Factors influencing in vivo and in vitro micrografting of sandalwood (Santalum album L.): an endangered tree species

In vivo micrografting of Santalum album was achieved (50%) by grafting 4- to 5-cm-long scions, collected from a candidate plus tree (CPT) of 50–60 years of age, onto 90-day-old nursery-grown rootstock. Scion size, rootstock age, and scion collection season were found to influence graft success. Grafted plants were incubated under greenhouse conditions for 6–8 weeks during the graft union process. In vitro micrografts were achieved by placing 1- to 2-cm-long scions derived from nodal shoot segments (collected from CPT) onto the hypocotyl of 45-day-old in vitro rootstocks. Use of in vitro grown shoots as a source of scion gave better graft success (60%) than scions collected directly from field-grown trees. In vitro grafting was also influenced by scion size and rootstock age. Under favorable conditions, scions and hypocotyls unite to form complete plants that produced two to four leaves after 6–8 weeks. This is the first report on in vivo and in vitro micrografting of S. album having potential for production of disease-free clonal plants for conservation and improvement targets.     

Micropropagation of an endangered Indian sandalwood (Santalum album L.)

Santalum album is known as East Indian sandalwood. It is the most economically important tree harvested for heartwood oil, and India is among the chief exporters of sandalwood and its products. Multiple shoots were induced from nodal shoot segments derived from a 50- to 60-year-old candidate plus tree (CPT) on Murashige and Skoog (MS) medium supplemented with 0.53 μM α-naphthaleneacetic acid (NAA) and 11.09 μM 6-benzylaminopurine (BA). In vitro differentiated shoots were multiplied on MS medium with 0.53 μM NAA, 4.44 μM BA, and additives: 283.93 μM ascorbic acid, 118.10 μM citric acid, 104.04 μM cystine, 342.24 μM glutamine, and 10% (v/v) coconut milk. New shoots were harvested repeatedly for up to three subculture passages on fresh medium at 4-week intervals. Microshoots treated with 98.4 μM indole-3-butyric acid (IBA) for 48 h produced roots on growth-regulator-free, quarter-strength MS basal salts medium with vitamin B₅ and 2% sucrose. In vitro root induction was achieved from microshoots pulsed with 1230 μM IBA for 30 min in soilrite rooting medium. The percentage of rooting in soilrite was higher than that for agar medium, and in vitro raised plants were established in the field and showed normal growth.     

Complete genome characterization of Sugarcane yellow leaf virus from India: Evidence for RNA recombination

Yellow leaf (YL) caused by Sugarcane yellow leaf virus (SCYLV) has become a serious constraint for sugarcane production in different countries. Worldwide seven genotypes have been reported, with five based on complete and two based on partial genome characterization. We have previously reported the occurrence of three different SCYLV genotypes in India based on their partial genome sequences. A further four SCYLV isolates from sugarcane from Coimbatore (in India) were characterized after complete genome sequencing (~ 5,875 nt). These isolates (SCYLV-IND) exhibited amino acid (aa) sequence differences of 29.2–31.8, 28.1–34.4 and 30.7–33.4 % with REU, HAW-PER and BRA in partial ORF0 sequences, respectively. Similarly IND isolates have 21.4–23.7, 22.5–25.0 and 21.4–23.9 % aa sequence differences with REU, HAW-PER and BRA, respectively in partial ORF1. However, the difference was found to be least in ORF5. The genotype reported from China, CHN1 shared a very close relationship with IND isolates with minimum differences of 4.3–5.3 %, 4.8–5.8 % and 2.5–3.0 % in ORF0, 1 and 5 in aa sequences, respectively and 4.4–5.3 % in complete nucleotide sequences. Phylogenetic analyses showed a separate lineage for IND isolates. Evidence of recombination was found in ORF1 to ORF5 with the maximum number of sites occurring in ORF2. The high incidence of SCYLV recombination suggests that recombination plays an important role in SCYLV evolution.