PhD

An investigation entitled “Evaluation of propagation techniques and
rootstock studies of mango (Mangifera indica L.)” was carried out during 2016–
2019 at Department of Pomology and Floriculture, College of Agriculture,
Vellayani. The investigation aimed to screen local mango varieties/ collections for
polyembryony, to study the pre-sowing treatments, sowing positions and age of
stone after extraction from fruit on germination of mango stones, to screen local
mango varieties for use as dwarfing rootstocks and to study the effect of two
propagation methods in three modified environments on three varieties of scions.
Out of twenty local mango varieties collected from different parts of
Thiruvananthapuram district of Kerala, seventeen were polyembryonic while
three were monoembryonic. The mango var. Kappa Manga (T19) recorded the
highest germination per cent (73.33 %), germination index (2.41) and seedling
vigour index on growth basis (2795.20). The mean germination time (17.50 days)
was the least in Vellari Varikka (T18). Kotookonam Varikka recorded the highest
per cent polyembryony (65.13 %) and produced the highest number of plantlets
per stone (5.00). Microsatellite analysis of all the plantlets from two varieties viz.,
Kotookonam Varikka and Kochu Kilichundan that exhibited the highest
percentage of polyembryony were done using 20 SSR primers and the products
were compared with their respective mother plants. All the seedlings obtained
from the respective stones had identical SSR profile to the mother plant, which
indicated nucellar origin of seedlings having similar genetic composition to the
mother plant. The zygotic seedling might have degenerated at very early stage of
growth and the remaining nucellar seedlings were all vigorous.
To study the effect of pre-sowing treatments, sowing positions and age of
stone after extraction from the fruit on germination of mango stones, an
experiment was laid out in completely randomized design with 42 treatment
combinations replicated thrice. The treatments comprised two sowing positions
viz., flat (S1) and stalk end up (S2), three age of stones after extraction from fruit,
viz., freshly extracted (A1), 10 days (A2) and 20 days after extraction (A3) and
seven pre-sowing treatments viz., 100 ppm GA3 (T1), 200 ppm GA3 (T2), 1 ppm
KNO3 (T3), 2 ppm KNO3 (T4), cow dung slurry(T5), water (T6), control [without
treatment (T7)] and their combinations. The variety Kotookonam Varikka was
utilized for the study. The stalk end up sowing method and freshly extracted
stones proved to be the best with respect to germination and vigour of mango
seedlings. The stones treated with 200 ppm GA3 required minimum number of
days for initiation of germination (22.62 days), 50 % germination (31.78 days),
exhibited the highest germination percentage (62.59 %), rate of germination
(0.48), vigour index on growth basis (2310.02) and weight basis (657.09).
Treatment with 100 ppm GA3 produced the highest seedling length (35.70 cm)
and dry weight (10.39 g) at 4 month after sowing (MAS). Interaction effects also
indicated that the freshly extracted stones sown by stalk end up method after
treatment with 200 ppm GA3 for 24 hours resulted in significantly the highest
germination rate (0.74) and the least number of days for initiation of germination
(13.00 days).
An attempt was made to identify the local mango varieties for use as
dwarfing rootstock based on morphological, physiological and anatomical
features. The experiment was laid out in completely randomized design (CRD)
with ten genotypes replicated thrice. At 4 MAS, the lowest seedling length (29.48
cm) was noticed in Kochu Kilichundan (T4), followed by Unda Varikka (T10) and
the highest seedling length (56.11 cm) was in Kappa Manga (T8). Moreover, the
germination percentage of Kochu Kilichundan (46.67 %) was on par with all the
varieties except Kappa Manga (71.11 %) along with the lowest vigour index-I and
vigour index- II was on par with Unda Varikka. However, the least dry matter of
seedling (9.66 g) was recorded in Unda Varikka.
