Deciding when to harvest

The image shows rice plants growing at IRRI.

  

CGIAR scientists at the International Rice Research Institute (IRRI) conducted a series of experiments to investigate the impact of seed maturity at harvest on longevity in storage. In one set of experiments, twenty Oryza sativa accessions were harvested at 24, 31, 38 and 45 days after flowering. They were then dried in the genebank’s drying room, grown-out, and their longevity (p50) calculated. In many cases, the greatest longevity was in seeds that had been harvested at 45 days, although some peaked at 38 days and declined after that. Figure 5 shows what a difference a delay can make:

The graph shows how viability of twenty different accessions of rice is affected by the timing of harvesting. The x axis shows the harvesting date (days after flowering). The y axis shows the length of time it takes for viability to fall to fifty percent. In most accessions, the viability improves when harvested after twenty-four days. A few accessions reach peak viability when harvested at thirty-eight days, while others show peak viability when harvested at forty-five days. Some flatten out between thirty-eight and forty-five days.
Figure 5: effect of harvest time on longevity

By allowing seeds to mature for as long as possible on the parent plant, it is possible to improve their longevity in storage. But the seed’s maturation process is not the only pre-storage factor that can have an effect on longevity. The weather can make a difference too.

Seed dispersal mechanisms

Conditions in the field