Drought tolerance and impacts of four rootstock genotypes on the morphology, yield and fruit quality of Fuji scion apple under drought conditions

Drought is one of the major abiotic stresses that limits apple production. Rootstocks provide roots for grafted fruit trees. The rootstocks absorb water and mineral nutrients and affect the growth and development of the tree and the quality of fruit and its yield. Furthermore, the appropriate rootstock for drought conditions is key to the sustainable production of apple (Malus spp.). Chistock #1 is a new semi-dwarfing apple rootstock. The drought tolerance of Chistock #1 was compared with that of M9, M26 and M. prunifolia through pot and field experiments. In pot experiments, drought tolerant rootstocks were selected by comparing the root configuration, leaf anatomical structure, electrical conductivity and SPAD value. The results showed that the roots of Chistock #1 and M. prunifolia were long and well developed. Under drought stress, M. prunifolia can close its stomata in time to reduce water loss, followed by Chistock #1 and M26, while M9 was the slowest at closing its stomata. After drought treatment, the leaf and palisade tissue thickness and SPAD value of Chistock #1 were the highest at 121.56 μm, 42.03 μm and 43.00 μm, respectively. The fruit yield and quality of different scion and rootstock combinations were measured in field experiments. A Fuji scion cultivar grafted to Chistock #1 had a higher yield and better quality as determined by its suitable ratio of total soluble solids and titratable acid. Finally, a membership function combined with a principal component analysis was used to comprehensively evaluate the drought tolerance of the four rootstocks. The results were as follows: Chistock #1 was the most drought tolerant of the four rootstock genotypes, M. prunifolia and M26 were the second and third most drought tolerant rootstocks, while M9 was the least drought tolerant.