Efficacy of virus elimination from apple by thermotherapy coupled with in vivo shoot‐tip grafting and in vitro meristem culture

Abstract

Ten varieties of potted apple were subjected to thermotherapy coupled with in vitro meristem culture and in vivo shoot‐tip grafting. Using reverse transcription–polymerase chain reaction assays prior to treatment, all treated apple varieties were infected by more than two viruses, and nine of ten varieties were infected by Apple chlorotic leaf spot virus (ACLSV), Apple stem pitting virus (ASPV) and Apple stem grooving virus (ASGV). After treatment, the survivals of the two methods were more different. Total survival rates of the seven apple varieties (YF9, XYF3, X2001, GL, HF, A123 and ZZ5) treated by thermotherapy coupled with in vitro meristem culture were 25.9% (14/54). The survival rate of YF9, XYF3, X2001, GL, YF6, JJ and XNH treated by thermotherapy coupled with in vivo shoot‐tip grafting was from 33.3% to 75.0%, and the average rate (63.0%, 34/54) was twice than that of meristem culture. The virus‐free apple plants were acquired only from in vitro variety HF and A123, and the elimination rate of A123 was highest, up to 71.4% (5/7). Fourteen apple survival grafting plants from five varieties (YF9, XYF3, X2001, YF6 and XNH) were detected virus‐free. The average elimination rate of the meristem culture and shoot‐tip grafting was very close, 42.9% (6/14) and 41.2% (14/34), respectively.

In vitro tissue culture of apple and other Malus species: recent advances and applications

“…In vitro culture is a successful method to eradicate apple viruses and detailed information on this subject before the twenty-first century can be found in several comprehensive reviews (Laimer and Barba 2011;Panattoni et al 2013;Barba et al 2015). Advances on this subject since 2000 reported improvements of in vitro-based methods for apple virus eradication, including thermotherapy (Paprštein et al 2008;Hu et al 2015bHu et al , 2017Vivek and Modgil 2018;Wang et al 2018b), chemotherapy (James et al 1997;Paprštein et al 2013;Hu et al 2015b), combining chemotherapy with thermotherapy (Hu et al 2015b), shoot tip culture from adventitious buds (Wang et al 2016), cryotherapy (Li et al 2016;Romadanova et al 2016a;Bettoni et al 2018) and combining thermotherapy with cryotherapy (Zhao et al 2018) (Fig. 5).…”

“…Four of five clones of 'Idared' were free of apple chlorotic leaf spot virus (ACLV), apple stem pitting virus (ASPV) and apple stem grooving virus (ASGV), but no virus-free plants were found in 'Sampion', as analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Hu et al (2017) reported a thermotherapy procedure for apple virus eradication. Pot-grown diseased plants were heat-treated at 38 °C for 30 days.…”

Thermotherapy Followed by Shoot Tip Cryotherapy Eradicates Latent Viruses and Apple Hammerhead Viroid from In Vitro Apple Rootstocks

“…This decreases the viral particle load in infected shoot tips, permitting the use of larger meristems than those used for meristem culture without thermo-treatment [ 48 , 51 , 53 , 54 , 55 ]. Previous studies have shown that exposing plants to thermotherapy can be effective for ACLSV, ASGV, ApMV (Apple mosaic virus), and ASPV eradication in diseased apple cultivars [ 56 , 57 ]. The efficacy of producing virus-free apple plants varied according to the virus species and the nature of infection (single or mixed), cultivars, and the virus–host combination.…”

“…While four of five clones of ‘Idared’ were free of ACLV, ASPV, and ASGV, no virus-free plants were found in ‘Sampion’ [ 57 ]. Working on seven apple varieties, Hu et al [ 56 ] also found that the effectiveness of thermotherapy in eradicating apple viruses was related to the cultivar and virus species. Incubation of pot-grown diseased plants at 38 °C for 30 days followed by excision of 1 mm shoot tips resulted in 71.4% (five out of seven plants) of the regenerated plants of ‘Apple 123’ being free of ACLSV and ASPV, and one out of two regenerated plants of ‘Huafu’ being free of ACLSV, ASGV, ASPV, and ApMV.…”

“…Incubation of pot-grown diseased plants at 38 °C for 30 days followed by excision of 1 mm shoot tips resulted in 71.4% (five out of seven plants) of the regenerated plants of ‘Apple 123’ being free of ACLSV and ASPV, and one out of two regenerated plants of ‘Huafu’ being free of ACLSV, ASGV, ASPV, and ApMV. None of the recovered plants from other varieties were free of virus [ 56 ]. In the present study, an alternating temperature of 36 °C (day) and 32 °C (night) for four weeks followed by the excision of 1 mm shoot tips resulted in low efficiency of ASGV (8%) and ACLSV (5%) eradication, and did not produce any AHVd-free plants.…”