Stratification and Incubation: Essential for Pecan Germination?

Abstract

Pecans (Carya illinoinensis L.) germinate heterogeneously and in low percentages, but by applying pre-germination treatments, such as imbibition, stratification, incubation and the application of hormones, the rate of germination can be homogenized and the percentage of germinated seeds can be increased. Taking into account the results of previous investigations, it is necessary to compare the effect of stratification without media against the effect of wet stratification in pecans to determine an optimal pre-germination treatment. The objective of this investigation was to evaluate germination induced by bare and wet stratification in mature pecans. Three pre-germination treatments were applied to seeds of cultivars Wichita and Western Schley, namely: stratification without media (stratification at 4 °C for one month, followed by incubation at 30 °C for 17 days), wet stratification (stratification at 4 °C with irrigation supply, for one month, followed by incubation at 30 °C for 17 days) and a control (naked stratification at 4 °C for one month, followed by greenhouse seeding). Here we show that stratification without media, followed by incubation at 30°C, can have a significant beneficial effect on germination percentage, shoot and root length, as well as decreasing the incidence of microbial infections in pecans. The positive effect of incubation on pecan germination observed in this research agrees with the results of previous works. It was observed that the germination percentage of the pecans of cv. Wichita was significantly superior to bare stratification compared to wet stratification. The results imply that many pecan seeds can prescind from incubation to complete the germination process, however, the percentage of pecans of cv. Wichita that germinated was six times superior when including an incubation stage in the pre-germination treatment. In the case of pecans of cv. Western Schley, the percentage of germination was 28 times higher in the incubated seeds, in comparison with pecans that were not incubated. On the other hand, the present study was unable to prove the need of stratification in inducing germination of pecans, since all the pecans used in this experiment were stored in refrigeration before being subjected to the different treatments.