POLLEN VIABILITY IN LYCHEE

The lychee (Litchi chinensis Sonn,) has two types of pollen-releasing flowers-M-1 and M-2. 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 microsco pe did not reveal any consistent morphological differences between the two pollen types, However, M-2, pollen was found to have a consistent and significant advantage over M-1 pollen in in vitro germination tes ts. M-2, 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 degrees C than M-1 pollen from those same cultivars, Th e optimal incubation temperature for in vitro pollen germination was 3 0 degrees C for M-1 pollen of all five cultivars studied; adequate ger mination rates were also found at 35 and 25 degrees C, The optimal tem perature for M-1 pollen germination was also 30 degrees C for 'Mauriti us' and 'No Mai Chee', but was not well defined for the other three cu ltivars. No pronounced advantage of M-2 pollen-tube growth could be di scerned 48 h after hand pollination. However, final fruit set was cons istently and significantly higher after hand pollination with M-2 poll en, relative to M-1 pollen, Hot (32/27 degrees C) and warm (27/22 degr ees C) regimes during flower development had a pronounced detrimental effect on pollen viability compared to a cool (22/17 degrees C) regime ,'Floridian' was much more susceptible than 'Mauritius' in this respec t.