Pollen viability in lychee

Abstract

The lychee (Litchi chinensis Sonn.) has two types of pollen-releasing flowers-M1 and M2. We compared the morphology and viability of these two pollen types, mainly for the two commercial cultivars in Israel: 'Mauritius' and 'Floridian'. Observation by scanning electron microscope did not reveal any consistent morphological differences between the two pollen types. However, M2 pollen was found to have a consistent and significant advantage over M1 pollen in in vitro germination tests. M2 pollen from 'Mauritius', 'Floridian', 'No Mai Chee', 'Wai Chee', and 'Early Large Red' had a much higher germination rate at 15, 20, 25, 30, and 35 °C than M1 pollen from those same cultivars. The optimal incubation temperature for in vitro pollen germination was 30 °C for M2 pollen of all five cultivars studied; adequate germination rates were also found at 35 and 25 °C. The optimal temperature for M1 pollen germination was also 30 °C for 'Mauritius' and 'No Mai Chee', but was not well defined for the other three cultivars. No pronounced advantage of M2 pollen-tube growth could be discerned 48 h after hand pollination. However, final fruit set was consistently and significantly higher after hand pollination with M2 pollen, relative to M1 pollen. Hot (32/27 °C) and warm (27/22 °C) regimes during flower development had a pronounced detrimental effect on pollen viability compared to a cool (22/17 °C) regime. 'Floridian' was much more susceptible than Mauritius in this respect.