Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent: II. GA3 increases yield and fruit size of ‘Hass’ avocado only in the on-crop year of an alternate bearing orchard

Abstract

Despite problems of low fruit set, small fruit size and alternate bearing, the Hass cultivar dominates commercial avocado production worldwide. To increase yield and fruit size, gibberellic acid (GA 3) (25 mg L −1) was applied at different stages of 'Hass' avocado tree phenology: (i) mid-late April (flower abscission), end of June-beginning of July (fruit abscission and beginning of the exponential phase of fruit growth), and mid-January (beginning of pre-harvest fruit drop); (ii) end of June-beginning of July; and (iii) mid-September (near the end of the major fruit abscission period; period of exponential fruit growth). In both years of the research, applications of GA 3 in April and June-July were within the periods of intense flower and fruit abscission, respectively; fruit abscission was low in September and January. Maximum air temperature was not related to flower or fruit abscission. In the on-crop year (391 fruit per untreated control tree), a single application of GA 3 at the end of June-beginning of July significantly increased total yield (kilograms only) and yield of commercially valuable fruit (178-325 g/fruit) (as kilograms and number per tree) compared with the control (P < 0.0001). GA 3 applied in September increased total yield (kilograms only) and yield of commercially valuable fruit (kilograms and number per tree) to values intermediate to and not significantly different from all other treatments, except trees receiving multiple applications of GA 3. This treatment reduced total yield and yield of commercially valuable fruit (kilograms and number per tree) relative to all treatments (P ≤ 0.0002). In contrast, during the off-crop year (32 fruit per control tree), no GA 3 treatment had a significant effect on yield or fruit size compared with the control and all other GA 3 treatments. For 'Hass' avocado, there was no negative effect from applying GA 3 at the end of June-beginning of July in both the off-and on-crop years; 2-year cumulative total yield and yield of commercially valuable fruit were increased by 27 kg (128 fruit) and 22 kg (101 fruit) per tree, respectively, above the yield of untreated control trees (P < 0.0001).

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

“…The global avocado industry is dominated by the 'Hass' cultivar despite production problems of low fruit set, small fruit size, and alternate bearing (Garner et al, 2011). In particular, the California 'Hass' avocado industry suffers from low yields, with a mean yield for the last 20 years of only 6847 kg · ha -1 (California Avocado Commission, 2017).…”

Boron Effects on Fruit Set, Yield, Quality and Paternity of Macadamia

“…Global crop yields are currently trending below anticipated food demand [1,2]. Tree crops contribute over 600 million tons of the 10,600 million tons of annual global food production [3][4][5], and fruit number and fruit size are key components of tree crop yield [6][7][8]. Tree yields can be constrained by the percentage of flowers that are pollinated and fertilised, the percentage of fruit that develop to maturity, and the mass of the fruit components that contribute to yield [9][10][11][12].…”

Properly Timing Foliar-applied Fertilizers Increases Efficacy: A Review and Update on Timing Foliar Nutrient Applications to Citrus and Avocado

“…Alternate bearing has been documented to influence results obtained with foliar-applied fertilizers; treatments increased yield in the on-crop year, which exacerbated the off-crop year of apple (Izadyar et al, 1998). In light of this and recent research showing that plant growth regulator treatments were effective in only off-or on-crop years of alternate bearing Clementine mandarin (Chao et al, 2011) and 'Hass' avocado orchards (Garner et al, 2011), respectively, it is critical to determine the effect of crop load on the capacity of properly timed foliar fertilizers to increase yield or fruit size.…”