Elimination of sugarcane mosaic virus, sugarcane yellow leaf virus, and co-infections in sugarcane (Saccharum spp. hybrids) shoot tips via osmo- and cryo-therapy

Cryopreservation for sugarcane (Saccharum spp. hybrids) germplasm conservation is well established. Virus elimination using droplet-vitrification (D-V) and cryo- or osmo-therapy has only been recently reported for sugarcane mosaic virus (SCMV). In this study, exposing large (3 mm) in vitro shoot tips of cultivars N12, N19, N58, and NCo376 infected with sugarcane yellow leaf virus (SCYLV) and NCo376 co-infected with SCMV and SCYLV were tested for virus elimination using both of the above-mentioned techniques. Cryo-therapy involved the exposure of infected in vitro shoot tips to the D-V protocol followed by recording recovery and virus-free shoot tips 16 wk after treatment. Osmo-therapy, consisting of the same treatment as cryo-therapy without immersion in liquid nitrogen (LN), was included for comparative purposes. Cryo-therapy resulted in 100% of the recovered shoots being SCYLV-free in cultivars N19, N58, and NCo376 and 83% in N12 when compared with untreated material. Osmo-therapy showed 58% (N12), 91% (N19 and N58), and 100% (NCo376) of shoots being clear of SCYLV when compared with untreated in vitro control plants (0 to 8%). Both techniques reduced the regrowth levels of treated shoot tips (22 to 57% recovery) when compared with untreated controls (92 to 97%). A novel finding of the study was that NCo376 co-infected with SCMV and SCYLV showed 100% virus-free recovered shoots after cryo-therapy and 92 to 100% of healthy shoots after osmo-therapy, compared with controls, which had 17 to 42% virus-free shoots. Plants from all cultivars that were re-tested 4 mo after hardening maintained their virus-free status. The described techniques for virus eradication offer a promising solution for the provision of clean vegetative planting propagules and safer germplasm exchange.