Leaf anatomical traits of macadamia cultivars with potential links to drought tolerance

Abstract

In South Africa, Macadamia integrifolia, Macadamia tetraphylla, and their hybrids are commonly grown for their edible nuts and consequent nutritional benefits. To improve yields, irrigation is used to grow these trees in regions with inadequate rainfall. Selecting cultivars with desirable leaf anatomical traits, capable of withstanding drought, is one strategy to increase water use efficiency. In this study, we investigated differences in multiple traits related to water use efficiency in common South African macadamia cultivars, including stomatal density, palisade and spongy parenchyma thickness, Huber value, and vein density to determine if cultivars differed in their anatomical characteristics. Cultivar ‘814’ consistently exhibited higher stomatal densities, thicker palisade parenchyma, thicker spongy parenchyma, and higher Huber values compared to cultivars ‘816; ‘695’, ‘842’, and ‘A4’. In contrast, ‘695’ showed greater vein density. The variability in leaf and petiole anatomy was influenced by factors such as the timing of vegetative flush, leaf type, location, and cultivar. Although climate may have played a role, no clear patterns emerged. Genetic factors likely contributed significantly to the observed differences among macadamia cultivars. These findings have implications for selecting drought-tolerant cultivars and improving water management practices in macadamia cultivation, especially in regions with inadequate rainfall.