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

Abstract

Many tree crops experience sub-optimal yields and low fruit quality due to inadequate pollination, low fruit set, and poor crop nutrition. Boron (B) is a critical crop nutrient for fruit set because B levels affect pollen germination and pollen tube growth. However, the relationship between floral B concentration and fruit set is not well understood. The aim of this study was to determine the effect of B applications on the initial fruit set, yield, quality, and paternity of macadamia (Macadamia integrifolia). Cultivar ‘816’ trees received one of three treatments: (a) 0 g, (b) 15 g, or (c) 30 g B per tree prior to flowering. Boron application increased the B concentration of macadamia flowers. Application of 15 g B increased fruit set at 3 weeks after peak anthesis, but this higher initial fruit set was not translated into higher fruit set at 6 or 10 weeks after peak anthesis or higher yield. Boron application increased B concentrations in kernels but did not affect nut-in-shell (NIS) mass, kernel mass, kernel recovery, kernel oil concentration or incidence of whole kernels. Cultivar ‘816’ was highly outcrossing, with 97–98% cross-paternity among kernels from all treatments. Our results indicate that higher B concentration in macadamia flowers can be associated with an increased initial fruit set. However, high B levels did not affect yield, nut quality, or the proportion of self-pollinated fruit at maturity. The heavy dependence on outcrossing highlights the importance of inter-planting different cultivars and managing bee hives to sustain the productivity of macadamia orchards.

Understanding chemical pathways of brown centre formation in laboratory induced and conventionally dried nut-in-shell macadamia kernels

“…However, we observed a higher calcium concentration in the induced brown centres compared with induced white centres. Nutrient concentrations in macadamia kernel could be controlled by preharvest fertilisation [ 37 ]. However, our results of nutrient concentration differences between brown and white sections of the macadamia were not very conclusive.…”

Hyperspectral Imaging of Adaxial and Abaxial Leaf Surfaces as a Predictor of Macadamia Crop Nutrition

“…The experimental trees had a mean height of 8.0 ± 0.1 m and trunk circumference of 63 ± 1 cm (± SE) at 10 cm above the graft union (n = 30). Each experimental tree was randomly allocated to one of three boron-fertiliser treatments (0, 15 or 30 g B per tree) that were applied prior to flowering [ 52 ]. We collected leaves from each tree on four occasions between September 2018 and March 2019, specifically at 0 weeks after peak anthesis (peak flowering), 6 and 10 weeks after peak anthesis (premature fruit drop) and 26 weeks after peak anthesis (commencement of harvesting) [ 53 ].…”

Manipulation of flowering and fruiting induction through branch bending and fertilizer application in mandarin citrus cv. Batu 55

“…Mosambi fruit set, fruit retention, yield, and fruit quality. As reported by [42], Boron (B) is a crucial crop nutrient for fruit set, because B levels affect pollen germination and pollen tube growth.…”