ROLE OF VENTILATION, CALCIUM AND BORON ON SHOOT TIP NECROSIS AND HYPERHYDRICITY REDUCTION OF IN VITRO ROORSTOOCKS OF PISTACIO ‘BADAMI’ ȘI ‘UCB1’

Shoot tip necrosis (STN) is one of the main physiological disorders in the micropropagation of pistachios. In the current study, the effects of CaNO3.4H2O at 196 mg/L and 291 mg/L, H3BO3 at 196 mg/L and 291 mg/L, and CaCl2.2H2O at 2,980 mg/L on STN and hyperhydricity reduction of Pistacia vera L., ‘Badami’ and ‘UCB1’ rootstocks were assessed, compared to the MS standard medium containing 3% sucrose, 0.7% agar supplemented with benzyladenine (BA) (1.5 mg/L), indole butyric acid (IBA) (0.1 mg/L). For ventilation parameter, filter container vessels with a 50-µm microporous polypropylene membrane (Pardis®) were used. Based on the results, an increase in calcium chloride content of the MS standard medium prevented hyperhydricity in the UCB1 rootstock, whereas it increased STN, yellow leaves, decreasing the multiplication of shoots in the ‘Badami’ rootstock. The results also showed that increasing boric acid from 196 mg/L up to 291 mg/L decreased STN in the UCB1 rootstock and increased this disorder by 37% in the ‘Badami’ rootstock. Ventilation showed no significantly reducing effect on the percentage of STN in the regenerated shoots of the ‘Badami’ rootstock, whilst it decreased the STN of the ‘UCB1’ rootstock to the lowest percentage. For the ‘Badami’ rootstock, CaNO3.4H2O at 196 mg/L led to the highest proliferation rate, shoot height, shoot diameter, and leaf number, but for the ‘UCB1’ rootstock, an increase in the concentration of CaNO3.4H2O up to 291 mg/L under ventilated conditions resulted in an increase in proliferation, shoot height, and shoot diameter.

Boron on in vitro growth and enzymatic activity of Blueberry

Boron (B) is essential for plants metabolism and most culture mediums use the same concentration, but in different quantities this nutrient may provoke growth alterations. Thus, the purpose of this study was to examine the effect of B on in vitro growth of blueberry in three experiments. The first experiment of multiplication (evaluated at 90 days) used 3 concentrations of 2-isopentenyladenine-2iP with 4 concentrations of boric acid-BA (factorial scheme 3x4). The second used 4 concentrations of BA and 1 concentration of 2iP and the third (rooting) used 4 concentrations of BA and 1 concentration of indolbutyric acid-IBA both evaluated at 180 days (unifactorial scheme). All the experiments had 4 replicates with explants. 6.2 mg L-1 of B and 5.0 mg L-1 of 2iP generated the highest shoot quantity (18.4, 25.5 respectively). From the interaction of these concentrations, there was the highest activity of POD and PPO enzymes. Under B deficit was seen a larger number of shoot-tip necrosis (9), red leaves (31) and high activity of the PAL, IAAO and POD enzymes. With IBA the correlation between IAAO and the roots’ growth was positive, showing that blueberry rooting depends of both B and IAAO regulation.

Control of in vitro shoot tip necrosis in Carob Ceratonia siliqua L.

Shoot tip necrosis (STN) is a physiological abnormality whereby the apical shoot initially becomes necrotic and subsequently dies leading to considerable loss of shoots and hampering any commercial application of carob (Ceratonia siliqua L.) micropropagation. The objective of the present study is the optimization of a method to alleviate STN during in vitro multiplication of carob dealing with a range of culture media compounds. Obtained results showed that macroelement strength of the culture medium as well as cytokinin and calcium concentrations were the most important factors in controlling STN incidence in carob. In fact, Zimmerman macroelements are most efficient in terms of STN reduction (only 5% STN observed) and shoot multiplication (28.75 shoots with 26.8 leaves and 4.73 cm length). Moreover, shoots cultured on Zimmerman or Ca enriched ½MS showed higher mineral nutrient contents than those cultured on low Ca media. On the other hand, most shoots recovered from STN have produced roots in presence of 1 mg.L-1 IAA (70%) and 83% survived after transfer to ex vitro conditions. The performance of Zimmerman macroelements is most likely due to its high Ca concentration (7.3 mM) compared to the other media. This is confirmed by the steep reduction of STN intensity obtained on ½MS enriched with Ca.

Shoot tip necrosis of in vitro plant cultures: a reappraisal of possible causes and solutions

Main conclusion Shoot tip necrosis is a physiological condition that negatively impacts the growth and development of in vitro plant shoot cultures across a wide range of species. Abstract Shoot tip necrosis is a physiological condition and disorder that can arise in plantlets or shoots in vitro that results in death of the shoot tip. This condition, which can spread basipetally and affect the emergence of axillary shoots from buds lower down the stem, is due to the cessation of apical dominance. STN can occur at both shoot multiplication and rooting stages. One of the most common factors that cause STN is nutrient deficiency or imbalance. Moreover, the presence or absence of plant growth regulators (auxins or cytokinins) at specific developmental stages may impact STN. The cytokinin to auxin ratio within an in vitro plant can be modified by varying the concentration of cytokinins used in the culture medium. The supply of nutrients to in vitro shoots or plantlets might also affect their hormonal balance, thus modifying the occurrence of STN. High relative humidity within culture vessels and hyperhydricity are associated with STN. An adequate supply of calcium as the divalent cation (Ca2+) can hinder STN by inhibiting the accumulation of phenolic compounds and thus programmed cell death. Moreover, the level of Ca2+ affects auxin transport and ethylene production, and higher ethylene production, which can occur as a result of high relative humidity in or poor ventilation of the in vitro culture vessel, induces STN. High relative humidity can decrease the mobility of Ca2+ within a plant, resulting in Ca2+ deficiency and STN. STN of in vitro shoots or plantlets can be halted or reversed by altering the basal medium, mainly the concentration of Ca2+, adjusting the levels of auxins or cytokinins, or modifying culture conditions. This review examines the literature related to STN, seeks to discover the associated factors and relations between them, proposes practical solutions, and attempts to better understand the mechanism(s) underlying this condition in vitro.