PhD.

The present investigation entitled “Induced mutagenesis for delayed flowering and
high tillering in guinea grass (Panicum maximum Jacq.)”, was carried out at College of
Agriculture, Vellayani during the period 2014-2017. The major objective of the study was to
develop high yielding guinea grass types with delayed flowering and high tillering through
induced mutagenesis.
The first experiment consisted of evaluation and characterization of germplasm
accessions of guinea grass. For assessing genetic variability and diversity, thirty seven
germplasm accessions were studied with respect to fourteen morphological and three
biochemical characters. ANOVA revealed highly significant differences among the
genotypes for all the traits analysed except length of internode. High estimates of phenotypic
coefficient of variation (PCV) and genotypic coefficient of variation (GCV) were obtained
for green fodder yield, dry fodder yield, leaf stem ratio, weight of seeds hill-1 and gibberellic
acid content and high PCV and moderate GCV were obtained for leaf area index, number of
tillers hill-1, number of leaves hill-1 and number of panicles hill-1. Moderate values of PCV
and GCV were obtained for crude protein content and crude fibre content. High heritability
coupled with high genetic advance as percent of mean was observed for number of tillers hill -
1
, leaf stem ratio, weight of seeds hill-1, crude protein content, crude fibre content and
gibberellic acid content. High heritability coupled with moderate genetic advance as percent
of mean was observed for days to flowering and length of panicle. Moderate heritability
coupled with high genetic advance as percent of mean was observed for number of leaves
hill-1, number of panicles hill-1 and green fodder yield. Green fodder yield showed significant
positive correlation with dry fodder yield and weight of seeds hill -1 at phenotypic level. Green
fodder yield showed significant positive correlation with dry fodder yield, weight of seeds
hill-1 and crude fibre content at genotypic level. Path coefficient analysis revealed that green
fodder yield showed high positive direct effect on dry fodder yield followed by length of
panicle, weight of seeds hill-1, plant height and leaf stem ratio. Based on observations four
varieties viz. two early flowering (FP-553, MS-4690) and two late flowering (PGG-208, MS-
4600) were selected for further studies.
The second experiment included induced mutagenesis using physical mutagens on
seeds and slips. The physical mutagen used was gamma rays from 60Co source and the initial
trial was for fixing LD50 value. For this, seeds of four varieties viz., FP-553, MS-4600, MS-
4690 and PGG-208 were treated with six doses of gamma rays ranging from 60 to 140 Gy
along with control. The effects of gamma rays were studied on different parameters such as
germination percent, seedling height and survival in M1 generation. Reduction of
germination, seeding height and survival were studied. Accordingly LD50 doses were fixed
and three doses 60, 80 and 100 Gy were administered to the seeds of four different varieties
and field planting of M1 was done. M1 was evaluated for fifteen morphological characters.
Statistical analysis of quantitative characters showed that for an increase in gamma ray doses,
a proportionate significant increase for various plant growth parameters was evident.
Occurrence of major viable mutants from seedling to adult growth stages varied viz., broad
and narrow leaves, paired panicle, early and late maturity, dwarf and tall plants, low and high
number of tillers and leaves hill-1, short and long internode.
Mutagenesis by gamma ray irradiation was employed to treat slips of four genotypes
viz., FP-553, MS-4600, MS-4690 and PGG-208. They were treated with six doses of gamma
ray ranging from 20 to 100 Gy along with control for fixing LD50 value. The effects of the
irradiation doses were studied on regeneration, survival of shoots and height of plants. Based
on LD50 value, three doses 20, 40 and 60 Gy were administered along with control to the
different varieties and field planting of M1V1 was done. M1V1 were evaluated for fifteen
morphological characters. Most of quantitative characters showed an increase in mean values
with increase in doses of mutagen. Analysis of data showed that all characters studied were
significantly affected by irradiation at 60 Gy.
The third experiment was the study of frequency and spectrum of chlorophyll and
viable mutants, mutagenic efficiency and effectiveness in M2 generation while employing the
three doses of gamma rays and one control. In general the frequencies of chlorophyll
mutations increased in linear fashion at low (60 Gy) and medium (80 Gy) doses and the
frequency was erratic at higher (100 Gy) doses. The spectrum of chlorophyll mutants
included albina and xantha. The highest frequency of viable mutants was produced at 60 Gy
dose. There were variations in the occurrence of major viable mutants during the crop growth
period stages viz., broad and narrow leaves, paired panicle, days to maturity, dwarf and tall
plants, high and low tillering with variations in number of leaves hill-1, short and long
internode, plant height, protein content, fibre content and gibberellic acid content.
In the M1V2 generation, the chlorophyll mutation frequency increased in a linear
fashion at low (20 Gy) and medium (40 Gy) doses and was erratic at higher doses (60 Gy).
The chlorophyll mutant spectrum included albino and xantha. The frequency of these mutants
varied with treatments. Superior plants with high green fodder yield as a result of increased
number of tillers ranging from 37-42 were observed in 60 Gy populations of MS-4600 and
PGG-208 when compared to the control (30-32 tillers). Based on single plant performance,
plants which recorded high biomass were identified and M1V2 slips were collected and
studied in further generations. The mutagenic treatments were effective in inducing various
types of chlorophyll and morphological mutants, such as those with significant change in
days to flowering, plant height, leaf mutations (narrow, broad, wrinkled); panicle mutations
(twin panicle, compact, spread) and biochemical variations in protein content, fibre content
and gibberellic acid content.
The fourth experiment was the study of M3 and M1V3 generation. The altered
morphological traits were stable as shown by their growth performance in different seasons.
The mutagenic treatments were effective in inducing both qualitative and quantitative
characters. Tall mutants with delayed flowering, high green fodder and dry fodder yield
displayed two fold increase in number of tillers and leaves hill-1 compared to control at 60 Gy
irradiation. Considerable variation was observed with regard to leaf stem ratio at 60 Gy from
slips.
To conclude genetic variability was found to be high among the genotypes of guinea
grass. Gibberellic acid content was found to vary with genotypes. Genotypes with late
flowering habit had low gibberellic acid content. Gamma rays induced variations in both
seeds and slips for plant height, days to flowering, number of tillers hill-1, number of leaves
hill-1, green fodder yield, crude protein content and gibberellic acid content at dose of 60 Gy.
The study yielded mutants with delayed flowering and high tillering which were found to be
stable in growth performance in M3 and M1V3. These stable genotypes could be carried
forward to develop better varieties.