Development, histological observations and Grapevine leafroll‐associated virus‐3 localisation in in vitro grapevine micrografts

Abstract

Development, histological process and Grapevine leafroll-associated virus-3 localisation were studied in micrografts of three scion/rootstock combinations: healthy/healthy, healthy/infected and infected/healthy. Earlier bud break and faster growth in scions of micrografts were obtained when the healthy shoot segments were used as scions, while earlier bud break in rootstocks and greater fresh weight of roots in micrografts were produced when the healthy shoot segments were used as rootstocks. All histological processes including callus initiation and formation in micrografting conjunctions, and initiation of new cambial cells followed by vascular bundle development connecting scions and rootstocks were similar in micrografts, regardless of the sanitary status of the scions and rootstocks used for micrografting. Virus infection in micrografting conjunctions and systematic infection in micrografts were much more efficient and faster in micrografting combination of the infected scions/healthy rootstocks than in the healthy scions/infected rootstocks. To the best of our knowledge, this is the first report addressing histological process of micrograft development and virus localisation in micrografts. In vitro culture system established in this study facilitates studies on the 'pure' impact of the viral infection on micrografting.

Validation of micrografting to identify incompatible interactions of rootstocks with virus‐infected scions of Cabernet Franc

“…The combination of GLRaV‐1 and GVA, however, was more detrimental than sole infection with GLRaV‐1. Callus formation between the surfaces of scion and rootstock has been found 3 days after micrografting in other studies (Ribeiro et al , Hao et al ). We did not check the healing status of the graft union that early, but our results showed that clear and dense callus tissues were already visible in LR131 graft unions 7 days after grafting.…”

“…Our histological observation showed that LR131 did not have a significant impact on the healing of graft unions in the period of time evaluated, but LR132 appeared to prevent the healing process, causing the death of all the micrografts. Hao et al () found that GLRaV‐3 did not affect the healing process of Cabernet Sauvignon auto‐grafts, either. The combination of GLRaV‐1 and GVA, however, was more detrimental than sole infection with GLRaV‐1.…”

“…Results from measuring vegetative growth found that both scions and rootstocks were more affected by GLRaV‐1 in graft combinations with Freedom and 101‐14 than in combinations with St. George and AXR1 (Figures ). Hao et al () reported that grapevine leafroll‐associated virus 3 (GLRaV‐3) affected the growth of both scion and rootstock in micrografting using Cabernet Sauvignon/Cabernet Sauvignon auto‐grafts, but they did not compare the impacts on different rootstocks. Our results found that LR131 delayed root initiation of Freedom and 101‐14 and found that virus was transmitted from scion to rootstocks within 10 days after grafting.…”

“…Vines were micrografted according to Hao et al () with some modifications. Shoot segments (2 cm in length) were excised from 8‐week‐old plantlets and the leaves were removed.…”

“…Histological observations on the development of the micrografts were conducted according to Hao et al (). Briefly, graft unions were collected at different time points after micrografting and fixed with a solution consisting of 18:1:1 of 50% ethanol/formalin/acetic acid for 24 h, followed by dehydration in a series of solutions of ethanol increasing from 50, 70, 85, 95 to 100%, for a duration of 3 h for each ethanol soak.…”