A multifactorial study of conditions influencing longevity of neem (Azadirachta indica) seeds

The longevity of neem, Azadirachta indica, seeds from African Sahelian (Bur kina Faso) and Asian (Sri Lanka) provenances was studied over two years of storage under different conditions of moisture and temperature. After dryin g to equilibrium moisture content (MC) at different relative humidities at 20 degrees C, seeds were placed in open storage at 20 degrees C or hermetic ally sealed in packets at temperatures ranging from -20 to +20 degrees C. T here was hardly any difference in storage behaviour between seed batches / lots, whatever their provenance. Seeds originating from mature yellow fruit s lived longer than seeds from green or brown fruits. In all storage experi ments with seeds having MCs greater than or equal to 10%, viability was pre served best at 10-15 degrees C, indicating that neem seed is chilling (and freezing) sensitive. There was no survival longer than 2 years under these conditions. At MCs of 4-8%, seeds were considerably more tolerant of low te mperature storage and had 40-60% viability after 2 years at all temperature s tested (-20 to +20 degrees C). However, the seeds were sensitive to imbib itional stress, which could be alleviated by imbibition at temperatures of 25-30 degrees C or above. The difficult storage behaviour of neem seed seem s to stem from: (1) the sensitivity to low temperatures at MCs greater than or equal to 10%; (2) the extreme sensitivity to imbibitional stress after storage at less than or equal to 8% MC; (3) underestimation of the water ac tivity due to the high oil content of the neem seeds, causing unexpected me tabolic stress in the higher MC and temperature range.