Effect of Phosphorus and Micronutrients

Fertilization Accompanied with VA- Mycorrhizal Fungi in Controlling Rhizoctonia Damping-off on the Growth and Nutritional Status of

Cotton Plants

[74]

Elwan¹, I.M.; Samya E.H. Omran² and Hoda Z. Mohamed³

ABSTRACT

An experiment was carried out under outdoor conditions to study the effect of phosphatic, iron and manganese fertilization along with VA-mycorrhizal inoculation as a biocontrol agent on Rhizoctonia damping-off , growth and nutritional status of cotton plants. Results show a significant reduction of disease incidence pre and post-emergence of cotton seedlings.Also, inoculating the soil with obligate symbiotic fungi (VAM), compared to un-inoculated soil, gave the highest percentage of healthy survival cotton seedlings. Shoot and root dry weights of cotton mycorrhizal plants were significantly higher than in non-mycorrhizal plants grown in either  infested or non-infested soils. Data also show that  iron treatment increased dry matter content of shoot by 18% at lowest P level, but at the highest level of P, the iron treatment increased shoot dry weight three times than at the lowest level. An opposite trend was obtained with Mn treatments at the highest P level. The highest response to mycorrhizal inoculation in root dry weight was obtained at P_IIMn_I and P_I in infested and non-infested soils respectively. For relative water content of cotton leaves, data show that mycorrhizal infection had a negative but non significant effect on RWC% in either infested or non-infested soils, except at P_IFe_I and P_IFe_II in infested soil along with P_I, P_IIFe_II and P_IIMn_II in non-infested soils. Plants grown in infested soils had a  higher values of root mycorrhizal colonization compared to non infested soils at all concerned treatments. Chlorophyll a, b and carotenoid of cotton mycorrhizal plants were significantly higher than in non mycorrhizal plants grown in soil infested with Rhizoctonia solani. In mycorrhizal cotton plants, P fertilizer,
regardless of iron or Mn treatments, decreased K content in either infested or non-infested soils. An opposite trend was obtained with non-mycorrhizal plants. In
infested soil, iron treatment increased K- content in either mycorrhizal or non-mycorrhizal plants at both P-levels. The same trend was observed with Mn treatment, except at P_IIMn_I with mycorrhizal inoculation. The superior treatments for P content in infested soils were (P_IIFe_II + VAM) and (P_IIMn_I + VAM) but (P_IFe_I + VAM) and (P_IIMn_II + VAM) treatments in non-infested soils. For Mg content in
infested soils, iron treatments generally increased but Mn treatements decreased Mg content in mycorrhizal and non-mycorrhizal plants at all P-levels. Regardless of P, mycorrhizal inoculation increased both Fe and Mn contents in cotton plants. Iron content decreased with increasing P-level in both mycorrhizal and non-mycorrhizal cotton plants grown on infested soils regardless of Fe and Mn treatments. An opposite trend was found in non-infested soils. Iron content increased with increasing iron level in infested soils and decreased in non-infested soils irrespective of P-level and mycorrhizal inoculation. On the other hand, in both infested and non-infested soils, iron content decreased with increased Mn level regardless of mycorrhizal
inoculation. However, Mn and Zn contents slightly changed in both infested and non-infested soils by increasing P-level, regardless of Mn, Fe and mycorrhizal treatments. Also, increased Fe and Mn levels slightly increased or decreased Mn content in both infested and non-infested soils, regardless of mycorrhizal inoculation and P-level.