<i>In Vitro</i> Screening of Cactus [<i>Opuntia ficus-indicia</i> (L.) Mill] Genotypes for Drought Tolerance

Abstract

Drought is one of the complex environmental factors affecting growth and yield of crops in arid and semi-arid areas of the world. In this context, this investigation was carried out to select drought tolerance cactus genotypes under in vitro condition. An experiment was carried out at Laboratory of Mekelle Agricultural Research Center, Northern Ethiopia. Six cactus pear genotypes namely, Gerao, Keyih Beles, Shenkor, Limo, Lemats Beles and Suluhna were used. Areoles were used as explants in tissue culture. The non-ionic water soluble polymer polyethylene glycol (PEG) of molecular weight 6000 was used as osmoticum to simulate water stress. In the first culture, the MS medium was supplemented with (2, 4-D (4 mg/l) and BA (0.5 mg/l) for callus induction. In all cultures MS medium was supplemented with 0, 10, 20 and 40 g/l polyethylene glycol (PEG) and was solidified with 0.8% agar and 30 g of sucrose. Significant differences were observed among the genotypes, PEG levels. In the first culture highest number of explants initiated callus on medium supplemented with no PEG but had not shown significant difference with 10 g/l PEG. At 10 g/l PEG, the callus induction frequency, callus fresh weight and plantlet regeneration were recorded highest for Suluhna (83.3%, 5.5 g and 63.3%), respectively. At 40 g/l PEG, callus induction frequency, callus fresh weight and plantlet regeneration were produced highest for Suluhna (41.7%, 2.75 g and 45%), respectively but no significant difference with Gerao, Limo and Lemats Beles. However, Shenkor and Keyih Beles were induced callus but became reddish black within 35 days supplemented with 40 g/l PEG. Both shoot and root production decreased with increased PEG level in the medium. At 40 g/l PEG in MS medium, the highest shoot number was in Suluhna genotype (4.33) followed by Gerao (3.67). The highest shoot length was in Suluhna (2.11 cm) with no significant difference with Gerao (2.02 cm). Root number (5.00 and root length (1.41 cm) were in the genotype Suluhna. Survival percentage of in vitro regenerated plantlets was 100% during hardening. By taking into consideration, all the growth parameter tested revealed that Suluhna, Gerao, Limo and Lemats Beles showed better drought stress tolerance at the highest level of PEG while Keyih Beles and Shenkor appeared to be drought sensitive at the highest level of PEG.