Integrated control of dodder (Cuscuta pentagona Engelm.) using glyphosate, ammonium sulfate, and the biological control agent Alternaria destruens Simmons, sp. nov.

摘要

Cuscuta pentagona is an obligate parasite that is the most widespread and aggressive Cuscuta species in the world. It causes a serious weed problem in many economic and ornamental crops. Its minutely sized, easily dispersed, and highly viable seed makes it difficult to control. Alternaria destruens has been developed as a registered bioherbicide for Cuscuta species. A host-range study using 30 plants of economic importance belonging to 8 families ( Asteraceae, Convolvulaceae, Fabaceae, Malvaceae, Meliaceae, Poaceae, Rutaceae , and Solanaceae) indicated that A. destruens is pathogenic only to Cuscuta spp. In greenhouse trials of efficacy, seven treatments were applied: an untreated control; oil (PCC 588); A. destruens (Smolder(TM) WP); a mixture of A. destruens + oil; ammonium sulfate at 0.125% w/v in water; glyphosate at 0.02 kg (ae)/L of Roundup ProRTM; and a mixture of A. destruens + oil, glyphosate at 0.02 kg (ae)/L of Roundup Pro RTM, and ammonium sulfate at 0.125%. By 35 days after treatment, all Cuscuta plants treated with the last treatment were dead but not the host plant, citrus. Efficacy of A. destruens was further assessed in field trials. Four treatments consisting of an untreated control, oil, A. destruens + oil, and A. destruens were tested, but the levels of control did not differ among the treatments. To determine if this lack of difference was due to pathogen's dispersal, Alternaria isolates from randomly chosen Cuscuta tissue samples were collected from field and greenhouse trials and studied using nuclear rDNA internal transcribed spacer (ITS) region, including ITS1, ITS2, and the 5.8S rDNA. Neighbor joining analysis revealed that all 47 unknown isolates and the reference A. destruens isolate were 100% identical. The results indicated a high degree of conservation of the ITS region in A. destruens which made it impossible to conclude that the isolates from field and greenhouse samples were the same as the reference isolate used in these trials. Overall, this study has confirmed the effectiveness of an integrated system consisting of A. destruens , glyphosate, and ammonium sulfate to control Cuscuta spp.