The characteristics of litchi pollen have drawn increasing attention in recent years. Previous studies indicated that there are significant differences in the quantity and viability of litchi pollen grains among different varieties and flowering stages. Moreover, the same variety may show a different quantity of pollen grains and viability in different years. There is still a lack of systematic studies on the change of pollen germination rate and pollen amount in different varieties and at different flowering stages. In this study, the changes in the germination rate of pollen at different development stages were studied. It was primarily revealed that the pollen germination rate already approached its peak upon the filament extends fully, but the anther does not dehisce the developmental stage. In 2009 and 2010, the viability and number of pollen grains per anther were investigated in 65 litchi cultivars, and a difference was observed among cultivars. The pollen germination rate ranged between 20.14% (‘Wuchali’) and 54.69% (‘Donlongmili’). The number of pollen grains per anther ranged between 1555 (‘Zhongshanzhuangyuanhong’) and 7455 (‘Houye’). Sixty-five litchi cultivars were classified into six clusters based on the pollen quantity and germination rate. Most litchi cultivars can produce large amounts of viable and compatible pollen grains during the flowering period. Thus, our results indicate that the pollen amount and germination rate might not be the only factors restricting the successful pollination of litchi.
To find efficient ways to increase the percentage of seed germination and seedling emergence in litchi (Litchi chinensis Sonn.), we investigated the effects of soaking and high temperature on seed germination, as well as the influence of seed placement (orientation and burial depth) on seedling emergence. Seeds of most tested litchi cultivars soaked in water had a better germination performance than seeds without soaking. More than 90% germination of tested litchi seeds was obtained when the soaking times were 26–54 hours. During presprouting, short-term high temperatures (37–44 °C) exerted a negative effect on seed germination rate, but did not influence the germination percentage. In addition, high temperatures (>42 °C) compromised the further growth of sprouted litchi seeds. Burial depth and seed orientation both significantly influenced the seedling recruitment. There was a reduction in seedling emergence with an increase in burial depth. Seeds at the depth of 2 cm showed the best seedling emergence with an average percentage of 90%. Litchi seedling emergence was greatest and most rapid when seeds were sown 2 cm deep, positioned flat, on their sides, and with the radicle oriented downward.