Dynamics of root and stem disease development in Arachis hypogea L. var. Spanish

Abstract

Investigations concerning the diseases of peanut (A. hypogea L. var. Spanish) caused by Rhizoctonia solani Kühn and Sclerotium rolfsii Sacc. were carried out to determine: 1. The relative pathological importance of these fungi; 2. The interrelationship of inoculum potential and other soil microflora with disease development; and 3. The influence of soil fumigants on disease development and on the total population of soil microflora. Infection due to R. solani was more prevalent in Spanish peanuts from the field experiment than that caused by S. rolfsii. Examination of harvested pods, likewise, revealed that greater damage to the fruits was caused by R. solani. Fumigation of soil with chloropicrin and DBCP (1,2-dibromo-3-chloropropane) reduced the infection of peanut plants as well as the pod infection. Chloropicrin was found to be more effective in reducing disease development than DBCP. Although fumigation of soil with chloropicrin and DBCP resulted in disease reduction in peanuts, no significant increase in gross yield of pods was observed. The low disease development in peanuts was found to correspond with the low inoculum potential of the two fungi as determined by periodic assays of nonfumigated and fumigated soils. Assays of the soils collected from the experimental plots indicated that chloropicrin reduced fungal population more effectively than DBCP. Populations of actinomycetes were greatly increased in the soils fumigated with chloropicrin. Populations of these two groups of microorganisms in the DBCP treated soils were slightly decreased. ...