Morus serrata Roxb., is found widely distributed in temperate Himalaya between 4 to 9 thousand ft. altitude (Hooker 1885). It is commonly known as Himalayan Mulberry and recognised as a valuable timber species. The wood is used for furniture , sporting requisites, agricultural implements etc., (Anonymous 1962) . The tree is lopped for fodder and the leaves are also rarely used for feeding silkworms in Khasi and Jaintia hills (Kanjilal 1940) . Except for these floristic reports, no other information is available for the commercial ex ploitation of this native species as a food source of silkworms. Further, the only available cytological information on this species is the diploid chromosome number (2n=28) report by Janaki Ammal (1948). The present communication is the first report of hexaploidy in M. serrata.In addition, the meiotic behaviour of this hexanloid mulberry is also discussed . Material and methodsCuttings from a giant mulberry (Morus serrata) tree of Joshimath, Chemoli District (U. P., India) were collected and planted in mulberry germplasm of the institute. The species identification was got confirmed by National Herbarium, BSI, Calcutta. Male inflorescences of appropriate developmental stages from these plants were fixed in Cornoy's II solution for 24 hours and preserved in 70% ethanol. Anthers were squashed in 2% propionocarmine. Photomicrographs were made with temporary preparations. Number of observations were made to get confirmative results. ObservationsPollen mother cells (PMCs) revealed the gametic chromosome number of n=42 and ex hibited normal meiosis. At diakinesis, 42 bivalents are clearly seen and in majority of the cells two or three bivalents are found associated with the nucleolus (Fig. 1). In some cells, one hexavalent is found associated with nucleolus (Fig. 2). Various types of chromosomal associations ranging from uni to hexavalents are observed during diakinesis and metaphase I (Figs. 3 and 4). The range and mean frequency of such chromosomal associations scored in 100 PMCs is given in Table 1. Majority of cells (48%) showed 42 bivalents and frequ ency of multivalents per cell is much less compared to that of bivalents. Among the mul tivalents, the frequencies of trivalents (1.28) and tetravalents (1.20) are more than that of penta (0.04) and hexavalents (0.28). Univalents are observed in only 5% of cells with a frequency of 0.4. At metaphase I, all the bivalents regularly align on the equatorial plate (Fig. 5). Anaphase I disjunction (Fig. 6) and telophase I (Fig. 7) are regular. During prophase II and metaphase II also, 42 chromosomes in each daughter nuclei are clearly seen (Fig. 8). Subsequent stages of meiosis II are found to be normal leading to the formation of isobilateral or tetrahedral tetrad (Figs. 9 and 10). Pollen grains are of uniform size and showed 78 stainability.
Genetic improvement of crop plants is brought about by manipulating the genetic makeup through systematic breeding techniques or by employing modern biotechnological tools. Application of systematic breeding technique to a large extent is decided by the knowledge on the genetic control of the traits. Keeping this in view, nine mulberry genotypes were evaluated for different growth and yield attributing traits viz., number of tillers (NT), plant height (PH), total shoot length (TSL), nodal distance (ND), leaf fall % (LF), number of leaves/plant (NLP), weight of 100 fresh leaves (WFL), weight of 100 dry leaves (WDL), single leaf area (LA), leaf area index (LAI), aboveground biomass (AGB), leaf harvest index (LHI) and leaf yield (LY) and estimated the magnitude of genotypic and phenotypic variation, heritability, genetic advance and correlation coefficients. The broad sense heritability for these traits ranged from 63.942 (WFL) to 13.261 (PH). High heritability coupled with high genetic advance was recorded for the characters WFL, LF, LA, WDL and LY suggesting the higher genetic control over these traits. Leaf yield showed significantly positive phenotypic and genotypic correlations with all other growth traits except PH and LF. Leaf fall had significant negative correlations with all the highly heritable yield attributes viz., ND (-0.379), WDL (-0.225), LA (-0.346), LAI (-0.233) at 1% level and AGB (-0.148), LHI (-0.122) and LY (-0.146) at 5% level. Likewise, it showed positive correlations with TSL (0.558), NLP (0.264) and PH (0.221). Since mulberry is mainly cultivated for leaf yield, genotypes having higher WFL, LA, WDL and LY and less LF must be given importance during parent selection to evolve high yielding varieties with less leaf fall across different seasons in mulberry
Adventitious bud induction and plantlet regeneration were studied in a popular mulberry variety, V1 using leaf as an explant. Fully expanded leaf explants were cultured on Murashige and Skoog's (MS) medium supplemented with thidiazuron (TDZ) (0.5 -4.0 mg/l), 6-benzylaminopurine (BAP) (0.5 -2.0 mg/l), indole acetic acid (IAA) (2.0 mg/l), gibberlic acid (GA 3 ) (1.0 -2.0 mg/l) silver nitrate (AgNO 3 ) (2.0 mg/l) and different carbon sources such as sucrose, fructose and glucose (10% -30%) either individually or in combination to induce adventitious buds and regeneration. The highest percentage (63%) of adventitious bud formation and regeneration (68%) was achieved in the medium containing MS with TDZ (1.0 mg/l), IAA (2.0 mg/l) and AgNO 3 (2.0 mg/l). For subsequent regeneration and shoot elongation the MS medium having BAP (1.0 mg/l), GA3 (2.0 mg/l) and AgNO 3 (2.0 mg/l) was found to be suitable. Amongst the carbon sources tested, the most suitable carbon source was found to be sucrose (3%) followed by fructose (2%) for adventitious bud formation. Excised in vitro shoots were rooted (60% -80%) in half strength MS medium supplemented with indole-3-butyric acid (1.0 mg/l). The well rooted plantlets were hardened in soil + sand + farm yard manure (FYM) mixture with a success rate of 70% -90%. Since in vitro regeneration is highly genotype-dependent in mulberry, the standardized protocol can be effectively used for further improvement of this leading genotype using biotechnological approaches.
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