ANATOMICAL STRUCTURE OF 2 DAY-OLD LITCHI OVULES IN RELATION TO FRUIT-SET AND YIELD

The anatomical structure of litchi ovules was studied in two day old f emale flowers of cvs. Mauritius and Floridian. The typical litchi ovar y has two ovules. The embryo sac was absent from about 45% of the 495 ovules studied; in about 20% of the flowers, both ovules lacked an emb ryo sac. While most embryo sacs had a normal polar nucleus, most did n ot have a normal egg cell or synergids. The percentage of flowers foun d to have at least one normal ovule, and so could be considered as hav ing the potential for fruit set, fluctuated between 3.2 and 27.0. A fe w 'Mauritius' flowers were sampled in 11 mature commercial orchards fr om labelled inflorescences; almost all female flowers in these inflore scences were hand-pollinated. A significant positive correlation was f ound between the percentage of flowers with at least one normal ovule and initial fruit set in the same inflorescences, and even between the former and orchard yield. The presence of at least one normal synergi d was found to be significantly correlated with the percentages of bot h normal flowers and initial fruit set. These findings suggest that ov ule abnormality is one of the main factors responsible for poor litchi production. Two year old litchi plants, with small emerging infloresc ences, were kept under one of three temperature regimes (day/night): c ool (22/12 degrees C), warm (27/17 degrees C) or hot (32/22 degrees C) . Ovule normality was determined in two day old female flowers. Warm, and especially the hot temperature regimes were found to have a pronou nced detrimental effect on flower development, with 'Floridian' being more susceptible than 'Mauritius'.