Gamma Rays and CarbonIon-Beams Irradiation for Mutation ...

Stover’s scale modified by Gauhl (Orjeda, 1998) in which 0 = no
symptoms; 1 = presence of spot (up to 10 spot, stage 4 of the Fouré scale );
2 = less than 5% of the leaf affected; 3 = from 6 to 15% of the leaf affected;
4 = from 16 to 33% of the leaf affected; 5 = from 34 to 50% of the leaf
affected; and 6 = more than 50% of the leaf affected.
4. 2. 2. 2. Juglone toxin screening
Juglone (5-hydroxy-1,4-naphthoquinone) is one of the most
active toxin among the seven toxins produced by Mycosphaerella fijinesis
Morelet, that induce the formation of necrotic lesions of plants leaf cells
(Strobel et al., 1993). This toxin was used in this experiment to screen
young plants as an indicator of resistance/tolerance to black Sigatoka
disease. Previous results using different doses of juglone (Reyes-Borja et
al., 2005) found that 150 ppm of this toxin was a suitable dose to get
differences among the resistant cultivars and irradiated plants. The leaf-
discs (5 discs per plant) were taken from the second expanded leaf of both
ion-beams irradiated cultivars ‘Williams’ and ‘Cavendish Enano’ from the
field planted experiment. Leaf-discs samples of ‘FHIA-01’ (resistant
cultivar to black Sigatoka) were obtained from sucker plants available in
the banana collection of the Estación Experimental Tropical Pichilingue,
Ecuador.
One liter of solution containing 150 ppm of juglone was
prepared using distilled water. An amount of 10 mL were dispensed into a
Petri dish (90 mm) and the leaf-discs were immersed onto the solution.
Leaves were rinsed with distilled water and 1.5 mm-diameter discs were
removed using a cork borer (No. 8). Petri dishes with leaf-discs samples
were kept on light and room temperature during 24 hours (Fig. 33). A total
of 440 leaf discs were analyzed (87 plants x 5 leaf discs/plant). After 24
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