Abstract:

This study aims to systematically understand the flowering biological characteristics of 16 citrus rootstock resources, including trifoliate orange and citrange, and to provide references for rootstock germplasm creation and new variety breeding. 16 collected trifoliate orange and citrange resources were used as materials. The phenological stages were observed, and the characteristics of floral organs, including bud color, petal number, petal length and width, anther number, filament number, filament color, and stigma number, were compared. Additionally, pollen quantity, pollen grain size, pollen viability, and pollen germination ability were measured using an optical microscope and in vitro pollen germination method. Finally, a comprehensive evaluation of flowering biological characteristics was conducted using the weighted membership function method. (1) The results showed that trifoliate oranges and most of citrange resources were deciduous trees. Citrange trees exhibited a more erect growth habits and reached phenological stages slightly later than trifoliate oranges. Both trifoliate oranges and citrange primarily exhibited pale purple filaments, with most specimens having 20-24 anthers and filaments. However, the petals of trifoliate oranges were generally smaller than those of citrange. (2) Significant differences existed between trifoliate oranges and citrange in terms of pollen viability, pollen quantity, and pollen grain size. Trifoliate oranges generally exhibited higher pollen staining vitality and pollen germination rates compared to citrange. (3) Utilizing the weighted membership function method, trifoliate oranges such as common small-leaf trifoliate orange, M-3 and citrange Dayong No.3 were identified as rootstocks with superior pollen fertility. These results provide reference for evaluating and utilizing rootstock resources, as well as for interspecific and intraspecific hybridization breeding within the citrus genus to create new citrus rootstock germplasm.

Key words: citrus rootstocks, trifoliate orange, citrange, phenological period, floral organ characteristics, pollen fertility, evaluation, weighted membership function method