Developing Biotic and Abiotic Stress Tolerant Stylosanthes Cultivars: Biochemical and Molecular Aspects

Stylo is an important recently introduced forage range legume largely adapted to semi arid regions of the country. Of the more than forty species known in the genus Stylosanthes, six species namely S. scabra, S. hamata, S. viscosa, S. humilis, S. seabrana and S. guianensis are major forage species. However, limited germplasm and narrow genetic base hinders wider applicability of Stylosanthes. One of the major worldwide diseases is anthracnose caused by Colletotrichum gloeosporioides. Rate reducing resistance (RRR) lines of S. scabra, and S. seabrana (recently introduced species) indicated better adaptation in hard and cracking soils in complete rainfed conditions. Genotypes of S. scabra were more tolerant to drought over other lines as evidenced by high leaf thickness coupled with low carbon isotope discrimination values, more proline accumulation, content of sugars and chlorophyll. Though molecular mechanism of drought stress response and tolerance has been actively studied in a variety of plants, but such information is lacking in stylo. Targeting the traits associated with drought tolerance, the genetic map and QTLs analysis revealed a causal relationship among specific leaf area, transpiration efficiency and carbon isotope discrimination. These characters can be used in identifying the lines suitable for drought prone areas. The markers located on QTLs associated with anthracnose resistance identified with both intra-specific population (S. scabra 93116X S. scabra cv Fitzroy) and inter-specific population and their segregation in other F₂ population supported the use of such markers in identifying the lines for anthracnose resistance from core germplasm, progeny and in bred lines. A partial genetic map developed using inter-specific cross (S. scabra cv Seca X S. fruticosa) has further suggested the use of markers segregated in the large populations for validation. Improved and promising lines of Stylosanthes provided better scope for the introduction of this important range legume in India.