Compatibility and horticultural performance of Pera sweet orange clones grafted to Swingle citrumelo rootstock

Abstract

Despite its interesting agricultural traits, Swingle citrumelo (Citrus paradisi Macfad. 'Duncan' × Poncirus trifoliata L. Raf.) rootstock exhibits severe incompatibility when grafted with Pera sweet orange [Citrus sinensis (L.) Osb.] scions, and this fact limits its use for propagation purposes. Nonetheless, the existence of certain Pera sweet orange clones that are compatible with Swingle citrumelo represents a substantial gain for the entire citrus industry. This study investigated the compatibility between seven Pera sweet orange clones and Swingle citrumelo rootstock, regarding the presence of a necrotic line at the graft union junction, the difference in diameter between rootstock and scion, the influence of clonal cleaning by micrografting, and the horticultural performance of the selected combinations. No trees died because of grafting incompatibility, even after twenty years (trial I), except for clone CV1, or after six years and nine months (trial II) from planting. The rootstock/scion trunk diameter ratiowas not related to the presence of a necrotic line in the graft-union region. Additionally, these variables did not influence fruit yield and quality, and they were not affected by clonal cleaning or preimmunisation of the old Pera sweet orange clones.

Hybrid Rootstocks for Valencia Sweet Orange in Rainfed Cultivation Under Tropical Savannah Climate

“…The trunk bark from a 3 × 5 cm area was removed on the graft union with a penknife. Visual assessment was performed by two independent evaluators on six plants of each treatment, using the following score: 1) no symptoms of graft incompatibility; 2) fine line separating the scion and the rootstock tissues; 3) marked line separating the scion and the rootstock tissues; and 4) sharp and deep line separating the scion and the rootstock tissues with rootstock phloem yellowing, necrosis and gum exudation in the graft union (Fadel et al, 2019).…”

“…2 Estimated according to Pearce and Dobersek-Urbanc (1967). 3 Percentage of trees classified by the visual scores adapted from Fadel et al (2019): 1) no symptoms of graft incompatibility; 2) fine line separating the scion and the rootstock tissues; 3) marked line separating the scion and the rootstock tissues; and 4) sharp and deep line separating the scion and the rootstock tissues with rootstock phloem yellowing, necrosis and gum exudation in the graft union. Scores 3 and 4 were not observed.…”

Comparative transcriptomic analysis on compatible/incompatible grafts in Citrus

“…Although grafting is widely used in citrus production, some widely utilized rootstocks may still exhibit graft incompatibility in the orchard and this reaction can take years to manifest [ 2 ]. For example, Swingle citrumelo ( Citrus paradisi × Poncirus trifoliata ) is characterized by its tolerance to biotic stress and the superior fruit quality it confers on the scion, but is incompatible with some sweet orange clones ( Citrus sinensis ) [ 5 ]. Trifoliate orange ( P. trifoliata ) is a commonly used rootstock in the citrus industry due to its superior resistance to several abiotic and biotic stresses [ 6 , 7 ], while it is incompatible with some varieties of lemon ( Citrus limon ) [ 8 ] and pummelo ( Citrus maxima ) [ 9 ].…”

‘Tropical Sunki’ mandarin and hybrid citrus rootstocks under ‘Pera’ sweet orange in cohesive soil and As climate without irrigation

“…In 2019, the graft-compatibility was assessed by the visual examination of the graft union, after a bark strip of 2 × 4 cm was removed with a penknife in three trees randomly selected in each treatment. A grade scoring adapted from Fadel et al (2019) was performed: 0 -absence of symptoms; 1 -fine line at the graft union; 2 -marked line; 3 -sunken line; and 4 -sunken line and gum exudation at graft union, and tree yellowing and stunting. In addition, the trunk diameter was measured 5 cm above and below the graft union and the ratio was calculated.…”