Photosynthetic performance as a tool in detecting infection in tobacco (Nicotiana tabacum)
Photosynthesis is the key process for plant growth and development. By calculating the rates of chlorophyll fluorescence kinetics, it is possible to quantify the impacts of environmental stresses like phytopathogen infection on photosynthetic processes. Tobacco mosaic virus (TMV) is one of the most economically damaging plant viruses because of its wide host range and transmission mode. TMV is a positive-sense single-stranded RNA virus in the family Tobamovirus that attacks a variety of plants, particularly tobacco. The infection produces distinctive patterns on the foliage, such as "mosaic"-like mottling and discoloration, which can decrease photosynthetic efficiency and, as a result, yield and quality. Unfortunately, little is known about how viruses, particularly TMV, influences complex mechanistic processes like photosynthesis. The objective of the present study was to understand how the commonly available isolates of TMV found in Zimbabwe affect the mechanistic processes of photosynthesis and to generate data for future research on other commercially significant plant viruses. Ten plants of the tobacco variety ONC with established susceptibility to TMV and an additional ten plants of its isogenic variant ONCR with TMV resistance imparted by the N gene were grown in rainout shelter over the course of two seasons (2019-20 and 2022-23), at the Kutsaga Research Center in Harare, Zimbabwe. Results showed that infection decreased the maximum quantum yield of PSII (FV/FM), the effective quantum yield of PSII (ΦPSII), the CO2 assimilation rate (A) and the stomatal conductance (gs) in the studied TMV-susceptible plants, while non-photochemical quenching (NPQ) increased. This article will discuss in detail and demonstrate the usefulness of research on plant-virus interactions using modulated chlorophyll fluorescence measurements. In future, this will be especially important in circumstances where there are no visible signs of infection. Additionally, this research contributes to the body of information for future studies on other economically important plant viruses.