different levels viz , @ 12.5 mg / kg soil (PI), 25.0 mg /kg soil (P2), 37.5 mg /kg soil (P3) and 50.0 mg /kg soil (14), the 6 wheat vars. showed significant response at P1and P2 levels than without inoculation. At higher phosphorus levels (P3 and P4) there was no significant response in respect of VAM infection, fresh & dry weights and phosphorus concentration in plant tissues with or without inoculation. Inoculation with mixed rhizo base inocula of the 6 Glomus species in microplots deficient in available phosphorus (0.003 %), showed significant response when used @ 30 g / 65 cm row as compared to the doses of 10 g and 20 g / 65 cm row. Wheat var. Blue silver showed better response than l1exi-Pak, Pak-70, Pavon, Sindh-83 and ZA 77.
Separate or combined inoculation with G. macrocarpum and G. mosseae in soil pots with wheat var. Mexi-Pak resulted in the increase of population of both the VAM fungi in rhizospheric region at maturity of the plants over the control whereas similar inoculation of D. sorokiniana and P. culmorum in a similar setup showed exponential increase in population of both the fungi in the rhizospheric region up to growth stage and thereafter the population gradually declined with the age of plant. When D. sorokiniana and F. culmorum were interacted individually either with G. macrocarpum or G. mosseae the population of D. sorokiniana was reduced in the presence of G. macrocarpum and he population of F. calmorum was reduced in the presence of G. mosseae at S1 growth stage. When D. sorokiniana and F. culmorum were interacted separately in soil pots with mixed inocula of G. macrocarpum and G. mosseae, the population of both the parasitic fungi was significantly reduced at S1 growth stage which resulted in the inhibition of root rot disease complex of wheat.