INFLORESCENCE AND FLOWER DEVELOPMENT OF THE HASS AVOCADO (PERSEA-AMERICANA MILL.) DURING ON AND OFF CROP YEARS

Inflorescence and flower development of the 'Hass' avocado (Persea ame ricana Mill.) were investigated at the macro- and microscopic level wi th three objectives: 1) to determine the time of transition from veget ative to reproductive growth; 2) to develop a visual scale correlating external inflorescence and flower development with the time and patte rn of organogenesis; and 3) to quantify the effect of high (''on'') an d low (''off'') fields on the flowering process. Apical buds (or expan ding inflorescences) borne on summer shoots were collected weekly from July to August during an ''on'' and ''off'' crop year. Collected samp les mere externally described and microscopically analyzed, The transi tion from vegetative to reproductive condition probably occurred from the end of July through August tend of shoot expansion), During this t ransition the primary axis meristem changed shape from convex to flat to convex, These events were followed by the initiation of additional bracts and their associated secondary axis inflorescence meristems, A period of dormancy was not a prerequisite for inflorescence developmen t. Continued production of secondary axis inflorescence meristems was observed from August to October, followed by anthesis seven months lat er. In all, eleven visual stages of bud development were distinguished and correlated with organogenesis to create a scale that can be used to predict specific stages of inflorescence and flower development. In florescence development was correlated with minimum temperature less t han or equal to 15 degrees C, whereas yield had little effect on the t iming of developmental events of individual inflorescence buds. Howeve r, the high yield of the ''on'' year reduced inflorescence number and increased the number of vegetative shoots. No determinate inflorescenc es were produced during the ''on'' gear. For the ''off'' year, 3 % and 42 % of shoots produced determinate and indeterminate inflorescences, respectively.