MSc

The present study entitled ‘Standardisation of grafting in bitter gourd
(Momordica charantia L.) and watermelon (Citrullus lanatus (Thunb.))’ was
undertaken with the objectives of identifying the best rootstocks for grafting bitter
gourd and watermelon, comparison of two grafting methods namely, hole
insertion grafting (HIG) and tongue approach grafting (TAG) and evaluation of
various cucurbitaceous rootstocks on survival, growth and yield of bitter gourd
and watermelon.
Bitter gourd (var. Preethi) and watermelon (var. Sugar Baby) were used as
the scion materials for standardisation of grafting. Six different rootstocks namely
ash gourd, bottle gourd, smooth gourd, pumpkin, oriental pickling melon and self
rootstocks were used in the study. Grafting experiments were laid out in
completely randomized design (CRD) with four replications and 25 plants per
replication. Field experiments were laid out in randomised block design (RBD)
with three replications and three plants per replication.
Based on days taken for germination and days to attain graftable size,
sowing of rootstock and scion seeds were adjusted so that they attain grafting
stage uniformly. Criteria for rootstock and scion to attain graftable size was based
on hypocotyl thickness of stock and scion and its suitability for grafting operation.
Pumpkin (9.99 days) and bottle gourd (10.43 days) took lesser number of days to
attain graftable size due to larger diameter of hypocotyls (7.17 mm and 9.93 mm
respectively). Even though OP melon took less number of days for germination,
days taken to attain graftable size (17.57 days) was more due its slender hypocotyl
(3.13 mm). To confirm the best stage of rootstocks for grafting, three age groups
viz., 5-7, 10-12 and 15-17 days old rootstocks were used for grafting scions of age
group 7-10 days. For ash gourd, smooth gourd and OP melon, optimum age group
was from 10-12 days after germination while bottle gourd, pumpkin and bitter
gourd had no significant difference in graft success among the age groups studied
and all the age groups performed equally well. Grafting was not successful when
watermelon was used as rootstock in all the three age groups.
In terms of graft success, in HIG, for bitter gourd the best rootstock was
smooth gourd (80.00 %) followed by pumpkin (77.00 %), bottle gourd (75.00 %),
ash gourd (66.00 %), OP melon (56.00 %) and self rootstock (48.00 %) and for
watermelon the best rootstock was bottle gourd (75.00 %) followed by smooth
gourd (73.00 %), pumpkin (66.00 %), ash gourd (50.00 %) and OP melon (46.00
%). In TAG, graft success was not significant among the rootstocks in both bitter
gourd and watermelon. On comparing the two grafting methods in terms of final
graft success, HIG was superior to TAG. In bitter gourd and watermelon final
graft success was 67.00 per cent and 62.00 per cent respectively for HIG while for
TAG graft success was 15.17 per cent and 14.60 per cent respectively. Grafting
done during the months of June, July and August gave higher graft success
compared to May, September and October. Relative humidity had highly
significant positive correlation with graft success while temperature had highly
significant negative correlation. Anatomical studies of graft union revealed
formation of necrotic layer in response to wound repair and proliferation of cells
of rootstock and scion which is the stage prior to callus formation. Since the graft
success and survival were very poor in tongue approach grafts, only hole insertion
grafts were evaluated in the main field for studying the performance of various
rootstocks.
In bitter gourd, self rooted plants had highest survival rate (100.00 %) in
the main field followed by plants grafted on smooth gourd (84.44 %) and bottle
gourd (77.78 %). Plants grafted on bottle gourd showed earliness in terms of days
to first male flower (28.45 days) and female flower (31.45 days) and days to first
harvest (44.33 days) among the grafts and they were on par with self rooted
control plants. Vine length, growth rate and number of primary branches were
high in seedling plants and they were on par with plants grafted on smooth gourd.
Plants grafted on ash gourd had fruit length of 21.03 cm which was on par with
control plants. Among the grafts, highest fruit girth of 17.60 cm was noted in
plants grafted on bottle gourd which was comparable to fruit girth of control
plants (17.73 cm). Highest flesh thickness of 1.33 cm was noted in plants grafted
on bottle gourd and self rooted control. Number of harvests per plant (10.67), crop
duration (110.67 days) and total yield (3.30 kg) were higher in plants grafted on
smooth gourd compared to self rooted control plants. In organoleptic evaluation,
fruits obtained from plants grafted on bottle gourd was the most accepted one with
a total score of 20.00, closely followed by fruits from grafts on pumpkin
rootstock. Fruits were less bitter in grafts on bottle gourd and pumpkin compared
to other grafts.
In watermelon, survival rate was highest in plants grafted onto bottle
gourd (79.99 %) followed by plants grafted on ash gourd (77.78 %) and smooth
gourd (77.78 %). Least number of days to first female flower was noted in
seedling plants (40.67) which was on par with plants grafted on ash gourd (42.33
days). Lower node to first female flower appearance was noted in control plants
(21.00) followed by plants grafted on bottle gourd (22.97). The period of graft
success did not coincide with the actual planting season of watermelon in Kerala
and therefore the performance of grafts in the field was very poor. There was
severe vine decline during reproductive stage of watermelon crop.
Further research should focus on screening of rootstocks for pest and
disease resistance, optimisation of graft healing conditions for year round
production of grafted seedlings and optimisation of grafting time in watermelon
such that it coincides with planting season in Kerala.