M Sc

The present study entitled “Irradiation and seed coating for enhancing storage life of
grain cowpea (Vigna unguiculata (L.) Walp.)” was carried out in the Department of Seed
Science and Technology, College of Agriculture, Vellayani during 2020-2021, with an
objective to standardize the dose of gamma rays for irradiation and concentration of chitosan
for seed coating for enhancing the storage life of grain cowpea. The study was divided into
two experiments which were conducted in Completely Randomized Block Design (CRD)
with three replications. The first experiment was irradiation of cowpea seeds with gamma
rays and the second experiment was seed coating of cowpea seeds with chitosan. The seeds
were irradiated with five different doses (100 Gy to 500 Gy) at Indian Institute of
Horticultural Research (IIHR), Bangalore. Another set of seeds were coated with chitosan at
five different concentrations (1 % to 5 %) at two different quantities for each concentration as
1ml 50g-1
of seeds and 5ml 50g-1
of seeds. Coated seeds were then shade dried and packed in
polythene bags and stored for six months along with control.
In the first experiment, the cowpea seeds irradiated with 300 Gy, 400 Gy and 500 Gy
gamma rays were not affected by pulse beetle infestation till the end of six months of storage.
However, in control, the seed damage was observed which varied from 0.333% in first month
to 56.333% in sixth month of storage with a seed weight loss of 28.182 per cent. The damage
percentage recorded was 2.667 percent and 0.667 per cent in treatment T1 (100 Gy) and T2
(200 Gy) respectively in the sixth month of storage. Thus the gamma ray irradiation in all
doses proved to be effective in controlling pulse beetle infestation.
Germination parameters were studied in the undamaged seeds to study the effect of
irradiation in seed aging. Among the different doses of gamma irradiation, T2 (200 Gy)
recorded the highest seed germination percentage (84.33%), speed of germination (32.13
days), seedling shoot length (11.83 cm), seedling dry weight (0.703 g) and seedling vigour
index I (2130.49) and II (59.29). All the germination parameters showed increased value at
lower doses of gamma rays (100 Gy and 200 Gy) and declined at higher doses (300 Gy, 400
Gy, and 500 Gy) compared to control.
Morphological evaluation of gamma irradiated seeds grown in field showed that the
morphological parameters did not vary significantly from the control in treatments with
gamma doses 100 Gy and 200 Gy. Gamma irradiation at 300 Gy also did not show variation
in morphological parameters compared to control except for field germination percentage.
But progressive decrease in all morphological parameters was observed for the treatments
with gamma doses 400 Gy and 500 Gy. Reduction in germination percentage, plant height,
number of pods plant-1
, number of seeds pod-1
and 100 seed test weight was observed when
compared to control. Few crinkled leaves were observed in 400 Gy and 500 Gy irradiated
treatments at earlier stages. No significant variation was observed in 100 Gy, 200 Gy and
control.
In the second experiment, among the different chitosan treatments, no seeds were
observed with insects upto four months of storage. Although insect eggs and infestation were
noticed in treatments such as T1 (1% 1 ml 50g-1
), T2 (1% @ 5 ml 50g-1
), T3 (2% @ 1 ml 50g1
) and T5 (3% @ 1 ml 50g-1
) at the end of storage period, the percentage of infestation
decreased with an increase in concentration and quantity of chitosan used.
The grain cowpea seeds coated with different concentrations of chitosan from lower
to higher (1% to 5%) have different degrees of improvement in germination parameters
compared to control. Among the different treatments of chitosan, T10 (5 % @ 5 ml 50g-1
)
recorded the highest seed germination percentage (89.37 %), maximum speed of germination
(36.83), seedling shoot length (14.90 cm), seedling root length (17.53 cm), seedling dry
weight (0.747 g). seedling vigour index I (2898.28) and II (66.79).
In this study Gamma irradiation proved to be an effective method for controlling
pulse beetle infestation during storage in grain cowpea. However the treatment with higher
doses 400 Gy and 500 Gy affected the germination parameters negatively and produced some
abnormalities in the progeny. Thus, the gamma irradiation at 200Gy and 300 Gy can be
recommended for safe storage of grain cowpea seeds.
Chitosan at 5% @ 5 ml 50g-1
exhibited higher values for seed germination parameters
and showed no pulse beetle infestation till the end of the storage period of six months.
Chitosan treatment at 5% @ 5 ml 50g-1
can be recommended for safe storage of grain cowpea
seeds. Both gamma irradiation and chitosan seed coating maintained the longevity of seeds
during storage and were effective in controlling the storage pests. Seed coating with chitosan
had an additional advantage of substantial improvement of seed germination parameters.
Gamma irradiation and chitosan seed coating are eco-friendly methods in enhancing the
storage life of grain cowpea. Since gamma irradiation requires special facilities for seed
treatment, chitosan seed coating will be a better technology for small scale farmers.