A study of some biochemical and histopathological responses of wet-stored recalcitrant seeds of Avicennia marina infected by Fusarium moniliforme

Although fungi cause a recognized problem during storage of recalcitrant seeds of many tropical species, there are no data to date on defence strategies of these seeds against fungal attack. To ascertain whether recalcitrant seeds of Avicennia marina elaborate compounds that might suppress fungal proliferation during hydrated storage, the production and efficacy of beta-1,3-glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) were studied in relation to histopathological changes. Freshly harvested seeds had low beta-1,3-glucanase and chitinase activities and fluorescence microscopy revealed progressive deterioration of the internal tissues of these seeds associated with fungal infection during hydrated storage. In seeds treated to minimize associated fungi (clean seeds), beta-1,3-glucanase and chitinase activities increased significantly during 10 d of hydrated storage. Similar high levels of activity were observed when these seeds were experimentally infected with Fusarium moniliforme and subjected to further storage. The histopathological observations indicated delayed disease development in the 10-d clean-storage period, although the hypersensitive response was not observed. The results suggest that, although the recalcitrant seeds of A. marina elaborate some antifungal enzymes, there is a lack of effective defence strategies that might lead to successful responses against fungal infections.