MSc

An experiment ‘Seed invigoration to overcome dormancy in ash gourd
(Benincasa hispida (Thunb.) Cogn.),’ was conducted during 2014-2016 in the
Department of Seed Science and Technology, College of Horticulture, Kerala
Agricultural University (KAU), Vellanikkara, Thrissur, following a completely
randomized design with 16 treatments and three replications. The experiment
aimed to elucidate the effect of seed invigoration on dormancy in ash gourd, to
ascertain the anatomical changes in seed coat on seed treatment and to assess the
storage potential of treated seeds under ambient conditions. Seed invigoration was
resorted to by soaking seeds of variety KAU Local in water (hydro priming) for
24 hours, thiourea (0.5%) for 24 hours, KNO3 (0.4%) for 24 hours, KNO3 (0.7%)
for 24 hours, KH2PO4 (10-1 M) for 24 hours, vinegar (pH 3.7) for 2 hours,
polyethylene glycol 6000 (-0.5 MPa) for 24 hours, salicylic acid (60 ppm) for 12
hours, salicylic acid (60 ppm) for 24 hours, kinetin (10 ppm) for 12 hours, kinetin
(10 ppm) for 24 hours, CaCl2 (50 mM) for 12 hours, CaCl2 (50 mM) for 24 hours,
Psuedomonas fluorescens (1x106 cfu.ml-1) for 12 hours, Psuedomonas fluorescens
(1x106 cfu.ml-1 ) for 24 hours. Untreated seeds served as control (T16).
Both treated and untreated seeds, dried to < 8 per cent moisture content
were packed in polythene bags (400 guage) and stored under ambient conditions
upto ten months. The seed quality parameters viz., germination, germination
index, coefficient of velocity of germination, energy of germination, mean time to
germination, vigour indices I and II, and electrical conductivity of seed leachate
were recorded at monthly intervals during storage. Seed microflora as well as
histochemical studies to analyse the changes occurring in the dimensions of
embryo and proportions of different fractions of seed coat were assessed at
bimonthly intervals.
Results pointed out the existence of significant differences in the impact of
various invigoration treatments on the seed quality and histochemical parameters
observed both within 35 days of invigoration as well as during storage.
Majority of the seed invigoration treatments were effective in breaking
dormancy in ash gourd. Dormancy was first broken in seeds treated with KH2PO4
and kinetin. In the above treatments germination reached above 60 per cent (the
minimum standards for seed certification (MSCS) prescribed for ash gourd) on
the 11th day after invigoration (DAI). Dormancy in untreated seed was broken
only on the 35th day after extraction. However, seed invigoration with salicylic
acid, vinegar and PEG 6000, proved to be detrimental.
Seed invigoration also helped in extending the viability of seeds.
Germination in seeds treated with CaCl2 for 24 hours, was found to be retained
above MSCS for seven months during storage, whereas, in untreated seeds,
germination above 60 per cent was observed for two months only. Seeds treated
with salicylic acid failed to germinate by 35th DAI while those treated with
vinegar and polyethylene glycol (PEG) failed to attain MSCS throughout the
period of study. The viability of seeds treated with kinetin or CaCl2 for 12 hours
and those treated with Pf for either 12 or 24 hours was found to be retained for six
months of storage.
Germination index, coefficient of velocity of germination, energy of
germination, vigour indices I and II in both treated and untreated seeds, increased
by 35th DAI and marginally decreased over the period of storage. In all the
invigoration treatments, the above mentioned parameters were invariably higher
than that of untreated control. However, the performance of seeds treated with
salicylic acid, vinegar and PEG 6000 was lower than the untreated seeds.
Invariably, the germination index, coefficient of velocity of germination, energy
of germination, vigour indices I and II were high in seeds treated with CaCl2 for
24 hours followed by treatment with Pf for 12 hours and CaCl2 for 12 hours. The
mean time to germination, electrical conductivity of seed leachate, the thickness
of seed coat and its component layers as well as the microbial infection of seed
was also observed to be low in these treatments.
High and significant positive correlation was found to exist between
germination and speed of germination, coefficient of velocity of germination,
vigour indices I and II. It became evident that germination in ash gourd will be
strongly affected with an increase in thickness of total seed coat or its outer layerthe
testa. The thickening of seed coat owing to the thickening of testa will be
accompanied with an obvious decrease in germination, germination index and
coefficient of velocity of germination, vigour indices I and II.
Results thus indicated that poor germination in seeds of ash gourd may be
due to water impermeable seed coat (physical dormancy) mainly resulting from
thickening of the outer layer (testa). Such dormancy in ash gourd can be best
overcome by seed invigoration with CaCl2 (50 mM) for 24 hours. In addition,
enhancement of seed viability, seed quality and seedling performance over storage
was also achieved. Seed treatment with CaCl2 (50 mM) or Psuedomonas
fluorescens (1x106 cfu.ml-1), for 12 hours were found to be the next best to
treatment with CaCl2 (50 mM) for 24 hours. Hence, these can also be
recommended for breaking dormancy and maintaining high seed quality in ash
gourd.