ABSTRACT Mulberry leaf production plays a key role in the sustainability of silk industry as the silkworm Bom-byx mori can not survive on any other leaf. In fact, silkworm merely acts as an instrument to convert mulberry leaf proteins into the silk proteins. In India, West Bengal is the second highest silk producing state but with varied climatic conditions and suffers to a great extent from non-availability of adequate quantity of quality leaf during the colder months. Delayed sprouting, slow growth rate and higher leaf fall are the major factors contributing this leaf scarcity. To overcome these problems, nine mulberry genotypes, developed through systematic breeding, were tested against the current popular variety for 3 consecutive years taking into account of their performance during the colder months. Annual leaf yield was highest in CT-44 (48 mt/ha/ year) followed by CT-11 (44 mt/ha/year). Leaf senescence was least in CT-44 (9.8%) followed by CT-11 (16.8%) while the check variety showed 20% leaf senescence. Significantly higher values were observed for net photosynthetic rate (Pn) (14.83 µ mol. m-2·s-1); physiological water use efficiency (pWUE) (1.16 8 mol CO2, mol–1 H2O); total soluble protein (TSP) (27.87 mg·g–1·fw); total soluble sugar (TSS) (39.74 mg·g–1 fw); nitrate reductase activity (NRA) (17.78 8 mol. NO2·g–1·fw·h–1) in CT-44. Correlations of these physiological and biochemical characters with leaf yield and leaf senescence (%) revealed highly significant positive correlations of leaf yield with Pn (0.536), TSP (0.674), NRA (0.610), pWUE (0.433), LAI (0.776) and negative correlations with leaf senescence (–0.239). TSS (0.292) and TSP (0.780) had positive association with NRA. Leaf senescence (%) had significant negative association with Pn (–0.755), TSP (–0.462), NRA (–0.438) and pWUE (–0.359). Path coefficient analysis revealed the direct effect of Pn (0.218), TSP (0.449) and LAI (0.730) on leaf yield. The study, therefore, indicated the possibility of using Pn, TSP, NRA and LAI for selecting varieties with higher leaf yield with low leaf fall during colder months.
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