Graft compatibility of new scion-rootstock combinations

Authors: ALBRECHT, UTE - University Of Florida; MEYERING, BO - University Of Florida; CHAPARRO, JOSE - University Of Florida; Bowman, Kim

Submitted to: Citrus Industry
Publication Type: Trade Journal
Publication Acceptance Date: 10/15/2021
Publication Date: 11/15/2021
Citation: Albrecht, U., Meyering, B., Chaparro, J., Bowman, K.D. 2021. Graft compatibility of new scion-rootstock combinations. Citrus Industry. pp 10-13. https://crec.ifas.ufl.edu/media/crecifasufledu/extension/extension-publications/2021/2021_november_graft.pdf

Interpretive Summary: New citrus scions and rootstocks are being developed in Florida at an unprecedented pace to provide superior cultivars to survive in a disease-endemic environment. Most graft combinations of existing citrus scions and rootstocks are graft-compatible. But as more complex genetic combinations are used to obtain more disease-resistant cultivars, in some cases graft combinations of new scions and rootstocks can result in an incompatibility reaction that causes the tree to grow poorly or die. We are currently investigating the anatomical and physiological mechanisms of observed incompatibility reactions with new scions and rootstocks. This will help us understand the causes of the compatible or incompatible reaction and also identify which graft combinations with new cultivars are likely to fail. Early identification of potential graft incompatibilities is important to prevent economic losses

Technical Abstract: New citrus scions and rootstocks are being developed in Florida at an unprecedented pace to provide superior cultivars to survive in a huanglongbing-endemic environment. Testing these scions and rootstocks and their different combinations in the field takes a long time. In most cases, numerous combinations of specialty scions and rootstocks are being evaluated only after commercial release of the individual cultivars. In 2014, the rootstock US-1283 was released by USDA based on field performance over 14 years with ‘Hamlin’ scion. US-1283 is a mandarin × trifoliate orange hybrid like many other rootstock cultivars. During propagations for new field trials over the last three years, abnormal growth was observed for this rootstock in combination with ‘Bearss’ lemon, ‘Star Ruby’ grapefruit, and ‘Tango’ mandarin. The incompatibility reaction appeared to be most consistent in combination with ‘Bearss’ lemon, and was manifested as a swelling above the graft union, sometimes with extensive overgrowth of the graft union. Symptoms were variable in their intensity and ranged from mild to moderate to severe, and in some cases death of the plants. A similar early manifested incompatibility has been observed for the recently released new UF-Gainesville scion cultivars ‘Sherman’ and ‘Sunray’ when budded on US-942 rootstock. Both cultivars show scion swelling above the graft union and a necrotic ring at the graft union. We are currently investigating the anatomical and physiological mechanisms of these incompatibility reactions to identify a marker for early diagnosis of scion-rootstock incompatibility. When propagating new combinations of scions and rootstocks, it is advisable to pay close attention to any abnormal swelling of the scion trunk, or abnormalities of the rootstock trunk (grooving and necrosis underneath the bark) to detect potential incompatibilities and prevent economic losses.