At 6 MAS, majority of the morphological features were the highest in
Kappa Manga. The highest starch content (8.53 %) was estimated to be in
Kasthuri (T2). Kochu Kilichundan and Unda Varikka exhibited dwarfism with less
plant height (38.77 cm and 40.20 cm respectively), but the former had the least
internodal length (3.16 cm). The highest values for number of leaves (23.20), leaf
length (12.59 cm), leaf width (4.07 cm) and average leaf area (22.57 cm2) were
recorded in Unda Varikka compared to Kochu Kilichundan. However, the highest
number of roots (28.53), root length (35.02 cm), dry weight of root (3.10 g), dry
weight of shoot (1.46 g) and stomatal density (51.68) were recorded in Kochu
Kilichundan while total leaf area of the two varieties were on par. Moreover,
Kochu Kilichundan had the highest phenol content in apical bud (60.57 mg/g) and
leaves (29.03 mg/g) and bark percentage of root (23.69 %) and shoot (34.02 %) of
all the varieties. Membrane stability index, relative water content, transpiration
rate and leaf temperature were non-significant. The anatomical studies revealed
the highest phloem-xylem ratio both in stem (0.99) and root (1.35) and the least
total conduit area of root (6.38 mm2) in Unda Varikka while the least total conduit
area of stem (5.42 mm2) was in Kochu Kilichundan, indicating the dwarfing
potential of both Kochu Kilichundan and Unda Varikka.
To study the effect of propagation methods and modified environments on
different varieties of scion, an experiment was laid out in completely randomized
design with eighteen treatment combinations replicated thrice. The treatments
comprised two propagation methods viz., epicotyl (P1) and softwood grafting
(P2), three modified environments viz., climate controlled [fan and pad (M1)],
humid chamber (M2) and natural shade [75 % shade (M3)] and three varieties of
scions, Kalapady (V1), Neelum (V2) and Kotookonam Varikka (V3) and their
combinations. The grafts produced by epicotyl grafting resulted in significantly
higher scion length (15.80 cm), had the least number of days for leaf opening
(15.07days) , first (12.19 days) and last sprouting (22.02), higher number of grafts
sprouted at weekly intervals, higher initial success percentage (83.21 %), graft
establishment percentage (72.22 %), number of leaves per graft (15.40), leaf
length (15.27 cm), leaf width (3.36 cm), leaf area (41.69 cm2), number of nodes
on scion (21.63), internodal length (5.20 cm), number of growth flushes per graft
(1.76), lower number of days taken between grafting to first vegetative flush
(26.06 days) as well as to second vegetative flush (44.98 days) and higher final
survival of grafts (65.19 %). The micro climate controlled by fan and pad system
produced most conducive conditions for vegetative growth of mango grafts.
Among the different varieties of scions, Kotookonam Varikka recorded the
highest girth of rootstock, girth of scion, length of scion, graft height, spread of
plant in N-S direction and E-W direction, number of grafts sprouted at weekly
intervals, initial success percentage, percentage of graft establishment, leaf width,
number of nodes on scion, internodal length, number of growth flushes per graft
and the lowest number of days taken between grafting and second vegetative
flush. Kalapady recorded the least number of days for first and last sprouting, leaf
opening and for first vegetative flushing. The greatest sprout length, number of
leaves, leaf length and leaf area were recorded in Neelum. The scion did not
influence the final survival of grafts. The treatment combinations had no influence
on root length. Interaction effects also confirmed that epicotyl grafting method
with Kotookonam Varikka variety as scion under controlled conditions using fan
and pad system resulted in grafts with higher scion length (16.80 cm), sprout
length (6.05 cm), more number of growth flushes per graft (2.33) and earlier
second vegetative flush (40.87 days).
Based on the above findings it could be concluded that the highest
percentage of polyembryony was in Kotookonam Varikka and microsatellite
analysis revealed the nucellar origin of plantlets and confirmed higher vigour of
nucellar seedlings over sexual seedling. Stalk end up sowing of freshly extracted
stones treated with 200 ppm GA3 for 24 hours recorded better germination and
vigour of mango seedlings. The mango variety Kochu Kilichundan and
UndaVarikka were identified as promising rootstocks to impart dwarfness and
Kochu Kilichundan was superior in most of the morphological and physiological
characters. The epicotyl grafts of Kotookonam Varikka under controlled climate
by fan and pad system recorded better graft establishment, survival, vegetative
and growth parameters.