**4. Biophysical basis of resistance**

In a study Silva et al. [20, 21] evaluated ninety-nine F3 families derived from an interspecific cross using *Solanum lycopersicum* and *Solanum pimpinellifolium* 'TO-937-15' (multiple pest resistance accession with type IV glandular trichomes and acylsugar accumulation) for their resistance against the whitefly. The higher resistance levels of BTR331 were associated with a positive combination of higher type IV trichome density and higher acylsugar levels. From the breeding stand point, the genetic similarity between *S. lycopersicum* and *S. pimpinellifolium* would allow a more efficient resistance introgression by facilitating recombination and minimizing the potentially undesirable linkage drag associated with this trait.

Niranjana et al. reported that the biophysical characteristics in brinjal genotypes *viz*., shoot thickness at 2.5 cm below the tip, number of trichomes on lower surface of leaves, pedicel length, calyx length and diameter of fruit were correlated with the level of infestation by *L. Orbonalis*. Results revealed that the infestation in shoot was not significantly correlated with number of trichomes on leaves and positively correlated with shoot thickness. Fruit infestation was positively but not significantly correlated with length of pedicel and calyx whereas non-significant and negative correlation was recorded between fruit infestation and fruit characters *viz.,* length and diameter of fruit. The shape and color of fruit had no significant influence on the level of infestation.

## **5. Categorization of resistance**

According to the response of the plant to the pathogen.


Based on number of genes governing the resistance trait as


Resistance is classified based on biotype reaction as.


Resistance is classified based on population/Line concept


Plants once infected by a specific pathogen become resistant to further infections by the same one. This was discovered in the beginning of 20th century. This concept is involved in viral cross-protection and induced systemic resistance. Induced systemic resistance in plants is of several types of which *Systemic Acquired Resistance (SAR)* is the most important one. It is long lasting and effective against viral, bacterial and fungal pathogens. It ranges from a oversensitive response to necrotic lesions. SAR is due to high level of salicylic acid which is essentially needed for the development of SAR. Salicylic acid acts as a phloem translocated signal that mediates SAR. It is also due to SAR genes which is different in monocotyledonous and dicotyledonous plants. In tobacco, SAR genes cover a set of non-allelic genes that can be classified on the basis of proteins they encode such as the pathogenesis related (PR) genes. These genes play an active role in the disease resistance as their expression in transgenic plants impart significant disease resistance. SAR genes in various species differ in considerable extent.
