Resistance mechanisms of late leaf spot and rosette diseases in drought tolerant groundnut genotypes

Groundnut has been identified as less susceptible to drought which produces moderate yield under drought conditions. Also, drought can enhance effects of late leaf spot and groundnut rosette diseases. However, to reduce rate of the damage by these constraints, plants produce various defensive metabolites. This investigation was undertaken to study how drought tolerant groundnut genotypes respond under late leaf spot and rosette diseases. Eleven drought tolerant genotypes, comprising 4 resistance to both diseases, 4 resistant to leaf spot and 3 resistant to rosette disease were selected for the study. The experiments were conducted in the screen house at two locations (Namulonge and Kabanyolo) and arranged in a complete randomized design. Diseases and drought were artificially imposed two weeks after germination. Data collected included aphid counts, chlorophyll, phenolic and tannin content. The analysis of variance showed significant differences (P<0.001) in most of the studied traits for the two sites, genotypes and the interaction. Rosette resistant genotypes recorded the lowest aphid counts and the highest tannin contents. The lowest total chlorophyll was shown by late leaf spot susceptible genotypes. Tannin content was negatively correlated with chlorophylls and aphid counts whiles total phenolic content was negatively correlated with aphid counts but was positively correlated with chlorophyll. The negative correlation between the measured metabolites and chlorophyll with aphid population, rosette and leaf spot disease indicated that an increase in these biochemical content led to a decrease in disease occurrence and therefore, increasing metabolites could contribute to the bio-protection of host plants against these diseases.