Abstract
The present research work was carried out in the Tissue Culture Laboratory and Plant Growth
Chamber of the Department of Genetics and Plant Breeding, Bangladesh Agricultural
University, Plant Genetic Resource Center (PGRC) of Bangladesh Agriculture Research Institute
(BARI), Joydevpur and Field Laboratory of the Plant Breeding Division, Bangladesh Institute of
Nuclear Agriculture (BINA), Mymensingh, Bangladesh during the period of 2013 to 2016.
Synthetic B. napus was produced through interspecific hybridization between the nine varieties
of B. rapa and only one exotic variety of B. oleracea var. alboglabra Bailey along with exogenous
application of gibberellic acid (GA3) before pollination. The chromosomes of the interspecific
hybrids were doubled through the treatments of adult plants and also the germinating seeds.
Nine varieties of B. rapa consists of three ecotypes i.e. B. rapa var. yellow sarson, brown sarson
and toria were used in this study. A total of eighteen crosses including their reciprocals were
made between the two species. Crossability in both directions of crossing in between the two
species of Brassica were not equally success. The degree of success in the interspecific crosses
was significantly influenced by maternal genotypes. On average, the success of crossing was
8.42% when the varieties of B. rapa used as female parents in contrast to 2.88% when B. rapа
used a pollen parents. The crosses Binasarisha-6 × Albglabra-1, Safal × Alboglabra-1 and
Sampad x Alboglabra-1 showed better performance when B. rapa used as female parents. On
other hand, the crosses Albglabra-1 × Binasarsha-6 and Alboglabra-1 × Sampad also showed
higher performance when B. rapa used as pollen parent. Among the four concentrations, 25, 50,
75 and 100 ppm of GA3, 75 ppm gave highest response for different crossability characters in
both way of cross directions. The hybrids were intermediate for most of the morphological
characters and contained 19 (10+9) somatic chromosomes which were the sum of the gametic
chromosome number of B. rapa and B. oleracea. The hybrids showed poor pollen fertility ranging
In
of
from 1.0-8.0%. Of the two methods, followed to induce chromosome doubling in the adult
plants, the Modified Injection Method was found more effected than the Cotton Plug Method.
Modified Injection Method, among the three concentrations (0.10%, 0.15% and 0.20%)
colchinine 0.20% gave the highest success (66.67%) of chromosome doubling in the hybrids. The
survival of the treated plants ranging from 33.33 to 80.00% with an average 52.86%. In cotton
plug method, the highest 58.33% success of chromosome doubling was found with the
of
application of 0.15% colchicine. The survival of treated plants ranging from 25.00 to 70.00% with
an average 42.97%. Colchicine application in sprouting seeds, percent of seedling survival
varied with the cross combinations. It ranged from 50 to 61.25%, 34.92 to 45.69%, 19.81 to 27.3%
and 7.3 to 14.89% at 7, 14, 21 days and final regeneration respectively. Again, percent
seedling survival at 7, 14, 21 days and final regeneration varied with the different
concentrations of colchinine. Among the three concentrations (0.125%, 0.25% and 0.50%) of
colclicine, 0.125% gave to highest value for all the characters studied. All the colchiploid (C)
plants contained 38 (20+18) chromosomes in their somatic cells which were the sum of the
somatic chromosomes of both species. The genomes of better performing RS (Resynthesized)
lines were also identified through Brassica genome specific SSR markers. The presence of
markers for both A and C genome was detected in all RS lines suggesting that their genomic
constitution was AACC. Synthetic B. napus had increased growth and exhibited wider range of
variations than parents for plant height leaf and floral characters, siliquae related characters,
flowering and maturity characters, yield and yield contributing characters and sterility and
siliquae shattering characters. On the basis of mean values of RS lines for plant height, leaf
length, leaf width, petal length and petal width were scored for individual characters. Again, on
the basis of average score and rank position; the RS lines RS-14, RS-11, RS-15, RS-10 and RS-7
have been selected. The RS lines RS-9, RS-14, RS-6, RS-10 and RS-13 found to be best for siliquae
related characters-siliquae length, break length, length of main fruiting axis, siliquae density
and siliquae angle. On the basis of flowering and maturity characters-1st, 50% and 90%
flowering and days to maturity, the RS lines RS-7, RS-10, RS-11, RS-14 and RS-15 scored higher
than other remaining RS lines. Days to maturity of mentioned five RS lines were earlier than
check variety but not early maturing B. rapa parent Tori-7. The RS lines RS-14, RS-1, RS-15, RS-9
and RS-5 found to be promising for yield, yield contributing characters-primary and secondary
branches per plant, siliquae per plant, seeds per plant, 1000 seeds weight, seed yield per plant
and oil content. On the basis of sterility and shattering characters-pollen sterility %, siliquae
setting, sterile seeds per siliquae, siliquae shattered at harvest and siliquae shattered after 7 days
of harvest, the RS lines RS-1, RS-2, RS-3, RS-7 and RS-14 showed better results than others.
Therefore, considering the all the 26 characters the RS lines RS-14, RS-15, RS-9, RS-1, RS-5, RS-6,
RS-7, RS-10, RS-11, RS-2, RS-3 and RS-13 were identified as promising for future breeding
programme.