Some implications of associated mycoflora during hydrated storage of recalcitrant seeds of Avicennia marina (Forssk.) Vierh.

Abstract

Three questions are considered in the context of the possible effects of seedassociated

mycoflora, typified by Fusarium moniliforme, during hydrated

storage of recalcitrant seeds of the tropical species, Avicennia marina. These

are: 1) whether fungal infection reduces storage lifespan; 2) whether seeds

become more susceptible to fungal attack during storage and whether they

posses defence mechanisms that might suppress fungal proliferation in

hydrated storage (production of antifungal compounds and 13-1,3-glucanase

(EC 3.2.1.39) and chitinase (EC 3.2.1.14)] and 3) whether it is possible to

discriminate ultrastructurally between inherent deteriorative changes and

those that are fungally-induced.

1) The data indicate unequivocally that if fungal activity is curtailed, then the

hydrated storage lifespan of A. marina seeds can be considerably extended.

2) When inoculated immediately with F. moniliforme, newly harvested seeds

were extremely susceptible to the adverse effects of the fungus, while seeds

that had been wet-stored for 4 days showed a considerably heightened

resilience to the effects of the fungus prior to inoculation. The enhanced

resilience, although declining, persisted in seeds stored hydrated for up to 10

days prior to inoculation, being lost after 12 days. This finding was supported

by significant increase in 13-1,3-glucanase and chitinase and in antifungal

compound production during 10 days of wet storage. After 14 days of wetstorage,

seeds become more susceptible to the effects of fungusthanthose in

the newly harvested condition.

3) The resilience of seeds that had been stored in the short-term was

associated with ultrastructural changes indicative of enhanced metabolic

activity associated with the onset of germination (e.g. increase in vacuolation,

well-developed mitochondria and endomembrane system [ER and Golgi

bodies]). However, with sustained stress associated with wet-storage

IV

conditions, the seeds became increasingly badly affected by the fungus,

showing some ultrastructural fungally-induced abnormalities (e.g. nuclear

lobing, presence of lipid bodies and prevalence of Golgi bodies that had many

associated vesicles) and a decrease in 13-1,3-glucanase and chitinase activity.

It is suggested that the decreased susceptibility of A. marina seeds during

short-term storage relies on the ability to create an antifungal environment

prior to infection (through synthesis and accumulation of pre-formed and

induced antifungal compounds and antifungal enzymes), which would also be

an effective strategy during germination in the natural environment.