Inflorescence and Flower Development of the `Hass' Avocado (Persea americana Mill.) during “On” and “Off” Crop Years

Abstract

<jats:p>Inflorescence and flower development of the `Hass' avocado (<jats:italic>Persea americana</jats:italic> Mill.) were investigated at the macro- and microscopic level with three objectives: 1) to determine the time of transition from vegetative to reproductive growth; 2) to develop a visual scale correlating external inflorescence and flower development with the time and pattern of organogenesis; and 3) to quantify the effect of high (“on”) and low (“off”) yields on the flowering process. Apical buds (or expanding inflorescences) borne on summer shoots were collected weekly from July to August during an “on” and “off” crop year. Collected samples were externally described and microscopically analyzed. The transition from vegetative to reproductive condition probably occurred from the end of July through August (end of shoot expansion). During this transition 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 development. Continued production of secondary axis inflorescence meristems was observed from August to October, followed by anthesis seven months later. 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. Inflorescence development was correlated with minimum temperature ≤15 °C, whereas yield had little effect on the timing of developmental events of individual inflorescence buds. However, the high yield of the “on” year reduced inflorescence number and increased the number of vegetative shoots. No determinate inflorescences were produced during the “on” year. For the “off” year, 3% and 42% of shoots produced determinate and indeterminate inflorescences, respectively.</jats:p>

Partitioning of Dry Matter into Fruit Explains Cultivar Differences in Vigor in Young Olive (Olea europaea L.) Trees

“…These results are in line with previous finding that vegetative growth (i.e., vigor) is reduced by the presence of fruit, which compete for resources (Berman and DeJong, 2003;Castillo-Llanque and Rapoport, 2011;Chandler and Heinicke, 1926;Connor and Fereres, 2005;Costes et al, 2000;Dag et al, 2010;Embree et al, 2007;Forshey and Elfving, 1989;Lauri and T erouanne, 1999;Lavee, 2007;Mochizuki, 1962;Monselise and Goldschmidt, 1982;Obeso, 2002;Rallo and Su arez, 1989;Salazar-García et al, 1998;Stevenson and Shackel, 1998;Verheij, 1972). This is not to say, however, that more abundant fruiting cannot be a consequence, rather than the cause, of reduced vigor.…”

“…However, the opposite is also true: once reproduction starts, the crop will compete with, and reduce, vegetative growth and, therefore, vigor, as shown also by modeling (Grossman and DeJong, 1994;Smith and Samach, 2013). This is the case for mature trees of many species (Berman and DeJong, 2003;Costes et al, 2000;Lauri and T erouanne, 1999;Salazar-García et al, 1998;Stevenson and Shackel, 1998), including olive (Castillo-Llanque and Rapoport, 2011;Connor and Fereres, 2005;Dag et al, 2010;Lavee, 2007;Monselise and Goldschmidt, 1982;Obeso, 2002;Rallo and Su arez, 1989). In young trees, the removal of all blossoms or fruits results in dramatic increases in growth relative to the fruiting trees (Chandler and Heinicke, 1926;Embree et al, 2007;Forshey and Elfving, 1989;Mochizuki, 1962;Verheij, 1972).…”

Optimal Nutrient Concentration Ranges of ‘Hass’ Avocado Cauliflower Stage Inflorescences—Potential Diagnostic Tool to Optimize Tree Nutrient Status and Increase Yield

“…The source of the specific nutrients that accumulated in CSI tissue is unclear. The emergence of the inflorescence from the bud (Stage 7) to CSI (Stage 8) occurs within 2-4 weeks during February to March under low average maximum and minimum air and soil temperatures (Salazar-García et al, 1998). During this period, stored nutrients may be transported to different degrees from neighboring leaves into the developing CSI.…”

Properly Timed Soil-applied Nitrogen Fertilizer Increases Yield and Fruit Size of `Hass' Avocado

“…In the 4-year study presented herein, we quantified the effect on yield of applying a double dose of N (56 kg·ha -1 ) at one of several key times in the phenology of the 'Hass' avocado tree that were already included as one of the six application times in the grower practice. The application times included in the grower practice corresponded to the following phenological stages and calendar dates: 1) end of vegetative shoot growth, shoot apices have about four secondary axes of the inflorescence present, additional secondary axes are being initiated (November); 2) early bud swell = the total number of secondary axes (10) of the inflorescence are formed, the oldest are beginning to elongate and to initiate flower organs (January); 3) buds swollen = the youngest secondary axes of the inflorescence are elongating, oldest secondary axes have fully formed flowers with the gynoecium in the early stages of development (February); 4) anthesis to early fruit set and initiation of the spring vegetative flush at the apex of indeterminate floral shoots (April); 5) end of Stage I (initial cell division phase) of fruit development and beginning of the June drop period (June); and 6) beginning of Stage II of fruit development (rapid increase in fruit size) and end of the June drop period (July) (Salazar-Garcia and Lovatt, 1998). The objective was to identify the optimal N fertilization strategy to obtain maximum yield, fruit size, and annual cropping of 'Hass' avocado.…”