SEX EXPRESSION AND FLOWER ANATOMY OF LITCHI (Litchi chinensis Sonn.)

Abstract

Litchi flowers differ in their degree of development and they are classified in Types I, II and III, according to their sex expression and order of appearance along the inflorescence. Flowers Types I and III function only as males, whereas Type II act like females. In Culiacán Valley, Sinaloa, México, ‘Brewster’ litchi bloom period last for 52 d. Flower orientation (north or south) on the tree affected their sexual expression. Type I flowers were more abundant in the south (85 %), that in the north (54 %), and it was the only type observed during the first 8 d of bloom. Type II flowers initiated anthesis 12 d after the beginning of flowering; they also outnumber (27 %) the other types in north-oriented inflorescences. Type III flowers started anthesis 20 d after the beginning of bloom, mostly in the north sections (19 %), as compared to southern ones (4 %). In ‘Brewster’ litchis the general distribution of flower Types I, II and III was of 70, 19 and 11 %, respectively, with Type I as the earliest and III as the latest. Type I flowers have a hardly visible ovary (1 mm in length) and presented a rudimentary ovule. Type II showed complete ovules without irregularities, whereas Type III ovaries, were also complete, although smaller than in Type II, however their nucellus and integuments have deformities. Styles are dichotomous and only Type II have stigma. According to pistil morphological and anatomical characteristics, the Type II flowers are the only ones capable of being pollinated and set fruit.