PARENT SESSION
Poster Session # 8: Agro-Ecology.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Isolation and identification of cyanogenic rhizobacteria from the roots of peach [Prunus persica (L.) Batsch].

Tanner, Shann^*,1, Wells, Christina¹, Reighard, Gregory¹, Kluepfel, Daniel¹, Riley, Melissa¹, ¹ Clemson University, Clemson, South Carolina

ABSTRACT- Peach replant disorder (PRD) occurs when peach trees are replanted to an orchard previously cropped with peaches: lower growth rates and yields are observed in the replanted trees. Methyl bromide fumigation adequately controls PRD, suggesting that the disorder is the result of harmful interaction(s) between the soil faunal community and peach roots. As methyl bromide fumigation is phased out, the task of determining the specific cause of PRD is now an important goal. One theory suggests that prunasin (D-mandelonitrile -D-glucoside), a cyanogenic glycoside found in peach tissues, may play a critical role in replant disorder. Many soil bacteria have the ability to degrade cyanogenic glycosides and release cyanide, a potent respiratory poison. Bacteria capable of degrading prunasin may release cyanide when feeding on decomposing roots of old peach trees, thus inhibiting root growth of the new trees. We examined the rhizosphere bacterial community of peach to determine whether it contained bacteria capable of evolving cyanide from prunasin. Rhizobacteria were isolated from the fine roots of 7-year-old peach trees on M9 carbon source utilization media containing 0.05% prunasin as the sole carbon and nitrogen source. Five visually distinct colonies were selected and grown-out in pure culture on trypticase soy broth agar (TSBA) plates. The prunasin-degrading rhizobacteria were then tested for their cyanogenic potential using a picrate paper assay. All five prunasin isolates exhibited some cyanogenic potential; two strains were strongly cyanogenic. The cyanogenic isolates were identified using fatty acid methyl ester (FAME) analysis, and the two strongly cyanogenic strains were identified as Arthrobacter globiformis and Cellulomonas cartae. To determine whether cyanogenic bacterial activity can cause growth reductions in peach trees, we are inoculating peach seedlings with the cynanogenic bacterial isolates in the greenhouse and monitoring their growth and root system development.

Key words: Rhizosphere, Deleterious rhizobacteria, Prunus persica (L.) Batsch, Cyanide