The effect of fungal colonization on the morphine production of poppy (Papaver somniferum L.) capsules

Abstract

SUMMARYAbnormally low concentrations of morphine in capsules of poppy (Papaver somniferum L.) in the 1970–1 season were associated with heavy fungal colonization. The effect of fungal colonization on the morphine production of capsules was later studied in a series of field, glasshouse and in vitroexperiments.In a field experiment morphine concentration of severely colonized (> 30% surface cover) intact capsules was 20% less (P <0·01) than slightly colonized (< 10% surface cover) capsules. Colonization of these field-grown capsules was generally localized in the top half and the morphine concentration of the top half was about 20% less than the bottom half for all colonization categories. In contrast, glasshouse-grown capsules were free of fungal colonization and the top and bottom halves had similar morphine concentrations.In a field experiment studying the effect of fungicides, 2 kg benomyl (50% a.i.) + 2 kg mancozeb (80% a.i.)/ha were applied as a spray at 10-day intervals from flowering till 1 month after commercial harvest and plants were harvested at weekly intervals from 10 days after full bloom. The mean dry-matter yield of sprayed capsules was 11% greater (P <0·01) than non-sprayed with a similar trend for morphine concentration and morphine yield. In addition, the sprayed treatment significantly reduced the area covered by sporulating lesions on the surface of the capsule after dry maturity. This superficial fungal cover had a NNE orientation in both sprayed and non-sprayed capsules.In an in vitroexperiment using capsules from the field fungicide study, fungi were isolated from the interior of green capsule wall tissue as early as 17 days after flowering. Colonization increased with successive harvests and culturing of fungi from the interior of capsule wall tissue showed the presence of fungi in both sprayed and non-sprayed capsules with no difference in the degree of colonization.Two of the major fungi isolated from the field experiment were identified as Dendryphion penidllatum (Corda) Fr. and Alternaria alternata (Fr.) Keissler and the individual effect of these was assessed in an in vitro experiment using ground capsule material. D. penidllatuvi and A. alternata reduced the morphine concentration of ground capsules in 24 days to 7 and 11% respectively of non-inoculated controls.