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

Abstract

Selecting Macadamia cultivars with anatomical traits capable of withstanding drought may improve water management in their cultivation. Macadamia integrifolia, Macadamia tetraphylla, and their hybrids are commercially grown in South Africa for their high-value edible nuts, however, to improve yields, irrigation is required. This study examined leaf and petiole anatomical traits linked with plant water-use strategies in four commonly planted cultivars: ‘695′, ‘814′, ‘816′, and ‘A4’. Key traits investigated included stomatal density, mesophyll thickness (palisade and spongy parenchyma), vein density, and petiole Huber value. Fully matured macadamia leaves with their petioles were collected from Komatipoort, Nelspruit, and KwaZulu-Natal South Coast during the spring flush of 2021 and the summer flush of 2022 for anatomical analysis. Box plots illustrated significant variations in leaf and petiole anatomical traits among macadamia cultivars and regions. Cultivars ‘814′ and ‘695′ exhibited higher stomatal densities and higher vein densities, while cultivar ‘814′ also showed thicker mesophyll tissues and higher petiole Huber values. These traits suggest that cultivars ‘814′ and ‘695′ may have improved water transport and potential drought tolerance than cultivars ‘816′ and ‘A4’. Seasonal variation accounted for 45 % of the observed variability in leaf and petiole anatomy, highlighting a strong influence of environmental factors during leaf development. However, the anatomical variation was shaped not only by environmental factors but also by cultivar-specific characteristics. These findings suggest that these leaf and petiole anatomical traits could serve as indicators of drought tolerance and help improve the water management practices in macadamia cultivation, particularly in regions with inadequate rainfall.

HIGHLIGHTS • The water requirements of macadamia trees remain unexplored. • Leaf and petiole anatomy varies significantly across cultivars and regions. • Environmental conditions and genetic factors influenced leaf and petiole anatomy. • Selecting drought-tolerant cultivars improves the water management practices in macadamia cultivation.