Effects of meta-topolin derivatives and temporary immersion on hyperhydricity and in vitro shoot proliferation in Pyrus communis

Although micropropagation in temporary immersion systems might increase plant growth and multiplication, it can also cause specific problems such as hyperhydricity and losses by contamination. A new commercial temporary immersion bioreactor, SETIS™, was used to micropropagate two Tunisian pear cultivars, ‘Arbi’ and ‘Mahdia 6’. The latter cultivar was endogenously contaminated by Sphingomonas. Hyperhydricity was inevitable when 5 µM benzyladenine was applied. However, the symptoms could be reduced by lowering the immersion frequency to 3 times per day. Applying 5 µM meta–Methoxy topolin riboside (MemTR) or meta–Topolin riboside (mTR) completely inhibited hyperhydric shoot formation. Moreover, the addition of Plant Preservative Mixture was effective to control Sphingomonas and allowed the plants to proliferate. For both pear cultivars, the highest number of shoots per explant was induced by 5 µM MemTR, whereas the highest leaf area was obtained with 5 µM mTR. The longest shoots were obtained with 5 µM mTR for ‘Arbi’ and 5 µM MemTR for ‘Mahdia 6’. Key message Methoxy topoline-riboside (MemTR) and meta-topoline-riboside (mTR) were used as alternatives to benzyladenine to prevent hyperhydricity during the micropropagation of pears in a new temporary immersion system. These cytokinins also increased the number of good quality shoots, characterized by large leaves and longer shoots

Sanitary Selection of Virus-Tested Fig (Ficus carica) Cultivars in Tunisia

Field surveys were carried out during autumn 2011 and spring 2012, in different fig orchards located at Rafraf, Takelsa, Mornag, Djebba, Sousse, and Sfax to select virus-free plants. A total of 202 trees representing 26 fig cultivars were prospected and sampled. Total nucleic acids were extracted from leaf veins and tested by RT-PCR for the presence of FMV,FLMaV-1, FLMaV-2, FMMaV, FCV, and FFkaV using specific primers. PCR results indicate that all these viruses were present in the Tunisian fig orchards. The average of infection level determined by RT-PCR was 63.86%. FMV was proved to be the most widespread virus (37.12%), followed by FLMaV-1 (11.9%), FFkaV (11.4%), FCV (8.9%), FMMaV (8.4%), and finally FLMaV-2 (5.9%). Among the 26 tested cultivars, only 7 (Marghrebi, Boukhobza, Zagfar, Assafri, Kahli, Chetoui, Delgane) were free from the tested viruses. By the contrary, the sanitary status of the main Tunisian cultivars Bayoudhi, Bouhouli, Soltani, Zidi and Bither, seemed heavily degraded (75, 70.37, 69.23, 66.03, and 46.15% of infection, respectively). Seven cultivars (Wahchi, Khartoumi, Thguegli, Besbessi, Bidh-Bghal, Njeli and Khedhri) were totally infected. This study allowed the identification of at least one “virus-tested” candidate clone from 19 different fig cultivars which can represent the potential mother plants for propagating materials in order to establish new fig nurseries and orchards

Efficacy of Tissue Culture in Virus Elimination from Caprifig and Female Fig Varieties (Ficus carica L.)

Fig mosaic disease (FMD) is a viral disease that spreads in all Tunisian fig (Ficus carica L.) orchards. RT-PCR technique was applied to leaf samples of 29 fig accessions of 15 fig varieties from the fig germplasm collection of High Agronomic Institute (I.S.A) of Chatt-Mariem, to detect viruses associated to FMD. Analysis results show that 65.5% of the accessions (19/29) and 80.0% (12/15) of the fig varieties are infected by FMD-associated viruses. From all fig accessions, 41.4% of them are with single infection (one virus) and 24.1% are with multi-infections (2 virus and more). Viruses infecting fig leaf samples are Fig mosaic virus (FMV) (20.7%), Fig milde-mottle-associated virus (FMMaV) (17.25%), Fig fleck associated virus (FFkaV) (3.45%), and Fig cryptic virus (FCV) (55.17%). A reliable protocol for FCV and FMMaV elimination from 4 local fig varieties Zidi (ZDI), Soltani (SNI), Bither Abiadh (BA), and Assafri (ASF) via in vitro culture of 3 meristem sizes was established and optimized. With this protocol, global sanitation rates of 79.46%, 65.55%, 68.75%, and 70.83% respectively for ZDI, SNI, BA, and ASF are achieved. For all sanitized varieties, the effectiveness of meristem culture for the elimination of FCV and FMMaV viruses was related to meristem size. Meristem size 0.5 mm provides the highest sanitation rates ranging from 70% to 90%