Seeds of Azadirachta indica A. Juss: Orthodox or Recalcitrant?

Abstract

Seeds are classified into two categories, i.e. orthodox and recalcitrant, depending on their physiological behaviour. Azadirachta indica (Neem) is a well-known medicinal plant that thrives well in tropical regions. There are different views regarding the nature of the Neem seeds. Some researchers say that it is orthodox, while others say it is recalcitrant by nature. The present study was carried out to classify the Neem seed, as proper categorization is important in terms of seed viability. Healthy seeds (average weight 0.32 g) were collected. Seed sowing for control was done immediately after collection of seeds, while for treatments (T₁ and T₂), the seeds were stored in different climatic conditions. For T₁, the seeds were air-dried (temperature 29.7 °C; relative humidity < 57%) and for T₂, the seeds were just kept in open tray (temperature 33.7 °C; relative humidity > 98%). The germination for control was 86%, while for T₂, it was 50%. No seed germination was observed in T₁. Likewise, for control and T₂, initiation of germination was 9.66 and 10.33 days, mean germination time was 8.33 and 11.98 days and germination rate was 1.94 and 1.77 per day, respectively. No germination in T₁, 30% increase in mean germination time and 9% poorer germination in T₂ indicated the limited tolerance of the Neem seeds towards desiccation. These findings along with the complete loss of viability in T₁ and poorer germination in T₂ in comparison with the control indicate the loss of moisture in seeds below critical limit, thus indicating the recalcitrant nature of the Neem seeds.