Pathogens attack plants to derive nutrients, and the plants may protect themselves by depriving pathogen of available nutrients. Sugars are recognized as signaling molecules in plants (Rolland et al., 2006). It can be speculated that the change in sugar level is sensed by the plant and these signals get integrated with those derived from sensing pathogen-associated molecular patterns (Moghaddam and Van den Ende 2012). The coordinated interaction of sugar and hormonal pathway in plants leads to immune response (Moghaddam and Van den Ende 2012).
To Understand the inheritance of resistance, the identification and location of resistance (R) gene is required (Rhoades 1935; Andersen et al., 2018). The gene-for gene hypothesis was explained by H. H. Flor, it is a concept that describes interaction between plant R gene and pathogen’s avirulence (Avr) gene (Flor 1942). The Avr gene is expressed and the Avr protein interacts with the R proteins to activate the plant defense response against the pathogen (McDowell and Woffenden 2003). A virulence protein can become an avirulence protein upon recognition by plant R protein.
Multiple disease resistance (MDR) can be defined as host-plant resistance to two or more disease (Nene 1988). This may include qualitative and quantitative resistance. Quantitative resistance is phenotypically incomplete (i.e. allowing some reproduction by the pathogen and therefore some epidemic progress) and is based on joint effect of several gene, each contributing quantitatively to the level of plant defense (Niks et al., 2015). Quantitative variation in crops involves epistatic or pleiotropic interaction. Epistatic interaction, in which the effect of one gene (genetic locus) on a trait is influenced by one or more other genes, that can mask or enhance the expression of certain traits (Dwivedi et al., 2024). MDR can be controlled by single gene with pleiotropic effect or by several genes across the genome which are effective against different pathogens (Wiesner-Hanks and Nelson 2016). The term pleiotropy was introduced by a German geneticist Ludwig Plate in 1910 refers to the phenomenon where a single locus affects two or more distinct phenotypic traits (Stearns 2010).
Some MDR QTL (quantitative trait loci) are associated with resistance to diverse fungal pathogens with different lifestyles such as biotrophic, hemibiotrophic and necrotrophic, while others were associated with resistance only to biotrophs (Wiesner-Hanks and Nelson 2016). Dual specificity to R gene has been noted in Arabidopsis thaliana. The A. thaliana RPM1 gene confers dual specificity disease resistance against the pathogen Pseudomonas syringae expressing either of the two unrelated avirulence (Avr)genes (AvrRpm1 or the AvrB) (Grant et al., 1995; Tornero et al., 2002). The two distinct bacterial effector proteins interact with the same host protein kinase (Pto kinase of tomato) to activate host resistance against the bacterial pathogen Pseudomonas syringae (Kim et al., 2002).
MDR phenomenon can be traced to a single chromosome or chromosome translocation, especially when dealing with progeny from interspecific or intergeneric hybrids (Friebe et al., 1996; Salina et al., 2015; Fedak et al., 2021). Most of the time the disease resistance genes were in the same region on different chromosomes and may be under strong selection pressure in the maize breeding (Ali et al., 2013). MDR is a highly valued trait in plant genetic resources. Resistance at the whole-genome scale can be conditioned by multiple unlinked loci, and each providing protection against single pathogen or by chromosomal segment(s) that individually provide MDR (Wiesner-Hanks and Nelson 2016).
To resist pathogen attack, rice plant has a complex defense system in which transcription factors, plant disease resistance genes and catalytic enzymes participate in disease resistance (Fu et al., 2024). Resistance to false smut in rice is controlled by QTL. Quantitative trait loci mapping is effective for studying the genetic complex forms of plant disease resistance (Young 1996). Therefore, there is a need to screen resistant germplasm source and identify disease resistance QTL. Multiple QTL associated with resistance to false smut were identified on different chromosome of rice (Han et al., 2020). Identification of genes/QTLs for false smut resistance facilitates control of the disease. Loci controlling quantitative resistance contain some same causal genes that mediate qualitative resistance (Corwin and Kliebenstein 2017). Most causal genes for quantitative resistance encodes for biosynthesis of defense compound or strengthening of the cell wall (Corwin and Kliebenstein 2017). The MDR loci with significant effects on more than one disease are rare than loci with single disease effects (Lopez-Zuniga et al., 2019). The lines resistant to both fungi and bacteria were identified, as well as loci that confer resistance to both bacterial and fungal diseases (Qiu et al., 2024). MDR is governed by diverse mechanism at the locus and gene level. The information on genetically correlated trait can help in achieving resistance to multiple disease.
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BIOLOGICAL PROCESSES- A NATURE'S GIFT 