| Chlorophyll concentrations of leaves may be of interest in breeding programs
where the objective is to increase photosynthesis. Arabian (dark) and other
cultivars (light) represented the extreme of the visual color classifications.
When expressed on dry weight basis generally dark cultivars were approximately
50% higher in total chlorophyll content than the light cultivars. Differences
among cultivars should allow for the improvement of the content of chlorophyll.
Therefore, the visual differences between dark and light color of cultivars
are apparently actual differences in chlorophyll concentrations. EMS 0.4%
at 3 1/2 hr duration in Hinta Madina displayed highest increase (8.70 mg/gdw)
in total chlorophyll as compared to the rest of the treatments, which indicates
the specific effect of this treatment in this particular genotype whereas,
the same treatment does not showed similar effect in other genotypes. Most
of the treated populations in variety Arabin displayed decrease in total
chlorophyll content as compared to the parent. The highest reduction in
total chlorophyll content was displayed by 0.2% at 3 1/2 hr duration in
this genotype. Chlorophyll deficiency is inherited character in these plants.
The tillering capacity of the plants in these treatments was considerably
high during the early growth stages but the percentage of productive tillers
were quite low. Majority of the tillers produced from 30 to 60 days degenerated
without flowering and fruiting. The chlorophyll deficiency may be one of
the main reason for this, because the chlorophyll deficient genotypes are
unable to meet the metabolic requirements of the plant which ultimately
disturbs the whole physiology of a plant. However, the efficiency of the
mutagen in not only dependent on dose alone but also on other variables
such as presoaking time and pH of the mutagen solution Results
(Table 1) also indicate that positive changes
in the alteration of chlorophyll synthesis in most of the M1
populations has been brought by EMS and the simplest explanation is the
accumulation and presence of more loci having dominant or partially dominant
genes in these M1 populations. The ratio of chlorophyll a : b was higher for the light cultivars/M1 populations than the dark cultivars/M1 populations. In few M1 populations chlorophyll b was higher than chlorophyll a, indicating that the EMS has affected photosystem I (PS I) in which chlorophyll a predominates on the contrary, PS II was accelerated by EMS in which chlorophyll b predominates. The light cultivars exhibited 29% higher ratio of chlorophyll a : b than the dark cultivars. JOHNSON & OHKI (1981) reported negative relationship between total chlorophyll and the ratio of chlorophyll a : b on dry weight basis and concluded that chlorophyll a was not increasing at the same rate as chlorophyll b. Highly significant (P >= .01) differences among varieties were detected for all the traits measured (Table 2), suggesting that varieties under study varied significantly from each other for these parameters. Although variation among varieties and treatments occurred for total chlorophyll, chlorophyll a, chlorophyll b and chlorophyll a : b, but the differences among treatments were not statistically significant. The breakdown of treatments into dose, duration and dose x duration also reveal non-significant effects suggesting that the doses at different durations were not effective in inducing significant genetic changes in the parameters studied. The interactions between varieties x dose, varieties x durations and varieties x dose x durations were highly significant indicating that varieties did not perform uniformly accross different doses and durations. |
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